The spectral emissivity and transmissivity of zinc sulphide (ZnS) infrared windows in the spectral region from 2 to 12 μm and temperature range from 20 to 700°C is measured by a facility built at the Harbin Institute of Technology (HIT). The facility is based on the integrating-sphere reflectometry. Measurements have been performed on two samples made of ZnS. The results measured at 20°C are in good agreement with those obtained by the method of radiant energy comparison using a Fourier transform infrared spectrometer. Emissivity measurements performed with this facility present an uncertainty of 5.5% (cover factor=2 ).
The absorption spectra of ethylene (C2H4) located at v5+v9 band near 1626nm involve some strong peaks that are suitable for trace gas concentration detection. They are interference free from other abundant molecules that are normally present in the atmosphere. An ethylene analysis system has been developed based on the tunable diode laser absorption spectroscopy. The high resolution transmission of ethylene near 1626nm has been measured by this system under different concentration. The severe overlapping between neighboring spectral lines of ethylene is observed and they cannot be separated with each other easily under atmospheric pressure and room temperature, so a multi-peaks spectrum recognition method is proposed to separate the ethylene spectrum from other interference gas while the ethylene concentration is ultra low. A mixture of high concentration methane, low concentration ethylene with air is used to evaluate the recognition efficiency. The result shows that the ethylene line can be abstract from strong background interference using multi-peaks spectrum recognition method and the accuracy of concentration measurement can reach about 5% comparing with a mass flow meter.
The emissivity is a key parameter to measure the surface temperature of materials in the radiation thermometry. In this paper, the surface emissivity of metallic substrates is measured by the multi-wavelength emissivity measurement apparatus developed by the Harbin Institute of Technology (HIT). The measuring principle of this apparatus is based on the energy comparison. Several radiation thermometers, whose emissivity coefficients corrected by the measured emissivity from this apparatus, are used to measure the surface temperature of stainless steel substrates. The temperature values measured by means of radiation thermometry are compared to those measured by means of contact thermometry. The relative error between the two means is less than 2% at temperatures from 700K to 1300K, it suggests that the emissivity of stainless steel substrate measured by the multi-wavelength emissivity measurement apparatus are accurate and reliable. Emissivity measurements performed with this apparatus present an uncertainty of 5.9% (cover factor=2).
According to radiation temperature measurement theory, the key of temperature measurement is to choose the appropriate temperature model, which depends on the type of measured material. So how to identify the material type is significant to measure its surface temperature. Different materials have different spectral characters at the same temperature. In this paper, a method based on spectrum analysis is proposed to identify material. The spectrum of four kinds of materials is measured using Fourier transform infrared spectrometer (FTIR) at the same temperature 873K. The peak values extracted from each spectrum are used to train the identification algorithm. Then one material is chosen from the measured materials to verify the identification algorithm if the type of material can be identified. The experimental results suggest that the new method based on spectrum analyses can accurately identify the type of material.
CO2 gas bubbles have a great effect on the &mgr;DMFC (Micro Direct Methanol Fuel Cell) as the anode resultants.
Visualization technique is one of the most important tools to study the formation, movement, and removal of CO2 gas
bubbles. This paper presents an air-breathing micro direct methanol fuel cell made of PMMA for the visualization
research. Four types of flow fields are fabricated in the anode plates. Different from the traditional &mgr;DMFCs, the
stainless steel mesh is adopted as the current collector. The observation and study of CO2 bubbles behavior show that the
quantities and bulks of CO2 gas bubbles increased as the current densities became higher. In addition, anode methanol
solution flow rates and cell orientations also have complicated influence on the &mgr;DMFC performance.
We designed and fabricated a new portable passive DMFC stack with its volume significantly reduced. Its high
efficiency and load regulation performance were also demonstrated through experiments, and its stability seemed to be
very good. We achieved a maximum power density of 3.9mW/cm2 with a 2M methanol concentration under ambient
conditions. This performance is better than that of a conventional DMFC. The volume of the 10-cell series connection
DMFC stack is only 42mm x 42mm x 40mm. Due to its stable performance and easy fabrication, this structure is believed
to be applicable for portable small-scale DMFC stack.
