Toward a Flying MEMS Robot

The work in this thesis includes the design, modeling, and testing of motors and rotor blades to be used on a millimeter-scale helicopter style flying micro air vehicle (MAV). Three different types of motor designs were developed and tested, which included circular scratch drives, electrostatic motors, and comb drive resonators. Six different rotor designs were tested; five used residual stress while one design used photoresist to act as a hinge to achieve rotor blade deflection. Two key parameters of performance were used to evaluate the motor and rotor blade designs: the frequency of motor rotation and the angle of deflection achieved in the rotor blades. One successful design utilized a scratch drive motor with four attached rotor blades to try to achieve lift. While the device rotated successfully, the rotational frequency was insufficient to achieve lift-off. The electrostatic motor designs proved to be a challenge, only briefly moving before shorting out; nonetheless, lessons were learned. Comb drive designs operated over a wide range of high frequencies, lending them to be a promising method of turning a rotary MAV. None of the fabricated devices were able to achieve lift, due to insufficient rotational rates and low angles of attack on the rotor blades. With slight modifications to the current designs, the required rotational rates and rotor blade deflections would yield a viable MAV. The ultimate objective of this effort was to create an autonomous MAV on the millimeter scale, able to sense and act upon targets in its environment. Such a craft would be virtually undetectable, stealthily maneuvering and capable of precision engagement

Study of MEMS Silicon-based Nuclear Microbattery

传统的能源已经不能满足MEMS技术微型化、集成化的趋势对微能源提出的新需求。微型核电池由于具有能量密度高、寿命长、易于微型化和易于集成等优点，已经引起了国内外的广泛关注。然而，目前制备的微型核电池能量转换效率普遍偏低，关于这方面的理论研究也不多见。本文正是基于这个出发点，在理论和实验的基础上对如何提高微型核电池能量转换效率做了若干研究。 本文首先对β辐生伏特微型核电池进行理论分析，建立了单晶硅p-n结微型核电池的一维模型，通过求解少数载流子的连续性方程得出了辐生电流密度的表达式；然后将Ni-63、H-3和Pm-147三种放射性同位素的β谱引入数值计算和模拟，分别研究了单晶硅n+-p和p+-n...Traditional energy sources cannot meet the new demands raised by the trend of integration and miniaturization of MEMS technology. Nuclear microbattery has attracted wide attention due to its advantages of high density, long life, easy miniaturization and easy integration. However, the energy conversion efficiency of current nuclear microbatteries is generally low and theoretical studies in this ar...学位：工学硕士院系专业：物理与机电工程学院物理学系_微电子学与固体电子学学号：1982008115303

The influence of pore size on the indentation behavior of metallic nanoporous materials : a molecular dynamics study

In general, the influence of pore size is not considered when determining the Young's modulus of nanoporous materials. Here, we demonstrate that the pore size needs to be taken into account to properly assess the mechanical properties of these materials. Molecular Dynamics simulations of spherical indentation experiments on single crystalline nanoporous Cu have been undertaken in systems with: (i) a constant degree of porosity and variable pore diameter; and (ii) a constant pore diameter and variable porosity degree. The classical Gibson and Ashby expression relating Young's modulus with the relative density of the nanoporous metal is modified to include the influence of the pore size. The simulations reveal that, for a fixed porosity degree, the mechanical behavior of materials with smaller pores differs more significantly from the behavior of the bulk, fully dense counterpart. This effect is ascribed to the increase of the overall surface area as the pore size is reduced, together with the reduced coordination number of the atoms located at the pores edges

InGaP electron spectrometer for high temperature environments

In this work, a 200 μm diameter InGaP (GaInP) p+-i-n+ mesa photodiode was studied across the temperature range 100 °C to 20 °C for the development of a temperature-tolerant electron spectrometer. The depletion layer thickness of the InGaP device was 5 μm. The performance of the InGaP detector was analysed under dark conditions and then under the illumination of a 183 MBq 63Ni radioisotope beta particle source. The InGaP photodiode was connected to a custom-made low-noise charge-sensitive preamplifier to realise a particle counting electron spectrometer. Beta spectra were collected at temperatures up to 100 °C with the InGaP device reverse biased at 5 V. The spectrum accumulated at 20 °C was compared with the spectrum predicted using Monte Carlo simulations; good agreement was found between the predicted and experimental spectra. The work is of importance for the development of electron spectrometers that can be used for planetary and space science missions to environments of high temperature or extreme radiation (e.g. Mercury, Jupiter’s moon Europa, near-Sun comets), as well as terrestrial applications

Fundamental development of a thermophotovoltaic device using porous media combustion

