Heater Line Research Articles

Практические рекомендации по расчету вакуумной колонны и оценке степени уноса остатка на качество вакуумного газойля

The study provides a view on the typical reasons and consequences of the residue entrainment to the gas oil heaviest draw within the vacuum distillation column. The above-stated phenomenon leads to the gas oil coking ability growth, as well as its metals content and draw rate decrease while achieving the definite limits for the heat duty and the critical velocities of the gas phase for vacuum heater and transfer line respectively. Entrainment minimization criteria and its quantitative estimation methods were reviewed in this work. We propose an approach to assess the entrainment impact on the vacuum gas oil quality, developing a non-equilibrium model of vacuum distillation column.

Pulsed thermoreflectance imaging for thermophysical properties measurement of GaN epitaxial heterostructures.

Multilayer heterostructures composed of a substrate and an epitaxial film are widely utilized in advanced electronic devices. However, thermal bottlenecks constrain their performance and reliability, and efficient approaches to comprehensively measure the thermophysical properties of heterostructures are urgently needed. In this work, a pulsed thermoreflectance imaging (PTI) method is proposed, which combines the transient temperature mapping of thermoreflectance thermal imaging with transient pulsed excitation. By executing merely three transient tests, six thermophysical properties, including the film thermal conductivity and specific heat capacity, the substrate thermal conductivity and specific heat capacity, the film-substrate thermal boundary resistance, and the equivalent thermal conductivity of the insulating layer, can be simultaneously measured in a heterostructure sample. The proposed method applies a pulsed current excitation to a metal heater line on the sample surface and utilizes the thermoreflectance thermal imaging system to measure the temperature of different spatial regions on the sample surface at different time windows. The temporal and spatial variation information of the temperature field is then extracted and combined with finite element method inversion calculation to obtain the thermophysical properties of heterostructures. To validate the accuracy and reliability of this method, we conducted measurements on a GaN-on-SiC heterostructure sample and obtained thermophysical properties consistent with the representative literature data that have previously been reported. The proposed PTI method, characterized by its high sensitivity, demonstrates good efficiency and reliability in conducting comprehensive thermophysical property characterization of GaN epitaxial heterostructures.

Low Power High Concentration Gas Sensor Based on 3ω-Method Using a Suspended Nanowire Heater

IntroductionThese days, the use of various industrial and personal equipment using hazardous gases is on the rising such as H2 for fuel cells. To utilize these gases, the low concentration sensor(~ppm) for leakage detection as well as the high concentration sensor (~%) for monitoring hazardous gasses in the industrial sites are essential. Semiconductor type and electrochemical type sensors are commonly used for gas detection but they are not suitable for high concentration because they are easily saturated in high concentration. In contrast, thermal conductivity type sensors are used as high concentration sensors because they measure resistance change of the heat loss of heated wire(heater) to a gas environment without sensor signal saturation in high concentration. However conventional thermal conductivity type sensors require large power (hundreds of milliwatts to watts) and relatively large size. In the previous study, a microscale bridge-type heater-based gas sensor was developed using MEMS technology for low power consumption and small size [1, 2]. This sensor used the 3ω-method to measure accurately heat loss to the gas with a high signal to noise ratio.Here, we developed a 3ω-method based high concentration gas sensor using a suspended nano-sized wire heater to minimize the required power and size. The suspended nano-sized wire heater consists of a suspended nanowire backbone, an eave structure and a thin gold heater on the suspended nanowire. The suspended nanowire backbone structure was fabricated by pyrolyzing suspended photoresist wire, and a thin gold layer as a heater material, which ensures high sensitivity due to its high-temperature coefficient of resistance, was selectively coated on the suspended carbon nanowire by virtue of the eave structure. The 3ω-method based gas sensor exhibited high sensitivity and wide linear range with ultra-small power consumption because of its suspended architecture, small size, high aspect ratio and high surface to volume ratio. In addition, all the processes of the 3D nanostructures were carried out at a wafer-level enabling cost-effective manufacturing owing to novel eave structures and carbon-MEMS processes (consisting of photolithography and pyrolysis) [3]. Method The suspended nanowire heaters were fabricated by a three-step process. First, eave structures for the selective metal coating on a suspended carbon nanowire was fabricated by oxide etching and isotropic silicon etching. Then, suspended microscale suspended polymer wires were patterned by two successive photolithography processes and the micro polymer wire was converted into a carbon nanowire by a dramatic volume reduction in pyrolysis. The pyrolysis temperature was set to 700℃ for low carbon electrical conductivity so that the electrical charge flows only through the gold. The last step was the deposition of gold as a heater line. A 50-nm-thick gold was deposited using evaporation. Owing to the eave structure and anisotropic evaporation, the gold layer is solely connected through the suspended wire as shown in Figure a. Results and Conclusions The gold-coated suspended carbon nanowire and the eave structure were well-defined as shown in Figure b. The gold-coated nanowire exhibited a very stable 3ω voltage output signal compared to bare carbon nanowire with high conductivity (Figure c). The thermal penetration depth reduces as the input frequency increases, the 3ω voltage decreases with increasing input frequency (Figure d). The 3ω voltage linearly changed with gas concentration depending on the relative thermal conductivity of target gas in comparison to that of N2 (Figure e). Therefore, selective gas detection is feasible. Figure f showed the response and recovery time of the sensor when it is exposed to 100% Ar and 5% H2. The sensor measures a gas concentration based on the thermal equilibrium between heater structure and gas environment only. Thus, very fast response and recovery time within 3s can be achieved even at high gas concentrations. In addition, the power consumption was only 0.107 mW due to suspended nanowire-type heater configuration.

Suspended Heater Embedded Metal Oxide Nanowire Based Gas Sensor Platform

Introduction Over the past few decades, different types of gas sensors have been developed based on different sensing materials and methods. Among them, semiconducting metal oxide nanomaterials are suitable for gas sensing applications due to their high electron mobility, high surface-to-volume ratio, high crystallinity, and long-term stability. Considerable efforts have been made to improve the performance indicators of metal oxide gas sensors such as sensitivity, selectivity, reaction and recovery time [1]. However, in recent years, there has been growing demand for miniaturization, low power consumption, low cost and mass production, which are the characteristics required for continuous and systematically integrated monitoring and management in the sensor market [2]. Besides, widely used materials for metal oxide gas detection are wide-bandgap semiconducting oxides such as zinc oxide, tin oxide, gallium oxide or indium oxides, which are operate at elevated temperatures (250–600°C) since enough thermal energy of surface redox reaction is required to overcome the activation energy barrier and increase the reaction kinetics in order to realize sensing measurement. Therefore, additional heater systems are required to metal oxide gas sensor and it may cause high power consumption, high cost or occupying a lot of space. Hearin, we propose a nano-heater integrated metal oxide gas sensor that capable of sensing with low power consumption and fast response and of being fabricated at a wafer level through C-MEMS which facilitated sub-micrometer-level carbon patterning due to a dramatic volume reduction during the polymer pyrolysis. The temperature of the metal oxide, the sensing material, can be heated immediately to 600°C within a low power of 7mW. In addition, the maximum temperature of the metal oxide can be easily controlled according to the applied voltage. Therefore, only a voltage source is needed to heat the sensing material. Method Our sensor platforms as shown in Figure a, were fabricated in several steps. First, eave structures for the selective metal coating on a suspended carbon nanowire were fabricated by oxide etching and isotropic silicon etching. Then, the suspended carbon nanowire was fabricated through C-MEMS consisting of two successive photolithography and polymer pyrolysis [3]. Then, we deposited gold on a carbon wire using evaporation as a heater line. Owing to the eave structure and anisotropic evaporation, the gold layer could be connected only through the suspended wire as shown in Figure b. The next step was the deposition of HfO2 as an insulation layer by Atomic Layer Deposition. In what follows, the ZnO nanowire forest (Figure c) was integrated selectively on the middle of a suspended wire structure via seed layer patterning and a hydrothermal process in an autoclave [4]. Due to the high aspect ratio of the carbon nanowire, heat is hard to be released to both posts, resulting in a uniform temperature distribution over 80% of the total length of the wire. Therefore, we used ZnO nanowire forest as a sensing site by growing in the center of the carbon nanowire selectively where the temperature is kept uniform and within the range of the sensing target temperature according to the simulation results (Figure d). In the last, to obtain the electrical signal of sensing material, we deposited gold once more using an E-beam evaporator. Results and Conclusions We have identified the possibility of gas sensing with heater integrated metal oxide sensor platform. Observing that the resistance of the metal oxide decreased rapidly when a voltage was applied, we speculated that the temperature of the metal oxide would have risen immediately according to the Joule-heating principle. Furthermore, the resistance of the metal oxide decreased continuously as the applied-voltage gradually increased. When we applied 1.2V to a gold heater, the resistance of the ZnO dropped to about 1/20 of its room temperature resistance (Figure e) similar when it is heated by an external heater to about 250℃, which is occasionally used temperature condition in the MOS type gas sensor. Detailed gas sensing results will be presented at the conference.

Influence of the interval length of hydraulic packer systems on thermally-induced pore pressure measurements in rock

During the past several decades, hydraulic packer systems have generally been used to measure the thermally-induced pore pressures in many in-situ experiments in nuclear waste management programs. The measured value using hydraulic packer system is a combined value of the pore pressures in the rock along the packer interval, and not the pore pressure at the middle point. The suitability of using the packer system measured value to represent the thermally-induced pore pressure at the middle point of the packer interval needs to be assessed. The accuracy of using hydraulic packer systems is examined in this paper using a coupled thermal-hydraulic-mechanical (THM) model for fully saturated conditions developed using the finite element program COMSOL. The results indicate that there could be large errors in the measured values, with the size of the error dependent on the size of the packer interval, the variation of pore pressure gradient along that interval and the orientation of the packer measurement borehole. To improve the accuracy of the measurement using packer systems, the variation in pore pressure gradient along the packer interval should be small; or if a substantial gradient variation is expected, the length of the packer interval should be made as small as possible. A packer interval with a length less than 0.5 m is suggested. If a packer system has been installed with a large interval length in a location where a large pore gradient variation may exist, calibration of any associated numerical model using this measurement should incorporate the packer measurement system. The numerical results of this coupled THM model are in good agreement with the integration of a point heat source theoretical solution throughout the heater line.

Low Power High Concentration Gas Sensor Based on 3ω-Method Using a Suspended Nanowire Heater

Introduction These days, the use of various industrial and personal equipment using hazardous gases is on the rising such as H2 for fuel cells. To utilize these gases, the low concentration sensor(~ppm) for leakage detection as well as the high concentration sensor (~%) for monitoring hazardous gasses in the industrial sites are essential. Semiconductor type and electrochemical type sensors are commonly used for gas detection but they are not suitable for high concentration because they are easily saturated in high concentration. In contrast, thermal conductivity type sensors are used as high concentration sensors because they measure resistance change of the heat loss of heated wire(heater) to a gas environment without sensor signal saturation in high concentration. However conventional thermal conductivity type sensors require large power (hundreds of milliwatts to watts) and relatively large size. In the previous study, a microscale bridge-type heater-based gas sensor was developed using MEMS technology for low power consumption and small size [1, 2]. This sensor used the 3ω-method to measure accurately heat loss to the gas with a high signal to noise ratio.Here, we developed a 3ω-method based high concentration gas sensor using a suspended nano-sized wire heater to minimize the required power and size. The suspended nano-sized wire heater consists of a suspended nanowire backbone, an eave structure and a thin gold heater on the suspended nanowire. The suspended nanowire backbone structure was fabricated by pyrolyzing suspended photoresist wire, and a thin gold layer as a heater material, which ensures high sensitivity due to its high-temperature coefficient of resistance, was selectively coated on the suspended carbon nanowire by virtue of the eave structure. The 3ω-method based gas sensor exhibited high sensitivity and wide linear range with ultra-small power consumption because of its suspended architecture, small size, high aspect ratio and high surface to volume ratio. In addition, all the processes of the 3D nanostructures were carried out at a wafer-level enabling cost-effective manufacturing owing to novel eave structures and carbon-MEMS processes (consisting of photolithography and pyrolysis) [3]. Method The suspended nanowire heaters were fabricated by a three-step process. First, eave structures for the selective metal coating on a suspended carbon nanowire was fabricated by oxide etching and isotropic silicon etching. Then, suspended microscale suspended polymer wires were patterned by two successive photolithography processes and the micro polymer wire was converted into a carbon nanowire by a dramatic volume reduction in pyrolysis. The pyrolysis temperature was set to 700℃ for low carbon electrical conductivity so that the electrical charge flows only through the gold. The last step was the deposition of gold as a heater line. A 50-nm-thick gold was deposited using evaporation. Owing to the eave structure and anisotropic evaporation, the gold layer is solely connected through the suspended wire as shown in Figure a. Results and Conclusions The gold-coated suspended carbon nanowire and the eave structure were well-defined as shown in Figure b. The gold-coated nanowire exhibited a very stable 3ω voltage output signal compared to bare carbon nanowire with high conductivity (Figure c). The thermal penetration depth reduces as the input frequency increases, the 3ω voltage decreases with increasing input frequency (Figure d). The 3ω voltage linearly changed with gas concentration depending on the relative thermal conductivity of target gas in comparison to that of N2 (Figure e). Therefore, selective gas detection is feasible. Figure f showed the response and recovery time of the sensor when it is exposed to 100% Ar and 5% H2. The sensor measures a gas concentration based on the thermal equilibrium between heater structure and gas environment only. Thus, very fast response and recovery time within 3s can be achieved even at high gas concentrations. In addition, the power consumption was only 0.107 mW due to suspended nanowire-type heater configuration.

