Ultrasonic transducer response correction via inverse filtering. Characterization in the time-frequency plane

'Edited by D.C. Thompsonand D.E. Chimenti, pp. 849-856. Plenum Press (1989), ISBN 0 306 43209 9 A general formulation regarding the relationship between scatterer pmpertics and experimental signals was presented in a ~mpenion paper. In order to peffmm the theoretical uakuletions, the fonnuintion requires knowledge of the radiation and reception ~ e s of the probes involved and the combined properties of the pulser and the receiver (system ~ y ) . Thus, the objective of this paper is to discuss methods for ob~ining the characwristk~ of measurement systems as required in the above-mentioned formulatiun. As an example, the case of acoustic wave scattenng from a sphere of finite size is examined. Experimental verifications of results are included. 43339 Hsu, D.K.; Wormley, SJ.; Thompson, D.O. Muitivlewinlg ultrasonic t r a n s d u c e r system for flaw reconstruction Review of Progress in Quantitative Nondestructive Evaluation, Vol. 8A. Edited by D.C. Thompson and D.E. Chimenti, pp. 913-920. Plenum Press (1989), ISBN 0 306 43209 9 At Ames LabonUory, multi-u'ensducer ultrasonic instrumen~ion as well as the associated data acquisition and signal processing algorithms, have been developed for the utilization and a d v ~ t of flaw reconstruction methodologies. In this paper details of the "second generetiun" instnm'tentation are described and results of an example reconmvction are shown. The expanded insmunentation has a large number of degrees of freedom and serves as an ideal research and testing tool for flaw characterization. Several new topics me being pursued and two will be briefly discussed here. First, the signal amplitude contour is obtained for an arbitrarily oriented general ellipsoid. Second, the multiview ultrasonic system is applied to flat crack-like flaws much larger than a wavelength. Angular scans me made to reveal the crack-like nature and to detenniue the orientation of the flaw. The size of the crack is then estimated from the two tip diffraction signals. 43150 Kawashima, K. Nondestructive characterization of texture and plastic strain ratio of metal sheets with electromagnetic acoustic transducers Journal of the Acoustical Society of America, Vol. 87, No. 2, pp. 681- 690 (Feb. 1990) All the lowest-order independent CODF (crystallite orientation distribution function) coefficientsW4o0, W~Aoof rolled steel abeeta, with thickness less than I rnm, have been obtained nondesmu~vely by using the known single-crystal elastic constants and the relative ultrasonic velocities measured with F_2vlATs(eie~t,oruasuetic acoustic ~ ) . The ultrasonic velocities of all the waves, longitudinal waves, shear waves propagating in the through thickness direction, and SHO (shear horizontal) plate waves, were mes~md by the EMATs. No acoustic coupling medium was neceuaty, making posalble quick, accurate, and reproducible measurements. It is shown that the CODF coeffidients can be obtained as the solutions of three linear equations in which the measured relative ultrasonic velocities are included. There was an overall correspondence between the ultrasonic pole figures drawn using the obtained CODF coefficientsand x.ray pole figures. All nine elastic constants of a steel sheet were also calculated. Average Young's modulus E and planar variation in Young's modulus dE calculated using the nine elastic constants were consistent with average plastic strain ratio r and planar variation in plastic strain ratio dr, respectively, showing that the ultrasonicmethod hare is well adapted for practical use. 43114 Brunk,J.A.; Valenza, C J.; Bhardwaj, M.C. Applications a n d advantages of dry coupling ultrasonic transducers for materials c h a r a ~ n a n d Inspection AcousU>-Ullrnsonics, Theory and Appfical/on. Edited by J.C. Duke, Jr., pp. 221-237, Plenum pless, 353pp (1989). ISBN 0306430134 Practical self-coupling (dry coupling) piezoelectric ultrasonic transducer designs have been optmized for center frequencies up to at least 25MHz for longitudinal wave generation and at least 20MHz for zero degree incidence shear wave generation. While originally developed for exenlinatiun of materials which would be damaged by liquid contact, they have been found to have practical and technical advantages for many materials characterization, discontinuity evaluation and gaging requirements. 42908 Le Brun, A.; Champigny, F. U l t r u s o u k t r a n s d u c e r characterization: two applications in the nuclear industry Proceedings of Ultrasonics International 89, Madrid (Spain), 3-7 July 1989, pp. 525-530, Butterwonh Scientific Ltd. ISBN 0408054182 (1989) In this paper, we describe two methods to improve the ultrasonic NDT reliability in nuclear industry applications: 1 - An electrical measurement method to verify the stability of the transducer sensitivity and to optimize the electrical matching between the transducer end the cable, for the automated pressure vessel inspections. 2 - An optical technique for the ultrasonic beam characterization, in order to verify the specifications of high- frequency miniature and focalized transducers. The optical detector used allows a non-contact high-bandwidth and point-size mapping of the acoustical pressure field in the focal region, with high precision and reliability. 42898 Som,A.K.; Shiloh, K.; Bond, L.J. Modulation transfer function of high frequency ultrasonic transducers Proceedings of Ultrasonics International 89, Madrid (Spain), 3-7 July 1989, pp. 730-735, Butterworth Scientific Ltd. ISBN 0408054182 (1989) The concept of the Modulation Transfer Function, which is used in optics, has been adapted to charucter~ high frequency ultrasonic transducers. A 2-D MTF characteriser which can be compun~l with the 1- D fun~un found in optics was developed based on the nature of ultrasonic imaging. A full pmeedom is reported applied to evaluate mtn~_u~_nin water. This procedure can be used to give a measureof performance for compression wave transducers, applied to both surface and volumetric imaging and also for the complete system which uses them.