This paper presents a design configuration of silicon-based micro direct methanol fuel cell (DMFC) stack in a planar
array. The integrated series connection is oriented in a "flip-flop" configuration with electrical interconnections made by
thin-film metal layers that coat the flow channels etched in the silicon substrate. The configuration features small
connection space and low contact resistance. The MEMS fabrication process was utilized to fabricate the silicon plates
of DMFC stack. This DMFC stack with an active area of 64mm x 11mm was characterized at room temperature and
normal atmosphere. Experimental results show that the prototype stack is able to generate an open-circuit voltage of
2.7V and a maximum power density of 2.2mW/cm2, which demonstrate the feasibility of this new DMFC stack
Micromachined accelerometers are one of the most widely used MEMS transducers. The theory of force-balance MEMS
accelerometers is presented in the thesis. Meanwhile the paper accomplishes the system-level simulation and analysis of
the force-balance MEMS accelerometer with different structure parameters. Based on the analysis, the conclusion is that
the parameters of folded-spring (such as the length of the beam, the width of the beam) especially influence the output
The microfabrication and performance of a micro direct methanol fuel cell (μDMFC) by silicon processes are presented in this paper. Using the silicon micromachining techniques, including thermal oxidation, optical lithography, wet etching, silicon anodization, physical vapor deposition, electroless plating, laser beams cauterization, and anodic bonding, we have successfully made single μDMFC as small as 10mmx8mmx3mm. The main reason for the use of MEMS technology is the prospective potential for miniaturization and economical mass production of micro direct methanol fuel cells. The double side of silicon wafer deep wet etching was employed for the gas channels and fuel chamber preparation. The formation of porous silicon (PS) layers for electrode supports by electrochemical process is the key technologies to improve the MEMS-based μDMFC. The method of catalyst deposition reported here differs from previous work in the specific method of electroless plating Pt-deposition and platinum with ruthenium (Pt-Ru) co-deposition on the porous silicon substrates. The power density of the single cell reached only 2.5mW/cm2 lower than that single cell with traditional MEA (4.9mW/cm2) at the same operation conditions, but further improved performance of the μDMFC with the electro-catalytic electrodes is expectant. Moreover, using the MEMS technology makes the batch fabrication of μDMFC much easier and can reduce the usage of rare metals.
The design and fabrication for a novel silicon-based micro direct methanol fuel cell (μ-DMFC) of 0.64cm2 active area on <100> silicon wafer are described in this paper. The novelty of the DMFC structure is that the anodic micro channels arranged in the asymmetric mesh have been fabricated, and the first objective of the experimental trials is to verify the feasibility of the novel structure on the basis of MEMS technology. The effect of different operating parameters on μ-DMFC performances is experimentally studied for two different flow field configurations (grid and spiral). Preliminary testing results show that this novel μ-DMFC demonstrates the better performances using 2M methanol feed at room
temperature, and the output characteristics of μ-DMFC with the grid flow field exceed the one with the spiral flow field. Results have demonstrated a maximum output power density of about 2.3mW/cm2 using 2M methanol solution.
The damping effects of MEMS inertial devices like micro accelerometers is studied. The damping analysis governing equation, the Reynolds equation, is the fundamental equation in this work. For small amplitude sinusoidal motions, which are governed by the linearized form of the Reynolds equation, both damping and compressibility effects are modeled numerically. Analytical solutions of the linearized Reynolds equation for micro inertial structures with various simple geometries are summarized. A procedure of solving the linearized model using typical commercial finite element analysis software is demonstrated. A numerical example of dynamical macromodel for a capacitive accelerometer indicates that viscous damping dominates at the dynamic characteristic of inertial devices. The theory and method of estimating damping effects for inertial devices with small amplitude motions are also presented. The theory is derived from the structural dynamic modal analysis and the simulation of the linearized Reynolds equation. The theoretical damping analysis equation for inertial microstructures is derived for the application of the small deflections. Simulation analysis can be used to compute the damping including the squeeze film and slip film cases. The method is applicable for general conditions, and makes it easy to make the dynamic lumped simulation model. It is useful at the beginning of the design of MEMS inertial devices affected by the damping effect.
In this paper, we report a high power of cryogenic cooling Tm(8 at %), Ho(1.4 at %):YLF dual end pumped by two fiber coupled laser diodes at 792nm. Each pumping laser head delivers 15W power in an inner fiber core area of 0.4mm and numerical number of 0.3. The highest continuous-wave (cw) power of 10.2W at 2.051μm is attained under pumping power of 30W, corresponding to optical-optical conversion efficiency of 33%, and the slope efficiency is greater than 36%. The maximum acousto-optical Q-switched quasi-continuous wave output power is 9.2 W at pulse repetition frequency of 10kHz, corresponding to greater than 90% extraction efficiency in the full-width half-maximum pulse width of 34ns.
This paper report the A-O Q-switched LD end pumped 8% Tm, 1.4%Ho:YLF laser. The fiber-coupled pump laser deliver maximum 15W around 792nm At 10 KHz pulse repetition frequencies (PRF), The average output power of 4.1 W, the pulse width of 32ns and peak power of 0.012MW at 2.05um were achieved. The pulse fluctuation is less than ± 2%. The pulse amplitude instability at last higher rate equation was analyzed.
This paper presents a novel method for the fabrication of micro electromagnetic relays based on MEMS technology. Fabrication process and the partial test results are given in detail. Th emian advantages of the micro relay include small volume, low weight, rapid response, and longevity. In addition, it takes the performance between the common electromagnetic relay and the solid-state one, thus the proposed micro relay may be promising in the future.