Diamagnetic Levitation for Passive Tilt Sensors
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0998-J08-16
Diamagnetic Levitation for Passive Tilt Sensors Lihong (Heidi) Jiao, and Martin Winistöerfer School of Engineering, Grand Valley State University, 301 W. Fulton St., Grand Rapids, MI, 49504 ABSTRACT When diamagnetic materials are exposed to an external magnetic field, a weak magnetic field in the opposite direction to the external field is induced and a magnetic force is generated causing diamagnetic materials to be expelled from the external magnetic field. The magnitude of the force increases with increase of the magnitude of diamagnetic susceptibility, χm. In this study, the levitation of graphite in the magnetic field was investigated. To levitate a graphite rod in a magnetic field, the balance is to be established between the diamagnetic force and the gravitational force. The diamagnetic force is proportional to both the magnitude and gradient of the external magnetic field. Four Samarium-Cobalt permanent magnets were selected to provide high-density magnetic field. Different configurations of the permanent magnets were studied and the special locations that can levitate the graphite rod were identified. The graphite rod levitating in the magnetic field can move frictionlessly in the longitudinal direction (z-axis). Such configuration was used to build the tilt sensor where the tilt angle is proportional to the position of the floating graphite rod in z-axis. The tilt sensor consists of a graphite rod, four permanent magnets and an optical sensing system used to measure the position of the graphite rod. To improve the sensitivity of the tilt sensor, the longitudinal magnetic field distribution was studied. This type of tilt sensor distinguishes itself from other technologies in the market through its temperature stability, accuracy and costeffectiveness. INTRODUCTION In applications such as leveling, automotive testing, and tilt monitoring it is necessary to accurately locate the true horizontal level and measure small angles relative to it. Highly accurate tilt sensors are often used to find the true horizontal level. These tilt sensors need to measure small angles in the range of a few arc seconds, be cost-effective, and be independent of temperature. Current tilt sensor technologies include vial sensor, electrolytic sensor, accelerometer and inclinometer. The vial sensor, which is the commonly used tilt sensor, is the cost-effective solution [1]. However, its signal is not only highly dependent on temperature but also on assembly processes. Both electrolytic sensor and accelerometer are temperature dependent. Even though inclinometers exhibit high accuracy and low temperature dependency, the manufacturing cost is high.
To overcome these problems a passive diamagnetic tilt sensor, based on the diamagnetic levitation [2][3], is presented. A passive diamagnetic tilt sensor utilizes diamagnetic levitation to float a graphite rod in a magnetic field generated by permanent magnets. The tilt angle is directly proportional to the longitudinal position of the graphite rod, which can be measured with an
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