ELECTROSTATIC EXCITATION AND CAPACITIVE DETECTION OF FLEXURAL PLATE-WAVES

A novel type of interdigital transducer has been developed for the excitation and detection of flexural plate-waves on very thin membranes. The launching transducer employs electrostatic forces for generating A0-mode flexural plate-waves. The receiving transducer detects the plate-waves via capacitive changes. The transducers operate without a piezoelectric substrate or layer. The proposed principle has been theoretically analyzed and experimentally tested. Results from the experiments confirm the theory and verify the principle. Additional improvement of the sensor output is achieved with a novel phase-locked-loop circuitry for electronic feedback. The absence of the piezoelectric layer facilitates the fabrication process of the sensor and allows extremely thin membranes to be developed with increased sensitivity for chemical and biological sensing. The design of moveable interdigital transducers has been demonstrated, with conceivable applications in position sensing, material characterization, and the theoretical investigation of flexural plate-waves.