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Jun 1977

Volume 61, Issue S1, pp. S1-S96

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back to top Session H. Engineering Acoustics I and Physical Acoustics II: Solid State and Transducers
Contributed Papers
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Arrival times of scattered ultrasonic signals from a solid inclusion in an elastic solid (A)

Deborah J. Rhodes and Wolfgang Sachse

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S16-S16 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Measurements are reported of the arrival times of broadband ultrasonic pulses scattered by a circular, cylindrical, solid inclusion imbedded in a matrix whose longitudinal wave speed is lower than that of the cylinder. The wavenumber‐inclusion radius product, ka, ranged from approximately 1 to 15. The matrix materials were water, acrylic, and brass and the inclusion materials were copper, quartz, stainless steel, and tungsten. A strong, scattered pulse, corresponding to a circumferential wave on the cylinder is observed for cs > cl, where cs is the shear wave speed of the inclusion material and cl is the longitudinal wave speed of the matrix material. These observations are in agreement with published results. The experiments also show that the pulse corresponding to the circumferential wave is not observed for cs < cl. It is shown how the approximate diameter and longitudinal wave speed of the inclusion can be determined from the arrival times of the scattered pulses. [Supported by NSF Grant ENG75‐13703.]
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Spectral analysis of elastic pulses scattered from two cylindrical cavities in a solid (A)

Selcuk Sancar, Yih‐Hsing Pao, and Wolfgang Sachse

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S16-S16 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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A solution for the scattering of plane harmonic waves from two traction‐free, cylindrical cavities in an elastic solid is obtained in terms of cylindrical wave functions. The scattered waves are expressed as an infinite sum of orders of scattering, the first order being the usual single scattering approximation and each successive order being expressed in terms of single cylinder scattering coefficients. The exact eigenfunction solution is numerically evaluated for incident plane waves of frequency ranging from 0 to 10 MHz and the power spectrum of the backscattered radial stress amplitudes resulting from a delta‐function incident pulse is calculated for various combinations of cavity radii and separations. Approximate high‐frequency, farfield solutions are derived and compared with the exact solution. Experimental backscattering spectra with broadband ultrasonic pulses are obtained in specimens of aluminum containing two side‐drilled, parallel holes. The experimental results are compared with both the exact and the approximate solutions. The approximate high‐frequency solution is exploited in an attempt to derive simple expressions which explain the major details of the spectra and which can be used for quantitative flaw characterization in ultrasonic nondestructive testing. [Supported by NSF Grant ENG75‐13703.]
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Extraordinary magnetoelastic coupling measured ultrasonically in Tb0.3Dy0.7Fe2 (A)

S. Rinaldi, G. V. Blessing, and J. R. Cullen

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S16-S16 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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We measured the magnetic field dependence of the transverse acoustic velocities in single crystal Tb0.3Dy0.7Fe2, a highly magnetostrictive material with low anisotropy. All measurements were made with the sample magnetically saturated. The field was in the plane perpendicular to [110] and containing the [001] and [110] directions. The propagation direction was [110] in all cases; the polarizations were along [001] and [1̄10]. The former is the usual configuration for determining C44, the latter for (C11 − C12). We measured reductions of 50% in the C44 elastic constant with the onset of magnetoelastic coupling (∼ 5 kOe) in this nominally cubic ferrimagnet. This is the largest such reduction ever reported for a cubic material. From the C44 variation with the magnitude of the field, we were able to determine the magnetoelastic coupling constant b2. By contrast, evidence of higher‐order magnetoelastic effects was found in the 2% (C11 − C12) variation with magnetic field orientation, in accordance with magnetosfriction measurements which show that λ100 ≪ λ111. [Work supported in part by ONR.]
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Two systems for measuring impedances from transducers (A)

B. D. Cook and E. Cavanagh

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S16-S16 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Two systems for measuring impedances of transducers have been used to evaluate the properties of dynamic, piezoelectric, and magnetostrictive transducers ranging from low audio frequency to ultrasonic frequencies. One consists of a computer interfaced with a frequency synthesizer and a phase‐gain meter. The other is constructed around a novel phase and quadrature detector. The computer‐oriented design allows a wider frequency range and has the advantage that it is automatic; whereas, the device designed by the authors can be interfaced with normal laboratory instruments, thus reducing the cost of the system.
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Measurement of power from a planar ultrasonic transducer; experimental consistency study (A)

