摘要:

Certain changes in pulse shape do not affect the resolution capability of a sonar system. These changes can be expressed as mathematical transformations that leave invariant important properties of the wide‐band ambiguity function. Such transformations provide a large number of signal and filter functions, all of which satisfy a given range‐Doppler resolution requirement. The sonar designer can then choose the signal and filter that best satisfy other system constraints (e.g., ease of signal generation and filter synthesis, clutter suppression capability, and peak power).

ISSN:0001-4966    

DOI:10.1121/1.1913438

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The statistical properties of estimators for plane‐wave parameters are discussed. A thick large‐aperture array is assumed to be detecting a signal emanating from an unknown continuous wave source. The signal is assumed to be a plane wave embedded in a spatially incoherent Gaussian noise field. Maximum‐likelihood estimators of velocities and directions are derived and their root‐mean‐square errors are obtained, for single and multiple arrivals for linear arrays and square arrays with a large number of sensors. The rms errors of the propagation parameter estimators are proportional toK−1for a square‐lattice array ofKsensors and toK−3/2for a linear array ofKsensors. The rms error of the waveform estimator, however, is proportional toK−1/2in each case. Thus, for the propagation parameters, the figure of merit for rms signal‐to‐noise gain of the array isKfor a square array ofKsensors andK3/2for a linear array ofKsensors.

ISSN:0001-4966    

DOI:10.1121/1.1913439

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A system for measuring sound intensity is described which can also be used for measuring very low sound levels.

ISSN:0001-4966    

DOI:10.1121/1.1913440

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

An experiment was performed to determine whether high scores typically obtained with the Modified Rhyme Test (MRT) in the evaluation of speech‐communication systems can be attributed to the closed‐response format of the test. The 300‐word MRT vocabulary was recorded by an adult male speaker and administered to two groups of listeners at two signal‐to‐noise ratios. The first group came for five test sessions during each of which they heard the six MRT lists at each test condition and utilized an open‐response (write‐down) format. The second group came for one test session and heard the six MRT lists at each test condition; they utilized the regular closed‐response (multiple‐choice) format. Test scores obtained from the listeners utilizing the open‐response format and having considerable exposure to the test vocabulary were not appreciably different from test scores obtained from the listeners utilizing the regular closed‐response format having no previous exposure to the test vocabulary. Additional tests administered to two other groups of listeners showed that MRT scores do not rise as listening experience is acquired.

ISSN:0001-4966    

DOI:10.1121/1.1913441

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A microwave acoustic exciter is described which utilizes an efficient thin‐film piezoelectric transducer in a re‐entrant cavity configuration. Measurements of conversion loss by input impedance and pulse‐echo methods yield a 2.5‐dB one‐way conversion loss at 1.58 GHz. The observed conversion‐loss bandwidth is 20 MHz and is limited by the cavity resonance.

ISSN:0001-4966    

DOI:10.1121/1.1913442

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Interesting reflected and re‐radiated ultrasonic waves from a plane liquid‐solid interface have been observed using a cylindrical transducer and a pulsed schlieren system. The reflected cylindrical waves show variations in amplitudes as a function of angle. Plane waves, apparently re‐radiated into the liquid by surface waves propagating along the interface, have also been observed by an optical technique.

ISSN:0001-4966    

DOI:10.1121/1.1913443

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Calculated reflection parameters for a quasi‐longitudinal wave incident upon a stress‐free boundary are presented for zinc, magnesium, and cadmium.

ISSN:0001-4966    

DOI:10.1121/1.1913445

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A method for the analysis of the free waves and natural frequencies of continuous curved beams is presented based upon the use of the dynamic three‐moment equation.

ISSN:0001-4966    

DOI:10.1121/1.1913446

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

This letter describes a method of reducing the noise generated by a fluid stream flowing subsonically over a plate and also presents some substantiating test data. This concept may prove useful for reducing the noise of STOL aircraft employing the externally blown flap or the augmenter wing, which configurations are now under exploratory development.

ISSN:0001-4966    

DOI:10.1121/1.1913447

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

It has been found that various measurements commonly made on piezoelectric transducers are simplified by use of the current probe, a commercially available instrument. Examples are impedance, ultrasonic interferometry, and power.

ISSN:0001-4966    

DOI:10.1121/1.1913448

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP