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Jun 1979

Volume 65, Issue S1, pp. S2-S142

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back to top Session R. Engineering Acoustics II: Ultrasonic Transducers, Arrays, and Devices
Contributed Papers
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Concerning the ultrasonic Doppler flowmeter (A)

T. Rey

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S46-S46 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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The ultrasonic Doppler flowmeter is used in medical diagnosis and research to indicate velocity of blood in a vessel to which transducers are coupled externally. In this note, the observed frequency shift is shown to be proportional to the magnitude of the acceleration of the blood flow, rather than its velocity.
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Acoustic harmonic interaction effects in biomedical ultrasonic arrays (A)

K. Benjamin and P. R. Stepanishen

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S46-S46 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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Arrays of piezoelectric transducers are being used in an increasing number of biomedical applications. As a result much work is being done using digital computers to design and develop such arrays. This paper will address the effects on array performance of the acoustic harmonic interactions among elements in arrays of piezoelectric thickness expanders. A distributed parameter transducer model, with acoustic interactions, was used to investigate the effects of the interactions on array beamforming and focusing in the transmit and receive modes of operation. The perturbations due to interactions were studied as a function of frequency, beaming, tuning, transducer backing, and element spacing for various transducer materials. The study which included finite and infinite two‐dimensional array configurations showed significant interactions for densely packed elements in the MHz range. This effect generally increased as the array was phase steered off axis. It was also found that the interactions could be significantly reduced by using a matched backing material. Numerical results will be presented to illustrate material. Numerical results will he presented to illustrate typical results of the interactions which were obtained during the study. [Work supported by NIH.]
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Acoustic transient interaction effects in biomedical ultrasonic arrays (A)

J. Guigli and P. R. Stepanishen

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S46-S46 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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The transient response of ultrasonic biomedical transducers and arrays is becoming increasingly important as a result of the wideband excitations which are currently envisaged for various biomedical applications. In the present paper, a computer model is developed to evaluate the transient transmit/receive response of multielement beam steered arrays of acoustically coupled piezoelectric thickness expander transducers. Each transducer is represented by a distributed parameter model which includes the effects of mechanical backing and matching materials. A set of coupled convolution integral equations are developed from the model to characterize the transient transmit/receive response of an army and scatterer configuration. These equations are an extended version of earlier work [P. Stepanishen, J. Acoust. Soc. Am. 50, 964–974 (1971)] and can be readily solved using recursire techniques. Numerical results are presented to illustrate typical transient acoustic field and receive phenomena which result from the short pulse excitation of phased arrays of ultrasonic transducers in the MHz range of biomedical interest. [Work supported by NIH.]
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Tank coatings for ultrasonic echo reduction (A)

R. D. Corsaro and J. D. Klunder

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S46-S46 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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A filled‐rubber materials system with selectable and continuously variable acoustic properties is described and used to form broadband anechoic tiles. By applying these tiles to the inside walls of acoustic testing tanks, wall reflections are reduced by 20 to 35 dB at frequencies from 0.5 to 10 MHz. This is advantageous since it allows the use of smaller examination tanks, for example in ultrasonic testing and biomedical applications, and permits the use of cw tanks of tractable size, for example in schlieren and acoustic‐visualization studies. The tank coatings developed include one and two layer tiles, 0.15 to 0.65 cm thick. Using a theoretical model of sound propagation in multilayer media, we first calculated the optimum material properties needed to construct tiles meeting specific echo reduction requirements. These materia] requirements were then met by choosing the type and concentration of fillers added to an RTV‐602 silicone rubber base. The subsequently measured performance of these tiles agree with that initially predicted by theory.
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Precise control of the relative phases of two ultrasonic purses using digital logic circuitry (A)

John M. Mills and Thomas H. Carolus

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S46-S47 (1979); (2 pages)

Online Publication Date: 11 Aug 2005

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Description is given of a recently constructed device for use in ultrasonic experiments that employ two matched transducers. The device produces two sinusoidal bursts of substantially identical waveform, but with an adjustable delay between their starting times. The bursts are derived digitally from an external frequency standard (crystal clock), with a frequency of 5 MHz; the master frequency for sine wave synthesis can be any integer fraction of this clock frequency. The period of each cycle is ten times the reciprocal of that integer fraction of the master frequency. Any integer number of sinusoidal cycles, from one to nine cycles, are generated as a burst. A delay counter is started coincident with the sinusoidal waveform generator. Upon completion of this preset delay interval a second sine counter is started, which then generates the same number of cycles as there were in the first burst. The delay interval may be adjusted to any integer number of master clock cycles. Thus the two sine wave pulses can be delayed by any integer multiple of one tenth of a period of one sinusoid. The three‐decade delay counter allows the total delay between the two pulses to be as much as 100 cycles. Sinusoidal output frequency, the number of cycles in a burst, and the delay between two successive bursts are all adjustable during the course of an experiment. [Work supported by NASA.]
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New digital acoustic signal processing for use in ultrasonic intrusion alarm systems (A)

Donald P. Massa

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S47-S47 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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It has been the accepted belief that air turbulence in an ultrasonic alarm system produces a Doppler shift similar to that produced by a moving target, resulting in false alarms. A mathematical analysis of the entire acoustic system shows that this assumption is not true. It is shown that the received ultrasonic signal can be represented by a rotating phasor whose head exhibits circular motion when a moving target is present. The circular motion is virtually non‐existent when a moving target is absent regardless of the presence of environmental disturbances, such as air turbulence and noise transients. The mathematical findings have been confirmed experimentally. An electronic circle detector incorporating a microprocessor was developed for recognizing the presence of circular motion in the head of a rotating phasor when it occurs in the received signal. This permits the system to absolutely detect a moving target while remaining immune to false alarms due to air turbulence and other environmental disturbances. This microprocessor‐based digital signal processing also totally eliminates the need for any sensitivity controls as are required by all prior art systems.
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SAW hydrophone (A)

