Design of a MEMS micromirror actuated by electrostatic repulsive force

A microelectromechanical system (MEMS) micromirror actuated by electrostatic repulsive force is demonstrated. The design is based on the principle that an asymmetric electric field produced by special layout of the electrodes can generate a repulsive force, which moves the mirror surface upwards. The factors affecting the magnitude of the driving force of the micromirror actuator are analyzed by FEA. The prototype is fabricated using a commercial available surface micromachining process and successfully tested using a Zygo NewView7300 interferometer. The displacement of the micromirror reaches 1.2 μm at 60 V.     

A study of electrostatic spring softening for dual-axis micromirror

Electrostatic spring softening is an important characteristic of electrostatically actuated dual-axis micromirror, since it lowers the resonant frequencies. This paper presents an approach based on approximating the electrostatic forces by the first-order Taylor's series expansion to investigate this characteristic. The dual-axis micromirror studied in this paper has three motion modes, two torsional (about x- and y-axis, respectively) and one translational (about z-axis). The stiffnesses of all these modes are softened by a DC bias voltage applied to the mirror plate. The resonant frequencies are lowered with the increment of the bias voltage. The relationship of the bias voltage and the resonant frequencies of all the motion modes is derived. The analytical results show that the resonant frequency curves are affected by the capacitor geometries, i.e. the gap between the mirror plate and the electrodes and the electrodes size. The lowering curves drop slowly when the bias voltage is small. While for large bias voltage, the lowering curves drop rapidly. The experiment results are consistent with those obtained by the analytical approach.     

Optimization designed large-stroke MEMS micromirror for adaptive optics

A novel micromirror based on the PolyMUMPs process is designed and presented. The hexagonal micromirror with a diameter of 450 μm consists of three supporting bilayer cantilevers and a mirror plate. The bilayer cantilevers, formed with a polysilicon layer and a gold layer, elevate the mirror plate according to residual stress-induced bending. Both analytical and finite element analysis (FEA) models are built to calculate the elevated height of the free end of the cantilever. The analytical solution is in accordance with the FEA simulation results, with longitudinal stresses applied only. Results of a three-dimensional (3D) simulation with two direction stresses applied also show the elevated height to be proportional to the width of the cantilever and the length of the gold layer. Due to the torque of the joint, the elevated heights of the two kinds of cantilevers assembled with the mirror plates are much smaller than those of the free end of the cantilevers. Both micromirrors with different cantilevers are fabricated. The elevated heights of the fabricated micromirrors are measured using Veeco optical profiler, which show good coincidence with simulation results.     

光梯度力驱动的纳米硅基光开关

通过一道光改变另一道光的传输路线是光子集成网络中重要而长远的目标, 然而, 由于硅材料的光学非线性较弱, 在硅材料上实现开关的全光控制难以实现. 因此本文提出了一种由光梯度力驱动的纳米硅基光开关, 实现了硅基光开关的全光控制. 该光开关由一个部分悬空的微环谐振器和一个交叉波导结构构成, 当通入一道控制光时, 悬空的微环谐振器在光梯度力的作用下发生弯曲, 微环谐振器的谐振波长随之发生变化, 从而实现光信号的传输路线发生改变. 该光开关利用纳米光子制造技术在标准绝缘体上硅晶圆上制造, 实验数据得出其最小消光比为10.67 dB, 最大串扰为 -11.01 dB, 开关时间分别为180 ns和170 ns. 该光开关具有尺寸小, 响应速度快, 低损耗和可拓展等优点, 在片上集成光路、高速信号处理以及下一代光纤通信网络中具有潜在应用.     

Numerical model for the calculation of the electrostatic force in non-parallel electrodes for MEMS applications

In this paper, we investigate the electrical behavior of an electrostatic actuator made of a non-parallel plate's electrodes configuration. The resultant actuation force is caused by the asymmetry of the subsequent electric fringing-fields. This is designed due to the out-of-plane asymmetry of a non-stationary electrode and its two sides actuating stationary electrodes. The electrostatic force is numerically calculated through the results of a two-dimensional numerical solution of the electrostatic problem using Finite-Element Method (FEM). The main objective in this work is to examine the influence of the design parameters on the actuating resultant electrostatic force in this particular arrangement. Four key design parameters were examined: the width and thickness of the electrodes (movable and stationary) as well as the lateral and vertical separation distances between the movable and grounded electrodes. We found out, through several simulations, that both lateral and vertical offsets as well as the electrodes thickness are significant factors in the optimization of the performance of the actuator in such configuration, while the performance seemed to be independent of the electrodes widths. The resultant actuating force level increased with increasing the electrode thickness and with decreasing the electrodes lateral separation distance.     

A tunable bragg cavity for an efficient millimeter FEL driven by electrostatic accelerators

A comparison between three possible cavity configurations, the confocal cavity, the ring cavity and the Bragg cavity is presented for a millimeter FEL set within the high voltage head of an electrostatic accelerator. A simple mechnical design to make the Bragg cavity tunable is proposed. The usual theory of the sinusoidal Bragg corrugation, in cylindrical geometry, is extended to the rectangular corrugation and, further, the theory of the Bragg mirror is extended to rectangular geometry. The features of a Bragg mirror in cylindrical and rectangular geometry are compared.     

Manipulation of single particles by utilizing electrostatic force

Because manipulation of single particles is of great importance in the fields of electronics and biology, the author has been investigating an electrostatic manipulation system. The manipulation probe consisted of dipole pin electrodes. When voltage was applied between the electrodes, the dielectrophoresis and coulombic force generated in the non-uniform electrostatic field was applied to the particle near the tip of the electrode. The particle was captured by the application of voltage and then it is released from the probe by turning off the voltage application. It was possible to manipulate not only insulative but also conductive particles. However, if a particle was charged, the Coulomb adhesion force prevented the release of the particle even when the voltage application was turned off. This condition was generally observed for small particles. Asymmetric and coaxial electrode systems were developed so that the release of the attached particle was independent of the position of the probe. Instead of turning off the voltage application, high voltage was applied to the electrodes to blow off the particle by the ionic wind generated in a corona discharge field, and the applicability of this system was demonstrated. Further, a vibration separator was developed. A three-dimensional field calculation was conducted to calculate the dielectrophoretic force by using the finite difference method and the calculated force was compared to the measured force. It was deduced that the predominant force for the particle adhesion was not dielectrophoresis but Coulomb force generated due to triboelectrification.     

Variable optical attenuator based on a vertical comb drive actuated MEMS micromirror

This letter presents the design, simulation, fabrication, and successful demonstration of a variable optical attenuator (VOA) based on a micromachined micromirror combined with an optical fiber collimator. The micromirror has a size of 500 μm in diameter and a rotational resonance of 4.94 kHz. The micromirror was actuated by vertical comb drive which was fabricated by bulk micromachining process on a silicon on insulator (SOI) wafer. The VOA operates at a low driving voltage of 4.4 V corresponding to the rotation angle of 0.3°. The turn-on and turn-off response time of the VOA are 1.6 ms and 2.74 ms, respectively. Finally, the optical attenuation was measured and an optical attenuation as large as 40 dB was obtained.     

周期性外力驱动的混沌摆

为了简单直观地呈现混沌现象,研制了受周期驱动力驱动的混沌摆实验系统. 实验系统由力学机构、采集机构和数据处理分析仪组成. 力学机构是受周期外力驱动的复摆;采集机构采用无触点角度传感器,通过串口通信实时将数据传输给计算机;数据处理分析仪用虚拟仪器平台LabVIEW软件编程实现. 该系统可实时显示反映混沌基本特征的角度时序图、角速度时序图和相图.     

Observation of electrostatic instability driven by cross-field current and ion heating

Applying an external voltage perpendicularly to a static magnetic field, the electrostatic instability ascribed to the cross-field current due to the E × B drift of electrons could be excited near the lower hybrid frequency, and the ion heating was observed.     

The flute instability of a plasma driven by the electrostatic high-frequency eigenmodes

The dispersion equation of the low-freguency flute instability driven by the high-frequency electrostatic eigenmode excited in a plasma slab is studied. If the amplitude of h.f. mode is small the equation is solved and the explicit formula for the maximum growth rate is obtained. As an example we investigate this problem numerically for a slab with the parabolic density profile. In our model we are able to consider the heating only in the frequency band stretching from the lower hybrid frequency to the electron cyclotron frequency. For this case it follows from our calculation that the danger of the low-frequency disruption of a plasma in the process ofheating is serious.     

