Analytical multipoint moment matching reduction of distributed thermal networks

In this paper, the multipoint moment matching method for model order reduction of discretized linear thermal networks is extended to distributed linear thermal networks. As a result, from the analytical canonical forms of distributed linear thermal networks, reduced thermal networks are derived analytically. This direct construction of the reduced network, from the exact analytical solutions, avoids the inevitable inaccuracies inherent in conventional surface and volume meshing. It allows nearly exact reduced thermal network construction by domain decomposition for arbitrarily complicated structures.     

Thermal networks from heat wave equation

In this paper passive and reciprocal thermal networks are introduced which model the finite velocity of heat propagation. In particular it is shown that the theory of distributed and discretized thermal networks deduced from the heat diffusion equation and the multi-point moment matching technique for deriving approximated lumped thermal networks of small state-space dimensions can be extended to thermal networks ruled by the hyperbolic heat equation.     

Modeling and Simulation of a Hybrid Photovoltaic Module Equipped With a Heat-Recovery System

This paper presents a multiphysics model of a hybrid solar panel equipped with a solar concentrator and a cooling interface with heat-recovery capability. It is shown how the temperature profile along the cells can be predicted as a function of the cooling strategy. From this information, the I-V electrical characteristic of the whole module can be derived. An original compact electrothermal macromodel of the photovoltaic module is employed which allows one to properly incorporate the effect of temperature gradients along the cells. By exploiting this macromodel, accurate and efficient electrothermal simulations of the solar system can be carried out with a conventional electrical simulator, like Spice.     

Fabrication of a Thermoelectric Nanocomposite via Multiple Roll Bonding of Cast Bi-22at.%Sb Alloy

A Bi-22at.%Sb alloy was water-quenched from 973 K; its microstructure was dendritic with primary Sb-rich arms up to 50 μm in diameter. The cast alloy was first rolled to tape, then cut into equal lengths and subjected to multiple roll bonding (MRB) processes. The evolution of the microstructure during deformation was followed by optical microscopy, scanning electron microscopy (SEM), field-emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), and x-ray diffraction analysis. After three MRB cycles, an overall area reduction ratio of 4 × 10³ was achieved. Due to the relatively low process temperature, a relevant fraction of dendrites was preserved. Plastic strain caused dendritic arms to elongate in the rolling direction and to flatten in the transverse direction. As a result of different starting size and orientation, the dendritic arms were transformed into Sb-rich inclusions of various shapes and dimensions at the end of the MRB process. In particular, inclusions with a transverse size down to 20 nm were observed.     

Compact Models of Dynamic Thermal Networks with Many Heat Sources

A novel approach, based both on multipoint moment matching and principal component analysis, is proposed for generating passive compact models of dynamic thermal networks with many heat sources. As main result, the generated passive compact dynamic thermal networks both assure a prescribed accuracy and have a number of elements linearly related to the number of heat sources.     

Structure Function Representation of Multidirectional Heat-Flows

The relation between the structure function of a one-port dynamic thermal network and the spatial distribution of thermal properties in a heat diffusion problem with applied boundary conditions is generalized from 1D heat flows to multidirectional heat flows. A strategy for exploiting this relation is derived which allows an accurate localization of defects and measurement of thermal properties in components and packages not only when the heat diffusion problem is 1D but also 3D.     

Canonical forms of one-port Passive Distributed thermal networks

In this paper, it is shown that, one-port passive distributed thermal networks admit four canonical representations which generalize the four canonical forms of one-port passive lumped RC networks: Foster I and II canonical forms, Cauer I and Cauer II canonical forms. Insights on the physical significance of these four generalized canonical representations are given.     

An Arnoldi based thermal network reduction method for electro-thermal analysis

In this paper we consider the problem of approximating the large discretized thermal network that models the heat conduction phenomenon in an electrical system by means of models of reduced state-space dimensions. To this aim we present an efficient and numerically stable Arnoldi type algorithm by which a multi-point moment matching approximant of the discretized thermal network is obtained and we apply it to the electro-thermal analysis of an operational transconductance amplifier.     

Effects of Metal Particles Decoration on n-Type Chalcogenides Processed by Open Die Pressing

The effects of copper particles dispersed into Bi_1.9Sb_0.1Te_2.85Se_0.15 nanopowders and sintered by open die pressing (ODP) have been investigated. Submicrometric copper particles were obtained by decomposing copper acetate molecules dispersed into chalcogenides nanopowders. The acetate powders were decomposed during the sintering process at 390 °C obtaining a fine dispersion of copper particles with dimensions in the order of 500 nm. Contents up to 0.2 wt.% of copper were investigated. ODP, previously introduced as a forming process for sintering and texturing p-type (Bi_0.2Sb_0.8)₂Te₃ nanopowders, has been applied to n-type chalcogenide: the mixed alloy nanopowders and copper acetate were compacted inside a metallic protective shell and fast pressed between two heated plates, keeping the composite under load for sintering. ODP processing ensures complete consolidation of nanopowders and material texturing with the basal (00l) planes of the hexagonal crystal cell oriented parallel to the plates. The X-ray diffraction pattern shows an orientation factor, f, obtained by the Lotgering method, up to 64 %. Thermoelectric performance of the samples was measured by the Harman method in the range of 20–170 °C. Figure of merit (ZT) behavior with temperature was improved in copper-dispersed samples showing a shift of the maximum value at higher temperatures. This effect can be mainly associated with an improvement of electrical conductivity, due to the presence of the copper particles.     

Time-Domain Simulation of Nonlinear Circuits Through Implicit Runge–Kutta Methods

This paper presents a novel approach to the accurate time-domain simulation of nonlinear circuits that employs a class of high-order implicit Runge-Kutta (RK) formulas. The RK methods that are here considered are selected among the wide family of known RK methods as being particularly suited to the task of analog simulation. The properties of stability and accuracy of these RK methods are briefly reviewed while the implementation in the flow of an analog simulator is described in detail. When compared to standard multistep methods, the considered RK techniques reveal to be much more reliable and thus particularly suited to the analysis of those circuits, such as circuits for RF applications or sharply nonlinear switched circuits, that are critical for conventional integration methods