![]() Magnetic actuation can either be used for actuating 1D or 2D MEMS mirrors. The working principle is that a metallic coil is placed on the moving MEMS mirror itself and as the mirror is placed in a magnetic field, the alternating current flowing in the coil generates Lorentz force that tilts the mirror. ![]() Magnetic actuators offer very good linearity of the tilt angle versus the applied signal amplitude, both in static and dynamic operation. For beam positioning and applications which are to be static-actuated or linearized-scanned, quasi-static drives are required and therefore of great interest. Resonant operation is the most energy-efficient. For that reason many highly developed microscanners today utilize a resonant mode of operation, where an eigenmode is activated. Nevertheless, the highly non-linear drive characteristics in some parts of the deflection area can be hindering for controlling the mirror properly. As a rule of thumb, vertical comb drives are utilized here. For the realization of quasi-static components with positive and negative effective direction, two drives with positive and negative polarity are required. In contrast to an electromagnetic drive, the resulting drive force between the drive structures cannot be reversed in polarity. Įlectrostatic actuators offer high power similar to electromagnetic drives. Existing piezoelectric scanners are more efficient using direct drive. ![]() Indirect drives have been implemented for electromagnetic, electrostatic, as well as piezoelectric actuators. This is in contrast to the more common direct drive, where the actuator mechanism moves the mirror directly. In an indirect drive, a small motion in a larger mass is coupled to a large motion in a smaller mass (the mirror) through mechanical amplification at a favorable mode shape. Thermoelectric actuators are not applicable for high-frequency resonant scanners, but the other three principles can be applied to the full spectrum of applications.įor resonant scanners, one often employed configuration is the indirect drive. Specifically, the mechanical solutions required for resonant scanning are very different for those of quasi-static scanning. Because the physical principles differ in their advantages and disadvantages, the driving principle is chosen according to the application. In practice, the relevant principles for driving such a mirror are the electromagnetic, electrostatic, thermoelectric, and piezoelectric effects. The required drive forces for the mirror movement can be provided by various physical principles. For high end display applications the common choice is raster scanning, where a resonant scanner (for the longer display dimension) is paired with quasi-static scanner (for the shorter dimension). This configuration is energy efficient, but requires complicated control electronics. Translational (piston type) microscanners, can attain a mechanical stroke of up to approx. Mechanical deflection angles of micro scanning devices reach up to ☓0°. For these applications, actuation using a Lissajous pattern can accomplish sinusoidal scan motion, or double resonant operation. Many applications requires that a surface is addressed instead of only a single line. With microscanners that are capable of tilting movement, light can be directed over a projection plane. The deflection movement is either resonant or quasi-static. The scan frequencies depend upon the design and mirror size and range between 0.1 and 50 kHz. Larger mirror apertures with side measurements of up to approx. If a single array mirror accomplishes the desired modulation but is operated in parallel with other array mirrors to increase light yield, then the term microscanner array is used.Ĭommon chip dimensions are 4 mm × 5 mm for mirror diameters between 1 and 3 mm. Microscanners are different from spatial light modulators and other micromirror actuators which need a matrix of individually addressable mirrors in order to accomplish the desired modulation at any yield. ![]() Resonant translational mirror in pantograph design with a deflection of ±500 μm ![]()
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