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A compliant capacitive sensor for acoustics
About
Sensors that rely on changes in capacitance are used in a very large number of important electronic products and systems. When detecting small motion, flow, or sound pressure, the performance of the sensor is normally improved when the effective stiffness between the moving and fixed electrodes is reduced. In sensitive microphones, the use of highly compliant moving electrodes having mass and stiffness as small as possible has not been achievable due to the adverse effects of large bias voltages such as pull-in instability. The compliant acoustic capacitive microphone is a novel approach for sensing sound that provides an electrode design/configuration that minimizes the effects of electrostatic stiffness on the microphone performance and which is stable under all operating conditions. This configuration enables incorporation of highly compliant and thin electrode materials that present the least possible resistance to motion, and are particularly useful for sensing sound. Measured results show that a large bias voltage of 400 volts can be applied without influencing the electrode motion. The electrical sensitivity to sound is approximately 0.5 volts/pascal, two orders of magnitude greater than typical acoustic sensors. R. N. Miles. A compliant capacitive sensor for acoustics: Avoiding electrostatic forces at high bias voltages. IEEE Sensors Journal, 2018 RB559
Key Benefits
(1) Enables the design of moving electrodes having altogether negligible mechanical stiffness in their primary direction of motion. (2) Bias voltage applied to the moving electrode can be set to a high value (e.g. 400 volts) which improves the overall electrical sensitivity (~0.5 volts/pascal). (3) Assurance of stability for the entire range of possible motions and bias voltages. (4) Can be miniaturized for manufacturability.
Applications
Acoustic sensors