P. Das and C. Lanzl

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S47-S47 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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A hydrophone which senses both absolute pressure and changes in pressure has been developed using a surface acoustic wave (SAW) delay line on a piezoelectric substrate. The pressure applied to the hydrophone is converted to a flexural loading of the piezoelectric plate which alters the surface wave velocity on the plate. This change in SAW velocity is measured as a change in the phase shift between the input and output signals of the delay line using a mixer and low‐pass filter. The piezoelectric plate thickness and length and the center frequency of the interdigital transducer (IDT) can be chosen to optimize the sensitivity of SAW hydrophone. The SAW delay line is a planar structure, therefore, it is simple and inexpensive to manufacture. This paper presents performance data of a number of SAW hydrophones using delay lines having IDT at 50 100 and 200 MHz. Extensive measurements of sensitivity and frequency response have been made for delay lines fabricated on LiNbO3 and S‐T‐cut quartz substrates and compared with measurements obtained from commercial hydrophones in the same setup. It is to be mentioned that a SAW transmitting hydrophone can also be fabricated using a SAW delay line in the feedback loop of an amplifier to form an oscillator. However, if transmitting mode is unnecessary, extensive simplification can be achieved in the detector circuits using the phase detection described in this paper.
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Asymmetric distribution of SAW power flux emitted from LFM IDT (A)

Zhang Shu‐yi and Fang Song‐ru

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S47-S47 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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According to the prediction of theories, both acoustic power flux distribution between the right and left acoustic ports emitted from LFM IDT is asymmetric. By means of optical diffraction, we have detected the distribution of acoustic fields excited by the LFM IDT. Three unapodized LFM IDT which have different parameters are studied. These transducers with aluminum electrodes were deposited on the piezoelectric substrates of YZ‐LiNbO3. The experimental results show that the SAW power run radiated from the high frequency port of LFM IDT is found to be stronger than that from the low frequency one. The asymmetry increases with the number of the finger pairs, but decreases with the band width. In general, the asymmetry increases with the excited frequency but the relation is not monotonic. Some theoretical models are taken for numerical evaluation of the asymmetric distribution. The comparison between the theoretical curves and the experimental results are presented and discussed briefly. However, in the theoretical calculations the mode‐conversion from SAW into BAW induced by the interdigital electrodes, has not been taken into consideration.
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Generation characteristics of SAW in the excited IDT (A)

Zhang Shu‐yi, Shui Yong‐an, and Fang Song‐ru

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S47-S47 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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By utilizing the optical diffraction produced by acousto‐optical interaction, the generation characteristics of SAW in the excited interdigital transducer may be observed directly and measured quantitatively. Both the method of dark field imaging and that of simple optical probing have been used. The periodic IDT and LFM IDT deposited on the substrates of YZ‐LiNbO3 have been investigated. For the periodic IDT, the experimental investigations show that the SAW generation characteristic are of symmetric growth in both emission directions of the excited IDT, but in the case of LFM IDT, the experimental results indicate asymmetric. Observations of the latter will be described and discussed in some length. Theoretical calculations have been made and their comparison with experimental data are presented. As concluding remarks, it is pointed out that all the intensities (or power flux) of SAW under investigation are represented both in theory and in experiment by the intensities of the superposition of two‐directional radiations of each finger pairs, which were considered separatively by Zuliani and Ristic [J. Appl. Phys. 49, 3018–3024 (1978)] for the periodic IDT.
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The interelectrode multireflection effect of surface acoustic wave (A)

Shui Yong‐an

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S47-S48 (1979); (2 pages)

Online Publication Date: 11 Aug 2005

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In general, a series of matrix multiplication is used in the calculation of SAW interelectrode multireflection effect. Usually complicated numerical calculations are required but the relations between the characteristics and the parameters of the arrays are not formulated by such approach. In this report some analytical expressions for SAW interelectrode multireflection effects are given. together with the frequency response and generation characteristics of interdigital transducers including the dispersive transducers discussed. The effect of multireflection of a symmetric periodic transducer could be included by the multiplication of a frequency‐dependent weighting factor to the original frequency response. The relation between this weighting factor and the parameters (the number of electrodes and the strip width, etc) is discussed. The unsymmetrical acoustic power output of the dispersive transducer is shown, with the influence of the parameters discussed. It is shown that the reflective arrays of SAW resonators of different strip width could be considered as equivalent to the arrays of different impedance discontinuity with the same reflective characteristics. The reflection outside the forbidden band is also discussed.
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Study of a SAW nonlinear FM dispersive line (A)

Zhang Xiaorong, Gan Chang‐min, and Lu Zhoug‐nan

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S48-S48 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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Study of a SAW nonlinear FM dispersive delay line (NLFM‐DDL) for generating and processing power series FM (PFM) signals with time bandwidth product of 160 and fractional bandwidth of 32% is reported. Firstly, it deals with the SAW NLFM single dispersive delay line (SDDL), with it's design, theoretical and experimental result of the frequency response and the self‐correlation pulse. It has been shown that the DDL can be used to produce signals with a power series frequency modulation and the observed sidelobe level of the self‐correlated pulse of this NLFM‐DDL is smaller than that of the LFM‐DDL with transducers having no weightings. Secondly, a double dispersive delay line (DDDL) is discussed and shown that a wider bandwidth is easier to obtain by using a DDDL than by a SDDL. It is also to be shown that by the combined action of a pair of dispersive transducers, the total pulse length which is the combined response of the two is found equivalent to the response of a PFM signal. This design has been performed by means of computer.
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