John H. Thompson

Acoustic transducer for sending and receiving acoustic communication signals

A uniquely designed acoustic transducer comprising a stack of piezoceramic elements (other piezoelectric materials may be used) mounted upon a tuned, shaped transmit/receive head made of hardened metal alloy. The ceramic stack is preloaded to the head via a stress bolt. Insulator electrodes used in the ceramic stack are selected to minimize compliance in the stack for maximum efficiency. All the material properties, sizes, weights, etc., as well as the overall transducer design are carefully selected to act in combination to match the impedance of the load (i.e. metal structural framework). The diameter of the tip of the tuned, shaped driving head is sized such that when clamped to a metal framework, the base metal of the material just under the tip is compressed to or slightly beyond its yield point. This eliminates the requirement for surface preparation because any coatings will be displaced under the applied pressure and any surface irregularities will be flattened out. The underside of the clamping member used to hold the transducer assembly in place consists of a half wave length reflecting waveguide designed to reflect any absorbed energy back into the load. Thus, the attachment points for both the reflector and the transducer head of the clamping device effectively appear invisible to the driving transducer under load.

Broad beam transducer

A transducer made up of a plurality of piezoceramic tubes arranged in end to end relationship with elastomeric material between tubes. The tubes are poled and driven axially; however, the hoop mode of operation is utilized to obtain a fan-shaped beam extremely narrow in one direction and extremely broad in the direction perpendicular thereto. A suitable backing arrangement is provided for the transducer when mounted on a support body to prevent degradation of the beam pattern.

Sonar test system and method

A single test transducer or a line array of test transducers is placed above the transducers of an array under test and provided with a simulated flow noise signal. The response of all of the transducers under test is derived and stored whereupon the test transducer or line array of test transducers is moved to a subsequent position wherein the process is repeated. After all positions are indexed, the stored signals representing the outputs of all of the transducers of the array under test for all transmissions are combined and processed to derive a transducer array output signal for analysis purposes.

Transducer assembly for self-calibration

An acoustic homing torpedo having an array of transducers wherein each transducer has a head mass, tail mass, and a main active element therebetween. An auxiliary active element is placed on the tail mass so that when given a predetermined signal it will cause the main element to provide a corresponding output signal so as to simulate the reception of an actual acoustic wave. By energizing the main element, the response of the auxiliary element may be examined for testing the transducer and the array in a transmit mode of operation.

Image formation by multiple shading

A novel method for obtaining an improved image from an array of hydrophones is described. The technique involves generating a set of different images. These images are then combined using an appropriate algorithm. The composite image is superior to any one of the original images. The technique achieves good angular resolution with low spurious side lobes. Three examples are given for a 16‐element array using computer simulation. The procedure is applicable to line arrays, planar arrays, and conformal arrays.

High‐Frequency Ultrasonic Sound Probe for Making Near‐Field Acoustic Measurements

This paper briefly describes the construction and test results of an ultrasonic sound probe used for measuring the particle velocity at the face of elements in a hydrophone array. The problems of Fresnel zone interference and field disturbances make near‐field measurements of pressure difficult to interpret. The sound probe described overcomes these difficulties by measuring the particle velocity. This is accomplished by proper mechanical and electrical loading. Comparison of the results is shown by use of velocity probes and pressure probes.