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In this letter, we present an electromagnetically actuated microspeaker with microelectromechanical systems (MEMS) technology to reduce form factor, cost, and power consumption in hearing aid applications. The microspeaker has multilayer copper coils, a NiFe soft magnet on a polyimide membrane, and a NdFeB permanent magnet on the perimeter. The coil impedance is measured at 1.5 Omega and shows a very flat response across the audio frequency range. The device operates at a very low power, the lowest in MEMS speakers, comparable to that of the macro- size counterparts. A single-turn microspeaker with a diameter of 2.5 mm consumes 11.6 and 0.13 mW to generate a sound pressure level of 129 and 106 dB at 1 kHz, respectively. The measurement uncertainty is less than 10%, and the reproducibility is within 36% among the tested devices.
Date of Publication: Aug. 2008