摘要:

An approach is presented to compute the time‐dependent force on a piston of arbitrary shape which results from the specified velocity of a circular piston in a rigid planar baffle. The force is expressed as the convolution of the specified piston velocity with an impulse response which is equivalent to the time‐dependent force on the piston of arbitrary shape that results from an impulsive velocity of the circular piston. The mutual radiation impedance is shown to be equivalent to the Fourier transform of the impulse response. A circular piston and concentric annular ring are then investigated using the approach. A closed‐form expression for the impulse response is presented and the impulse response is shown to consist of two pulses, each of which is associated with an edge of the ring. Numerical results are presented to illustrate the effect of changing the relative size of the piston and ring on the impulse response and mutual radiation impedance. Several interesting characteristics of the mutual radiation impedance are discussed and are shown to be in agreement with those obtained from an approximate solution.

ISSN:0001-4966    

DOI:10.1121/1.1913656

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

In the course of the study of the transmission properties of broad‐band pseudorandom noise signals as a function of range, water depth, and other environmental parameters, relationship between correlation peak time differences and multipath time differences was determined. Illustrations of the measured cross correlation between a reference and high‐resolution pseudorandom noise signal versus time and calculated ray paths are presented. Peak correlation values range from 0.31 to 0.63 for the demonstration data. Only minor discrepancies were observed in the measured time differences between the correlation peaks and those calculated from XBT data.

ISSN:0001-4966    

DOI:10.1121/1.1913657

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The problem of focusing a pressure wave by a thick, elliptical cylindrical liquid lens has been treated in a rigorous manner. The size of the lens is of the order of or slightly greater than the wavelength of the incoming acoustic signal. Detailed computation has been carried out for a representative case in which a liquid lens with an index of refraction of 1.8 and a density of 1900 kg/m3is assumed to be immersed in seawater. It is shown that a slight deformation of the boundary surface of a circular liquid lens results in significant changes in the location of the focal region and that an elliptical lens may provide stronger focusing than an equivalent circular lens. This research also points out the necessity of pursuing an investigation on thin lenses where the focal regions are located outside the lenses.

ISSN:0001-4966    

DOI:10.1121/1.1913658

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Mismatch in a beamformer occurs when the knowledge of the signal directional properties is imprecise. The effects of mismatch on a conventional beamformer and two optimum beamformers are compared. One optimum beamformer is based on inversion of the noise cross‐spectral matrix while the other is based on inversion of the signal‐plus‐noise cross‐spectral matrix. When there is mismatch, the inclusion of the signal in the matrix inversion process can lead to dramatic reductions in the output signal‐to‐noise ratio when the output signal‐to‐noise ratio of a perfectly matched beamformer would be greater than unity. However, the corresponding effect on the total beamformer output is less dramatic since an increase in the noise response partially offsets the decrease in signal response. The question of suppressing mismatched signals is closely related to the question of resolving closely spaced sources. Exact conditions are presented for resolution of closely spaced sources by an optimum beamformer. These results are applied to a line array and compared with the resolution capability of a conventional beamformer. It is found, for example, that an output signal‐to‐noise ratio of about 47 dB is required to achieve a resolving power with an optimum processor which is ten times that given by the classical Rayleigh limit. Conditions are also presented for the resolution of two sources of unequal strength.

ISSN:0001-4966    

DOI:10.1121/1.1913659

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The basic difference between phased‐array sonar and acoustical holography lies primarily in the order in which the temporal and spatial processing operations are carried out. However, it is shown that this difference can result indirectly in an advantage for holography in either signal‐to‐noise performance or processing complexity.

ISSN:0001-4966    

DOI:10.1121/1.1913660

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Four chinchillas were trained to lick a drinking tube located in one end of a double‐grille cage to obtain their daily ration of water. When the licking rate stabilized (4–5 licks/sec) in daily sessions of about 20 main, avoidance conditioning began. The animal was required to leave the tube and cross a midline barrier to avoid shock when one sound, the positive conditioned stimulus (+CS), was presented, while he could continue licking without threat of shock when another round, the negative conditioned stimulus (−CS), was presented. The chinchillas quickly learned a near perfect association of crossing the barrier to +CS and not crossing to −CS, which was maintained throughout the 30 daily sessions of the experiment. Intertrial crossing were virtually absent and licking rates provided a sensitive, additional measure of an animal's response to the stimuli

ISSN:0001-4966    

DOI:10.1121/1.1913661

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The brains of several representative species of echolocating bats were found to contain regions concerned with the emission of species‐specific orientation sounds. When the dorsal part of the reticular formation in the midbrain or the lateral part of the central gray matter is stimulated with a short train of electric pulses, the bat moves its mouth and pinnae and emits sounds identical to orientation sounds, with a latency of 25 to 60 msec. The acoustic parameters of the electrically elicited sounds and the temporal patterns of emissions vary with the location of the stimulating electrodes. Bats of the genusMyotis(little brown bat) emitted short frequency‐modulated (FM) sounds both in nature and when electrically stimulated.Pteronotus parnellii(mustache bat) responded with sounds containing long constant‐frequency (CF) and short FM components that were typical of the species.Eptesicus fuscus(big brown bat),Pteronotus suapurensis(naked‐backed bat), andNoctilio leporinus(fish‐catching bat) also made characteristic orientation sounds when electrically stimulated. It appears that the midbrain contains neural circuits for the emission of species‐specific orientation sounds and that a part of the vocalization system is located in the regions juxtaposed to the inferior colliculus, an important neural center for echolocation.

ISSN:0001-4966    

DOI:10.1121/1.1913662

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

This is a report of a method found useful in finding defects easily in the response of acoustical chambers and sound systems. The method employs a complex sound or speech signal, which is successively recorded and reproduced several times in the chamber under test with the same double magnetic recording‐reproducing system. The final results after several repetitions of the process are then studied.

ISSN:0001-4966    

DOI:10.1121/1.1913663

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

This letter describes the principle and the fundamental results of experiments of a synthetic aperture sonar which enables us to resolve objects both in angle and range more sharply than the conventional ultrasonic imaging system. The basic idea of this technique is to introduce pulsed waveforms to ultrasonic holography and its operations consist of collecting hologram signals with ultrasonic pulses and using a computer for storage of these signals and image calculation. The elementary experiments were carried out using a single‐wire target and ultrasonic waves of 1 MHz whose pulse duration was 12 μsec. The wire was set at a distance of 158 mm below the transducers and they were scanned over the hologram aperture of 50 mm across the wire. The results of the computer reconstruction were coincident with the theoretically expected values.

ISSN:0001-4966    

DOI:10.1121/1.1913664

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Using numerical techniques presented in a previous paper [J. C. Novarini and J. W. Caruthers, J. Acoust. Soc. Am.53, 876–884 (1973)], the statistical character of five acoustic fields in the range 0.75–3.00 kHz scattered from an ensemble of model sea surfaces for a wind speed of 4 m sec−1is presented. Total intensity, degree of coherence, and phase and amplitude fluctuations are studied in the range of transition from a smooth to a rough surface.

ISSN:0001-4966    

DOI:10.1121/1.1913665

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP