Capacitive transducers with curved electrodes

The design, performance, and potential applications are described for capacitive transducers with curved electrodes. A curved electrode governs the deflection of a compliant electrode under applied stress. A dielectric film on one electrode provides a variable region of fixed electrode spacing. The sensitivity and linear dynamic range of the transducers are higher and wider than devices with parallel electrodes. An electrical advantage is obtained from the permittivity of the dielectric film and a mechanical advantage from its thinness. Transducers have been constructed with silicon diaphragms that bend and polymer membranes that stretch in response to uniform pressure. The silicon sensors measured dynamic pressure changes over a linear range of 125 dB. An 885% change in capacitance was obtained for a sensor with a thin silicon diaphragm. Sensors with polycarbonate membranes demonstrated the ability of a low-cost transducer to measure pressure, fluid flow, displacement, and tilt. An active capacitive bridge circuit was developed to linearly measure capacitance changes up to 1000% and to control electrostatic actuators by force-balanced feedback. Methods and materials to construct microscale transducers are discussed along with the performance limitations of electrostatic actuation.