Suspended Heater Embedded Metal Oxide Nanowire Based Gas Sensor Platform

Introduction Over the past few decades, different types of gas sensors have been developed based on different sensing materials and methods. Among them, semiconducting metal oxide nanomaterials are suitable for gas sensing applications due to their high electron mobility, high surface-to-volume ratio, high crystallinity, and long-term stability. Considerable efforts have been made to improve the performance indicators of metal oxide gas sensors such as sensitivity, selectivity, reaction and recovery time [1]. However, in recent years, there has been growing demand for miniaturization, low power consumption, low cost and mass production, which are the characteristics required for continuous and systematically integrated monitoring and management in the sensor market [2].Besides, widely used materials for metal oxide gas detection are wide-bandgap semiconducting oxides such as zinc oxide, tin oxide, gallium oxide or indium oxides, which are operate at elevated temperatures (250–600°C) since enough thermal energy of surface redox reaction is required to overcome the activation energy barrier and increase the reaction kinetics in order to realize sensing measurement. Therefore, additional heater systems are required to metal oxide gas sensor and it may cause high power consumption, high cost or occupying a lot of space. Hearin, we propose a nano-heater integrated metal oxide gas sensor that capable of sensing with low power consumption and fast response and of being fabricated at a wafer level through C-MEMS which facilitated sub-micrometer-level carbon patterning due to a dramatic volume reduction during the polymer pyrolysis. The temperature of the metal oxide, the sensing material, can be heated immediately to 600°C within a low power of 7mW. In addition, the maximum temperature of the metal oxide can be easily controlled according to the applied voltage. Therefore, only a voltage source is needed to heat the sensing material. Method Our sensor platforms as shown in Figure a, were fabricated in several steps. First, eave structures for the selective metal coating on a suspended carbon nanowire were fabricated by oxide etching and isotropic silicon etching. Then, the suspended carbon nanowire was fabricated through C-MEMS consisting of two successive photolithography and polymer pyrolysis [3]. Then, we deposited gold on a carbon wire using evaporation as a heater line. Owing to the eave structure and anisotropic evaporation, the gold layer could be connected only through the suspended wire as shown in Figure b. The next step was the deposition of HfO2 as an insulation layer by Atomic Layer Deposition. In what follows, the ZnO nanowire forest (Figure c) was integrated selectively on the middle of a suspended wire structure via seed layer patterning and a hydrothermal process in an autoclave [4]. Due to the high aspect ratio of the carbon nanowire, heat is hard to be released to both posts, resulting in a uniform temperature distribution over 80% of the total length of the wire. Therefore, we used ZnO nanowire forest as a sensing site by growing in the center of the carbon nanowire selectively where the temperature is kept uniform and within the range of the sensing target temperature according to the simulation results (Figure d). In the last, to obtain the electrical signal of sensing material, we deposited gold once more using an E-beam evaporator. Results and Conclusions We have identified the possibility of gas sensing with heater integrated metal oxide sensor platform. Observing that the resistance of the metal oxide decreased rapidly when a voltage was applied, we speculated that the temperature of the metal oxide would have risen immediately according to the Joule-heating principle. Furthermore, the resistance of the metal oxide decreased continuously as the applied-voltage gradually increased. When we applied 1.2V to a gold heater, the resistance of the ZnO dropped to about 1/20 of its room temperature resistance (Figure e) similar when it is heated by an external heater to about 250℃, which is occasionally used temperature condition in the MOS type gas sensor. Detailed gas sensing results will be presented at the conference.

Monte Carlo prediction of ballistic effect on phonon transport in silicon in the presence of small localized heat source

Understanding phonon transport at nanoscale is critically important for thermal nanometrology applications including scanning thermal microscopy, three-omega and time domain thermoreflectance experiments. In this paper, a multidimensional non-gray Monte Carlo simulation is developed to investigate the ballistic phonon transport in a silicon sample heated on the top by a small localized heater line. We observed that heat confinement occurs for very small heat sources. This result contradicts the classical Fourier model, according to which the heat penetration depth is always significant, even with small sources. The temperature fields inside the sample exhibit different penetration depths depending strongly on the heater line size. Maximum thermal resistance and a large interface temperature jump take place in the limit of very small heater width compared to the phonon mean free path due to the nonequilibrium and ballistic nature of phonon transport. Increasing the heater width leads to a decrease in the heat flux and temperature jump. In the limit of a very large heat source, the heat flux and temperature jump become independent of heat source size. In accordance with experimental investigations for the case of sapphire material (Siemens et al 2010 Nature Mat. 9 26–30), the thermal resistance of the silicon sample due to the localized heat source decreases and then tends to reach a plateau with increasing source size from tens of nanometers to micrometers. These results are important, not only for understanding the thermal transport in the sample during nanometrology experiments, but also for the design and manipulation of heat at nanoscale.

PERPATAHAN FATIK MATERIAL ALUMINIUM 2024-T3 DENGAN PENGELASAN FSW

Resilient, machine processed, shapped aluminium using pulling power for pure aluminium with 4-5kgf/mm2. Aluminium fusion with series 2024-T3 is a metal fusion whose low weldability so it is very difficult to be conducted the welding process because it tends to occur hot cracking or being porous, and precipitation hardening when conducting welding process due to segregation of copper (Cu) fusion subtance. One of welding method to obtain the good aluminium welding result is by using FSW (friction stir welding). The purpose of this research is to find out the shape and type of fracture on aluminium fusion with FSW welding by dealing TTT. The fracture is created from fatik substance test. The reserach method was conducted by welding of plate aluminium fusion 2024-T3 using FSW technique by dealing transient thermal tensioning (TTT). Transient thermal was conducted by resigning heater line with weld tool/pin. The speed of determined FSW welding was 11 mm/minutes and 1200 rpm. The conducted test was fatigue test and factografi test with SEM. The result of the reserach shows that the number of fatik test cycle is 765.250 with sigmoidal curve visually. Then, the result of fractography using SEM shows that the occured fracture is brittle.

Mid-infrared tunable Vernier filter on a germanium-on-insulator photonic platform

We demonstrate the operation of a tunable Vernier filter at a mid-infrared wavelength of approximately 1.95 μm. To enable efficient tuning through the thermo-optic effect, the filter is implemented on a germanium (Ge)-on-insulator photonic platform. Heat is generated from an overlaying metal heater line to induce the thermo-optic effect to tune the filter output without incurring excessive loss. Owing to the higher thermo-optic coefficient of Ge, the tunability of a single microring resonator is 0.083 nm/mW or 0.175 nm/°C, which is approximately twofold higher than that of silicon. Through the implementation of the Vernier effect by cascading two microring resonators, the tunability of the filter is increased to 0.753 nm/mW or 1.487 nm/°C, which is more than ninefold higher than that of a single microring resonator.

Pipe stress analysis of first wall helium cooling system for conceptual design development of IN LLCB TBM

Indian TBM team is developing Lead-Lithium Cooled Ceramic Breeder (IN-LLCB) Test Blanket Module (TBM) along with its associated systems for testing in ITER. The outer box of LLCB TBM is cooled by first wall helium cooling system (FWHCS) which is designed to remove the heat load of ∼300 kW. FWHCS is a high temperature high pressure closed loop which produces significant movements and propagates high stresses in the piping system. This, in turn, leads to forces and moments on the supports and equipment nozzles. FWHCS may experience a high acceleration (∼59.69 m/s2) during seismic events, the deflection of pipes in this scenario may increase the complexity in the loop operation.This paper describes pipe stress analysis, methodology and results of FWHCS. The pipe stress analysis is performed for sustained and occasional load combinations for various ITER operating states as envisaged for TBMs. FWHCS piping is subjected to category I (likely event) and IV (extremely unlikely event, SL-2) loading conditions. The Pipe stress analysis is performed in accordance with ASME B31.3. The calculated stresses are within the limits for the considered cases. The highest value of stress (about 0.65 times the allowable stress) and the maximum displacement of 23 mm (x direction), 15 mm (y direction) and 11.5 mm (z direction) is observed in recuperator to electrical heater line. The obtained reaction and moment forces are needed as an input for the selection of pipe supports, location of supports and the verification of embedded plates loading criteria. This pipe stress analysis is also used in the optimization of FWHCS layout and further these inputs would be utilized in preliminary design phase.

Effect of Fluid Flow Rate on Efficacy of Fluid Warmer: An In Vitro Experimental Study.

Introduction In patients who require a massive intraoperative transfusion, cold fluid or blood transfusion can cause hypothermia and potential adverse effects. One method by which to prevent hypothermia in these patients is to warm the intravenous fluid before infusion. The aim of this study was to determine the effect of the fluid flow rate on the efficacy of a fluid warmer. Methods The room air temperature was controlled at 24°C. Normal saline at room temperature was used for the experiment. The fluid was connected to an infusion pump and covered with a heater line, which constantly maintained the temperature at 42°C. The fluid temperature after warming was measured by an insulated thermistor at different fluid flow rates (100, 300, 600, 900, and 1200 mL/h) and compared with the fluid temperature before warming. Effective warming was defined as an outlet fluid temperature of >32°C. Results The room temperature was 23.6°C ± 0.9°C. The fluid temperature before warming was 24.95°C ± 0.5°C. The outlet temperature was significantly higher after warming at all flow rates (p < 0.001). The increases in temperature were 10.9°C ± 0.1°C, 11.5°C ± 0.1°C, 10.2°C ± 0.1°C, 10.1°C ± 0.7°C, and 8.4°C ± 0.2°C at flow rates of 100, 300, 600, 900, and 1200 mL/h, respectively. The changes in temperature among all different flow rates were statistically significant (p < 0.001). The outlet temperature was >32°C at all flow rates. Conclusions The efficacy of fluid warming was inversely associated with the increase in flow rate. The outlet temperature was <42°C at fluid flow rates of 100 to 1200 mL/h. However, all outlet temperatures reached >32°C, indicating effective maintenance of the core body temperature by infusion of warm fluid.

Simulation, Microfabrication, and Control of a Microheater Array

This paper describes the simulation, fabrication, and feedback control of a microheater array designed for the implementation of real-time control during thermal evolution of microstructure. The ten-channel heating array was designed through finite element simulation and microfabricated to be compatible with in situ imaging in a scanning electron microscope. Control algorithms are implemented that demonstrate cooperative control of the temperature (using calibrated Ti heater line resistances as a proxy) across the set of channels in the array. The goal of this system is to be able to generate controlled thermal, and thus microstructural, and property distribution during processing of polycrystalline materials.

Magnetic tunnel junctions with integrated thermometers for magnetothermopower measurements

Magnetic tunnel junction (MTJ) micropillars were fabricated with integrated thermometers and a heater line (HL) for thermovoltage measurements. This novel thermometer configuration enabled a direct measurement of ΔT across the MTJ micropillar. The MTJ devices were patterned from a CoFeB/MgO/CoFeB stack, with a 1.2 nm to 1.6 nm MgO wedge across the wafer, resulting in resistance area products in the range of 0.7 kΩ · µm2 < R × A < 55 kΩ · µm2. This allowed the measurement of thermoelectric properties as a function of the tunnel barrier thickness. The thermometers showed a homogeneous heating behavior for all devices across the wafer. Combining the in-stack temperature measurements and finite element simulations the thermal profile across the MTJ structure and the thermopower were estimated with a noticeable improvement of the measurement accuracy. The studied MTJ structures showed tunneling magnetoresistance (TMR) ratios up to 125%, and tunneling magnetothermopower (TMTP) up to 35%.

Sub-Beam Size Temperature Measurement of Heavily Doped Silicon Heater Using Two-Wavelength Thermoreflectance Microscopy

This work describes a novel technique for simultaneously determining local temperature and thickness of a heavily doped Si heater having a submicron width by using two-wavelength thermoreflectance microscopy. The doped silicon line heater, whose thickness and width are, respectively, 480 nm and 900 nm, is fabricated by conventional microfabrication techniques on a fused silica wafer. The full width at half maximum (FWHM) of the focused laser beam is measured to be 2.00 μm and 2.28 μm for green (λ = 516 nm) and red (λ = 640 nm) lasers, respectively. Because the heater width is narrower than the focused laser beam size, the reflected beam contains background information (i.e., reflection from the fused silica substrate) in addition to the thermoreflectance signal from the doped silicon heater. With precise knowledge of the laser beam size, heater width, and exact location of the laser beam spot on the heater, one can quantitatively model the reflectance. In reality, however, due to the difficulty of aligning the laser beam with respect to the submicron-wide Si heater, precise determination of local temperature from thermoreflectance signal is not easily attained. In the present study, instead of aligning the laser beam to the center of the submicron silicon heater, the probe laser horizontally scans over a region of the heater. By taking into account the size of the focused laser beam and the width of the doped silicon heater, it is possible to determine the absolute temperature of a local region of the heater from the measured reflectance during the scanning, even though the width of the heater line is only 39% of the size of the laser beam.

A 3 omega method to measure an arbitrary anisotropic thermal conductivity tensor.

Previous use of the 3 omega method has been limited to materials with thermal conductivity tensors that are either isotropic or have their principal axes aligned with the natural cartesian coordinate system defined by the heater line and sample surface. Here, we consider the more general case of an anisotropic thermal conductivity tensor with finite off-diagonal terms in this coordinate system. An exact closed form solution for surface temperature has been found for the case of an ideal 3 omega heater line of finite width and infinite length, and verified numerically. We find that the common slope method of data processing yields the determinant of the thermal conductivity tensor, which is invariant upon rotation about the heater line's axis. Following this analytic result, an experimental scheme is proposed to isolate the thermal conductivity tensor elements. Using two heater lines and a known volumetric heat capacity, the arbitrary 2-dimensional anisotropic thermal conductivity tensor can be measured with a low frequency sweep. Four heater lines would be required to extend this method to measure all 6 unknown tensor elements in 3 dimensions. Experiments with anisotropic layered mica are carried out to demonstrate the analytical results.

3ω Measurements for Tracking Freezing Fronts in Biological Applications

ABSTRACTOne approach to treating atrial fibrillation relies on freezing tissue of the heart wall. This surgical technology requires sub-millimeter spatial resolution when dynamically tracking the freezing of pulmonary vein; conventional techniques such as ultrasound lack the necessary precision. Here we use an electrothermal “3ω” method to track propagating freezing fronts in nearly real time. The heater line is excited with multiple frequencies simultaneously, and the freezing front detected as it passes through the various penetration depths due to the contrast between thermal conductivities on either side of the front. Comparison of water freezing experiments with video images further suggests the accuracy of the method. Analysis and experiments show how the uncertainty, time response, and measurement range depend on the frequencies and thermal conductivity contrast. Finally, the method is demonstrated on biological tissue as further proof of principle for medical applications.

Thermal Conductivity Measurements of Thin Biological Tissues Using a Microfabricated 3-Omega Sensor

Thermal Conductivity Measurements of Thin Biological Tissues Using a Microfabricated 3-Omega Sensor

Lean Production Applications in a Manufacturing Company

&#x0D; &#x0D; &#x0D; Lean production is a production model which comes about the pursuit of companies to be able to meet competition and make effective production. The main purpose of lean production is to get control about the wastage. This study includes the requirements for the success of the lean production and how the lean production system can be established. In this paper, lean production techniques were applied to the electric water heater line. Measurements using lean initiatives were made, operation cycle times were determined, and Kaizen improvement methods and line balancing methods were applied according to the results. And the last section of study showed conclusion of lean implementation.&#x0D; &#x0D; &#x0D;

Tunneling Magnetothermopower in Magnetic Tunnel Junction Nanopillars

We study tunneling magnetothermopower (TMTP) in CoFeB/MgO/CoFeB magnetic tunnel junction nanopillars. Thermal gradients across the junctions are generated by an electric heater line. Thermopower voltages up to a few tens of μV between the top and bottom contact of the nanopillars are measured which scale linearly with the applied heating power and hence the thermal gradient. The thermopower signal varies by up to 10 μV upon reversal of the relative magnetic configuration of the two CoFeB layers from parallel to antiparallel. This signal change corresponds to a large spin-dependent Seebeck coefficient of the order of 100 μV/K and a large TMTP change of the tunnel junction of up to 90%.