Thermoelectric Energy Harvesting Using Phase Change Materials (PCMs) in High Temperature Environments in Aircraft

Wireless, energy-autonomous structural health-monitoring systems in aircraft have the potential of reducing total maintenance costs. Thermoelectric energy harvesting, which seems the best choice for creating truly autonomous health monitoring sensors, is the principle behind converting waste heat to useful electrical energy through the use of thermoelectric generators. To enhance the temperature difference across the two sides of a thermoelectric generator, i.e. increasing heat flux and energy production, a phase change material acting as thermal mass is attached on one side of the thermoelectric generators while the other side is placed on the aircraft structure. The application area under investigation for this paper is the pylon aft fairing, located near the engine of an aircraft, with temperatures reaching on the inside up to 350 °C. Given these harsh operational conditions, the performance of a device, containing erythritol as a phase change material, is evaluated. The harvested energy reaching values up to 81.4 J can be regulated by a power management module capable of storing the excess energy and recovering it from the medium powering a sensor node and a wireless transceiver.     

High Thermoelectric Power Factor Near Room Temperature in Full-Heusler Alloys

We present results on the electrical resistivity, Seebeck coefficient, and thermal conductivity for the Heusler alloys Fe₂VAl_1–x Si _x and Fe₂VAl_1–x Sn _x synthesized using standard arc-melting techniques. While alloys with x = 0 are p-type, upon substitution of Si or Sn for Al the alloys can be made n-type with optimized sample compositions exhibiting thermoelectric power factors in excess of that of bismuth telluride near room temperature. The lattice thermal conductivity κ _L of these alloys is too large to produce a high figure of merit; the prospects for and initial attempts at lowering κ _L are discussed.     

大面积高分辨率光刻技术研究

以NSR1755i7A型投影曝光机为基础,分析了影响大面积精细光刻图形分辨率的主要因素。利用表面平坦化技术、BARC工艺技术和PEB工艺技术,解决了高分辨率和聚焦深度的矛盾,消除了曝光过程中出现的表面反射和因驻波造成曝光图形边缘罗纹状的现象,实现了大面积（17．5mm×17．5mm）、高长宽比（160）、高密集（占空比36％）、高分辨率亚微米（0．5um）精细线条光刻。同时提出了采用两次曝光技术在NSR1755i7A型投影曝光机上实现了厚胶高分辨率图形的制作。     

Large Area Electronics Using Printing Methods

After the demonstration of the first organic FET in 1986, a new era in the field of electronic began: the era of organic electronics. Although the reported performance of organic transistors is still considerably lower compared to that of silicon transistors, a new market is open for organic devices, where the excellent performance of silicon technology is not required. Several commercial applications for organic electronics have been suggested: organic RFID tags, electronic papers, imagers, sensors, organic LED drivers, etc. The main advantage of organic technologies over silicon technologies is the possibility of making low-cost, large area electronics. The main processes which allow patterning with suitable resolution on a large areas are printing methods. Here we will provide an overview of methods that can be useful in the low-cost production of large area electronics.     

高温半导体器件的研究现状

金刚石和碳化硅的热特性及电特性决定了它们在电子器件半导体材料中具有最高的材料优质系数，特别适用于在高温环境中应用。本文重点或介绍了金刚石、ＳｉＣ的材料特性、薄膜生长技术和最近器件的研究结果，同时给出了目前存在的问题及解决这些问题的方法。     

Evaluating Thermoelectric Power Generation Device Performance Using a Rectangular Microchannel Heat Sink

In this work, a microchannel heat sink is applied to a thermoelectric power generation (TEG) device and compared with a traditional heat sink. The advantages and disadvantages of using each heat sink in a TEG device are evaluated. The microchannel hydraulic diameter is 5.33 × 10⁻⁴ m and that of the macrochannel is 2.13 × 10⁻³ m. Pressure drops and heat removed in the micro heat sink configuration are obtained for six different mass flow rates for the laminar and turbulent fluid flow regimes. By computationally applying a constant temperature difference between the hot and cold sides of the TEG, the fluid and thermal parameters are considered for both laminar and turbulent regimes in the channels. Furthermore, using the temperature difference through each TEG, the system efficiency is calculated. The results show that the microchannel heat sink gives a higher pressure drop, but the heat flow across the TEG device and the mass flow rate needed to provide the same generated power are less than for the macrochannel heat sink.     

具有优良温度特性的大功率器件

本文介绍了一种大功率器件,其耐压大于100V,I_(CM)>6A,P_(CM)>50W,f_T～200MHz,温度从-55℃变化到+150℃时,其共射极电流放大系数几乎不变。     

Finite Element Thermomechanical Modeling of Large Area Thermoelectric Generators based on Bismuth Telluride Alloys

A recent investigation was carried out to evaluate the level of mechanical stress generated in a thermoelectric (TE) module subjected to a temperature gradient. The study was based on the numerical simulation of the thermomechanical behavior of realistic TE generator modules under various operating conditions and leg lengths. By the use of finite element analysis the behavior of large modules (30 × 30 mm² and 40 × 40 mm²) was examined under realistic boundary conditions at the heat exchange interfaces. For example, the module was constrained between two rigid plates under a given compressive load, and different sliding conditions were assessed. The plastic deformation of the soldering alloys was shown to reduce the amount of stress in the legs. One of the main results indicated that an increase in the maximum stress values appeared in the legs as they were closer to the edges. For such large modules, the simulation predicted a measurable displacement of the ceramic plates between the center and the edges of the module under steady state operation with a temperature difference of 100°C. We provide a satisfactory experimental validation by optical profiler measurements.     

宽温超高频双极静电感应晶体管研制

描述了宽温超高频ｐｎｐ双极静电感应晶体管的结构、工作原理、设计与制造。测试结果表明,环境温度从２３℃升到１８０℃时,器件的ｈＦＥ随温度平均变化率小于４０％,优于同类型的常规双极结型晶体管,平均改善３０％。     

Terahertz Oscillating Devices Based Upon the Intrinsic Josephson Junctions in a High Temperature Superconductor

Recent developments of coherent terahertz (THz) oscillators based on the intrinsic Josephson junctions (IJJs) in mesas of the high temperature superconductor Bi₂Sr₂CaCu₂O_8+δ are reviewed. Experimental and theoretical studies of the emission from equilateral, right-angled isosceles, and acute isosceles triangular mesas are compared with those obtained from rectangular, square, and disk mesas, in order to determine the role of the mesa geometry. The superconducting properties and emission frequency f spectra are presented for a variety of triangular mesa geometries. Analytic and finite difference time domain numerical calculations of the emissions from the internal electromagnetic (EM) cavity modes of triangular mesas are compared with experiment. The experimental f always satisfies the ac Josephson relation, and its narrow linewidth arises from the synchronized emissions from many IJJs. For some mesa geometries, f also strongly locks onto an EM cavity mode frequency, enhancing the emission’s stability and output power. For other geometries, such cavity mode locking is weak, and f is highly tunable.     

Large Mode Area Fibers for High Power Applications

We review our recent work toward designing large mode area fibers for high power applications. We show that appropriately designed doped multimode fibers can be used to provide robust single-mode output when used in fiber laser cavities. Single-mode (SM) fiber mode field diameters of ∼ 35 μm are demonstrated with record SM pulse energies of 0.5 mJ at 1550 nm with a repetition rate of 200 Hz. Energies approaching 1 mJ are obtained with a slight compromise in mode quality. A modification in the laser cavity results in a passively modelocked laser giving femtosecond pulses with nanojoule energies.     

Development of a Thermal Buffering Device to Cope with Temperature Fluctuations for a Thermoelectric Power Generator

To stabilize the heat input to a thermoelectric generator (TEG) and protect it from large temperature fluctuations, a thermal buffering device (TBD) was fabricated and examined using a typical Bi-Te TEG module and a brand-new Mg₂Si TEG module. The TBD comprises two adjoining heat storage containers, each containing different alloys, which can be optimized for the temperature range of the TEG. The combination of two alloys in series diminishes the thermal fluctuations, stabilizing the heat input to the TEG module. This is achieved by having two metallic materials with large enthalpies of fusion that can be placed between the heat source and the TEG. The combination of the two alloys can be optimized for the temperature ranges of Bi-Te, Pb-Te, or Co-Sb. For the Bi-Te TEG, 15Al-85Zn and 30Sn-70Zn alloys were used for the heat source side and the TEG side, respectively. The corresponding alloys for the Mg₂Si TEG were 20Ni-80Al and 7Si-93Al. With the use of a TBD, the Bi-Te TEG exhibited no notable damage even in the rather high temperature range beyond ??573?K. For the Mg₂Si TEG, no operational damage of the Mg₂Si TEG module was observed even with a temperature of 1020?K.     

Measurement of Thermal Conductivity Using Steady-State Isothermal Conditions and Validation by Comparison with Thermoelectric Device Performance

A new technique for measuring thermal conductivity with significantly improved accuracy is presented. By using the Peltier effect to counterbalance an imposed temperature difference, a completely isothermal, steady-state condition can be obtained across a sample. In this condition, extraneous parasitic heat flows that would otherwise cause error can be eliminated entirely. The technique is used to determine the thermal conductivity of p-type and n-type samples of (Bi,Sb)₂(Te,Se)₃ materials, and thermal conductivity values of 1.47?W/m?K and 1.48?W/m?K are obtained respectively. To validate this technique, those samples were assembled into a Peltier cooling device. The agreement between the Seebeck coefficient measured individually and from the assembled device were within 0.5%, and the corresponding thermal conductivity was consistent with the individual measurements with less than 2% error.     