Porous media combustion (PMC) is characterised by intense heat exchange from the combustion gases to the solid media, enabling higher temperatures at the outer surface of the solid matrix, which makes it suitable for coupling with thermophotovoltaic (TPV) systems. This research, for the first time, experimentally and numerically investigates how to regulate combustion and the radiative emission of a porous media matrix to achieve stable spectral control for an active TPV system. As such, this thesis provides a series of systematic steps towards developing a fundamental understanding of a PMC-TPV system, including: a flame stability analysis, combustor design optimisation, radiative control, PV cell characterisation, and system-level optimisation. A radiant reflector was found to shift the stable flame regime and increase the radiant efficiency to 63% at an operating temperature of 1356 C. Additionally, a 24-cell gallium antimonide (GaSb) array, which was attached to a heat sink to prevent overheating, was used to harvest the radiant emission from a hot (>1200 C), yttria-stabilised zirconia/alumina composite (YZA) ceramic foam (both erbia-coated and uncoated). A low-cost erbia (Er2O3) coating on a novel porous media combustion-based thermophotovoltaic (PMC-TPV) reactor was shown to achieve continuous combined heat and power generation. The results indicate that the erbia coating on the YZA foam increased performance, achieving a maximum in-band emission fraction of 25.4% at a firing rate of 1300 kW/m2 (i.e. a 10% of increase compared to the non-coated configuration), which provides a temperature of 1285 C and a 1 Watt electrical output. An electrical model of GaSb cells shows that an undamaged cell array could reach an output power 2.28 W for this configuration. A system-level simulation confirmed that the GaSb-based PMC-TPV system is the most cost-effective option relative to other cell types. Overall, this work has identified promising new directions for how the fields of PMC and PV can be brought together with respect to choosing porous materials, the optical properties of the components (i.e. emitter coatings and filters), and the PV cell type. It is expected that these insights and contributions will form the basis for a new generation of high-performance TPV systems

Energy harvesting using photovoltaic and betavoltaic devices

There is an important need for improvement in both cost and efficiency of photovoltaic cells. For improved efficiency, a better understanding of solar cell performance is required. An analytical model of thin-film silicon solar cell, which can provide an intuitive understanding of the effect of illumination on its charge carriers and electric current, is proposed. The separate cases of homogeneous and inhomogeneous charge carrier generation rates across the device are investigated. This model also provides for the study of the charge carrier transport within the quasi-neutral and depletion regions of the device, which is of an importance for thin-film solar cells. Two boundary conditions, one based on a fixed charge carrier surface recombination velocities at the electrodes and another based on intrinsic conditions for large size devices are explored. The device\u27s short circuit current and open circuit voltage are found to increase with a decrease of surface recombination velocity at the electrodes. The power conversion efficiency of thin film solar cells is observed to depend strongly on impurity doping concentrations. The developed analytical model can be used to optimize the design and performance of thin-film solar cells without involving highly complicated numerical codes to solve the corresponding drift-diffusion equations. The third generation polymer photovoltaic solar cells, the first generation includes monocrystalline silicon solar cells and second generation being thin-film solar cells, and photodetectors are researched widely in the last few years due to their low device processing cost, mechanical flexibility, and lightweight. Organic photovoltaic materials such as poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT: PCBM) blend are usually cheaper than inorganic materials, but have a limitation of lower power conversion efficiency (PCE) than their inorganic (for example, Si) counterparts. These organic devices need to be optimized to achieve the maximum possible PCE. One way to do this is to achieve the optimal thickness of the optically active layer of P3HT:PCBM while fabricating these organic photovoltaic devices. The influence of the active layer\u27s thickness of P3HT:PCBM blend on performance of polymer solar cells and photodetectors are experimentally investigated. The fabricated device structure is glass/ITO/PEDOT:PSS/P3HT:PCBM/A1, where ITO is the indium tin oxide, and PEDOT:PSS stands for poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) used as a buffer layer to collect holes effectively at the ITO anode. Aluminum is used as a cathode. Chlorobenzene is used as a solvent to prepare the polymer-fullerene blend. Spin coating technique was utilized to deposit the active layer and the concentration of P3HT, PCBM, and spin-coating speeds were varied to achieve a wide range of the active layer\u27s thicknesses from 20 mn to 345 mn. The PCE of solar cell devices and the external quantum efficiency ( EQE) of the photodetectors are found to increase with the thickness of the active layer. The maximum PCE of 1.09% is obtained for the active layer\u27s thickness of 345 mn. The ongoing advanced space exploration requires the novel energy sources that can generate power for extreme duration without need of refill. The need for such extreme-duration lightweight power sources for space and terrestrial applications motivates the study and development of polymer-based betavoltaic devices. The betavoltaic devices based on the semiconductive polymer-fullerene blend of P3HT:ICBA, where ICBA is indene-C60 bisadduct, are demonstrated here for the first time. Both direct and indirect energy conversion methods were explored. For the indirect conversion method, a scintillator intermediate layer of cerium-doped yttrium aluminum garnet (Ce:YAG) was used. A high open circuit voltage of 0.56 V has been achieved in the betavoltaic device fabricated on polyethylene terephthalate (PET) substrate with the indirect energy conversion method at 30 keV electron kinetic energy. The directional and external interaction losses are significantly reduced using thin PET substrates. The maximum output electrical power of 62 nW was achieved at 30 keV input electron beam energy. The highest betavoltaic PCE of 0.78% was achieved at 10 keV of electron beam energy. The performance of two different scintillators, Ce:YAG and Thallium doped Cesium Iodide (CsI:TI), were compared in the indirect conversion betavoltaic devices experimentally and the interaction of electron beam with Ce:YAG and CsI:TI was studied using Monte Carlo simulations. The catholuminescence profiles from simulation showed that CsI:TI is more-efficient to generate photons when hit by electron beam compared to Ce:YAG, which is further verified experimentally with 20% PCE enhancement using CsI:TI at 30 kV e-beam compared to betavoltaic devices with Ce:YAG. The directional loss in the indirect conversion devices is further reduced by applying thin reflecting aluminum film on top of the scintillator. The PCE increased by 26.7% with 30 nm thin aluminum film on top of Ce:YAG scintillator at 30 keV electron beam energy. The experimental results showed that the output electrical power from betavoltaic devices increased with the increase in incident electron beam energy

NASA Tech Briefs, January 1992

Topics include: New Product Ideas; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Fabrication; Mathematics and Information Sciences; Life Sciences