Miniaturized electrostatic receiver with small-sized backing electrode

Abstract

A miniaturized electrostatic receiver design, having a central cylindrical backing electrode of small radius surrounded by a flat annular cavity behind the circular membrane, can lead to both a higher sensitivity and a larger frequency bandwidth compared to the ones achieved with other designs, while bringing a geometrical simplicity which is advantageous from the point of view of microfabrication. An appropriate computational method, relying on a specific 2-D axisymmetrical simulation using an adaptive mesh and accounting for both viscous and thermal boundary layer effects, provides results against which analytical results can be tested. An analytical approach, which leads to solutions based on the eigenmode expansion of the membrane displacement, the acoustic pressure field depending on the radial coordinate in the central fluid gap but being assumed quasi-uniform in the annular cavity, is much faster in terms of running time and appears to be sufficiently accurate to achieve final optimization of this kind of devices.

Optimization of Capacitive Acoustic Resonant Sensor Using Numerical Simulation and Design of Experiment

“…The equation governing the vibration of the thin circular membrane of thickness , radius , and density under constant radial force per unit length ( ) acting on its edge, driven by uniform harmonic incident acoustic pressure over the membrane surface, loaded by the pressure field , also known as reaction pressure at the membrane surface, can be expressed as [ 9 , 10 , 16 , 17 ]: …”

“…The solution of the mean displacement of the circular membrane over the backplate electrode driven by the constant incident pressure due to the sound field can be expressed as follows [ 9 , 10 ]: …”

“…To date, many capacitive acoustic sensors have been developed, and some of them are commercially available. However, its design varies based on the application domains, and the majority of these are targeted for audio applications with nearly uniform sensitivity over a relatively wide range of frequencies in the human hearing range, 20 Hz–20 kHz [ 4 , 5 , 6 , 7 , 8 , 9 , 10 ].…”

“…Recently, a new simplified design concept has been proposed to fabricate a capacitive acoustic transducer, which consists of a central cylindrical rigid backing electrode of small radius surrounded by a flat annular cavity below a vibrating membrane clamped at its periphery separated by an air gap, which provides good sensitivity and a large frequency bandwidth [ 9 , 10 ]. Honzik et al [ 9 ] have reported that this design leads to a higher sensitivity, as well as a larger frequency bandwidth.…”