F. A. Andrews

Catholic University of America

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i-10 index

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Document Type

Co-Authors

Harry A. DeFerrari

University of Miami

C. F. Teacher

Eltron Research

William E. Collins

University of Oklahoma Medical Center

John V. Bouyoucos

Hydroacoustics (United States)

Alan V. Oppenheim

Massachusetts Institute of Technology

John J. Gilheany

Catholic University of America

H. Helms

Technische Universität Braunschweig

John M. Heinz

TU Wien

Charles M. Rader

MIT Lincoln Laboratory

F. K. Harvey

Cooperative Institutions

Catholic University of America

University of America

Massachusetts Institute of Technology

University of California, Santa Barbara

Nokia (United States)

National Institute of Standards and Technology

United States Naval Research Laboratory

National Oceanic and Atmospheric Administration

NSWC Carderock Division

United States Naval Academy

Author Statistics

Papers

Citation

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Research Field

Measurement of the Phase of Vibrational Displacement by a Laser Interferometer

The Journal of the Acoustical Society of America (1969)

M. R. Serbyn F. A. Andrews

A method of measuring the phase of vibrational displacement, utilizing a Michelson interferometer with a laser source, has been developed and applied to the study of underwater-sound transducers. The technique makes possible direct determination of transducer mechanical impedance and electromechanical coupling factor as functions of frequency, and permits point-by-point measurements of phase throughout the vibrating surface. It is a sensitive indicator of the effect of radiation loading and the degree of nonlinearity. Examples of these measurements are presented and discussed.

Radiation impedance

Acoustic impedance

10.1121/1.1973682

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Citations (3)

An Optical Heterodyne System for Measurement and Analysis of Vibration

The Journal of the Acoustical Society of America (1970)

F. J. Eberhardt F. A. Andrews

Calibration and use of an optical heterodyne system for nonsinusoidal vibration measurements is described. A low-power ultrasonic cell produces Raman-Nath diffraction of a 6328Å laser beam to give an 11-MHz frequency shift. The frequency shifted beam is heterodyned in a photomultiplier with the unshifted central light beam, which has been phase modulated by motion of a reflecting surface. The output of the phototube is an rf phase-modulated signal, which is amplified and passed to a limiter-discriminator receiver. The detected signal is integrated and is a linear reproduction of the surface vibration as long as the frequency-amplitude product is within limits. The linearity and a calibration technique have been tested out to a product of 13 kHz×4700 Å. At lower frequencies, higher vibration amplitudes can be measured. The average calibration accuracy is witin 5% of laser homodyne measurements used for comparison. A minimum amplitude measurement of 3.5Å was obtained. Measurement of time delay or spatial cross-correlation functions is domonstrated using two heterodyne detectors.

Heterodyne (poetry)

Discriminator

Direct-conversion receiver

SIGNAL (programming language)

Heterodyne detection

10.1121/1.1973929

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Citations (2)

The Thermal Conductivity of Copper, Aluminum and Tin at Low Temperatures.

F. A. Andrews

Source

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Citations (0)

Current Practice in the Safety Testing of Radiation Sources

RADIOISOTOPES (1971)

F. A. Andrews K.E. Fletcher

10.3769/radioisotopes.20.7_349

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An array optimization technique

L. A. Mole F. A. Andrews

During the past two decades considerable emphasis has been expended on improving acoustic array performance, as is evidenced by the wide variety of theoretical techniques and algorithms which have been proposed for this purpose. In contrast to these techniques, this paper proposes a procedure for improving performance by selective sensor exclusion. The analysis is predicated on the fact that the signal to noise ratio varies from sensor to sensor. The analytical development demonstrates that improvement in signal to noise ratio can be realized when the choice is made to use "n-1" rather than "n" sensors from an "n" sensor array. The decision criteria are formulated by evaluating separately the influence on array performance of variations of the signal's amplitude and phase and the noise's amplitude and phase.

