Mirror Plate Research Articles

An electromagnetic indirect-driving scanning mirror for wide-field coaxial LiDAR applications

This paper reports an electromagnetic indirect-driving scanning mirror with an enlarged mirror plate (17mm×17mm) supported by high-strength polymer hinges for wide-field coaxial LiDAR (Light Detection and Ranging) applications. An indirect-driving mechanism was developed to achieve large tilting angle through mechanical amplification, while maintaining a relatively high resonance frequency of the enlarged mirror plate. A prototype mirror was designed, fabricated, and tested. A Hall scan position sensor was integrated to monitor the pose of the mirror in real time. The testing results show a coupled resonance frequency of 54.9 Hz with an optical tilting angle of ±60°, corresponding to a field of view (FoV) of 120°. A wide-field coaxial LiDAR system was also built based on the indirect-driving scanning mirror, and 2D imaging was demonstrated.

MEMS fast steering mirror with a large optical aperture and high surface quality for free-space optical communication

This work presents a MEMS fast steering mirror fabricated by an 8-inch AlScN platform, with a large optical aperture of up to 10 mm and high surface quality (RMS < 20 nm, PV < 120 nm), intended for free-space optical communication. The device comprises a high reflective mirror plate, a pillar and four cantilever beams with AlScN thin films. This device is prepared by a wafer-level eutectic bonding process. A reinforcement structure is proposed to increase the resonant frequency and the resistance to deformation. The mechanical performance, including resonant frequency, step response, linearity, and long-term stability are characterized. The maximum tilting angle is 1.38 mrad at 68 V, the settling time is improved from 400 ms in the open-loop control mode to 0.5 ms with the double step algorithm. The relationship of the resonant frequency, surface figure, and the depth of reinforced ribs is studied through characterizing devices with different depths of reinforced ribs. The bonding quality and the mutual melting states of bonding layers interface are investigated.

AlScN-based quasi-static multi-degree-of-freedom piezoelectric MEMS micromirror with large mirror plate and high fill factor

A quasi-static multi-degree-of-freedom piezoelectric MEMS micromirror with large mirror plate and high fill factor based on AlScN is presented. It consists of two individual components, namely the mirror plate and the actuator. They are fabricated separately and vertically assembled together to form the final combination. In current case, a square mirror plate with side length of 5 mm is used. The actuator is designed into a gimbal-less structure, which involves a central connection platform with a mounting hole and four groups of piezoelectric actuators that are connected to the platform's corners via serpentine springs. This configuration provides multi-degree-of-freedom driving capabilities, allowing tip-tilt-piston mirror movement. The piezoelectric actuator is composed of three-stage cantilever-type actuation units that are connected in series, and they are intentionally arranged into S-shape so as to be completely hidden beneath the mirror plate. Moreover, the driving performance is further improved by optimizing the electrode coverage region on each actuation unit. As a result, not only large displacement but also nearly 100 % fill factor as well as high optical utilization efficiency can be achieved. From experimental results, the as-fabricated MEMS micromirror demonstrates static mechanical tilt angles of approximately ±2.2° about two orthogonal axes and piston vertical movement of ±54.9 μm within ±50 VDC driving voltage range with excellent linearity. Given the large mirror size, high fill factor and multi-degree-of-freedom motion advantages, the proposed micromirror could be found application perspective in light field shaping, free space optical communication and projection lithography areas.

A Large-Scan-Range Electrothermal Micromirror Integrated with Thermal Convection-Based Position Sensors.

This paper presents the design, simulation, fabrication, and characterization of a novel large-scan-range electrothermal micromirror integrated with a pair of position sensors. Note that the micromirror and the sensors can be manufactured within a single MEMS process flow. Thanks to the precise control of the fabrication of the grid-based large-size Al/SiO2 bimorph actuators, the maximum piston displacement and optical scan angle of the micromirror reach 370 μm and 36° at only 6 Vdc, respectively. Furthermore, the working principle of the sensors is deeply investigated, where the motion of the micromirror is reflected by monitoring the temperature variation-induced resistance change of the thermistors on the substrate during the synchronous movement of the mirror plate and the heaters. The results show that the full-range motion of the micromirror can be recognized by the sensors with sensitivities of 0.3 mV/μm in the piston displacement sensing and 2.1 mV/° in the tip-tilt sensing, respectively. The demonstrated large-scan-range micromirror that can be monitored by position sensors has a promising prospect for the MEMS Fourier transform spectrometers (FTS) systems.