光电反馈式静电悬浮及静电力机制研究

本文介绍了光电反馈式静电悬浮方法 ,给出了静电悬浮力的理论计算公式 ,讨论了静电力与电极电压、电极 -悬浮体间距、悬浮体材料等因素之间的关系。通过实验测定了静电力与上述因素之间的关系曲线 ,获得了理想的结果。理论分析与实验结果均表明 ,实现导体与常规非导体的静电悬浮是完全可行的     

The flute instability of a plasma driven by the electrostatic high-frequency eigenmodes

The stability problem of a plasma immersed in a high frequency field is studied on a simple model. It is supposed that the fundamental h. f. electrostatic eigenmode having the frequency lower than the electron cyclotron frequency is excited in a slab of a cold collisionless magnetized plasma with the symmetrical density profile. The stability of low-frequency short-wavelength flute perturbations is investigated. Averaging over fast time oscillations and by using the WKB method to cope with the problem of the space inhomogeneity we have obtained the expression for the electron drift velocity. Making use of this velocity and quasineutrality condition we have derived the local dispersion equation. It is shown how the growth rate depends on the amplitude of the h. f. mode and that h. f. eigenmodes having the frequency close to the plasma frequency in the middle of the slab can partially stabilize the gravitational flute instability.The authors wish to thank Dr. R.Klíma for helpful discussion.     

巧用电子秤测量静电力及真空电容率

介绍了用电子秤测量平行板电容器两极板间的静电力和真空电容率的原理和方法。     

Dual Q-switched laser outputs from a single lasing medium using an intracavity MEMS micromirror array

An intracavity array of individually controlled microelectromechanical system scanning micromirrors was used to actively Q-switch a single side-pumped Nd:YAG gain medium. Two equal power independent laser outputs were simultaneously obtained by separate actuation of two adjacent micromirrors with a combined average output power of 125?mW. Pulse durations of 28?ns FWHM at 8.7?kHz repetition frequency and 34?ns FWHM at 7.9?kHz repetition frequency were observed for the two output beams with beam quality factors M² of 1.2 and 1.1 and peak powers of 253?W and 232?W, respectively.     

Electrostatics of individual single-walled carbon nanotubes investigated by electrostatic force microscopy

We report an experimental study of static charge distribution in individual single-walled carbon nanotubes grown on a Si+115 nm SiO2 substrate. From these experiments, we conclude that charges are distributed uniformly along the nanotubes. We demonstrate that electrostatic force microscopy can accurately measure the amount of charges per unit length. We found that this amount is diameter dependent and in the range of 1 electron per nanometer for a 2.5 nm nanotube at a potential of -3.5 V.     

光梯度力驱动纳谐振器的非线性动力学特性研究

光梯度力作为纳谐振器的一种新型驱动方式,得到了广泛关注.本文研究了光梯度力的固有非线性特性,建立了光梯度力驱动圆环与辐条谐振系统的动力学模型.揭示了入射光功率以及几何参数对系统的非线性动力学响应的影响规律.研究表明:光梯度力会引起系统呈现刚度软化效应,随着入射光功率增大,系统主共振峰值明显增大,且谐振频率随着振幅增大而产生较大偏移;两环初始间隙增大,系统振动幅值和谐振频率均下降;辐条厚度越大,系统主共振峰值和谐振频率均减小.因此,可以通过调节入射光功率来实现圆环辐条谐振器的频率调节,为光梯度力驱动纳谐振器动力学设计和性能预测提供理论参考.     

Enhanced dielectric constant resolution of thin insulating films by electrostatic force microscopy

Electrostatic force microscopy has been shown to be a useful tool to determine the dielectric constant of insulating films of nanometer thicknesses that play a key role in many electrical, optical and biological phenomena. Previous approaches have made use of simple analytical formulas to analyze the experimental data for thin insulating films deposited directly on a metallic substrate. Here we show that the sensitivity of the EFM signal to changes in the dielectric constant of the thin film can be enhanced by using dielectric substrates with low dielectric constants. We present detailed numerical calculations of the tip-sample electrostatic interaction in the following setup: an insulating thin film, a dielectric substrate (or spacing layer) of known low dielectric constant and a metallic electrode. The EFM sensitivity to the dielectric constant increases with the thickness of the spacing layer and saturates for thicknesses above 100-300 nm, when it is close to that of an infinite medium.     

Electrostatic instability in magnetically confined inhomogeneous plasma driven by nonlinear force

A theoretical investigation on amplification of electrostatic ion acoustic wave in magnetically confined plasma has been presented in this paper. This investigation considers nonlinear wave–particle interaction process, called plasma maser effect, in presence of drift wave turbulence supported by magnetically confined inhomogeneous plasma. The role of associated nonlinear dissipative force in this effect in a confined plasma has been analyzed. The nonlinear force, which arises as a result of resonant interaction between electrons and modulated fields, is shown to drive the instability. Using the ion fluid equation and the ion equation of continuity, the nonlinear dispersion relation of a test ion acoustic wave has been derived, and the growth rate of ion acoustic wave in presence of low frequency drift wave turbulence has been estimated using Helimak data.