摘要:

The calculation of input power and response of simple models of rooms and structures is described. The approach is essentially statistical. Random variations in time are not considered; these fluctuations are averaged out. Randomness is introduced into the system models by considering basic parameters such as resonance frequencies and observation position to be selected statistically. Simplifying assumptions on the damping and mode shapes are made. The average and variance of power injected by point sources are calculated. The statistics of response near and away from the driving point are also found. It has not been possible to calculate the exact forms for the response distributions. Accordingly, in order to find confidence coefficients for estimation intervals, a distribution is chosenad hoc. The selected one, the gamma distribution, has several desirable features. It is, in fact, exact for some important cases. Two kinds of estimation intervals are derived and applied to some simple examples. Finally, an interesting alteration of the frequency‐spacing statistics, inspired by nuclear spectroscopy, is explored. It is found that a “level‐repulsion” phenomenon causes small separations in resonance frequency to be less probable. This can smooth the multimodal response of systems in some important, practical instances.

ISSN:0001-4966    

DOI:10.1121/1.1911422

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

A pulse‐transmission technique is described that allows the determination of small changes of the acoustic velocities in high‐loss materials. The technique employs phase comparison between a transmitted acoustic pulse and the input rf signal to establish a null pattern in the superimposed output. The method has useful applications in situations where it is necessary to detect changes as small as one part in 104in the velocities. It has been used in ultrasonic investigations employing propagation frequencies higher than 10 MHz and for total attenuation losses as high as 50 dB. Data are presented illustrating the shear velocity as a function of one‐dimensional stress in polymethylmethacrylate.

ISSN:0001-4966    

DOI:10.1121/1.1911423

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

An expression, valid in the Raman‐Nath region, is derived for the integrated optical effect experienced by a light beam traversing the sound field of a plane piston transducer of arbitrary shape. Specific results for circular and rectangular transducers are discussed. Of particular interest is the optical effect produced by a square transducer aligned so that the light beam propagates in a direction parallel to one of the diagonals. In this case, the integrated optical effect is nearly constant over a fairly large region in space, suggesting the possibility of using this configuration to make absorption measurements.

ISSN:0001-4966    

DOI:10.1121/1.1911424

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

A systematic study of acoustically induced birefrigence in castor oil is described. Particular emphasis is placed upon the evaluation of a measuring technique based upon a polarization analysis of the Fraunhofer optical diffraction spectrum. Results obtained using this measuring technique are compared with results of measurements made in the optical nearfield.

ISSN:0001-4966    

DOI:10.1121/1.1911425

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

An ultrasonic method for measuring thermodynamic parameters in liquids has been developed. By the pulse‐repetition technique, the velocity of sound is determined in a cylindrical sample of fixed length. These data are then used to determine the change in height of a similar cylindrical sample of variable length. A preliminary investigation in mercury was accomplished to evaluate the technique. Thermal expansion and isothermal compressibility data are presented over the ranges 20°–90°C in temperature and 1–2000 bars in pressure. Estimated accuracies for thermal expansion and isothermal compressibility at 2000 bars are 1% and 3%, respectively.

ISSN:0001-4966    

DOI:10.1121/1.1911426

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The effect of static and dynamic stress on the mechanical loss of a piezoelectric ceramic has been measured. Static stress was applied pneumatically along the axis of a radially polarized tube of lead zirconate titanate measuring 2.54 cm long by 0.317 cm wall thickness. It was found that immediately after applying a static compressive stress of 3000 psi, the mechanical loss, proportional to the reciprocal mechanical quality factorQm−1increased from 1.27×10−3to 4.54×10−3. The mechanical loss of the ceramic was determined by measuring theQfactor of the ceramic and its support, and correcting for the support losses. A similar tube was statically biased with a stress bolt by incorporating the tube as the active element in a small model transducer. The transducer was then coupled to a high‐power ultrasonic driver by means of which large dynamic stresses were generated in the ceramic. A dynamic stress of 3000‐psi peak was superposed on a static biasing stress estimated at 5000 to 10 000 psi. The bias alone increased theQm−1factor of the tube from 4.00×10−3to 2.45×10−2, and the superposed dynamic stress further increased theQm−1factor to 6.30×10−2. Upon removing the dynamic stress, theQm−1factor gradually reduced to 1.67×10−2. Surface temperature rise did not exceed 5°C.

ISSN:0001-4966    

DOI:10.1121/1.1911427

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The Watson transformation has been developed for diffraction problems in the frequency region where the numerical values can be obtained more easily than by the use of the exact normal‐mode series. A physical interpretation of this mathematical technique was given by Franz as creeping waves that travel around the surface at a velocity less than that in free space and that are attenuated by radiation. Thus far, only indirect measurements have been made experimentally. Herein is presented the report of a series of experiments that give direct verification of these waves for scattering by rigid spheres and cylinders in air. Radiation of creeping waves circumnavigating the obstacle was verified by interference measurements in the backscattered field with continuous waves. To detect the “isolated” creeping wave as it circumnavigated the scatterers, incident wave pulses in conjunction with high‐speed digital logic techniques were used. Coincidence techniques were used for precise measurement of velocity, and amplitude decay was determined by sampling and comparing CW pulses at two points in space and time by Lissajous pattern techniques.

ISSN:0001-4966    

DOI:10.1121/1.1911428

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The problem of the cavity with a small aperture is reduced to the solution of an integral equation, which is solved both for low frequencies and frequencies around a resonant value. Use of a reciprocity principle leads directly to an equivalent circuit for the cavity.

ISSN:0001-4966    

DOI:10.1121/1.1911429

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

Exact solutions of the equations of the fully coupled linear theory of piezoelectricity are obtained for some simple types of two‐dimensional waves in an infinite plate. It is shown that the coupling of the mechanical and the electrical fields can give rise to dispersion curves with complex branches and to waves that are largely confined to the region near the major surfaces of the plate.

ISSN:0001-4966    

DOI:10.1121/1.1911430

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

A continuous‐wave single‐frequency seismic carrier for transmitting information by amplitude, phase, and frequency modulation has proven useful and practical in situations where electromagnetic means of communication are not feasible. An 80‐Hz, 20‐kg seismic transducer using 10 W maximum power was utilized for transmission through low‐velocity media; an 80‐Hz, 300‐kg transducer using 200 W maximum power was utilized for transmission through high‐velocity media. For reception, an 80‐Hz resonant seismic transducer equipped with a frequency trimmer was used. Efficient signal insertion into soil was achieved by employing an artificial mechanical‐elastic transmission line as an impedance transformer. A mathematical model for a slotted steel tube, which operates as an impedance transformer, is presented with a mathematical description of the impedance transformation process. Seismic‐coupling efficiency was derived by comparing an actual system with a theoretically ideal transducer‐medium system. Experimental and theoretical results based on data recorded during tests on various seismic media are analyzed in terms of the mathematical model employed. Results verify the validity and soundness of design and operation of a seismic communications system.

ISSN:0001-4966    

DOI:10.1121/1.1911431

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP