Equivalent Electrical Circuit Approach Research Articles

Theoretical modeling of thermal conductivity of alumina aerogel composites based on real microstructures

As compared with silica aerogels, alumina aerogels have excellent high-temperature stability, and hence, are regarded as a promising candidate for high-temperature thermal insulation materials. However, heat transfer mechanisms for such materials remain insufficiently explored. In this study, based on real material microstructures, an analytical thermal conductivity model for alumina aerogel-fiber-opacifier composites is developed via a modified parallel-series equivalent electrical circuit approach. The model takes into account solid, gaseous, and solid-gas coupling heat conduction in aerogels, solid heat conduction in both fibers and opacifier particles, and radiation in aerogels, fibers, and opacifier particles. The model is validated by comparing its predictions with measured thermal conductivity data. The model predictions reveal that there are two kinds of solid-gas coupling heat transfer mechanisms, which occur in the corner regions between interconnected secondary particles and in the slit regions between adjacent chains, respectively. Because of this coupling, the contribution of gaseous heat conduction is comparable to that of solid heat conduction and radiation of aerogels, fibers, and opacifier particles, which is well supported by experimentally measured data of thermal conductivity. The model is also used to analyze effects of various parameters on the thermal insulation performance of the composites, such as diameters and volume fractious of both fibers and opacifier particles.

Comparison Sound Absorption Methods of Multilayer Micro-perforated Panels

Micro-perforated panel (MPP) absorbers as the next-generation sound absorbers are getting more widely use in aviation, automobiles, construction and other fields. It’s a complex problem to predict the acoustic performance using surface impedance methods. The acoustic absorption performance of micro-perforated panels were compared in terms of Transfer matrix method and Equivalent electric circuit approach (EECA). The calculated results show that transfer matrix method is more convenient and effective than the equivalent circuit approach especially to multiply layer micro-perforated absorbers.

Electrical impedance measurements for detecting artificial chemical additives in liquid food products

Analyzing the content of artificial chemical additives in food products is important due to their twofold role in food processing and consumption, i.e., their positive impact on the shelf life or sensory properties of food products and possible negative effect on human health. The objective of the research was to evaluate the usefulness of the impedance spectroscopy technique in food quality control by testing its potential for determining the additives content in liquid food products. The impedance readings of one- and two-component solutions of twelve common food additives and six natural juices, both pure and with additions of selected chemical additives, were collected within the frequency range from 20 Hz to 2 MHz. The resulting spectra were interpreted with the use of the equivalent electrical circuit approach. An optimal circuit which allowed to describe electrical properties of the investigated samples was selected. It was characterized by four physical parameters, two of which may be used for the differentiation among food additives. The impedance spectroscopy technique has a potential to become an effective method for food quality and safety control in the context of the artificial additives content, because it allows to describe the content in a relatively simple manner when the compounds of interest are present in small quantities in chemically complex materials such as foods.

Thermal modeling and optimization of a thermally matched energy harvester

The interest in energy harvesting devices has grown with the development of wireless sensors requiring small amounts of energy to function. The present article addresses the thermal investigation of a coupled piezoelectric and bimetal-based heat engine. The thermal energy harvester in question converts low-grade heat flows into electrical charges by achieving a two-step conversion mechanism for which the key point is the ability to maintain a significant thermal gradient without any heat sink. Many studies have previously focused on the electrical properties of this innovative device for energy harvesting but until now, no thermal modeling has been able to describe the device specificities or improve its thermal performances. The research reported in this paper focuses on the modeling of the harvester using an equivalent electrical circuit approach. It is shown that the knowledge of the thermal properties inside the device and a good comprehension of its heat exchange with the surrounding play a key role in the optimization procedure. To validate the thermal modeling, finite element analyses as well as experimental measurements on a hot plate were carried out and the techniques were compared. The proposed model provided a practical guideline for improving the generator design to obtain a thermally matched energy harvester that can function over a wide range of hot source temperatures for the same bimetal. A direct application of this study has been implemented on scaled structures to maintain an important temperature difference between the cold surface and the hot reservoir. Using the equations of the thermal model, predictions of the thermal properties were evaluated depending on the scaling factor and solutions for future thermal improvements are presented.

