Dual-Band Independent Permittivity Sensor Using Single-Port With a Pair of U-Shaped Structures for Solid Material Detection

This study proposes a single-port dual-band independent microwave sensor for detecting solid materials. The sensor structure consists of a pair U-shaped resonators connected by a power divider and a microstrip feed line with an impedance of 50 Ohms with two different sensing hotspots. The
$1^{\text {st}}$
and
$2^{\text {nd}}$
resonators operate at a frequency of 1.200 GHz and 2.100 GHz, respectively. The type of material under test (MUT) is a standard material with a size of 10 mm
$\times10$
mm (RO5880, RO4003C, and FR4). The proposed sensor had a very high accuracy compared with both of using permitivitty from datasheet and calibrated frequency from simulation for the
$1^{\text {st}}$
and
$2^{\text {nd}}$
resonator, respectively. Moreover, the pair of the U-shaped resonators had independent performances and they did not affect each other when the MUT was loaded. Furthermore, it can also operate with single-port measurement, which is a more efficient resource. Finally, the proposed microwave sensor can be a promising solution for detecting different permittivity of solid materials independently with high accuracy for applications such as the food industry, material quality control, and biomedical.