Electronically Tunable Metamaterial Sensor for Broadband Dielectric Measurement of Liquid Materials

In this article, a novel dual-frequency-tunable metamaterial microwave sensor has been evaluated to determine the complex permittivity of the liquid materials. The presented structure consists of a dipole antenna and two pairs of varactor-loaded split-ring resonators (VLSRRs), lumped isolate inductors, and voltage tuning networks. Varactors are mounted to the capacitive regions of the VLSRRs to regulate the varactor value from 0.40 to 3.20 pF. Four variable capacitance varactors possess the capability for independent operational functionality via the voltage tuning networks. The sample under test (SUT) is contained inside the 3-D microfluidic channel. When the varactor does not work, the first and second resonant frequencies of the sensor are found to be 4.20 and 5.60 GHz, respectively. The proposed sensor enables elevated sensitivity over a broad frequency spectrum by utilizing diverse voltage tuning techniques for four varactors. The wide tuning frequency range of up to 2.0 GHz is achievable by regulating the voltages of the two resonant regions using equal values. Conversely, achieving high sensitivity requires independent control of the voltages in the two resonant regions with unequal values. Hence, the proposed sensor achieves a continuously stepped resonant frequency across a wide bandwidth, thereby enhancing sensitivity at any resonant frequency within the operational bandwidth. This novel design enables the development of a broadband tunable metamaterial sensor for predicting the dielectric permittivity of tested samples.