Multimodal Damage Detection in Self‐Sensing Fiber Reinforced Composites

Internal delamination damage is detected in fiber reinforced polymer composite materials containing active functionality. Damage‐triggered magnetization of the delaminated zone is accomplished using a vascular system to deliver fluids that precipitate magnetic particles upon mixing. Multiple modes of detection are used to sense the presence of this magnetic material. Visual detection is accomplished by the high contrast between damaged and undamaged areas provided by the biomimetic “bruise” formed by the magnetic particles. Magnetic scanning is also used to detect the particles, even if obscured by paint or by opaque reinforcement, such as carbon fiber. Additionally, thermal detection is accomplished by inductively heating the magnetic particles and sensing the temperature differential with an infrared camera. The effectiveness of each detection mode is discussed and compared to industry standard C‐scan to assess accuracy. Using the damage area measured with C‐scan as the benchmark, visual detection measures the damage area with 76% accuracy, and magnetic detection measures the damage area with 91% accuracy. Thermal detection accuracy is time‐dependent as expected. All detection modes consistently detect the presence of damage. The multifunctionality of this material can tailor damage detection techniques for the application and provide a parallel system to augment and potentially enhance self‐healing.     

一种高精度医学红外热像图的实现方法

医学红外热像设备测得的红外数据及转换得到的温度数据难以直接判定其所属的人体区域,常需将其转为图像数据,利用图像处理技术得到感兴趣区域并从区域内温度数据得到生物特征,实现疾病的筛查或诊断。然而,从14位红外数据转换到8位图像数据存在严重的数据精度损失,导致处理性能欠佳。本文提出一种新的热像图表达方法,所得到的彩色热像图含原精度的温度数据信息,且含温度观察窗设定尺度下的彩色增强效果,同时载有温度数据记录和观察窗设定规则,通过对图像数据的逆变换,可以再现原始温度数据,并可改变彩色增强效果。该方法提供的热像图无需额外存取温度数据文件,在不同的红外热像系统间具有通用性,将更符合大数据和人工智能的发展趋势。     

SThM Temperature Mapping and Nonlinear Thermal Resistance Evolution With Bias on AlGaN/GaN HEMT Devices

Channel temperature has a strong impact on the performance of a microwave power transistor. In particular, it has a strong influence on the power gain, energetic efficiency, and reliability of the device. The thermal optimization of device geometry is therefore a key issue, together with precise measurements of temperature within the channel area. In this paper, we have used scanning thermal microscopy to perform temperature mapping, at variable dc bias points, on an AlGaN/GaN high-electron mobility transistor made on epilayers grown on silicon carbide substrate. We have analyzed the variation of the thermal resistance values, which are deduced from these measurements, with bias conditions V_GS and V_DS. The observed nonlinear behavior is found to be in excellent agreement with physical simulations, strongly pointing out the large variability of the extension of the dissipation area with the dc bias conditions     

A high precision high PSRR bandgap reference with thermal hysteresis protection

To meet the accuracy requirement for the bandgap voltage reference by the increasing data conversion precision of integrated circuits,a high-order curvature-compensated bandgap voltage reference is presented employing the characteristic of bipolar transistor current gain exponentially changing with temperature variations.In addition,an over-temperature protection circuit with a thermal hysteresis function to prevent thermal oscillation is proposed.Based on the CSMC 0.5μm 20 V BCD process,the designed cir...     

Development of a thermal resistance model for chip-on-board packaging of high power LED arrays

The performance of high power LEDs strongly depends on the junction temperature. Operating at high junction temperature causes degradation of light intensity and lifetime. Therefore, proper thermal management is critical for LED packaging. While the design of the heat sink is a major contributor to lowering the overall thermal resistance of the packaged luminaire, another area of concern arises from the need to address the large heat fluxes that exist beneath the die. In this study we conduct a thermal analysis of high power LED packages implementing chip-on-board (COB) architecture combined with power electronic substrate focusing on heat spreading effect. An analytical thermal resistance model is presented for the LED array and validated by comparing it with finite element analysis (FEA) results. By using the analytical expression of thermal resistance, it is possible to understand the impact of design parameters (e.g., material properties, LED spacing, substrate thickness, etc.) on the package thermal resistance, bypassing the need for detailed computational simulations using FEA.     

