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An investigation of non-uniformly excited wide-band ultrasonic transducers
A numerical method was developed for predicting the radiated acoustic field from arbitrarily shaped ultrasonic transducers. The numerical method was first verified for a spherical transducer, and it was found that the numerical results agreed very well with exact analytical results. The numerical method was then applied to other transducer shapes: toroidal, elliptical, conical, and parabolic transducers. As will be shown in this paper, an ultrasonic transducers geometrical shape affects the radiated acoustic field and acoustic beam pattern, and thus characterizes its specific application. For both the focusing- and nonfocusing-type transducers, the ultrasonic characteristics of focal length, depth of field/dapth of penetration, beam radius, sidelobe level, and its radial location were calculated and are discussed. 42455 Debelleval, J.F. Characterization a n d modeling of acoustic b e a m s f r o m ultrasonic t r a n s d u c e r s in solid or liquid media (In French) Universite de Technologic de Compiegne (France), N89-17465/0, 20 pp. (Aug. 1988) The prediction of time or frequency response of transducers in all points of the acoustic field were studied. Measurements were carried out using a transducer immersed directly in a fluid or coupled with a plane or cylindrical solid interface. Computer programs were developed to describe these fields, with input either from models or measurements. The method allows one to detect a number of parasitic effects such as double beams and focusing errors. 42454 Alers, G.A. Railroad rail flaw detection system based on electromagnetic acoustic transducers Magnasonics, Inc., Albuquerque (United States), PB89-163091, 82 pp. (Sep. 1988) The report describes the design, construction and preliminary testing of an ultrasonic inspection vehicle intended for the detection of flaws in railroad tracks that are in commercial service. It differs from existing inspection systems in that it employs an ultrasonic transducer that does not require any kind of coupling liquid between the sensor head and the rail. A computer had been incorporated into the data processing channel to allow recording of all the ultrasonic signals as well as for presenting the operator with deflections on a strip chart recorderthat both act as alarm indications as well provide information on the characteristics of the flaw.
Brittain, R.H. An investigation of n o n - u n i f o r m l y excited wide-band ultrasonic tran-
42453
sducers Ph.D. Thesis, City University (London), School of Electrical Engineering and Applied Physics, 167 pp. (May 1988) New transducers to directly replace: conventional, uniformly-excited, wide-band transducers were produced by varying the piezoelectric excitation of transducer elements as a function of their radius i.e. apodisation. To do this it was necessary to re-examine the technology of poled fermclectric or piezoelectric ceramics of PZT and PMN. The construction of wide-band transducers is analysed in terms of the K L M transmission line model and their acoustic fields are described by the plane- and edge-wave model. The impulse response method is applied to transducers and useful forms of non-uniform excitation am described. Details a m given of nmasuring the planar electromechanical coupling factor of a piezoelectric element and of how standard photofabrication methods using photoresist were adapted to cope with the comparatively rough surfaces of ceramics working right up to and including the edges of the substrates. The wide-band excitation and receiving system is described. Computer-calculated results illustrate the effect of various types of transducer excitation ranging from the theoretical to the practically-attainable. Measured results confirm these calculations and also present some of the physical characteristics of the piezoelectric ceramics. Both uniformly and non-uniformly excited transducers are considered. The thesis concludes that it is possible to make non-uniformly excited transducers by controlling the strength of the piezoelectric excitation within the transducer element. 42398 Gallego-Juarez, J.A. Piezoelectric ceramics a n d ultrasonic t r a n s d u c e r s Journal of Physics E. Scientific Instruments, Vol. 22, No. 10, pp. 804- 816 (Oct. 1989) This paper reviews the basic characteristics and progress in transducer properties of the different types of piezoelectric ceramics. The application of these materials in practical ultrasonic transducers is also reported. 42218 Kira,K.Y.; Niu, L.; Castagnede, B.; Sachse, W. Miniaturized capacitive t r a n s d u c e r for detection of b r o a d b a n d ultrasonic displacementsignals Review of Scientific Instruments, Vol. 60, No. 8, pp. 2785-2788 (Aug. 1989) This article describes a miniaturized version of the capacitive transducer for the detection of broadband, ultrasonic diaplacement signals at the surface of a specimen. The overall size of the capacitive transducer is a cylinder of 11.11 nan in diameter and 22.86 nun in length, in which four different sizes of the sensing area of the capacitive electrode have been successfully tried, ranging from I to 5 nun in diameter. Examples of detected waveforms resulting from such excitations as a glass capillary fracture and the formation of cracks on the surface of a specimen are provided using the specimens of glass and epoxy plates, respectively. The amplitudes of the detected signals are shown to be proportional to the displacements normal to the surface of the specimen. These small transducers are especially well suited for measurements on a iaborstory specimen which requires several of them to study an acoustic emission source, to characterize an elastic (or a viscoelastic) behavior of the material, or simply to study the wave propagation.
