Materials with required dielectric properties: Computational development and production of polymer‐ceramic composites
TL;DR: In this paper, an inverted power-law mixing rule model computing volume fractions in which three or more prime materials should be taken to get in the resulting homogeneous mixture the required dielectric properties.
Abstract: Many applications in wireless communication, microelectronics, and microwave power engineering rely on dielectrics with particular dielectric properties. This article proposes an original approach that can be used for producing materials with required complex permittivity. The technique is based on an inverted power-law mixing rule model computing volume fractions in which three or more prime materials should be taken to get in the resulting homogeneous mixture the required dielectric properties. Functionality of the approach is demonstrated by production of composites from a polymer matrix (polymethyl methacrylate) and two inorganic fillers (silicon and alumina). The composites are made by mechanically mixing the powders and axially hot-pressing and cooling the mixture. Complex permittivity of the samples is measured by a split-post resonator method. Experimental data on dielectric properties of the samples help calibrate the technique; for the used powders, the Looyenga power-law model is found to be most adequate. In the produced samples, the target values of dielectric constant are reached with a higher precision than the ones of the loss factor; however, analysis of the production process and error propagation in the computations suggest that deviations of the resultant complex permittivity fall in the anticipated ranges. Features and issues of both computational and production parts of the technique are finally discussed. POLYM. ENG. SCI., 58:319–326, 2018. VC 2017 Society of Plastics Engineers
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01 Jan 2016
TL;DR: The electrodynamics of continuous media is universally compatible with any devices to read and is available in the book collection an online access to it is set as public so you can get it instantly.
Abstract: Thank you for reading electrodynamics of continuous media. Maybe you have knowledge that, people have look numerous times for their chosen books like this electrodynamics of continuous media, but end up in infectious downloads. Rather than reading a good book with a cup of tea in the afternoon, instead they cope with some malicious bugs inside their computer. electrodynamics of continuous media is available in our book collection an online access to it is set as public so you can get it instantly. Our book servers saves in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the electrodynamics of continuous media is universally compatible with any devices to read.
898 citations
TL;DR: In this paper, the LD125 modified glass fiber (GF) was introduced to the CaO-Li2O-Sm2O3-TiO2 (CLST)/PTFE composite, to reduce the thermal expansion coefficient (CTE) of the composites.
Abstract: Ceramic and polytetrafluoroethylene composites as dielectric materials have a low dielectric loss at high frequency and play an important role in the modern communication field. However, room temperature phase transformation of PTFE resins, which is accompanied by a large volume change (> 400 ppm/oC), seriously affects the dimensional stability and performance stability of materials. The LD125 modified glass fiber (GF) was introduced to the CaO-Li2O-Sm2O3-TiO2 (CLST)/PTFE composite, to reduce the thermal expansion coefficient (CTE) of the composites. The tri-phase composites (CLST/PTFE/GF) show the low dielectric loss and excellent machine-ability. The effect of GF content on the dielectric properties and CTE was also investigated. The CLST/PTFE filled with 5% GF exhibits the best overall performance, which is a promising microwave dielectric material for microwave communication.
9 citations
TL;DR: In this article, a modification of the Lichtenecker-Rother model is proposed for the dielectric permittivity of polymer composites that takes into account aggregation of filler particles into clusters.
Abstract: A modification of the Lichtenecker–Rother model is proposed for the dielectric permittivity of polymer composites that takes into account aggregation of filler particles into clusters. The governing equations for the real and imaginary parts of the complex permittivity of a composite involve three adjustable parameters with transparent physical meaning. These quantities are determined by fitting experimental data on a number of polymers reinforced with ceramic, magnetic and carbon particles. Good agreement is demonstrated between the results of simulation and observations on the dielectric constant and dielectric loss at microwave frequencies. It is shown that the model can be applied to extract dielectric parameters of filler from observations on polymer composites.
5 citations
18 Sep 2018-Compel-the International Journal for Computation and Mathematics in Electrical and Electronic Engineering
TL;DR: In this article, the authors proposed a computational technique capable of determining the geometry and complex permittivity of a supplementary dielectric insert making distributions of microwave-induced dissipated power within the processed material as uniform as possible.
Abstract: Purpose
This paper aims to introduce and illustrate a computational technique capable of determining the geometry and complex permittivity of a supplementary dielectric insert making distributions of microwave-induced dissipated power within the processed material as uniform as possible.
Design/methodology/approach
The proposed technique is based on a 3D electromagnetic model of the cavity containing both the processed material and the insert. Optimization problem is formulated for design variables (geometrical and material parameters of the insert) identified from computational tests and an objective function (the relative standard deviation [RSD]) introduced as a metric of the field uniformity. Numerical inversion is performed with the method of sequential quadratic programming.
Findings
Functionality of the procedure is illustrated by synthesis of a dielectric insert in an applicator for microwave fixation. Optimization is completed for four design variables (two geometrical parameters, dielectric constant and the loss factor of the insert) with 1,000 points in the database. The best three optimal solutions provide RSD approximately 20 per cent, whereas for the patterns corresponding to all 1,000 non-optimized (randomly chosen) sets of design variables this metric is in the interval from 27 to 136 per cent with the average of 78 per cent.
Research limitations/implications
As microwave thermal processing is intrinsically inhomogeneous and the heating time is not a part of the underlying model, the procedure is able to lead only to a certain degree of closeness to uniformity and is intended for applications with high heating rates. The initial phase of computational identification of design variables and their bounds is therefore very important and may pre-condition the “quality” of the optimal solution. The technique may work more efficiently in combination with advanced optimization techniques dealing with “smart” (rather than random) generation of the data; for the use with more general microwave heating processes characterized by lower heating rates, the technique has to use the metric of non-uniformity involving temperature and heating time.