Stray Light Analysis and Suppression for an Infrared Fourier Imaging Spectrometer

To improve the accuracy of infrared radiation characteristics measurement in the aviation field, an infrared Fourier transform imaging spectrometer based on a double-swing solid angle reflector was designed. This imaging spectrometer operates in the 3–5 μm wavelength range and has a field of view of 1.7° × 1.7°. This article presents a comprehensive analysis of the system’s stray light and also studies the impact of external stray light on the imaging quality, along with the influence of internal stray light on the interference effects and the spectral resolution. It also present the design of a hood that suppresses the point source transmittance of the external stray light down to the order of 10−4. Based on this, we propose a method that incorporates the introduction of wedge and inclination angles. Additionally, a numerical range is provided for the addition of these angles on the beam splitter mirror and compensation plate. This ensures the effective suppression of any internal stray light. This study fills the gap in the knowledge about Fourier transform imaging spectrometers operating in the mid-infrared band for aviation applications, and proposes a suppression method suitable for interference systems, which is also suitable for Fourier transform imaging spectrometers based on other types of interferometers. This study broadens the application field of Fourier transform imaging spectrometers in stray light, and has great significance to promote the development of Fourier transform imaging spectrometer.

Development of a miniaturized PZT-based MEMS Fabry-Perot interferometer with eutectic wafer bonding and its interface electronics

A miniaturized lead zirconate titanate (PZT)-actuated Fabry-Perot interferometer (FPI) was developed for an 850 nm light beam selection by modulating the air gap between two refractive mirrors. The developed FPI consists of mirrors, a PZT actuator for air gap modulation, metal electrodes, and interface electronics capable of applying a square voltage at a frequency of 0.1 Hz. Eutectic wafer bonding method was employed to bond two mirrors through rapid thermal annealing (RTA) and applying mechanical pressure for a short time to minimize the interdiffusion between layers. The PZT actuator and metal electrodes serve as a thickness spacer to create an air gap between the two mirror plates. Alternating high and low dielectric layers (TiO2 and SiO2) with precise thickness and high crystallization quality were utilized for the formation of the refractive mirror because these layers offer high reflectivity and low absorption loss, enabling effective transmission of a specific wavelength in the incident light beam. By applying 0.1 Hz square pulses to the PZT actuator, the air gap was modulated, resulting in significant shifts in the center wavelength of the filtered beam at the desired wavelength. The study demonstrates the successful modulation and optimization of transmission peaks, ensuring a sharp full width at half maximum (FWHM) and high transmission rate. It also provides comprehensive experimental process factors for optimizing heat treatment conditions for PZT and refractive mirrors, minimizing metal interdiffusion between the dielectric layers, and ensuring mirror plate flatness. The device parameter effects such as cavity length orders, sequence of refractive indices for dielectric layers, and the extent of elongation of PZT with applied voltage were systematically studied to achieve optimal performance of FPI filter. The developed interface electronics allow voltage modulation up to 21.9 V at a frequency of 0.1 Hz, while preserving the elasticity of the PZT actuator.

Piezoelectric 1D MEMS scanning micromirror fabricated with bulk PZT laminated on stainless steel plate

In this research, a piezoelectric metal scanning micromirror with a large reflective surface area is presented. Unlike conventional scanning micromirrors fabricated with single-crystal silicon, stainless steel plate is used as the structural layer material. Two distinct device models, varying in cantilever and connector geometry, were conceptualized and experimentally assessed. These fabricated devices utilized the strain induced in bulk PZT (lead zirconate titanate) plates affixed to the cantilevers on opposing sides of the reflective surface. A 5 mm-diameter gold-coated silicon mirror plate served as the reflective surface. We evaluated the performance of two bulk PZT plates, PZT-5H and PZT-8. Our experimental results reveal that model #1, driven by PZT-5H with a sinusoidal input voltage of 200 Vpp, achieved a maximum optical scan angle of 26°, while model #2 exhibited a more substantial maximum scan angle of 44°. The average resonant frequency of the PZT-5H samples was 1264 Hz for model #1 and 995 Hz for model #2. These findings underscore the viability of stainless steel plates as a robust structural layer for piezoelectric scanning micromirrors. The proposed design holds potential for integration into a 3D LiDAR system when combined with an additional slow vertical scanner.

Crosstalk-free large aperture electromagnetic 2D micromirror for LiDAR application

This paper presents a novel design of a 2D electromagnetic micromirror without crosstalk. The proposed micromirror uses a flexible printed circuit board (FPCB) and four layers of coils embedded in the polyimide layers. The insulated layers of the coil allow for independent actuation of the mirror plate to rotate about two orthogonal axes. The diamond shaped micromirror uses a hyperbola-shaped magnetic field on the coils under the mirror plate and a 45-degrees magnetic field on the coils embedded in the FPCB frame to eliminate the mechanical crosstalk. Finite element analysis was used to predict the novel 2D micromirror’s behavior. The novel 2D micromirror prototype is used in scanning LiDAR, The results indicate that the crosstalk-free pattern yielded significantly clearer results, particularly for detecting object boundaries and reducing barrel distortion. The experimental test has verified the novel crosstalk-free 2D micromirror working principle and showed good scanning quality: no crosstalk and an improvement in the horizontal field of view up to 19% But with the cost of reducing the vertical field of view by up to 12%. The novel 2D micromirror prototype has a large aperture of 19 × 19 mm2, which is very suitable for coaxial scanning LiDAR.

Modeling of Rapid Pam Systems Based on Electrothermal Micromirror for High-Resolution Facial Angiography.

In this paper, a portable photoacoustic microscopy (PAM) system is proposed based on a large stroke electrothermal micromirror to achieve high resolution and fast imaging. The crucial micromirror in the system realizes a precise and efficient 2-axis control. Two different designs of electrothermal actuators with "O" and "Z" shape are evenly located around the four directions of mirror plate. With a symmetrical structure, the actuator realized single direction drive only. The finite element modelling of both two proposed micromirror has realized a large displacement over 550 μm and the scan angle over ±30.43° at 0-10 V DC excitation. In addition, the steady-state and transient-state response show a high linearity and quick response respectively, which can contribute to a fast and stable imaging. Using the Linescan model, the system achieves an effective imaging area of 1 mm × 3 mm in 14 s and 1 mm × 4 mm in 12 s for the "O" and "Z" types, respectively. The proposed PAM systems have advantages in image resolution and control accuracy, indicating a significant potential in the field of facial angiography.

Performance analysis of a novel model of photovoltaic PV-TEGs system enhanced with flat plate mirror reflectors

Recently, the combination of photovoltaic (PV) modules and thermoelectric generators (TEGs) have shown optimal models of energy harvesting from solar photovoltaic/thermal systems. In this regard, the design of solar collectors with simpler models and compatible with TEGs attract attention. The following article is a report on the simulation of a simple new model of photovoltaic PV-TEGs system enhanced with flat plate mirror reflectors. The energy output of the system is hot water flowing in aluminum tubes with a rectangular cross-section connected to the cold surfaces of the series TEGs. Arranged experimental results were used for the power and efficiency relationships of the series of TEGs in the simulation. The results showed that the difference in electrical energy produced by PV module and TEGs due to the presence and absence of reflectors are equal to 1095.448 (kJ) and 80.874 (kJ), respectively. Also, the daily thermal efficiency of the system was about 42%.

On the design of piezoelectric MEMS scanning mirror for large reflection area and wide scan angle

This study designs and implements the piezoelectric MEMS scanning mirror with large scan angle and reflection area for light beam manipulating applications. In this design, the scanning mirror has a large mirror plate (3 mm in diameter) supported by two T-shape torsional springs. The U-shape piezoelectric cantilever acts as the actuator to drive the scanning mirror through the transmission spring. The analytical model is established to provide the design guideline of transmission spring to increase the scan angle. In application, the proposed designs are fabricated on the SOI (silicon on insulator) wafer deposited with the PZT film. Measurements indicate the fabricated mirror could reach an optical scan angle of 140-degree (mechanical scan angle of ±35-degree) when driving at its resonant frequency of 1.5 kHz with a unipolar driving voltage of 42 V. Moreover, no vacuum environment is required for the presented scanning mirror to achieve the above scan angle. This is an extremely large optical scan angle for the MEMS scanner with a mirror plate of 3 mm in diameter. In addition, another U-shape piezoelectric cantilever serves as the position sensor to detect the scan angle of mirror plate. The sensing signals show good linearity with the scan angles and can be exploited as the feedback control. Measurements also demonstrate that the micro scanner could withstand 1500 g shock loading, and the deviation of scan angle is less than 10% after the cycling test under 10 V pp resonant driving in 95%RH and room temperature for 0.2 billion cycles.

Компьютерное моделирование процесса формирования изображений в гиперспектральной системе на базе интерферометра Фабри-Перо

The article deals with the issues of computer simulation of the processes of spectral image formation in a hyperspectral system based on the Fabry-Perot interferometer, designed to work in the visible spectrum. A mathematical model of a hyperspectral system and its main variable parameters for evaluating the obtained characteristics of spectral selectivity are considered. A block diagram illustrating the simulation process is given. The results of computer simulation are presented. The characteristics of spectral selectivity obtained by computer simulation are given, depending on the air-gap distance between the mirror plates of the Fabry-Perot interferometer at a fixed angle of incidence of the radiant flux. The possibility of singlechannel and three-channel registration of spectral responses of the interferometer corresponding to RGB channels of a standard color matrix photodetector is shown. The variants of the structural schemes of the hyperspectral system are analyzed based on the existing compromises between the sensitivity of the system, its spectral selectivity, speed, accuracy, resolution, and complexity of implementation.

Electromagnetic 2D scanning micromirror fabricated with 3D printed polymer parts for LiDAR applications

In this research, an omnidirectional scanning micromirror fabricated using a three-dimensional (3D) printing process and manual assembly is presented. The core part of the scanning micromirror is printed with photocurable resin using vat polymerization based on digital light processing. Externally fabricated 6mm-diameter aluminum-coated silicon mirror plate, self-supported coils, and permanent magnets were assembled with the printed part to provide a reflective surface and electromagnetic actuation. Two types of devices with different spring shapes were designed and tested. Modal analyses were performed for each model with different magnet combinations in the design phase. To optimize the 3D printing process, resin mixtures with various mixing ratios were tested. An optical scan angle of 8.98° has been obtained for model #1 printed with an ABS-like resin at 309 Hz and an input current of 0.2 A rms . For model #2 printed with a 9:1 mixture of ABS-like resin and B9R-2-Black resin, an optical scan angle of 6.04° at 356 Hz an input current of 0.2 A rms has been obtained. Spiral scan patterns with various modulation depths were generated using model #1. • An omnidirectional scanning micromirror fabricated using a 3D printing process • Core part of the device is printed with vat polymerization using DLP • Resin mixtures with various mixing ratios were tested to optimize the fabrication • Two types of devices with different spring geometries were designed and tested

