Description
Arthur Von Hippel’s book, Dielectric Materials and Application, was published in 1954. At the time, the development of composites for electrical and electromagnetic technologies was just beginning. Thus, dielectric and magnetic theory, models, measurement techniques, and measured data that were presented by Von Hippel emphasized homogeneous isotropic materials composed of a single molecular species or compound. The vast majority of those materials were electrically insulating and nonmagnetic.
Semiconductor production was in developmental phase, but samples for waveguide measurements (as used by Von Hippel) were not available and the importance of semiconductors for everyday technology was not yet recognized. Shockley’s patent on the transistor (#2569347) was just 6 years old. Ferrites were known; however, their application in radio and microwave technology for phase shifters, filters, and isolators were just being realized. They are now applied for suppression of radio frequency interference on computer mother boards, integrated circuits, communication networks, and in electrically small antennas. The use of fiber and laminate-based composites in electromagnetic technologies did not begin until the 1970s.
The Electromagnetic Composites Handbook is designed as an engineering and scientific handbook that extends the Von Hippel text to include data on additional nonconducting dielectrics, semiconducting, conducting, and magnetic materials and composites composed of two or more molecularly distinct compounds that are distributed in size scales from nanometers to centimeter dimensions. The development of models that attempt to predict composite constitutive parameters, using constitutive parameters of their constituents, is a parallel effort. The models support predictions of and comparison to measured permittivity and permeability. Permittivity, permeability, impedance, and conductivity data for solids and composites are presented for frequencies from about 1 MHz to 1000 GHz.
Chapters of this book are devoted to the descriptions of electromagnetic constitutive parameter sources, procedures and equipment to measure the parameters, propagation models in composites, prediction of composite properties, and measured constitutive parameter data for the electromagnetic spectrum of wavelengths larger than a few micrometers but mostly in the meter to millimeter wavelengths. Each chapter concludes with a list of references for that chapter. These are indicated in each chapter’s text in brackets. MK units are primarily used throughout this book; however, English or CG units may occasionally enter into discussion. The analysis crosses scientific and technological boundaries and thus the scientific complex operator, i, sometimes appears rather than the engineering j for the complex numbers. Note that in the data tables a positive sign, +, is adopted for dielectric and magnetic loss. Modeling and theory chapters discuss various composite models and then apply the most successful analytical and numerical methodologies to typical electromagnetic design problems that often use electromagnetic composites in their solution, again for wavelengths larger than a few micrometers.
Reflection and transmission line measurements, such as those of Von Hippel, are the framework from which composite material measurements began and those measurement techniques are reviewed. The review is followed by a discussion of advances in the measurement technology since 1980. For example, the microwave and millimeter wave application of lens-based open cavities and free space measurements, common for infrared and optical spectra, is one advance. The techniques include Fabry–Perot and etalon derivatives. The adoption of the infrared and optical techniques for millimeter, centimeter, and even meter wavelengths and the use of various multi-mode resonant cavity configurations, was facilitated by the second major technology addition, i.e., the development of the automatic network analyzer (ANA) and digital receivers–transmitters that had modest power (hundreds of milliwatts), broad bandwidth frequency, synthesized sources, and matched adapters. A third advance was microwave and millimeter antennas with bandwidths larger than 20:1. Advances in electromagnetic tools, instrumentation, and “borrowing” of lens-based measurements now allow accurate measurement of isotropic or anisotropic constitutive properties for single samples from a few hundred megahertz to above 100 GHz.
Some composites may contain constituents that are distributed in size scales of nanometer to centimeter dimensions. The larger scales make the composite electrically inhomogeneous at higher frequencies since inhomogeneity is determined by the ratio of the physical size of the composite phases and the electromagnetic wavelength. Characterizing the large-scale composites by effective permittivity and/or permeability is not sufficient. In cases where physical scales of the composite components are small but their electrical scale approach unity, diffuse and/or bistatic electromagnetic scatter modeling and measurements may be used to expand understanding of electromagnetic observables (reflection, transmission, and absorption) and calculated, effective magnetic permeability and electrical permittivity of composites. Measurement techniques that apply to some electrically inhomogeneous composites can also be used for isotropic, homogeneous materials. Numerical models will be discussed that give insight into electromagnetic properties of inhomogeneous electromagnetic composites and the problems that may be encountered in their utilization.
The advances discussed in this handbook are significant to both electromagnetic engineers and theoreticians. ANA advances now allow continuous measurement and thus material parameter data over 1000:1 or greater bandwidths. With such a dense database, experimentalists and engineers can confidently design broadband meter, microwave, and millimeter wave devices and material constructs. A physicist, chemist, or material scientist benefits from the high data density in verification of electromagnetic composite material theories over bandwidths that encompass multiple physical and electrical scales, material dimensionalities, and material physics. Examples are multiphase magnetics, periodic dielectrics exhibiting photonic bandgaps, and material constructs with negative index behavior.
The book concludes by presenting dielectric and magnetic parametric fits to measured data for almost 300 composites and/or composite components. Many gigabytes of data contributed to the preparation of this book and a comprehensive presentation of complex permittivity and permeability in tabular form were not possible due to space limitations; however, a digital database is planned for the future. For now, the parametric fits of Chap. 12 supply frequency and temperature dispersive data that are presented as analytic equations whose forms are based upon solid-state physics. The frequency and/or temperature range used for each fit are annotated with the equation parameters. Measurements range from 1 MHz to a few hundred gigahertz. Data density was typically at 1 MHz intervals below 100 MHz, 10 MHz spacing from 100 MHz to 1 GHz, and 100 MHz spacing above 1 GHz. The complex magnetic permeability and permittivity are fit to a range of relaxation models. Measurement frequencies are above characteristic solid-state Debye relaxation frequencies and below terahertz to infrared molecular relaxations. Power laws in frequency coupled with a single resonant model produce excellent parameterizations for permittivity data, especially those of composites containing semiconducting components. Overall, the parametric fits aid in spanning measurement frequency gaps and in interpretation of material physics.
Selected composite data are presented for measurements made before and during exposure to environmental extremes of temperature. For example, ceramic and ceramic composites are often used in high-temperature environments; thus data are shown from ambient to temperatures in excess of 2200 K. Exponential functions (typical of semiconductors) are used for temperature dependence of ceramics and ceramic fibers.
Select materials were chosen to overlap data of Von Hippel and other publications for comparison. Some data are repeated for identical material compositions, but from different suppliers, and thus illustrate unsurprising variability. Data on composites may be for “identical” compositions but are included to illustrate variability in manufacturing and source.