3-D thermal models calibration by parametric dynamic compact thermal models

Detailed 3-D thermal models of electronic systems require the calibration of unknown parameters to accurately describe the experimental data, which is usually obtained by a least square optimization of the measured transient thermal response to a given set of power inputs. This paper presents an extremely efficient technique to perform the identification of boundary conditions, material thermal properties, and geometrical sizes, which is based on the adoption of the trust region algorithm in combination with parametric dynamic compact thermal models. The calibration of parameters of a Package-on-Package system is performed by a simulated experiment procedure to validate the applicability and accuracy of the proposed approach. It is shown that using parametric compact models allows for a significant reduction in computational effort in comparison to conventional brute-force optimization. The calibration robustness with respect to input degradation is examined by observing the variation in the extracted parameters at different levels of noise.     

Nonlinear dynamic compact thermal models by structure-preserving projection

A novel projection-based approach is proposed for constructing compact models of nonlinear heat diffusion problems for electronic components. The method is robust since it preserves the non-linear structure of the heat diffusion equations. It is efficient, since it is constructed by determining few moments of Volterra׳s series expansions of the solution. It leads to compact models of small state-space dimensions which can be numerically solved at negligible computational cost and to accurate approximations of the whole space-time distribution of temperature rises for all significant waveforms of the injected powers.     

Bayesian methods for pharmacokinetic models in dynamic contrast-enhanced magnetic resonance imaging

This paper proposes a new method for estimating kinetic parameters of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) based on adaptive Gaussian Markov random fields. Kinetic parameter estimates using neighboring voxels reduce the observed variability in local tumor regions while preserving sharp transitions between heterogeneous tissue boundaries. Asymptotic results for standard errors from likelihood-based nonlinear regression are compared with those derived from the posterior distribution using Bayesian estimation with and without neighborhood information. Application of the method to the analysis of breast tumors based on kinetic parameters has shown that the use of Bayesian analysis combined with adaptive Gaussian Markov random fields provides improved convergence behavior and more consistent morphological and functional statistics.     

Simulation of LED based luminaires by using multi-domain compact models of LEDs and compact thermal models of their thermal environment

Fast and accurate prediction of hot lumens of LEDs installed in luminaires is an important step in the design of robust and reliable products. A possible approach to this is to create a multi-domain circuit model of a complete LED chip + package + luminaire system that can be simulated by any Spice-like circuit simulator with electro-thermal capabilities. Many LED chip and LED package models and modeling techniques have been published recently, but compact thermal modeling of luminaires as multi heat-source system was not yet dealt with in the literature. This paper aims to fill this gap be describing a systematic approach for system (luminaire) level analysis aimed at solving the combined thermal, electrical and light output simulation problem consistently by describing a method for creating a compact thermal model of LED luminaries with an approach borrowed from the layout based electro-thermal simulation of analog ICs. The applicability of the described method is demonstrated with a real life example, including the validation of the results with thermal measurements.     

Steady-state and dynamic thermal models for heat flow analysis of silicon-on-insulator MOSFETs

Self-heating in silicon-on-insulator (SOI) MOSFETs has become one of the vital issues for design, characterization, optimization and reliability prediction of SOI devices and integrated circuits due to the low thermal conductive buried oxide (BOX) and the continual increase in the microelectronic packaging density. Thermal models that are accurate and detailed enough to provide device temperature profiles and efficient enough for large scale electro-thermal simulation are therefore strongly desirable. This paper discusses the fundamental concepts for modeling of heat flow in semiconductor devices. A brief overview for the conventional approaches to thermal modeling of the SOI devices is given. Improved steady-state and dynamic SOI heat flow models based on the SOI film thermal resistance for efficient prediction of steady-state and dynamic temperature variations in SOI devices are presented. These improved models are applied to investigate temperature distributions and temporal evolution of the junction temperature in SOI nMOSFETs.     