超大口径在轨组装红外望远镜遮阳罩热设计

超大口径在轨组装红外望远镜体积大、工作温度低,各组装模块间存在相互干扰,传统热控手段不能完全满足其热控需求。为达到热控指标,分析、利用日地-L2点轨道外部热环境特性,设计了一个面向超大口径在轨组装红外望远镜的五层遮阳罩。使用UG软件建立了该望远镜有限元模型,并进行了仿真分析。结果显示:来自太阳的1 296 W/m2的热辐射经过遮阳罩的遮挡后,到达低温区的辐射强度降低到0.036 W/m2,望远镜在遮阳罩展开后约210天时通过辐射被动制冷降温至50 K以下,满足热控需求。该设计为未来我国建造超大口径空间望远镜进行了热控技术探索,具有一定的参考价值。     

晶体管发射区归一化面积的温度谱

从芯片表面的红外热像图中提取出了发射区热像图,提出了一种定量描述晶体管结温不均匀性的新方法,即发射区热谱分析方法。发射区热谱是发射区归一化面积的温度谱,也就是发射区温度所占有的发射区归一化面积对温度的直方图。本文提供了由红外热像图导出发射区热谱的过程及结果。     

基于环境参数的地表热辐射时序变化模拟方法

地表热辐射时序变化模拟是红外场景仿真的核心环节。利用地表热传导差分计算地表热辐射是物理上较严谨的模拟方法，但受限于差分方程边界条件的不确定性，在红外场景仿真中未得到广泛应用。提出一种基于光照、气温、湿度等环境参数的地表热辐射时序变化计算方法。重点根据地质热环境变化规律设计闭环迭代过程，自动修正初始和下边界热辐射值，解决了边界条件的不确定问题，提高了地表热传导计算精度和算法适应性。野外实验结果表明:该算法计算温度与实测温度绝对误差小于2 K，等效黑体辐射度相对误差小于3%，为准确模拟红外动态场景提供基础。此外，利用该方法对山区地表的热辐射分布时序变化进行了模拟，显示了其在红外场景仿真方面的初步应用效果。     

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.     

Thermal resistance of light-emitting diodes

A detailed analysis of the heat flow in a light-emitting diode is carried out in the present paper. In the thermal model of a light-emitting diode, the heat flow from the active region throughout the area between it and the top contact, the nonuniform heat flux density distribution in the active region due to the current-spreading effect as well as the temperature dependence of the thermal conductivity of the semiconductor material, are taken into account. The solutions of the thermal conduction equation for a light-emitting diode are obtained for both the steady-state condition and the transient-state condition. The heat-spreading in the heat-sink is analyzed. The effect of LED construction parameters on its thermal resistance is illustrated in numerous figures.     

基于Landsat-8陆地卫星数据的火点检测方法研究

传统的火点检测算法通常利用高温地物在中红外波段或热红外波段的高发射率特性来提取火点, 然而受制于影像空间分辨率的限制如MODIS、AVHRR等, 使得很多小规模火情现象被漏检.研究发现短波红外数据也同样能被用于高温地物的识别和检测, 并且相较于热红外波段数据对低温和高温地物的区分度更大, 在精确识别和定位高温目标方面更加准确.文章利用空间分辨率为30米的Landsat-8 OLI传感器数据, 根据高温火点在近红外及短波红外波段的波谱特性, 利用改进的归一化燃烧指数(NBRS)结果自适应地确定阈值来提取疑似火点, 然后再利用高温火点在短波红外的峰值关系进行误检点剔除, 从而得到最终的火点产品.提出的算法能检测到所占像元面积10%左右的火点, 并能够有效地排除云层及建筑物的干扰, 在保证较低漏检率的同时还能达到90%左右的准确率, 相比于传统算法的火点提取精度有很大的提高.     

基于红外注意力提升机制的热成像测温区域实例分割

AI+热成像人体温度监测系统被广泛用于人群密集的人体实时温度测量。此类系统检测人的头部区域进行温度测量,由于各类遮挡,温度测量区域可能太小而无法正确测量。为了解决这个问题,该文提出一种融合红外注意力提升机制的无锚点实例分割网络,用于实时红外热成像温度测量区域实例分割。该文所提出的实例分割网络在检测阶段和分割阶段融合红外空间注意力模块(ISAM),旨在准确分割红外图像中的头部裸露区域,以进行准确实时的温度测量。结合公共热成像面部数据集和采集的红外热成像数据集,制作了“热成像温度测量区域分割数据集”用于网络训练。实验结果表明:该方法对红外热成像图像中头部裸露测温区域的平均检测精度达到88.6%,平均分割精度达到86.5%,平均处理速度达到33.5 fps,在评价指标上优于大多数先进的实例分割方法。     

基于CA-Markov模型的南京市热环境格局演变及预测分析

基于Landsat5 TM和Landsat8 OLI/TIRS数据,利用辐射传输方程法反演南京市地表温度,结合景观格局指数进行热环境格局 演变分析,并利用CA-Markov模型预测了2024年南京市热环境变化。结果表明,2000~2017年南京市高温区面积增加了456.55 km², 增幅为149.75%,中温区、低温区及次低温区面积呈现持续减少的趋势;在斑块类型水平上,高温区斑块在热力景观格局中的 优势度在迅速上升,2000~2010年热岛高温区斑块破碎度下降,斑块复杂程度降低,而2010~2017年则与之相反。 在景观水平上,南京市热力景观格局破碎程度降低,各类型斑块面积趋于均匀化,斑块间聚集程度增加。基于CA-Markov模型 模拟的2017年南京市热环境空间分布具有较高的精度,各热岛类型平均误差小于6%,模型总体Kappa系数为78.36%。 2024年南京市热环境的预测结果表明,2024年南京市热岛高温区及次高温区面积分别增加了94.96 km²、126.91 km², 中温区、次低温区及低温区面积延续了减少的趋势。     

半导体薄片激光器窗口散热模式的热效应

基于垂直外腔面发射半导体激光器窗口散热模式的传热模型,用有限元法计算了不同条件下量子阱有源区的温度变化,建立了量子阱最高温度的等效热阻模型和计算公式,并通过拟合确定了热阻模型的相关参数.计算表明量子阱最高温度与抽运功率存在线性关系,与光斑面积近反比关系,窗口散热片可显著降低量子阱有源区温度和温度的不均匀度.等效热阻模型表明由于半导体晶片内热流在径向难以扩散,热传导中存在较大串联热阻,使得散热片热扩散能力趋于饱和,其中碳化硅的散热性能约为金刚石的75%.     

From chip to inverter: Electro-thermal modeling and design for paralleled power devices in high power application

Power loss and thermal stress of semiconductor components are closely related to the reliability of high power inverter. In addition to the inverter electrical parameters, the size of semiconductor is also an important factor in inverter electro-thermal performance. In this paper, an electro-thermal model correlated with chip area and chip paralleled number is built to calculate the power switch loss and junction temperature. Then, the relationship between chips size and inverter loss/thermal behaviors can be established by this model, enabling more flexible in chip design to optimize the inverter efficiency and thermal loading. Finally, the inverter electro-thermal design procedure is established to properly select the chip area and number in a power switch. As a case study, the optimal chip paralleled structure in the high power inverter is estimated and the results are compared under varying inverter output frequency. By selecting the chip area and number in the target region, junction temperature can maintain in the limited range.     

