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Ultrasonics international 1973
ULTRASONICS INTERNATIONAL 1973 27-29
March
1973,
Without doubt this meeting was a great success. As a result the event will now take a regular place in the ultrasonics calendar. And if support for future meetings is as enthusiastic as that given for this one, then Ultrasonics International looks set to become Europe’s international forum of discussion on ultrasound technology. Hopefully this should contribute to balancing the number of international conferences on each side of the Atlantic. Altogether some 380 delegates representing over 30 countries attended and heard a total of 59 papers, while in the exhibition the number of visitors topped the 1 000 mark. As expected, the papers given during the highpower sessions enjoyed the largest support, interest in the other topics being spread fairly evenly. This also applied to the evening seminars which were all extremely well attended and lasted, in some cases, to well after closing time! The exhibition enjoyed enthusiastic support from over 30 exhibitors. Equipment was shown from the UK, USA, Eastern and Western Europe and Asia. The excellent facilities offered by Imperial College also helped in setting the right atmosphere, so much so that the College has now been booked for the next meeting - Ultrasonics International 1975 - to be held from 25 March to 27 March 1975. The conference proceedings will be published later this year and will contain all the papers plus reports of questions, answers and contributions to the discussion. Summaries of the papers can be found in the Special Supplement which accompanied the March issue of the journal. However, for delegates curious to know the highlights of sessions they were unable to attend, and for our readers, reports on each of the sessions are given below.
Professor Mori giving his paper on ultrasonic
ULTRASONICS.
JULY 1973
imperial
College,
London
High-power ultrasonics - general Following the official opening, the first session on general applications of high-power ultrasonics began with R. Pohlman (international editor, ULTRASONICS) and W. V. Richings (Dawe Instruments, UK) as co-chairmen. The first two papers dealt with the subject of ultrasonically enhanced liquid filtering. In the first by A. Semmelink of the University of Cape Town, South Africa, it was shown that substantial increases in the flow rate of a liquid through a filter could be achieved, the main reason for the increase being the prevention of a filter cake forming on the element. Filtering efficiency was found to depend only on the pore size of the filter element, while best results were obtained when the transducer was not connected to the filter element but when placed close to it. Furthermore, it was found that the material used for the filter element largely determines the increase in flow rate with ultrasonic irradiation. H. V. Fairbanks of West Virginia University, USA, confined his paper to the filtering of liquid hydrocarbons. He concluded that, under proper conditions, ultrasonic irradiation was capable of producing substantial increases in the rate of filtration and found that: (a) increasing the pressure of the system and the pressure drop across the filter media along with ultrasonic radiation increased the filtration rate; (b) for every filtration system there appears to be a set of optimum conditions of pressure and ultrasonic power for maximum rate of filtration and; (c) when ultrasonic radiation is introduced into a system countercurrent to the liquid flow it is possible to use a filter media whose channels are larger than the size of the particulate. In the discussion that followed the authors were asked about potential applications such as reverse osmosis.
cleaning
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Replying, H. V. Fairbanks said that the frequency would have to be very high and the power requirements could be prohibitive. However, ultrasound could be used to keep the surface of the membrane clean, but as yet no pilot plant work had been done and the economics of scale-up were uncertain. Plastics welding was the subject of the next paper by S. Kaneko et al (Shibaura Institute of Technology, Japan) who had been looking at ‘the temperature rise effect associated with ultrasonic plastics welding. Plastics bars had been longitudinally vibrated at 20 kHz and amplitude distributions measured by means of a standing-wave method. It was found that the temperature rise was greatest at the node of the amplitude distribution of vibration and lowest at the node of vibration strain. The relationship between generated heat and magnitude of the vibrating strain had also been investigated. E. Mori and K. Itoh of the Tokyo Institute of Technology, Japan, discussed normal modes of vibration in a rectangular ultrasonic cleaning tank. A wideband travelling-wave transducer had been used to excite the modes and it was found that the sound-pressure distribution in the water bath could be made fairly uniform by utilizing the highorder normal modes of vibration arranged close together in the water bath. S. C. Scrivastava (international editor, ULTRASONICS) gave the next paper on the possibility of using ultrasonics to extract shychnine and brucine from nuxvomica seeds on an industrial scale. The time of extraction had been reduced to 30 minutes compared to eight hours or more by conventional methods. Although further work was needed on the optimum frequency required, intensities of 3-5 W cme2 are a practical proposition. As a result a 20 kW generator would be sufficient to produce 50 kg of alkaloid per day. The final paper of the morning session was given by K. F. Graff of Ohio State University, USA. He had been looking at the application of sonic power to rock cutting. A 10 kHz, 10 kW transducer had been used in an impact coupling technique. In this method a loose-coupled cutting tool impacts the transducer tip and rebounds, impacting against the load. So far the method had been found not so efficient as conventional techniques, a result that was not surprising, according to one delegate, who explained that the energy loss at the horn-tool interface would be high. He went on to point out, however, that a different material could be used for the horn to suit energy transmission and for the tool to suit the rock cutting - a point not thought of by the speaker. High-power
ultrasonics - metallurgy
E. A. Neppiras (international editor, ULTRASONICS) and R. D. Finch (University of Houston, USA) were cochairmen for this session. The first paper, given by B. Langenecker of PVL-Physikalische Versuchsanstalt, Austria, outlined basic and applied research on metal deformation processes in macrosonic fields. The report was in two parts. The first part continued previous reports from PVL, explaining how the laboratories are using ultrasonic methods to gain a better understanding of loss mechanisms in crystalline solids under non-linear conditions, especially in the plastic stress range. But they do
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Professor Semmelink to give their papers
(left) and Professor Fairbanks
(right) waiting
not appear to have made any notable new discoveries in the past year. Most of the progress seems to have been in developing reliable automatic equipment for producing and measuring metal deformation, described in the second part of the paper. The system developed uses electronic self-drive and controlled stress (or strain) drive conditions. However, the author did not make clear how these were achieved. The control arrangements are currently being used in ultrasonic wire-drawing systems, but are also applicable to tube-bending, riveting, welding and casting. D. E. MacDonald (Pennsylvania State University, USA) presented an interesting paper on slip modes in ultrasonic metal fatigue. The author uses specimens of copper, brass, iron or titanium, shaped so that the strain is almost constant over a sizeable region. Monitoring can be carried out accurately. By using optical and scanning-electron microscope methods, it was possible to correlate the observed slip and fissure development with four distinct regions into which the internal friction curve could be divided: the elastic region; the anelastic region; the plastic region; and the fatigue region. These four regions were clearly evident in all specimens tested, although the stress regions over which they operated were widely different for the different metals. In all these metals the initial ultrasonic slip is highly localized within isolated grains. These develop directly into fissures which are the forerunners of the propagating microcrack. At very low frequencies the slip-zone fissuring is much more widespread than at ultrasonic frequencies. In iron, low-frequency fatigue comes about through grain-boundary weakening and fissuring. In titanium transcrystalline shear-cracking causes fatigue. The chief difference between high-frequency and low-frequency fatigue, however, is in the transition from microcrack to macrocrack. At high frequency this occurs through deliberate propagation of the individual fissures: whereas at low frequencies it is by random linking of many microcracks.
ULTRASONICS.
JULY
1973
Joints produced by ultrasonic welding at 20 kHz were compared with those obtained,in ordinary fretting using a very low frequency (30 Hz) in the paper given by J. L. Harthoorn of Philips, The Netherlands. The total number of cycles, clamping pressure, and oscillatory displacement were all kept constant while the frequency was changed. After examination it was concluded that there was almost no difference between joints made by the two processes. Joint formation in both ultrasonic welding and fretting was ascribed to plastic deformation of a thin interfacial layer, about 30 pm thick. Diffusion did not play an important role. During the discussion Dr Eisner pointed out that theory predicted an amplitude-threshold below which fretting would not occur however many cycles were used, and asked whether the author had observed any such threshold. The author thought that if the threshold existed it must have been very small. R. Pohlman (international editor, ULTRASONICS) distinguished between two mechanisms for droplet formation in his paper on atomization of liquids and molten baths. These were cavitation and surface-wave break-up. Uniform-sized droplets are obtained when surface waves are used, the droplet diameters are then easily inferred by using the Faraday surface-wave formula. The capillary surface waves are formed on the liquid surface as a square grating or interference pattern and the droplets are thrown off from the crests when the amplitude is large enough. To discriminate against cavitation it is necessary to reduce and control the thickness of the liquid layer on the vibrator surface. This was achieved by the ‘secondary-spray’ method where the liquid to be atomized is sprayed onto the vibrator surface using an appropriate droplet size. The vibrator was also operated under amplitude control to avoid load changes producing a large change in the radiated intensity. Atomization is easiest at low frequencies (20-60 kHz) and these were used for atomizing molten metals at rates up to 30 kg per hour. An interesting film was shown, taken at high-speed and played back slowly, which showed exactly how the liquid droplets form and detach at the crests of the capillary waves. The deep-drawing of cans with ultrasonic radial oscillations applied to the die is only one part of the work now going on at the University of Aston, Birmingham, in the area of metal-deformation processes applied to industry. D. Biddell and D. H. Sansome who gave the paper were concerned mainly with equipment design and comparison of different methods of achieving pure radial oscillations. For some reason not discussed, the authors have no$,considered using a radial-mode transducer-ring-type magnetostrictive laminations for example. Instead, the authors use a series of equi-spaced rod-type transducers coupled to a flat ring which they try to resonate in its radial mode. They also tried tapering the ring in various ways to get amplitude transformation. Useful results were obtained on small cans (about 3/4 in. in diameter) of soft aluminium and of soft and half-hard brass. Deeper depths of draw (up to 50%) were obtained in some cases. Maximum punch loads and ironing loads could be reduced while surface finish was not affected. C. Daly of Dawe Instruments, UK, discussed the safety precautions necessary in operating high-power ultrasonic
ULTRASONICS.
