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RF and IoT Sensors: Design, Optimization and Applications
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RF and IoT Sensors: Design, Optimization and Applications

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: 31 December 2024 | Viewed by 12504

Special Issue Editor

Prof. Dr. Youchung Chung

E-Mail Website
Guest Editor
Information and Communication Engineering Department, Daegu University, Kyungsan 38453, Republic of Korea
Interests: computational electromagnetics; optimized antenna and array design; conformal and fractal antennas; smart wireless sensors; aging aircraft wire detection sensors; optimization techniques; electromagnetic design automation tool development; radio-frequency identification; genetic algorithms
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Non-contact and contagious electromagnetic sensors (RF, IoT, RFID, Sensor Tag, UHF, near-field, electric, magnetic, acoustic, etc.) are used for detecting signals emitted by insulation defects, either internally or externally. RF/IoT sensors have been extensively utilized in diverse applications, such as chemical sensors for homeland security, industry, academia, and recently implantable biosensors and RF physical sensors. RF antennas find ubiquitous applications in items such as mobiles, laptops, radiofrequency identification (RFID), Global Positioning System (GPS) applications, etc.

The aim of this Special Issue is to report on recent advances relating to RF/IoT components (antennas and sensors) and to contrive antennas and sensing schemes for advanced applications and optimization techniques.

Prof. Dr. Youchung Chung
Guest Editor

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Published Papers (6 papers)

