Frequency-tunable soft composite antennas for wireless sensing

In this study, flexible and uniform multiwall carbon nanotube embedded polydimethylsiloxane (PDMS) sheets were prepared using a vacuum filtration and transfer process. The resistance of the sheets and microstructures were investigated for the fabrication of ideal probe-fed and microstrip-fed patch antennas. Simulation results showed that the resonance and gain of an antenna were affected by the conductivity of the patch significantly. The return loss and gain are acceptable when a conductivity of 105 S/m is used. The stretchability test indicated that a gold-coated sheet was more stable than a pristine sheet. Its resistance has a change of 0.5% only, with a displacement of 2500 μm. The frequency-tuning capability was demonstrated using an air inflatable microstrip-fed patch antenna. The working frequency can be tuned by 6.5% with a displacement of 1500 μm, which was higher than that of previously reported MEMS bridge and electrostatic force tunable antennas. This is the first time that a frequency tunable antenna fabricated by PDMS/carbon nanotube is reported. The optimization methods for this type of antenna are discussed and some potential applications such as remote wireless pressure sensors are proposed.