How do USound MEMS speakers work?
USound’s technology is based on piezoelectricity. Crystals with these properties are for example aluminium nitride (AlN) or lead zirconate titanate (PZT). These materials expand or shrink in an electric field. In a practical configuration, such an electric field is generated between electrodes, covering a piezoelectric layer. This stack is put on top of a substrate (for example a silicon plate). So, if an electric field is applied across its electrodes, the top layer contracts and bends the whole plate upwards.
The bending movement must be translated into a one-dimensional piston-like movement to drive a loudspeaker membrane. For this, multiple bending cantilevers are attached to a central element via spring structures. Therefore, in a symmetric arrangement, the plate will then only move up and down.
To radiate sound, air must be moved. To move more air, the small MEMS structure is connected to a membrane that expands the movement over a larger surface.
The result is a system working just like a standard electrodynamic speaker, but with the bulky magnet-coil engine replaced by integrated piezo-actuators on a MEMS chip.