Agricultural Waste‐Based Radar Absorbing Structures With Improved Thermal, Mechanical, and Microwave Absorption Properties

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Abstract
This work describes the effective use of rice husk ash (RHA) as an alternative to commercial silica in the epoxy–glass (EP/GF) composite to develop radar absorbing structures (RAS). The EP/GF/RHA hybrids with RHA loading of 0 to 15 wt% were prepared and their thermal, mechanical, electromagnetic (EM), and microwave absorption properties were investigated. Scanning electron microscopy showed almost uniform dispersion of RHA in the matrix. The addition of RHA improved the dimensional stability of the hybrids remarkably in the out‐of‐plane direction. The coefficient of thermal expansion (CTE) of the hybrid was decreased by 34.3% as compared to the composite without RHA. The uniform dispersion and better adhesion of RHA with the matrix led to a remarkable improvement in tensile strength and elastic modulus. With increasing RHA loading, the real ( ε ′) and imaginary ( ε ″) parts of the complex permittivity of the EP/GF/RHA hybrids increased slightly. The hybrid with 15 wt% RHA and 4 mm thickness revealed excellent microwave absorption properties with maximum reflection loss (RL max ) of −26.38 dB at 9.04 GHz and effective absorption bandwidth (< −10 dB) of 1.33 GHz. These results highlight the potential of EP/GF/RHA hybrids as eco‐friendly and sustainable RAS with better thermal and mechanical properties for defense applications.

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