JULY 1973
equipment. These are electrical, mechanical, and acoustical. Medical hazards were not discussed in detail, but the author referred to the well-known papers by Drs Hill and Knight. The final paper was given by A. S. Sliwinski (international editor, ULTRASONICS) who reviewed ultrasonic progress in Poland. The most rapid progress since 1967, according to the author, has been in the area of ‘physical and physicochemical studies’, or what we would call ‘ultrasonic physics’; followed by transducers; medical and biological ultrasonics; ultrasonic measurements; and underwater ultrasonics. More than two-thirds of all papers published in the last five years are in these areas. Non-destructive testing, power ultrasonics, and others, are less active areas. There is little new research going on in macrosonics, although cleaning and plastics welding are expanding steadily. The author mentioned the interest in electrochemical processes and referred to the good review paper presented on this subject at the 1971 Ultrasonics Conference. High-power ultrasonics - metal forming Three papers were presented in this evening session on metal forming, but only one directly concerned such processes. This was a paper by A. W. Smith and D. H. Sansome who described an experiment using a wedge-shaped analogue of the deep-drawing process in which the die and/or punch could be insonated at about 13 kHz. The experiment was part of an extensive programme of work presently being undertaken at the University of Aston in Birmingham on metal deformation. Consideration was given in the paper to both die and punch insonation and it was concluded that oscillation of the punch alone, while reducing the mean load in accordance with stress superposition, does not reduce the maximum punch load. It was also found that the oscillation of the die enabled an increase of about 3% in the limiting draw ratio together with a reduction of punch load of 10%. Some discussion followed on the question of frictional effects as against the insonation effects and also on the efficiency of the system as a whole. The paper and discussion were well complemented by a visit to the University of Aston following the conference, which enabled delegates to see a number of projects in operation and to discuss the problems with Dr Sansome’s group. The other two papers were concerned with fatigue at 20 kHz. B. Weiss from the University of Vienna presented a paper on a new system for fatigue testing in which two co-axially arranged transducers are used in a pulsed mode in experiments during which heating effects are minimized. This paper produced a considerable amount of discussion related to the conclusions drawn, particularly in respect of environmental effects and the frequency effect in fatigue. J. P. Wallace from the University of Columbia presented a paper on high-power ultrasonic fatigue in nickel -based alloys. The results indicated that environmental effects were suppressed at 20 kHz and that ultrasonic fatigue testing was useful as a tool for studying fatigue crack growth. The ensuing discussion, related to both papers, indicated a continuing interest in the field of fatigue at 20 kHz. This interest was centred on the work of B. Weiss et al, D. E. McDonald (Pennsylvannia State University, USA),
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J. P. Wallace et al and B. Hockenhull (Cranfield Institute of Technology, UK). There is not space to state all of the arguments proposed but it was clear that three groups experimenting in this field had many points in common as well as a great many of dissention. During another part of the discussion interest was centred on the role of the environment and the relative importance of crack initiation and crack propagation in the fatigue process. The one point made clear at the end was that in both metal forming and fatigue studies a great deal remains to be done. Visualization This session was one of the best attended of the evening seminars and resulted in an extremely useful and lively discussion at the end. The meeting was also honoured by the presence of Professor Dennis Gabor, the inventor of holography and the 197 1 Nobel prize winner for physics. Chairmen for the session were G. Kossoff (international editor, ULTRASONICS) and C. R. Hill (Institute of Cancer Research, UK). The first paper was by M. J-M. Clement and J. W. Griffiths of Loughborough University of Technology, UK. It described the theory of a scanned ultrasonic holography system operating at 2.5 MHz. The arrangement used three transducers which moved in the translated circular mode. Reconstruction of a coarse-sampled hologram of a 10 in spanner was shown. The advantage of this system lies in its ability to give relatively good results with fairly fast scanning. The paper caused considerable interest and in the subsequent discussion Professor Gabor raised the question of synthetic aperture methods in relation to holography. Further discussion related to different scanning methods and their relative performances. The paper by H. W. Jones, an international editor of ULTRASONICS, reviewed methods of imaging in the range 1- 100 MHz and compared the relative abilities of each in respect to sensitivity, imaging time and resolving power. The usefulness of holography as a step in the imaging process was shown to depend on the physical properties of the receiver used. In some cases the methods of holography were essential to the success of the system, in other cases it provided no advantages. Some discussion concerning sensitivity of the various methods as well as the virtue of direct imaging with lenses followed. P. Greguss (international editor, ULTRASONICS) presented a paper on real-time acoustical-to-optical convertors. This was a most interesting contribution and described a new type of cell akin to the Pohlman cell and designated an AOCC (acoustical-to-optical convertor cell) by the author. The principal of operation depends on the change of birefringence of a thin layer of liquid crystals sandwiched between two plates and viewed with polarized light when insonified. The device was claimed to be effective over a range of sensitivities from about 10 mW cmm2 to an upper limit of about several W cme2. Examples of the images formed were shown, including a film showing the beats between two sources of sound at different frequencies. Discussion concerning the principle of operation followed the paper. J. E. Jacobs of Northwestern University, USA, presented a paper on the use of discrete, shaped matching elements to increase the aperture of the Sokoloff tube. A new
type of piezo-receiver uses 3/4 wavelength hemispheres of metal-loaded resin on the outer surface of the image conversion plate and allows the angular response to be increased to 30 degrees off axis instead of 12-15 degrees normally available. A film showing the performance of the Jacobs-type tube was shown, illustrating qualitatively the differences between the two types of tubes with and without this artifact. The results were impressive and a number of delegates suggested that by using this technique, the Sokoloff tube could well find a new lease of life. In subsequent discussions J. Wardley of EMI, UK, described another tube face which used a thick layer of metal-loaded epoxy resin in an electronic image convertor with a large front face. The tube was capable of receiving over a fairly large range of angles. An additional and final paper was presented by H. J. Wickramasinghe of University College, London, on acoustical holography in solids. In this he described solid surface holography systems for producing acoustical holograms at 150 MHz. The hologram is derived from converting the phase modulation of a laser beam to an amplitude modulated signal by means of a Fabry-Perot interferometer. This system gives a very sensitive receiver with a resolution of 90 pm in the reconstructed image (for more details on this work turn to page 146). The evening concluded with a discussion on the comparative performances of P. Greguss’s AOCC and Jacobs’ image convertor tube. The physics of ultrasonics Cavitation nucleation in liquid helium was reviewed by R. D. Finch (University of Houston) and E. A. Neppiras (advisory editor, ULTRASONICS) during this session chaired by J. H. Collins (University of Edinburgh) and R. W. B. Stephens (advisory editor, ULTRASONICS). Their work had shown that mechanisms believed to explain nucleation in water cannot be operative in superfluid helium, but that the measured thresholds in helium were much lower than its tensile strength. Moreover, the nuclei were thought to be quantized vortices in this case. Recent results showed that the attenuation of second sound was increased by high amplitude normal sound, which probably produces quantized vortices in a turbulent form as a precursor to cavitation. The action of ultrasound on viscoelastic solids was reported by H. M. Frost and W. L. Nyborg of the University of Houston. A wedge-tipped ultrasonic horn had been vibrated against the edge of a strain-birefringent plastics sample. Time dependent isochromatics were observed through a polarizing microscope and could be ‘recorded’ or ‘erased’ at will. As a substitute for the third scheduled paper by G. Bradfield, R. A. Brown reported progress in the development of ultrasonic bubble chambers at CERN. Two parallel plane wave transducers resonant at 100 kHz were pulsed so that standing waves were briefly established between them. Tracks of ionizing radiation were first observed in helium, which requires relatively low pressure excursions. Recent work has been concentrated on liquid hydrogen which is more desirable from the viewpoint of high energy physics but which requires greater pressure excursions (see March ULTRASONICS, p 5 1). The problem of coupling a pzt transducer to the liquid has been met with a X/4 perspex plate and isopentane bonding.
ULTRASONICS,
JULY 1973
M. Pappalardo and D. Assenza from the Instituto di Acustica ‘0. M. Corbino’, Rome, described a transducer intended to produce a scanning beam for medical diagnostics. The device consists essentially of a number of pzt rectangular elements which act as a linear array. The transducer operates at about 600 kHz and the beam may be swept by variable phasing. R. W. B. Stephens and K. T. Lee (Imperial College, London) reported results of measurements of ultrasonic velocity and attenuation in liquid metals and amalgams over a complete range of concentrations. They found absorption peaks at certain atomic concentrations which they believed indicated the existence of molecular association. Some aspects of finite amplitude wave propagation in liquid-filled tubes were discussed by L. Bj&n$ of the Technical University of Denmark. Peak pressures of up to 150 bar and rise times of less than 0.5 ps were attain. able with the author’s apparatus. An elegant presentation of the theory of impedance matching with transition layers was made by P. J. Highmore of the University of Loughborough in the next paper. Finally, important new results on the transmission and reflection of surface waves at corners and steps were presented by M. Munasinghe and G. W. Farnell of McGill University, Montreal. These results have been obtained numerically using a finite difference iterative method. Transmission and reflection coefficients as well as phase shifts were computed together with the conversion of energy to bulk wave form. The extension of the method to anisotropic, piezoelectric media via the use of equivalent isotropic parameters was also discussed.
Underwater
ultrasonics
Chaired by L. Bj&nQ (Technical University of Denmark) and A. S. Sliwinski (international editor, ULTRASONICS) the session opened with V. Welsby of the University of Birmingham, who, in his usual relaxed style, gave a paper on high-frequency marine sonars and acoustic telemeters. He said that in the past there had been a lack of commercial initiative in putting underwater acoustic systems on the market. However, with the rapidly-growing interest shown by the oil and gas supply industries, particularly in the results obtained with sonars capable of producing high angular resolutions and working at frequencies up to several hundred kilohertz, this could soon change. He went on to discuss image forming sonars, acoustic holographic systems, acoustic communication links, mechanicallyscanned sonars, ‘phase-only’ sonars, and acoustic telemetry links. He also described a within-pulse electronically-scanned sonar with a beam angle of 0.05 degrees. The field covered by D. Manley of Vacuum Reflex Ltd, UK, was acoustic position-fixing in which by comparison of the phases of waves received at two receivers to within one degree, a high accuracy could be obtained at ranges up to three miles. The next paper was by R. Haslett of Kelvin Hughs, UK, who packed in a considerable amount of information about his calibrated target-strength measuring equipment operating at five frequencies between 30 and 547 kHz. This had now been automated and produced numerous back-scattering diagrams for fish. It is also being used for comparative scale-model work.
ULTRASONICS.
