This chapter summarises the aspects which are relevant to industrial high frequency heating and formulate simple models for the processes involved which should lead to better understanding of the behaviour of many industrial materials under high frequency fields. The chapter discusses dielectric loss, dielectric constant and magnetic loss factors.

This chapter describes the physical parameters which play an important role in the interaction of a dielectric with microwave energy. The power dissipated within the material is derived from first principles and leads to a simple expression involving the electric field established in the material E, which is linked to the field developed within the microwave device containing the material and known as the applicator. The power is attenuated as the electromagnetic fields penetrate the dielectric, an effect depending upon the dielectric properties. Some aspects of the electric field strength within microwave applicators and its determination through various methods are described. A simplified form of the equations controlling the internal transport processes such as heat, mass and total pressure are presented. This is followed by a qualitative discussion of the physical principles of high frequency drying, stressing the importance of total internal pressure on the drying characteristics of a material in the presence of a volumetric heat source, particularly when the temperature of the liquid phase attains its boiling point. A simple formulation of moisture profiling or end drying is presented. Finally, the skin depth' for metals, which is akin to the penetration depth in insulators, is derived and discussed in terms of the best choice of metallic surface to be used for the internal wall of applicators to minimise losses and therefore maximise their efficiency.

This chapter presents the principle of the multimode oven applicator, which is used in domestic and industrial ovens. It discusses the field distribution, heating uniformity, Q-factors, field intensity, wall currents, power density, the choice of wall materials, doors, and multiple generator feeds.

The last three Chapters (5, 6 and 7) described applicators which broadly adhere to recognised categories, namely travelling wave, multimode and single mode resonant cavities respectively. Although the majority of industrial microwave equipment does in general conform to one of these three categories, there are other forms of applicator which are special by the nature of their construction or are hybrids of the recognised categories discussed previously. This chapter gives breadth to the subject of microwave applicators by selecting from numerous publications in the literature, a small number of atypical design configurations which can, under special circumstances, be used successfully in industry: The order in which these applicators are presented in the following paragraphs is not significant since we are dealing with special designs of individual applicators which may be treated in isolation. Because of the vast number of different design con figurations available, it is not possible to present a comprehensive survey, and those presented are not treated rigorously but, instead, qualitative descriptions of design and performance are given in order to highlight the important features.

This chapter presents the hazards of radio-frequency and microwave energy exposure to the human body in an industrial settings. It also presents possible sources of leakage and offers safety precautions as recommended by the Bureau of Radiological Health in the USA.

The proportion of water in a wet substance can be defined on either a wet or dry basis. In wet basis, the moisture content, M', is defined as the weight of water W_w over the weight of water W_w plus the weight of dry matter W_d; this is the dry basis definition (referred to in industry as “percentage regain”). Another definition involves the percentage pick-up, M'', defined as the weight of water picked up by the material W_wp over the total weight at equilibrium. Finally, another expression for the moisture content is that on a percentage solids basis, M'''.

This appendix contains some useful trigonometric functions and formulae.

This appendix contains some useful constants and the realtionship between temperatures in Kelvin, degrees Celsius, degrees Fahrenheit and degrees Rankine.

This appendix contains a table listing waveguide frequency ranges, dimensions and official designations, both UK and US.