Generalized Lamb-wave multisensor

Integrated-circuit fabrication techniques were used to make a versatile silicon-based sensor that uses elastic wave propagation in a plate that is thin compared with the wavelength. In-plane tension raises the velocity of the lowest antisymmetric flexural wave (474 m/s) above that predicted for a pure Lamb wave (422 m/s). Because of the low velocity, when in contact with a fluid the device excites an evanescent disturbance that extends just tens of micrometers from the membrane. The device is quite sensitive to loading: contact with a 6-μl droplet of water shifts the oscillation frequency downward 36%, in excellent agreement with theory. The device could operate as a microphone, biosensor, chemical vapor or gas detector, scale, manometer, densitometer, viscometer, radiometer, or thermometer. It is concluded that the sensor offers unique means for separating out the influences of multiple measurands