A repulsive magnetic force driven translation micromirror

Abstract

This paper presents a repulsive magnetic force driven micromirror with large displacement and high surface quality which well solves the limitation of the previous design, i.e. large variation in translation starting position and low repeatability, caused by the touching points between the moving film and substrate before and in operation. The new design utilizes a driving mechanism, i.e. permanent magnet ring above and electromagnet underneath the moving film, to lift the moving film from touching the substrate and generate a repulsive magnetic force (instead of attractive force in the previous design) to push the moving film up and away from the substrate for translation. Due to the touching, the previous design has to pre-oscillate for 20-30 min at 1 Hz before usage (after resting for a few hours) to reduce the starting position variation from ~15 µm to 3-4 µm. Even after the pre-oscillation, the repeatability is still low, which is 14.2% because of the touching in operation. In the design presented in this paper, the touching between the moving film and the substrate is completely eliminated before and in operation. As a result, the starting position of the translating mirror is constant each time and the repeatability is <1%. In addition, this design does not need the residual stress gradient to curve up the moving film. The maximum displacement of 144 µm can be achieved when 140 mA current is applied on the electromagnet. As an application, the micromirror is used as the movable mirror in a Michelson interferometer to measure the wavelength of a laser beam. The result shows a measurement accuracy of 2.19% for a 532 nm laser beam.

Development of an Electromagnetic Actuator based Translation Micromirror as a Movable Mirror in a Miniaturized FTIR Spectrometer

“…As shown in Figure 5.4, the packaged compensation system, which includes the assembled repulsive force translation micromirror [153], a 1D rotation micromirror, a reflecting mirror, and the driven circuits, has a size of 7 cm (length) x 3.7 cm (width) x 4 cm (height), in which the rotation and the reflecting mirrors are both 5 mm x 5mm. Since the tilt angle of most translation micromirrors is small, e.g.…”

“…The repulsive force micromirror does not have the touching issue, so the problem existing with the attractive force translation micromirror is avoided [90], such as the variation of the starting position and low repeatability. However, the prototype of the repulsive force micromirror in [153] is not suitable for the tilt compensation system, e.g., the ring shape permanent magnet is far from the mirror plate, so the angle between the incident and reflecting beam is too small and the optical path is affected. Therefore the attractive force translation micromirror is used as M1 in the experiment.…”

Review of MEMS Based Fourier Transform Spectrometers

“…The mirror achieved a high surface quality with 15.6 nm curvature radius and 2 nm surface roughness. A repulsive magnetic force driven out-of-plane micromirror with large displacement and high surface quality was later developed for FTS by Xue et al in 2017 [48]. This design did not need the residual stress gradients to curl up the moving film.…”

A tilt compensation system for translation micromirror

“…The tilt can be caused by multiple reasons, for example, the fabrication process variation leads to discrepancies between actuators; 16 and the manufacturing/ assembly error lead to the uneven magnetic fields applied to micromirror's symmetric part. 6,8 Since those undesired tilt causes are normally constant/unchanged during the translation of the mirror, the tilt is normally about a fixed axis. This article proposes a tilt compensation system to compensate for the translation micromirror's tilt, which is about a fixed axis.…”

“…Benefiting from the microelectromechanical systems (MEMS) fabrication technology, 1 the translation micromirror 2–8 has been used in Michelson interferometer–based 9–13 miniaturized Fourier transform infrared spectrometers (FTIRs). 14–18 However, the undesired tilt existing in the translation affects the quality of the generated interference pattern.…”