A petrol adulteration sensor based on a rectangular shaped hollow-core photonic crystal fiber is proposed and numerically analyzed in the terahertz regime. The performance of the proposed sensor was evaluated when it is employed to characterize different kerosene mixtures. In this research, the adulterated fuel sample is filled in the rectangular hollow channel and the electromagnetic signal of the terahertz band is also driven through the same channel. The received signal after the interaction of fuel with the terahertz signal will advise the refractive index of the fuel oil inside the core, which will also bear the information of how much extrinsic component is present in the fuel. The finite element method based simulation shows that the proposed sensor can reach a high relative sensitivity of 89% and presents low confinement losses at 2.8 THz. The reported sensing structure is easily realizable with the conventional manufacturing techniques. Consequently, this proposed fiber may be treated as an essential part of real-life applications of petrol adulteration measurements.

https://www.mdpi.com/2079-6439/8/10/63/pdf

Numerical Modeling of a Rectangular Hollow-Core Waveguide for the Detection of Fuel Adulteration in Terahertz Region

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.

Submersible High Sensitivity Microwave Sensor for Edible Oil Detection and Quality Analysis

Real-Time Measurement of Liquid Permittivity Through Label-Free Meandered Microwave Sensor

In this paper, a sensor using modified Split Ring Resonators (SRRs) is designed, simulated, fabricated, and used for advanced investigation and precise measurements of the real part and imaginary part solid dielectrics’ permittivity. Adding vertical strips tightly coupled to the outer ring of the SRR leads to the appearance of two resonant frequencies at 1.24 GHz and 2.08 GHz. This modified geometry also assures an improved sensitivity. Using the full wave electromagnetic solver, both the unloaded and loaded sensors are investigated. The numerical simulations are used to develop a mathematical model based on a curve fitting tool for both resonant frequencies, allowing to obtain analytical relations for real and imaginary parts of permittivity as a function of the sample’s thickness and quality factor. The sensor is designed and fabricated on 1.6 mm thick FR-4 substrate. The measurements of different samples, such as transparent glass, acrylic glass, plexiglass, and Teflon, confirm that the modified SRR sensor is easy to implement and gives accurate results for all cases, with measurement errors smaller than 4.5%. In addition, the measurements highlight the importance of the second resonant frequency in the cases in which numerical limitations do not allow the usage of the first resonant frequency (1 mm thick sample).

Modified Split Ring Resonators Sensor for Accurate Complex Permittivity Measurements of Solid Dielectrics

Most of the humidity or gas sensing researches focus on the optimization of sensitive materials, while the studies of microwave detection focus on its sensitive-field control. It is necessary to implement the cooperative study on microwave detection with different types of sensitive materials for a better understanding of the operation mechanism as well as providing a way for performance enhancement. This study presents the double split-ring resonator as the sensitive electrode, where various sensitive materials, including polymer by pure Polyimide (PI), ceramic composite by PI-TiO2, metal composite by PI-Ag composite, are respectively tested as the sensing materials. The S-parameter is tested as the humidity indicators after coating on the sensitive regions with a strong electric-magnetic field. Owing to the improved dielectric properties by doping strong-polarity TiO2 nanoparticles into PI, the higher sensitivity with the maximum of 880.0 kHz/%RH and 0.322 dB/%RH is realized. The introduction of Ag nanoparticles facilitates the water vapor adsorption and desorption showing the sensitivity of 330.0 kHz/%RH and 0.149 dB/%RH, due to the high active-site density and surface roughness. By analyzing variations in resonant frequency and return loss, the microwave sensing mechanism of different sensitive materials is fully discussed from the perspective of polarization, dielectric property, and sensitive area.

Microwave detection with various sensitive materials for humidity sensing

In order to improve the sensitivity of liquid dielectric constant measurements, a liquid dielectric constant sensor based on a cubic container structure is proposed for the first time. The cubic container, which consists of a dielectric substrate with a split resonant ring (SRR) and microstrip lines, can enhance the electric field intensity in the measuring area. High sensitivity can be obtained from measuring the dielectric constant with the characteristics of the structure resonate. The research results show that the resonant frequency of the sensor is shifted from 7.69 GHz to 5.70 GHz, with about a 2 GHz frequency offset, when the dielectric constant of the sample varied from 1 to 10. A resonance frequency offset of 200 MHz for the per unit dielectric constant is achieved, which is excellent regarding performance. The permittivity of oil with a different metal content is measured by using the relation between the fitted permittivity and the resonant frequency. The relative error is less than 1.5% and the sensitivity of measuring is up to 3.45%.

https://www.mdpi.com/1424-8220/20/19/5598/pdf

Design of a High Sensitivity Microwave Sensor for Liquid Dielectric Constant Measurement.

In order to solve the low-sensitivity problem of the dielectric constant with the resonant cavity method, a sensor based on a substrate-integrated waveguide structure loaded with a multi-complementary open resonant ring is proposed. With the enhanced resonance characteristics of the sensor, this design realized the measurement of complex dielectric constants in a wide range. The frequency selectivity of the sensor is improved by the high-quality factor of the substrate-integrated waveguide. By loading three complementary resonant rings with different opening directions in the ground plane, a deeper notch and better out-of-band suppression are achieved. The effect of the complex dielectric constant on both resonant frequency and quality factor is discussed by calculating the material under test with a known dielectric constant. Simulation and experimental results show that a resonance frequency offset of 102 MHz for the per unit dielectric constant is achieved. A wide frequency offset is the prerequisite for accurate measurement. The measurement results of four plates match well with the standard values, with a relative error of the real part of the dielectric constant of less than 2% and an error of less than 0.0099 for the imaginary part.

Design of Substrate-Integrated Waveguide Loading Multiple Complementary Open Resonant Rings (CSRRs) for Dielectric Constant Measurement.

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Design of a High Sensitivity Microwave Sensor for Liquid Dielectric Constant Measurement.

Design of Substrate-Integrated Waveguide Loading Multiple Complementary Open Resonant Rings (CSRRs) for Dielectric Constant Measurement.