JULY 1973
A tremendous amount of detail on the temperature microstructure and acoustic intensity fluctuations in New Zealand coastal waters was given by F. Sagar, an international editor of ULTRASONICS. His measurements, the result of a ten year study, have confirmed by means of computer and analogue calculations of spectral densities, the Kolmogrov turbulence theory. M. A. Wright of the Royal Aircraft Establishment, UK, reviewed some of the techniques using underwater scale models of aircraft and ultrasonic waves to simulate radar echoes. Two characteristics are important: the size of the echo and the apparent movement of the radar centre. A Sokoloff-tube system operating at 2 MHz is being built to visualize the highlights. The final paper in this session was given by M. Matsuda of the Electra-Communication University, Japan, who had developed a method of increasing the efficiency of an underwater sparker to 20%. His technique used a highcurrent discharge through a tungsten wire stretched between two spheres; normal efficiency without the wire is about 4%. Another advantage of the system is that the pulse is shorter and cleaner. As expected, the paper by A. Barone on boomer arrays was not given. Transducers This evening session was again well attended, indicating that many physicists and engineers working in ultrasonics still need information on this more or less classical field. The construction of the pre-stressed transducer and the piezoelectric ceramic transducer were well covered, despite the fact that at the very last moment it was found that two papers on the former topic could not be presented by the authors themselves, a fact which inevitably limited the discussion. A. P. Hulst of Philips, The Netherlands, described the general outlines of pre-stressed compound piezoelectric transducers consisting of: (a) oppositely poled ceramic piezoelectric rings electrically excited in parallel on both sides of the excursion node; (b) two metallic end pieces (Mg, Al, T&alloy, brass or steel) constituting the remaining length of the half-wavelength transducer, and; (c) a central pre-stressing bolt exerting an axial compressive stress of 3-4 kgf mmm2 (” 5 000 psi) on the ceramic rings. The author presented a theoretical analysis of the electrical impedance and the electroacoustic efficiency which was supported by much experimental data. Additional data was presented in the paper by E. A. Neppiras (advisory editor, ULTRASONICS) and read by J. P. Perkins, and in the paper by W. Pajewski (Institute of Fundamental Technical Research, Warsaw) and read by A. S. Sliwinski. All three papers assumed the use of some modified lead zirconate titanate ceramic as the active piezoelectric material. The last paper by F. W. Ainger (Plessey Ltd, UK) described the interesting effects of adding small amounts of iron to the lead zirconate titanate formula. Additions as small as 0.03 to 0.3 weight per cent of iron cause a dramatic reduction in the losses and variation of permittivity with ac voltage amplitude. Also ageing and depolarization are considerably reduced at the high-ultrasound intensities involved.
Surface acoustic waves Surface acoustic waves are such that they are accessible at all points on their two-dimensional propagation path. This feature, coupled with their low propagation loss and ease of efficient transduction makes them very attractive for a wide range of real-time signal processing applications. In this session on SAW appljcations, chaired by E. A. Ash (University College, London) and L. Pantani (Consiglio Nazionale delle Ricerche, Italy), P. M. Grant of the University of Edinburgh described SAW analogue matched filters which are a convenient means of generating and correlating coded waveforms. They are attractive for digital communication systems employing band-spreading, and several such systems were discussed. Experimental results confirmed the theoretical reduction in error rate which is obtained by using matched filters if noise or interference is present, and showed the importance of choosing the correct threshold setting in the receiver. The surface wave convolver, described by D. P. Morgan of the University of Edinburgh, can also correlate a coded waveform if an additional coded reference waveform is provided. This device is highly programmable. Special techniques were described which substantially reduced the level of spurious signals produced by a degenerate convolver. An alternative convolver, using a tapped delay line with each tap connected to a diode, was shown to be very efficient. Convolvers have the disadvantage that they are not asynchronous. However, in some applications this is not a problem and an example of a possible system for a secure radio altimeter was given. G. Socino (Instituto di Acustica ‘0. M. Corbino’, Italy) described experiments on the deflection of a light beam passing through a crystal supporting a surface wave. The efficiency of the deflector depends on the angle of incidence and polarization of the light, and on the crystal cut. Close agreement between theory and experiment was found. Optimum polarizations and incidence angles were established for several cuts of lithium niobate. Quartz was shown to be much less efficient. J. Chambers of University College, London, described waveguides for surface waves, particularly the wedge waveguide where the wave travels along the apex of a wedge. This slow, non-dispersive wave has been observed in pzt and lithium niobate, and wedge waveguides have also been made on a silicon wafer by selective etching. A convolver using this waveguide on pzt gave substantially increased efficiency due to the confinement of the wave. It was also shown that non-linear effects can be used to couple a surface wave into a gold film waveguide oriented perpendicular to the propagation direction. Finally, L. Pantani reviewed techniques for the measurement of surface wave velocities. Along with methods applicable to bulk-wave delay lines, new techniques are made possible by the accessibility of surface waves. These include use of a double transducer structure which can be used to measure delay by using a pulse superposition technique. Results obtained with this technique showed an accuracy of 0.1%. Non-destructive
testing
The chairmen for this session were R. Sharpe of the Nondestructive Testing Centre, Harwell. and L. X. Nepomuceno
160
of the Laboratorio de Acustica e Sonica, Sao Paulo, Brazil. Mr Sharpe opened the session with a short speech in which he remarked that ndt was still the main outlet for ultrasonics, although he thought that the morning’s programme emphasized the more specialized techniques rather than the usual industrial applications. He hoped that the general discussions would lose none of the liveliness that characterized the previous Ultrasonics for Industry conferences. The only speaker in the session who covered the field in general was L. X. Nepomuceno who spoke about ultrasonics in Brazil. The history of ultrasonics in Brazil is short. In the early fifties there was some activity in Brazilian universities, all of which, however. ceased in the mid-sixties. On the other hand, industrial applications increased from a very low level to the level of intense activity seen today. Sales of ultrasonic equipment are now worth &I 000 m a year. This situation has meant that the number of trained technicians is far too low, a situation which the speaker described as dangerous. There were some signs, however, that a government initiative would ameliorate the situation. Two speakers made contributions on ultrasonic visualization. H. Slater reported the work at Tube Investments on schlieren visualization using a computer. His research group had mathematically analysed the transformations of ultrasound at corners and compared the computer images with schlieren visualization. The method has been quite successful with crater-like cracks in metals although the calculation of defect size is still a problem because of the non-linear response. This difficulty, however, is confidently expected to be resolved. L. W. Kessler of Zenith Radio Corporation, USA, described an acoustic microscopy system which was capable of resolving to better than 10 ym at frequencies as low as 220 MHz. His experimental technique uses the dynamic ripple pattern generated on a plastics mirror by the object beam. The pattern is scanned by a focused laser beam from which, by means of a photodiode, an acoustic image or an acoustic hologram of the object is obtained. During the discussion the author was asked whether heating caused by sound absorption was observed in specimens and whether the technique was restricted to thin samples. Dr Kessler replied that heating effects depended on sensitivity but said that with the present real-time presentation using 0.25 W cm-l, heating was not significant. On the question of sample size he said that the limitation was the same as with optical microscopes. Finally, the author said, in reply to a question on ultimate limits to resolution, that as far as he could see, it was at least possible to go down to a fraction of a micrometre - below half a micrometre say ~- and in principle the technique could do better than light microscopy. An up-to-date ultrasonics conference would be incomplete without a mention of acoustic emission. There were two papers on the subject. R. Hill of the University of Aston, Birmingham, spoke on the evaluation of transducers for this technique. He compared some of the electrical properties of various transducers and went on to discuss coupling media. He felt that solid couplants were inferior to greases such as vacuum grease. Mr Arrington of Cambridge Consultants, UK, read a paper for his colleague, A. A. Pollock. He very quickly went through a list of the advantages of acoustic emission and then spoke about some of the disadvantages. For example, it is always necessary to stress the structure but the stressing may differ from actual stress in use. The use of acoustic emission also depends on the
ULTRASONICS
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1973
material parameters of the structure, although in practice it is fortunate in that steel presents comparatively few problems. The other disadvantage mentioned was the existence of spurious emissions from rubbing and so on. R. E. Green of the Johns Hopkins University, USA, put forward attenuation measurement as a rival to acoustic emission. This too has advantages and disadvantages. There is no analogue to the Kaiser effect and many materials exhibit a memory of earlier changes in attenuation, that is, of earlier stressing. One notable disadvantage of the technique is the need to leave transducers in place over the time of investigation, sometimes for years. The session concluded with a paper for ndt engineers: a paper on a particular solution to a particular testing problem. D. E. Bray of the Federal Railroad Administration, Washington, USA, spoke of the use of surface waves to find flaws in railway wheels. His research group had used l/4 scale model railway wheels and attempted to locate simulated thermal cracks using both pulse-echo and attenuation methods. The extension of this work to full-size wheels with actual defects is currently in progress. J. Obraz’s paper on ultrasonic evaluation of flaw size in thin-walled plates was deleted from the programme. Medical and biological ultrasonics Eight papers were presented during this session chaired by P. N. T. Wells (University of Wales) and C. N. Smyth (international editor, ULTRASONICS). In the first paper G. Kossoff (international editor, ULTRASONICS) gave a review of ultrasonic research in medicine in Australia. He described the techniques developed by the Commonwealth Acoustic Laboratories to improve the grey scale, sensitivity and resolution of the echograms and illustrated these by examples of echograms of the pregnant uterus, the eye and the breast. The second portion of his paper was devoted to a description of methods to overcome the basic limitations of present techniques. These included the use of annular, linear and cross-phased array transducers, the applications of on-line digital processing of the ultrasonic data and in vivo measurement of attenuation and velocity of propagation.
The fourth paper by J. P. Jones (Bolt Beranek and Newman Inc, USA) described a new ultrasonic technique termed impediography which promises to have considerable application in non-destructive testing and medical diagnosis. The technique employs time deconvolution of echoes to produce a plot of impedance values along the propagation path of the ultrasonic beam. The paper was illustrated with results obtained in the examination of layers of rubber where it was shown that the technique is capable of determining changes in the acoustic impedance in rubber caused by stretching. In biological applications, the technique revealed the presence of a small blood clot behind skull bone and, by taking nine propagating paths, a crosssectional impedogram was constructed which showed good agreement with the cross-sectional section of the limb. R. S. Mackay, an international editor of ULTRASONICS, was not able to attend the meeting and present his results on the detection of decompression by ultrasonic imaging of gas bubbles in tissue. Instead, his work was illustrated by a film which showed the time course of development of gas bubbles in the limbs of animals subjected to various rates of decompression. A new method of detecting movements of bodies in electrolytes and colloids using the combined effect of ultrasonic and electric waves was described by C. Quentln (University of Paris). The introduction of ultrasonic waves in the electrolyte generates a periodic excess of anions and cations due to the difference in velocities imparted to these ions through their different mass and fractional coefficients. This creates a potential which is reflected in the impedance of the superimposed electric field. When a moving structure is present the reflected ultrasonic wave alters this potential and its movement is detected by measurement of impedance of the electric field. The application of the technique for monitoring fetal cardiac activity was described and, although it would appear more work is necessary before the method can be applied in a clinic, the paper certainly showed the potential of the method.
