Mirror Plate Research Articles

A quick method to fabricate large glass micromodel networks

The study of multi-phase fluid flow in microfluidic devices provides an opportunity for researchers to characterize effective factors and mechanisms in microscale. The application of microtechnology in various fields of science and engineering has always raised different technical problems that require further research and developments. This paper aims to address the associated challenges with micromodel studies that employ the chemical (wet) etching method for making glass micromodels. To overcome these challenges, recent advances in chemical etching are modified and combined to decrease the construction time and costs. The general steps in the chemical etching process are masking, etching, and bonding. First, the common masking step [projecting the designed pattern (regular or irregular) on the acid-resistant layer] in this work is simplified by engraving the mirror plates with a CO2 laser. This new technique skips the required facilities for photoresist layer deposition and UV lithography by using direct laser beam machining of pre-coated soda lime glasses (mirror). Moreover, the variety of mirror products and flexible functionality of laser machines make it possible to create larger size models with any desirable flow pattern. Next, the general composition of solution used in the etching step and the operating conditions of thermal bonding step are modified based on recent investigations in literature to enhance the mechanical strength of the micromodel. Finally, the fabricated model with this procedure is applied in a two-phase flow visualization study to examine the practical features under experimental conditions.

H∞ Robust Control of a Large-Piston MEMS Micromirror for Compact Fourier Transform Spectrometer Systems.

Incorporating linear-scanning micro-electro-mechanical systems (MEMS) micromirrors into Fourier transform spectral acquisition systems can greatly reduce the size of the spectrometer equipment, making portable Fourier transform spectrometers (FTS) possible. How to minimize the tilting of the MEMS mirror plate during its large linear scan is a major problem in this application. In this work, an FTS system has been constructed based on a biaxial MEMS micromirror with a large-piston displacement of 180 μm, and a biaxial H∞ robust controller is designed. Compared with open-loop control and proportional-integral-derivative (PID) closed-loop control, H∞ robust control has good stability and robustness. The experimental results show that the stable scanning displacement reaches 110.9 μm under the H∞ robust control, and the tilting angle of the MEMS mirror plate in that full scanning range falls within ±0.0014°. Without control, the FTS system cannot generate meaningful spectra. In contrast, the FTS yields a clean spectrum with a full width at half maximum (FWHM) spectral linewidth of 96 cm−1 under the H∞ robust control. Moreover, the FTS system can maintain good stability and robustness under various driving conditions.

Optical system for orbital detector of extreme-high-energy cosmic ray

An optical system of a Schmidt-type telescope for orbital detection is proposed. The system contains a spherical mirror and correction plate with one aspherical surface and has the following characteristics: field of view (FoV) is 40 deg, entrance pupil diameter is 2.5 m, diameter of spherical mirror is 4 m, and f-number is 0.74. The system with the described parameters has image spot size of 3.2-mm (RMS) diameter for the axial beam and 4 mm (RMS) on the edge of the FoV, which is less than the diagonal of the detectors square pixel of 3×3 mm2.

The Designing of Magnetic-Driven Micromirror for Portable FTIRs

Fourier transform infrared spectroscopy is a widely used instrument to analyze and test different materials including organic and inorganic. Most of current commercial Fourier transform infrared spectrometers are limited in miniaturization and scanning velocity by their macroscopic components. MEMS FTIR spectroscopy is one of the important applications of translational actuator-driven systems by using MEMS technology. The critical component in MEMS FTIRs is the large displacement translating micromirror and its actuator. The paper presents a large displacement and high-surface quality micromirror. The micromirror consists of a micromagnetic actuator and a micromirror plate. The mirror plate and the actuator are fabricated separately and bonded together afterwards, and its size is 3.6 × 3.6 mm2 high-surface quality square mirror plate and a 1cm2 moving part. The microactuator’s moving part is fabricated using MetalMUMPS, and its fixed part includes a ring permanent magnet and a solenoid to realize a large displacement. The mirror plate is fabricated using polished silicon coated with metal layer with high-surface prototypes that are fabricated and experimentally tested. A maximum stroke of 400 μm has been achieved in pull-in whereas only 140 μm stroke have been measured for a 4 to 5-volt DC-controlled displacement, and the resonance frequency is 10 Hz.

Development, research and metrological analysis of the measuring channel of a fiber-optic sensor for fluid flow parameters used in information-measuring systems

The article proposes a device for measuring parameters of liquid flows (volume and velocity) (FOSLFP). A physico-mathematical model of optical signal conversion in a fiber-optic flux transducer of the proposed sensor is developed, in which the perceiving element is a truncated cylinder mounted on the inner surface of the bellows, experiencing angular bending during measurements. The conversion of optical signals is carried out using a two-way mirror plate mounted on the outer surface of the bellows in an open fiber optical channel. A circuit-analytical model of a new variant of a differential circuit for converting optical signals to a FOSLFP was developed, in accordance with which a metrological model of the sensor was developed to determine the possible sources of measurement errors. The nominal and real functions of the FOSLFP transformation were derived, the additive and multiplicative components of the errors of the two measuring channels of the sensor and the ways to reduce them were determined.

A Fast Multiobjective Optimization Strategy for Single-Axis Electromagnetic MOEMS Micromirrors

Micro-opto-electro-mechanical (MOEMS) micromirrors are an enabling technology for mobile image projectors (pico-projectors). Low size and low power are the crucial pico-projector constraints. In this work, we present a fast method for the optimization of a silicon single-axis electromagnetic torsional micromirror. In this device, external permanent magnets provide the required magnetic field, and the actuation torque is generated on a rectangular multi-loop coil microfabricated on the mirror plate. Multiple constraints link the required current through the coil, its area occupancy, the operating frequency, mirror suspension length, and magnets size. With only rather general assumptions about the magnetic field distribution and mechanical behavior, we show that a fully analytical description of the mirror electromagnetic and mechanical behavior is possible, so that the optimization targets (the assembly size, comprising the mirror and magnets, and the actuation current) can be expressed as closed functions of the design parameters. Standard multiobjective optimization algorithms can then be used for extremely fast evaluation of the trade-offs among the various optimization targets and exploration of the Pareto frontier. The error caused by model assumptions are estimated by Finite Element Method (FEM) simulations to be below a few percent points from the exact solution.

FPCB Ring-Square Electrode Sandwiched Micromirror-Based Laser Pattern Pointer

This paper presents a laser pattern pointer based on flexible printed circuit board (FPCB) ring-square electrode sandwiched (FRSS) micromirror. It integrates two FRSS micromirrors, a laser, and a control circuit to project a static/rotating laser circle/ellipse, or a horizontal/vertical line with size adjustable. Compared with the conventional laser spot pointer, the laser pattern generated by this pointer is: 1) of higher capability to draw audience's attention; 2) more comfortable to eyes due to its no-glaring and uniform brightness with lower average laser power density within the time required for human's perception of an image; 3) able to highlight a row/column/area. The FRSS micromirror consists of a FPCB moving electrode sandwiched by a square and ring PCB electrodes. A silicon mirror plate is bonded on the moving electrode's top. The FRSS micromirror can accommodate the unflatness of polyimide supporting beams to significantly reduce the performance variation associated with the previously reported FPCB micromirror with 2–3 times higher torque. The FRSS micromirror's performance is simulated and the prototype is fabricated using FPCB/PCB process with very low cost (<$1), which is one order of magnitude lower than that of the conventional MEMS micromirrors. The laser pattern pointer is assembled and tested.

Investigation of dynamic thermal behaviors of an electrothermal micromirror

It is well known that the heat transfer at microscale is quite different from that at macroscale, but the dynamic thermal behavior of micro-actuators with movable microstructures still lacks comprehensive investigation. This work presents a thorough study on thermal behaviors of an electrothermally actuated scanning micromirror, which has a 1mm×1mm central mirror plate supported on four sides by four pairs of electrothermal bimorph actuators. The heat transfer from the thermal actuator to the ambience, including the substrate and the environmental air, are investigated experimentally with several different driving powers and various frequencies under natural convection, forced convection, and in vacuum. The results indicate that the heat conduction dominates the heat transfer process of electrothermal bimorph actuators, while the convection has little impact on the overall heat transfer even under strong forced convection. Furthermore, an equivalent circuit model of the electrothermal micromirror is developed and experimentally verified, from which the effective heat transfer coefficient of the electrothermal bimorphs is extracted to be in the range from 1900 to 2282W/(m2K), which is one to two orders of magnitude larger than that at macroscale.

Magnetic field assisted bonding technology for released micro actuator and mirror surface

A magnetic field pulling-force assisted bonding technology is reported, which is used to bond a mirror plate with a released microactuator using adhesive. This bonding technology is not sensitive to the micromachining process, i.e., any process for microactuator fabrication containing the ferromagnetic structure layer can be used and bonded with a high surface quality mirror plate after released. The conventional wafer bonding technology bonds unreleased actuator with a mirror plate but it limits to the process compatible with the wafer bonding with a releasing step suitable for wafer bonding. Consequently not all processes (such as those mature and commercially available, and those being able to generate large displacement) can be used to fabricate micromirrors. The bonding technology proposed in this paper applies non-touching magnetic field pulling-force, instead of conventional compression mechanical force through touching, to bring the microactutor and a mirror plate in contact for bonding such as to avoid: (1) any plastic deformation or damage to the released micro actuator; and (2) the risk of sticking the actuator moving part to the substrate due to the adhesive squeezed out from the bonding surfaces. The bonding method is introduced and the critical parameters of the bonding method, i.e., distance between the magnet to the actuator is determined through simulations. A bonding mechanism is built and two different designs are bonded. Bonding results are measured, which verifies the bonding method. The bonding is characterized to have a strength of withstanding vibration for a few hours in frequency 20–200 Hz with 2–5 g acceleration and surviving in the temperature of −30 to 80 °C. After bonding a mirror plate with 15.6 m of the curvature radius and 2 nm of the roughness, the bonded micromirror is tested to have a quasi-static displacement of 120 μm.

Design and Fabrication of a 2-Axis Electrothermal MEMS Micro-Scanner for Optical Coherence Tomography

This paper introduces an optical 2-axis Micro Electro-Mechanical System (MEMS) micromirror actuated by a pair of electrothermal actuators and a set of passive torsion bars. The actuated element is a dual-reflective circular mirror plate of 1 in diameter. This inner mirror plate is connected to a rigid frame via a pair of torsion bars in two diametrically opposite ends located on the rotation axis. A pair of electrothermal bimorphs generates a force onto the perpendicular free ends of the mirror plate in the same angular direction. An array of electrothermal bimorph cantilevers deflects the rigid frame around a working angle of 45 for side-view scan. The performed scans reach large mechanical angles of 32 for the frame and 22 for the in-frame mirror. We denote three resonant main modes, pure flexion of the frame at 205 , a pure torsion of the mirror plate at 1.286 and coupled mode of combined flexion and torsion at 1.588 . The micro device was fabricated through successive stacks of materials onto a silicon-on-insulator wafer and the patterned deposition on the back-side of the dual-reflective mirror is achieved through a dry film photoresist photolithography process.

A Large-Size MEMS Scanning Mirror for Speckle Reduction Application

Based on microelectronic mechanical system (MEMS) processing, a large-size 2-D scanning mirror (6.5 mm in diameter) driven by electromagnetic force was designed and implemented in this paper. We fabricated the micromirror with a silicon wafer and selectively electroplated Ni film on the back of the mirror. The nickel film was magnetized in the magnetic field produced by external current coils, and created the force to drive the mirror’s angular deflection. This electromagnetically actuated micromirror effectively eliminates the ohmic heat and power loss on the mirror plate, which always occurs in the other types of electromagnetic micromirrors with the coil on the mirror plate. The resonant frequency for the scanning mirror is 674 Hz along the slow axis, and 1870 Hz along the fast axis. Furthermore, the scanning angles could achieve ±4.5° for the slow axis with 13.2 mW power consumption, and ±7.6° for the fast axis with 43.3 mW power consumption. The application of the MEMS mirror to a laser display system effectively reduces the laser speckle. With 2-D scanning of the MEMS mirror, the speckle contrast can be reduced from 18.19% to 4.58%. We demonstrated that the image quality of a laser display system could be greatly improved by the MEMS mirror.

Physical Vapor Deposited Films of a Perylene Derivative: Supramolecular Arrangement and Thermal Stability

The analysis of supramolecular arrangement is essential to understand the role of this key factor on the optical and electrical properties of organic thin films. In this work, thin solid films of bis(phenethylimido) perylene (PhPTCD) fabricated using physical vapor deposition (PVD) technique (thermal evaporation), deposited simultaneously onto different substrates (Ag mirror, Ge, and quartz plates) contingent on the characterization technique. The main objective is to study the PhPTCD supramolecular arrangement and the thermal stability of this arrangement in PVD films. The ultraviolet-visible absorption reveals a controlled growth of the PVD films, and the micro-Raman scattering data show that the PhPTCD molecule is not thermally degraded in the conditions of these experiments. The microscopy also shows a homogeneous morphological surface of the PVD film at macro and micro scales, with molecular aggregates at nanoscale. Besides, the PVD film roughness does not follow substrate roughness. The X-ray diffraction indicates a crystalline structure for PhPTCD powder and an amorphous form for PhPTCD PVD film. The infrared absorption spectroscopy points to a preferential flat-on organization of the molecules in the PVD films. In addition, the annealing process (200 oC for 20 minutes) does not affect the supramolecular arrangement of the PhPTCD PVD films.