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42201 Kuttruff, H.; Schanz, V. Shaping the directional characteristics of u l t r a s o u n d t r a n s d u c e r s of polyvinylidene fluoride Acustica, Vol. 68, No. 3, pp. 200-208 (10 Jnl. 1989) In this paper several methods of shaping the directivity of plane circular ultrasound transducers of polyvinylidene fluoride (PVDF) are described. Two different goals are pursued: firstly the achievement of the best possible directivity including the suppression of side lobes, and secondly a radiation as uniform as possible. Comparison of calculated directivity patlems with measured ones show good agreement. Furthermore, the vibration pattern of the transducer surface was checked with an optical relief method. The observed velocity distribution confirmed the expected behaviour. 42184 Lal, R.; Gas-Gupta, D.K. Characterization of ultrasonic t r a n s d u c e r s IEEE "IPansactions on Electrical Insulation, Vol. 24, No. 3, pp. 473- 480 (Jun. 1989) A systematic approach in the design and evaluation of high-frequency piezoelectric transducers is presented. The transducers, prior to manufacture, may be modeled to generate an optimum response for a given specification. The design parameters may be adjusted until a physically realizable model of the transducer is achieved. This model of the transducer may then be constructed and characterised both in the time and frequency domains, and, the results compared with theoretical predictions. Furthermore, the acoustic output parameters as required by current international standard could then be estimated from data obtained by pulse-intensity integral measurements. Results for three ultrasonic transducers are presented to illustrate the procedures involved and to highlight the limitation of such ponderations. 42035 Schafer, M.E.; Lewin, P.A. T r a n s d u c e r characterization using the a n g u l a r s p e c t r u m method Journal of the Acoustical Society of America, VoL 85, No. 5, pp, 2202- 2214 (May. 1989) A measurement technique for analyzing the surface velocity patterns of ultrasonic transmitters is presented. The technique is based on the angular spectrum method of wave field analysis. In this approach, acoustic propagation between parallel planar surfaces is modeled using the two-dimensional (2-D) Fourier transform of the wave field, with each element in the spatial frequency domain multiplied by the appropriate phase factor. The technique was extended from the basic monochromatic model to the wideband pulsed case. An experimental system was built to measure the acoustic fields from various transducers, including single-element and multieleruent phased arrays. Backpropagatinn results are shown for circular planar, circular focused, and rectangular phase steered transducers. The results demonstrate the ability of the extended angular spectrum method to reconstruct the surface velocity distribution of complex acoustic radiators. 42021 Brittain, R.H. An investigation of non-uniformly excited, wide-band ultrasonic transducers Dissertation Abstracts International, Vol. 40, No. 10, p. 4457-B (Apr, 1989) The construction of wide-band transducers is analysed in terms of the KLM transmission line model and their acoustic fields are described by the plane- and edge-wave model. The impulse response method is applied to transducers and useful forms of non-uniform excitation are described. Details are given of measuring the planar electromechanical coupling factor of a piezoelectric element and of how standard photofabrication methods using photoresist were adapted to cope with the comparatively rough surfaces of ceramics working right up to and including the edges of the substrates. The poling apparatus designed to apply various poling regimes under conditions of constant temperature and time are detailed. Fabrication methods for producing wide-band transducers based on using a centrifuge to apply the required damping are given. The wide-hand excitation and receiving system is described. Computer-calculated results illustrate the effect of various types of transducer excitation ranging from the theoretical to the practically-attainable. Measured results confirm these characteristics of the piezoelectric ceramics. Both uniformly and nonuniformly excited transducers are considered. The thesis concludes that it is possible to make non-uniformly excited transducers by controlling the strength of the piezoelectric excitation within the transducer element. 41983 Yakovlev,L.A.; Peregudov, A.N.; Shevelko, M.M.; Nostyuk. A.N. Piezcelectric t r a n s d u c e r s for precision m e a s u r e m e n t s of ultrasonic velocity in solids Soviet Journal of Non-Destructive Testing, Vol. 24, No. 9, pp, 636-639 (May 1989) A design is proposed for a mechanically stable piezoelectric transducer to measure ultrasonic velocity at frequencies from 30 to 100 MHz. It consists of a piezoelectric plate coupled by means of a quarter-wave layer of cement to an acoustically stiff back plate. The feasibility of predicting reliably the phase characteristics of such transducers makes it possible to reduce the measuring errors to l-S and less.
Chan, H.L.W.; Unsworth, J. Simple model for piezoelectric ceramic/polymer 1-3 composites u s e d in
41981
ultrasonic t r a n s d u c e r applications IEE "lYansactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 36, No. 4, pp. 434-441 (Jul. 1989) A theoretical model is presented for combining parameters of 1-3 ultrasonic composite materials so as to be able to predict ultrasonic characteristics such as velocity, acoustic impedun~, eleetromechanical coupling factor and piezoelectric coefficients. Hence the model allows the estimation of resonance frequencies of 1-3 composite transducers.
N D T & E International Volume 25 Number 3 1992
Brittain, R.H. An investigation of n o n - u n i f o r m l y excited wide-band ultrasonic tran-
42453
sducers Ph.D. Thesis, City University (London), School of Electrical Engineering and Applied Physics, 167 pp. (May 1988) New transducers to directly replace: conventional, uniformly-excited, wide-band transducers were produced by varying the piezoelectric excitation of transducer elements as a function of their radius i.e. apodisation. To do this it was necessary to re-examine the technology of poled fermclectric or piezoelectric ceramics of PZT and PMN. The construction of wide-band transducers is analysed in terms of the K L M transmission line model and their acoustic fields are described by the plane- and edge-wave model. The impulse response method is applied to transducers and useful forms of non-uniform excitation am described. Details a m given of nmasuring the planar electromechanical coupling factor of a piezoelectric element and of how standard photofabrication methods using photoresist were adapted to cope with the comparatively rough surfaces of ceramics working right up to and including the edges of the substrates. The wide-band excitation and receiving system is described. Computer-calculated results illustrate the effect of various types of transducer excitation ranging from the theoretical to the practically-attainable. Measured results confirm these calculations and also present some of the physical characteristics of the piezoelectric ceramics. Both uniformly and non-uniformly excited transducers are considered. The thesis concludes that it is possible to make non-uniformly excited transducers by controlling the strength of the piezoelectric excitation within the transducer element. 42398 Gallego-Juarez, J.A. Piezoelectric ceramics a n d ultrasonic t r a n s d u c e r s Journal of Physics E. Scientific Instruments, Vol. 22, No. 10, pp. 804- 816 (Oct. 1989) This paper reviews the basic characteristics and progress in transducer properties of the different types of piezoelectric ceramics. The application of these materials in practical ultrasonic transducers is also reported. 42218 Kira,K.Y.; Niu, L.; Castagnede, B.; Sachse, W. Miniaturized capacitive t r a n s d u c e r for detection of b r o a d b a n d ultrasonic displacementsignals Review of Scientific Instruments, Vol. 60, No. 8, pp. 2785-2788 (Aug. 1989) This article describes a miniaturized version of the capacitive transducer for the detection of broadband, ultrasonic diaplacement signals at the surface of a specimen. The overall size of the capacitive transducer is a cylinder of 11.11 nan in diameter and 22.86 nun in length, in which four different sizes of the sensing area of the capacitive electrode have been successfully tried, ranging from I to 5 nun in diameter. Examples of detected waveforms resulting from such excitations as a glass capillary fracture and the formation of cracks on the surface of a specimen are provided using the specimens of glass and epoxy plates, respectively. The amplitudes of the detected signals are shown to be proportional to the displacements normal to the surface of the specimen. These small transducers are especially well suited for measurements on a iaborstory specimen which requires several of them to study an acoustic emission source, to characterize an elastic (or a viscoelastic) behavior of the material, or simply to study the wave propagation.
1 52
42201 Kuttruff, H.; Schanz, V. Shaping the directional characteristics of u l t r a s o u n d t r a n s d u c e r s of polyvinylidene fluoride Acustica, Vol. 68, No. 3, pp. 200-208 (10 Jnl. 1989) In this paper several methods of shaping the directivity of plane circular ultrasound transducers of polyvinylidene fluoride (PVDF) are described. Two different goals are pursued: firstly the achievement of the best possible directivity including the suppression of side lobes, and secondly a radiation as uniform as possible. Comparison of calculated directivity patlems with measured ones show good agreement. Furthermore, the vibration pattern of the transducer surface was checked with an optical relief method. The observed velocity distribution confirmed the expected behaviour. 42184 Lal, R.; Gas-Gupta, D.K. Characterization of ultrasonic t r a n s d u c e r s IEEE "IPansactions on Electrical Insulation, Vol. 24, No. 3, pp. 473- 480 (Jun. 1989) A systematic approach in the design and evaluation of high-frequency piezoelectric transducers is presented. The transducers, prior to manufacture, may be modeled to generate an optimum response for a given specification. The design parameters may be adjusted until a physically realizable model of the transducer is achieved. This model of the transducer may then be constructed and characterised both in the time and frequency domains, and, the results compared with theoretical predictions. Furthermore, the acoustic output parameters as required by current international standard could then be estimated from data obtained by pulse-intensity integral measurements. Results for three ultrasonic transducers are presented to illustrate the procedures involved and to highlight the limitation of such ponderations. 42035 Schafer, M.E.; Lewin, P.A. T r a n s d u c e r characterization using the a n g u l a r s p e c t r u m method Journal of the Acoustical Society of America, VoL 85, No. 5, pp, 2202- 2214 (May. 1989) A measurement technique for analyzing the surface velocity patterns of ultrasonic transmitters is presented. The technique is based on the angular spectrum method of wave field analysis. In this approach, acoustic propagation between parallel planar surfaces is modeled using the two-dimensional (2-D) Fourier transform of the wave field, with each element in the spatial frequency domain multiplied by the appropriate phase factor. The technique was extended from the basic monochromatic model to the wideband pulsed case. An experimental system was built to measure the acoustic fields from various transducers, including single-element and multieleruent phased arrays. Backpropagatinn results are shown for circular planar, circular focused, and rectangular phase steered transducers. The results demonstrate the ability of the extended angular spectrum method to reconstruct the surface velocity distribution of complex acoustic radiators. 42021 Brittain, R.H. An investigation of non-uniformly excited, wide-band ultrasonic transducers Dissertation Abstracts International, Vol. 40, No. 10, p. 4457-B (Apr, 1989) The construction of wide-band transducers is analysed in terms of the KLM transmission line model and their acoustic fields are described by the plane- and edge-wave model. The impulse response method is applied to transducers and useful forms of non-uniform excitation are described. Details are given of measuring the planar electromechanical coupling factor of a piezoelectric element and of how standard photofabrication methods using photoresist were adapted to cope with the comparatively rough surfaces of ceramics working right up to and including the edges of the substrates. The poling apparatus designed to apply various poling regimes under conditions of constant temperature and time are detailed. Fabrication methods for producing wide-band transducers based on using a centrifuge to apply the required damping are given. The wide-hand excitation and receiving system is described. Computer-calculated results illustrate the effect of various types of transducer excitation ranging from the theoretical to the practically-attainable. Measured results confirm these characteristics of the piezoelectric ceramics. Both uniformly and nonuniformly excited transducers are considered. The thesis concludes that it is possible to make non-uniformly excited transducers by controlling the strength of the piezoelectric excitation within the transducer element. 41983 Yakovlev,L.A.; Peregudov, A.N.; Shevelko, M.M.; Nostyuk. A.N. Piezcelectric t r a n s d u c e r s for precision m e a s u r e m e n t s of ultrasonic velocity in solids Soviet Journal of Non-Destructive Testing, Vol. 24, No. 9, pp, 636-639 (May 1989) A design is proposed for a mechanically stable piezoelectric transducer to measure ultrasonic velocity at frequencies from 30 to 100 MHz. It consists of a piezoelectric plate coupled by means of a quarter-wave layer of cement to an acoustically stiff back plate. The feasibility of predicting reliably the phase characteristics of such transducers makes it possible to reduce the measuring errors to l-S and less.
Chan, H.L.W.; Unsworth, J. Simple model for piezoelectric ceramic/polymer 1-3 composites u s e d in
41981
ultrasonic t r a n s d u c e r applications IEE "lYansactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 36, No. 4, pp. 434-441 (Jul. 1989) A theoretical model is presented for combining parameters of 1-3 ultrasonic composite materials so as to be able to predict ultrasonic characteristics such as velocity, acoustic impedun~, eleetromechanical coupling factor and piezoelectric coefficients. Hence the model allows the estimation of resonance frequencies of 1-3 composite transducers.
N D T & E International Volume 25 Number 3 1992