A Micromirror With Large Static Rotation and Vertical Actuation

A micromirror with large rotation angle and vertical displacement is proposed and developed. The proposed micromirror is actuated by newly developed prestress comb drive actuators, which exhibit no pull-in, no hysteresis, and large vertical displacement range characteristics. The micromirror was fabricated using commercially available PolyMUMPs. Experimental results indicated that the maximum rotation angle and vertical displacement of the device are 26 and 45 mum, respectively     

Electrostatic MEMS variable optical attenuator with rotating folded micromirror

The design and fabrication of an electrostatic MEMS variable optical attenuator (VOA) is described. The VOA is a reflection type with a folded micromirror actuated by a comb-drive actuator. The VOA is fabricated by a simple single-mask process. One photolithography and subsequent deep silicon reactive ion etching define all the microstructures of the VOA. The folded micromirror structure can reduce the overall size of the device by enabling the parallel alignment of an input fiber and an output fiber. Lensed fibers are used to maximize the coupling efficiency and the ease of assembly. The electrooptic characteristics and dynamic characteristics of fabricated VOA are measured. The initial insertion loss is 0.5 dB at 1550 nm and the maximum attenuation is 45 dB, respectively. The polarization dependent loss is measured to be 0.2 dB at 20-dB attenuation. The response time for maximum attenuation is less than 5 ms.     

Superresolution Digital Image Enhancement by Subpixel Image Translation With a Scanning Micromirror

This paper reports on a superresolution digital image enhancement technique using subpixel image translation with a scanning micromirror. We demonstrate that the spatial resolution of digital photomicrography, employing typical black-and-white pixelated image sensors, can be improved by acquiring multiple images with predetermined subpixel shifts and combining them with a superresolution image reconstruction algorithm. A two-axis gimbaled micromirror fabricated with a bulk-micromachining process is used to control the translational image displacements with subpixel accuracy     

Electromagnetic 2/spl times/2 MEMS optical switch

This paper presents the design, fabrication, and measurement results of a 2/spl times/2 microelectromechanical systems optical switch. The switch comprises an electromagnet and lensed fibers assembled with a micromachined movable vertical micromirror. The optical switch utilizes the out-of-plane motion of the vertical micromirror actuated by electromagnetic force compared to the comb-driven linear actuation achieved by the electrostatic force. At a wavelength of 1550 nm, the insertion loss of 0.2-0.8 dB and the polarization-dependent loss of 0.02-0.2 dB are measured. The switching time is 1 ms. A novel method of realizing a latchable optical switch using an electromagnetic actuator is also provided and verified. The latch mechanism is based on the latchability of the electropermanent magnet instead of the mechanical one using conventional arch-shaped leaf springs.     

A Varifocal Convex Micromirror Driven by a Bending Moment

A varifocal micromirror is designed and fabricated using silicon micromachining technology. A spherical convex surface of mirror is generated by applying a bending moment to the circumference of micromirror. This method is different from the conventional technique in which a distributed force is exerted on the central area of mirror. On the basis of the theory of materials strength, the deformation of a plate is purely spherical if only a bending moment is applied to the circumference. Spherical surface is well approximated to be a parabola if deflection is small. In order to generate only a bending moment, a force is applied to the plate in the region outside the fulcrum, by which the plate is supported freely in rotation. The proposed mirror was fabricated from a silicon on insulator wafer and a glass plate, which were connected by anodic bonding. The deviation in surface profile of mirror from a parabola was measured with an optical interferometer to be less than 4.7 nm rms in the mirror region inside the 400-mum-diameter fulcrum at the voltage lower than 215 V. The focal length of the fabricated mirror was varied from approximate infinity to 24 mm.     

Surface micromachined segmented mirrors for adaptive optics

This paper presents recent results for aberration correction and beam steering experiments using polysilicon surface micromachined piston micromirror arrays. Microfabricated deformable mirrors offer a substantial cost reduction for adaptive optic systems. In addition to the reduced mirror cost, microfabricated mirrors typically require low control voltages (less than 30 V), thus eliminating high-voltage amplifiers. The greatly reduced cost per channel of adaptive optic systems employing microfabricated deformable mirrors promise high-order aberration correction at low cost. Arrays of piston micromirrors with 128 active elements were tested. Mirror elements are on a 203-μm 12×12 square grid (with 16 inactive elements, four in each corner of the array). The overall array size is 2.4 mm square. The arrays were fabricated in a commercially available surface micromachining process. The cost per mirror array in this prototyping process is less than $200. Experimental results are presented for a hybrid correcting element comprised of a lenslet array and piston micromirror array, and for a piston micromirror array only. Also presented is a novel digital deflection micromirror that requires no digital to analog converters, further reducing the cost of adaptive optics systems     

一种带电磁屏蔽的绕组混合绕制非接触变压器

非接触变压器的耦合系数是影响感应式无线电能传输系统效率的关键因素。为提高非接触变压器的耦合系数,同时尽量减小其体积重量,提出由平面绕组和垂直绕组构成的绕组混合绕制的非接触变压器。然而垂直绕组的引入使得变压器外侧增加了一个新的漏磁路径。为抑制该漏磁,提高耦合系数,选择金属铝进行电磁屏蔽。通过磁路分析给出了屏蔽层的最佳长度公式。最后,为验证变压器有效性及优化方法正确性,制作了一个新型变压器并进行对比实验。与现有变压器相比,在10 mm气隙下,变压器耦合系数从0.523提高到0.583,尺寸从90 mm减小到73 mm。     

Gimbal-less monolithic silicon actuators for tip-tilt-piston micromirror applications

In this paper, fully monolithic silicon optical scanners are demonstrated with large static optical beam deflection. The main advantage of the scanners is their high speed of operation for both axes: namely, the actuators allow static two-axis rotation in addition to pistoning of a micromirror without the need for gimbals or specialized isolation technologies. The basic device is actuated by four orthogonally arranged vertical comb-drive rotators etched in the device layer of an silicon-on-insulator wafer, which are coupled by mechanical linkages and mechanical rotation transformers to a central micromirror. The transformers allow larger static rotations of the micromirror from the comb-drive stroke limited rotation of the actuators, with a magnification of up to 3/spl times/ angle demonstrated. A variety of one-axis and two-axis devices have been successfully fabricated and tested, in all cases with 600-/spl mu/m-diameter micromirrors. One-axis micromirrors achieve static optical beam deflections of >20/spl deg/ and peak-to-peak resonant scanning of >50/spl deg/ in one example at a resonant frequency of 4447 Hz. Many two-axis devices utilizing four rotators were tested, and exhibit >18/spl deg/ of static optical deflection at <150 V, while their lowest resonant frequencies are above 4.5 kHz for both axes. A device which utilizes only three bidirectional rotators for tip-tilt-piston actuation achieves -10/spl deg/ to 10/spl deg/ of optical deflection in all axes, and exhibits minimum resonant frequencies of 4096 and 1890 Hz for rotation and pistoning, respectively. Finally, we discuss the preliminary results in scaling tip-tilt-piston devices down to 0.4 /spl times/ 0.4 mm on a side for high fill-factor optical phased arrays. These array elements include bonded low-inertia micromirrors which fully cover the actuators to achieve high fill-factor.     

Segmented silicon-micromachined microelectromechanical deformablemirrors for adaptive optics

Deformable mirrors improve optical efficiency of a system by correcting the wave front aberration caused by imperfections in the system components or by turbulent atmosphere in case of telescope optics. Micromachined mirror technology has the potential to substantially reduce the cost of adaptive optics systems. First, a brief review of the work in this field is presented with the goal of informing the reader of the challenges in the micromachined adaptive optics and the implementation tradeoffs including stress-induced curvature of multilayer mirrors. Then, recent results on the silicon micromachined, hybrid integrated microelectromechanical deformable mirrors for adaptive optics developed at the University of Colorado are presented. Various microfabrication processes including surface micromachining, bulk micromachining, and flip-chip assembly are implemented to fabricate high optical fill factor and large-stroke piston-type micromirror arrays. The achieved micromirror deflection for some designs is in the range of 2 to 3.5 μm, which results in the operating wavelength within infrared spectrum. Techniques to integrate microlenses on top of the micromirrors using self-aligned solder or transfer of ultrasmooth mirror plates on top of the micromirror actuators using flip-chip create high optical fill factor devices. Experimental results of aberration correction with such devices are presented     

