Rubber composites based on renewable resources and their potential for application in flexible wearable antennas

This work deals with the development of novel composites from renewable resources applicable for manufacturing flexible wearable antennas. Two types of fillers (rice husk ash (RHA) and microcrystalline cellulose (MCC)) from renewable resources and an alternative filler (standard silica) were incorporated into the natural rubber (NR) to examine the influences of different fillers on the electromagnetic and mechanical properties of the prepared composites. The electromagnetic parameters of the materials determined by the resonant-perturbation method were in the frequency range of 2.5–4.0 GHz. RHA-filled composites were found to have lower dielectric loss tangent and the best mechanical properties. Seven numerical models and four antennas prototypes were fabricated using the proposed composites. A detailed study on the influence of the electromagnetic parameters of the composites on the wearable antennas performance (i.e., radiation efficiency, gain, and radiation pattern) was presented. The results showed that good impedance matching and radiation efficiency of more than 53% could be achieved over ISM 2.45 GHz band (for industrial, scientific, and medical purposes) for wearable antenna with layers from NR-based composite containing silica from rice husk incineration as filler. Consequently, the rubber composites based on renewable materials exhibited great potential for practical applications in manufacturing flexible wearable antennas, given the low processing cost, economic, and environmental benefits to the telecommunications industry.