The problems in the quarter-wavelength model and impedance matching theory in analysising microwave absorption material

It is shown here that many concepts in current mainstream microwave absorption theory are used inappropriately. Reflection loss RL has been used to characterize microwave absorption from material instead of film and the results have been rationalized by impedance matching theory. The quarter-wavelength model states that the reflection of microwaves with wavelength l from a film is minimized if the thickness of the film is m l /4 where m is an odd integer. But we show here that the model is wrong because the phase effects from interfaces have been overlooked. RL is an innate property only for metal-backed film. Impedance matching theory is developed from transmission-line theory for scattering parameter s 11 but cannot be generalized to RL.

Spatially Dependent Resonance Cross Sections in a Fuel Plate

The classical resonance absorption theory known as equivalence theorem which treats two-region problem (Fuel/Moderator) has been generalized to arbitrary sub regions of fuel pin by Stoker/Weiss technique and SDDM (Spatially Dependent Dancoff Method). Stoker/Weiss technique and SDDM were derived only for infinite cylinders. To calculate the shielded resonance cross sections for sub regions in the fuel plate, a method is presented by geometrical derivation of first flight blackness for slab geometry. To validate the method, probability approximation and cross section generation are all compared to the benchmark problems. It is concluded that this method is practically useful and appropriate for generating the effective cross-sections in sub regions of a fuel plate.