Fundamental Characteristics of Differential Transformer Type Displacement Sensor Using a YBCO Superconductor

A displacement sensor was constructed using a YBCO superconductor. The sensor consisted of an excitation coil, a differential coil, and a superconducting YBCO rod. The inductance of the differential coil decreased as a result of perfect diamagnetism (the Meissner effect) when the YBCO rod entered the coil. The YBCO rod could be shifted by as much as ±12 mm in the center of the differential coil, along the axis of the rod, by moving the holder attached to the rod. The relationship between the output voltage of the differential coil and the displacement of the rod was measured using a lock-in amplifier. Experimental results indicate that the displacement sensor characteristics, including sensitivity, linearity, stability, frequency dependence, and absence of hysteresis, are satisfactory. Together with the above results, the electrical properties of the superconducting materials were also examined and compared with those of ferrite and soft iron.