Preface

Microwave heating is the process whereby the electromagnetic field of the microwave range (300–3000 MHz) interacts with diverse dielectric materials and mediums that take up electromagnetic energy. In practice, the most popular frequencies for microwave heating are 915 and 2450 MHz. The process of absorption and transformation of electromagnetic energy inside a volume of various objects results in self-heating (or in a manifestation of the so-called thermal effect). The energy efficiency of the given process depends on both the dielectric properties of the materials (specific conductivity, loss factor, water content, etc.) and the parameters of the electromagnetic field (as a rule, they are the amplitude, the frequency, and the operation modes—continuous or pulse). It should be noted that in the case of microwave heating, the impact of electromagnetic energy on objects takes place at the molecular level. This is its main feature compared to conventional heating techniques. This property of microwave heating has advantages associated with uniformity, efficiency, higher speed, and ecological compatibility.

More than 80 years of experience in the practical application of electromagnetic energy in various fields of human activity (including industry, agriculture, science, medicine, etc.) suggests that microwave heating is an effective application of the energy of the electromagnetic field. Essentially, new microwave technology was created to solve numerous problems in diverse applied fields. The modern technology of microwave heating is constantly evolving. Primarily, this is associated with further enhancing the efficiency of microwave heating and applying the thermal effect to the solution of problems in microwave chemistry (so-called green chemistry), producing new materials possessing new properties, plasma physics, and more. It is important to pay attention to the questions related to the nonthermal microwave effect, taking into account that the mechanism of the given effect has not yet been sufficiently studied and understood. Based on the available information, the nonthermal effect of microwave irradiation (usually, in the range of 40–60 GHz) can be defined as information impact. This process occurs on a cellular level with a subsequent impact on the macro parameters of all considered systems as a whole. As a rule, such an impact regime of microwave irradiation is used in medicine for treating some human diseases as well as in biology and virology for changing the conditions of existing microorganisms (viruses, bacteria, etc.).

This book presents the latest investigations related to the application of microwave energy in various fields. It is divided into two sections on thermal and non-thermal effects of microwave radiation on materials and mediums. The book includes eight chapters written by various authors presenting academic and industrial interests. Chapters 1 and 2 focus on the advantages of using microwave energy for the extraction (recovery) of bioactive compounds from plant materials. Chapter 3 reviews recent developments in the microwave-assisted synthesis of functional dyes for subsequent use in hi-tech applications, such as optoelectronics, photochromic materials, liquid crystal displays, newer emissive displays, biomedicine, electronic materials (organic semiconductors), and imaging technologies. Chapter 4 discusses the effective use of microwave heating for high-quality nanomaterial synthesis in solutions where doping is necessary to tune the electronic and optoelectronic

properties of nanomaterials used in various applications. Chapter 5 examines the influence of microwaves on the chemical reactions that take place during sol-gel synthesis as well as on the properties of the resulting samples. Chapters 6 and 7 study the influence of microwaves on gaseous mediums and hard materials (rocks). Chapter 6 focuses on the experimental and theoretical results of exciting a lowtemperature plasma with the help of a gaseous medium by both the regular field (in a regime with dynamic chaos) and random electromagnetic fields. The chapter also reviews and analyzes the stochastic heating mechanisms of plasma-derived for greater efficiency. Chapter 7 generalizes a practical experience of the application of microwaves for rock-breaking operations. It presents a mechanism of the rockbreaking operation concerning the heating characteristics of the rocks and their mechanical properties. Chapter 8 focuses on the influence of microwaves on the chemical reactions occurring in situ at a molecular level using microwave irradiation nuclear magnetic resonance spectroscopy and molecular dynamics simulation. It shows that the chemical reaction rate can be sped up due to the ordered state of the polar molecules that were induced by a nonthermal effect.

I would like to thank all the authors for their excellent contributions. I would also like to take this opportunity to thank Author Service Manager Ms. Sara Debeuc at IntechOpen for her efforts and help.

> **Gennadiy I. Churyumov** Professor, Antennas and Microwave Engineering Center, Microwave Engineering Department, Harbin Institute of Technology, China Professor,

Section 1

Thermal Effect of

Electromagnetic Field

Department of Physical Foundation of Electronic Engineering, Faculty of Electronic Engineering, Kharkiv National University of Radio Electronics, Ukraine Section 1
