Microwave‐Material Interactions and Dielectric Properties, Key Ingredients for Mastery of Chemical Microwave Processes

Abstract

The main focus of the revised edition of this first chapter is essentially the same as the original -to explain in a chemically intelligible fashion the physical origin of microwave-matter interactions and, especially, the theory of dielectric relaxation of polar molecules. This revised version contains approximately 60% new material to scan a large range of reaction media able to be heated by microwave heating. The accounts presented are intended to be illustrative rather than exhaustive. They are planned to serve as introductions to the different aspects of interest in comprehensive microwave heating. In this sense the treatment is selective and to some extent arbitrary. Hence the bibliography contains historical papers and valuable reviews to which the reader anxious to pursue particular aspects should certainly turn.It is the author's conviction, confirmed over many years of teaching experience, that it is much safer -at least for those who rate not trained physicists -to deal intelligently with an oversimplified model than to use sophisticated methods which require experience before becoming productive. Because of comments about the first edition, however, the author has included more technical material to enable better understanding of the concepts and ideas. These paragraphs could be omitted, depending on the level of comprehension of the reader. They are preceded by two different symbols -k for TOOLS and j for CONCEPTS.After consideration of the history and position of microwaves in the electromagnetic spectrum, notions of polarization and dielectric loss will be examined. The orienting effects of electric fields and the physical origin of dielectric loss will be analyzed, as also will transfers between rotational states and vibrational states within condensed phases.Dielectric relaxation and dielectric losses of pure liquids, ionic solutions, solids, polymers and colloids will be discussed. Effect of electrolytes, relaxation of defects within crystals lattices, adsorbed phases, interfacial relaxation, space charge polarization, and the Maxwell-Wagner effect will be analyzed. Next, a brief overview of 1 thermal conversion properties, thermodynamic aspects, and athermal effects will be given.

Low Frequency Radio Wave Detection of Electrically Active Defects in Dielectrics

“…For molecular dipoles, however, the thermal energy counteracts this tendency and the system finally reaches a new statistical equilibrium and the medium becomes slightly anisotropic. 21 The RF insertion losses we observe in this work stem from polarizations due to the reorientation of terminated dangling bonds, and the peak frequency, f p in Figure 3, represents the upper limits of the frequency range in which the functionalized dangling bonds can perfectly keep up with rotating applied electric fields. Thus, it is possible to delineate the various charge transport mechanisms using a broad band radio-frequency excitation.…”

“…As discussed below, while changes were observed in both the reflection (S 11 , S 22 ) as well as in the insertion loss (S 12 , S 21 ), we chose to use the latter as metrics for monitoring the defects in the liner dielectric. 21 ) magnitude (the real part of the loss function), in the measured RF range, of an 'asprocessed' / 'as-received' and after 500 thermal cycles of a prototypical TSV sample selected from the top left quadrant of a 300 mm wafer. The S 21 magnitude spectrum after thermal cycling was much different from that of the 'as-received' sample.…”

Development of a microwave sintered TiO2 reinforced Sn–0.7wt%Cu–0.05wt%Ni alloy

“…9b contains many small nano-scale crystalline areas. These small crystals (indicated with a white dotted line around the perimiter) may have formed due the migration of Ti ions which may occur due to the rapid microwave heating and the presence of microwave induced vibrations [50,51]. Different lattice planes were observed for both Sn and nano crystals in the HRTEM images.…”

Microwave-assisted low temperature fabrication of ZnO thin film electrodes for solar energy harvesting

“…The interaction of microwaves with matter is quantified by the two complex physical quantities; dielectric permittivity, ε, and permeability (magnetic susceptibility), μ [15]. In reality, the permittivity and permeability are complex quantities which are defined as ε* and μ*, respectively, as shown in Eqs.…”