This article presents a dual-band planar microwave sensor to characterize the permittivity of liquid samples. The sensor utilizes a splitter–combiner microstrip segment loaded with two pairs of triangular-shaped complementary split-ring resonators (CSRRs). By integrating a meander slot into the CSRRs and incorporating inter-resonator coupling between the CSRRs, the proposed sensor achieves enhanced frequency shifts, resulting in improved sensitivity. An adulteration detection experiment is conducted to validate the sensor’s performance by mixing mineral oil into castor oil with a polydimethylsiloxane container placed on the sensing area. The variations in resonant frequency and peak attenuation are employed to extract the permittivity of the loaded liquid sample. The peak sensitivities in determining the real permittivity are measured to be 6.34% and 5.7% for the first and second frequency bands, respectively. The measured errors for extracting the real and imaginary parts of the complex permittivity are approximately 3.95% and 7.47% for the first frequency band and 3.67% and 6.28% for the second frequency band, respectively. The proposed dual-band microwave sensor, with its high sensitivity, compact size, small sample volume, and low cost, demonstrates great potential for applications in the quality monitoring of agricultural and industrial products.

This paper presents a planar microwave sensor for the noninvasive detection of glucose concentration in diabetic patients. The designed sensor operates from the 3.8 to 6.2 GHz frequency band, which covers the 5.8 GHz Industrial Scientific and Medical (ISM) band. The designed sensor shows a percentage bandwidth of 23.8% with a reflection coefficient (S11) of −50 dB at the resonance frequency of 5.7 GHz. The detection was carried out by varying the relative permittivity of the blood in accordance with the glucose concentration based on the Cole–Cole model. The measured result is calculated in terms of varying resonance frequency with variation in the reflection coefficient |S11| of the designed sensor. The observed frequency shift and corresponding sensitivity of the sensor are found at 1.7 GHz and 0.089 MHz/mg dL−1, respectively. An experimental validation has also been performed, and the frequency shift is analyzed by interacting the human thumb with the sensor. The simulated and experimental results of the designed sensor suggest that it can be useful for detecting glucose concentration noninvasively for diabetic patients.

This paper introduces a symmetric bar chart-shape (SBCS) microwave sensor for measuring permittivity of fluidic samples. For designing purposes, the introduced sensor was used based on the field changes between the SBCS and rectangular loop microstrip (RLM) structure. When a sample is placed on the sensing location, interaction between SBCS and RLM varies the field intensity. The vinegar samples were combined with water and then they are placed on the sensor. The change in field intensity changes the resonance frequency. However, there is a relationship between the permittivity of samples and the resonance frequencies. The proposed sensor is implemented on the substrate of RO4003C. The relative permittivity of samples changed from 59 to 77 and the resonance frequencies changed from 2.3 to 1.4 GHz. The quality factor is 3544 and the sensitivity is 2.2%.