2D FPCB micromirror for scanning LIDAR

This paper presents a 2D flexible printed circuit board (FPCB) micromirror and a scanning 3D light detection and ranging (LIDAR) based on it by integrating the 2D FPCB micromirror with a commercially available single point LIDAR. The 2D FPCB micromirror retains the benefits of previously developed 1D FPCB micromirrors, i.e. large aperture and low cost while providing rotation of the mirror plate about two orthogonal axes to be able to scan a laser beam about both vertical and horizontal axes to achieve 2D scanning. One 2D FPCB micromirror is integrated with a single point LIDAR to achieve a 3D scanning LIDAR, which, in comparison to the previously developed 1D FPCB micromirror based 3D LIDAR, achieved more compact structure and easier fabrication/assembly due to no strict requirement on the alignment between two micromirrors while only one 2D micromirror rather than two 1D micromirrors used. Prototypes of the 2D FPCB micromirror and the 3D LIDAR based on it are fabricated and tested. The test results demonstrate that the 2D FPCB micromirror based 3D LIDAR achieved a volume reduction over the previous 1D FPCB micromirror based 3D LIDAR from 1042 cm3 to 754 cm3 with a field of view of 40°× 24° at 150 Hz horizontal scanning and 2 Hz vertical scanning.

Unsteady characteristics of lubricating oil in thrust bearing tank under different rotational speeds in pumped storage power station

Oil mist accumulation and leakage in hydropower generator bearings are common. However, they undermine not only the operational safety and stability of the generator but also the balance of living organisms downstream of rivers. Most studies on oil flow patterns are based on steady flow field simulations, which may result in potential errors particularly due to initial and unforeseen velocity increases. The unsteady multiphase flow numerical simulation method was used to calculate the motion behavior of lubricating oil in thrust bearing tanks at different rotating speeds. The variations in lubricating oil flow, pressure distribution characteristics, velocity, temperature, oil level, and vorticity at different times were obtained. The results show that the flow and pressure field distributions in an oil tank are mainly affected by the rotation of the thrust head and mirror plate and by the cooling circulation method, respectively. The lubricating oil motion becomes a function of gravity, centrifugal force, and Coriolis force. The oil surface of the volume fraction exhibited periodic motion around the tank and a climbing movement in the oil-retaining ring and oil slinger. The oil-retaining ring performs well at a speed of 500 rpm; however, minute oil droplets and mist rapidly spread in the tank due to violent oil fluctuations. Large vortices with periodic oil surfaces are also observed in regions with high turbulence intensity owing to shear and centrifugal forces. The method and framework presented can be used to optimize the structural design of thrust bearing assembly and reduce the formation of oil and gas mixtures.

Solar heat for biodiesel production in microchannel

The limited resources of fossil fuels and environmental pollution have led researchers to use renewable green fuels such as biodiesel. The important costs in the biodiesel production process are heating and raw materials. To reduce these costs, in this work, by transesterification of waste cooking oil in two T-shaped and helical glass microreactors, which are located inside the boxes equipped with mirror plates, the chamber temperature reached 63 °C and led to 90 % energy savings. The operating parameters of retention time were the catalyst concentration and the oil to methanol volume ratio. XRF, XRD, FTIR, and SEM tests were used to determine the elemental and morphological characteristics of KOH and CaO catalysts. This transesterification via methanol using the Box-Behnken method was designed which capable of producing biodiesel with a purity of 99.97 %. Under optimal conditions of 300 sec for CaO, a catalyst dose of 10 %, and the oil to methanol volume ratio 2 the purity was 99.97 % and for KOH at 420 sec, a catalyst dose of 3 %, and the oil to methanol volume ratio 2 the purity was 98.99 %. The performance of the two microreactors was evaluated under optimal conditions; the performance of the helical type was better due to its geometric structure and greater T-shape mixing. The results show that the use of the glass microreactor assisted by solar heat can significantly reduce the operating cost by increasing the mixing, shortening the residence time, and maintaining the reaction temperature in the range of 50–63 °C, resulting in a 90 % reduction in energy consumption.

GaN-based green resonant-cavity light-emitting diodes with Al mirror and copper plate.

In this Letter, GaN-based green resonant-cavity light-emitting diodes (RCLEDs) with a low-cost aluminum (Al) metal bottom mirror, a dielectric top mirror, and a copper (Cu) supporting plate were fabricated. The green-emitting epitaxial wafer was grown on a patterned sapphire substrate (PSS) to ensure high crystal quality (CQ). Laser lift-off (LLO) of the PSS and electrical plating of a Cu supporting plate were then carried out to realize the vertical device structure. The emission wavelength and full width at half maximum (FWHM) of the main emission peak of the device are ∼518 nm and 14 nm, respectively. Under the current density of 50 A/cm2, a relatively high light output power (LOP) of 11.1 mW can be obtained from the green RCLED. Moreover, when the current injection is 20 mA (8 A/cm2), the corresponding forward bias voltage is as low as ∼2.46 V. The reasons for the low operating voltage and high LOP can be attributed to the improvement of CQ, the release of residual compressive stress of the GaN-based epilayer due to the removal of PSS, and better heat dissipation properties of the Cu supporting plate.

