Microheater Array Research Articles

Inverse heat transfer analysis for design and control of a micro-heater array

A non-linear inverse heat source identification problem is described and solved. The inverse problem analysis is used in the design of an embedded micro-heater array and to estimate the required control settings, which are the input currents to each heating element, to generate as close as possible to a prescribed temperature profile on the surface of a thin copper film. The purpose of the micro-heater array is to control the local copper microstructure through control of the local temperature field. A finite element model of the micro-heater system is used to define a discrete set of non-linear equations used as a basis for the inverse problem solution. Two methods are explored to solve the inverse problem, a direct minimization method with Tikhonov regularization and a passivity-based feedback control algorithm. A uniform and a linear temperature distribution could be attained in the central region above the micro-heater array, but the temperatures near the edges of the domain could not be controlled due to heat loss at the edges. Thus, to control the temperature field over the full width of the domain, the heater array must extend beyond the domain of interest. Both methods to solve the inverse problem are found to perform well. The regularization method allows for a smoother solution, while the feedback control method is simpler as the coefficient matrix for which the update remains unchanged for each iteration.

Development of a Novel 2-Dimensional Micro-Heater Array Device with Regional Selective Heating

<p class="1Body">This paper reports the development of a micro-heater array device that can be selectively heated at an arbitrary location. To confirm the heating characteristics of this micro-heater array device, heating experiments using a thermo-responsive gel were conducted. Since a micro-heater can supply heat with a rapid-response on a micro-scale, various applications have been studied. Based on these characteristics, micro-heaters have often been used in recent research applications involving biological cells. To expand the versatility of the micro-heater, the development of micro-heater array systems that can supply heat selectively at an arbitrary location is required. In this work, to support micro-heater applications in the field of biochemistry, the design and materials of a micro-heater array device were optimized and a fabrication process was established. Furthermore, the usefulness of this device was verified using a thermo-responsive gel, and control of the temperature distribution on a glass substrate was successfully demonstrated. This micro-heater array device can be heated with regional selectivity, and each region can be controlled to an arbitrary temperature, so the device is also capable of generating temperature gradients.<strong></strong></p>

Substrates with Programmable Heater Arrays for In-Situ Observation of Microstructural Evolution of Polycrystalline Films: Towards Real Time Control of Grain Growth

ABSTRACTAn integrated experimental – simulation – control theory approach designed to enable adaptive control of microstructural evolution in polycrystalline metals is described. A micro-heater array, containing ten addressable channels, is used to create desired temperature profiles across thin polycrystalline films in situ to a scanning electron microscope (SEM). The goal is that on heating with controlled temperature profiles, the evolution of grain growth within the film can be continuously monitored and compared to Monte Carlo simulations of trajectories towards a desired microstructure. Feed-forward and feedback control strategies are then used to guide the microstructure along the desired trajectory.

Transporting droplets through surface anisotropy

AbstractThis review article examines digital microfluidic systems that manipulate droplets through surface anisotropy. These systems are categorized as surface tension driven or contact line driven. Surface tension driven systems include electrowetting on dielectric, Marangoni flow on microheater arrays, and chemical gradient surfaces, whereas contact line driven systems include anisotropic ratchet conveyors, nanostructured Parylene ratchets, and tilted pillar arrays. This article describes the operating principles and outlines the fabrication procedures for each system. We also present new equations that unify several previous models of contact line driven systems. The strengths and weaknesses of each system are compared, with a focus on their ability to perform the generation, switching, fusion, and fission of droplets. Finally, we discuss current and potential future applications of these systems.

1P1-N08 ヒータアレイデバイスを利用した微小対象物の任意パターニング手法の開発

1P1-N08 ヒータアレイデバイスを利用した微小対象物の任意パターニング手法の開発

Optical Crosspoint Matrix Using Broadband Resonant Switches

A low loss, broadband crosspoint switch matrix using high-order resonant optical switch elements is designed, and fabricated for the first time. Multi-path routing is demonstrated for a broad range of representative paths across the circuit. Connections are assessed between eight inputs and four outputs to show losses as low as 0.9 dB per off state ring and 2.0 dB per on state ring. Analysis of the on-state and off-state transfer functions reveal switch extinction ratios exceeding 20 dB for operational bandwidths of 100 GHz for twenty-five different path combinations. Switching is implemented with thermo-optic tuning to give 100-GHz passbands and stopbands. Thermo-optic actuation with a 2-D array of on-chip microheaters allows rise and fall switching times of 17 and 4 microseconds respectively. Power penalties of less than 1.0 dB at 10 Gb/s are observed for twenty eight paths and comparable performance is observed for 40 Gb/s routing on representative paths through the switch matrix without significant signal degradation.

Effect of bubble coalescence on the wall heat transfer during subcooled pool boiling

This study experimentally investigates the effects of bubble coalescence on the heat fluxes during nucleate pool boiling. A microheater array was used to generate vapor bubbles in FC-72 liquid with constant surface temperature boundary conditions while the heat flux at selected locations was measured for various superheats using a high speed data acquisition system. The heat flux for boiling with coalescence was found to fluctuate much more than when only a single bubble formed on the surface due to the vaporization of the liquid layer trapped between the bubbles and oscillations of the bubbles after coalescence which resulted in relatively long periods of fairly high heat fluxes. The observations also showed that some coalescence events were not accompanied by an increase in the heat transfer rate as the liquid layer between the bubbles was physically pushed away by the rapid bubble growth during the inertial bubble growth stage instead of evaporating. A mechanistic model was developed to predict the conditions for which the heat fluxes do not increase during coalescence. In many other instances, the coalescence dynamics were such that the only bubble remaining on the surface was swept off by the liquid motion from the previous coalescence event with no nucleation of another bubble. This was followed by a long period without bubble nucleation followed by sudden nucleation and explosive coalescence of two bubbles giving rise to a large bubble which departed violently with a large increase in the heat transfer rate.

Effects of nucleation site arrangement and spacing on bubble coalescence characteristics

The effects of the nucleation site spacing on the bubble coalescence characteristics were experimentally studied with a microheater array. Five nucleation sites with different separation distances were arranged in a two-site pattern and a triangular three-site pattern. Each nucleation site was approximately 300μm×300μm. The dimensionless spacings were 0.49, 0.80, 0.98 and 0.94. The nucleation sites were all kept at 100°C by the control circuits. Bubble images were captured while the heat fluxes from each heater were simultaneously measured. The results show that different nucleation site arrangements and spacings greatly affect the bubble coalescence type, bubble departure diameter, departure frequency and heat flux distributions on the surface. Nucleation sites that are too close result in single bubbles without coalescence, while large separation distances result in horizontal coalescence between adjacent bubbles. Moderate spacing results in sequential coalescence with higher bubble departure frequencies. The bubble coalescence frequency is much higher with the triangular three-site pattern than with the two-site arrangement, with the bubble departure frequency and then the average heat flux greatly enhanced by the higher coalescence frequency. However, the departure diameters are slightly smaller with the triangular pattern due to the shorter growth times.

Analysis of coalescence phenomena on microheaters at two surface superheats

The bubble dynamics and detailed heat flux distributions under bubbles were investigated during coalescence on a microheater array at two surface temperatures to detail the effect of the superheat. Vertical coalescence events were observed at the lower surface temperature during single bubble boiling which increased the heat flux by pulling the smaller second bubble from the surface. The departure frequency at the lower superheat was faster than at the higher superheat during single bubble events due to more necking at higher superheats. The coalescence dynamics also differed for the two surface temperatures. Detailed analyses of the heat flux characteristics under the bubbles showed how the heat fluxes in the dryout area and around the contact line differed. The average heat fluxes were higher for the heaters outside of the contact line at higher superheats but were lower for the inner heaters. Transient conduction and vapor generation caused by rewetting were the main reasons for the heat flux enhancement. Bubble interactions including liquid motion around the bubble during the deformation process and jet flows from the smaller bubble towards the larger bubble were observed at both temperatures. The jet flows pushed the larger bubble so that the base area shrank which further increased the heat transfer.

Pool Boiling Heat Transfer on the International Space Station: Experimental Results and Model Verification

The relatively poor understanding of gravity effects on pool boiling heat transfer can be attributed to the lack of long duration high-quality microgravity data, g-jitter associated with ground-based low gravity facilities, little data at intermediate gravity levels, and a poor understanding of the effect of important parameters even at earth gravity conditions. The results of over 200 pool boiling experiments with n-perfluorohexane as the test fluid performed aboard the International Space Station (ISS) are presented in this paper. A flat, transparent, constant temperature microheater array was used to perform experiments over a wide range of temperatures (55 °C < Tw < 107.5 °C), pressures (0.58 atm < P < 1.86 atm), subcoolings (1 °C ≤ ΔTsub ≤ 26 °C), and heater sizes (4.2 mm ≤ Lh ≤ 7.0 mm). The boiling process was visualized from the side and bottom. Based on this high quality microgravity data (a/g<10−6), the recently reported gravity scaling parameter for heat flux, which was primarily based on parabolic flight experiments, was modified to account for these new results. The updated model accurately predicts the experimental microgravity data to within ±20%. The robustness of this framework in predicting low gravity heat transfer is further demonstrated by predicting many of the trends in the pool boiling literature that cannot be explained by any single model.