Emphasis (telecommunications)

SIGNAL (programming language)

Sensor array

10.1109/icassp.1979.1170726

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Citations (0)

Two 50% probabilities

The Journal of the Acoustical Society of America (1975)

F. A. Andrews

The concept, detection probability, is used in two different ways in assessing sonar performance. In both cases, the value 50% appears frequently. The first use occurs in the detection process itself, where the signal−to−noise power required for a detection probability of 50% is usually called ’’recognition differential’’ and sometimes ’’detection threshold.’’ The second use occurs in the prediction of the sonar range under conditions of uncertainty. In this latter case, the range at which one−half the members of an ensemble of targets and environmental conditions will be detected is often called ’’50% probability detection range.’’ The relation between the two probabilities will not be found in standard text books on sonar systems, and is therefore submitted here. Subject Classification: 60.10.

Statistical power

Detection theory

SIGNAL (programming language)

10.1121/1.380433

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Citations (6)

Vibrational Displacement and Mode-Shape Measurement by a Laser Interferometer

The Journal of the Acoustical Society of America (1967)

Harry A. DeFerrari R. A. Darby F. A. Andrews

Four experimental methods are described in a tutorial way for use with a laser interferometer in measuring vibrational displacements and mode shapes of a transducer face. The relative merits and experimental difficulties of the methods are discussed. Quantitative data to show the type of experimental agreement that one might expect between the various methods and two illustrative mode shape measurements are given. In general, by proper choice of one or more of the methods, displacement measurements of magnitude 0.1–6000 Å at sonic and ultrasonic frequencies can be made at a point 0.1 mm in diameter. Mode shapes are determined simply by moving the laser beam a measured distance between points. Displacement data presented show a random error for all methods of 5% in the range 0.5–80 Å and less than 5% above 80 Å.

Mode (computer interface)

10.1121/1.1910707

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Citations (87)

Measurements of radiation impedance

The Journal of the Acoustical Society of America (1975)

John J. Gilheany Leonard McCumber F. A. Andrews

A method is described for measuring the free−field radiation impedance of a single−degree−of−freedom underwater transducer. The displacement amplitude and phase of the vibrating surface in air and in water are measured with a laser interferometer and with an accelerometer. From these values and the input current, the radiation impedance may be computed. Measurements of the radiation resistance and reactance of a J9 transducer at 0.5−kHz intervals from 5.0 and 10.0 kHz are reported. The radiation resistance is also calculated from reciprocity calibrations and measurements of the directivity patterns at 5.0, 7.5, and 10.0 kHz. Excellent agreement is observed between the two methods. Subject Classification: 30.50.

Radiation impedance

Directivity

Reciprocity

Reactance

10.1121/1.380398

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Citations (17)

Measurement of the Phase of Vibrational Displacement by a Laser Interferometer

The Journal of the Acoustical Society of America (1969)

M. R. Serbyn F. A. Andrews

A method of measuring the phase of vibrational displacement, utilizing a Michelson interferometer with a laser source, is described. Results of several applications are presented and discussed.

10.1121/1.1911658

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Citations (7)

Predicting the Detectibility of Complex Signals

The Journal of the Acoustical Society of America (1973)

W.J. Tanski F. A. Andrews

A series of investigations have been conducted to determine to what extent one may predict the aural detectibility of a complex signal in a background of masking noise. Observers were tested binaurally using the two-alternative forced-choice procedure to obtain psychometric functions for simple signals. Modeling the auditory system as an energy detector preceded by a set of bandpass filters, and knowing the statistics of the masking noise and signal plus noise distributions, one may determine the difference distribution statistic upon which the auditory system bases its decisions. The psychometric functions allow one to determine the inefficiency factor for the auditory system and, combining this knowledge with the difference distribution statistics, it is possible to develop a procedure for predicting the detectibility of various complex signals. The results of tests with signals consisting of various combinations of tones and noise will be compared with predictions. Limitations will be discussed.

Statistic

SIGNAL (programming language)

Psychometric function

10.1121/1.1982268

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