Functionally graded elastomeric composites as microwave shielding media

Abstract

Magnetic particle-filled elastomeric composites are of significant importance in microwave shielding applications. An attempt has been made to enhance the microwave reflection properties of such composites by introduction of a magnetic filler concentration gradient along the thickness. Iron powder-filled functionally graded elastomeric composites (FGECs) are prepared by a construction-based method, wherein the volume fraction of iron powder is varied along the sheet thickness. The reflection losses of the uniformly dispersed elastomeric composites (UDECs) and of the FGECs, both employing same average amount of filler, has been measured through a reflection method with a vector network analyser, using the complex scattering parameter S₁₁. FGECs with equal sample thickness and filler volume fraction exhibit 2.5 times higher microwave reflection over a broader frequency range, as compared to that of the UDECs. For a volume fraction of 0.39, the reflection losses of FGECs and UDECs at 12.3 GHz are observed to be −50 dB and −19 dB, respectively. The corresponding frequency bandwidth for reflection loss ≤ −15 dB is observed to be 9.4 GHz for FGECs compared to that of 3.5 GHz for UDECs.