A multilayer planar inductor based proximity sensor operating at 4.2Â K

- An eddy current proximity sensor, comprising of a multilayer planar inductor as sensing element and a cold electronics based oscillator operating down to 4.2 K.
- The cold electronics based oscillator will frequency modulate (FM) the displacement data onto a carrier signal and integrated into a single PCB along with the sensing element.
- The sensor full scale sensing range is 0-5 mm, peak sensitivity of 14.77 μm/kHz with an accuracy of ±1.84 μm and a resolution of 40 μm in 0.85 mm-1.5 mm range.
- Performance analysis of the cold electronics based oscillator circuit is also discussed.
- Stability, temperature coefficient and every important parameter for the sensor is analysed.

The design, development and testing of a multilayer planar inductor based eddy current proximity/displacement transducer is presented. Proximity/displacement of a metal surface/target in the range of 0-5 mm could be measured. The use of a cold electronics based LC oscillator operating at 4.2 K using thermal cycled stable components is reported. The frequency modulated (FM) oscillator output is a function of displacement. Calibration of the developed sensor at cryogenic temperatures was performed to ascertain the sensitivity and repeatability. Impedance analysis of the planar multilayer inductor is presented and its Q-factor is determined. Experimental results of the noise characteristics of the oscillator at various temperatures are also discussed. The developed sensor has good thermal stability, sensitivity and repeatability at the cryogenic operating temperatures.