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Research

13 pages, 3334 KiB  
Article
Gelatin-Coated High-Sensitivity Microwave Sensor for Humidity-Sensing Applications
by Junho Yeo and Younghwan Kwon
Sensors 2024, 24(19), 6286; https://doi.org/10.3390/s24196286 (registering DOI) - 28 Sep 2024
Abstract
In this paper, the humidity-sensing characteristics of gelatin were compared with those of poly(vinyl alcohol) (PVA) at L-band (1 ~ 2 GHz) microwave frequencies. A capacitive microwave sensor based on a defected ground structure with a modified interdigital capacitor (DGS-MIDC) in a microstrip [...] Read more.
In this paper, the humidity-sensing characteristics of gelatin were compared with those of poly(vinyl alcohol) (PVA) at L-band (1 ~ 2 GHz) microwave frequencies. A capacitive microwave sensor based on a defected ground structure with a modified interdigital capacitor (DGS-MIDC) in a microstrip transmission line operating at 1.5 GHz without any coating was used. Gelatin is a natural polymer based on protein sourced from animal collagen, whereas PVA is a high-sensitivity hydrophilic polymer that is widely used for humidity sensors and has a good film-forming property. Two DGS-MIDC-based microwave sensors coated with type A gelatin and PVA, respectively, with a thickness of 0.02 mm were fabricated. The percent relative frequency shift (PRFS) and percent relative magnitude shift (PRMS) based on the changes in the resonant frequency and magnitude level of the transmission coefficient for the microwave sensor were used to compare the humidity-sensing characteristics. The relative humidity (RH) was varied from 50% to 80% with a step of 10% at a fixed temperature of around 25 °C using a low-reflective temperature and humidity chamber manufactured with Styrofoam. The experiment’s results show that the capacitive humidity sensitivity of the gelatin-coated microwave sensor in terms of the PRFS and PRMS was higher compared to that of the PVA-coated one. In particular, the sensitivity of the gelatin-coated microwave sensor at a low RH from 50% to 60% was much greater compared to that of the PVA-coated one. In addition, the relative permittivity of the fabricated microwave sensors coated with PVA and gelatin was extracted by using the measured PRFS and the equation was derived by curve-fitting the simulated results. The change in the extracted relative permittivity for the gelatin-coated microwave sensor was larger than that of the PVA-coated one for varying the RH. Full article
(This article belongs to the Special Issue RF and IoT Sensors: Design, Optimization and Applications)
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21 pages, 4211 KiB  
Article
The Transformer Bridge Principle Circuit Using RF Admittance Technology
by Fanfan Liu, Chaojie Zhang, Wenyong Guo and Xinglong Pan
Sensors 2023, 23(12), 5434; https://doi.org/10.3390/s23125434 - 8 Jun 2023
Cited by 1 | Viewed by 1081
Abstract
To investigate the problem of the lag stability of the capacitance value during the level drop of the dirty U-shaped liquid level sensor, the equivalent circuit of the dirty U-shaped liquid level sensor was analyzed, and the transformer bridge’s principle circuit that uses [...] Read more.
To investigate the problem of the lag stability of the capacitance value during the level drop of the dirty U-shaped liquid level sensor, the equivalent circuit of the dirty U-shaped liquid level sensor was analyzed, and the transformer bridge’s principle circuit that uses RF admittance technology was designed accordingly. Using the method of controlling a single variable, the measurement accuracy of the circuit was simulated when the dividing capacitance and the regulating capacitance had different values. Then, the right parameter values for the dividing capacitance and the regulating capacitance were found. On this basis, the change of the sensor output capacitance and the change of the length of the attached seawater mixture were controlled separately under the condition of removing the seawater mixture. The simulation outcomes showed that the measurement accuracy was excellent under various situations, validating the transformer principle bridge circuit’s efficacy in minimizing the influence of the output capacitance value’s lag stability. Full article
(This article belongs to the Special Issue RF and IoT Sensors: Design, Optimization and Applications)
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12 pages, 3822 KiB  
Article
Resonant-Based Wireless Power Transfer System Using Electric Coupling for Transparent Wearable Devices and Null Power Points
by Kyeungwon Bang, Hongguk Bae and Sangwook Park
Sensors 2023, 23(3), 1535; https://doi.org/10.3390/s23031535 - 30 Jan 2023
Cited by 3 | Viewed by 2584
Abstract
This study provides information on the transfer efficiency of four-plate-structured copper plate and metal mesh sheet couplers, the cause of null-power point. The couplers are compared based on the equivalent circuit model analysis, experimental results of fabricated couplers, and simulation results of the [...] Read more.
This study provides information on the transfer efficiency of four-plate-structured copper plate and metal mesh sheet couplers, the cause of null-power point. The couplers are compared based on the equivalent circuit model analysis, experimental results of fabricated couplers, and simulation results of the High-Frequency Structure Simulator (HFSS) tool. It was confirmed that the metal mesh material exhibits the same performance as the existing copper plate and can be fully used as a coupler material for the electrical resonance wireless power transfer system. In addition, the null-power point phenomenon is only determined by the main coupling and cross coupling between the transmitter and receiver, which are most dominantly affected by the coupler structure. Full article
