摘要:

A nonlinear design technique is described for predicting the high power sound output and efficiency of a magnetostrictor. The method is based upon the assumption that the magnetic permeability of the active material is strain invariant. An experimental perturbation technique, and an alternative method involving the measured strain field, are used to determine the complex transformation ratio of a Ni‐Co ferrite at various values of the field, induction and strain. The results are plotted as sets of nonlinear design characteristics. The transformation ratio is used in conjunction with the Van Dyke equivalent circuit to predict the nonlinear sound output and efficiency of a magnetostrictor formed from the ferrite. The magnetostrictor is a slotted bar transducer resonating at 24.8 kHZ in the fundamental‐length mode. A novel feature of the experiments is the use of a piezoelectric transducer (dummy load) to backdrive the magnetostrictor to vary the strain independently. The magnetostrictor sound output is predicted to an accuracy greater than 15% at induction swings as large as one‐third of saturation. The shape of a skewed resonance curve is successfully predicted indicating that nonlinearity is a cause of the resonance curve distortion.

ISSN:0001-4966    

DOI:10.1121/1.1911550

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

Results of judgment tests on the noisiness of aircraft sounds published during the past decade [and cited by K. D. Kryter, J. Acoust. Soc. Amer.43, 344–361 (1968)] have been analyzed collectively to find the relative precision with which the judgments are explained by calculated perceived noise level, calculated loudness level, and Sound LevelsA, B, C,andD(formerlyN). For consistency, all levels have been recalculated, in accordance with current rules, from published noise spectra. Application of standard statistical procedures to the available data indicates that differences among the first three levels and the sixth, in their correlation with judged noisiness, are not statistically significant; only theBandClevels are clearly inferior as predictors of noisiness. A new weighting derived simply from two cascaded RC circuits, with corner frequencies at 2 and 8 kHz, leads to levels of better precision than any of the others, but adoption of this new weighting is not proposed without further study. Since Sound LevelApredicted the judged noisiness of the aircraft sounds as precisely as did calculated loudness level or perceived noise level, this readily measured sound level may well be applied to the rating of aircraft noise along with other noises in the community.

ISSN:0001-4966    

DOI:10.1121/1.1911552

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The amplitudes of sustained vowels were measured at the dominant amplitude peak of each fundamental period of the acoustic signal picked up by a microphone coupled to the pretracheal skin. Serial correlation coefficients were computed and correlograms were made for each sample to investigate the periodicity in the modulation of the amplitude. Three groups of subjects were studied: 15 cases with laryngeal neoplasms, six cases with unilateral laryngeal paralysis, and 20 normal subjects as a control group. In each group of subjects, a high correlation was often found between the consecutive dominant amplitude peaks. The correlograms for patients with laryngeal neoplasms often displayed strong periodicities with periods of three to 12 fundamental periods, while for the paralysis cases no evidence of periodic modulations in the same range was found. The results seem to indicate that amplitude information may be useful for the development of an objective measure to evaluate laryngeal dysfunction and to detect some pathologies in the larynx.

ISSN:0001-4966    

DOI:10.1121/1.1911554

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

When the free surface is anisotropic, mode of elastic surface‐wave propagation can arise that has many of the properties of a normal surface wave but has a phase velocity higher than that of the transverse bulk waves in the corresponding direction. The pseudo surface wave is a coupled mode involving terms decaying rapidly beneath the free surface and a term representing a bulk wave radiating into the solid. For many choices of crystal and plane of propagation, the contribution of the bulk term over a range of directions is small enough that the energy of the wave is essentially concentrated within a few wavelengths of the free surface and flows parallel to the surface as with the normal elastic surface waves. Moreover, in certain specific directions, the bulk term disappears completely and the pseudo‐surface wave has all the properties of a normal surface wave. The method of computation of the characteristics of the pseudo surface waves is outlined here and typical results of velocity, displacements and energy flow are given for an assortment of anisotropic crystals and planes of propagation.

