Westinghouse Electric Corporation

John DEKlerk

Herbert Warren Cooper

Bevil J Shaw

John Acevedo

The disclosure relates to an acoustic surface wave device and method for long signal delays and bulk wave discrimination through the folding of a surface wave propagation path. A surface wave device is formed on the surface of an acoustic substrate and a surface wave, acoustic discontinuity is formed in the propagation path of surface waves propagated along the surface of the substrate. The acoustic discontinuity defines a reflecting surface for acoustic surface waves thereby deflecting incident surface waves along a reflecting path differing from the propagation path. Substantially all of the bulk waves propagated along the propagation path continue along this path and can be absorbed or otherwise dissipated. As a result, a substantially pure surface wave mode signal can be detected along the reflecting path. The surface waves may be reflected in this manner, i.e., by folding the path of the surface waves, a number of times as required to obtain a desired delay.

Surface acoustic wave delay line with bulk wave discrimination

A specimen or in-service structural member in which strain is to be measured is fabricated as a unit which generates a signal in response to strain occurring in a given region of its surface. A film of piezoelectric material is deposited upon the surface in a manner providing a strong molecular bond between the specimen or member and the piezoelectric film. The film material is chosen from the class having a 6 mm type crystal lattice structure and is formed as a crystalline deposit with the c-axis perpendicular to the surface of the specimen or member. An arrangement of electrodes is provided for direct electrical coupling between spatially separated portions of the piezoelectric film. The electrodes form an output coupling for an electrical signal generated by the piezoelectrically active properties of the piezoelectric film in response to strain mechanically coupled from the substrate surface to the piezoelectric film through the molecular bond. In constructions in which there is a possibility of the electrode arrangement becoming short-circuited through minute vacancies present as imperfections in the piezoelectric film, an ultrathin film of insulating material is deposited adjacent one or the other sides of the piezoelectric film.

Strain gauge apparatus

A thin film piezoelectric transducer generates bulk mode ultrasonic elastic waves which propagate into a transmission medium, such as silicon. The wave is reflected back towards the first transducer by a reflecting surface. A second transducer is located adjacent to the first transducer and receives the acoustic wave from the reflected surface. The path length of the ultrasonic wave from the first transducer to the second transducer is long enough to enable the bulk wave to be in the Fraunhofer field. An acoustic absorbing material, such as indium, may be placed on the reflecting surface and on the surface containing the two transducers in selective areas to reduce undesired reflections. The structure is suitable for use in the microwave region wherein the insertion loss may be relatively constant over a given frequency band.

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Pittsburgh, PA, United States of America

John DEKlerk