In the second paper F. Weill (Centre Hospitalier et Universitaire de Besangon, France) described the crosssectional evaluation of pericardial diffusions. This study was carried out using a commercial instrument which quickly scans the ultrasonic beam thus allowing a real-time display of moving structures. The paper was illustrated by a film which clearly showed the movement of the anterior wall of the heart and the changes that occur in this motion when liquid is present between the chest and the anterior heart wall.
In response to the increased concern shown in the dose of ultrasound received by a patient during a pulsed ultrasonic examination, T. A. Whittingham from the Regional MedicalPhysics Department, Newcastle-upon-Tyne, UK, described a method which automatically measures the number of energiz. ing pulses applied to the transducer. Allowance is made for the times when the transducer is not in contact with the patient. It was suggested that the number so obtained could be related to absolute units of energy for each transducer. The acoustic output could then be displayed on a digital readout system of the type now being increasingly used to display other information obtained by the echoscope
In the third paper T. G. Brown (Royal Infirmary, Edinburgh, UK) described a design for an inexpensive mechanical scanner for rapid three-dimensional scanning of tissues. The transducer is scanned in a conical manner with the transducer being held at the apex, the whole scan taking less than ten seconds. The design is still in the development stage and the author did not present any results obtained with the technique.
In a final paper, A. J. Last from the Ontario Research Foundation, Canada, described the development of a new type of sterilizing solution which is effective over shorter periods of time and which, when combined with ultrasonic cleaning, reduces the sterilization of surgical and dental instruments to a period of less than one hour. A description was also given of a specialized tank designed for use with this solution.
ULTRASONICS.
JULY 1973
161
Exhibition With a record number of stands a great deal of interest was shown in the exhibition - a fact borne out by the total attendance figure of well over 1 000. On the stands a lot of the equipment was new, much of it being shown in public for the first time. Non-destructive testing equipment naturally took a fair share of the stand space. Baugh & Weedon unveiled their latest portable thickness gauge, the PA1040, featuring a measurement range of 0.010-10 in with an accuracy of 1% f one digit. Other features included digital display, automatic ranging, automatic gain control, and, according to the makers, a competitive selling price. Baugh & Weedon also showed for the first time their PA1010 portable flaw
zation system with automatic scanning and storage-tube presentation and comes complete with a range of shear and longitudinal wave probes. Videoson also showed their pulse-echo, pulse-transmission apparatus, PEPTRA, designed initially with the help of the National Physical Laboratory. Ultrasonoscope, who have just finished supplying an in-line ultrasonic plate testing system to the British Steel Corporation, showed a selection from their extensive range of ndt equipment. Exhibits included battery portable units and immersion systems with motorized x-y scan and quantized C-scan recorders. French ndt equipment was shown on the stand of Magnitech, who have now become the UK distributers for Ultrasonic Meaux of Paris. Ultrasonic Meaux produce a wide range of both ndt and medical ultrasonic equipment. Examples of their equipment included portable thickness gauges and flaw detectors, and a six-channel rotary inspection system designed for in-line monitoring of tube and rod diameters. A new logarithmic (pulser-receiver) amplifier was shown giving logarithmic characteristics for minimum variation of input voltage of 70 dB. From India came equipment produced by the Electronics Corporation of India, a state run venture set up in 1967 by the Department of Atomic Energy. They showed their UFD-67 flaw detector which has been in production for about a year and is sold widely throughout India. The unit is capable of resolving to 6 mm, is battery operated and all solid state. The Corporation also produces ultrasonic leak detectors, examples of which were shown.
Baugh 81 Weedon’s PA 1010 flaw detector use
adapted for underwater
As usual the Nondestructive Testing Centre, Harwell, had much of interest on its stand, The Centre investigates fundamental ndt problems as well as undertaking contract research into specific problems for individual companies. Examples of ultrasonic testing systems developed included: a high-precision thickness gauge that measures thickness from 75 pm to 3 mm, typically to an accuracy of ?O. 1%; a simple B-scan flaw detector built from units of Harwell’s wide range of compatible ndt electronic modules; and an
detector encased in a pressure-tight housing for underwater use. Sonatest’s stand included their new UFDl flaw detector and their latest battery portable unit, the UFD2, a versatile lightweight set available with or without monitor. More new equipment was shown on Automation Industries’, stand who displayed their new Sperry UJ portable flaw detector (with a range of over 10 m in steel) and their improved UM77.5 and UM771 Reflectoscopes. Improvements included rotary controls for delay and range, and better overall stability. The latest instruments from Terratest were the TT-200 flaw detector featuring a broadband (0.5-10 MHz) amplifier, and the BT-22 materials tester. The BT-22 is an improved version of the established BT-2 tester giving a wider range of frequencies (10 kHz to 1 MHz) and featuring modular circuit construction. Both BT-2 and BT-22 have digital readouts to 0.1 gs and binary coded digital outputs. Only two B-scan flaw detectors were on show and one, the FPl type A, was on Videoson’s stand. This is a visuali-
162
The six-channel Meaux
tube and rod inspection
system made by Ultrasonic
ULTRASONICS.
JULY 1973
to 0.5 km. The system is able to operate for about 20 days, although this is dependent on pulse rate, and uses a carrier frequency of 74 kHz. Kerry Ultrasonics showed welding and cleaning equipment together with some forward engineering applications of surface wave lines made by their offshoot, Sonicstore. Other stands showing cleaning equipment were those of William Boulton, L & R Ultrasonics, Beech & Son, and Raydne who revealed their new UVD-2 300 W two-stage mini degreaser (see May ULTRASONICS, p 107).
Wiredrawing machine for high-strength macrosonic control unit
Kerry Ultrasonics’
Vibrason
steel using the PVL CUlOOO
system for industrial and laboratory
applications
acoustic emission system for the detection of crack growth in thin plates, again built from the modular range. A portable acoustic impedance meter was also shown which, in one mode, could detect liquid levels in enclosed vessels with steel or fibre-glass walls up to l/4 in thick and, in another, could register changes in a materials density or attenuation properties. In addition, two of the Centre’s services were featured: the probe-beam testing service and the quality technology information service ‘QUALTZS’ - the newly introduced subscriber information service.
Stands showing high-power equipment were also plentiful. Dawe Instruments showed their latest 1 200 W plastics assembly system, the 703gA, together with their new E-series 40 kHz Soniclean generators. A macrosonic control unit made by PVL of Austria was also shown. Known as the CUlOOO, the unit was designed for the measurement and control of macrosound from 16-10d kHz, either in general laboratory use or in industrial applications such as wire or deep drawing, welding, drilling, casting and riveting. Another high-power measuring instrument on show was the Wave Energy Systems, 20 kW wattmeter on the stand of H. Tinsley. A new design of transducer incorporating a magnesium transmission line giving a very high acoustic efficiency was another WES product. The generator, which produces a variable output and is self tuning, was shown operating with a Fourier-curve microprobe with a step ratio of 40 : 1. Output was 200 W at 23 kHz. Tinsley were also showing their latest equipment, an ultrasonic fish tagging system with a range of up
ULTRASONICS.
JULY 1973
Four companies showed their range of ceramic materials. Plessey, who make transducers in barium titanate and lead zirconate titanate, displayed working exhibits of a transparent light-sensitive lead lanthanum zirconate titanate material, and a metered fuel atomizer. The atomizer, made from lead zirconate, operates at 50 kHz and produces oil droplets from 50-300 pm in diameter. Typical applications include use in steady engines (such as those in boats) and heaters, dispersion of slurries, and chemical processing. Mullard too displayed piezoelectric ceramic components available in various grades of lead zirconate titanate suitable for both high and low-power applications. Piezoelectric ceramics, acoustic elements, igniters, filters, air and sandwich transducers were among the exhibits on Vernitron’s stand. One late addition to the exhibition was Channel Industries of California, makers of piezoelectric ceramics for over 15 years. Again they produce lead zirconate titanate and barium titanate materials but specialize in unusual shapes and small quantities. Examples of their products included discs, plates, tubes, spheres and hemispheres. On the medical stands Nuclear Enterprises demonstrated their award-winning Diasonograph NE4102 (see Ultrasonics News, p 149) and their new modular Diasonoscope NE4121. Designed for routine clinical use the NE4121 features four-mode display and can, with the aid of a plug-in cardiac module, be used for time-position or moving structure examinations. GEC, who recently became the UK distributors for Picker International
High-power
plastics welding equipment
on Radyne’s stand
163
(USA) showed the Midliner, a computerized echoencephalograph with digital readout. Doppler units for obstetric use were also on show together with equipment for B-scan laminography. It had been hoped that examples of Japanese medical equipment would be shown on the stand of ES1 Nuclear and Old Delft. However, the distance between the UK and Japan proved too much and we had to be content with glossy photographs of equipment made by Toshiba. Among Toshiba’s most recent developments is a computer system for obtaining patterns on a colour display of simultaneous tomographic images. The distance between the UK and France did not prove too much for Delalande Electronique of France, makers of Doppler blood-flow monitors. Their display consisted of the DU flowmeter, an instrument for measuring blood-flow circulating in the tubes of artificial kidneys. Accuracy is claimed to be 210% t 10 ml on tubes of known internal diameter. A second instrument shown was the DUD flowmeter which measured instantaneous flow rate and mean rates of flow. Operating frequency was 4 MHZ.
Compact
the latest addition to Kretztechnik’s range of pocket Doppler instruments - the 9 MHz Minivason (see May ULTRASONICS, p 105). In addition to the commercial exhibits, two stands showed equipment designed by universities. The University of Loughborough showed a translated circular scanner for sensitive but fast acoustical holography. The equipment was the subject of a paper given during the conference by M. J-M. Clement and J. W. R. Griffiths. The University also showed an ultrasonic resonance technique for finding depth location of a non-bond in a multilayered medium. Another college exhibit was an ultrasonic cross-correlation flowmeter shown by Teesside Polytechnic. The instrument was of the type used for measuring flow rates of difficult fluids in the chemical process industry. In measuring two-phase flow its accuracy is an order of magnitude better than that given by other known methods. At present this is about 1.5% compared to 15% for most other instruments. Full details are given in the paper by J. Coulthard in the March issue of ULTRASONICS (pp 83-88).
A cardiographic diagnostic ultrasonoscope, the Ekoline 20A, was displayed on Smith Kline’s stand and was used in conjunction with the Cambridge fibre-optic medical recorder. The recorder can be used with any commercial echocardioscope providing continuous echocardiogram recordings simultaneously with up to 11 other physiological tracings. Two new equipments were seen on TEM Sales’ stand who distribute Kretztechnik medical equipment. The first was the 7200 MA ophthalmoscope (see May ULTRASONICS, p 105) which features a high-accuracy amplifier and display system for accurate tissue differentiation. The second was
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Without doubt this meeting was a great success. As a result the event will now take a regular place in the ultrasonics calendar. And if support for future meetings is as enthusiastic as that given for this one, then Ultrasonics International looks set to become Europe’s international forum of discussion on ultrasound technology. Hopefully this should contribute to balancing the number of international conferences on each side of the Atlantic. Altogether some 380 delegates representing over 30 countries attended and heard a total of 59 papers, while in the exhibition the number of visitors topped the 1 000 mark. As expected, the papers given during the highpower sessions enjoyed the largest support, interest in the other topics being spread fairly evenly. This also applied to the evening seminars which were all extremely well attended and lasted, in some cases, to well after closing time! The exhibition enjoyed enthusiastic support from over 30 exhibitors. Equipment was shown from the UK, USA, Eastern and Western Europe and Asia. The excellent facilities offered by Imperial College also helped in setting the right atmosphere, so much so that the College has now been booked for the next meeting - Ultrasonics International 1975 - to be held from 25 March to 27 March 1975. The conference proceedings will be published later this year and will contain all the papers plus reports of questions, answers and contributions to the discussion. Summaries of the papers can be found in the Special Supplement which accompanied the March issue of the journal. However, for delegates curious to know the highlights of sessions they were unable to attend, and for our readers, reports on each of the sessions are given below.
Professor Mori giving his paper on ultrasonic
ULTRASONICS.
JULY 1973
imperial
College,
London
High-power ultrasonics - general Following the official opening, the first session on general applications of high-power ultrasonics began with R. Pohlman (international editor, ULTRASONICS) and W. V. Richings (Dawe Instruments, UK) as co-chairmen. The first two papers dealt with the subject of ultrasonically enhanced liquid filtering. In the first by A. Semmelink of the University of Cape Town, South Africa, it was shown that substantial increases in the flow rate of a liquid through a filter could be achieved, the main reason for the increase being the prevention of a filter cake forming on the element. Filtering efficiency was found to depend only on the pore size of the filter element, while best results were obtained when the transducer was not connected to the filter element but when placed close to it. Furthermore, it was found that the material used for the filter element largely determines the increase in flow rate with ultrasonic irradiation. H. V. Fairbanks of West Virginia University, USA, confined his paper to the filtering of liquid hydrocarbons. He concluded that, under proper conditions, ultrasonic irradiation was capable of producing substantial increases in the rate of filtration and found that: (a) increasing the pressure of the system and the pressure drop across the filter media along with ultrasonic radiation increased the filtration rate; (b) for every filtration system there appears to be a set of optimum conditions of pressure and ultrasonic power for maximum rate of filtration and; (c) when ultrasonic radiation is introduced into a system countercurrent to the liquid flow it is possible to use a filter media whose channels are larger than the size of the particulate. In the discussion that followed the authors were asked about potential applications such as reverse osmosis.
cleaning
155
Replying, H. V. Fairbanks said that the frequency would have to be very high and the power requirements could be prohibitive. However, ultrasound could be used to keep the surface of the membrane clean, but as yet no pilot plant work had been done and the economics of scale-up were uncertain. Plastics welding was the subject of the next paper by S. Kaneko et al (Shibaura Institute of Technology, Japan) who had been looking at ‘the temperature rise effect associated with ultrasonic plastics welding. Plastics bars had been longitudinally vibrated at 20 kHz and amplitude distributions measured by means of a standing-wave method. It was found that the temperature rise was greatest at the node of the amplitude distribution of vibration and lowest at the node of vibration strain. The relationship between generated heat and magnitude of the vibrating strain had also been investigated. E. Mori and K. Itoh of the Tokyo Institute of Technology, Japan, discussed normal modes of vibration in a rectangular ultrasonic cleaning tank. A wideband travelling-wave transducer had been used to excite the modes and it was found that the sound-pressure distribution in the water bath could be made fairly uniform by utilizing the highorder normal modes of vibration arranged close together in the water bath. S. C. Scrivastava (international editor, ULTRASONICS) gave the next paper on the possibility of using ultrasonics to extract shychnine and brucine from nuxvomica seeds on an industrial scale. The time of extraction had been reduced to 30 minutes compared to eight hours or more by conventional methods. Although further work was needed on the optimum frequency required, intensities of 3-5 W cme2 are a practical proposition. As a result a 20 kW generator would be sufficient to produce 50 kg of alkaloid per day. The final paper of the morning session was given by K. F. Graff of Ohio State University, USA. He had been looking at the application of sonic power to rock cutting. A 10 kHz, 10 kW transducer had been used in an impact coupling technique. In this method a loose-coupled cutting tool impacts the transducer tip and rebounds, impacting against the load. So far the method had been found not so efficient as conventional techniques, a result that was not surprising, according to one delegate, who explained that the energy loss at the horn-tool interface would be high. He went on to point out, however, that a different material could be used for the horn to suit energy transmission and for the tool to suit the rock cutting - a point not thought of by the speaker. High-power
ultrasonics - metallurgy
E. A. Neppiras (international editor, ULTRASONICS) and R. D. Finch (University of Houston, USA) were cochairmen for this session. The first paper, given by B. Langenecker of PVL-Physikalische Versuchsanstalt, Austria, outlined basic and applied research on metal deformation processes in macrosonic fields. The report was in two parts. The first part continued previous reports from PVL, explaining how the laboratories are using ultrasonic methods to gain a better understanding of loss mechanisms in crystalline solids under non-linear conditions, especially in the plastic stress range. But they do
156
Professor Semmelink to give their papers
(left) and Professor Fairbanks
(right) waiting
not appear to have made any notable new discoveries in the past year. Most of the progress seems to have been in developing reliable automatic equipment for producing and measuring metal deformation, described in the second part of the paper. The system developed uses electronic self-drive and controlled stress (or strain) drive conditions. However, the author did not make clear how these were achieved. The control arrangements are currently being used in ultrasonic wire-drawing systems, but are also applicable to tube-bending, riveting, welding and casting. D. E. MacDonald (Pennsylvania State University, USA) presented an interesting paper on slip modes in ultrasonic metal fatigue. The author uses specimens of copper, brass, iron or titanium, shaped so that the strain is almost constant over a sizeable region. Monitoring can be carried out accurately. By using optical and scanning-electron microscope methods, it was possible to correlate the observed slip and fissure development with four distinct regions into which the internal friction curve could be divided: the elastic region; the anelastic region; the plastic region; and the fatigue region. These four regions were clearly evident in all specimens tested, although the stress regions over which they operated were widely different for the different metals. In all these metals the initial ultrasonic slip is highly localized within isolated grains. These develop directly into fissures which are the forerunners of the propagating microcrack. At very low frequencies the slip-zone fissuring is much more widespread than at ultrasonic frequencies. In iron, low-frequency fatigue comes about through grain-boundary weakening and fissuring. In titanium transcrystalline shear-cracking causes fatigue. The chief difference between high-frequency and low-frequency fatigue, however, is in the transition from microcrack to macrocrack. At high frequency this occurs through deliberate propagation of the individual fissures: whereas at low frequencies it is by random linking of many microcracks.
ULTRASONICS.
JULY
1973
Joints produced by ultrasonic welding at 20 kHz were compared with those obtained,in ordinary fretting using a very low frequency (30 Hz) in the paper given by J. L. Harthoorn of Philips, The Netherlands. The total number of cycles, clamping pressure, and oscillatory displacement were all kept constant while the frequency was changed. After examination it was concluded that there was almost no difference between joints made by the two processes. Joint formation in both ultrasonic welding and fretting was ascribed to plastic deformation of a thin interfacial layer, about 30 pm thick. Diffusion did not play an important role. During the discussion Dr Eisner pointed out that theory predicted an amplitude-threshold below which fretting would not occur however many cycles were used, and asked whether the author had observed any such threshold. The author thought that if the threshold existed it must have been very small. R. Pohlman (international editor, ULTRASONICS) distinguished between two mechanisms for droplet formation in his paper on atomization of liquids and molten baths. These were cavitation and surface-wave break-up. Uniform-sized droplets are obtained when surface waves are used, the droplet diameters are then easily inferred by using the Faraday surface-wave formula. The capillary surface waves are formed on the liquid surface as a square grating or interference pattern and the droplets are thrown off from the crests when the amplitude is large enough. To discriminate against cavitation it is necessary to reduce and control the thickness of the liquid layer on the vibrator surface. This was achieved by the ‘secondary-spray’ method where the liquid to be atomized is sprayed onto the vibrator surface using an appropriate droplet size. The vibrator was also operated under amplitude control to avoid load changes producing a large change in the radiated intensity. Atomization is easiest at low frequencies (20-60 kHz) and these were used for atomizing molten metals at rates up to 30 kg per hour. An interesting film was shown, taken at high-speed and played back slowly, which showed exactly how the liquid droplets form and detach at the crests of the capillary waves. The deep-drawing of cans with ultrasonic radial oscillations applied to the die is only one part of the work now going on at the University of Aston, Birmingham, in the area of metal-deformation processes applied to industry. D. Biddell and D. H. Sansome who gave the paper were concerned mainly with equipment design and comparison of different methods of achieving pure radial oscillations. For some reason not discussed, the authors have no$,considered using a radial-mode transducer-ring-type magnetostrictive laminations for example. Instead, the authors use a series of equi-spaced rod-type transducers coupled to a flat ring which they try to resonate in its radial mode. They also tried tapering the ring in various ways to get amplitude transformation. Useful results were obtained on small cans (about 3/4 in. in diameter) of soft aluminium and of soft and half-hard brass. Deeper depths of draw (up to 50%) were obtained in some cases. Maximum punch loads and ironing loads could be reduced while surface finish was not affected. C. Daly of Dawe Instruments, UK, discussed the safety precautions necessary in operating high-power ultrasonic
ULTRASONICS.