(This article belongs to the Special Issue RF and IoT Sensors: Design, Optimization and Applications)
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11 pages, 2188 KiB  
Communication
Isolation Improvement in Reflectarray Antenna-Based FMCW Radar Systems
by Hesham Yamani and Jihwan Yoon
Sensors 2022, 22(22), 8972; https://doi.org/10.3390/s22228972 - 19 Nov 2022
Viewed by 1829
Abstract
This paper presents an optimization of reflectarray-based RF sensors for detecting UAV and human presence. Our previous human detection radar system adapted a center-fed reflectarray antenna to a commercially available radar system, successfully increasing the gains of the transmit (TX) and receive (RX) [...] Read more.
This paper presents an optimization of reflectarray-based RF sensors for detecting UAV and human presence. Our previous human detection radar system adapted a center-fed reflectarray antenna to a commercially available radar system, successfully increasing the gains of the transmit (TX) and receive (RX) antennas by 21.18 dB and the range for detecting human targets 3.4 times. However, because the TX and RX antennas were placed in the focal point of the reflectarray, the TX signal reflected by the reflectarray was directly propagated into the RX antenna, causing desensitization or damage to the receiving circuit if high powers were used. To reduce this direct reflection, we propose a novel radar antenna configuration in which the TX and RX antennas are placed back-to-back with each other. In this configuration, the RX antenna does not directly face the reflectarray, thus direct path between the TX to RX through the reflectarray is removed. The results demonstrate that this approach achieves the optimum isolation level of 51.3 dB. With the reflectarray, the TX antenna gain increases to 30.6 dBi, but the RX antenna gain remains at 16 dBi since the RX antenna does not utilize the reflectarray. The TX and RX gain difference (14.6 dB) is a trade-off for good isolation and may be reduced by utilizing a high-gain receiver amplifier. Full article
(This article belongs to the Special Issue RF and IoT Sensors: Design, Optimization and Applications)
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15 pages, 1709 KiB  
Article
4th Order LC-Based Sigma Delta Modulators
by Evelyn Cristina de Oliveira Lima, Antonio Wallace Antunes Soares and Diomadson Rodrigues Belfort
Sensors 2022, 22(22), 8915; https://doi.org/10.3390/s22228915 - 18 Nov 2022
Viewed by 1486
Abstract
Due to the characteristic of narrow band conversion around a central radio frequency, the Sigma Delta Modulator (ΣΔM) based on LC resonators is a suitable option for use in Software-Defined Radio (SDR). However, some aspects of the topologies described in [...] Read more.
Due to the characteristic of narrow band conversion around a central radio frequency, the Sigma Delta Modulator (ΣΔM) based on LC resonators is a suitable option for use in Software-Defined Radio (SDR). However, some aspects of the topologies described in the state-of-the-art, such as noise and nonlinear sources, affect the performance of ΣΔM. This paper presents the design methodology of three high-order LC-Based single-block Sigma Delta Modulators. The method is based on the equivalence between continuous time and discrete time loop gain using a Finite Impulse Response Digital-to-Analog Converter (FIRDAC) through a numerical approach to defining the coefficients. The continuous bandpass LC ΣΔM simulations are performed at a center frequency of 432 MHz and a sampling frequency of 1.72 GHz. To the proposed modulators a maximum Signal-to-Noise Ratio (SNR) of 51.39 dB, 48.48 dB, and 46.50 dB in a 4 MHz bandwidth was achieved to respectively 4th Order Gm-LC ΣΔM, 4th Order Magnetically Coupled ΣΔM and 4th Order Capacitively Coupled ΣΔM. Full article
(This article belongs to the Special Issue RF and IoT Sensors: Design, Optimization and Applications)
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14 pages, 6342 KiB  
Article
Design of a Tri-Band Wearable Antenna for Millimeter-Wave 5G Applications
by Sarosh Ahmad, Hichem Boubakar, Salman Naseer, Mohammad Ehsanul Alim, Yawar Ali Sheikh, Adnan Ghaffar, Ahmed Jamal Abdullah Al-Gburi and Naser Ojaroudi Parchin
Sensors 2022, 22(20), 8012; https://doi.org/10.3390/s22208012 - 20 Oct 2022
Cited by 28 | Viewed by 4153
Abstract
A printed monopole antenna for millimeter-wave applications in the 5G frequency region is described in this research. As a result, the proposed antenna resonates in three frequency bands that are designated for 5G communication systems, including 28 GHz, 38 GHz, and 60 GHz [...] Read more.
A printed monopole antenna for millimeter-wave applications in the 5G frequency region is described in this research. As a result, the proposed antenna resonates in three frequency bands that are designated for 5G communication systems, including 28 GHz, 38 GHz, and 60 GHz (V band). For the sake of compactness, the coplanar waveguide (CPW) method is used. The overall size of the proposed tri-band antenna is 4 mm × 3 mm × 0.25 mm. Using a watch strap and human tissue, such as skin, the proposed antenna gives steady results. At 28 GHz, 38 GHz, and 60 GHz, the antenna’s gain is found to be 5.29 dB, 7.47 dB, and 9 dB, respectively. The overall simulated radiation efficiency is found to be 85% over the watch strap. Wearable devices are a great fit for the proposed tri-band antenna. The antenna prototype was built and tested in order to verify its performance. It can be observed that the simulated and measured results are in close contact. According to our comparative research, the proposed antenna is a good choice for smart 5G devices because of its small size and simple structure, as well as its high gain and radiation efficiency. Full article
(This article belongs to the Special Issue RF and IoT Sensors: Design, Optimization and Applications)
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