Inductive eddy current sensing as a displacement sensing mechanism for large piston/rotation micromirrors

This paper serves to demonstrate inductive eddy current based sensing as a promising piston position and tilt angle sensing mechanism for large vertical displacement micromirrors that exhibit piston scan ranges above 100 μm. The sensor consists of two microfabricated coils packaged under the mirror plate, and supports both amplitude and frequency detection modes. Amplitude detection is achieved by sensing the coupling change between the coils when the mirror plate moves, and a piston sensing range of 1 mm with 306 nm resolution (or 130 μm with 20 nm resolution) could be obtained. Frequency detection is achieved by sensing the inductance change of both coils, and can simultaneously monitor piston position and tilt angle over a 500 μm range.