A Re-evaluation of the mechanism of microwave absorption in film – Part 2: The real mechanism

Microwave absorption of film explained accurately by wave cancellation theory

“…However, RL(x 1 -)/dB is not a monotonic function of d thus it cannot be used to characterize the absorption of material. The multipeaks RL(x 1 -)/dB originate from the fact that the phase of beam t is a function of d and thus the peaks of RL(x 1 -)/dB are due to the fact that the phase difference φ of beams t and 1 r is periodically out of phase by π as d increases [7,8]. This provides a good example of the observation that the property of a portion of material is different from that of the material itself.…”

“…Relevant expressions are fully derived in the Appendix. It is first demonstrated from numerical calculations [7] and then proved theoretically from angular effects [8] that the most efficient absorption takes place when φ = (2n + 1)π resulting in full wave cancellation and the least absorption takes place where φ = 2nπ, where n is an integer. Since the absorption of film is characterized by the cancellation of beams 1 r and t, films providing efficient absorption can be composed of poor absorption material and at absorption peaks, films can absorb more microwaves than can the material alone.…”

“…The cancelation of beams 1 r and t provides the key to differentiate the mechanism of absorption of film from that of material. In fact, for most materials, the imaginary parts of permittivity ε r " and permeability µ r " are small, and the strongest beam t provides the most efficient absorptions at φ = (2n + 1)π and the weakest provides the least absorption at φ = 2nπ [7,8]. This can be easily understood by considering energy conservation for a film that does not absorb microwaves [8,11], which involves returning the required energy to the open space by beam t when it is canceled or enhanced by beam 1 r [7,8].…”

“…They consider a block of material making up a film to have the same properties as the material in general. However, while permittivity ε r and permeability µ r can be properties of material [13], scattering parameters such as reflection loss RL are parameters for devices and not for material [7,8,11,13]. Film, which has thickness, is a device made of material but thickness obviously cannot be a general property of material.…”

“…Thus, properties unique for the block cannot be attributed to the material. There is much evidence showing that many wrong theories in this field have been developed by overlooking this basic tenet [8,11,12].…”