Zhiyin Gan

Optical analysis of an 80-W light-emitting-diode street lamp

Optical analysis is critical to the evaluation of a light-emitting diode (LED) street lamp, especially when the lamp is still in its early stage of development and applications and when optimization is needed for making use of unique characteristics of LEDs. In this study, optical analysis of an 80-W LED street lamp was conducted. Experimental research on such a lamp was first undertaken. The results demonstrated that the average illumination was about 8.25 lx and the total uniformity was 0.364 for a 20-m-long and 10-m-wide test area at a height of 8 m, which is acceptable for the current standard for a submain road. Numerical simulation was also conducted; the feasibility of the numerical model was proven by comparison of the simulations with the experimental data, which will be used for future optimization study and other novel designs of the optical system of street lamps. Through the simulations and the corresponding analysis, it was found that the tested 80-W LED street lamp had reasonable performance in average illumination, but multiple shadows existed, which would need to be removed in future designs. Improvements are suggested to reduce the number of optical elements, to reduce the lamps volume, and to enhance the illumination performance. Two design methods for LED street lamps are summarized, based on the optical analysis.

Computational study of thermocompression bonding of carbon nanotubes to metallic substrates

Thermocompression bonding of carbon nanotubes (CNTs) to metallic substrates is studied using molecular dynamics. The interaction of the CNT and the metal cluster at high temperature is investigated first. For the diffusion bonding process, the effects of temperature and external pressure are examined. In addition, we apply the tensile loading to examine the mechanical properties and the failure modes during the debonding process. The results show that formation of coalescence structure between the CNT and the metal cluster provides a nanoscale metal surface to facilitate diffusion bonding. Both high temperature and high pressure will enhance the bonding. In addition, the debonding position of the samples under the tensile loading depends on the competition of CNT-metal and metal-metal interface strength. For samples bonded under high temperature and high pressure, the debonding first occurs at the CNT-metal interface. While for samples bonded under low temperature and low pressure, the interdiffusion is n...

A PZT insulin pump integrated with a silicon micro needle array for transdermal drug delivery

Many of the compounds in drugs cannot be effectively delivered using current drug delivery techniques (e.g., pills and injections). Transdermal delivery is an attractive alternative, but it is limited by the extremely low permeability of the skin. Because the primary barrier to transport is located in the upper tissue, micro-electro-mechanical-system (MEMS) technology provides novel means in terms of both micro needles array and PZT pump, with the former one to increase permeability of human skin with efficiency, safety and painless delivery, and the latter one to decrease the size of the pump. Micro needles array has many advantages, including minimal trauma at penetration site due to the small size in needle, no condition limit, painless drug delivery for penetration depth with few nerves, and precise control of penetration depth for micro needle extension length. The micro needles array drug delivery is precise, painless, effective, clean and neatness, without any inconvenience. This promotes the development of biomedical sciences and technology and makes medical devices more humanized. So far most of the insulin pump has been using mechanical pump in clinical practices. We present the first development of this novel technology which can assemble the PZT pump and the micro needles together for diabetes mellitus. The micro needle array based on a flexible substrate can be mounted on non-planar surface or even on flexible objects such as a human fingers and arms. The PZT pump can pump the precision insulin much more accurately than the mechanical pump and the overall size is much smaller than those mechanical pumps. The hollow wall straight micro needles array is fabricated on a flexible substrate by deep-reactive ion etching (DRIE) and anisotropic wet etching techniques. The fabricated hollow micro needles are 200/spl mu/m in length and 30/spl mu/m in diameter. The micro needle array, which may be built with on-board fluid pumps, have potential applications in the chemical and biomedical fields for localized chemical analysis, programmable drug-delivery systems, and very small, precise fluids sampling. The micro needles array has been installed in an insulin pump for demonstration and a leak free packaging is introduced.

Contact configuration modification at carbon nanotube-metal interface during nanowelding

Contact configuration modification at carbon nanotube (CNT)-metal interface during nanowelding is investigated using molecular dynamics simulation. It is found that the nanowelding could be accomplished at a temperature much lower than the melting point of the metal, during which a side contact structure and core filling nanowires form at the CNT-metal interface. Metal atoms prefer entering into the core to moving along the outer surface of the CNTs. Also, the filling of the metal atoms into the CNT can enhance the local melting of the metal at the interface, which would facilitate the metal atoms wetting on the outer walls and dramatically increasing the contact length.