JULY 1973
equipment. These are electrical, mechanical, and acoustical. Medical hazards were not discussed in detail, but the author referred to the well-known papers by Drs Hill and Knight. The final paper was given by A. S. Sliwinski (international editor, ULTRASONICS) who reviewed ultrasonic progress in Poland. The most rapid progress since 1967, according to the author, has been in the area of ‘physical and physicochemical studies’, or what we would call ‘ultrasonic physics’; followed by transducers; medical and biological ultrasonics; ultrasonic measurements; and underwater ultrasonics. More than two-thirds of all papers published in the last five years are in these areas. Non-destructive testing, power ultrasonics, and others, are less active areas. There is little new research going on in macrosonics, although cleaning and plastics welding are expanding steadily. The author mentioned the interest in electrochemical processes and referred to the good review paper presented on this subject at the 1971 Ultrasonics Conference. High-power ultrasonics - metal forming Three papers were presented in this evening session on metal forming, but only one directly concerned such processes. This was a paper by A. W. Smith and D. H. Sansome who described an experiment using a wedge-shaped analogue of the deep-drawing process in which the die and/or punch could be insonated at about 13 kHz. The experiment was part of an extensive programme of work presently being undertaken at the University of Aston in Birmingham on metal deformation. Consideration was given in the paper to both die and punch insonation and it was concluded that oscillation of the punch alone, while reducing the mean load in accordance with stress superposition, does not reduce the maximum punch load. It was also found that the oscillation of the die enabled an increase of about 3% in the limiting draw ratio together with a reduction of punch load of 10%. Some discussion followed on the question of frictional effects as against the insonation effects and also on the efficiency of the system as a whole. The paper and discussion were well complemented by a visit to the University of Aston following the conference, which enabled delegates to see a number of projects in operation and to discuss the problems with Dr Sansome’s group. The other two papers were concerned with fatigue at 20 kHz. B. Weiss from the University of Vienna presented a paper on a new system for fatigue testing in which two co-axially arranged transducers are used in a pulsed mode in experiments during which heating effects are minimized. This paper produced a considerable amount of discussion related to the conclusions drawn, particularly in respect of environmental effects and the frequency effect in fatigue. J. P. Wallace from the University of Columbia presented a paper on high-power ultrasonic fatigue in nickel -based alloys. The results indicated that environmental effects were suppressed at 20 kHz and that ultrasonic fatigue testing was useful as a tool for studying fatigue crack growth. The ensuing discussion, related to both papers, indicated a continuing interest in the field of fatigue at 20 kHz. This interest was centred on the work of B. Weiss et al, D. E. McDonald (Pennsylvannia State University, USA),
157
J. P. Wallace et al and B. Hockenhull (Cranfield Institute of Technology, UK). There is not space to state all of the arguments proposed but it was clear that three groups experimenting in this field had many points in common as well as a great many of dissention. During another part of the discussion interest was centred on the role of the environment and the relative importance of crack initiation and crack propagation in the fatigue process. The one point made clear at the end was that in both metal forming and fatigue studies a great deal remains to be done. Visualization This session was one of the best attended of the evening seminars and resulted in an extremely useful and lively discussion at the end. The meeting was also honoured by the presence of Professor Dennis Gabor, the inventor of holography and the 197 1 Nobel prize winner for physics. Chairmen for the session were G. Kossoff (international editor, ULTRASONICS) and C. R. Hill (Institute of Cancer Research, UK). The first paper was by M. J-M. Clement and J. W. Griffiths of Loughborough University of Technology, UK. It described the theory of a scanned ultrasonic holography system operating at 2.5 MHz. The arrangement used three transducers which moved in the translated circular mode. Reconstruction of a coarse-sampled hologram of a 10 in spanner was shown. The advantage of this system lies in its ability to give relatively good results with fairly fast scanning. The paper caused considerable interest and in the subsequent discussion Professor Gabor raised the question of synthetic aperture methods in relation to holography. Further discussion related to different scanning methods and their relative performances. The paper by H. W. Jones, an international editor of ULTRASONICS, reviewed methods of imaging in the range 1- 100 MHz and compared the relative abilities of each in respect to sensitivity, imaging time and resolving power. The usefulness of holography as a step in the imaging process was shown to depend on the physical properties of the receiver used. In some cases the methods of holography were essential to the success of the system, in other cases it provided no advantages. Some discussion concerning sensitivity of the various methods as well as the virtue of direct imaging with lenses followed. P. Greguss (international editor, ULTRASONICS) presented a paper on real-time acoustical-to-optical convertors. This was a most interesting contribution and described a new type of cell akin to the Pohlman cell and designated an AOCC (acoustical-to-optical convertor cell) by the author. The principal of operation depends on the change of birefringence of a thin layer of liquid crystals sandwiched between two plates and viewed with polarized light when insonified. The device was claimed to be effective over a range of sensitivities from about 10 mW cmm2 to an upper limit of about several W cme2. Examples of the images formed were shown, including a film showing the beats between two sources of sound at different frequencies. Discussion concerning the principle of operation followed the paper. J. E. Jacobs of Northwestern University, USA, presented a paper on the use of discrete, shaped matching elements to increase the aperture of the Sokoloff tube. A new
type of piezo-receiver uses 3/4 wavelength hemispheres of metal-loaded resin on the outer surface of the image conversion plate and allows the angular response to be increased to 30 degrees off axis instead of 12-15 degrees normally available. A film showing the performance of the Jacobs-type tube was shown, illustrating qualitatively the differences between the two types of tubes with and without this artifact. The results were impressive and a number of delegates suggested that by using this technique, the Sokoloff tube could well find a new lease of life. In subsequent discussions J. Wardley of EMI, UK, described another tube face which used a thick layer of metal-loaded epoxy resin in an electronic image convertor with a large front face. The tube was capable of receiving over a fairly large range of angles. An additional and final paper was presented by H. J. Wickramasinghe of University College, London, on acoustical holography in solids. In this he described solid surface holography systems for producing acoustical holograms at 150 MHz. The hologram is derived from converting the phase modulation of a laser beam to an amplitude modulated signal by means of a Fabry-Perot interferometer. This system gives a very sensitive receiver with a resolution of 90 pm in the reconstructed image (for more details on this work turn to page 146). The evening concluded with a discussion on the comparative performances of P. Greguss’s AOCC and Jacobs’ image convertor tube. The physics of ultrasonics Cavitation nucleation in liquid helium was reviewed by R. D. Finch (University of Houston) and E. A. Neppiras (advisory editor, ULTRASONICS) during this session chaired by J. H. Collins (University of Edinburgh) and R. W. B. Stephens (advisory editor, ULTRASONICS). Their work had shown that mechanisms believed to explain nucleation in water cannot be operative in superfluid helium, but that the measured thresholds in helium were much lower than its tensile strength. Moreover, the nuclei were thought to be quantized vortices in this case. Recent results showed that the attenuation of second sound was increased by high amplitude normal sound, which probably produces quantized vortices in a turbulent form as a precursor to cavitation. The action of ultrasound on viscoelastic solids was reported by H. M. Frost and W. L. Nyborg of the University of Houston. A wedge-tipped ultrasonic horn had been vibrated against the edge of a strain-birefringent plastics sample. Time dependent isochromatics were observed through a polarizing microscope and could be ‘recorded’ or ‘erased’ at will. As a substitute for the third scheduled paper by G. Bradfield, R. A. Brown reported progress in the development of ultrasonic bubble chambers at CERN. Two parallel plane wave transducers resonant at 100 kHz were pulsed so that standing waves were briefly established between them. Tracks of ionizing radiation were first observed in helium, which requires relatively low pressure excursions. Recent work has been concentrated on liquid hydrogen which is more desirable from the viewpoint of high energy physics but which requires greater pressure excursions (see March ULTRASONICS, p 5 1). The problem of coupling a pzt transducer to the liquid has been met with a X/4 perspex plate and isopentane bonding.
ULTRASONICS,
JULY 1973
M. Pappalardo and D. Assenza from the Instituto di Acustica ‘0. M. Corbino’, Rome, described a transducer intended to produce a scanning beam for medical diagnostics. The device consists essentially of a number of pzt rectangular elements which act as a linear array. The transducer operates at about 600 kHz and the beam may be swept by variable phasing. R. W. B. Stephens and K. T. Lee (Imperial College, London) reported results of measurements of ultrasonic velocity and attenuation in liquid metals and amalgams over a complete range of concentrations. They found absorption peaks at certain atomic concentrations which they believed indicated the existence of molecular association. Some aspects of finite amplitude wave propagation in liquid-filled tubes were discussed by L. Bj&n$ of the Technical University of Denmark. Peak pressures of up to 150 bar and rise times of less than 0.5 ps were attain. able with the author’s apparatus. An elegant presentation of the theory of impedance matching with transition layers was made by P. J. Highmore of the University of Loughborough in the next paper. Finally, important new results on the transmission and reflection of surface waves at corners and steps were presented by M. Munasinghe and G. W. Farnell of McGill University, Montreal. These results have been obtained numerically using a finite difference iterative method. Transmission and reflection coefficients as well as phase shifts were computed together with the conversion of energy to bulk wave form. The extension of the method to anisotropic, piezoelectric media via the use of equivalent isotropic parameters was also discussed.
Underwater
ultrasonics
Chaired by L. Bj&nQ (Technical University of Denmark) and A. S. Sliwinski (international editor, ULTRASONICS) the session opened with V. Welsby of the University of Birmingham, who, in his usual relaxed style, gave a paper on high-frequency marine sonars and acoustic telemeters. He said that in the past there had been a lack of commercial initiative in putting underwater acoustic systems on the market. However, with the rapidly-growing interest shown by the oil and gas supply industries, particularly in the results obtained with sonars capable of producing high angular resolutions and working at frequencies up to several hundred kilohertz, this could soon change. He went on to discuss image forming sonars, acoustic holographic systems, acoustic communication links, mechanicallyscanned sonars, ‘phase-only’ sonars, and acoustic telemetry links. He also described a within-pulse electronically-scanned sonar with a beam angle of 0.05 degrees. The field covered by D. Manley of Vacuum Reflex Ltd, UK, was acoustic position-fixing in which by comparison of the phases of waves received at two receivers to within one degree, a high accuracy could be obtained at ranges up to three miles. The next paper was by R. Haslett of Kelvin Hughs, UK, who packed in a considerable amount of information about his calibrated target-strength measuring equipment operating at five frequencies between 30 and 547 kHz. This had now been automated and produced numerous back-scattering diagrams for fish. It is also being used for comparative scale-model work.
ULTRASONICS.