无线充电系统电磁屏蔽与效率优化技术研究

在电动汽车无线电能传输系统中,磁屏蔽效果往往以牺牲传输效率为代价,如何减少磁泄漏的同时提高传输效率是一 个难题。 为此本文提出了一种新型强耦合磁屏蔽结构来减少系统磁泄漏。 首先,提出了一种强耦合磁屏蔽线圈结构,基于提出 的屏蔽线圈结构,分析了屏蔽线圈阻抗特性对系统漏磁与传输效率的影响;其次,给出了一种漏磁优化流程,运用提出的优化流 程,得到了满足设计要求的各线圈参数;最后,根据得到的线圈参数研制了一套基于电动汽车带磁屏蔽结构的无线充电系统,通 过仿真和实验验证了所提结构与方法的有效性。 结果显示,提出的新型强耦合磁屏蔽线圈不仅使系统的磁泄漏有效降低了 28%,且传输效率提升了近 4%。     

Magnetically actuated micromirror and measurement system for motioncharacteristics using specular reflection

Micromachined magnetically actuated torsional micromirrors have been fabricated. The micromirrors based on silicon were actuated by moving magnet system using hard magnetic (Co-Pt) or soft magnetic (Fe-Ni) thin films. And a system to measure motion characteristics of the micromirrors was assembled with an optical table, optical mounts, and optics. The system is based on a specular reflection of He-Ne laser from the micromirrors. We measured static and resonance characteristics of the micromirrors with Co-Pt film or Fe-Ni film. Then we measured Q factors of the micromirrors; with Co-Pt film in vacuum. Using our system for measurements, we obtained motion characteristics of micromirrors at large angular deflections. Measured resonance characteristics of all micromirrors are in good agreement with the equation of forced vibration with viscous damping. Micromirrors with Co-Pt films have better reproducibility of torsional motions than ones with Fe-Ni films in both dc magnetic field and ac magnetic field. And micromirrors with Fe-Ni films have torsional motion with subpeak at resonance characteristics. The Co-Pt film is more useful as a magnetic film for the micromirror than the Fe-Ni film at static and resonance characteristics     

Two-Axis Gimbal-Less Electrothermal Micromirror for Large-Angle Circumferential Scanning

In this paper, we present the design, simulation, fabrication, and characterization of a two-axis gimbal-less micromirror optimized for large-angle circumferential scanning applications. The single-crystal silicon micromirror consists of novel folded bimorph electrothermal actuators, flexural springs, and a mirror plate coated with a high-reflective Cr/Au thin film. A modified silicon-on-insulator microelectromechanical system process has been applied on the micromirror fabrication. The single-wafer process is based on deep reactive ion etching in order to achieve high fill factor as well as small outline of the micromirror chip. A new mechanical design of bimorph actuators is developed to further increase the mechanical deflection. Both theoretical and experimental results demonstrate that the micromirror can provide a uniform mechanical deflection up to ~9deg with multichannel driving voltages of less than 2.3 V to any angle in full 360deg circumference.     

Assembly of Micro-3-D Components on SOI Wafers Using Novel SU-8 Locking Mechanisms and Vertical One-Push Operation

A novel out-of-plane assembly technique of 3-D microstructures is proposed and demonstrated by using simple vertical one-push operations. This one-push method has large probe positioning tolerance in both vertical and lateral directions to reduce the overall complexity of the assembly process. Micromirrors and corner cube reflectors are fabricated on silicon-on-insulator wafers using SU-8 photoresist as a second structure layer in a low-temperature process. Batch assembly of multiple mirrors assembled simultaneously is demonstrated.     

Theory and experiments of angular vertical comb-drive actuators for scanning micromirrors

We report on the theory and experiments of scanning micromirrors with angular vertical comb-drive (AVC) actuators. Parametric analyses of rotational vertical comb-drive actuators using a hybrid model that combines two-dimensional finite-element solutions with analytic formulations are described. The model is applied to both AVC and staggered vertical comb-drive (SVC) actuators. Detailed design tradeoffs and conditions for pull-in-free operations are discussed. Our simulation results show that the fringe fields play an important role in the estimation of maximum continuous rotation angles, particularly for combs with thin fingers, and that the maximum scan angle of the AVC is up to 60% larger than that of the SVC. Experimentally, a large dc continuous scan angle of 28.8/spl deg/ (optical) has been achieved with a moderate voltage (65 V) for a 1-mm-diameter scanning micromirror with AVC actuators. Excellent agreement between the experimental data and the theoretical simulations has been obtained.     

