This paper introduces a novel highly sensitive wideband differential microwave sensor based on substrate-integrated waveguide (SIW) technology for dielectric testing on microwave substrates. The sensor is a single-layer 3-port device and consists of a wideband mode converter that transforms the quasi-TEM mode of a microstrip line into the SIW’s dominant TE20 mode, and two independent SIW cavities operating with TE101 mode. One of these cavities is the test cavity and the other is the reference cavity. The performance of the proposed differential sensor in detecting the relative permittivity of microwave substrates was evaluated. The average and Bode sensitivities were computed and showed an outstanding sensitivity to negative frequency shifts. The sensor was designed and fabricated on an RT5880 Duroid Substrate, and standard microwave substrates were tested. The sensor achieves an extremely low decoupling factor, indicating effective noise or interference rejection; high sensitivity, and a wideband operation. The sensor outperforms existing SIW-based differential sensors, especially in terms of sensitivity and decoupling.

This paper revisits the electric, magnetic, and toroidal dipolar moments in the metamaterial structure and presents the flatland design for generating a toroidal dipolar response for the electromagnetic plane wave at normal incidence. Based on the numerical analysis of the surface current, the electric field, the magnetic field, and the quantitative analysis of scattered power supported by the electromagnetic multipole theory, it is shown that the earlier design involving symmetric unit cells is not able to produce toroidal dipolar moment. This study resulted in a new design of a planar metasurface, which provides a toroidal response for a normal wave incidence. The scattered power calculated for the flatland metamaterials confirms the presence of toroidal moment in the proposed asymmetric structure. The scattered power due to the toroidal dipole in the proposed design is found to be at least 70 times and 8x108 times larger than the electric dipole and the magnetic dipole, respectively, in the z-direction.