Resonant sensor assembly

A triple beam resonator (10) is provided with three beams or tines (12, 14, 16) aligned in parallel alongside each other and joined at a decoupling zone (18) at each end, which is in turn connected to the surrounding material. The central beam (14) is twice the width of the two outer beams (12, 16). The resonating element has a length of 15.5 mm, a thickness of 0.25 mm and beam widths of 2 mm and 1 mm. The distance between the beams is 0.5 mm. Finite element analysis predicts the modal behavior with stress distribution and eigenfrequencies of the resonator (10). Thick-film PZT elements (20, 22) were printed on separate regions at each end of the central beam (14), where maximum stresses exist as the resonator (10) operates in its favored mode of vibration. The PZT element (20) at one end drives the vibrations, while the PZT element (22) at the other end detects them. Positioning the PZT driving and sensing elements (20,22) on the regions of maximum stresses maximizes the degree of mechanical coupling between the active piezoelectric layer and the resonator for generation of both driving forces and sensing signals. Very high quality factors of 3100 and higher have been experienced. Furthermore, the resonator can be manufactures by batch production techniques while maintaining high reliability and reproducibility.