Zhongzhu Liang

Simulation of pressure distribution in a pyrophyllite high-pressure cell by finite-element analysis

The pressure-transmitting behavior and pressure distribution of a pyrophyllite cell in a cubic-anvil large volume high-pressure apparatus is investigated by finite-element analysis (FEA). The mechanical equations describing pyrophyllite under high pressure are given, which are composed of the Drucker–Prager criterion and a linear equation of state. The related material parameters such as cohesive strength, angle of internal friction etc. are experimentally measured. The FEA simulation includes the non-uniformity deviatoric stress caused by plastic deformation and the isotropy hydrostatic pressure of the pyrophyllite cell caused by volume compression. The results demonstrate that, in such a pyrophyllite cell, almost 90{%} of the pressure is isotropy hydrostatic pressure, and the pressure gradient mainly arise from non-uniform deviatoric stresses. Simulated data are displayed using the contour and the path plots.

Finite element analysis of high-pressure anvils according to the principle of lateral support

In order to extend the lifetime of an anvil made of tungsten carbide used in a large volume cubic high-pressure apparatus (CHPA), we analyzed the properties of an anvil with different magnitudes of interference, matching the steel supporting ring under high pressure using finite element method. It is found that the peak value and distribution of the von Mises stress does not change obviously when the magnitude of interference is smaller than 0.3mm. When the magnitude of interference reaches 0.3mm, the peak value of the von Mises stress and its distribution changes substantially, due to which the performance of the anvil can be significantly affected. Thus, the magnitude of interference ought to be between 0.1 and 0.25mm. The simulated results have been approved in many high-pressure experiments in CHPA.

Design and fabrication of a micro-optic switch

In this paper, a polyimide cantilever micro-optic switch of electromagnetic actuation is studied. The model of the electromagnetic actuation is proposed and simulated using finite element method. The best efficiency of electromagnetic force for switching operations is obtained and the parameters of the coil and magnet are determined. During the practical fabrication, the thick resist patterning and electroplating technology is employed to fabricate the electromagnetic actuation. Both the theoretical and experimental results indicate that the balanceable distance of the polyimide cantilever for implementing optical switches is about 1.28 mm with 0.4 A current pulse input, The final experimental results of optical performance for the fabricated micro-optic 1 x 4 switch include the switching time of about 20 ms and the insertion loss of about 0.73 dB.

Theoretical and experimental analysis of AlGaInP micro-LED array with square-circle anode

An array of 320 × 240 micro-light-emitting diodes (micro-LEDs) based on an AlGaInP epitaxial wafer and with a unit size of 100 µm×100 µm was designed and fabricated. The optimum width of the isolation groove between adjacent light-emitting units was determined based on a compromise between full isolation of each LED and maximization of the light emitting area, and was found to be 20 µm. The grooves were filled with a mixed Si granule-polyurethane composite medium, because this type of insulating material can reflect part of the emitted light from the sidewall to the window layer in each light-emitting unit, and could thus improve lighting output efficiency. The 10-µm-wide square-circle anode was designed to increase the light emitting area while simultaneously being simple to fabricate. The device current used was in the 0.42–1.06 mA range to guarantee internal quantum efficiency of more than 85%, with a corresponding voltage range of 2–2.3 V. The layered temperature distribution in a single unit was simulated under a drive voltage of 2.2 V, and the maximum device temperature was 341 K. The micro-opto-electro-mechanical systems (MOEMS) technology-based fabrication process, experimental images of the device and device test results are presented here.

Micro assembled Fourier transform spectrometer

With the trend of minimization of Fourier transform spectrometer (FTS) which is particularly pronounced in many applications, a model of a micro FTS with no moving parts is proposed and analyzed. During analyzng, the gradients which mainly introduce phase error are accounted. Based on these assumptions and the improved Mertz phase correcting method, the spectrum of signal is simulated with real extended light source. The resolution can be up to 3.43nm@800nm, with high signal-to-noise ratio (SNR) limiting resolving ability 6.8dB. In addition, the fabrication method of components are illuminated and demonstrated, which can not only make it bear some advantages over conventional micro dispersive spectrometers, but also afford some new concepts on the design of spectrometers with improved performance.

Design of spatio-temporally modulated static infrared imaging Fourier transform spectrometer

A novel static medium wave infrared (MWIR) imaging Fourier transform spectrometer (IFTS) is conceptually proposed and experimentally demonstrated. In this system, the moving mirror in traditional temporally modulated IFTS is replaced by multi-step micro-mirrors to realize the static design. Compared with the traditional spatially modulated IFTS, they have no slit system and are superior with larger luminous flux and higher energy efficiency. The use of the multi-step micro-mirrors can also make the system compact and light.

Design and fabrication of step mirrors used in space-modulated Fourier transform infrared spectrometer

A model of miniaturized space-modulated Fourier transform infrared spectrometer (FTIR) is given. The two step mirrors as the key components are designed and a lithography-electroplating technique used to fabricate the small step mirror is proposed. We analyze the effect of the experiment results resulted from fabricating technics on the recovery spectrum in theory, and demonstrate that the lithography-electroplating technique is an effective method to fabricate the step mirror, which make miniaturized FTIR realized. We believe that the performances of FTIR can be better realized by optimizing experimental conditions to make this fabricating method more attractive.

Spectrum constructing with nonuniform samples using least-squares approximation by cosine polynomials

The least-squares approximation of cosine polynomials is used to construct the spectrum from the simulated nonuniform samples of the interferogram given by a step-mirror-based static Fourier transform spectrometer. Numerical and experimental results show the stability of the algorithm and a spectrum-constructing error of 0.03%.

Thermal Analysis and Design of AlGaInP-based Light Emitting Diode Arrays

LED arrays with pixel numbers of 3×3, 4×4, and 5×5 have been studied in this paper in order to enhance the optical output power and decrease heat dissipation of an AlGaInP-based light emitting diode display device (pixel size of 280×280 μm) fabricated by micro-opto-electro-mechanical systems. Simulation results showed that the thermal resistances of the 3×3, 4×4, 5×5 arrays were 52°C/W, 69.7°C/W, and 84.3°C/W. The junction temperature was calculated by the peak wavelength shift method, which showed that the maximum value appears at the center pixel due to thermal crosstalk from neighboring pixels. The central temperature would be minimized with 40 μm pixel pitch and 150 μm substrate thickness as calculated by thermal modeling using finite element analysis. The modeling can be used to optimize parameters of highly integrated AlGaInP-based LED arrays fabricated by micro-opto-electro-mechanical systems technology.

Heat dissipation analysis of bendable AlGaInP micro-LED arrays

A strategy for fabricating bendable AlGaInP light emitting diode (LED) arrays is presented in this paper. Sample LED arrays with 8 × 8 pixels were fabricated and subjected to bending. Bending only weakly affected the light output power and the current–voltage characteristics of the arrays. LED arrays suffer from a thermal problem owing to the energy loss during the electrical-to-optical energy conversion. We have designed a three-dimensional heat conduction model for analyzing the effect of the polymer substrate, the configuration of pixels, and the micro-structure on heat dissipation in bendable LED arrays. Thermal conductivity of the polymer substrate critically affected the heat dissipation, suggesting that the substrate thickness should be in the 500–1000 μm range. A larger pixel distance yielded more distributed heat sources and more uniform temperature distribution. Micro-structured polymer substrates yielded lower temperature, especially for the fins array micro-structure. Based on enhancing the po...