Collaboratively Far-Field and Near-Field Regions for Dual-Modalities Microwave Permittivity Sensor Using T-Shaped Resonator Embedded With IDC

This letter introduces collaboratively far-field and near-field regions for dual-modalities permittivity sensor to characterized solid materials. The proposed sensor comprises a T-shaped resonator featuring a single port embedded with interdigital capacitor (IDC). The first resonator, operating at
f_r1
= 2.43 GHz as the long-distance detection, utilizes the far-field region, while the second resonator, working at
f_r2
= 1.64 GHz, functions as the contact detection, utilizes the near-field region. These resonators possess distinct sensing hotspots, enabling independent utilization. Contact detection is achieved by utilizing the near-field region by placing the material under test (MUT) directly above the surface of the second resonator, while the first resonator for long-distance detection utilized the far-field region by using the interrogator antenna at a distance of d = 10 cm. The experimental results demonstrate that the proposed sensors exhibit a maximum sensitivity of 5.13% and 3.40% for near-field and far-field detections, respectively. Moreover, the average accuracy for both contact and long-distance detections is 95.99% and 95.16%, respectively, when compared to the permittivity values obtained from the datasheet within the range of 1–6.15. This research holds significant practical value for the contact and long-distance characterizations of solid materials, particularly in applications, such as biomedical, quality control, and pharmaceutical industries.