Nearly Perfect Polycrystalline, Large-Grained Silicon Arrays Formed at Low-Temperature Ambient by Local Pyrolysis

We report low-temperature ambient synthesis of high-quality, several micrometer thick polycrystalline silicon arrays on soda lime glass substrates by local pyrolysis, where SiH4 gas is locally decomposed near and condensed on the resistively heated microheater arrays with an average growth rate of 50 nm/s. The silicon arrays had nearly perfect crystallinity and a minimum grain size larger than 0.2 μm, as determined by spatially resolved Raman spectroscopy and transmission electron microscopy. Boron-doped silicon arrays by the local pyrolysis was further fabricated to yield concentric p-i-n heterojunction arrays with rectifying current–voltage or photovoltaic characteristics.

Boiling in variable gravity under the action of an electric field: results of parabolic flight experiments

Results from the variable gravity pool boiling experiments performed during the 52nd ESA parabolic flight campaign are reported in this paper. During a typical parabola, the gravity acceleration changes from 1.8gE (high gravity) to ∼0gE (low gravity) and finally back to 1.8gE. The two high gravity periods and the microgravity period are each roughly maintained for 20 seconds while the transition from high gravity to low gravity and vice versa occurs over a period of 3–5 seconds. Use of the high feedback frequency microheater array allowed quasi-steady boiling data over the continuous range of gravity levels (0gE-1.8gE). The experimental apparatus consisted of a boiling chamber with a 7×7 mm2 microheater array in a 10×10 configuration. Each heater in the array was individually controlled to maintain a constant temperature. The array could be operated in a full configuration or a selectively powered reduced set of 3×3 heaters. Experiments were performed with FC-72 as the test fluid, the pressure was maintained at a constant value between 1 and 1.13 atm and the subcooling ranged from 27 to 11 K. An external electric field was imposed over the boiling surface by means of a grid consisting of 4 rods, laid parallel to the surface; voltages up to 10 kV were applied. The electric field was effective in reducing the size of the detaching bubbles, and increasing the heat transfer compared to the values in low-g, although its effectiveness decayed as the heat flux/superheat increased. The current results compared well with previous results obtained in the ARIEL apparatus that was operated in orbital flight.

A biopsy tool with integrated piezoceramic elements for needle tract cauterization and cauterization monitoring

This paper reports the feasibility of biopsy needle tract cauterization and cauterization monitoring using an embedded array of piezoceramic microheaters. Circular heaters of lead zirconate titanate (PZT-5A), with 200μm diameter and 70-80μm thickness, are fabricated using a batch mode micro ultrasonic machining process. These are then assembled into cavities in the walls of 20-gauge stainless steel needles and sealed with epoxy. Experiments are performed by inserting the proposed biopsy needle into porcine tissue samples. The needle surface exceeds the minimum target temperature rise of 33°C for either radial or thickness mode vibrations. The corresponding input power levels are 236mW and 325mW, respectively. The tissue cauterization extends 1-1.25mm beyond the perimeter of the needle and is uniform in all directions. After cauterization, the fundamental anti-resonance frequency and the corresponding impedance magnitude of the PZT heater decrease by 4.1% and 42.6%, respectively, thereby providing a method to monitor the extent of tissue cauterization. A sensing interface circuit capable of measuring the resonance frequency shift of the PZT elements is built and tested using discrete integrated circuit components. The circuit detects the resonance frequency shift from 8.22MHz to 7.96MHz of the PZT elements when the biopsy needle is inserted into wax medium. An interface circuit for actuation of the PZT elements for tissue cauterization is also described.

Prediction of PF-5060 Spray Cooling Heat Transfer and Critical Heat Flux

Spray cooling heat transfer measurements of PF-5060 on smooth flat surfaces were obtained using a microheater array operated at constant temperatures using two nozzles (hollow cone and full cone), three nozzle-to-heater standoff distances (3, 5, and 7 mm), four nozzle operating pressures (207 kPa, 345 kPa, 483 kPa, and 689 kPa), and three subcooling levels (11 °C, 21 °C, 31 °C). A separate test setup was used to measure the local normal pressures produced by the sprays. The critical heat flux was found to depend primarily on the local normal pressure and the liquid subcooling. Furthermore, the temperature at which CHF occurred was within a narrow temperature band (about ±5 °C) for smooth flat surfaces over a wide range of spray conditions. The single-phase correlation previously proposed by the authors and the CHF correlation presented in this work were then combined to predict local spray cooling curve within ±25% of the measured values in the spray impingement zone.

