A new magnetic displacement sensor and linear actuator device

A magnetic device that can be used either as a displacement sensor or as a linear actuator is described and analyzed, the analysis being conducted by making use of Maxwell's equations in integral form together with energy considerations. The magnetic circuit, with coaxial symmetry, includes an n-turn winding and a movable conducting ring, both them placed around the inner cylinder rod of the magnetic circuit; the magnetic field lines are radial at the air-gap between the inner and outer cylinders. It is shown that by monitoring the equivalent self-inductance of the winding at rest any change in the position of the conducting ring can be linearly sensed, the sensitivity of the sensor being inversely proportional to the air-gap size and proportional to the radius of the inner cylinder rod. In addition, it is shown that once a time-varying current is made to flow in the winding, a driving force is exerted on the ring, making it move away from the winding; the actuating force is independent of the ring position and can be controlled by controlling the current. (C) 2000 American Institute of Physics. [S0021-8979(00)71108-X].