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Microwave sensors based on electrically small planar resonant elements are investigated in this season. Due to the high sensitivity of these resonators to the properties of their environment, especially the dielectric constant and the loss coefficient, these sensors are of particular importance for the dielectric characterization of solids and liquids and for measuring the composition of materials. This chapter also deals the main advantages and limitations of planar microwave resonant sensors, and several prototypes are reported, mainly including sensors for measuring the dielectric properties of solids, and sensors based on microfluidics (useful for liquid characterization and liquid composition). The proposed sensors have great potential for use in real scenarios (including industrial processes and characterization of bio-samples).

In this paper, a novel compact planar coronavirus antenna is proposed for wide band applications. In the design of this antenna, the idea of the radiating part has been taken from the 3-D model of the coronavirus, which is fed by a 50 Ω coplanar waveguide. The patch structure and the feed line of the proposed antenna, which have been made of gold, are located on a polyamide substrate with a thickness and dielectric constant of 45 µm and 3.5, respectively, and the antenna has compact physical dimensions of 300 × 300 µm 2 . The simulation results of the antenna have been analyzed in terms of S 11 , VSWR, radiation pattern, gain and surface current distribution. The designed antenna covers the frequency band from 0.3627 to 0.5918 THz for S 11 ≤ − 0 dB with a fractional bandwidth of > 47.98% and with a bandwidth ratio of 1.63:1. This extended bandwidth coverage allows the antenna to be suitable for a wide range of applications including wireless communications, internet of things, wearable devices, on-chip antennas and multiple-input multiple-output systems. Also, the results of the far-field show an omnidirectional radiation pattern with an average gain and efficiency of 4 dBi and 93% throughout the frequency band, respectively.