Magnetically levitated vibration sensors possess wide frequency response ranges and high sensitivity. Compared with springs and cantilevers, the levitated magnet suffers no mechanical abrasion, allowing minimized mechanical fatigue after prolonged exposure to vibration. However, magnetic levitated sensors are mostly based on fully rigid components, which are difficult to match the soft and curvilinear surface of the biological tissues and machines. Here, an innovative vibration sensor based on magnetic levitation has been developed. The proposed sensor contains two parallel magnetic membranes, one of which is levitated by magnetic force and connected to a specially designed sensor package. The surfaces of the membranes are modified with micropyramid arrays to enhance the magnetism and integrated with flexible coil arrays to maximize the changes in magnetic flux during vibration. The sensor exhibits a wide frequency response ranging from 1 Hz to 20 kHz and high sensitivity of 0.82 mV/μm at an operating frequency of 120 Hz. Various applications have been demonstrated through bone-conducted speech acquisition, sound recording, human motion detection, and machine condition evaluation. The sensor is one of the first flexible vibration sensors based on magnetic levitation. Its innovative levitated sensing structures may inspire development of novel flexible sensors with soft mechanical moving structures for force and displacement sensing in healthcare and industrial monitoring.
Keywords: electromagnetic vibration sensor; flexible device; magnetic levitation; magnetism enhancement; microstructure.