Theoretical and finite element analysis of dynamic deformation in resonating micromirrors

Dynamic deformation is one of the limiting factors in the design of high frequency resonating microscanners that are intended for high definition raster scanning display applications. Out-of-plane deformation resulting from high acceleration loads causes beam divergence, which will in turn reduce the optical resolution. This paper presents a detailed analysis on the mechanical design aspects contributing to dynamic deformation such as the micromirror layout and the micromirror-spring linkage design. The applicability of one-dimensional plate bending theory in evaluating micromirror deformation due to inertial loads is investigated using finite element analysis. Improved analytical dynamic deformation predictions, which take into consideration the two-dimensional mirror plate twist, will also be presented. A comparison among a number of layout designs was carried out with the aim of increasing micromirror bending stiffness in a direction parallel to the axis of rotation. Moreover, spring-linkage effects were also addressed and a significant improvement in dynamic deformation was achieved with the inclusion of a gimbal structure between the micromirror and the torsion springs. A parametric analysis was also carried out in order to optimise the gimbal frame design in order to comply with the Rayleigh diffraction limit criterion.

Static recrystallization behavior of 25CrMo4 mirror plate steel during two-pass hot deformation

The static recrystallization behavior of 25CrMo4 mirror plate steel has been determined by hot compression testing on a Gleeble 1500 thermal mechanical simulation tester. Compression tests were performed using double hit schedules at temperatures of 950–1150 °C, strain rates of 0. 01–0. 5 s−1, and recrystallization time of 1–100 s. Results show that the kinetics of static recrystallization and the microstructural evolution were greatly influenced by the deformation parameters (deformation temperature, strain rate and prestrain) and the initial austenite grain size. Based on the experimental results, the kinetics model of static recrystallization has been generated and the comparison between the experimental results and the predicted results has been carried out. It is shown that the predicted results were in good agreement with the experimental results.

Two-axis water-immersible microscanning mirror for scanning optics and acoustic microscopy

Fast multiaxis scanning is useful for not only optical but also acoustic microscopic imaging. Although they have been used for optical scanning, the application of (MEMS) scanning mirrors in acoustic microscopy is still very limited due to their small mirror plate size, and more importantly, inability to operate in liquids (as ultrasound coupling media). A microfabricated two-axis water-immersible scanning mirror for optical and acoustic microscopy is reported. It has an optical and acoustically reflective mirror plate (6 mm×4 mm) to provide numerical aperture for ultrasound beam steering. Electromagnetic and mechanical analysis and simulation were conducted to estimate the mechanical tilting angle and resonance frequency of both fast and slow axes, which matches well with the measurement results. The fast axis has a resonant frequency of 320 Hz in air and 220 Hz in water, which is more than 10 times higher than that of the slow axis (24 Hz in air and 14 Hz in water). Under a 100-mA driving current, the scanning angles of the fast axis reached ±9.5 deg in both air and water at the resonance frequency, respectively. The scanning angles of the slow axis reached ±15 deg in air and ±12.5 deg in water at resonant frequencies, respectively. Raster scanning of a collimated laser beam was achieved by driving both axes simultaneously close to their own resonance frequencies. The feasibility of using the two-axis water-immersible scanning mirror in scanning acoustic microscopy was also demonstrated.

A translation micromirror with large quasi-static displacement and high surface quality

A large displacement with high surface quality translation micromirror is presented. The micromirror consists of a magnetic actuator and a mirror plate. The actuator and the mirror plate are fabricated separately using two processes and then bonded together. The actuator consists of a moving film which is a 20 µm thick nickel film fabricated by MetalMUMPs and a solenoid located underneath the moving film. The moving film is designed to curve up through the residual stress gradient in the nickel film and a curve-up mechanism which includes four trapezoidal plates and anchoring springs. The mirror plate is simply diced from a polished silicon wafer and coated with a metal thin film. The mirror plate is bonded onto the central ring of the moving film. A solenoid attracts the moving film along with the mirror plate downwards to realize translation. A quasi-static displacement of 123 µm is achieved at a driving current of 400 mA. A high mirror surface quality is realized, e.g. 15.6 m of curvature radius and 2 nm surface roughness.

