Analysis of Dielectric Properties of Polydimethylsiloxane (PDMS) as a Flexible Substrate for Sensors and Antenna Applications

In this paper, a complete analysis of the complex dielectric constant of a flexible substrate from the silicon-based polymer- Polydimethylsiloxane (PDMS) is performed, and the obtained results are discussed. Two experimental methods are applied in this research. The first Two-resonator method is based on resonance measurements by excitation of two types of TE- and TM-mode cylinder resonators with PDMS disks, ensure an accurate determination of the dielectric constant and dielectric loss tangent in both parallel and perpendicular directions (e.g., ε _par and ε _perp ). The second method is based on the tight coverage of planar microstrip ring resonators with non- metalized PDMS samples gives reliable information for the equivalent dielectric parameters (e.g., ε _eq , tan δ _εeq ). The obtained results show that PDMS substrates have relatively weak but measurable uniaxial anisotropy and well-expressed frequency dependencies of the extracted dielectric parameters in the range 1-40 GHz, namely ε _par ~ 2.82-2.7; ε _perp ~ 2.73-2.52 and ε _eq ~ 2.75-2.64, tan δ _εeq ~ 0.017-0.048. The results are confirmed by several other complementary methods. The considered pair of methods are also applied in the temperature interval-40/ + 70 ^° C; the measured temperature dependencies on the dielectric parameters turn out to be relatively strong. The possible origin of the measured PDMS uniaxial anisotropy has been discussed; in fact, it appears mainly in the temperature range-30/ + 40 ^° C.