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Advanced Microwave Circuits and Systems Part 17

Tham khảo tài liệu 'advanced microwave circuits and systems part 17', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 474 Advanced Microwave Circuits and Systems Fig. 1. Repelling in response of Sunne pest to electromagnetic exposure 2.2 Electromagnetic heating Dielectric materials such as most plants can store electric energy and convert electric energy into heat. Each material has a complex permittivity e in general. According to measurements usually this value is noticeably frequency dependent. The imaginary part e of this value is responsible for absorption of electromagnetic waves in each material. Eq.1 shows the general form of the first Maxwell s equations considering e . V X H jms E J jms E ơE 1 j o e - j E jrn e - js r E m As a consequence total power absorption in a specific material is achieved if the second part of the equation is integrated over the material volume as follows. Ps J E JdV J ơ E 2 dV m s E 2 dV 2 v v v The basic idea is to use e to warm up the selected materials which are located far from an electromagnetic source. On the other hand the E-field distribution inside the absorbing material highly depends on the shape of absorber and surrounding scatterers compared to wavelength and also the source of excitation. For instance regarding the distribution of a cluster of walnuts inside an oven the resulted electromagnetic wave inside one of them is a function of its shape the shape and the position of other walnut as external scatterers and the oven and its exciting antenna as the source. Hence not only the total absorbed energy resulted from 2 is important but also the uniformity of the electromagnetic field distribution is crucial. If the dimensions of the exposed object are electrically small we can assume the E-field distribution inside the object is uniform. For bigger objects the penetration of the wave inside the object i.e. skin depth can be calculated using 3 depending on frequency used and the dielectric properties of the sample under test especially conductivity. Electromagnetic Solutions for the Agricultural Problems 475 s 3 Wherein 8 is the skin .