Simulation on thermal characteristics of LED chips for design optimization

As thermal performance is importance for high-power LED devices, there exists a need to build a validated model to clarify the thermal transfer mechanisms in the LED chip in terms of the chip materials and structures. High-power LED was numerically investigated using the finite element method. A series of substrate materials with different thermal conductivity and thicknesses were studied. The impact of varying cooling capacities on chip junction temperature is also presented.

Dynamic mechanical properties of the transparent silicone resin for high power LED packaging

Aiming to study dynamic mechanical properties of the transparent silicone resins for LEDs packaging and the effects of dynamic mechanical properties on the reliability of high power LEDs, dynamic mechanical analysis (DMA) has been adopted to study one silicone resin used for packaging high power white light LEDs. The viscoelastic behavior of silicone resin was obtained from multi-frequencies dynamic mechanical temperature spectra measured by dynamic mechanical analysis instrument in compression mode. The order of storage modulus was 106 whether in the glassy state or rubbery state, storage modulus in glassy state was about 50 times more than that in rubber state. Glass transition was found at 40degC and the frequency had increased accompanied by growing of temperature of glass transition. The activation energy of glass transition was also calculated. A master curve of storage modulus was generalized according to time-temperature superposition principle and WLF equation. Furthermore, characteristics of storage modulus, loss factor, glass transition, etc. were used for exploring how to increase the reliability of LEDs and the reasons which led to the failure of LEDs.

A micro channel integrated gas flow sensor for high sensitivity

In order to enhance measurement accuracy, a gas mass flow sensor integrated with micro channels is proposed in this paper. The uniqueness of this flow sensor is that there is thermal convection effect on two sides of diaphragm, which results in a more sensitive temperature distribution. The temperature characteristics of the novel flow sensor are simulated at different flow rates, and the optimization positions of the test resistor pair on the membrane are obtained from the simulations. Compared with traditional flow sensors, this flow sensor has higher measurement precision. When the incoming flow velocity is 3 m/s, its temperature difference between the upstream and the downstream can reach about 38.6 K, which is much higher than 26.8 K for the traditional flow sensor. In addition, the effects of physical parameters such as heater temperature and heater width are investigated. The results illustrate that the measurement accuracy increases but the measurement range narrows with increase of the heater temperature. The measurement accuracy increases and the measurement range widens with increase of the heater width.

Vacuum measurement on vacuum packaged MEMS devices

This paper investigates the relationship between the resonance impedance of a tuning fork quartz oscillator and the small size cavity vacuum pressure and develops an on-line vacuum measurement system to track real-time vacuum pressure in MEMS devices. Furthermore, authors completely analyze all facts that affect the resonance impedance. A set of metal vacuum packaged devices have been monitored for more than 10 months using this on-line vacuum measurement system. The results indicate that it is very critical to investigate vacuum packaging processes, reliability and durability of the vacuum devices by using this on-line vacuum measurement system.

Application of Microwave Drilling to Electronic Ceramics Machining

Ceramic materials are important in electronic industry. A number of ceramics are used in micro-electronic packaging and substrate manufacturing. However, hardness and brittleness of ceramics cause many difficulties in their machining. In this paper, a novel method is introduced for ceramic machining which uses the microwave energy. The method is based on the phenomenon of local hot spot produced by near-field microwave radiation. It is cheaper and more effective to the process of ceramics, and has advantages in improving process quality. The paper offers a model of microwave-drilling on a slice of ceramics and investigates the effect area of microwave. Parametric study is conducted and documented based on the proposed drilling model. In addition, a comparison is presented between the proposed microwave method and other methods, with the focus on the holes drilling of ceramics. Finally the paper discusses the prospect and issues of microwave-drilling in actual applications to micro-electronics industry

Selective Induction Heating for Microsystem Packaging

Preliminary research on selective induction heating to achieve wafer bonding is presented in this paper. Some effects of bonding layer materials, coil design and impedance matching on induction heating are discussed. By choosing a suitable frequency of high frequency power supply and optimizing the induction coil, selective induction heating for wafer bonding has been achieved. Induction heating patterns in terms of bonding layer should be in closed loop, which is also effective for hermetic packaging, while other open-loop-patterns such as circuits, pads, et al., cannot be effectively heated because no eddy current or little eddy current can be inducted and are kept to be at low temperature, there damages on some temperature-sensitive devices can be avoided. The new technique can be applied to various IC and MEMS packaging such as eutectic bonding, solder bonding, and diffusion bonding