Characterization of wideband ultrasonic transducers using pulse preshaping

Characterization of wideband ultrasonic transducers using pulse preshaping

disturbances at cladded components. Since specular reflections are exploited a reasonable amplitude evaluation is possible. The LLT-techniqne can be a...

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disturbances at cladded components. Since specular reflections are exploited a reasonable amplitude evaluation is possible. The LLT-techniqne can be applied to the inspection of thick wall components such as vessels or turbine shafts or thin wall components such as mhes and sheets. Defect characterization is improved and classification possibility becomes a possibility. A set of three ultrasonic transducers for the LLT-techniqee has been designed and the sensitivity areas calculated. 41197 Ohta, K.; Watanabe, T.; Jinzhong, Y.; Daji, T.; Henghui, C. L o w frequency ultrasonic probe for testing concrete s t r u c t u r e Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands), 23-28 Apr. 1989, Vol. 2, pp. 1582-1585. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989. In order to design a low frequency probe for testing concrete, a multi- layer piezo--electric transducer has been prepared and its characteristics have been analyzed by means of Mason's equivalent circuit. The resonators material and its thickness must he selected according to the analysis. The frequency and impulse response of probe are shown. The probe must be matched acoustically to the specimen and also matched electrically to the equipment. 40979 Lhemery, A.; De Vadder, D. Calculation and characterization of the impulse response of ultrasonic broad-band t r a n s d u c e r s Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands) 23-28 Apr. 1989, Vol. 1, pp. 200-202. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989. For theoretical and numerical simulations of propagation in transient ultrasonics, the hypothesis often used is that the vibration amplitude distribution of the transducer is constant (piston-case). It is therefore assumed that the main perturbation is a decrease in the amplitude near the edge of the transducer. The shape of the vibration remains constant. An experimental method is proposed to characterize the vibration amplitude distribution for plane or slightly focused disk transducers. The proof of this method is based on a theoretical calculation which is a combination of three extensions of classical calculations of the field radiated by pistons, in term of impulse- response. The first extension is a derivative formulation of the classical calculations of impulseresponses, which permits an easy physical interpretation; the second permits the calculation of the impulse-response of a transducer having an arbitrary vibration amplitude distribution; the third permits the calculation of the impulse-response in transmit-receive mode after diffraction by a small target. The basic hypotheses ate: the medium of propagation is fluid - the equation of propagation is the time-dependent linear wave equation. 40791 Souffiet, C.; Fink, M.; Lhermitte, T.; De Mol, R. Ultrasonic non-destructive testing a n d characterization of graphiteepoxy composites with a new random phase t r a n s d u c e r Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands) 23-28 Apr. 1989, Voi. 1, pp. 637-642. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989 A new method has been developed to estimate local ultrasonic attenuation from the backscaner pulse-echo in graphite epoxy composites. New random phase transducers are used in this technique with short time Fourier analysis and envelope detection. Random Phase Tranducers (R.P.T.) consist in moving a Random Phase Screen (R.P.S.) located in front of a coherent transdocer. The ultrasonic beam generated by the transducer is thus transmitted and received through the moving R.P.S. Short time Fourier analysis and envelope detection are processed by averaging the data acquired for different location of the R.P.S. This technique is compared to the spatial compounding technique. Experimontals results will show the strong efficiency of this technique. Flaws (delaminages, inclusions, porosity) in graphite/epoxy plates were simulated and this technique applied on these plates. A contrast improvement between flaws and noise, was obtained as well as a good estimation of the local attenuation. 40671 Nohr Larsen, P.; Bjorno, L. T r a n s d u c e r defect studies using light diffraction tomography Ultrasonics, Vol. 27, No. 2, pp. 86-90 (Mar. 1989) This paper describes an optical technique which can distinguish between a perfect transducer and a transducer with a defect. For some defects this technique is able to classify the particular type of defect. The technique is based on a combination of the theory of light diffraction by ultrasonic fields and the theory of tomography. The experimental set-up uses a 5 mW He-Ne laser, low cost optics and a light intensity meter, with data processing performed by a personal computer. The optical technique has been applied to 4.5 MHz, 25 ram diameter transducers with introduced characteristic defects. Promising results have been obtained.

