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High-sensitivity sensor of low relative humidity based on overlay on side-polished fibersABSTRACT: In this article, a miniaturized rectangular printed antenna that meets the ultrawideband (UWB) characteristics in terms of bandwidth and reflection coefficient is proposed. The designed antenna with dimension of 25316 mm 2 (L 3 W) was fabricated on FR-4 epoxy dielectric with relative permittivity of 4.4. SMA female connector is used for feeding with characteristic impedance of 50 X. The antenna exhibits good UWB characteristics and has the capability of operating between 3.92 to 11.32 GHz. The proposed antenna has omnidirectional radiation pattern on most of the operating band. The measured reflection coefficient of the proposed antenna is compared with the simulated one; good agreement is observed. Also, radiation pattern and gain of the antenna are presented. All simulations are carried out using the EM commercial simulators, HFSS, and CST.

A long period grating (LPG) coated with hydrogel has been developed for monitoring the relative humidity (RH) levels. The response wavelength of the LPG varies with the changes of the relative humidity. The four-layered step index waveguide model is presented to explain this observation, which is based on the effect of the hydrogel thin film, the index of which increases with the increasing RH. Experiment shows that the hydrogel-coated LPG sensor is highly sensitive between 38.9% and 100% RH, and behaves linearly with humidity with an accuracy of ±2.3% RH. The small-size and low-cost LPG fibre sensor will have extensive applications in various areas, such as remotely measuring RH, building health monitoring, medical facilities and goods' preservation.