A matrix doubling formulation of internal emission from a layerwith irregular boundaries

A formulation for internal emission from a thermal scattering layered medium with irregular boundaries is developed. The matrix doubling method is utilized to obtain the upward and downward thermal intensities inside the scattering layer. The scattering layer is assumed to be a slab embedded with randomly positioned thermal scattering particles, and the upper and lower boundaries are assumed to be random rough surfaces. The developed emission model may be useful for the understanding of the internal emission problem where a radiometer is located inside an emitting medium with irregular rough boundaries     

体内异常热源参数与体表温度关系的热像研究

人体内异常热源的位置信息在体表上表现为对应部位温度较高。体表温度可以通过医用红外热像仪摄取,这是诊断体内异常热源的方法之一。但是其摄取的体表温度分布并不能直接反应体内异常热源位置等信息,因此对热源深度、温度、热物性等参数与体表温度分布之间相互关系的研究是非常必要的。该文基于生物热传导方程,通过建立有限元模型,仿真分析了体内热源参数对体表温度分布的影响;将研制的温度可调的恒温热源埋于分层生物组织内,并以红外热像仪摄取各层生物组织的温度,给出体内、体表温度场的分布,对理论仿真结果进行实验验证。研究结果表明,体表温度分布与体内热源深度的关联性最大,为体内异常热源诊断的热像技术研究提供理论与实验依据。     

The Thermal Response of a Human in the Near-Zone of a Resonant Thin-Wire Antenna

The thermal response of a human in the near-zone of an antenna was determined by numerical procedures. The approach taken was to modify the heat transfer equations for man in air to account for thermal loading due to the energy absorbed from the radiating antenna. The absorbed power density distribution in the human body was determined by considering the body and antenna to be a coupled system in which the resulting system of equations were solved by moment method procedures. This information was then analyzed by a thermal response model consisting of a series of transient conduction equations with internal heat generation due to metabolism, internal convective heat transfer due to blood flow, external interaction by convection and radiation, and cooling of the skin by sweating and evaporation. Internal heating patterns were calculated for two cases: a human in the near-zone of a quarter-wave monopole and a half-wave dipole operating at 45 and 200 MHz, respectively. It was found that negligible heating occurred for antennas with input power levels of less than 50 W.     

用于生物组织电特性重建的探头研究

对适用于分层生物组织电特性重建的宽带同轴贴片探头进行了研究.采用时域有限差分(FDTD)法分析了同轴贴片探头在三层生物组织中的场分布,结合遗传算法(GA)优化了探头的尺寸.优化设计出的圆形同轴贴片探头具有轴对称特点,辐射近场在生物组织中透入深、分布集中,反射系数的频率响应特性好,适用于局部分层生物组织电特性的重建,实验证明探头的设计优化是正确的.     

Experimental and numerical study of 3D stacked dies under forced air cooling and water immersion cooling

3D stacked die structure is a promising architecture to realize small feature size and enhance electronic performance. However, thermal performance in 3D stacked die has aroused extensive attention for its high density integration. In this paper, a stacked dummy die structure integrated with polyimide heater inside is presented to investigate the thermal behavior of 3D stacked dies. One-dimensional thermal resistance network is built and calculated to analyze thermal resistance distribution of the stacked dies. Under natural convection, the thermal resistance of convective heat transfer greatly influences total thermal resistance and limits heat dissipation ability of stacked dies. To significantly reduce the thermal resistance of convective heat transfer, forced air cooling and water immersion cooling have been applied in the stacked die structure. Experiment and numerical simulation have been conducted in this work. In the experiment, forced air cooling and water immersion cooling systems are set up to cool down the stacked die structure. The temperature dependence of the stacked die structure is obtained by thermocouples. The measured thermal resistances between junction and ambient environment of the stacked die structure decrease to 7.6 °C/W under forced air cooling and to 0.6 °C/W under water immersion cooling, respectively. Then heat dissipation abilities of forced convection cooling for the stacked die structure are analyzed. Simulation models are built for experimental validation and further thermal analysis. Temperature influences on the internal structure of the stacked dies with different power map are discussed. The simulation results can well capture the experimental results with 5.8% variation under forced air cooling and with 7.4% variation under water immersion cooling when total power of 3 W is applied.     

基于主动红外的倒装芯片缺陷检测研究

传统的倒装芯片无损检测技术并不能完全满足倒装焊检测需要,为此提出了一种基于主动红外的倒装芯片缺陷检测方法。通过非接触方式对倒装芯片施加热激励,并结合红外测温设备检测芯片温度分布情况,从而对芯片内部缺陷进行诊断与识别。实验研究表明,该方法能较好地检测出倒装焊点缺陷,可应用于倒装焊芯片的缺陷检测与诊断研究。     

航空复合材料内部缺陷差动式激光红外热成像检测

航空复合材料内部缺陷的存在严重威胁着飞行安全。以航空碳纤维复合材料层合板为检测对象,利用激光作为红外热成像检测技术的热激励源,充分利用激光的远距离精准加热、高功率密度等优点,实现对复合材料内部分层缺陷的定位检测。利用激光红外热成像技术对缺陷试件和参考试件进行多次差动检测,并且依据试件与热像仪的空间位置关系,选择温差最大时刻计算内部分层缺陷的直径。实验结果表明:激光红外热成像技术可有效检测航空碳纤维复合材料内部分层缺陷。同时,首次使用的差动式激光红外方法可有效消除激光能量分布不均对检测结果带来的影响,使缺陷成像结果更清晰。     

Time domain direct and inverse problems for a nonuniform LCRG linewith internal sources

In this paper, direct and inverse problems for a nonuniform LCRG line with internal transient voltage and current sources are considered. In the inverse source problem, the compact Green functions approach based on wave splitting is used to reconstruct the transient voltage and current sources from the transient signals that are received at the two endpoints of the nonuniform line. The location of the sources is assumed to be known or possible to estimate from the arrival times of the signals. The compact Green functions are convolution kernels in the map from the received signals (at the two endpoints) to the internal split voltages. The partial differential equations for the compact Green functions are given together with the initial and boundary conditions. The present approach to the inverse source problem is exact and noniterative. To obtain independent synthetic input data for the inverse problem, the direct problem is solved by a finite difference scheme. Numerical results for reconstructions using both clean and noisy data are presented     

Two-dimensional model of heat flow in broad-area laser diode: Discussion of the upper boundary condition

This paper presents a discussion of the upper boundary condition, which should be assumed in calculations of temperature distribution in a laser diode. Using the isothermal condition instead of convection or thermal insulation is proposed. Theoretical results are compared with temperature map obtained by thermoreflectance method. The model is based on the solution of two-dimensional, stationary heat conduction equation obtained by separation-of-variables approach. Full analytical expressions are provided. All considerations deal with p-side down mounted devices.     

An efficient calculational approach to evaluation of microwave specific attenuation

An efficient calculational approach using the scattering-radiation conversion is developed in this paper to evaluate the microwave attenuation by arbitrarily distorted raindrops. For this modified first-order approach, the perturbation technique and the spherical vector eigenfunction expansion method are employed. A method of obtaining the volumetric current distribution of the assumed source that generates the plane waves is developed in the paper and the current distribution of such a source is derived. The electromagnetic fields outside the distorted raindrop scatterers are formulated in terms of integrals consisting of a volumetric current distribution located at infinity and the dyadic Green's functions. To illustrate the validity of this approach, the spheroidal raindrop and the Pruppacher and Pitter (1971) raindrop model of varying shapes are specifically investigated. Numerical results of the extinction cross sections and the specific attenuation due to the two models are obtained. While the former agrees well with the published results, the latter is in good agreement with the experimental specific attenuation data collected at 21.225 GHz in Singapore.     

Induction of hyperthermia using an intracavitary multielementultrasonic applicator

In this paper, the possibility of inducing controlled hyperthermia in rectal or vaginal wall tumors using an intracavitary ultrasonic applicator was investigated. A computer model that took into account the thermal and ultrasonic properties of tissues and surface cooling was used to optimize the transducer parameters to obtain desirable temperature distributions for different perfusion situations in the tumor. Also, an applicator that consisted of a cylindrical array of five independently controllable ultrasonic transducers was developed. This array was then tested in degassed water to determine the functional characteristics. This same applicator, modified to include water cooling of the tissue surface, was tested in vivo in dogs. The temperature distributions were found to be promising and with modifications this approach will be used in clinical treatments of suitable tumors.     

