Microwave absorption of film explained accurately by wave cancellation theory

Abstract

It has been proved theoretically that in the field of microwave absorption, film and material are confused, and that the impedance matching theory (IM) which is usually applied to metal-backed film is inadequate. IM is defined by the difference between the absolute values of the input impedance of the film Zin and the characteristic impedance of open space Z0. Before the scientific community accepts any new theories, it is necessary to validate them with a variety of experimental data such as those obtained from films of different materials. By analysis of experimental data, it is shown here that the problems with IM cannot be solved even if different criteria such as the value of |Zin - Z0| or the phase difference between Zin and Z0 are used and therefore it needs to be replaced by wave cancellation theory. The analysis of published data in this work supports the following conclusions. The value of reflection loss RL is determined by energy conservation, specific to film since it is related to the amplitude of the resultant of the two beams reflected from the two interfaces in the film and the angular effect from the phase difference between the two beams is vital for understanding microwave absorption from film.

Theory, Modeling, Measurement, and Testing of Electromagnetic Absorbers: A Review

“…However, recently, several authors [11,[21][22][23][24] have pointed out the confusion between film and material in the current EMW absorption theory for film absorbers. The authors contend that adopters of the current theory are confused in maintaining that absorption of EMW in film and in the material are both determined by the exact same mechanism, which is the attenuation power of the material.…”

The wave mechanics for microwave absorption film-Part 3: Film with multilayers

“…The structure-dependent EM response mechanisms as unveiled by artificial intelligence are believed to offer more opportunities for a precise prediction and optimization of EMW absorption performance." [1] However these difficulties are an inevitable consequence of confusing film and material [1,3,5,7,[32][33][34][35] in that film parameter reflection loss RL is wrongly applied to material [36,37].…”

“…The condition Zin = Z0 claimed by IM to be critical is a misinterpretation of Eq. ( 1) since nearly all the reported minima in RL/dB occur at positions where Zin  Z0 [36,48]. The real reason for the absorption peaks represented by |RL| is wave cancellation rather that the superficial reason claimed by the Zin = Z0 condition [46,48].…”

“…The absorption of film originates from the wave cancellation of the beams reflected from the two interfaces in the film [39,46,50] rather than the attenuation power of material [51,52]. Thus, successful design of the material for absorption film should be focused on what values of the relative permittivity r and permeability r of the material can ensure the maximum cancellation of the two beams [38].…”

“…The crucial question in design is to establish how changes in the structure of material will affect its own properties, in particular r and r and their responses to frequency so that the most efficient absorption film can be established using the wave cancellation theory. With proper theory [54] as developed in this work, it is possible to study how the material structure affect the values of r and r and their responses to frequency.…”