New Sensor Concepts Using Vibrating Cantilevers

Two new, sensor concepts using small, piezoelectrically driven, vibrating cantilever blades are described. A magnetic-field sensor is realised by depositing a multiturn planar coil of aluminum on the blade. When the blade is driven at a cantilever resonance (1–3 kHz) in the presence of a magnetic field, an ac emf is induced in the coil proportional to the field strength at the site of the coil, Operation is exactly analogous to that of an ac generator. In a gas-sensitive device, an air gap is established by placing the blade of the cantilever a few millimeters from a multilayer ceramic piezoelectric actuator. When the actuator is driven at the resonance frequency of the blade, the vibration induced in the blade by means of the gas coupling is “read out” with a piezoelectric element attached to the base of the blade. The pressure or average atomic mass of the gas can be sensed by monitoring the amplitude of the blade.