Simultaneous Realization of Stabilized Temperature Characteristics and Low-Voltage Driving of a Micromirror Using the Thin-Film Torsion Bar of Tensile Poly-Si

The tense thin-film torsion bar of polycrystalline (poly-) Si has been recently introduced into a micromirror. A tensile stress is obtained by the crystallization of amorphous Si. The poly-Si has almost the same coefficient of thermal expansion as that of Si substrate. An electrical connection is obtained with doping without the use of metal overlayer. The thin-film torsion bar of poly-Si is fabricated with a revised process so as to protect against the crystalline Si etching. Considering the earlier advantages and techniques, the stabilized temperature characteristics and the low-voltage driving are simultaneously realized.     

Average optical power monitoring in micromirrors

The thermal properties of tip-tilt micromirrors have been analyzed theoretically and measured experimentally for devices operated in air and in vacuum. Typical micromirror thermal conductances are shown to range from 10^-3 W/K for devices operated close to the substrate in air to 10^-5 W/K for devices operated in a vacuum. These results demonstrate that micromirror temperatures are extremely sensitive to the average optical signal incident upon them and can be used as probes of incident power in much the same way as thermal infrared detectors. This has been experimentally demonstrated using a λ = 661 nm diode laser with polysilicon micromirrors, and sensitivities reaching below 70 nW of absorbed optical power, limited by the Johnson and 1/f noise of the micromirrors and measurement system. Average optical power monitoring could be useful in large cross connects or other applications, where the additional integration of a tap/beamsplitter plus photodiode assembly is undesirable     

Performance of Tense Thin-Film Torsion Bar for Large Rotation and Low-Voltage Driving of Micromirror

In this paper, a micromirror device is developed by realizing the large rotation with the low-voltage driving. The maximum rotation angles observed at 5 V are 8.6deg with hysteresis and 7deg with little hysteresis at the static condition. The thin-film torsion bars contribute to decrease in the torsional spring constant. The tension is included for maintaining the compliance in the rotation of the mirror and for increasing stiffness in other movements. The performance of the torsion bar is investigated. The observed hard-spring effect is significant and this can be explained by the combination of the tension and the vertical displacement of the torsion bar     

邻近耦合无线电能传输系统的高效屏蔽设计与优化

在无线电能传输技术的实际应用中,当多个距离相近的无线电能传输系统同时工作时,系统间漏磁场引起的耦合会对周围的电磁环境产生影响,干扰系统谐振参数,进而降低系统工作效率。针对此问题,文中设计了一种谐振屏蔽线圈以消除系统间邻近耦合,分析了其工作原理及其对改善邻近耦合和传输效率的影响。通过仿真及实验,研究了线圈形状及匝数对屏蔽效果的影响,并对屏蔽线圈进行了结构优化。结果表明,方形密绕线圈屏蔽效果较好,可有效降低系统间邻近耦合造成的参数扰动,有助于系统调谐以提高邻近耦合下的系统传输效率。     

1000 kV特高压输电线路防绕击问题的探讨

绕击是1000 kV特高压输电线路雷击跳闸的主要原因,为探讨此问题,分析并比较了目前输电线路绕击计算方法—规程法与电气几何模型法,指出电气几何模型将雷电的放电特性与线路的结构尺寸结合起来,很好解释了线路屏蔽失效现象,用于特高压的绕击计算中,并依据电气几何模型的原理提出减小1000kV线路绕击跳闸率的措施:减小避雷线保护角、安装可控放电避雷针、架设旁路屏蔽地线。     

SCR脱硝装置大颗粒灰拦截技术试验研究

针对部分SCR烟气脱硝装置运行中发生的较为严重的大颗粒灰堵塞催化剂问题,采用冷态物理模型试验予以研究,分析了大颗粒灰拦截网的开孔形状、外形结构与安装位置对拦灰效率与系统阻力的影响,并对灰斗、导流、拦截网相结合的多个方案进行比较。研究结果表明：拦截网阻力与开孔率的三次方成反比;对于拦截网阻力和拦灰效率,拦截网开长条形孔优于开正六边形孔和开正方形孔;屋脊式和平板式拦截网的阻力、拦灰效果基本相同;在省煤器出口采用导流挡板+深灰斗+低拦灰网/挡板方案的大颗粒灰拦截效果最佳,其拦截效率可达95%以上,在SCR入口竖直烟道设置灰斗和折线形后墙可进一步提升拦灰效果。