摘要:

An analysis based on linear theory is presented for determining the dynamic response and the conditions of resonance for a simply supported rectangular plate acted upon by two types of moving loads corresponding to: (1) a point force of variable magnitude oscillating about a fixed position on the plate, and (2) a point force of constant magnitude traveling in a circular orbit about a fixed position on the plate. In addition to the ordinary resonance as produced by a variable magnitude load concentrated at a fixed position on the plate, resonance of the plate may occur due to the changing position of the load on the plate. It is shown that an infinitely countable number of load movement frequencies may excite a given principal frequency of the plate for them,nth mode of vibration. Numerical examples of typical deflection profiles and time rate of deflection buildup are presented for two sets of initial conditions corresponding to: (1) a load initially at rest on the deflected beam, and (2) an accelerating load dropped from zero height on an initally undeformed beam.

ISSN:0001-4966    

DOI:10.1121/1.1910634

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Measurements of changes in permittivity, tanδ, andd∂∂as function of compressive stress parallel to the polar axis are presented for lead zirconate—lead titanate transducer ceramics. The “hard” ceramics (PZT‐4 and PZT‐8) suitable for high‐power application show large changes of properties for stresses to 20 kpsi, but have good recovery on release of stress. The “soft” donor‐doped ceramics (PZT‐5A and PZT‐5H) suitable for detector applications show serious degradation with successive stress cycles. However, for peak stress below about 10 kpsi, their variation of properties and hysteresis within any cycle are less than those of the hard ceramics. Permittivity and tanδ of all these ceramics increase with increase of ac electric field. For the soft ceramics, the tanδ increase is great enough to eliminate their consideration for uses where efficiency or cool operation are necessary. High ac electric fieldcombinedwith compressive stress reduces these detrimental increases for the soft ceramics and increases them for the hard ceramics. Nevertheless, the hard ceramics remain far superior for high‐power high stress uses, with PZT‐8 being superior to PZT‐4.

ISSN:0001-4966    

DOI:10.1121/1.1910635

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The shielding properties of infinite strip and half‐plane baffles are examined. The baffles may have different acoustic reactances on the opposite sides. The field in the shadow of the baffle is calculated as a function of the acoustic baffle reactances. For a plane‐wave noise incident from behind the baffle and a plane‐wave signal incident from the front, the signal‐to‐noise ratio is maximum when both sides of the baffle are pressure release surfaces.

ISSN:0001-4966    

DOI:10.1121/1.1910636

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Though the self‐reciprocity technique provides a simple means of obtaining absolute calibrations of electroacoustic transducers, it does not seem to have found wide acceptance. While the acoustic impedance of water and air differ sufficiently to make the loss of acoustic energy through a water‐air interface negligible, the ocean surfaces is generally not a plane, and hence, would not seem to be a suitable reflector for use with the self‐reciprocity technique. However, by using the mean of the returns from a number of pulses, it is possible to use the ocean surface. The accuracy of the technique is a function of the number of pulses, and possibly, variations in wind and sea conditions. With this technique one can make free‐field calibrations of large, low‐frequency transducers at high hydrostatic pressures and determine any variation as a function of pressure.

ISSN:0001-4966    

DOI:10.1121/1.1910637

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

This article contains a discussion of correlation detection in which the coherent processing interval is limited by source/receiver accelerations and/or medium instabilities. A method is described, which, in effect, computes ann‐dimensional correlation function uniquely related to target trajectory. Groups of relatively short waveforms that are individually insensitive to source accelerations, etc., are, after coherent reception, combined via pattern‐recognition techniques. Curves are presented that give the processing gain of the method for various conditions. A numerical example is given for the sonar case.

ISSN:0001-4966    

DOI:10.1121/1.1910638

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Coherent likelihood‐ratio detectors (having the structure of cross‐correlation receivers) designed for binary detection of directional signals in directional noise fields with transducer arrays are investigated. Optimum array geometries for these detectors (ignoring beam‐forming requirements) are linear in directional noise fields. Examples ofN‐element coherent detector performance in propagating and turbulent boundary‐layer noise fields are given. They indicate that signal‐to‐noise ratio (S/N) gains of 10 log10N plus 10 dB per decade decrease in the coherence loss by the noise in traveling between adjacent elements can be obtained ifXN1≃1, whereXN1is the product of the data bandwidth times the magnitude of the difference between the noise and signal travel times across the entire linear array.

ISSN:0001-4966    

DOI:10.1121/1.1910639

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

An improved capacitive transducer has been designed for use in attenuation and second‐harmonic generation experiments in solids. The transducer can be used as both a driver and receiver, and completely eliminates bond corrections in attenuation measurements. Further, it is a broad‐band transducer and should prove to be very useful in measurement of attenuation as a function of frequency.

ISSN:0001-4966    

DOI:10.1121/1.1910640

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

It is pointed out that Fitzgerald's particle‐wave theory of deformation in solids is based upon a misconception regarding the nature of phonons. Some experimental objections to the theory are reviewed, and an “Einstein” mass—energy equation is derived from more plausible assumptions than were used by Fitzgerald.

ISSN:0001-4966    

DOI:10.1121/1.1910641

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The inadequacy of the teaching of sound in secondary schools is emphasized, particularly the laboratory aspect. Mention is made of a project for improvement.

ISSN:0001-4966    

DOI:10.1121/1.1910642

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP