摘要:

A capacitive‐driver–capacitive‐detector system for generation and detection of ultrasonic waves has been developed. This eliminates the necessity of bonding piezoelectric transducers to solid samples. With the capacitive‐driver–capacitive‐detector system, free–free boundary conditions exist at the sample surfaces and longitudinal ultrasonic‐wave velocities in solids can be measured accurately without correcting for ultrasonic‐wave phase shifts due to sample‐bonded transducer interfaces. The capacitive driver has a mica dielectric which increases the breakdown potential, but maintains the free–free boundary conditions at the solid specimen surfaces. This allows for a larger‐amplitude ultrasonic signal to be generated in the sample than is possible with an air‐gap capacitive driver. This improves the precision of the measurement. The accuracy of the method is comparable with that of bonded‐transducer methods, after bond corrections are made.

ISSN:0001-4966    

DOI:10.1121/1.381330

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

An investigation is made of the dynamics of a liquid free surface in the presence of a reflecting sound field. A finite‐amplitude surface standing wave is also specified and the resulting unbalanced vertical stress at the surface is equated to the acoustic pressure. Second‐ and third‐order terms are retained in the surface‐wave description (and fourth‐order in the nonlinear interaction model). By further equating the viscous dissipation in the surface wave with the net upward acoustic energy flux, the surface‐wave parameters are determined in terms of the acoustic‐field parameters. Three major results are obtained: no surface waves can exist below an acoustic‐intensity threshold (same value as predicted by using Mathieu’s differential equation), above the threshold the square of the surface‐wave amplitude is linearly dependent on the acoustic‐driving amplitude (for small surface‐wave slopes), the sensitivity of the surface waves to driving amplitude is essentially independent of frequency except near the region of resonant gravity–capillary coupling. Comparisons are made with measurements (primarily at ultrasonic frequencies) and reasonable agreement is shown to exist.

ISSN:0001-4966    

DOI:10.1121/1.381331

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Keller’s geometrical theory of diffraction is applied to three‐dimensional elastodynamics, in particularly to diffraction of longitudinal waves by a crack. The theory provides useful approximations for large frequencies and/or large distances from the edge of the crack. For the class of problems considered in this paper, the canonical solution is provided by the fields describing diffraction by a semi‐infinite crack of a plane longitudinal wave which is incident under an arbitrary angle with the edge of the crack. The formal solution to the canonical problem is obtained by means of integral transform techniques in conjunction with an application of the Wiener–Hopf method to a set of coupled equations. The pertinent asymptotic expressions for the diffracted field are evaluated, and the diffraction coefficients which enter the geometrical theory are determined. As an example, the three‐dimensional problem of diffraction of a point‐source field by a semi‐infinite crack is worked out in detail.

ISSN:0001-4966    

DOI:10.1121/1.381332

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

An analysis is made for the longitudinal vibrations of a thin, multielectrode, piezoelectric bar composed ofNferroceramic materials. Resonant and antiresonant eigenfrequency equations are derived, and an equivalent electrical circuit of the transducer is developed from the admittance matrix. Numerical solutions are presented for the fundamental resonant frequencies and corresponding normalized frequency differences of a uniformly polarized, two‐electrode, PZT‐4 bar with nonzero interelectrode spacing.

ISSN:0001-4966    

DOI:10.1121/1.381333

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Force transmissibility, driving‐point impedance, and transfer impedance of a simply supported rectangular orthotropic sandwich plate are investigated. The plate is driven by a sinusoidally varying point force either at the plate center or at any arbitrary location. The variation of force transmissibility and impedance with frequency, and the manner in which this is influenced by the various sandwich‐plate parameters are studied and presented graphically.

ISSN:0001-4966    

DOI:10.1121/1.381334

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A system of plate equations for the thickness‐shear and flexural vibrations superposed on large initial deflection due to bending is derived; in the stress–strain relations the terms associated with the fourth‐order elastic stiffness coefficients are retained. An explicit formula for the change in the fundamental cutoff thickness shear frequency is obtained and the effects of the terms associated with the fourth‐order constrants appear to be significant for large gradients of the rotation angles.

ISSN:0001-4966    

DOI:10.1121/1.381335

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The eigenvalue problem and transverse response of a circular plate, that is free at the periphery and that slides freely along the axis of symmetry without bending rotation, are theoretically analyzed. The occurance of eigenvalues in the boundary conditions is accounted for with an extended operator definition in the equation of transverse motion. The stability of these plates under concentrated loads moving at uniform speed is analyzed for (i) harmonic transverse loading and (ii) loading proportional to transverse displacement and velocity. The harmonic loading case leads to a classical, critical‐speed analysis. The proportional loading case represents the excitation of the plate by transverse position guides. The number, orientation, and mechanical properties of the guides determine the transverse stability of the plate‐guide dynamic system.

ISSN:0001-4966    

DOI:10.1121/1.381284

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

This is a special joint session sponsored by the Technical Committees on Noise and on Architectural Acoustics. There were six invited papers.

ISSN:0001-4966    

DOI:10.1121/1.381336

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Sound‐power ratings of machinery are becoming more important for a number of reasons. Industrial installations must comply with recently enacted state and local noise control codes, and sound power ratings are needed to predict compliance. In addition to this, The Federal Noise Control Act of 1972 requires labeling of machinery to show maximum noise emission, and this, logically, may be in terms of sound power. There are several ways to determine the sound power of machinery under laboratory conditions, but these procedures are usually not applicable in industrial environments. The two‐surface method offers the best practical approach to the problem of calculating sound power ratings of large machinery installed indoors, under actual operating conditions.

ISSN:0001-4966    

DOI:10.1121/1.381337

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

For determination of sound power of sources by the ’’method of enveloping measurement surfaces,’’ the test environment should provide a measurement surface which lies (1) outside the nearfield of the sound source under test and (2) inside a sound field free of undesired sound reflections from room boundaries or reflecting objects near the source. Methods to check the free‐field conditions and to qualify a given measurement surface for an actual source under test are (1) theabsolutecomparisontestusing a (small) calibrated reference sound source, (2) therelativecomparisontestusing a small test sound source which radiates broadband noise that remains essentially constant during the measurement, and (3) thereverberanttest, which requires measurement of reverberation time. Method 3 is only applicable in closed spaces (rooms). Methods 1 and 2 may be used in rooms and outdoors. Methods 1 and 2 require replacing the source under test by the reference sound source or test sound source in the test site. If the source under test cannot be removed, methods 1 and 2 still allow qualification for free‐field conditions, with less accuracy. This paper deals mainly with therelativecomparisontest(method 2) and gives information about the accuracy of the determination of the environmental corrections factorKunder different field conditions.

ISSN:0001-4966    

DOI:10.1121/1.381285

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP