LARGE-AREA ULTRASONIC GAP PROFILE MEASUREMENTS USING 2-DIMENSIONAL PVDF BLANKET-ARRAY TRANSDUCERS

A technique is described for utilizing two-dimensional ultrasonic tran sducer arrays to accurately measure the spacing (i.e, the gap profile) between large-area mating surfaces, The acoustic measurement theory f or pulse-echo and pitch-catch gap profile measurements is derived from a generalized KLM model representation of ultrasonic transducers loca ted within the gap between two mating structures. Expressions for the ultrasonically measured gap spacing are derived in terms of the thickn esses and longitudinal acoustic velocities of the constituent layers o f the transducer element(s), adhesive layers(s), and gap medium, Extre mely thin PVDF two dimensional arrays were fabricated and adhered to t he inside of a precision gap profile device for demonstrating the meas urement technique. Two-dimensional gap profile measurements were made to +/- 0.001'' accuracy for a variety of gap profiles in the range of 0 -0.200'' thickness. Gap profile measurements were made with both liq uid and air as the gap medium and the results show potential for measu ring otherwise inaccessible gap profiles between structures.