ISSN:0001-4966    

DOI:10.1121/1.1911556

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

For measuring attenuation by the ultrasonic pulse‐echo method, a selected echo—obtained by pulse modulating a very stable CW carrier—is directly heterodyned to produce a video signal with a beat frequency of a few hertz. This signal is then sampled at the repetition rate and filtered to give a low‐frequency CW output with a signal‐to‐noise ratio some 30 dB greater than for the selected echo. Phase shift at the wave frequency produces an equal phase shift at the beat frequency, and can be measured with a phase meter. The detection system is sensitive for weak signals and is linear. Readout of amplitude and phase can be made on standard recorders. In a second arrangement, the selected echo is added algebraically to a reference signal having a slightly different frequency. with the CW beat frequency resulting processed as before. Because of the good phase stability, this method can be used at frequencies in the high megahertz range.

ISSN:0001-4966    

DOI:10.1121/1.1911558

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

Methods for detecting ultrasonic images are briefly reviewed, and discussed in light of their potential application to nondestructive test problems. In a typical nondestructive test system involving a water immersion tank, the ultrasonic image detector should respond to an ultrasonic intensity of 10−2W/cm2or less. This requirement eliminates from consideration number of detection methods involving photographic, chemical, or thermal mechanisms. Of the remaining image detection systems, only a few have been applied to nondestructive test problems. These include the surface relief technique, the Pohlman cell, and scanning methods involving piezoelectric transducers. The latter method has been most used for image applications, with mechanical movement of the transducer(s) in aCscan method. Electron scan of a single piezoelectric detector to provide a television presentation is coming into wider use. A description of one such system is given. For a thin, flat inspection object, the system offers good inspection speed, resolution, and sensitivity to inhomogeneities. Thick, irregularly shaped inspection objects present problems because lens systems are involved. Lenses for imaging are not well developed. Also, the use of a lens tends to slow the inspection of a thick object because one must examine the object by focusing at different depths. Pulsed television systems and holographic techniques offer some promise in that area. A new phase‐sensitive color television ultrasonic image system offers hope for improved detection of subtle discontinuities.

ISSN:0001-4966    

DOI:10.1121/1.1911560

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

A method of realizing an underwater acoustic lens that forms an image with no aberration of an object lying at infinity in a given direction is described. The lens is nearly spherically symmetric so that the aberrations for objects off this axis are small. It makes use of two existing materials of uniform acoustic velocity as the lens media. The equations governing the structure of such a lens and some results of their solution are given.

ISSN:0001-4966    

DOI:10.1121/1.1911561

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

An ultrasonic image conversion cell utilizing the liquid‐surface‐levitation effect has been developed. This effect is based upon the principle that the surface of a free liquid will be deformed in accordance with the cross‐sectional intensity distribution of an impinging ultrasonic beam. The image‐conversion cell has been successfully applied for nondestructive‐testing purposes. It can be coupled directly to an ultrasonically excited test specimen to obtain characteristic liquid‐surface relief patterns depicting internal discontinuities. A significant advantage of the conversion cell is the fact that it does not require the test specimen itself to be immersed in a liquid. Also, because the conversion cell produces a “real‐time” image, pulsed, frequency‐modulated, and continuous‐wave modes of ultrasonic excitation can be used, and thus, various types of ultrasonic images can be obtained.

ISSN:0001-4966    

DOI:10.1121/1.1911562

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The paper discusses a technique in which a laser flying spot scanner is used to record an acoustic hologram by reading out the periodic deformations of a solid surface caused by an incident sound field. The technique is compared with the Sokolov tube method and shown to have comparable sensitivity, while not being restricted to low frequencies and small areas. A description is given of experiments using sound frequencies of 2 and 9 MHz, and photographs are presented showing holograms and reconstructions obtained with this technique.

ISSN:0001-4966    

DOI:10.1121/1.1911563

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

A wave solution has been obtained for the acoustic fields inside a class of perfectly focusing spherical lenses that have been previously described by Luneberg and Gutman. Plane‐incident radiation on a lens having a continuous radially varying refractive index, prescribed by Gutman, is assumed. The radial functions for the eigenfunction expansion are defined by an integral solution of the radial portion of the separated scalar Helmholtz equation for the interior of the lens. This defining integral leads immediately to recurrence relations that are useful in the computations. The integral may also be evaluated asymptotically for large wavenumber‐aperture products, for functions of low order, in order to normalize suitably the sequences of functions generated recursively. Axial and polar patterns were obtained for various lenses for wavenumber‐aperture products up to 240.

ISSN:0001-4966    

DOI:10.1121/1.1911564

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP