Silicon elastomer as flexible substrate: dielectric characterization and applications for wearable antenna

Abstract

In this paper, low-cost mold silicone and silicone elastomers are investigated as substrates for the realization of flexible antennas. A methodical dielectric characterization is carried out, followed by a detailed explanation of the manufacturing process of the silicone elastomers. The prepared silicone elastomer substrates are also subjected to mechanical tests to ensure flexibility and robustness. The mechanical tests corroborated the utilization of the prepared silicone elastomers for the flexible antennas. Silicone has limited adhesion to metal, so when producing a silicone substrate, a 0.5 mm deep cavity is created with a negative impression of the intended metal component. Consequently, the metal layer is embedded within the silicon substrate, aligning the top surface of the metal flush with the silicone substrate edges. The radio frequency (RF) structure incorporates ridges within the silicone substrate to form a gap, effectively securing the metal on the surface of the silicone. Finally, to prevent the metal from falling from the silicone substrate, Kapton tape is laminated on the substrate. The wrapping of the Kapton tape additionally provides protection from moisture since the silicone elastomer substrate is prone to moisture absorption. The proposed technique is experimentally verified by designing and prototyping a coplanar patch antenna using copper and conductive woven fiber on the silicone substrate. The simulation analysis and experimentation results authenticated the effectiveness of the proposed technique to design a flexible antenna on the silicone elastomer substrates. It is also concluded that the conductive woven fiber-based prototype offers higher flexibility as compared to the copper-based prototype. It is also clinched that there exists a trade-off in flexibility and performance characteristics due to the conductivity and texture difference between the copper and conductive woven fiber.