GaN transistors efficient cooling by graphene foam

© 2018 Elsevier Ltd Graphene conductive foams have shown very high potential as cooling material in electronic systems. Its exploitation with discrete GaN transistors is demonstrated in this paper. A proper experimental setup is developed to extract the high temperature thermal performance of this material at different test conditions. The results are very promising, showing a noticeable reduction of the device maximum temperature, especially at high dissipated power densities. Moreover, experimental results allowed the validation of a 3D finite element model of the assembled device, which can be used for thermal layout optimization. Finally, preliminary stress tests are in progress, to evaluate the stability of electrical and thermal performance of the proposed graphene based assembly. Good stability was obtained, both at low and high ambient temperatures

a simplified multiscale model of degenerate graphite clusters in grey cast iron

Abstract To take into account the weakening effect of defects clusters in real microstructures, we propose a multiscale model in a two-dimensional setting. At a small scale, single defects are described as elliptical voids randomly distributed and randomly oriented in an isotropic matrix. Using an effective field method proposed by Tandon and Weng [5,6], the effective properties of a porous equivalent material can be estimated in a simple closed form. At a larger scale, defects clusters are modelled as single large elliptical inclusions characterized by the weakened effective properties calculated in the first step and embedded in an infinite, elastic, isotropic matrix under remote loading. The method allows to examine the dependence of defects interaction on some basic microstructure parameters (porosity density, voids aspect ratio, inclusion aspect ratio)

Non-linear thermal simulation at system level: Compact modelling and experimental validation

In this work, a general methodology to extract compact, non-linear transient thermal models of complex thermal systems is presented and validated. The focus of the work is to show a robust method to develop compact and accurate non-linear thermal models in the general case of systems with multiple heat sources. A real example of such a system is manufactured and its thermal behaviour is analyzed by means of Infra-Red thermography measurements. A transient, non-linear Finite-Element-Method based model is therefore built and tuned on the measured thermal responses. From this model, the transient thermal responses of the system are calculated in the locations of interest. From these transient responses, non-linear compact transient thermal models are derived. These models are based on Foster network topology and they can capture the effect of thermal non-linearities present in any real thermal system, accounting for mutual interaction between different power sources. The followed methodology is described, verification of the model against measurements is performed and limitations of the approach are therefore discussed. The developed methodology shows that it is possible to capture strongly non-linear effects in multiple-heat source systems with very good accuracy, enabling fast and accurate thermal simulations in electrical solvers

A simple 1-D finite elements approach to model the effect of PCB in electronic assemblies

In this paper, a simple method to describe the effect of Printed Circuit Board (PCB) and environment on the thermal behavior of packaged devices is addressed. This approach aims at exploiting the benefit of compact thermal models, which are necessarily one-dimensional, together with the advantage of Finite Element (FE) modeling, which retains all the three-dimensional geometrical details, only in the regions of the model that must be accurately described. The main focus is on correct modeling of long power pulses for subsequent electro-thermal and thermo-mechanical analysis at chip level

THERMAL AND ELECTRO-THERMAL MODELING OF COMPONENTS AND SYSTEMS: A REVIEW OF THE RESEARCH AT THE UNIVERSITY OF PARMA

This paper reviews the activity carried out at the Department of Information Engineering of the University of Parma, Italy, in the field of thermal and electro-thermal modeling of devices, device and package assemblies, circuits, and systems encompassing active boards and heat-sinking elements. This activity includes: (i) Finite-Element 3D simulation for the thermal analysis of a hierarchy of structures ranging from bare device dies to complex systems including active and passive devices, boards, metallizations, and air- and water-cooled heat-sinks, and (ii) Lumped-Element thermal or electro-thermal models of bare and packaged devices, ranging from purely empirical to strictly physics- and geometry-based

A cost-efficient DC active load laboratory solution

The increased use of DC renewable energy resources and DC storage systems, combined with the necessary reduction of energy waste, is boosting the development of DC smart grids. In this scenario, DC load emulation is of great importance. From the hardware point of view, DC buses stability of smart grids and the different DC/DC converter topologies must be tested. From the software point of view, smart grid strategies and job schedulers must be tested with different power absorption profiles. Moreover, DC load emulation can be useful for many other purposes, such as battery characterization, power supply testing, photovoltaic I-V curve measurements, etc. In this work, a cost-efficient DC Active Load (AL) solution is proposed. The principle of the circuit topology is a buck-boost-derived converter. This solution can be designed and tested considering the required voltage, current, and maximum input power. Both simulation and experimental results are shown on a 400 W size prototype. Thermal and electrical results validate the simulation model and the AL feasibility

A methodology to determine reliability issues in automotive SiC power modules combining 1D and 3D thermal simulations under driving cycle profiles

