A dual-axis pointing mirror with moving-magnet actuation

Abstract

A large-aperture and large-angle MEMS-based 2D pointing mirror is presented. The device is electromagnetically actuated by a moving-magnet/stationary-coil pair and potentially suited for high power laser beam shaping and beam pointing applications, such as LIDAR. The 4×4 mm2 mirror, the radially symmetric compliant membrane, and the off-the-shelf permanent magnet are manually assembled, with the planar coil kept at a well-defined vertical distance from the permanent magnet by simple alignment pins. The mirror and the compliant membrane structures are separately microfabricated on bulk silicon and SOI wafers, respectively. The hybrid integration of microfabricated and off-the-shelf components enable low-risk/high-yield fabrication, while limiting the throughput. The device features minimum inter-axis cross coupling and good linearity and is highly immune to alignment and assembly imperfections, thanks to the robust actuation principle. All the components including the bi-axial electromagnetic actuator provide a device footprint as small as the top mirror, allowing the design to be used in compact and high-fill-factor mirror arrays. With a drive coil of 400 mA and 5.12 W drive power, the total uniaxial dc rotation exceeds ±16° (optical) for both axes with good decoupling. At maximum measured angle (biaxial 10° (mechanical)), a position stability better than 0.05° over 7 h, and a position repeatability of 0.04° over 5000 switching cycles is reported. Thermally, the simulated mirror temperature increases to 64 K above the heat sink temperature with a thermal in-flux of 1 kW m−2, under absolute vacuum.

Electromagnetically actuated biaxial scanning micromirror fabricated with silicon on glass wafer

“…However, electromagnetic actuators require the integration of either metallic coil or magnetic material with the micromirror structure and assembly to create magnetic force. The electromagnetically actuated scanning micromirrors with moving-magnet type driving scheme have been reported for the application to the LIDAR system (Aoyagi et al 2011;Ataman et al 2013). However, the moving magnet mounted on the micromirror structure increases moment of inertia of the mirror and requires large size package for external coil, in addition to difficulty in assembling magnets on the micromirror.…”

Optimization of the force and power consumption of a microfabricated magnetic actuator

“…By using permanent magnets, high energy densities can be achieved. Such devices have been demonstrated for a wide range of applications, including labon-a-chip valves arrays [2], micromirrors arrays [3] and tactile displays [4,5]. While much research has focused on single microdevices or small arrays of magnetic actuators, electromagnetic (EM) actuation scales well to very large arrays of microdevices by using arrays of microfabricated planar coils driving arrays of small permanent magnets.…”

“…The method can be applied to a wide range of electromagnetic actuators involving permanent magnets and planar coils, whenever a reduction of the power consumption is required, e.g. valves arrays [2] and micromirrors arrays [3].…”

2D MEMS scanner integrating a position feedback

“…This can be achieved optically [1] with a PSD or a 4 quadrant diode, electrostatically [2] or with an integrated piezoresistive sensor [3]. In previous work [4], we had reported the fabrication and testing of a biaxial electromagnetically actuated moving-magnet scanning mirror achieving a tilt of 8.6° with a squared shape mirror of 4mm width. This system worked in open loop mode and was composed of a mirror surface coated on both sides, a silicon compliant membrane acting as the MEMS deformable part, a magnet glued to the center of the membrane and a ceramic based coil for the actuation ( Figure 1).…”