Williamsburg, Virginia (United States), 22-26 Jun. 1987. Vol. 7B, pp. 1631-1638. Edited by D.D.Thompson and D.E. Chimenti, Plenum Press, 1988. The portable ultrasonic transducer characterization station (TCS) was developed in support of a U.S. Air Force (MANTECH) Contract. The program objective is to develop and demonstrate multiple commercial sources of well characterized, reproducible ultrasonic transducers. The overall task of this MANTECH program is to develop procedures to help users write performance specifications and to develop tools to help suppliers design ultrasonic transducers to meet performance specifications. This paper discusses the incentives for developing the TCS, and describes the measurement functions and the design aids provided by the TCS. 40035 Benson, S.E.; Clark, GA.; Lewis, D.K.; Cook, B.D. Characterization of widehand ultrasonic t r a n s d u c e r s using pulse preshaplng Review of Progress in Quantitative Nondestructive Evaluation, Williamsburg, Virginia (United States), 22-26 Jun. 1987. Vol. 7A, pp. 609-616. Edited by D.D.Thompson and D.E.Chimenti, Plenum Press, 1988. The use of ultrasonics to identify discontinuities in real time is limited in resolving ability by the multiple oscillations of the measured waveform. A single unipolar pulse reflection is generally considered the ideal solution to the problem. Signal post processing, has traditionally been used on the scauered signal to achieve this higher resolution. Pulse preshaping has also been suggested as a means of obtaining better resolution, but the physics of wave generation and propagation for an immersed piezoelectric transducer must be investigated first. In this experiment, a high speed digital to analog converter is used to generate Ganssian pulses of various half-widths. These are amplified and used to excite wideband commerical ultrasonic transducers of different nominal frequencies. The ultrasonic beam is reflected off of a fiat smooth surface orthogonal to the beam and at a known distance. The experiment is done in the pulse-echo mode and uses the same transducer as a receiver. These reflected waveforms are analyzed. 40034 Kihel, B.EI.; de Belleval, J.F.; Gatignol, P. Vibration characteristics of the front face of an ultrasonic t r a n s d u c e r deduced f r o m his acoustical radiation Review of Progress in Quantitative Nondestructive Evaluation, Williamsburg, Virginia (United States), 22-26 Jun. 1987. Vol. 7A, pp. 603-608. Edited by D.D.Thompson and D.E.Chimenti, Plenum Press, 1988. The use of sophisticated methods of signal processing such as spectral analysis needs to separate the influence of the transducer from the one of the defects in the echographic signal. But, if measurements of echographic signals in all the radiated field are made a strong variation of this signal is seen depending on the position of the target. Thus characterization of the radiated field spatially for every position in time or in frequency is needed. Methods of measurements for the acoustic field have been developed by means of hydrophnnes or small targets in echograpbic mode. At the same time numerical methods have been developed to predict the acoustic field of a transducer in one medium or in two media separated by plane interfaces. This permits comparison of the computations and experiments. The velocity profile on the front face of a transducer is seen to he related to the measured acoustical radiation.

Kwun, H.; Jolly, W.D.; Light, G.M.; Wheeler, E. An evaluation of design p a r a m e t e r tolerances for p r o d u c i n g ultrasonic

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t r a n s d u c e r s of reproducible p e r f o r m a n c e characteristics Review of Progress in Quantitative Nondestructive Evaluation, Williamsburg, Virginia (United States), 22-26 Jan. 1987. VoL 7A, pp. 595-602. Edited by D.D.Thompson and D.E.Chimenti, Plenum Press, 1988. Tolerance limits on design parameters of ultrasonic transducers required to maintain their performance characteristics within certain specifications ate evaluated analytically. A computer program for calculating transducer perfomaance including centre frequency, bandwidth, and insertion loss was used to determine the effect of design parameter variations on transducer performance. By using Hademard matrix experimental designs, the effects of each of these design parameters on transducer performance were determined. Using this result, the variability in performance of nominally the same transducers caused by random variation of design parameters of constituent parts within specified tolerance limits was evaluated. Tolerances on design parameters required to maintain performance characteristics within a specified range were then determined.

Borloo, E.E. PISC II parametric studies: Round Robin Test on the measurement of UT instrument and t r a n s d u c e r characteristics ( M r r c )

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ed.type normal probe (In Japanese)

International Journal of Pressure Vessels and Piping, Vol. 35, pp. 207- 212 (1988). (Proceedings of 5th International Seminar on Nondestructive Examination in Relation to Structural Integrity, Davos, Switzerland, 26-27 August 1987) Within PISC II, a Round Robin Test has been performed by 9 teams on the measurement of certain characteristics of ultrasonic testing (LrI') instruments and transducers. The participating teams were requested to apply the measurement procedures they normally apply when characterizing their equipment or when performing meintenanoe control. The obtained results have shown a broad dispersion, the reasons for which are c o ~ t e d upon and important guidelines result for organizations involved with Codes and Standards.

Journal of Japanese Society for Non-Destructive Inspection, Vol. 37, No. 9A, pp. 801-802 (Sep. 1988)

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Senda, T.; Yokoyama, K.; Yokono, Y.; Minami, Y.; lshibashi, M. angle beam technique - influence of directional characteristics of angle probe (In Study on accuracy of estimated reflector location in

Japanese) Journal of Japanese Society for Non-Destructive Inspection, Vol. 37, No. 9A, pp. 779-780 (Sep. 1988) 40595 Hirose, S.; Uragaki, H.; Onishi, M.; Isami, S. Distance-amplitude characteristics of various flaws detected by foens-

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Jolly, W.D.; Bruton, FA.; Fedor, C.

Ultrasonic t r a n s d u c e r characterization station Review of Progress in Quantitative Nondestructive

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Evaluation,

Dombret, Ph. PISC parametric study on the effect of defect c h a r a c ~ immersion focusing probe t e e i n g results

on

International Journal of Pressure Vessels and Piping, Vol. 35, pp. 119- 135 (1988). (Proceedings of 5th International Seminar on Nondestructive

N D T & E International Volume 25 Number 3 1992