Nearfield calibration array utilizing piezoelectric polymer

Abstract

The Trott nearfield calibration array (NFCA) concept allows the farfield acoustic properties of underwater transducers to be determined in measurement facilities that are too small for direct farfield measurements. As a projector, the NFCA produces a nearly uniform plane wave throughout a large adjacent volume. The farfield sensitivity of a receiver can then be measured directly by placing it in the “plane‐wave” volume. As a receiver, the NFCA measures only a single plane‐wave component of the sound radiated by a projector located in the “plane‐wave” volume. Existing NFCA's are primarily used as receivers and utilize small piezoceramic hydrophone elements arranged in planar or cylindrical configurations. The spacing between elements limits the upper frequency of operation of the NFCA; e.g., a 1‐in. spacing allows operation up to about 50 kHz. This paper describes the design and construction of a planar NFCA utilizing a mosaic of nonelectroded sheets of the piezoelectric polymer PVDF attached to full area electrodes that subdivide the array into independently controlled annular elements. The PVDF NFCA was tested successfully as both a projector and a receiver by calibration of a high‐frequency transducer. Although the available electronics limited the upper frequency of the test to 150 kHz, the PVDF NFCA should be useable, with suitable electronics, up to megahertz frequencies. [Work partially supported by ONR Code 220.]