Biological effects of electric and magnetic fields associated with ELF communications systems

The U.S. Navy has proposed a submarine communications system that operates at extremely low frequencies (ELF). The land-based transmitting antenna for this system consists of insulated conductors 50 to 100 km long, grounded at each end, and driven by a generator such that the flow of current would be along the cable, into the ground, deep in the earth, and return to the other grounded end of the cable. It would, in effect, be a large loop antenna in which the earth was part of the loop. Over the last ten years the Navy has sponsored a wide variety of research to evaluate the environmental impact of this system. A discussion of this work can logically fall into three periods: 1968 to 1973, 1973 to 1977, and work still in progress. The work during the first period was reviewed by an Ad Hoc Committee formed in 1973 by the Navy. A second committee was formed in 1976 by the National Academy of Sciences and charged to review all existing data. These committees have reported their findings but they are not readily available in the open literature. This paper does not duplicate the work of these committees but rather summarizes their results and combines them with more recent work some of which is still in progress.     

A model reduction approach for constructing compact dynamic thermal models of IGBT-modules of inverters

This paper presents a model reduction approach for constructing lumped RC thermal networks of IGBT-modules of inverters for which heat and subsequent temperature increases vary with time on different scales ranging from nanosecond to second. It was observed that the time-dependent heat and temperature profiles of transistors and diodes of IGBT-modules of inverters oscillate at two frequencies, one in the range 0.1–50 Hz corresponding to the load current modulation, and the other in the range 1–20 kHz corresponding to the switching frequency. The reduction approach consisted of decomposing the module into different elements, each being described with a number of RC cells selected according to the time-constant of the element with regard to the module. The lumped RC thermal networks were found in good agreement with the continuous model by offering a considerably lower computational time on the different time scales. For simplicity, the reduction approach is presented for one-dimensional heat flow through the cross-plane direction of the module.     

Innovative methodology to extract dynamic compact thermal models: Application to power devices

This paper presents a new and innovative methodology for power components manufacturers to generate accurate boundary condition independent dynamic Compact Thermal Models (“BCI” DCTMs). The originality of this methodology is summarized by taking into account the thermal behavior of electronic components containing several cooling surfaces, and representing the non-linear properties of materials, while keeping a simple and recurring structure of generated models. Moreover, the proposed method makes it possible to obtain DCTMs with a limited number of measurements or 3D thermal simulations. The methodology to construct the DCTM is based on the construction of an equivalent thermal RC network. The precision of the RC thermal network is improved using variable resistances and capacitances related to the heat fluxes so that the compact model can adapt automatically with boundary conditions.     

Tm激光与角膜作用的热效应模拟

激光角膜热成形技术(LTK)在矫正远视临床中占有重要的应用前景。为了了解铥激光与角膜组织热相互作用中激光参数和角膜光学及热物性参数对温度场分布的影响,选取50W/cm2,55W/cm2,60W/cm2三种功率密度,1s、2s、3s三种作用时间,用有限元方法模拟了激光作用下角膜组织内温度场的分布。模拟结果表明激光有效穿透深度与激光功率密度和时间都是正向相关,而与能量密度的正向相关性较差;激光作用时间越长,角膜组织中的温度梯度越小。模拟得到激光功率密度50W/cm2作用时间1s适合于LTK。     

Multi-port dynamic compact thermal models of dual-chip package using model order reduction and metaheuristic optimization

Delphi-like boundary condition independent (BCI) compact thermal models (CTMs) are the standard for modelling single die packages. However their extraction, particularly in the transient case, will be time consuming due to complex numerical simulations for a large number of external conditions. Lately, new approaches to extract a BCI dynamical CTM (DCTM), based on model order reduction (MOR) were developed. Despite the numerous advantages of this recent method, the lack of numerical tools to integrate reduced-order models (ROM) makes it difficult to use at board level. In this study, a novel process flow for extracting Delphi-inspired BCI DCTMs is proposed. Thus a detailed three-dimensional model is replaced by a BCI-ROM model using FANTASTIC matrix reduction code to generate the data used in the creation of a Delphi-style BCI DCTM. That hybrid reduction method has been applied, at first on a single-chip package (QFN16) then on a dual-chip package (DFN12). Their derived CTM and DCTM have been compared in term of accuracy and creation time using, or not, MOR reduction technique. The results show that for a similar accuracy, the integration of MOR technique allows minimizing the time-consuming numerical simulations and consequently reduce the thermal network creation time by 80%.     

