This paper presents a highly sensitive microwave sensor for dielectric sensing. One of the main disadvantages of microwave resonant-based sensors is cross-sensitivity originated by time-dependent uncontrolled environmental factors such as temperature that affect the material under test (MUT) behavior, leading to undesirable frequency shifts and, hence, lower accuracy. However, this work eliminates the unwanted errors using the differential measurement technique by comparing two transmission resonance frequencies during a unit test setup to measure the permittivity of MUT over time. The proposed structure comprises a spiral resonator with an extended horizontal microstrip line (EH-ML) coupled to a microstrip transmission line (MTL). Creating EH-ML within the structure comprises two primary contributions: enhanced sensitivity resulting from stronger fringing fields generated by increasing the effective area and improved resolution due to higher resonance frequencies caused by a lower total capacitive coupling effect. The proposed sensor is fabricated and tested using MUTs with a permittivity of less than 80 to verify the performance. In this regard, a frequency detection resolution (FDR) of 44MHz and a sensitivity of 0.85% are achieved at a maximum permittivity of 78.3. The results of theoretical analysis, simulation, and measurement are in relatively good agreement. Consequently, the proposed highly sensitive microwave sensor offers significant advantages, such as low complexity in design and fabrication. It also offers high resolution and precision in a wide range of permittivity, which can be an attractive candidate for dielectric sensing in health, chemical and agriculture applications.

In this paper, two wideband dual-polarized Dielectric Resonator Antennas (DRA) for X band radar applications are presented. The design procedure is started with designing a linear polarized DRA fed by a microstrip line. The feedline is optimized to excite the HEM11δ mode of DRA which corresponds to magnetic monopole like radiation. Then, a novel quadrature hybrid is designed in the feeding structure to provide both left (LHCP) and right-handed (RHCP) circular polarization. Finally, two antenna prototypes are fabricated and tested: a dual (right hand and left hand) circular polarization DRA with omni-directional pattern, and an enhanced gain version of dual-polarized CP DRA with a directive pattern. The measurement results of antennas confirm wideband impedance bandwidth (34% and 38.8%) as well as wideband Axial Ratio (AR) one (23% and 30%) in element and array structures, respectively. The antennas also provide both RHCP and LHCP radiation. The first antenna contains monopole-like radiation which is aimed at wireless systems with omnidirectional pattern requirements. The second, a 2*1 antenna array, which presents around 9 dB across the entire band. The presented antennas are good candidates for radar applications such as weather monitoring, air traffic control, and vehicle speed detection.

This work presents a low-cost, compact-size and highly sensitive sensor based on a Reconfigurable Phase Shifter (RPS) that is designed, simulated, fabricated and tested using the Time-Domain Transmissometry (TDT) technique. Generally, microwave sensors utilized in field measurement setups for dielectric sensing often face significant challenges, such as high costs, limited accuracy and resolution, and the potential need for extensive equipment. To address this, PIN diodes are incorporated into the structure, enabling tunable RPS to extend the capacity to measure phase variations across a broader range, leading to higher resolution while preserving the same compact form factor. Also, exciting the TDT-RPS sensor with a sine-wave signal instead of a pulse at a single frequency improves the accuracy since the Material Under Test (MUT) is dispersive. Moreover, two key components have been integrated into the RPS structure to estimate phase difference variations using the TDT technique: a power splitter and a compact commercial phase detector (AD8302). This integration minimizes the necessary measurement equipment in the testing setup. Consequently, the proposed TDT-RPS can be integrated into Wireless Sensor Networks (WSNs) and IoT systems for in-situ scenarios, making it a promising solution for use in various fields such as biomedical, agriculture, and chemical industries.

Soil salinity is a critical factor impacting agriculture and the environment. This study develops a frequency-dependent model to predict soil salinity based on the dielectric permittivity and volumetric water content. A targeted soil database was created, incorporating varied salinity and moisture levels from two soil types: sandy and clay. Real and imaginary parts of permittivity were measured across a frequency range of 10–295 MHz using the dielectric assessment kit vector network analyzer system, as permittivity in this band shows the highest variation and sensitivity to moisture and salinity. After analyzing the behavior of permittivity changes and minimizing prediction errors, two separate models were proposed for the real and imaginary parts. These models are significantly more sophisticated and flexible than previous ones, designed to accept inputs that are easily measurable by commercial sensors. The comparison between model outputs and measured data demonstrates a high level of alignment, indicating that the model can improve salinity prediction accuracy and extend its applications beyond agriculture to practical uses in geology and hydrology. The average prediction error was less than 8.2% for the real part and 9.3% for the imaginary part.

Blood glucose monitoring is crucial for managing diabetes, yet traditional finger-prick methods remain inconvenient and uncomfortable. Hypoglycemia (140 mg/dL post-meal) leads to severe organ damage. This highlights the urgent need for non-invasive glucose sensing solutions to enhance patient care. This study presents an innovative, non-invasive 3D oblique gap rectangular resonator (OGRR) sensor designed to detect glucose concentrations ranging from 65 to 105 mg/dL. Employing a differential measurement technique, it minimizes systematic errors and enhances accuracy. Additionally, dielectric assessment kit (DAK-12) is utilized for precise glucose sample analysis. The sensor features a lightweight, compact design integrating oblique gap resonators and defected ground structures, resulting in amplitude sensitivity of 0.422 dB/(mg/dL) and frequency sensitivity of 3.6 MHz/(mg/dL). There is a good agreement between simulation and measurement results. With superior performance and cost-effectiveness, this sensor holds promise for glucose level monitoring in biomedical applications.

Diabetes disrupts glucose regulation in both humans and animals, severely impacting liver and muscle function. Commonly used monitoring methods are invasive and cumbersome to implant, highlighting the need for non-invasive alternatives. This study focuses on developing a non-invasive, lightweight, and highly sensitive three-dimensional ear-conformed resonator (3D-ECR) sensor for glucose monitoring. Using a dielectric assessment kit (DAK), this work measures permittivity in standard aqueous glucose samples (35 to 110 mg/dL), covering the majority of the physiologically observed glucose range in humans and cattle. The 3D-ECR sensor analyzes resonance frequency and phase variations of S₂₁, achieving phase sensitivities of 1°/(mg/dL) at 2.45 GHz and 0.7°/(mg/dL) at 4.3 GHz, and frequency sensitivity of 3.2 MHz/(mg/dL). This innovative sensor offers a promising solution for glucose monitoring in biomedical and agricultural applications. This work serves as a laboratory-level proof of concept using standard aqueous glucose samples, with future studies planned for tissue-mimicking phantoms and clinical validation.