ELECTROSTATICALLY EXCITED DIAPHRAGM DRIVEN AS A LOUDSPEAKER

This paper is focused on a hermetically sealed cavity which can be ele ctrostatically excited and driven as a loudspeaker. The actuation prin ciple is based on a diaphragm that is rolling against the cavity botto m to reach both large displacements and strong electrostatic forces. T he loudspeaker is primarly intended for airborne ultrasound. Test spea kers have been manufactured by micromachining in silicon using anisotr opic and isotropic etching, and wafer bonding. Experiment shows an aco ustic output of 112 dB in sound pressure level at the resonance freque ncy of 127 kHz, measured at a distance of 10 mm with 50 V peak-to-peak in applied driving voltage. An empirical Q-value of 7 is found. Measu rements indicate that the resonance frequency of the loudspeaker can b e tuned with an applied biasing voltage.