JULY 1973
A tremendous amount of detail on the temperature microstructure and acoustic intensity fluctuations in New Zealand coastal waters was given by F. Sagar, an international editor of ULTRASONICS. His measurements, the result of a ten year study, have confirmed by means of computer and analogue calculations of spectral densities, the Kolmogrov turbulence theory. M. A. Wright of the Royal Aircraft Establishment, UK, reviewed some of the techniques using underwater scale models of aircraft and ultrasonic waves to simulate radar echoes. Two characteristics are important: the size of the echo and the apparent movement of the radar centre. A Sokoloff-tube system operating at 2 MHz is being built to visualize the highlights. The final paper in this session was given by M. Matsuda of the Electra-Communication University, Japan, who had developed a method of increasing the efficiency of an underwater sparker to 20%. His technique used a highcurrent discharge through a tungsten wire stretched between two spheres; normal efficiency without the wire is about 4%. Another advantage of the system is that the pulse is shorter and cleaner. As expected, the paper by A. Barone on boomer arrays was not given. Transducers This evening session was again well attended, indicating that many physicists and engineers working in ultrasonics still need information on this more or less classical field. The construction of the pre-stressed transducer and the piezoelectric ceramic transducer were well covered, despite the fact that at the very last moment it was found that two papers on the former topic could not be presented by the authors themselves, a fact which inevitably limited the discussion. A. P. Hulst of Philips, The Netherlands, described the general outlines of pre-stressed compound piezoelectric transducers consisting of: (a) oppositely poled ceramic piezoelectric rings electrically excited in parallel on both sides of the excursion node; (b) two metallic end pieces (Mg, Al, T&alloy, brass or steel) constituting the remaining length of the half-wavelength transducer, and; (c) a central pre-stressing bolt exerting an axial compressive stress of 3-4 kgf mmm2 (” 5 000 psi) on the ceramic rings. The author presented a theoretical analysis of the electrical impedance and the electroacoustic efficiency which was supported by much experimental data. Additional data was presented in the paper by E. A. Neppiras (advisory editor, ULTRASONICS) and read by J. P. Perkins, and in the paper by W. Pajewski (Institute of Fundamental Technical Research, Warsaw) and read by A. S. Sliwinski. All three papers assumed the use of some modified lead zirconate titanate ceramic as the active piezoelectric material. The last paper by F. W. Ainger (Plessey Ltd, UK) described the interesting effects of adding small amounts of iron to the lead zirconate titanate formula. Additions as small as 0.03 to 0.3 weight per cent of iron cause a dramatic reduction in the losses and variation of permittivity with ac voltage amplitude. Also ageing and depolarization are considerably reduced at the high-ultrasound intensities involved.
Surface acoustic waves Surface acoustic waves are such that they are accessible at all points on their two-dimensional propagation path. This feature, coupled with their low propagation loss and ease of efficient transduction makes them very attractive for a wide range of real-time signal processing applications. In this session on SAW appljcations, chaired by E. A. Ash (University College, London) and L. Pantani (Consiglio Nazionale delle Ricerche, Italy), P. M. Grant of the University of Edinburgh described SAW analogue matched filters which are a convenient means of generating and correlating coded waveforms. They are attractive for digital communication systems employing band-spreading, and several such systems were discussed. Experimental results confirmed the theoretical reduction in error rate which is obtained by using matched filters if noise or interference is present, and showed the importance of choosing the correct threshold setting in the receiver. The surface wave convolver, described by D. P. Morgan of the University of Edinburgh, can also correlate a coded waveform if an additional coded reference waveform is provided. This device is highly programmable. Special techniques were described which substantially reduced the level of spurious signals produced by a degenerate convolver. An alternative convolver, using a tapped delay line with each tap connected to a diode, was shown to be very efficient. Convolvers have the disadvantage that they are not asynchronous. However, in some applications this is not a problem and an example of a possible system for a secure radio altimeter was given. G. Socino (Instituto di Acustica ‘0. M. Corbino’, Italy) described experiments on the deflection of a light beam passing through a crystal supporting a surface wave. The efficiency of the deflector depends on the angle of incidence and polarization of the light, and on the crystal cut. Close agreement between theory and experiment was found. Optimum polarizations and incidence angles were established for several cuts of lithium niobate. Quartz was shown to be much less efficient. J. Chambers of University College, London, described waveguides for surface waves, particularly the wedge waveguide where the wave travels along the apex of a wedge. This slow, non-dispersive wave has been observed in pzt and lithium niobate, and wedge waveguides have also been made on a silicon wafer by selective etching. A convolver using this waveguide on pzt gave substantially increased efficiency due to the confinement of the wave. It was also shown that non-linear effects can be used to couple a surface wave into a gold film waveguide oriented perpendicular to the propagation direction. Finally, L. Pantani reviewed techniques for the measurement of surface wave velocities. Along with methods applicable to bulk-wave delay lines, new techniques are made possible by the accessibility of surface waves. These include use of a double transducer structure which can be used to measure delay by using a pulse superposition technique. Results obtained with this technique showed an accuracy of 0.1%. Non-destructive
testing
The chairmen for this session were R. Sharpe of the Nondestructive Testing Centre, Harwell. and L. X. Nepomuceno
160
of the Laboratorio de Acustica e Sonica, Sao Paulo, Brazil. Mr Sharpe opened the session with a short speech in which he remarked that ndt was still the main outlet for ultrasonics, although he thought that the morning’s programme emphasized the more specialized techniques rather than the usual industrial applications. He hoped that the general discussions would lose none of the liveliness that characterized the previous Ultrasonics for Industry conferences. The only speaker in the session who covered the field in general was L. X. Nepomuceno who spoke about ultrasonics in Brazil. The history of ultrasonics in Brazil is short. In the early fifties there was some activity in Brazilian universities, all of which, however. ceased in the mid-sixties. On the other hand, industrial applications increased from a very low level to the level of intense activity seen today. Sales of ultrasonic equipment are now worth &I 000 m a year. This situation has meant that the number of trained technicians is far too low, a situation which the speaker described as dangerous. There were some signs, however, that a government initiative would ameliorate the situation. Two speakers made contributions on ultrasonic visualization. H. Slater reported the work at Tube Investments on schlieren visualization using a computer. His research group had mathematically analysed the transformations of ultrasound at corners and compared the computer images with schlieren visualization. The method has been quite successful with crater-like cracks in metals although the calculation of defect size is still a problem because of the non-linear response. This difficulty, however, is confidently expected to be resolved. L. W. Kessler of Zenith Radio Corporation, USA, described an acoustic microscopy system which was capable of resolving to better than 10 ym at frequencies as low as 220 MHz. His experimental technique uses the dynamic ripple pattern generated on a plastics mirror by the object beam. The pattern is scanned by a focused laser beam from which, by means of a photodiode, an acoustic image or an acoustic hologram of the object is obtained. During the discussion the author was asked whether heating caused by sound absorption was observed in specimens and whether the technique was restricted to thin samples. Dr Kessler replied that heating effects depended on sensitivity but said that with the present real-time presentation using 0.25 W cm-l, heating was not significant. On the question of sample size he said that the limitation was the same as with optical microscopes. Finally, the author said, in reply to a question on ultimate limits to resolution, that as far as he could see, it was at least possible to go down to a fraction of a micrometre - below half a micrometre say ~- and in principle the technique could do better than light microscopy. An up-to-date ultrasonics conference would be incomplete without a mention of acoustic emission. There were two papers on the subject. R. Hill of the University of Aston, Birmingham, spoke on the evaluation of transducers for this technique. He compared some of the electrical properties of various transducers and went on to discuss coupling media. He felt that solid couplants were inferior to greases such as vacuum grease. Mr Arrington of Cambridge Consultants, UK, read a paper for his colleague, A. A. Pollock. He very quickly went through a list of the advantages of acoustic emission and then spoke about some of the disadvantages. For example, it is always necessary to stress the structure but the stressing may differ from actual stress in use. The use of acoustic emission also depends on the
ULTRASONICS
JULY
1973
material parameters of the structure, although in practice it is fortunate in that steel presents comparatively few problems. The other disadvantage mentioned was the existence of spurious emissions from rubbing and so on. R. E. Green of the Johns Hopkins University, USA, put forward attenuation measurement as a rival to acoustic emission. This too has advantages and disadvantages. There is no analogue to the Kaiser effect and many materials exhibit a memory of earlier changes in attenuation, that is, of earlier stressing. One notable disadvantage of the technique is the need to leave transducers in place over the time of investigation, sometimes for years. The session concluded with a paper for ndt engineers: a paper on a particular solution to a particular testing problem. D. E. Bray of the Federal Railroad Administration, Washington, USA, spoke of the use of surface waves to find flaws in railway wheels. His research group had used l/4 scale model railway wheels and attempted to locate simulated thermal cracks using both pulse-echo and attenuation methods. The extension of this work to full-size wheels with actual defects is currently in progress. J. Obraz’s paper on ultrasonic evaluation of flaw size in thin-walled plates was deleted from the programme. Medical and biological ultrasonics Eight papers were presented during this session chaired by P. N. T. Wells (University of Wales) and C. N. Smyth (international editor, ULTRASONICS). In the first paper G. Kossoff (international editor, ULTRASONICS) gave a review of ultrasonic research in medicine in Australia. He described the techniques developed by the Commonwealth Acoustic Laboratories to improve the grey scale, sensitivity and resolution of the echograms and illustrated these by examples of echograms of the pregnant uterus, the eye and the breast. The second portion of his paper was devoted to a description of methods to overcome the basic limitations of present techniques. These included the use of annular, linear and cross-phased array transducers, the applications of on-line digital processing of the ultrasonic data and in vivo measurement of attenuation and velocity of propagation.
The fourth paper by J. P. Jones (Bolt Beranek and Newman Inc, USA) described a new ultrasonic technique termed impediography which promises to have considerable application in non-destructive testing and medical diagnosis. The technique employs time deconvolution of echoes to produce a plot of impedance values along the propagation path of the ultrasonic beam. The paper was illustrated with results obtained in the examination of layers of rubber where it was shown that the technique is capable of determining changes in the acoustic impedance in rubber caused by stretching. In biological applications, the technique revealed the presence of a small blood clot behind skull bone and, by taking nine propagating paths, a crosssectional impedogram was constructed which showed good agreement with the cross-sectional section of the limb. R. S. Mackay, an international editor of ULTRASONICS, was not able to attend the meeting and present his results on the detection of decompression by ultrasonic imaging of gas bubbles in tissue. Instead, his work was illustrated by a film which showed the time course of development of gas bubbles in the limbs of animals subjected to various rates of decompression. A new method of detecting movements of bodies in electrolytes and colloids using the combined effect of ultrasonic and electric waves was described by C. Quentln (University of Paris). The introduction of ultrasonic waves in the electrolyte generates a periodic excess of anions and cations due to the difference in velocities imparted to these ions through their different mass and fractional coefficients. This creates a potential which is reflected in the impedance of the superimposed electric field. When a moving structure is present the reflected ultrasonic wave alters this potential and its movement is detected by measurement of impedance of the electric field. The application of the technique for monitoring fetal cardiac activity was described and, although it would appear more work is necessary before the method can be applied in a clinic, the paper certainly showed the potential of the method.
