Curved PVDF airborne transducer

摘要

In the application of airborne ultrasonic ranging measurement, anpartially cylindrical (curved) PVDF transducer can effectively couplenultrasound into the air and generate strong sound pressure. Because ofnits geometrical features, the ultrasound beam angles of a curved PVDFntransducer can be unsymmetrical (i.e., broad horizontally and narrownvertically). This feature is desired in some applications. In this work,na curved PVDF air transducer is investigated both theoretically andnexperimentally. Two resonances were observed in this transducer. Theynare length extensional mode and flexural bending mode. Surface vibrationnprofiles of these two modes were measured by a laser vibrometer. It wasnfound from the experiment that the surface vibration was not uniformnalong the curvature direction for both vibration modes. Theoreticalncalculations based on a model developed in this work confirmed thenexperimental results. Two displacement peaks were found in thenpiezoelectric active direction of PVDF film for the length extensionalnmode; three peaks were found for the flexural bending mode. The observednpeak positions were in good agreement with the calculation results.nTransient surface displacement measurements revealed that vibrationnpeaks were in phase for the length extensional mode and out of phase fornthe flexural bending mode. Therefore, the length extensional mode canngenerate a stronger ultrasound wave than the flexural bending mode. Thenresonance frequencies and vibration amplitudes of the two modes stronglyndepend on the structure parameters as well as the material properties.nFor the transducer design, the theoretical model developed in this workncan be used to optimize the ultrasound performance