Development of a Microwave Sensor for Solid and Liquid Substances Based on Closed Loop Resonator

In this work, a compact dielectric sensor for the detection of adulteration in solid and liquid samples using planar resonators is presented. Six types of filter prototypes operating at 2.4 GHz are presented, optimized, numerically assessed, fabricated and experimentally validated. The obtained experimental results provided an error less than 6% with respect to the simulated results. Moreover, a size reduction of about 69% was achieved for the band stop filter and a 75% reduction for band pass filter compared to standard sensors realized using open/short circuited stub microstrip lines. From the designed filters, the miniaturised filter with Q of 95 at 2.4 GHz and size of 35 mm × 35 mm is formulated as a sensor and is validated theoretically and experimentally. The designed sensor shows better sensitivity, and it depends upon the dielectric property of the sample to be tested. Simulation and experimental validation of the designed sensor is carried out by loading different samples onto the sensor. The adulteration detection of various food samples using the designed sensor is experimentally validated and shows excellent sensing on adding adulterants to the original sample. The sensitivity of the sensor is analyzed by studying the variations in resonant frequency, scattering parameters, phase and Q factor with variation in the dielectric property of the sample loaded onto the sensor.

Design and Optimization of Microwave Sensor for the Non-Contact Measurement of Pure Dielectric Materials

This article presents an optimized microwave sensor for the non-contact measurement of complex permittivity and material thickness. The layout of the proposed sensor comprises the parallel combination of an interdigital capacitor (IDC) loaded at the center of the symmetrical differential bridge-type inductor fabricated on an RF-35 substrate (εr = 3.5 and tanδ = 0.0018). The bridge-type differential inductor is introduced to obtain a maximum inductance value with high quality (Q) factor and low tunable resonant frequency. The central IDC structure is configured as a spur-line structure to create a high-intensity coupled electric field (e-field) zone, which significantly interacts with the materials under test (MUTs), resulting in an increased sensitivity. The proposed sensor prototype with optimized parameters generates a resonant frequency at 1.38 GHz for measuring the complex permittivity and material thickness. The experimental results indicated that the resonant frequency of the designed sensor revealed high sensitivities of 41 MHz/mm for thickness with a linear response (r2 = 0.91567), and 53 MHz/Δεr for permittivity with a linear response (r2 = 0.98903). The maximum error ratio for measuring MUTs with a high gap of 0.3 mm between the testing sample and resonator is 6.52%. The presented performance of the proposed sensor authenticates its application in the non-contact measurement of samples based on complex permittivity and thickness.

Substrate-Integrated Waveguide Microwave Sensor for Water-in-Diesel Fuel Applications

A water-in-diesel microwave sensor based on a substrate integrated waveguide (SIW) microwave applicator is designed and characterized in this study. The interaction between the microwave electromagnetic field and the diesel fuel contaminated with small concentrations of water is obtained via suitable radiating slots placed on the top of an SIW waveguiding structure. The SIW applicator working frequency is chosen by observing the behavior of the complex dielectric permittivity of the fuel–water blend based on a preliminary wide band investigation. The performances of the SIW microwave sensor are evaluated in terms of scattering parameter modulus |S21| as a function of the water concentration in ppm. The best sensitivity Δ|S21|Δρ=1.42 mdB/ppm is obtained at a frequency of f=9.76 GHz, with a coefficient of determination R2=0.94. The sensor is low-cost, low profile and ensures a good sensitivity for constant and real-time monitoring.

Technical realization of the device for integrated monitoring of the parameters of the microwave path

Two designs of a microwave sensor have been developed for a device for built-in monitoring of microwave path parameters, built on the basis of a broadband quadrature measurement method. The first sensor design is made on the basis of a symmetrical strip line, the second - on the basis of a segment of a coaxial line. Each of the microwave sensor designs consists of three parts: a directional coupler and two non-directional measuring probes. The microwave sensor is designed to operate in the 1 - 2 GHz frequency range. The paper also proposes a variant of the circuitry implementation of the built-in microwave control device, which implements the procedure for broadband automatic measurement of the complex reflection coefficient and the power level in the microwave path based on the method of quadrature measurements. The device solves the problem of long-term automatic monitoring of parameters and timely detection of the beginning degradation of the antenna-feeder path.

Cost-Effective Flexible CSRR-Based Sensor for Noninvasive Measurement of Permittivity of Biomaterials

A novel, cost-effective, flexible microwave sensor is proposed to facilitate point-of-care testing (POCT) methods for medical diagnosis. The sensor is based on the complementary split-ring resonator (CSRR) to accurately measure the permittivity of biomaterials over a wide range of frequencies. This ability can be used to characterize various materials under test (MUT) such as blood, saliva, tissue samples, etc. The flexibility of the proposed sensor means that it can be used when the accessibility of the sample has technical difficulties, such as on curved surfaces. Firstly, the optimized structure and coupling to the readout transmission line are evaluated using finite element method (FEM) simulations. Then, the prototype of the optimized structure is fabricated on a thin polydimethylsiloxane (PDMS) substrate as a biocompatible economical polymer, and aluminium is carefully chosen for the fabrication of CSRR and readout parts. The proposed flexible sensor is tested and compared to conventional rigid CSRR sensors. The proposed structure withstood the different bending positions well, and also showed an improvement in the results for curved MUT.

Investigation of microwave sensor and integrate with polydimethylsiloxane for medical imaging application

The small-sized wideband antenna is one of the antennas used in the medical field to detect body tissue. The antenna's direct contact with the human body causes reflected signal due to the high body coupling, and the narrower bandwidth tends to reduce the data transfer rate in transmission. Therefore, this paper aims to design a wideband antenna with wearable properties operated in the frequency range of 3 GHz to 6 GHz. The antenna is designed with a rectangular-shaped patch with notches and the t-slot shaped partial slot ground. The connected speech test (CST) studio suite software is used to design and optimize the miniature antenna, which measures 24 mm (W) x 38 mm (L) x 0.168 mm (H). The antenna is then embedded with polydimethylsilixane (PDMS) at the top half of the antenna with the dimension 24 mm (W) x 19 mm (L) x 1 mm (H) and also fully occupied. The antenna is configured with the bending capabilities to adapt the human body surface at an angle of 30º. The antenna is having the benefits of small size, cost-effective, and easy to fabricate. The antenna design can effectively detect unusual body tissue, and it safe to be used.

Intelligent Shopping Trolley (IST) - a social distancing device during pandemic shopping

Intelligent Shopping Trolley (IST) is a device that was built to help in fighting the Covid-19 pandemic. This Intelligent Shopping Trolley is equipped with a RFID and timer system, Indoor Positioning System (IPS) and Microwave Sensor Detection system to determine the distance and to alert customers as they shop in a supermarket. This Intelligent Shopping Trolley will also utilise the Internet of Things (IoT) to manage its functionality. The Intelligent Shopping Trolley will help customers to determine the distance between other customers while implementing social distancing measures that is recommended by the Ministry of Health Malaysia and manage their shopping time as well. Besides that, it helps supermarkets to track their customers after the time limit given to the customers ends. This paper explains the details on this Intelligent Shopping Trolley project. This project helps in making the community aware of the importance of social distancing.