"Looking Through Walls" – Actuator Position Measurement Through a Conductive Wall

This paper investigates the design of an Eddy Current Sensor (ECS) for position measurement of a moving conductive target located behind a fixed conductive shielding surface. Such a sensor can e.g. be used in completely sealed actuators with magnetically levitated rotor or mover for high purity applications. A detailed analysis of the sensor is conducted, starting from the conventional ECS and its equivalent circuit model, which is then further extended to an ECS looking through a conductive wall. With the aid of Finite Element Methods (FEM) simulations, a deeper understanding of the sensor operating principle is provided, together with guidelines to select its optimal excitation frequency, based on the properties of the selected materials for the target and the shielding surface. A sensitivity analysis is then conducted and the results are finally verified with measurements on a hardware sensor prototype, showing that the sensor can be used to capture the mover position in an active magnetic bearing control structure.