Reliability study of underfill/chip interface under accelerated temperature cycling (ATC) loading

Interface reliability issue has become a major concern in developing flip chip assembly. The CTE mismatch between different material layers may induce severe interface delamination reliability problem. In this study, multifunctional micro-moiré interferometry (M³I) system was utilized to study the interfacial response of flip chip assembly under accelerated thermal cycling (ATC) in the temperature range of −40 °C to 125 °C. This in-situ measurement provided good interpretation of interfacial behavior of delaminated flip chip assembly. Finite element analysis (FEA) was carried out by introducing viscoelastic properties of underfill material. The simulation results were found to be in good agreement with the experimental results. Interfacial fracture mechanics was used to quantify interfacial fracture toughness and mode mixity of the underfill/chip interface under the ATC loading. It was found that the interfacial toughness is not only relative to CTE mismatch but also a function of stiffness mismatch between chip/underfill.     

Mechanism and thermal effect of delamination in light-emitting diode packages

This work reports on the mechanism of delamination in light-emitting diode (LED) packages and its effects on thermal characteristics of LEDs. The LED samples were subjected to moisture preconditioning followed by heat block testing. Transient thermal measurements were performed to investigate the thermal behavior of the delaminated LEDs. Increase of thermal resistance with the degree of delamination was observed from the transient measurement. The thermo-mechanical and hygro-mechanical stress distributions calculated from coupled-field FEA simulation agree well with the micrographical evidence. It was found that the thermo-mechanical stress plays more important role than the hygro-mechanical stress for the development of delamination in the LED packages. Moisture preconditioning for 3 and 6 h under 85 °C/85RH conditions was found to make little contribution to the delamination between the chip and lead frame.     

拉盖尔-高斯光束作用下熔石英温度及应力研究

为了研究拉盖尔-高斯光束与熔石英相互作用,采用仿真计算的方法对TEM₀₀,TEM₀₁和TEM₁₀ 3种模式拉盖尔-高斯光束辐照下的熔石英的温度和热应力进行研究,取得了仿真数据。结果表明,激光光强的空间分布影响材料的温度分布和应力分布;温度的积累效应明显,经过连续激光脉冲作用后材料温度持续升高,焦点区域超过1900℃;温度梯度导致热应力产生,局部热应力接近50MPa。该仿真结果为熔石英的加工提供了有益的参考。     

含丙烯酸胶膜刚挠结合板钻通孔试验及其机理研究

为了提高刚挠结合板的挠曲次数,往往把挠性区做成两层或两层以上的分层结构。这种结构就要使用到单面软板。两个单面挠板的粘合一般都使用丙烯酸胶膜。和刚板不同的是,挠板中的PI（聚酰亚胺）和丙烯酸都有很大的塑性。钻完刚性区通孔后,孔内的挠板区由于材料还有一定的弹性恢复就会有几微米到几十微米的尺寸突出。在该区域,它与孔金属化铜层之间结合力会非常低。为此,本文将通过优化试验参数,获得最佳的试验参数,并通过机理的研究,指导制作出平整,优良的孔壁,获得优良的金属化孔。     

基于红外热图像灰度修正的辐射测温

基于红外热像仪的测温精度依赖于大气温度、相对湿度、大气透射率、翻转表像温度等参数的测量精度。为了减少这种依赖性和提高测量精度,提出了一种基于红外热图像灰度修正的辐射测温方法。首先基于高精度面源黑体建立了红外热图像灰度修正模型,然后通过灰度修正模型对实测的目标灰度进行修正,最后通过基于加权最小二乘法建立的热像仪辐射定标模型等计算出修正后的目标亮度和温度。在实验室环境下,分别基于红外热像灰度修正辐射测温法和直接用热像仪测温对目标进行了测量。结果表明,在实验室环境下,前者的平均测量精度较后者提高了3.6%。该方法对实验室环境下红外测温有较好的实用价值,对外场红外测温也有一定的借鉴意义。