New Displacement-Sensing Techniques for Magnetic Bearings

We report three new displacement-sensing techniques for magnetic bearings. An outstanding feature is that a carrier wave or demodulation is not needed, while performances comparable to that of existing techniques are obtained. The first is based on eddy-current energy loss, and has very simple sensor electronics. The second is capacitance type. It works by cyclic charge and discharge of a capacitor, and allows for direct fabrication on printed circuit board. The third is inductance type. It permits sensing across a 0.5-mm thickness wall of non-magnetic stainless-steel material, while the bandwidth is a few kHz.