Practical implications
While the procedure can be used for computer-aided design (CAD) of microwave applicators, a related practical limitation may emerge from the fact that the material with particular complex permittivity (determined in the course of optimization) may not exist. In such cases, the procedure can be rerun for the constant values of material parameters of the available medium mostly close to the optimal ones to tune geometrical parameters of the insert. Special manufacturing techniques capable of producing a material with required complex permittivity also may be a practical option here.
Originality/value
Non-uniformity of microwave heating remains a key challenge in the design of many practical applicators. This paper suggests a concept of a practical CAD and outlines corresponding computational procedure that could be used for designing a range of applied systems with high heating rates.
4 citations
References
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TL;DR: In this paper, the Bruggeman and Bottcher equation for the dielectric constant of a heterogeneous system is reconsidered and a theoretical model is designed from which both formulae can be derived.
Abstract: The equation of Bruggeman and that of Bottcher for the dielectric constant of a heterogeneous system are reconsidered. A theoretical model is designed from which both formulae can be derived. A refined use of the same model yields a apparently more general equation for the dielectric constant of a mixture, namely (e 1 3 − e1 1 3 )/(e2 1 3 −e1 1 3 ) = v2 , where v2 = the volume fraction of the dispersed component, e2 = the dielectric constant of this component and e1 = the dielectric constant of the other component. Comparison with experimental data indicates that the new equation performs very satisfactorily.
1,106 citations
01 Jan 2016
TL;DR: The electrodynamics of continuous media is universally compatible with any devices to read and is available in the book collection an online access to it is set as public so you can get it instantly.
Abstract: Thank you for reading electrodynamics of continuous media. Maybe you have knowledge that, people have look numerous times for their chosen books like this electrodynamics of continuous media, but end up in infectious downloads. Rather than reading a good book with a cup of tea in the afternoon, instead they cope with some malicious bugs inside their computer. electrodynamics of continuous media is available in our book collection an online access to it is set as public so you can get it instantly. Our book servers saves in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the electrodynamics of continuous media is universally compatible with any devices to read.
898 citations
"Materials with required dielectric ..." refers background or methods in this paper
...The rule (1) takes shapes of different models for the values of a in the interval between the Wiener boundary values [–1, 1] [23,25], namely, 21 (series model) [23], 0 (logarithmic/Lichtenecker model) [21,26], 1/2 (refractive/Birchak/Kraszewski model) [21,27,28], 1/3 (Looyenga/Landau-Lifshitz model) [21,29,30], (V1 – 0....
[...]
...Conversely, while the Looyenga model (also called the “permittivity of a mixture” [30]), being symmetrical with respect to the inclusion and environment, seems to be most accurate and physically most suitable for mixtures of powders, other models (though involving a reasonable number of arithmetic operations not to amplify the effect of error propagation) appropriate for other prime types of materials and other topologies of the mixtures (such as the Maxwell-Garnett model and the Bruggeman nonsymmetric formula [21]) may be explored....
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TL;DR: In this paper, the state-of-the-art progress on electric energy-storage performance in dielectric materials is summarized, and some general future prospects are also provided from the existed theoretical and experimental results in this work.
Abstract: With the fast development of the power electronics, dielectric materials with high energy-storage density, low loss, and good temperature stability are eagerly desired for the potential application in advanced pulsed capacitors. Based on the physical principals, the materials with higher saturated polarization, smaller remnant polarization, and higher electrical breakdown field are the most promising candidates. According to this rule, so far, four kinds of materials, namely antiferroelectrics, dielectric glass-ceramics, relaxor ferroelectric and polymer-based ferroelectrics are thought to be more likely used in next-generation pulsed capacitors, and have been widely studied. Thus, this review serves to give an overall summary on the state-of-the-art progress on electric energy-storage performance in these materials. Moreover, some general future prospects are also provided from the existed theoretical and experimental results in this work, in order to propel their application in practice.
730 citations
01 Jan 1974
TL;DR: In this paper, the response of a low-loss dielectric slab waveguide sensor has been calculated in terms of the effective Dielectric constant of the soil-water mixture, in reasonable agreement with experiment when effects of ionic conduction are accounted for.
Abstract: Implantable soil moisture sensors suitable for long-term monitoring of moisture in highway subgrades and for similar applications are needed. Two candidate designs of microwave sensors (operating range 4 to 6 GHz) have been investigated for such applications. One design uses the fringing field of a low-loss dielectric slab waveguide (relative dielectric constant of 25) to obtain good resolution for finely divided soil such as bentonite clay with moisture ranging from 10 to 50 percent by dry weight for effective sample volumes of 20 to 40 cm2. The response of the dielectric waveguide sensor has been calculated in terms of the effective dielectric constant of the soil-water mixture. A model based on index of refraction yields an effective dielectric constant in reasonable agreement with experiment when effects of ionic conduction are accounted for. Another sensor design, better adapted for coarse materials, such as crushed limestone aggregate, uses waves launched from a tapered dielectric slab. By using either frequency or spatial averaging methods, the launched wave sensor accommodated aggregate particles passed by a 0.63-cm mesh sieve, and was found to have satisfactory resolution for the range of 0- to 10-percent moisture by dry weight.
699 citations