Strict proof and applicable range of the quarter-wavelength model for microwave absorbers

Abstract In the research and applications on microwave absorption materials and electromagnetic absorbers, the quarter-wavelength model is widely used in describing the dependence of the reflection loss (RL) peak frequency on electromagnetic parameters and thickness, and in the preparation and design of microwave absorption materials. However, strict proof regarding this model based on transmission line theory is lacking. Moreover, a deviation between the absorption peaks obtained from the RL results and those from the quarter-wavelength model is observed in some materials, for which a universal and reasonable theoretical explanation is also lacking. Hence, in this work, we derive strict proof of the quarter-wavelength model based on transmission line theory, and develop a revised equation for this model to explain the above-mentioned deviation. The revised equation could well fit the deviations observed in our experimental results. Combined with the experimental results, we also discuss the applicable ranges for the quarter-wavelength model and the revised equation. Moreover, the results of this work show that the appropriate value of the phase angle is effective in reducing the absorber thickness.