Polymeric ultrasonic probe Free

A small piezoelectric polymer hydrophone has been made and tested. It can be used over a broad range of frequencies to probe the temporal and spatial variations of the sound field produced by transducers such as those used in medical ultrasonics. The hydrophone is bilaminar. Each layer consists of a poled central area having a 2‐mm diameter defined by evaporated aluminum electrodes on each side of a 25‐μm‐thick sheet of polyvinylidene fluoride about 7 cm in diameter. The combined sheets are held taut in a metal hoop. Well‐separated leads of evaporated aluminum to the outside of the hoop were applied after poling so that the polymer under the leads is inert. The response does not vary by more than a few decibels from 0.5 to 10 MHz. At about 1 MHz, the change in the received signal when the hydrophone is inserted between a source and receiver is less than 0.2 dB. The broadband response of the hydrophone makes it useful for determining the output pattern of diagnostic transducers which typically use pulses. Its transparency to ultrasound minimizes formation of standing waves between it and therapeutic transducers which are typically continuous wave. [Work has been sponsored by the Bureau of Radiological Health.]