Longitudinal component of aperture electric field in weakly-excited broadwall slot

For longitudinal slots cut in rectangular waveguides, the longitudinal component of the aperture electric field is found to be significant when the offset is small even for narrow slots. Ignoring the E-longitudinal component can introduce substantial error in the computed scattering parameters for weakly excited slots.<>     

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。     

Nd：YAG激光器热效应的计算模拟及实验研究

对Nd:YAG激光棒的热透镜效应、应力双折射、退偏效应采用自编软件进行计算模拟,并进行了相应的实验研究.     

Static and dynamic photoinduced magnetic effects in yttrium-iron garnet lightly doped with barium ions

In yttrium-iron garnet lightly doped with barium, direct measurements of the photoinduced changes in magnetostrictive strains disagree with those in magnetostriction constants at 78–100 K. This is attributed to a considerable photoinduced modification of the initial state in this sample due to a redistribution of the charge (during illumination) between cations of the ferromagnetic octahedral sublattice. In the same sample, the temperature dependence of the photoinduced disaccomodation of magnetic permeability characterizing the initial demagnetized state is measured and calculated. A change in the electron mechanism of the phenomenon during the transition to room temperature is shown. The conclusion about the promising prospects for using such samples for remagnetization by light is advanced.     

Simulation of thermal effects in integrated circuits with SPICE - a behavioural model approach

This paper reviews an approach to the simulation of thermal effects in integrated circuits with SPICE by using an analog behavioural modelling concept. Macro models for BJTs, diodes and resistors are presented, which consider the influence of self-heating, interaction thermals, as well as the nonlinear thermal conductivity of silicon on the circuit's behaviour. Such simulations give a first insight into the thermal sensitivity of the circuitry, even in a very early design phase.     

Generation of reduced dynamic thermal models of electronic systems from time constant spectra of transient temperature responses

This paper concerns the problem of generating reduced dynamic thermal models whose elements have physical interpretation. The compact models of an electronic system are generated here based on the analysis of the time constant spectra of system transient thermal responses. The proposed method is illustrated on a practical example of an integrated power amplifier with a heat sink. The experiments demonstrate the influence of contact resistance and cooling conditions on the resulting values of thermal model elements.     

Polynomial circuit models for component matching in high-levelsynthesis

Design reuse requires engineers to determine whether or not an existing block implements desired functionality. If a common high-level circuit model is used to represent components that are described at multiple levels of abstraction, comparisons between circuit specifications and a library of potential implementations can be performed accurately and quickly. A mechanism is presented for compactly specifying circuit functionality as polynomials at the word level. Polynomials can be used to represent circuits that are described at the bit level or arithmetically. Furthermore, in representing components as polynomials, differences in precision between potential implementations can be detected and quantified. We present a mechanism for constructing polynomial models for combinational and sequential circuits. Furthermore, we derive a means of approximating the functionality of nonpolynomial functions and determining a bound on the error of this approximation. These methods have been implemented in the POLYSYS synthesis tool and used to synthesize a JPEG encode block and infinite impulse response filter from a library of complex elements     

Static and dynamic finite element modelling of thermal fatigue effects in insulated gate bipolar transistor modules

The aim of this paper is to demonstrate the use of finite element techniques for modelling thermal fatigue effects in solder layers of insulated gate bipolar transistor (IGBT) – modules used in traction applications. The three-dimensional models presented predict how progressive solder fatigue, affects the static and dynamic thermal performance of such devices.Specifically, in this paper, the analysis of an 800 A–1800 V IGBT module is performed. In the first part, the static analysis is realised. The parameters assessed are thermal resistance, maximum junction temperature and heat flux distribution through the different layers comprising the module construction. In the second part of the paper, transient analyses are performed in order to study the dynamic thermal behaviour of the module. The constructed thermal impedance curves allow for calculation of the device temperature variations with time. Stress parameters, such as temperature excursion and maximal temperature at chip and solder interfaces, are determined. Calibration of all simulation models is achieved by comparison with alternative theoretical calculations and manufacturers’ measured values provided in the data sheet book.