Thermal distribution calculations for block level placement in embedded systems

Reliability is a very important concern for the embedded systems. Thermal distribution has become an important reliability concern for today’s integrated circuits and these circuits are being used increasingly in embedded systems. In traditional design flows, the temperature of the chip is assumed to be uniform across the substrate. However, non-uniform thermal distribution can be a major source of inaccuracy in delay and clock skew computations, and can have an impact on elctromigration reliability and self-heating effects for today’s very deep submicron technology. Hence, it has become necessary to obtain design with uniform temperature distribution to ensure minimum temperature gradient and avoid hot spots across the chip area. This will minimise reliability problems during the operation of the chip. The uniform temperature distribution can be achieved by appropriate placement of circuit blocks during the physical design. In this paper, thermal distribution of single chip embedded system on silicon is discussed. The thermal distribution calculations require evaluation of switching activity factor of circuit blocks. This factor is determined by computing activities of the blocks based on the application software of embedded system.     

涡轮叶片红外热波无损检测技术研究

涡轮叶片的造价昂贵,为了满足涡轮叶片缺陷检测中的安全性要求,提高检测效率,本文采用红外热波无损检测技术对航空涡轮叶片内部冷却风道的缺陷进行检测,该技术不同于传统的红外检测方法,它是通过主动控制激励热源和分析测量样件表面的温度场变化获得样件表面及内部的结构信息,从而达到检测目的的,提出了烘热激励法、冷热水交替喷流激励法、涡流激励法和蒸汽激励四种检测方案,所得图像表明该技术有其独特的先进性.     

A VERTICAL LAYERED SPACE—TIME CODE AND ITS CLOSED—FORM BLIND SYMBOL DETECTION

Vertical layered space-time codes have demonstrated the snormous potential to accommodate rapid flow data.Thus far,vertical layered space-time codes assumed that perfect estimates of current channel fading conditions are available at the receiver.However,increasing the number of transmit antennas increases the required training interval and reduces the available time in which data may be transmitted before the fading coefficients change.In this paper,a vertical layered space-time code is proposed.By applying the subupace method to the layered space-time code,the symbols can be detected without training symbols and channel estimates at the transmitter or the receiver.Monte Carlo simulations show that performance can approach that of the detection method with the knowledge of the channel.     

Health-monitoring method of note PC for cooling performance degradation and load assessment

Health monitoring technologies, which can evaluate the performance degradation, load history and degree of fatigue, have the potential to improve the effective maintenance, the reliability design method and the availability in the improper use conditions of electronic equipment. In this paper, we propose a method to assess the cooling performance degradation and load history of printed circuit boards in electronic equipment by use of a hierarchical Bayes model based on Computer Aided Engineering (CAE) results of thermal-stress simulation and experiment data from observed measurements. We applied this method to note PC that can monitor the device load factor and revolution number of cooling fan. It is shown that this method can estimate the temperature and deformation distribution of the printed circuit board from monitoring variables through latent variables such as thermal dissipation of the device and thermal boundary condition by use of the hierarchical Bayes model. And it is confirmed that the statistical load assessment concerning thermal cyclic load and the maximum load distribution can be conducted using the estimated temperature and deformation data. Furthermore, we verified that the cooling performance degradation can be assessed, if the temperature difference per unit thermal value between two suitable points on the printed circuit board can be obtained. It is concluded that the proposed method can be effective to assess the thermal load history and cooling performance degradation.     

