Solid materials characterization using split ring resonators enclosed by power divider

A highly sensitive microwave sensor for solid material characterization is proposed. A novel design consisting of split ring resonators (SRRs) within a three-port power divider is developed. The three-port junction is employed as the host to provide two output channels, and SRRs are loaded through electric coupling to the power divider as the sensing area. The SRRs are located symmetrically so that any change in the electric field of the SRRs is transferred equally to the transmission coefficients of the three-port junction. The operation of the proposed sensor is based on the downshifting of the transmission zero caused by the loading of samples. The two identical outputs help to control cross-sensitivity due to external effects. The performance of the fabricated prototype on a 22.2 x 18.8 x 1.6 mm3 printed circuit board is presented. It is shown that a 135 MHz shift per unit relative permittivity change can be achieved. The normalized sensitivity is found to be 3%, which is relatively higher than the sensors reported in the literature.