In the second paper F. Weill (Centre Hospitalier et Universitaire de Besangon, France) described the crosssectional evaluation of pericardial diffusions. This study was carried out using a commercial instrument which quickly scans the ultrasonic beam thus allowing a real-time display of moving structures. The paper was illustrated by a film which clearly showed the movement of the anterior wall of the heart and the changes that occur in this motion when liquid is present between the chest and the anterior heart wall.
In response to the increased concern shown in the dose of ultrasound received by a patient during a pulsed ultrasonic examination, T. A. Whittingham from the Regional MedicalPhysics Department, Newcastle-upon-Tyne, UK, described a method which automatically measures the number of energiz. ing pulses applied to the transducer. Allowance is made for the times when the transducer is not in contact with the patient. It was suggested that the number so obtained could be related to absolute units of energy for each transducer. The acoustic output could then be displayed on a digital readout system of the type now being increasingly used to display other information obtained by the echoscope
In the third paper T. G. Brown (Royal Infirmary, Edinburgh, UK) described a design for an inexpensive mechanical scanner for rapid three-dimensional scanning of tissues. The transducer is scanned in a conical manner with the transducer being held at the apex, the whole scan taking less than ten seconds. The design is still in the development stage and the author did not present any results obtained with the technique.
In a final paper, A. J. Last from the Ontario Research Foundation, Canada, described the development of a new type of sterilizing solution which is effective over shorter periods of time and which, when combined with ultrasonic cleaning, reduces the sterilization of surgical and dental instruments to a period of less than one hour. A description was also given of a specialized tank designed for use with this solution.
ULTRASONICS.
JULY 1973
161
Exhibition With a record number of stands a great deal of interest was shown in the exhibition - a fact borne out by the total attendance figure of well over 1 000. On the stands a lot of the equipment was new, much of it being shown in public for the first time. Non-destructive testing equipment naturally took a fair share of the stand space. Baugh & Weedon unveiled their latest portable thickness gauge, the PA1040, featuring a measurement range of 0.010-10 in with an accuracy of 1% f one digit. Other features included digital display, automatic ranging, automatic gain control, and, according to the makers, a competitive selling price. Baugh & Weedon also showed for the first time their PA1010 portable flaw
zation system with automatic scanning and storage-tube presentation and comes complete with a range of shear and longitudinal wave probes. Videoson also showed their pulse-echo, pulse-transmission apparatus, PEPTRA, designed initially with the help of the National Physical Laboratory. Ultrasonoscope, who have just finished supplying an in-line ultrasonic plate testing system to the British Steel Corporation, showed a selection from their extensive range of ndt equipment. Exhibits included battery portable units and immersion systems with motorized x-y scan and quantized C-scan recorders. French ndt equipment was shown on the stand of Magnitech, who have now become the UK distributers for Ultrasonic Meaux of Paris. Ultrasonic Meaux produce a wide range of both ndt and medical ultrasonic equipment. Examples of their equipment included portable thickness gauges and flaw detectors, and a six-channel rotary inspection system designed for in-line monitoring of tube and rod diameters. A new logarithmic (pulser-receiver) amplifier was shown giving logarithmic characteristics for minimum variation of input voltage of 70 dB. From India came equipment produced by the Electronics Corporation of India, a state run venture set up in 1967 by the Department of Atomic Energy. They showed their UFD-67 flaw detector which has been in production for about a year and is sold widely throughout India. The unit is capable of resolving to 6 mm, is battery operated and all solid state. The Corporation also produces ultrasonic leak detectors, examples of which were shown.
Baugh 81 Weedon’s PA 1010 flaw detector use
adapted for underwater
As usual the Nondestructive Testing Centre, Harwell, had much of interest on its stand, The Centre investigates fundamental ndt problems as well as undertaking contract research into specific problems for individual companies. Examples of ultrasonic testing systems developed included: a high-precision thickness gauge that measures thickness from 75 pm to 3 mm, typically to an accuracy of ?O. 1%; a simple B-scan flaw detector built from units of Harwell’s wide range of compatible ndt electronic modules; and an
detector encased in a pressure-tight housing for underwater use. Sonatest’s stand included their new UFDl flaw detector and their latest battery portable unit, the UFD2, a versatile lightweight set available with or without monitor. More new equipment was shown on Automation Industries’, stand who displayed their new Sperry UJ portable flaw detector (with a range of over 10 m in steel) and their improved UM77.5 and UM771 Reflectoscopes. Improvements included rotary controls for delay and range, and better overall stability. The latest instruments from Terratest were the TT-200 flaw detector featuring a broadband (0.5-10 MHz) amplifier, and the BT-22 materials tester. The BT-22 is an improved version of the established BT-2 tester giving a wider range of frequencies (10 kHz to 1 MHz) and featuring modular circuit construction. Both BT-2 and BT-22 have digital readouts to 0.1 gs and binary coded digital outputs. Only two B-scan flaw detectors were on show and one, the FPl type A, was on Videoson’s stand. This is a visuali-
162
The six-channel Meaux
tube and rod inspection
system made by Ultrasonic
ULTRASONICS.
JULY 1973
to 0.5 km. The system is able to operate for about 20 days, although this is dependent on pulse rate, and uses a carrier frequency of 74 kHz. Kerry Ultrasonics showed welding and cleaning equipment together with some forward engineering applications of surface wave lines made by their offshoot, Sonicstore. Other stands showing cleaning equipment were those of William Boulton, L & R Ultrasonics, Beech & Son, and Raydne who revealed their new UVD-2 300 W two-stage mini degreaser (see May ULTRASONICS, p 107).
Wiredrawing machine for high-strength macrosonic control unit
Kerry Ultrasonics’
Vibrason
steel using the PVL CUlOOO
system for industrial and laboratory
applications
acoustic emission system for the detection of crack growth in thin plates, again built from the modular range. A portable acoustic impedance meter was also shown which, in one mode, could detect liquid levels in enclosed vessels with steel or fibre-glass walls up to l/4 in thick and, in another, could register changes in a materials density or attenuation properties. In addition, two of the Centre’s services were featured: the probe-beam testing service and the quality technology information service ‘QUALTZS’ - the newly introduced subscriber information service.
Stands showing high-power equipment were also plentiful. Dawe Instruments showed their latest 1 200 W plastics assembly system, the 703gA, together with their new E-series 40 kHz Soniclean generators. A macrosonic control unit made by PVL of Austria was also shown. Known as the CUlOOO, the unit was designed for the measurement and control of macrosound from 16-10d kHz, either in general laboratory use or in industrial applications such as wire or deep drawing, welding, drilling, casting and riveting. Another high-power measuring instrument on show was the Wave Energy Systems, 20 kW wattmeter on the stand of H. Tinsley. A new design of transducer incorporating a magnesium transmission line giving a very high acoustic efficiency was another WES product. The generator, which produces a variable output and is self tuning, was shown operating with a Fourier-curve microprobe with a step ratio of 40 : 1. Output was 200 W at 23 kHz. Tinsley were also showing their latest equipment, an ultrasonic fish tagging system with a range of up
ULTRASONICS.
JULY 1973
Four companies showed their range of ceramic materials. Plessey, who make transducers in barium titanate and lead zirconate titanate, displayed working exhibits of a transparent light-sensitive lead lanthanum zirconate titanate material, and a metered fuel atomizer. The atomizer, made from lead zirconate, operates at 50 kHz and produces oil droplets from 50-300 pm in diameter. Typical applications include use in steady engines (such as those in boats) and heaters, dispersion of slurries, and chemical processing. Mullard too displayed piezoelectric ceramic components available in various grades of lead zirconate titanate suitable for both high and low-power applications. Piezoelectric ceramics, acoustic elements, igniters, filters, air and sandwich transducers were among the exhibits on Vernitron’s stand. One late addition to the exhibition was Channel Industries of California, makers of piezoelectric ceramics for over 15 years. Again they produce lead zirconate titanate and barium titanate materials but specialize in unusual shapes and small quantities. Examples of their products included discs, plates, tubes, spheres and hemispheres. On the medical stands Nuclear Enterprises demonstrated their award-winning Diasonograph NE4102 (see Ultrasonics News, p 149) and their new modular Diasonoscope NE4121. Designed for routine clinical use the NE4121 features four-mode display and can, with the aid of a plug-in cardiac module, be used for time-position or moving structure examinations. GEC, who recently became the UK distributors for Picker International
High-power
plastics welding equipment
on Radyne’s stand
163
(USA) showed the Midliner, a computerized echoencephalograph with digital readout. Doppler units for obstetric use were also on show together with equipment for B-scan laminography. It had been hoped that examples of Japanese medical equipment would be shown on the stand of ES1 Nuclear and Old Delft. However, the distance between the UK and Japan proved too much and we had to be content with glossy photographs of equipment made by Toshiba. Among Toshiba’s most recent developments is a computer system for obtaining patterns on a colour display of simultaneous tomographic images. The distance between the UK and France did not prove too much for Delalande Electronique of France, makers of Doppler blood-flow monitors. Their display consisted of the DU flowmeter, an instrument for measuring blood-flow circulating in the tubes of artificial kidneys. Accuracy is claimed to be 210% t 10 ml on tubes of known internal diameter. A second instrument shown was the DUD flowmeter which measured instantaneous flow rate and mean rates of flow. Operating frequency was 4 MHZ.
Compact
the latest addition to Kretztechnik’s range of pocket Doppler instruments - the 9 MHz Minivason (see May ULTRASONICS, p 105). In addition to the commercial exhibits, two stands showed equipment designed by universities. The University of Loughborough showed a translated circular scanner for sensitive but fast acoustical holography. The equipment was the subject of a paper given during the conference by M. J-M. Clement and J. W. R. Griffiths. The University also showed an ultrasonic resonance technique for finding depth location of a non-bond in a multilayered medium. Another college exhibit was an ultrasonic cross-correlation flowmeter shown by Teesside Polytechnic. The instrument was of the type used for measuring flow rates of difficult fluids in the chemical process industry. In measuring two-phase flow its accuracy is an order of magnitude better than that given by other known methods. At present this is about 1.5% compared to 15% for most other instruments. Full details are given in the paper by J. Coulthard in the March issue of ULTRASONICS (pp 83-88).
A cardiographic diagnostic ultrasonoscope, the Ekoline 20A, was displayed on Smith Kline’s stand and was used in conjunction with the Cambridge fibre-optic medical recorder. The recorder can be used with any commercial echocardioscope providing continuous echocardiogram recordings simultaneously with up to 11 other physiological tracings. Two new equipments were seen on TEM Sales’ stand who distribute Kretztechnik medical equipment. The first was the 7200 MA ophthalmoscope (see May ULTRASONICS, p 105) which features a high-accuracy amplifier and display system for accurate tissue differentiation. The second was
n
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