Low-frequency vibration sensors based on a cascaded gapped cantilever

This paper reports the development of low-cost high-performance vibration sensors based on a cascaded asymmetric-gapped cantilever for low-frequency sensing. The cascaded structure is implemented to reduce the spring constant for a high sensitivity and simultaneously avoid the undesirable shear bending. A prototype with a proof mass of 40 g and an overall size of 124 mm × 39 mm × 5.1 mm ( l × w × t ) has been successfully constructed. The sensor body was made of aluminum and two lead zirconate titanate sheets were implemented as the sensing element. Based on a coherence method, a noise equivalent acceleration close to the theoretical value has been achieved at 35 Hz (∼3 ng/√Hz). Finally, the prototype has been successfully demonstrated for ballistocardiogaph monitoring for both sitting and lying positions. (paper)