A Fourier Transform Spectrometer Based on an Electrothermal MEMS Mirror with Improved Linear Scan Range.

A Fourier transform spectrometer (FTS) that incorporates a closed-loop controlled, electrothermally actuated microelectromechanical systems (MEMS) micromirror is proposed and experimentally verified. The scan range and the tilting angle of the mirror plate are the two critical parameters for MEMS-based FTS. In this work, the MEMS mirror with a footprint of 4.3 mm × 3.1 mm is based on a modified lateral-shift-free (LSF) bimorph actuator design with large piston and reduced tilting. Combined with a position-sensitive device (PSD) for tilt angle sensing, the feedback controlled MEMS mirror generates a 430 µm stable linear piston scan with the mirror plate tilting angle less than ±0.002°. The usable piston scan range is increased to 78% of the MEMS mirror’s full scan capability, and a spectral resolution of 0.55 nm at 531.9 nm wavelength, has been achieved. It is a significant improvement compared to the prior work.

Miniature Fourier transform spectrometer with a dual closed-loop controlled electrothermal micromirror.

A large piston-displacement electrothermal micromirror with closed-loop control of both piston scan and tilting of the mirror plate is demonstrated for use in a miniature Fourier transform spectrometer. Constant scan velocity in an ultra large piston scan range has been demonstrated by the proposed closed-loop piston control scheme which can be easily implemented without considerably increasing system complexity. The experimental results show that the usable linear scan range generated by the micromirror has been extended up to 505 μm. The measured spectral resolution in a compact spectrometer reaches 20 cm-1, or 0.57 nm at 532 nm wavelength. Compared to other presented systems, this microspectrometer will benefit from the closed-loop thermal actuator approach utilizing both the piston servo and tilt control to provide more consistent spectral response, improved spectral resolution and enhanced robustness to disturbances.

Rebound Vibration of Two-Plates Bonded Model for an Internal Mirror of SLR Camera

In this study, the rebound vibration characteristics of the internal mirror of an SLR camera are investigated using experimental models. The mechanism of the mirror rebound phenomena is tested by using the two-rectangular-metal-plates model, which has two plates bonded by double-sided tape. The mirror (plates) model is supported by fixing its longitudinal edge on a horizontal rotatable shaft. The bonded-mirror-model swings down freely around a horizontal axis and hits a stopper. A laser displacement meter is used to measures the amount of rebound and the mirror model vibration behavior. The rebound angle varies by the stopper position and the bonded position of the double-sided tape. In the case of a small rebound angle, the mirror part of the plate (upper side plate) vibrates with large amplitude, and its movement is measured by a 3-dimentional high-speed camera.

Bond Strength of 3D-stacked Monocrystalline Silicon X-ray Mirrors

In view of high-performance light-weight X-ray optics, we developed a unique technology and assembly tool to stack structured and bend monocrystalline silicon plates resulting in a matrix-like pore structure, the so-called Silicon Pore Optics (SPO). The fully automated assembly robot is specifically developed to stack SPO of various sizes and is a combination of standard semiconductor systems and newly developed tools. The complete system has a footprint of a few square meters only and is installed in a particle free environment. The robot selects a plate for stacking and inspects it for particles. The plate is then handed over to the actual stacking tool, which will elastically bend it into a cylindrical or conical shape. After two bend and structured silicon plates have been hydrophilically bonded to each other, the figure and interfacial particular contamination is investigated with a Fringe Reflection Technique (FRT) machine. The process of stacking is getting repeated by the assembly tool till the stack reaches a height of up to 45 plates forming a stiff self supporting structure.In this presentation, we will give account of the production of SPO with different radii. We will mainly focus on our investigations of the bond strength of the directly bonded structured silicon mirror plates. The investigation of the mechanical strength of bonds of structured plates is of high importance as the bond strength is difficult to estimate in FE modeling, but is a critical point in the overall mechanical stability of the SPO. We performed tensile testing measurements to quantify the bond strength of two different types of samples, flat and curved direct bonded structuredmonocrystalline silicon plates. The failure modes found during this tests are either separation of the bond or failure of the structured silicon plates. Thereby, the tensile test results show clearly what failure mode it is. Furthermore, we post-annealed the samples at various temperatures and for different times in order to increase the bond strength and thus improve the stability of the stacks.