A surface pressure transducer using PVDF film

Abstract

A large area transducer was desired for the measurement of wall pressures beneath turbulent boundary layers. Characteristics desired were small thickness so that it could be applied to a surface without disrupting the flow, and cheapness so that it could be considered expendable and could be applied in mosaic patterns as wave-vector filter elements. A degree of flexibility was also desired for application to curved surfaces. A transducer design using PVDF film was developed toward these ends. The principle problem to be overcome was the sensitivity of the device to vibratory motion of the surface to which it is applied. The particular design includes a sandwich of films on a substrate with a pattern of line supports. The assembly is arranged to suppress outputs due to vibratory bending motion of the substrate while enhancing outputs due to normal stresses (pressure). The preliminary design was 0.020 in. thick and 1 in. square. It had a calculated sensitivity of -220 dB re V/μPa. The actual sensitivity to pressure and vibration was also measured.