钢轨轨脚裂纹红外热波无损检测实验(英文)

目前,超声检测在钢轨裂纹检测中得到了广泛的应用,但在钢轨裂纹检测过程中,超声波检测方法存在一定的盲区,未能检测到轨脚两侧的裂纹。针对超声波检测方法的不足,搭建了一种红外热波钢轨踏面裂纹无损检测平台。钢轨裂纹红外热波无损检测平台是红外无损检测领域的一个新的研究方向,实验平台的建立主要包括3部分:热激励源的选择、实验平台的搭建、红外图像的提取。该技术用于通过热激励源加热轨底表面。根据热波理论,钢轨表面到轨底内侧的传热过程受钢轨的物理特性和内部结构的影响,如果钢轨内部存在缺陷,则缺陷类型会影响钢轨表面的温度分布。根据钢轨表面温度信息的分布,确定钢轨内部缺陷的位置,达到检测钢轨裂纹的目的。实验结果表明,裂纹对应的轨底表面温度高于无裂纹对应的轨底表面温度,证明红外热波无损检测对钢轨裂纹检测是可行的。     

The relationship of surface reflectance measurements to opticalproperties of layered biological media

Reflectance from a turbid biological tissue is discussed for a diffusive light source illuminating the surface of the medium, and is related to the optical property distribution within the medium and to photon propagation through the medium. A three-dimensional photon diffusion model with closed form is developed to describe the photon diffuse intensity in a homogeneous medium. The solution is extended by numerical methods to the medium with layered structure. The concepts of photon flux paths and of reflectance indexes are utilized, together with reflectance data, to extract information about the internal optical properties of a medium. The flux path concept was corroborated by successfully detecting in vivo and ex vivo layered differences in optical properties within the biological medium. These studies suggest that the optical properties of subdermal tissue can be measured from light reflectance and that the effect of the upper skin layers can be eliminated.     

Time-Dependent Microwave Heating and Surface Cooling of Simulated Living Tissues

The equation of conduction of heat in a model of living tissues is solved in the case of time-dependent electromagnetic heating and surface cooling. This approach allows thermal transient phenomena in the tissue to be treated as the dynamic behavior of a linear infinite-dimension system. This approach is appropriate when the tissue temperature increase must he controlled. Some results are given in a numerical simulation.     

IGBT junction and coolant temperature estimation by thermal model

The capability of IGBT (Insulated Gate Bipolar Transistor) to handle heat is one of its main limitations of high power application. This paper aims to study an IGBT thermal model under flow cooling condition and estimate the IGBT module junction and coolant temperature. Firstly, this paper studies the IGBT module internal sandwich structure and calculates the thermal resistance and thermal capacitor for each layer using a 1D physical model. Then a Cauer electric model is built for the IGBT module to evaluate the thermal constant time of the model. The liquid cooling method is applied in this project for fast cooling and the thermal parameters are studied and measured since this cooling method involves both solid and liquid. In order to estimate the junction temperature, the sensing temperature from NTC (Negative temperature coefficient) resistor inside the module is used as reference temperature. The equivalent thermal models, also named Foster model, from both junction to NTC and NTC to coolant are built, respectively. With these thermal models, the junction and coolant temperature estimation methods are derived. For the purpose of making the estimation accurate, the thermal coupling effect is carefully studied. Finally, the thermal model is verified by inverter application with current steps sweeping; the estimated temperature is compared with thermal camera measurement result which demonstrates good accuracy of the thermal model. The estimated coolant temperature is also well matched with thermocouple measurement result.     

Heat Pipe Integrated in Direct Bonded Copper (DBC) Technology for Cooling of Power Electronics Packaging

Thermal dissipation in power electronics systems is becoming an extremely important issue with the continuous growth of power density in their components. The primary cause of failure in this equipment is excessive temperatures in the critical components, such as semiconductors and transformers. This problem is particularly important in power electronic systems for space applications. These systems are usually housed in completely sealed enclosures for safety reasons. The effective management of heat removal from a sealed enclosure poses a major thermal-design challenge since the cooling of these systems primarily rely on natural convection. In this context, the presented paper treats the heat pipes as effective heat transfer devices that can be used to raise the thermal conductive path in order to spread a concentrated heat source over a larger surface area. As a result, the high heat flux at the heat source can be reduced to a smaller and manageable level that can be dissipated through conventional cooling methods. The objective of our work is to describe the feasibility of a cooling system with miniature heat pipes embedded in a direct bonded copper (DBC) structure. The advantage of this type of heat pipe is the possibility for implementation of the component layout on the heat pipe itself, which eliminates the existence of a thermal interface between the device and the cooling system