Planar inductive sensor for small displacement

This paper presents a meander type displacement inductive sensor, developed in printed circuit board (PCB) technology. It also describes design, realization and the input inductance measurement of sensor. The displacement in two directions (less than 0.5 mm) can be detected by using two sensor's elements (i.e. two pairs of meander coils). In each pair, one of the coils is fixed, and between its terminals the input inductance was measured, while other coil is short-circuited. If one coil is moved above the other in directions of x- and z-axes, coupling between coils will change, as well as input inductance, which serves as a measure of displacement. In order to achieve better linearity of the sensor, gap is inserted in the middle of each conductive segment of fixed coils. Four sets of inductive sensors were realized: without gap and with three different gaps: 0.25 mm, 0.51 mm and 0.76 mm. In addition, a simple model of the inductive sensor is proposed. Using this model, the input inductance of displacement sensor was calculated and compared with measured values. A good agreement was found.