A diamagnetic levitation based inertial sensor for geophysical application

Abstract Diamagnetism as a fundamental physical phenomenon is commonly existed in many materials, such as water and even human body. Since the Nobel Prize laureate Prof. Geim successfully demonstrated the flying frog in 1997, diamagnetic levitation has attracted significant research interests due to the advantages of simple structure, stable and passive levitation without power consumption. There are several applications based on diamagnetic levitation, including container-less crystal growth, weightless fluid dynamics, low friction bearings, magnet rotors, energy harvesters and also inertial sensors. However, the developed diamagnetic levitation based inertial sensors cannot meet the low-frequency response and high sensitivity requirements of geophysical applications. This paper introduces a prototype of a diamagnetic levitation based inertial sensor which includes the diamagnetic levitation system and the optical displacement transducer. The proof mass is a floating magnet which is lifted by a fixed magnet above and sandwiched by two pyrolytic graphite sheets for stable levitation. A high precision optical displacement transducer has been developed with a noise floor of 2 nm/√Hz@0.5 Hz and 0.1 nm/√Hz@10 Hz at atmosphere and room temperature. The fundamental frequency of the levitation system was measured as 0.65 Hz, giving an acceleration noise floor of 20 ng/√Hz@0.5 Hz (3.4 ng/√Hz@0.5 Hz in theory). Benefitting on the excellent sensitivity and low-frequency responses, earth tremor peaks at 0.2∼0.3 Hz and 2∼3 Hz have been observed using this inertial sensor. The proposed inertial sensor is promising to be used for high-sensitivity vibration monitoring, seismic imaging and other geophysical applications.