Selective formation of GaN-based nanorod heterostructures on soda-lime glass substratesby a local heating method

We report on the fabrication of high-quality GaN on soda-lime glass substrates, heretoforeprecluded by both the intolerance of soda-lime glass to the high temperatures requiredfor III-nitride growth and the lack of an epitaxial relationship with amorphousglass. The difficulties were circumvented by heteroepitaxial coating of GaN onZnO nanorods via a local microheating method. Metal-organic chemical vapordeposition of ZnO nanorods and GaN layers using the microheater arrays producedhigh-quality GaN/ZnO coaxial nanorod heterostructures at only the desired regions onthe soda-lime glass substrates. High-resolution transmission electron microscopyexamination of the coaxial nanorod heterostructures indicated the formation ofan abrupt, semicoherent interface. Photoluminescence and cathodoluminescencespectroscopy was also applied to confirm the high optical quality of the coaxial nanorodheterostructures. Mg-doped GaN/ZnO coaxial nanorod heterostructure arrays, whoseGaN shell layers were grown with various different magnesocene flow rates, werefurther investigated by using photoluminescence spectroscopy for the p-type dopingcharacteristics. The suggested method for fabrication of III-nitrides on glass substratessignifies potentials for low-cost and large-size optoelectronic device applications.

Formation of 10-μm-level patterned organic thin film using microthermal evaporation

This article reports the fabrication of 10-μm-level stripe patterns on an organic layer using microthermal evaporation. During this process, an organic layer is coated on a glass substrate with a bridge-type microheater array, and then selectively evaporated and deposited to form a fine pattern onto another glass substrate, separated by a micron-scale gap from the microheater array. Using a unique numerical model for microthermal evaporation, thickness profiles of the pattern were calculated and matched to experimental data. Furthermore, high optical qualities of the transferred luminescent pattern layer were confirmed using microphotoluminescence spectroscopy. This microthermal evaporation method confirms the feasibility of fabricating fine organic patterns with scalability to larger sizes.

Carbon‐Nanotube‐Film Microheater on a Polyethylene Terephthalate Substrate and Its Application in Thermochromic Displays

Polyethylene terephthalate (PET) is used as the substrate of a carbon nanotube (CNT)-film heater to improve its mechanical robustness. The thermal response is improved by using thin PET and downsizing the CNT-film area. Thermal response times from room temperature to 100 °C of 2 and 5 s are achieved. An addressable microheater array is fabricated and used in thermochromic displays. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Development of a General Dynamic Pressure Based Single-Phase Spray Cooling Heat Transfer Correlation

One of the main challenges of spray cooling technology is the prediction of local and average heat transfer coefficients on the heater surface. It is hypothesized that the local heat transfer coefficient can be predicted from the local normal pressure produced by the spray. In this study, hollow cone, full cone, and flat fan sprays, operated at three standoff distances, five spray pressures, and two nozzle orientations, were used to identify the relation between the impingement pressure and the heat transfer coefficient in the single-phase regime. PF-5060, PAO-2, and PSF-3 were used as test fluids, resulting in Prandtl number variation between 12 and 76. A microheater array operated at constant temperature was used to measure the local heat flux. A separate test rig was used to make impingement pressure measurements for the same geometry and spray pressure. The heat flux data were then compared with the corresponding impingement pressure data to develop a pressure-based correlation for spray cooling heat transfer. The maximum deviation between the experimental data and prediction was within ±25%.

Development of Gold Microheater Array Devices for Investigation of Thermo-Mechanism of Heat Shock Proteins at Single Cell Level

Development of Gold Microheater Array Devices for Investigation of Thermo-Mechanism of Heat Shock Proteins at Single Cell Level

Selective Formation of Carbon Nanotubes and Its Application to Field-Emitter Arrays

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> At room-temperature ambient, carbon nanotubes (CNTs) were selectively synthesized on each bridge of the microheater array (MHA) formed on a glass substrate. Both multiwalled (MW) and single-walled CNTs could be formed by controlling the MHA temperature, which was confirmed from Raman spectroscopy. By incorporating the selectively grown MW CNTs into the lateral-gated field-emitter arrays, high current density of electron emission was observed with low device leakage. </para>