Current environmental concerns and fuel scarcity are leading to the progressive introduction of Electric Vehicles (EV) in the global fleet vehicle population. This requires significant design and research efforts from scientific community and industry to provide reliable automotive electric propulsion systems. The power modules used for automotive traction inverters can be considered as central elements of such systems. As they are subject to high electro-thermal stress during operation, Design-for-Reliability (DfR) approaches should be adopted. Thus, accurate models for electro-thermal simulations are relevant since the early design stages. However, such simulations become highly time consuming and complex when accurate thermal characterization through standardized or real driving conditions needs to be provided. In this context, this work proposes a simulation methodology that combines real-time simulation for electro-thermal characterization of the whole EV propulsion system, using a 1D equivalent thermal impedance circuit, in conjunction with 3D FEM thermal simulation. In this way, an accurate thermal characterization of the power module under driving cycles with long duration (of hundreds of seconds) can be obtained without computing heavy 3D FEM simulations. The proposed procedure allows to simplify and speed up the early design stages while maintaining high accuracy in the results.This work has been supported by the Department of Education, Linguistic Policy and Culture of the Basque Government within the fund for research groups of the Basque university system IT978-16, by the Government of the Basque Country within the research program ELKARTEK as the project ENSOL (KK-2018/00040), and by the program to support the education of researches of the Basque Country PRE_2017_2_0008

An Iterative Refining Approach to Design the Control of Wave Energy Converters with Numerical Modeling and Scaled HIL Testing

The aim of this work is to show that a significant increase of the e_ciency of aWave Energy Converter (WEC) can be achieved already at an early design stage, through the choice of a turbine and control regulation, by means of an accurate Wave-to-Wire (W2W) modeling that couples the hydrodynamic response calibrated in a wave flume to a Hardware-In-the-Loop (HIL) test bench with sizes and rates not matching those of the system under development. Information on this procedure is relevant to save time, because the acquisition, the installation, and the setup of a test rig are not quick and easy. Moreover, power electronics and electric machines to emulate turbines and electric generators matching the real systems are not low-cost equipment. The use of HIL is important in the development of WECs also because it allows the carrying out of tests in a controlled environment, and this is again time- and money-saving if compared to tests done on a real system installed at the sea. Furthermore, W2W modeling can be applied to several Power Take-O_ (PTO) configurations to experiment di_erent control strategies. The method here proposed, concerning a specific HIL for testing power electronics and control laws for a specific WECs, may have a more general validity.This work was supported by MARINET, a European Community—Research Infrastructure Action under the FP7 “Capacities” Specific Programme, grant agreement n. 262552

THERMAL AND ELECTRO-THERMAL MODELING OF COMPONENTS AND SYSTEMS: A REVIEW OF THE RESEARCH AT THE UNIVERSITY OF PARMA

This paper reviews the activity carried out at the Department of Information Engineering of the University of Parma, Italy, in the field of thermal and electro-thermal modeling of devices, device and package assemblies, circuits, and systems encompassing active boards and heat-sinking elements. This activity includes: (i) Finite-Element 3D simulation for the thermal analysis of a hierarchy of structures ranging from bare device dies to complex systems including active and passive devices, boards, metallizations, and air- and water-cooled heat-sinks, and (ii) Lumped-Element thermal or electro-thermal models of bare and packaged devices, ranging from purely empirical to strictly physics- and geometry-based

Cerebral hypoperfusion in post-COVID-19 cognitively impaired subjects revealed by arterial spin labeling MRI

Cognitive impairment is one of the most prevalent symptoms of post Severe Acute Respiratory Syndrome COronaVirus 2 (SARS-CoV-2) state, which is known as Long COVID. Advanced neuroimaging techniques may contribute to a better understanding of the pathophysiological brain changes and the underlying mechanisms in post-COVID-19 subjects. We aimed at investigating regional cerebral perfusion alterations in post-COVID-19 subjects who reported a subjective cognitive impairment after a mild SARS-CoV-2 infection, using a non-invasive Arterial Spin Labeling (ASL) MRI technique and analysis. Using MRI-ASL image processing, we investigated the brain perfusion alterations in 24 patients (53.0 ± 14.5 years, 15F/9M) with persistent cognitive complaints in the post COVID-19 period. Voxelwise and region-of-interest analyses were performed to identify statistically significant differences in cerebral blood flow (CBF) maps between post-COVID-19 patients, and age and sex matched healthy controls (54.8 ± 9.1 years, 13F/9M). The results showed a significant hypoperfusion in a widespread cerebral network in the post-COVID-19 group, predominantly affecting the frontal cortex, as well as the parietal and temporal cortex, as identified by a non-parametric permutation testing (p < 0.05, FWE-corrected with TFCE). The hypoperfusion areas identified in the right hemisphere regions were more extensive. These findings support the hypothesis of a large network dysfunction in post-COVID subjects with cognitive complaints. The non-invasive nature of the ASL-MRI method may play an important role in the monitoring and prognosis of post-COVID-19 subjects