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.     

EHD flow in a wide electrode spacing spike–plate electrostatic precipitator under positive polarity

In this work, results of two- and three-dimensional particle image velocimetry (PIV) measurements of the flow velocity fields in a wide spacing spike–plate electrostatic precipitator (ESP) under positive polarity are presented. A DC voltage of positive polarity (up to 28 kV) was applied to the spike electrode. The average gas flow velocity was 0.6 m/s. The PIV measurements were carried out in four planes perpendicular to the plate electrodes. Three parallel planes passed along the ESP while one plane passed across the ESP duct. The results show that electrohydrodynamic (EHD) secondary flow with relatively strong vortices exist in the ESP. The EHD secondary flow pattern depends on applied voltage and measuring plane position in respect to the spike tip. The strongest vortices occur in the plane passing through the tip of the upstream-directed spike. These relatively strong EHD vortices may hinder collection of the particles in the diameter range of 0.1–1 μm in the wide electrode spacing spike–plate ESPs.     

Particle-size sorting system of lunar regolith using electrostatic traveling wave

A particle-size sorting system of lunar regolith using an electrostatic traveling wave is developed for In-Situ Resource Utilization on the Moon to extract indispensable resources from the regolith and realize long-term exploration. The regolith is sorted by utilizing a balance between the electrostatic and gravitational forces, which are determined depending on particle size, in vacuum conditions where the particles are not subjected to air drag. In this study, the effect of particle charge on the particle motion is confirmed by conducting model experiments and numerical calculations based on the distinct element method. In addition, it was experimentally demonstrated that particles less than approximately 20 μm in diameter were efficiently separated from the bulk of a lunar regolith simulant FJS-1 in a vacuum condition (∼1.5 × 10⁻² Pa), and the performance of the size sorting system on the Moon was predicted by the numerical calculations. The system utilizes only the electrostatic force, and it does not require any gas, liquid, or mechanical moving parts.     

Design and fabrication of electrostatic micro-cantilever array as audible frequency generator

In assistive technologies involving voice communication, an audio signal with specific shape is needed. In this regard, the design and fabrication of an electrostatic cantilever array is proposed. An array of four metallic micro-cantilevers with dimensions 650 μm × 200 μm × 0.3 μm is fabricated on the silicon substrate. The working principle is based on the electrostatic effect generated due to a conductive path applied between the electrodes. The results are taken from zinc oxide (ZnO) piezoelectric thin film that allows making contact with the vibrating cantilevers on a specified applied input impulse signals. The results demonstrated the switching action of the cantilevers that depends on the polarity of the input pulses. The results obtained are compared with the FEM based (COMSOL Multiphysics) model that is designed and analyzed prior to the experiment. Further, the experimental results showed a good agreement with the predicted values calculated by the simulated model for the input impulse signal applied synchronously to all the micro-cantilevers. However, for asynchronous actuation mode, the result of the as-fabricated device showed a variation than the simulated results. The vibrations are generated periodically from all the cantilevers and the output shows the resultant signals that are very much in the audible frequency range.     

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.     

Electrostatic precipitation of airborne bio-aerosols

In this study, we report electrostatic precipitation of Escherichia Coli- and Yeast-aerosols in air. The aerosol size distribution and their electrostatic precipitation efficiency are monitored by using an Electrical Low Pressure Impactor. The results indicate that the E. Coil-aerosols are mainly around 0.8 μm in aerodynamic diameter and the Yeast-aerosols are in the range of 1.3–3.1 μm, respectively. At an average electric field of 1 kV/cm, the precipitation efficiencies of E. Coli- and Yeast-aerosols are about 31% and 5%, respectively. They rise to 79% and 71% when the field strength rises to 7.5 kV/cm. For H₂O-aerosols, the diameter is about 0.02 μm and the efficiency is almost 100% under the same condition.     

Enhanced output power for InGaAlP LEDs by contact-transferred and mask-embedded lithography

The authors applied a simple, low-cost, mass-producible contact-transferred and mask-embedded lithography (CMEL) to texture p-GaP window layer for the fabrication of InGaAlP light-emitting diodes (LEDs) emitting at 612 nm. Under 20 mA current injection, it was found that forward voltages were 2.25, 2.24 and 2.25 V for CMEL-400 nm LED, CMEL-2 μm LED and the conventional LED without CMEL, respectively. It was also found that the 20 mA output powers were 1.43, 1.28 and 1.16 mW for CMEL-400 nm LED, CMEL-2 μm LED and the conventional LED without CMEL, respectively.     

Super-resolution imaging in digital holography by using dynamic grating with a spatial light modulator

A super-resolution imaging method using dynamic grating based on liquid-crystal spatial light modulator (SLM) is developed to improve the resolution of a digital holographic system. The one-dimensional amplitude cosine grating is loaded on the SLM, which is placed between the object and hologram plane in order to collect more high-frequency components towards CCD plane. The point spread function of the system is given to confirm the separation condition of reconstructed images for multiple diffraction orders. The simulation and experiments are carried out for a standard resolution test target as a sample, which confirms that the imaging resolution is improved from 55.7 μm to 31.3 μm compared with traditional lensless Fourier transform digital holography. The unique advantage of the proposed method is that the period of the grating can be programmably adjusted according to the separation condition.     

