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Abstract-This work presents novel techniques for producing substrates for flexible antennas. The technique we propose is based on the use of an already existing and widely used substrate material Polydimethylsiloxane (PDMS), where the dielectric properties of the substrate are adjusted by loading the PDMS with low or high permittivity inclusions. The low adhesion characteristics of PDMS are overcome by immersing the conducting parts of the antenna inside the substrate, at the same time sealing the antenna against the influence of dust, or water. A patch antenna prototype is realized and characterized. The built antenna is soft and flexible and it shows good radiation characteristics in terms of input matching and total gain. Measurements are in a good compliance with the simulation results.

This letter presents a study on the Specific Absorption Rate (SAR) evaluation of UHF wearable antennas. A Planar Inverted F Antenna (PIFA) intended to operate in Wireless Body Area Networks (W-BAN) is taken as an example for the investigation. The presence of the ground plane introduces isolation between the body and the wearable antenna and decouples the antenna from the body, thus resulting in lower SAR values. The performed analysis of the proposed PIFA antenna indicate increased near-field regions close to the shorting wall, which directly leads to increased SAR values. This can be avoided if alternative current paths are provided, e.g. extending the ground plane slightly. The dielectric materials used as substrates partially reduce the SAR by confining part of the fields inside the dielectric. All the suggested solutions are easily applicable for a practical implementation.

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