Modeling and Experimental Validation of PbA battery - Supercapacitor Energy Storage System

This paper presents the development and the experimental validation of a dynamic model of a Hybridized Energy Storage System (HESS) consisting of a lead acid (PbA) battery and double layer capacitors (DLCs), intended for automotive applications. The dynamic modeling of both the PbA battery and the DLC is performed using an equivalent electric circuit approach, which is the best suited for our application. An identification experiment is designed for each device; the PbA battery parameters are estimated at different state of charge (SOC) levels and for the two possible directions of the current. By contrast, the DLC parameters are supposed to be insensitive to those variables, yet they are estimated at different temperatures. The model of the HESS is obtained as the parallel connection of the two models; since our study involves a passive HESS, there is no power electronic interface between the two devices. The outputs of the combined model are the system voltage and the currents flowing in the PbA battery and in the DLC module. A validation experiment is performed on a real HESS, aiming to reproduce the operation of the system in a vehicle equipped with the Start&Stop technology. Good agreement is found between the outputs predicted by the model and the corresponding measurements. The model is suitable for exploring the positive effects of the battery hybridization, for instance the impact of Start&Stop on the battery aging.

Evolução temporal da interfase aço inoxidável P558/solução de cloreto de sódio por espectroscopia de impedância eletroquímica

O aço inoxidável P558, isento de níquel, vem sendo estudado pelo grupo com o objetivo de verificar a viabilidade do seu emprego em implantes ortopédicos. Em trabalhos anteriores, foi mostrado, por técnicas eletroquímicas estacionárias, que ele apresenta, em meio de cloreto de sódio 0,11 mol L-1, comportamento semelhante ao do aço ISO 5832-9 e bem superior ao do aço ISO 5832-1, mais conhecido como F138. Nesse trabalho, foi estudada a evolução temporal da interfase aço inoxidável P558/NaCl 0,11 mol L-1 empregando a técnica de espectroscopia de impedância eletroquímica, no potencial de circuito aberto. Os intervalos de tempo observados foram de 10 min, 1 dia, 2 dias e 5 dias. Observou-se que o filme passivo se torna mais protetor, com o decorrer do tempo. Foi feita simulação dos resultados experimentais através de circuitos elétricos equivalentes, que permitiram sugerir a existência, no início da observação, de apenas um filme passivante menos protetor e, quando atingida a condição estacionária, a existência de um segundo filme mais compacto.

ISFET–neuron junction: circuit models and extracellular signal simulations

Purpose of this paper is to characterize the Ion-Sensitive Field-Effect Transistors (ISFET)–neuron junction, based on the equivalent electric-circuit approach. As a result, recording of action potentials can be simulated with a general-purpose circuit simulation program such as HSPICE. The neuronal electrical activity, extracellularly recorded by the ISFET, is analyzed as a function of the physical–chemical and geometric ISFET parameters, of the ionic currents in the neuron, and of the neuro–electronic junction parameters such as the sealing resistance, double-layer capacitance, and general adhesion conditions. The models of the neuron, of the coupling circuit, and of the ISFET implemented in HSPICE are first described. These models are then used to simulate the behavior of the junction between a patch of neuronal membrane (described by the compartmental model) and the ISFET.

Modeling the neuron-microtransducer junction: from extracellular to patch recording.

This paper is devoted to a detailed characterization of the neuron-to-microtransducer junction, based on the equivalent electric-circuit approach. As a result, recording of action potentials can be simulated with the general-purpose network-analysis program SPICE. Both noble-metal microelectrodes and insulated-gate FET's are considered. The responses of such devices are characterized as functions of several parameters, e.g., sealing impedance, density of ionic currents in the cell membrane, and spatial discontinuities of the adhesion process. It is shown that the various signal shapes reported in the literature can be reproduced and interpreted in terms of time derivatives of the action potential. In this way, the shape of any experimental signal can be interpreted on the basis of a specific sealing condition. Possible future improvements in microtransducer design, based on the proposed approach, are also suggested.