Abstract: An omnidirectional ultrasonic microprobe hydrophone is disclosed. Applicans include underwater mine detection, explosive shock testing, high wave number measurements, medical imaging, and therapeutic systems. The apparatus includes at least two lead zirconate titanate (PZT) pressure sensing elements having a plurality of columnar voids formed therein. The pressure sensing elements are deposited on a metallic or nonmetallic substrate which provides mechanical support for the microprobe hydrophone. Electrical connection to the pressure sensing elements is made by deposition of conductors and insulators on the substrate material. Wire bonds are used to attach wire leads for connection to a supporting structure containing a preamplifier. Line arrays and planar arrays of microprobe hydrophone elements are also disclosed.

Abstract: Apparatus for absorbing acoustic energy directed toward a wall. The appars includes a piezoelectric layer intermediate the wall and the source of the acoustic energy. Circuitry attached to the output of the transducer compensates blocked and motional capacitances of the transducer so that the output signal generates real current for dissipation in a resistor thereby to minimize any echo reflected from the piezoelectric layer.

Abstract: An acoustically transparent voided, polyvinylidene fluoride (PVDF) hydrope made of material whose impedance matches the characteristic acoustic impedance (.rho.c) of sea water, having drastically reduced diffraction and resonance effects. The frequency response is thus flat at frequencies less than one-half elastic wavelength in the PVDF material. An array of such hydrophones in front of a projector saves space without affecting projector performance.

Abstract: A broadband angle-beam transducer system for producing and/or receiving Reigh waves on the surface of a metal medium comprising a thickness mode piezoelectric polymer transducer element embedded within and impedance matched to a plastic wedge. The transducer element is oriented at an angle determined to be the critical angle for Rayleigh waves in the metal structure to be tested. As a transmitter, the transducer element generates discrete dilatational wave pulses, one of which propagates within the plastic wedge to the plastic face in contact with the metal structure. At this face some of the wave energy is reflected as dilatational and shear waves within the wedge and the remainder of the wave energy passes through a coupling medium into the metal structure producing a Rayleigh wave traveling along the surface of the structure.

Abstract: Apparatus and method for nondestructive detection of loose parts or faulty onds in sound transducers by measuring erratic second-order nonlinear difference-frequency responses of the test transducer to a pulsed high level dual-frequency sound field produced by a high power projector. Such field may be generated by combining a high frequency carrier signal at frequency f.sub.o with a low frequency tone burst signal at frequency f/2 in a double balanced modulator so as to produce the dual-frequency pulse at f.sub.o +f/2 and f.sub.o -f/2. The test transducer converts the dual-frequency pulse into a plurality of linear and nonlinear frequency components including the difference-frequency f.