Estimation of reflection loss in a microwave absorbing material based on the laser speckle method

Abstract

Abstract Microwave absorption has received much attention due to its prospective implementation in the extenuation of electromagnetic interference (EMI). The effectiveness of any microwave absorbing material (MAM) is demonstrated by its dielectric dependent properties, such as electric permittivity, magnetic permeability and computed parameters like tangent loss, attenuation and reflection loss (RL) etc. RL is one of the special features of MAMs, allowing the quality of a MAM to be identified by its surface condition and the composition of the fabricated material. As a surface phenomenon, RL depends on factors such as the surface roughness, thickness of the layering of the material and the nature of the surface. The present work emphasizes the effect of surface roughness on RL, studied using the laser speckle technique (LST). Three different compositions of 10 wt%, 30 wt% and 50 wt% of two carbon-based natural fiber composites are studied for microwave absorption. The surface roughness of the material is analyzed, based on the scattering signal of laser speckles recorded in a digital storage oscilloscope. Further, the roughness of the same composition was recorded through a stylus-based profilometer and compared with the measurements from the LST. The results indicate the effectiveness of the laser contrast technique for determining the surface roughness in the design of stealth materials for EMI shielding applications. The RLs of the designed material are found to be greatly enhanced, having a larger surface roughness value with increasing wt%. The RL of the material with 50 wt% composition has been found to be −23.62 dB at 10.498 GHz. This result clearly indicates the applicability of the LST for the estimation of surface conditions to assess the suitability of MAMs in the design of stealth materials.