On the Quality Criteria for Microwave Absorbing Materials

The majority of published studies evaluating microwave absorbing (MA) materials focus on calculating reflectivity, identifying materials with lower reflectivity as having “good absorption capability”. However, Rozanov et al. posited that reflection minimum depth is insufficient as the quality criteria—a viewpoint that remains under-recognized in scientific discourse so far. This study leverages the quarter-wavelength wavelength relationship in conjunction with transmission line theory to engineer various microwave absorbers composed of ferromagnetic or dielectric materials. The results indicate that each of these absorbers can achieves perfect matching (Z_in/Z₀ = 1), suggesting that, in practice, they can all achieve the best reflection loss (RL) value of negative infinity, thereby affirming Rozanov ′s perspective. In order to be able to better evaluate MA materials, it is identified that the squared refractive index at perfect matching, denoted as (με)_p, serves as a robust quality metric. Experimental results indicate that materials with a higher (με)_p value exhibit superior absorption performance. Furthermore, this metric offers valuable insights for the design of low-frequency thin-layer absorbers and for identifying better MA materials. These findings underscore an indissociable link between MA device performance and MA material characteristics.