Effect of particle size in fluidization of polyethylene particle mixtures on the extent of bed electrification and wall coating

In this work the effects of polyethylene fluidizing particle size (smaller than 400 μm) on the degree of fluidized bed electrification and wall coating formation was studied. Experiments were conducted in a stainless steel, 0.15 m diameter column, under ambient conditions. Polyethylene resin as received (20–1500 μm) as well as mono-sized and binary mixture of large (600–710 μm) and small (212–300 & 300–425 μm) polyethylene particles were fluidized while their mass, net specific charge and size distribution in the bulk of the bed and the wall coating were measured. For the binary mixture the fraction of the small particles examined were 5%–10% and 20%. The extent of wall coating varied between different cases tested with the mono-sized large particles resulting in the most amount coating. It was found that as the fraction of the small particles in the binary mixture was increased, these particles formed majority of the wall coating. At the mass fraction of 20%, the extent of wall coating and its net specific charge were similar to that of resin as received. Overall results implied that the magnitude of the smaller sized particles within the resin played an important role in the degree of particles electrostatic charging and the extent of the particles adhesion to the column wall. Small particles were found to generate a much larger net specific charge which although resulted in them coating the column wall but prevented the coating layer growth.     

Self-sustaining discharges in needle-to-plane geometry with hundreds of microns electrode gaps

Atmospheric pressure needle-to-plane discharges have been explored experimentally in electrode gaps from 100 μm to 400 μm. These discharges can be self-sustained and follow the form of existing empirical formulae describing the current-voltage characteristics of corona discharge. The discharge can also be self-sustained by its lower sustaining voltage applied between the two electrodes once it is ignited by the initial high output voltage from power supply. The experiments of charging aerosol particles by the self-sustaining discharge operating with a lowered power have shown that for particles with a diameter of 46 nm, the charging efficiency attained 43.6%.     

Fiber-based chromatic confocal microscope with Gaussian fitting method

The chromatic confocal microscopy is an effective method for displacement measurement. However, with relatively low detection efficiency, chromatic confocal systems from previous studies suffer from either a limited measuring range or an unsatisfying resolution. In this paper, a novel chromatic confocal system is proposed based on optical fiber with large diameter that is specifically chosen to allow more light to be detected, thus greatly improving the detection efficiency of the system. To accurately locate the peak wavelength of the recorded spectrum, four data processing methods are proposed and compared, within which the Gaussian fitting model is considered best for the system. A series of experiments are done to verify the feasibility, resolution and stability of the system. An applicable measuring range of 600 μm is discovered with a highly linear range of 400 μm. The system has a high resolution close to 0.10 μm with satisfying stability shown by a long-term displacement standard deviation of 0.16 μm.     

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.     

An effective thermal conductance tuning mechanism for uncooled microbolometers

With the increasing demand on infrared (IR) detectors for imaging harsh environment processes, widening the application range of uncooled microbolometer arrays has become an important research area. An efficient way of increasing this range is tuning the thermal conductance of the microbolometer array using electrostatic actuation, which is usually achieved by directly applying an actuation voltage to the substrate. However, this method does not allow pixel-by-pixel actuation, limiting the tunability. In this paper, we present a new method of actuation which uses the micromirror located below the microbolometer as the actuation terminal. We demonstrate that using micromirror actuation, the thermal conductance can be tuned by a factor of three. An analytical model to calculate the thermal conductance of this new type of microbolometer is presented. Results of the model are compared to finite element simulations and experimental measurements on a test structure fabricated for this purpose, showing good agreement. The new tuning mechanism provides a fairly linear thermal conductance tunability, thus making it a promising thermal conductance controlling mechanism for adaptive IR detectors.     

An experimental study of the relative response of plastic scintillators to photons and beta particles

A scintillation counting system has been constructed with the use of BC-400 and EJ-212 series plastic scintillators along with a subminiature photomultiplier tube to investigate the effect of increasing plastic scintillator thickness on system-integrated counts. Measurements have been carried out using four different gamma sources with different energies ranging from 6 keV to 1.332 MeV and a Ni-63 beta source with a maximum energy of 66 keV. Scintillator thicknesses ranged from 10 μm to 2500 μm. The response of the system was determined by measuring the integrated counts as a function of scintillator thickness. These experimental findings were used to empirically determine the optimum thickness of scintillator material with which to build a low energy beta detector which discriminates against high energy gamma photons in a mixed radiation field environment.     

