Physics-Based Compact Modeling of an Ultrasonic Modulation MEMS Speaker Concept

Conventional microelectromechanical systems (MEMS) speakers suffer from low sound pressure in low frequency bands due to their limited range of motion in the low <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{m}$</tex>-scale. By adding pressure strokes in the ultrasonic (US) range and applying modulation and demodulation techniques high sound pressure in the low frequency bands is achieved. A physics-based lumped element model (LEM) of such an ultrasonic modulation (UM) speaker concept with dimensions getting close to the wavelength is presented. The model is successfully validated against finite element method (FEM) simulations of the respective components. Applying the LEM, the computational costs can be drastically decreased, which lays the foundation for proper system-level design. Exemplary results of design studies obtained by the LEM, such as the specific <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1 / f$</tex>-characteristic of an UM speaker simulated with a harmonic balance analysis, are presented.