B. D. Cook and E. Cavanagh

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S16-S16 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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In a previous paper [“Precision acousto‐optic calibration of ultrasonic transducers,” B. D. Cook, Paper C3, J. Acoust. Soc. Am. 59, S7 (A) (1976)] a method of accounting for the nearfield in acousto‐optic power measurements was discussed. This paper describes the successes and difficulties encountered in implementing such a theory.
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Performance of a condenser microphone designed for operation at elevated temperatures (A)

Allan J. Zuckerwar

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S16-S17 (1977); (2 pages)

Online Publication Date: 11 Aug 2005

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A condenser microphone system has been developed to measure pressure fluctuations at elevated temperatures. Specifications achieved with a prototype microphone are the following: maximum operating temperature (continuous duty) >427°C; harmonic distortion at 170 dB SPL = 1.4%; noise floor (22.4 Hz to 22.4 kHz) = 105 dB; frequency response (± 2 dB) = 20 Hz to 10 kHz; thermal shock, <2 dB change in sensitivity during cooling at rate of 162°C/min; vibration sensitivity <0.5 Nm−2/g. The three predominant effects of temperature changes are changes in the membrane—backplate gap, membrane tension, and air viscosity. The microphone is designed so that changes in gap and membrane tension tend to have compensating effects upon the microphone sensitivity. [Work supported by NASA Grant NSG‐1039.]
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Some effects of environmental stress on the electret condenser microphone (A)

S. V. Djuric

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S17-S17 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Over the past several years improvements have been made in the basic design of electret condenser microphones. A thinner ,and tougher diaphragm and a new design of the diaphragm support have produced an exceptional resistance to mechanical and thermal shocks, During a mechanical shock test five microphones were let fall from a height of 2 m (6 ft, 7 in.) onto a hard floor (concrete covered with thin plastic tile). The sensitivities of these microphones changed between +0.1 and +1.4 dB. Two microphones were exposed to thermal shock by suddenly changing the ambient temperature from −40 to +25°C. Their sensitivity shifted +0.7 and +1.2 dB, respectively, and they were immediately covered by frost. Within 30 min they recovered to within 0.3 dB of initial sensitivity. These microphones have a temperature coefficient of sensitivity typically less than +0.01 dB/°C at frequencies below 2 kHz, and it remains less than +0.015 dB/°C through the frequency range up to 20 kHz. The inherent immunity to high humidity of electret microphones is further improved by using a better insulator material.
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Analysis and design of wave interference directional microphones (A)

Ted N. Carnes and Douglas D. Reynolds

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S17-S17 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Analytical models of a wave interference directional microphone were developed for use on a digital computer. Many microphone design parameters were analyzed in detail, Wave interference directional microphones consist of cylindrical tubes with sound pressure receiving ports spaced along their length. Electroacoustical transducers are placed near one end. Both ends are terminated by acoustical impedance elements. The microphone is classified as an end‐fire receiving array for air use. Variations of this type of microphone have existed for many years; however, a detailed analytical model was never developed and verified. The microphone was modeled using acoustical transmission line theory. Various microphone configurations were evaluated for frequency response and directivity. The most important effects on performance, tests proved, are caused by internal sound wave propagation, and these effects can alter performance drastically from that predicted by geometric line array theory. The models were verified by comparison of measured and predicted frequency response and directivity of actual microphones. Many design parameters of the directional microphone were analyzed, utilizing the theoretical models. This information will be presented.
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Design of transducers for multiple‐frequency operation (A)

S. E. Auyer and R. T. Winnicki

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S17-S17 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Use is frequently made of a λ/4 mechanical impedance matching section on the face of a transducer to improve coupling of acoustic energy from the transducer into the medium and to increase operating bandwidth of the transducer. It is shown that the addition of this matching section introduces additional, higher‐frequency, resonances in the transducer. By proper design of the transducer and matching section, the resonances can be independently controlled as to frequency and operating bandwidth so as to result in a device capable of operation at multiple, widely‐spaced, frequencies.
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New approach to a constant beamwidth transducer (A)

A. L. Van Buren and Peter H. Rogers

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S17-S17 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The theory of a broadband constant beamwidth transducer which is to be used primarily as a projector is presented. The transducer is a spherical cap of arbitrary half‐angle α shaded so that the normal velocity is given by ur  =  u0Pv(cosθ), where Pv is the Legendre function whose root of smallest angle occurs at θ = α. The required value for v can be obtained to within 1% for α ⩽ 1 rad from the approximation v ≃ 0.5(4.81/α − 1). The transducer is shown to have uniform acoustic loading, extremely low side lobes and an essentially constant beam pattern for all frequencies above a certain cutoff frequency. Under piezoelectric drive the transducer is shown to have a flat transmitting current response over a broad band.
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Diffraction fields of echosonde antennas (A)

S. Adeniyi Adekola

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S17-S17 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The scalar diffraction integral is used in the present paper to obtain transforms of aperture field‐distributions of an echosonde (acoustic echo‐sounding) antenna. A highly convergent Lommel series of the form Ω0m(ν, η), is used to obtain the antenna Fresnel‐zone field near the boresight of the antenna, The zero‐order Hankel transforms of the real aperture‐field distributions, which can also be used to synthesize the antenna‐pattern, are obtained for circularly symmetric aperture‐fields. The zero‐order Lommel transforms are applied in the case of complex aperture‐fields using the type of radial phase‐changes (across the aperture) previously discussed [Adekola et al., Radio Sci. 12, 11–22 (1977)], The zero‐order Lommel transforms arising from uniform excitations are expressed in closed forms using the Anger−Weber functions. Echosonde antennas are useful for investigating the thermal‐structures and dynamics of the lower atmosphere [S. A. Adekola, J. Acoust. Soc. Am. 60, 230–239 (1976)]. Halfpower beamwidth‐variations between 13.45° and 3.16° are obtained within 1–5 kHz. Sidelobe attenuations are between 50 and 60 dB. The theory is in good accordance with available experimental data. Atmospheric turbulence‐components producing the strongest scatter range from 0.165 m at 1 kHz through 0.035 m at 5 kHz. The antenna‐aperture is of several wavelengths from 3.7λ at 1 kHz through 25.7λ at 5 kHz. [Work supported by NRC.]
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Piezoelectric polymer receiving arrays for ultrasonic applications (A)

A. S. DeReggi, S. Edelman, S. Roth, H. Warner, and J. Wynn

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S17-S18 (1977); (2 pages) | Cited 1 time

Online Publication Date: 11 Aug 2005

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Broadband ultrasonic detector elements each approximately 2 mm in diameter and multielement linear arrays have been constructed using commercially available polyvinylidene fluoride sheet 25 μm thick. Electrode and electrical lead patterns were deposited on both surfaces by vacuum evaporation. Poling was achieved by applying ∼2000 V across the electroded parts of the sheet while the temperature was cycled from room temperature to ∼120°C over a period of ∼1 h. The open‐circuit responsivity of the samples to ultrasound was measured in the frequency range of 300 kHz to 1 MHz with the samples freely immersed in water, with the array backed by a steel ref1ector plate, and with the array a distance away from the reflector plate. The measurements were performed with the elements connected to a preamplifier by means of a 50 Ω coaxial tube about 30 cm long. Since the capacitance of an element is about 8 pF, the measured responsivity of about −230 dB re 1 V/μPa was degraded considerably by the cable capacitance. The results are consistent with a piezoelectric response mechanism where ultrasonic pressure fluctuations induce thickness compression of the polymer. Reflector plates provide up to 6 dB boost in the pressure sensed and a corresponding increase in response. Ease of fabrication, low cross‐talk between adjacent elements of an array, flat response over a wide range of frequency and low cost suggest usefulness in ultrasonic imaging systems.
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