A position sensing method for 2D scanning mirrors

This paper presents a cost-effective position sensing method for 2D scanning mirrors. The method uses only one 1D PSD (position sensitive detector) located at the backside of the 2D scanning mirror plate to retrieve the 2D rotation angle about the two axes separately in real time. Any 2D scanning mirror with resonant vibration about one axis and quasi-static vibration such as sinusoidal, saw tooth, triangular oscillation about the other axis can use this method. The two vibration axes are orthogonal to each other to form the scanning patterns, which are most desired in scanning 3D LiDAR systems. 3D scanning LiDAR is the targeted application for this research. The method uses timing measurement to measure the resonant vibration angle and Lagrange interpolation polynomial approximation to retrieve the quasi-static vibration angle. A prototype has been built to measure the 2D rotation angle of a 2D micromirror. The measured angle using the proposed method was verified using a 2D PSD. The largest errors for the vertical/horizontal angles were 9.6% and 5.36% respectively. The position sensing mechanism is also integrated to a scanning 2D micromirror based LiDAR system to demonstrate it as real time capability.

Modeling and Optimization of a Novel ScAlN-Based MEMS Scanning Mirror with Large Static and Dynamic Two-Axis Tilting Angles.

The piezoelectric MEMS (micro-electro-mechanical systems) scanning mirrors are in a great demand for numerous optoelectronic applications. However, the existing actuation strategies are severely limited for poor compatibility with CMOS process, non-linear control, insufficient mirror size and small angular travel. In this paper, a novel, particularly efficient ScAlN-based piezoelectric MEMS mirror with a pupil size of 10 mm is presented. The MEMS mirror consists of a reflection mirror plate, four meandering springs with mechanical rotation transformation, and eight right-angle trapezoidal actuators designed in Union Jack-shaped form. Theoretical modeling, simulations and comparative analysis have been investigated for optimizing two different device designs. For Device A with a 1 mm-length square mirror, the orthogonal and diagonal static tilting angles are ±36.2°@200 VDC and ±36.2°@180 VDC, respectively, and the dynamic tilting angles increases linearly with the driving voltage. Device B with a 10 mm-length square mirror provides the accessible tilting angles of ±36.0°@200 VDC and ±35.9°@180 VDC for horizontal and diagonal actuations, respectively. In the dynamic actuation regime, the orthogonal and diagonal tilting angles at 10 Hz are ±8.1°/Vpp and ±8.9°/Vpp, respectively. This work confirmed that the Union Jack-shaped arrangement of trapezoidal actuators is a promising option for designing powerful optical devices.

Transient TEHD Analysis of a Thrust Bearing Based on Two-Way Fluid-Solid-Thermal Interaction

Thrust bearing is a key component of hydroelectric generator and bears the axial load of the unit. During transient processes, such as start and stop of the unit, thrust bearing usually occurs wear phenomenon at pad surface, which affects the stable operation of the unit and reduces service life of the bearing. Based on two-way fluid-solid-thermal interaction, this paper did transient thermal-elastic-hydrodynamic (TEHD) analysis of a tilting pad thrust bearing under the pump mode. For the fluid region, the Reynolds equation and the viscosity-temperature equation are solved. For the solid region, transient heat conduction equation and basic thermal-elasticity equation are considered. The data transferred in the fluid-solid interface satisfy the fluid-solid-thermal interaction equation. The variation of the lubricant oil temperature, the oil film force, the pad surface inclination angle and axial velocity of pad and mirror plate are analysed, which provide theoretical basis for the design of bearing and the safe operation of the unit.