The basic principle of operation is that a material capable of supporting shear and torsional mechanical waves at ultrasonic frequencies can have those waves trapped or localized by creating specific features or geometries in the material. These trapped energy regions, or "resonant cavities" are set into motion with transducers and act as high quality resonators.

Resonance in the cavity area is initiated by an electrical impulse to the transducer, then the vibration decays or "rings down" like a bell that has been struck. A finger or gloved hand touching the front surface of the resonant cavity dampens the vibration and reduces the region's ring-down time. The reduction in ring-down time (decay rate) is detected with a microcontroller which is multiplexed for multiple switch positions. Since the sensor is actively "pinging" the sensor area every few milliseconds, the sensor has the inherent capability of self-diagnostics and self-adaptation in real-time.
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