Large-area ultrasonic gap profile measurements usingtwo-dimensional PVDF “blanket array” transducers

摘要

A technique is described for utilizing two-dimensional ultrasonicntransducer arrays to accurately measure the spacing (i.e., the gapnprofile) between large-area mating surfaces. The acoustic measurementntheory for pulse-echo and pitch-catch gap profile measurements isnderived from a generalized KLM model representation of ultrasonicntransducers located within the gap between two mating structures.nExpressions for the ultrasonically measured gap spacing are derived innterms of the thicknesses and longitudinal acoustic velocities of thenconstituent layers of the transducer element(s), adhesive layers(s), andngap medium. Extremely thin PVDF two-dimensional arrays were fabricatednand adhered to the inside of a precision gap profile device forndemonstrating the measurement technique. Two-dimensional gap profilenmeasurements were made to ±0.001" accuracy for a variety of gapnprofiles in the range of 0-0.200" thickness. Gap profile measurementsnwere made with both liquid and air as the gap medium and the resultsnshow potential for measuring otherwise inaccessible gap profiles betweennstructures