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Antennas made using rigid substrates are unsuitable in applications where space and surface conformability are a concern. This is a common issue for RFID, smart tags and wearable electronics applications which require conformability to the mounting structure, in addition to being weather-proof. Commercially available designs employ bendable substrates such as synthetic rubber, polymer, microfluids and plastics, but these materials are costly, at times difficult to manufacture, and offer limited electrical and mechanical properties. More importantly they are not environmental-friendly. On the other hand, natural rubber is abundant and easily produced. Being a natural product, they are weather-proof and environmental-friendly, the electrical properties are easily controlled and are stable at elevated frequencies. It is also one of the most flexible natural material available and yet can be designed to almost any shape. We report for the first time in this paper detailed characterization of RFID antennas based on natural rubber formulated with carbon black filler. Prototype patch and meander dipole antennas were simulated using CST Microwave Studio to operate at 921 MHz, using copper as the conductor and natural rubber as the substrate. Full characterization using scattering parameters and radiation patterns were carried out for flat and bent conditions. The prototypes offered performances comparable to existing designs which use synthetic materials, with maximum read range of about 1.8 m. Optimum processing conditions and the effects of material on the antenna performance are described here. The performance obtained is comparable to commercially-available designs, with added benefits offered by a natural material.
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