Power Consumption and Temperature Increase in Large Area Active-Matrix OLED Displays

We model and analyze the power consumption and resulting temperature rise in active-matrix organic-light-emitting device (AMOLED) displays as a function of the OLED efficiency, display resolution and display size. Power consumption is a critical issue for mobile display applications as it directly impacts battery requirements, and it is also very important for large area applications where it affects the display temperature rise, which directly impacts the panel lifetime. Phosphorescent OLEDs (PHOLEDs) are shown to offer significant advantage as compared to conventional fluorescent OLEDs due to high luminous efficiency resulting in lower pixel currents, reducing both the power consumed in the OLED devices and the series connected driving thin-film transistor (TFT). The power consumption and temperature rise of OLED displays are calculated as a function of the device efficiency, display size, display luminance and the type of backplane technology employed. The impact of using top-emission OLEDs is also discussed.     

A Large Area Flexible Array Sensors Using Screen Printing Technology

A flexible electronics sensor for large area sensing was developed using a screen printing technology with the thixotropy sol-gel materials to form the microstructure patterns on two polyimide (PI) sheets. A flexible sensor is 150$times$150 mm$^{2}$, including posts, resistances, bumps, and electrode traces. The space between the top electrode and the resistance layer provided a buffer distance for large bending. Experimental results show that array microstructures have good morphological profiles at a screen speed of 10 mm/s, a squeegee pressure of 213 kPa, and a separation speed of 0.4 mm/s using the print–print mode. A membrane with a bump protrusion had a large displacement and a quick sensitive response because the bump provided a concentrated force of von Mises stress on the membrane center. For printing thick structures, diffusion effects and dimensional shrinkages can be reduced when a paste material with a higher viscosity is used. The results exhibit a potential for using in the flexible sensing and higher temperatures. In additional, the fabrication is the low cost and potential higher throughput in flexible electronics applications.      

High Thermoelectric Performance in PbTe Due to Large Nanoscale Ag2Te Precipitates and La Doping

Thermoelectrics are being rapidly developed for waste heat recovery applications, particularly in automobiles, to reduce carbon emissions. PbTe‐based materials with small (<20 nm) nanoscale features have been previously shown to have high thermoelectric figure‐of‐merit, zT, largely arising from low lattice thermal conductivity particularly at low temperatures. Separating the various phonon scattering mechanisms and the electronic contribution to the thermal conductivity is a serious challenge to understanding, and further optimizing, these nanocomposites. Here we show that relatively large nanometer‐scale (50–200 nm) Ag₂Te precipitates in PbTe can be controlled according to the equilibrium phase diagram and these materials show intrinsic semiconductor behavior with high electrical resistivity, enabling direct measurement of the phonon thermal conductivity. This study provides direct evidence that even large nanometer‐scale microstructures reduce thermal conductivity below that of a macro‐scale composite of saturated alloys with Kapitza‐type interfacial thermal resistance at the same overall composition. Carrier concentration control is achieved with lanthanum doping, enabling independent control of the electronic properties and microstructure. These materials exhibit lattice thermal conductivity which approaches the theoretical minimum above ～650 K, even lower than that found with small nanoparticles. Optimally La‐doped n‐type PbTe‐Ag₂Te nanocomposites exhibit zT > 1.5 at 775 K.     

Exceptional Performance Driven by Planar Honeycomb Structure in a New High Temperature Thermoelectric Material BaAgAs

The discovery of new, high-performing thermoelectrics is of vital importance to promoting thermal energy conversion efficiency. Herein, a new p-type thermoelectric material BaAgAs with an exceptional figure of merit (zT) surpassing 1.1 at 970 K is present as a promising candidate for high-temperature applications. Verified by comprehensive experimental and theoretical investigations, BaAgAs possesses two intrinsic features in favoring zT: i) low lattice thermal conductivity, ascribed to the heavy element Ba in a loose mono-hexagonal layer, the large mass fluctuation in the Ag-As honeycomb layer, and the alternately interlayer stacking between mono-hexagonal and honeycomb layers; ii) good electrical properties contributed by multiple band transport, due to the small band offset between two valence band extremums and the strong anisotropic band effective mass. With enhanced phonon–phonon scattering via Sb/Bi substitution on the As sites, the lattice thermal conductivity is minimized, which results in significantly enhanced zT values. Additionally, an inspiring prediction via the first-principles calculation suggests that n-type BaAgAs can potentially outperform its p-type counterpart due to its higher conducting band degeneracy. This study will stimulate intense interests in the exploration of compounds with planar honeycomb structures as new high-performance thermoelectric materials.     

高温正向大电流下TiAl、TiPtAu栅GaAs MESFET的栅退化机理及其对器件特性的影响

针对ＧａＡｓ ＭＥＳＦＥＴ在微波频率的应用中的射频过驱动导致高栅电流密度现象,设计了Ｔｉａｌ栅和ＴｉＰｔＡｕ栅ＧａＡｓ ＭＥＳＦＥＴ的高温正向大电流试验,通过对试验数据和试验样品的扫描电镜静态电压衬度像以及试验中的失效样品进行分析,确定了栅寄生并联电阻的退化是导致器件的跨导ｇｍ、栅反向漏电流Ｉｓ、夹断电压Ｖｐ等特性退化,甚至导致器件烧毁失效的主要原因。