This paper describes a low-cost, small size, and high-sensitivity microwave sensor using a Complementary Circular Spiral Resonator (CCSR), which operates at around 2.4 GHz, for identifying liquid samples and determining their dielectric constants. The proposed sensor was fabricated and tested to effectively identify different liquids commonly used in daily life and determine the concentrations of various ethanol–water mixtures at by measuring the resonant frequency of the CCSR. Using acrylic paint, a square channel was drawn at the most sensitive position of the microwave sensor to ensure accuracy of the experiment. To estimate the dielectric constants of the liquids under test, an approximate model was established using a High-Frequency Simulator Structure (HFSS). The results obtained agree very well with the existing data. Two parabolic equations were calculated and fitted to identify unknown liquids and determine the concentrations of ethanol–water mixtures. Thus, our microwave sensor provides a method with high sensitivity and low consumption of material for liquid monitoring and determination, which proves the feasibility and broad prospect of this low-cost system in industrial application.

Polarization shaped terahertz sources play a key factor in terahertz wireless communications, biological sensing, imaging, coherent control in fundamental sciences, and so on. Recently developed spintronic terahertz emitters have been considered as one of the next-generation promising high performance broadband terahertz sources. However, until now, polarization control, especially for twisting the circularly polarized terahertz waves at the spintronic terahertz source, has not yet been systematically explored and experimentally achieved. In this work, we not only demonstrate the generation of circularly polarized terahertz waves in cascade spintronic terahertz emitters via delicately engineering the amplitudes, applied magnetic field directions, and phase differences in two-stage terahertz beams but also implement the manipulation of the chirality, azimuthal angle, and ellipticity of the radiated broadband terahertz waves. We believe our work can help with further understanding of the ultrafast optical magnetic physics and may have valuable contributions for developing advance terahertz sources and optospintronic devices.

In this work, a high-performance THz microstrip patch antenna is designed using defected ground structure and photonic band-gap. The operating frequency of the proposed antenna is 0.690 THz. DGS and PBG are used to enhance gain, directivity, return loss and VSWR of the antenna. The proposed antenna is simulated in two different design software’s (CST2015, HFSS2018). First, a rectangular microstrip patch antenna is designed, at 0.696 THz, than RSRR structures are used in the substrate as a PBG. Next, the same RSRR structures are used in the ground known as DGS which enhances the VSWR and return loss of the antenna. The last step decreases the size of the substrate to enhance the value of VSWR up to 1.0015 which is close to unity and return loss, gain and directivity are −64.16 dBi, 6.793 dBi, and 6.914 dBi respectively. The bandwidth of the antenna is 26.7 GHz.

In this paper, complementary metamaterial sensor is designed for nondestructive evaluation of dielectric substrates. The design concept is based on electromagnetic stored energy in the complementary circular spiral resonator (CCSR), which is concentrated in small volume near the host substrate at resonance. This energy can be employed to detect various electromagnetic properties of materials under test (MUT). Effective electric permittivity and magnetic permeability of the proposed sensor is extracted from scattering parameters. Sensitivity analysis is performed by varying the permittivity of MUT. After sensitivity analysis, a sensor is fabricated using standard PCB fabrication technique, and resonance frequency of the sensor due to interaction with different MUT is measured using vector network analyzer (AV3672series). The transcendental equation is derived for the fabricated sensor to calculate relative permittivity for unknown MUTs. This method is very simple and requires calculating only the resonant frequency, which reduces the cost and computation time.

A high sensitivity complementary multiple split ring resonator (CMSRR) based submersible microwave sensor for edible oil detection and quality analysis is proposed. The main part of the sensor is the CMSRR loaded flared microstrip patch, and the proposed single-port structure is quite attractive for liquid detection. The proposed sensor was fabricated and measured to operate at 8.49 GHz with very high Q factor, which agrees very well with the simulated results obtained by High Frequency Structure Simulator (HFSS). A strong electric field can be observed along the sides of CMSRR at resonance, creating a sensing region sensitive to changes in the nearby dielectric material. By simply immersing the sensor into some familiar oil samples and heated peanut oil, the device's resonance and peak attenuation change greatly. The measured results have proven the improved sensitivity of the proposed sensor on the liquid samples compared with the methods described in the literature. The complex permittivity of the oil samples can be estimated by establishing an approximate model in HFSS. Two empirical formulas were built and fitted to estimate the complex permittivity of unknown several oil samples and heated peanut oil samples. The estimated dielectric constants agree well with the existing data. The estimated error is within 1.4% and the measured sensitivity is up to 7.25%. The proposed sensor has advantages, being compact, inexpensive, reliable, easy to operate, and highly sensitive, and has potential applications in oil detection and quality analysis.

In this paper, an extremely sensitive microwave sensor is designed based on a complementary symmetric S shaped resonator (CSSSR) to evaluate dielectric characteristics of low-permittivity material. CSSSR is an artificial structure with strong and enhanced electromagnetic fields, which provides high sensitivity and a new degree of freedom in sensing. Electromagnetic simulation elucidates the effect of real relative permittivity, real relative permeability, dielectric and magnetic loss tangents of the material under test (MUT) on the resonance frequency and notch depth of the sensor. Experiments are performed at room temperature using low-permittivity materials to verify the concept. The proposed design provides differential sensitivity between 102% to 95% as the relative permittivity of MUT varies from 2.1 to 3. The percentage error between simulated and measured results is less than 0.5%. The transcendental equation has been established by measuring the change in the resonance frequency of the fabricated sensor due to interaction with the MUT.