Speaker
Description
MEMS loudspeakers are promising for next generation in ear headphones and hearing aids due to their compact size, low power consumption, and CMOS compatibility. However, their miniaturized structure requires large membrane displacements to achieve sufficient sound pressure levels. In piezoelectric actuators, these displacements often require higher input voltages, and both factors increase nonlinear distortion. While conventional loudspeakers mitigate distortion through structural design, active control offers a more adaptable solution by using a sensor to monitor membrane motion and adjusting the drive signal in a closed loop. In this work, we present a simulation of an active control scheme that integrates a collocated sensor and actuator within a MEMS loudspeaker.The loudspeaker considered is a clamped guided cantilever based structure, divided around the inflection point. One side is covered by a piezoelectric actuator and the other side is used as a collocated sensor. The voltage generated by the sensor provides a measure of the displacement, is amplified by a feedback gain Kp, and subtracted from the input voltage. The input signal is amplified with a feedforward gain Kff. The loudspeaker operates in an ear occluded coupler represented by an equivalent electrical circuit. The governing time domain equations are written in matrix form and discretized using a bilinear scheme, including linear parameters and nonlinear effects such as geometric nonlinearities, ferroelectric transduction, and varying capacitance.Simulations show that combining feedforward and feedback reduces total harmonic distortion by about 50 percent in the quasi static range, while preserving the frequency response.