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International V o l u m e 25 N u m b e r 3 1 9 9 2

42888 Zakharia, M.E. U l t r a s o n k t r a n s d u c e r response correction via Inverse filtering. Characterization in the time-frequency plane Proceedings of Ultrasonics international 89, Madrid (Spain), 3-7 July 1989, pp. 814-819, Butterworth Scientific Ltd, ISBN 0408054182 (1989) Ultrasonic tnmsducers responses are usually characterized in the time domain (impulse response) or in the frequency domain (transfer function). Such characterizations can be sufficient for flight time measurexmmts or attenuation coefficient estimation in homogeneous isctropic medium. More infommtion me contained in ultrasonic echoes, mainly in dispersive media. Their extraction need a better knowledge of the transducer response. This can be achieved via time-frequency representation (Wiguer-Ville Distribution). We will show an example of such a representation, for a commercial transducer. The transducer response can be corrected via inverse filtering (decunvniution in the time domain). Such a de,convolution has been achieved, in real-time. After deconvolution, all the frequencies will be transmitted at the same level and with the same phase (in a given frequency range). This amplitude and phase correction can also be displayed in the time- frequency domain. 42844 Hsu, D.K.; Margetan, F.J.; Thompson, D.O. Bessel beam ultrasonic transducer: fabrication method and experimental results Applied Physics Letters, Vol. 55, No. 20, pp. 2066-2071 (13 Nov. 1989) We report experimental results from a first-of-a-kind ultrasonic transducer that generates a beam with a Bessel function profile. Using a technique of nonuniform poling, an axially symmetric aessel function pattern in "polarized into" a piezoelectric ceramic element. The resulting circniar-disk transducer has the usual full-plating electrode configuration, but produces an ultrasonic beam with a radial displacement profile approximating that of the Bessel function J0 (r), both in amplitude and in phase. The radiation field of a 1-in.- diam, 2.25 MHz Bessel transducer mapped out with a point probe shows good agreement with calculated results using a Gauss-Hermite model. Bessel transducers are of particular interest in attempts to achieve "diffractioniess" beams. 42630 Korovin, V.M.; Lebedev, I.S.; Raikher, Y.L.; Epifanov, V.M. Magnetic system for the ultrasonic t r a n s d u c e r working with the magnetoliquid contact layer Soviet Journal of Nondestructive Testing, VoL 25, No. 3, pp. 184-189 (Nov. 1989) The authors propose a method of engineering design on the magnetic magnetic system for standard ultrasonic transducers for operation with the magnetoliqnid acoustic contact. The method was developed on basis of solving the problem of holding the droplet of the magnetic liquid in the thin layer in movement of the transducer on the surface of the inspected component and was confirmed by experiments and is now used to develop design documentation for standard transducers with a magnetic system characterized by high efficiency in automated ultrasonic inspection. 42626 Habeger, C.C.; Wink, WA. Development of a double-element pulse echo, PVDF t r a n s d u c e r Ultrasonics, Vol. 28, No. 1, pp. 52-54 (Jan. 1990) This paper presents a simple way to use PVDF piezoelectric films to construct a multiple active element ultrasonic transducer. With this transducer, pulse echo measurements can be made using a separate transmitter and receiver. This eliminates the need for special electrical circuitry and provides the opportunity for individual design of receiver and transmitter response characteristics. 42625 Hirao,M.; Fukuoka, H.; Fujisawa, K.; Murayama, R. Characterization of formability in cold-rolled steel sheets using electromagnetic acoustic t r a n s d u c e r s Metallurgical Transactions A, VoL 20A, No. 11, pp. 2385-2392 (Nov. 1989) The technique is based on the generalized dispersion relation, which correlates the velocity anistmpy of ultrasonic plate modes guided in the sheet plate to the texture defined by orientation distribution coefficients. Electromagnetic acoustic transducers (EMATs), constructed of permanent magnets and meander-line cuils, allow the accurate and easy measurement of transit times of the fundamental symmetric mode. The planar average of the transit times shows a close correlation with both the planar average of plastic strain ratios, obtained through tensile tests and the pole intensities, measured with the X-ray diffraction method. These favorable comparisons with the destructive tests indicate a good possibility of texture monitoring with the noncontacting EMAT's. 42622 Akcakaya, E.; Adler, EL.; Farnell, G.W. Apodization of multilayer bulk-wave t r a n s d u c e r s IEEE "lYansactions on Ultrasonics, Perroelectrics, and Frequency Control, Vol. 36, No. 6, pp. 628-637 (Nov. 1989) Recent experiments have demonstrated the use of super-lattice transducers for bulk acoustic waves in the GHz frequency range. The transducers consisted of multilayers of ZnO or LiNbO, with altematiog crystal orientations or polarizations. A procedure for calculating the electromechanical characteristics of general multilayer transducers in which the individual layers are anisotropic and piezoelectric and have arbitrary crystal orientation is described. A network model is also derived to provide both an approximate analysis of multilayer transducer performance and an insight into synthesis ~ u r e s . Examples compare the two approaches and illustrate an initial design procedure for broadband transducers. 42575 Sung, S.H. Acoustic wave-field analysis of ultrasonic t r a n s d u c e r s Journal of the Acoustic Society of America, Voi. 86, No. 4, pp. 1595- 1601 (Oct. 1989)

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