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.

The dielectric behavior of kaolinite, montmorillonite, allophane, and imogolite samples adjusted to a water potential of 33 kPa was examined using a time-domain reflectometry method over a wide frequency range of 103-1010 Hz. A dielectric relaxation peak owing to bound H2O was observed. The observation of this peak required the precise determination of the contributions of dc conductivity. The peak is located at 10 MHz, indicating that the relaxation time of the bound H2O is approximately ten times longer than the relaxation time of bound H2O with organic polymers, such as an aqueous globular-protein solution. The structure of bound H2O differs between phyllosilicates and amorphous phases, based on differences in relaxation strength and the pattern of distribution of the relaxation times. The dielectric process involving rotation of bulk H2O molecules was also observed at 20 GHz. The relaxation strength of bulk H2O increased with an increase in the water content. The interfacial polarization in the diffuse double layer occurred only in montmorillonite and kaolinite, indicating that mechanisms involving the Maxwell-Wagner and surface-polarization effects cannot be extended to include allophane and imogolite. Although these results suggest that additional work is required, a tentative conclusion is that a tangential migration of counter-ions along clay surfaces may be important.

In this paper, a novel SIW microwave sensor is designed to accurately determine the broadband complex permittivity of medium loss and dispersive liquids using a number of higher order modes in 11–20 GHz. To achieve a higher accuracy in characterization, the sensor is equipped with some methods such as Photonic Band Gap method, slow-wave via, and a new feedline, which enhances the quality factor for the higher order TE1,0,n modes. The operating principle of this sensor is based on the cavity perturbation technique, in which the resonant properties of the cavity are utilized to extract the dielectric properties of liquid under test. To provide a method to decrease the LUT consumption, a winding microfluidic channel is designed and embedded in the cavity. The channel increases the interaction between the induced electric field and the LUT. The accuracy of different perturbation technique for determination of permittivity is compared with each other.

In this work, the electrical characterization of nanocomposites made of epoxy resins with multiwalled carbon nanotubes is presented. As the filler, two different types of multiwalled carbon nanotubes with different aspect ratios (280, 1250) and defectiveness were selected. The production procedure, the morphological characterization, the I–V DC characteristics, and the low frequency complex permittivity (in the range 100 kHz–12 MHz) of these nanocomposites are discussed. To investigate the dispersion of the solution, a study which linked the mixing time to the zeta potential was performed. The experimental results show that with the same matrix and by using the same measurement techniques, the two nanocomposites give different results and can be correlated with the characteristics of nanotubes. The dc conductivity of the nanocomposites was measured by means of a two-point probe technique. The conductivity in the frequency range 100 KHz–12 MHz was evaluated using a circular disk capacitor and measuring the impedance. The measured conductivity follows a percolation scaling law of the form σ ∝ (p − p c)t . A best fit to the measured conductivity data was obtained and the values of the exponent t compared to those in the literature.

Ta2O5 added MgCuZn ferrites are prepared by the microwave-hydrothermal (M-H) processing. The nanocrystalline ferrites are sintered to a temperature of 900 °C using conventional sintering (CS) and microwave sintering (MW) methods. The effect of Ta2O5 addition on the microstructure, d.c. resistivity, and Curie temperature of the ferrites has been studied. By the addition of Ta2O5 to MgCuZn ferrites, resistivity decreases without grain growth. The complex permittivity and complex permeability of the prepared samples were measured in the frequency range from 10 kHz to 1.8 GHz. The value of ε′ and tan δ for all the samples decreases from 10 to 100 kHz and almost remains constant up to 300 MHz and increases further by increasing the frequency up to 1 GHz. The µ* spectra are analyzed into two magnetization processes with a focus on the grain size of the ferrite samples. The present ferrites exhibited high values of permeability (>1000) in the frequency range of 10 kHz to 50 MHz. Then the values of permeability are found to decrease with an increase in frequency up to 180 MHz and finally, frequency dispersion occurred at 200 MHz.

In this paper, it is proposed to use a cylindrical cell for the characterization of dielectric material. The extraction of complex permittivity is based on inverse gradient approach where the full-wave simulation results are mapped to experimental data to extract the complex permittivity. As the operational frequency of radio frequency (RF)/microwave devices is increased, it becomes difficult to accurately model waveguide transitions using traditional methods based on meshing such as finite-element method (FEM) where mesh size is determined according to the wavelength. Moreover, these techniques usually require extensive computational resources. Mode matching technique (MMT) is the full-wave tool implemented in this current work. It is used to compute the generalized scattering matrices (GSMs) of the different discontinuities of test setup. These GSMs model precisely discontinuities as they include the effects of all higher-order modes propagating and evanescent. Simulation and experimental results are included to validate the proposed approach for the rigorous modeling of those discontinuities and hence the extraction of complex permittivity.