Improvement of the minimum detectable energy of a recoil-proton spectrometer based on a silicon telescope

A recoil-proton spectrometer based on a monolithic silicon telescope coupled to a polyethylene converter was recently proposed and discussed in the literature. The device consists of a ΔE and an E-stage detector (about 2 μm and 500 μm in thickness, respectively) made out of a single silicon wafer and separated by a highly-doped layer acting as a common electrode.The detection system allowed continuous neutron spectra to be measured down to about 400 keV by discriminating against the contribution of low-LET radiation generated by photons from the distribution of the energy deposited in the E stage. This discrimination was carried out by selecting detected particles, event-by-event, with a ΔE ? E correlation. At neutron energies lower than 400 keV recoil-protons cannot reach the E stage owing to the thickness of the ΔE stage and therefore the discrimination failed.In order to further reduce the minimum detectable energy, an improved detection system, which also accounts for the energy deposited by recoil-protons in the ΔE stage, was studied and tested. The new set-up permits the total energy deposited in the telescope to be measured directly by collecting the charge carriers, generated in both stages, at the deep common electrode. The capability of reproducing continuous neutron spectra was also verified by irradiating the improved set-up with neutrons generated by protons striking a thick beryllium target at INFN – Laboratori Nazionali di Legnaro (Legnaro, Italy). The agreement of the unfolded spectra with literature data was satisfactory at energies higher than about 200 keV.     

Micromirror with large-tilting angle using Fe-based metallic glass

For enhancing the micromirror properties like tilting angle and stability during actuation, Fe-based metallic glass (MG) was applied for torsion bar material. A micromirror with mirror-plate diameter of 900?μm and torsion bar dimensions length 250?μm, width 30?μm and thickness 2.5?μm was chosen for the tilting angle tests, which were performed by permanent magnets and electromagnet setup. An extremely large tilting angle of over -270° was obtained from an activation test by permanent magnet that has approximately 0.2?T of magnetic strength. A large mechanical tilting angle of over -70° was obtained by applying approximately 1.1?mT to the mirror when 93?mAwas applied to solenoid setup. The large-tilting angle of the micromirror is due to the torsion bar, which was fabricated with Fe-based MG thin film that has large elastic strain limit, fracture toughness, and excellent magnetic property.     

Submicron particles trajectory and collection efficiency in a miniature planar DBD-ESP: Theoretical model and experimental validation

In this paper, the collection efficiency of a plane-to-plane dielectric barrier discharge electrostatic precipitator is investigated experimentally and theoretically using a new model. A parametric study is carried out to evaluate the effects of the applied voltage amplitude and frequency on submicron particles motion and collection within the size range from 0.18 to 0.7 μm. Results show that the amplitude of the particles oscillatory motion increases with the voltage and the particles diameter which increase their collection. The collection efficiency decreases at low frequencies because of the low charge of particles and at high frequencies because of particles fast oscillation.     

EHD flow measured by 3D PIV in a narrow electrostatic precipitator with longitudinal-to-flow wire electrode and smooth or flocking grounded plane electrode

In this work, results of three-dimensional (3D) Particle Image Velocimetry (PIV) measurements of the electrohydrodynamic (EHD) flow velocity fields in a narrow electrostatic precipitator (ESP) with a longitudinal-to-flow placed wire electrode are presented. The ESP was a narrow transparent acrylic box (90 mm×30 mm×30 mm). The electrode set consisted of a single wire discharge electrode and two plane collecting electrodes. Either two smooth stainless-steel plates or two stainless-steel plane meshes with nylon flocks were used as the collecting electrodes. The 3D PIV measurements were carried out in two parallel planes, placed longitudinally to the flow duct. The positive DC voltage of up to 9.5 kV was applied to the wire electrode through a 10 MΩ resistor. The collecting electrodes were grounded. The measurements were carried out at a primary flow velocity of 0.5 m/s. Obtained results show that the flow patterns for the smooth-plate electrodes and for the flocking plane electrodes are similar in the bulk of the flow. However, the flow velocities near the flocking plane electrodes are much lower than those near the smooth-plate electrodes. This is a beneficial phenomenon, because the lower the flow near the collecting electrodes, the lower re-entrainment of the particles deposited on the collecting electrodes occurs.     

Multi-object spectrometer with micromirror array

We have designed and built a multi-object spectrometer with micromirror array as a reconfigurable entrance aperture. In interactive mode, the instrument makes it possible to record both the hyperspectrum of the studied region as a whole and also sets of spectra of arbitrarily specified fragments. In this case, a spectral resolution of 0.8 nm or better is provided in the subranges 400–670 nm and 650–900 nm, aperture ratio of the spectroscopic channel at least 1:5. The analytical characteristics of the instrument make it possible to use it to solve a broad range of problems in modern multi-object spectroscopy and hyperspectroscopy.     

Heat affected zone in aluminum single crystals submitted to femtosecond laser irradiations

An experimental procedure is developed to quantify the radial dimension of the heat affected zone (HAZ) in metals submitted to laser pulses. A cube oriented aluminum single crystal is highly deformed by plane strain compression, then micro-drilled by 200 fs or 8 ns laser pulses, and finally analyzed by the electron back scattering diffraction technique. Recrystallized and recovered zones are observed as signatures of the HAZ. A typical value of 1.5 μm is found in the femtosecond regime of illumination, whereas for nanosecond pulses a value of 25 μm is measured. These results are in accordance with previous experiments and numerical simulations.