Sung-Ki Nam

Design and Characterization of a High Resolution Microfluidic Heat Flux Sensor with Thermal Modulation

A complementary metal-oxide semiconductor-compatible process was used in the design and fabrication of a suspended membrane microfluidic heat flux sensor with a thermopile for the purpose of measuring the heat flow rate. The combination of a thirty-junction gold and nickel thermoelectric sensor with an ultralow noise preamplifier, a low pass filter, and a lock-in amplifier can yield a resolution 20 nW with a sensitivity of 461 V/W. The thermal modulation method is used to eliminate low-frequency noise from the sensor output, and various amounts of fluidic heat were applied to the sensor to investigate its suitability for microfluidic applications. For sensor design and analysis of signal output, a method of modeling and simulating electro-thermal behavior in a microfluidic heat flux sensor with an integrated electronic circuit is presented and validated. The electro-thermal domain model was constructed by using system dynamics, particularly the bond graph. The electro-thermal domain system model in which the thermal and the electrical domains are coupled expresses the heat generation of samples and converts thermal input to electrical output. The proposed electro-thermal domain system model is in good agreement with the measured output voltage response in both the transient and the steady state.

Compact Thermal Network Model of the Thermal Interface Material Measurement Apparatus With Multi-Dimensional Heat Flow

Accurate prediction of operating temperatures in electronic parts at the component, package, board and system level computational fluid dynamics simulations, has engaged the engineering community for several years. The primary challenge was the difficulty of implementing accurate operating temperature predictions directly into system designs using near-exact physical models (known as detailed thermal models) due to the wide disparity in length scales that result in large computational inefficiencies. A compact thermal model (CTM) attempts to solve this problem by reducing the detailed model to a far less grid intensive representation, while preserving accuracy in predicting the temperatures at key points with a short calculation time. A CTM is condensed using thermal network modeling with thermal resistance and thermal capacitance. This paper focuses on the derivation of compact thermal network models to predict the transient temperature response of complex electronic equipment. The system model is based on a thermal interface material (TIM) measurement apparatus taking into consideration the lateral heat flow in the TIM. The thermal impedance and the temperature difference between the junction and ambient nodes are used to estimate the heat flow division on each heat transfer path. The validity of the dynamic thermal network method and the simple thermal analysis model is confirmed based on the result of the transient thermal analysis. In this paper we describe an application of the dynamic compact thermal network method to analyze the transient thermal response of a TIM measurement apparatus in multi-dimensional heat flow, and we propose a simple modelling procedure for the parametric estimation as a preliminary thermal design tool.

Characterization of fiber-optic light delivery and light-induced temperature changes in a rodent brain for precise optogenetic neuromodulation

Understanding light intensity and temperature increase is of considerable importance in designing or performing in vivo optogenetic experiments. Our study describes the optimal light power at target depth in the rodent brain that would maximize activation of light-gated ion channels while minimizing temperature increase. Monte Carlo (MC) simulations of light delivery were used to provide a guideline for suitable light power at a target depth. In addition, MC simulations with the Pennes bio-heat model using data obtained from measurements with a temperature-measuring cannula having 12.3 mV/°C of thermoelectric sensitivity enabled us to predict tissue heating of 0.116 °C/mW on average at target depth of 563 μm and specifically, a maximum mean plateau temperature increase of 0.25 °C/mW at 100 μm depth for 473 nm light. Our study will help to improve the design and performance of optogenetic experiments while avoiding potential over- and under-illumination.

Needle Type of Hybrid Temperature Probe for Both Diagnosis and Treatment of Musculoskeletal Pain Syndrome

This paper describes the development of needle type probe that measures temperature and injects medicine for both diagnosis and treatment of musculoskeletal pain syndrome (MPS). The size of trigger points is from several micrometers to millimeter. Therefore, it is required to develop a medical device that is capable of not only finding the trigger points by temperature measurement, but also injecting medicine at the exact location for treatment. To challenge these difficulties, thermocouple was fabricated on the surface of a needle using metal deposition process. Special type of stainless-constantan thermocouple was achieved from the stainless body of a needle itself and deposited constantan metal film. In particular, parylene coating enables to limit the temperature sensitive area to the end of the needle tip. Fabricated needle type probe produces 3.25 mV/°C of thermoelectric sensitivity and compared its performance with commercial T-type thermocouple in animal muscle sample.

Design of a liquid bridge heat switch system based on the liquid bridge control for electronics cooling

Recently, liquid bridge heat switch has been suggested as effective thermal management solutions for the various thermal problems. The liquid bridge heat switch can control the thermal resistance and the temperature of desired position by regulating the liquid bridge between objective areas. The liquid bridge heat switch system is composed of hot plate as an upper plate, cold plate as a lower plate, and actuators. “On” state demand, the supplied liquid generates liquid bridge between two plates and conducts heat from hot plate to cold plate. The amount of conducting heat and thermal resistance are controlled by the diameter and height of generated liquid bridge. To be an “Off” state, the generated liquid bridge is retrieved and ruptured eventually. At that time, the heat switch system has maximum thermal resistance. This result decreased conduction of heat. In order to realize the desired switch operation, the precise liquid bridge control is required. In this research, the liquid bridge behavior was studied to design the heat switch system. The effects of channel geometry and clearance on the liquid bridge behavior were verified and the liquid bridge rupture conditions were found out. Based on the investigation, the liquid bridge heat switch system was designed for the high power LED cooling system. In a series of experiment, the stable liquid bridge operation was achieved by designed channel geometry. The results also showed that proposed heat switch system was able to decrease the LED junction temperature and regulate the thermal resistance between hot and cold plate.

Nano-Watt Heat Flux Sensor Considering Contact Resistance at Thermopile Junctions

This paper presents design and fabrication procedures for nano-Watt resolution of heat flux sensor. To enhance the resolution, a contact resistance of thermopile is especially focused. CMOS (Complementary Metal-Oxide Semiconductor-compatible) process was used for deposition of gold and chromium which are composed of thermopile. The most important part of thermopile is the contact region of the junctions which generate electrical noises as well as thermoelectric power. The effect of contact conditions at junction point was investigated. The fabricated sensor has 100 thermocouples connected in series and its active junction is on the membrane which directly affects the sensitivity. Developed sensor system provides 0.0629V/nW of sensitivity and 1nW of high resolution.Copyright

MBE growth and characterization of highly tensile-strained InGaAs/InGaAlAs multi-quantum well for 1.3 /spl mu/m laser diodes

Highly tensile-strained InGaAs/InGaAlAs MQW was grown by MBE using the digital-alloy technique. Two peaks corresponding to electron-light hole transition (E1-LH1) and electron-heavy hole transition (E1-HH1) were clearly observed in the PL spectrum of MQW structure