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RF Sensors: Design, Optimization and Applications
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RF 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: closed (31 December 2021) | Viewed by 60984

Special Issue Editors

Prof. Dr. Youchung Chung

E-Mail Website
Guest Editor
Information and Communication Engineering Department, Daegu University, Kyungsan 38453, 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
Prof. Dr. Cynthia M. Furse

E-Mail Website
Guest Editor
Electrical and Computer Engineering, University of Utah,50 S. Campus Drive, Salt Lake City, UT 84112, USA
Interests: capacitance measurement; capacitors; cellular biophysics (REMOVE); commerce; electric impedance; electric impedance measurement; electromagnetic fields; fats (REMOVE); fault diagnosis

Special Issue Information

Dear Colleagues,

Non-contact and contagious electromagnetic sensors (RF, UHF, near field, electric, magnetic, acoustic, etc.) are used for detecting signals emitted by insulation defects either internally or externally. RF sensors have been extensively utilized in diverse applications, such as chemical sensors for homeland security, industry, academia, and, recently, implantable biosensors, RF physical sensors. RF Antennas find ubiquitous applications in items such as mobiles, laptops, radio-frequency-identification (RFID), global-positioning-system (GPS) applications, etc.

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

Prof. Youchung Chung
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Antenna and RFID
  • Radar
  • Sensors
  • Optimization

Published Papers (17 papers)

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Research

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14 pages, 6889 KiB  
Communication
A Sensor for Characterisation of Liquid Materials with High Permittivity and High Dielectric Loss
by Chen Wang, Xiaoming Liu, Zhixiang Huang, Shuo Yu, Xiaofan Yang and Xiaobang Shang
Sensors 2022, 22(5), 1764; https://0-doi-org.brum.beds.ac.uk/10.3390/s22051764 - 24 Feb 2022
Cited by 18 | Viewed by 2751
Abstract
This paper reports on a sensor based on multi-element complementary split-ring resonator for the measurement of liquid materials. The resonator consists of three split rings for improved measurement sensitivity. A hole is fabricated at the centre of the rings to accommodate a hollow [...] Read more.
This paper reports on a sensor based on multi-element complementary split-ring resonator for the measurement of liquid materials. The resonator consists of three split rings for improved measurement sensitivity. A hole is fabricated at the centre of the rings to accommodate a hollow glass tube, through which the liquid sample can be injected. Electromagnetic simulations demonstrate that both the resonant frequency and quality factor of the sensor vary considerably with the dielectric constant and loss tangent of the liquid sample. The volume ratio between the liquid sample and glass tube is 0.36, yielding great sensitivity in the measured results for high loss liquids. Compared to the design based on rectangular split rings, the proposed ring structure offers 37% larger frequency shifts and 9.1% greater resonant dips. The relationship between dielectric constant, loss tangent, measured quality factor and resonant frequency is derived. Experimental verification is conducted using ethanol solution with different concentrations. The measurement accuracy is calculated to be within 2.8%, and this validates the proposed approach. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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12 pages, 2786 KiB  
Communication
UHF RFID Temperature Sensor Tag Integrated into a Textile Yarn
by Sofia Benouakta, Florin Doru Hutu and Yvan Duroc
Sensors 2022, 22(3), 818; https://0-doi-org.brum.beds.ac.uk/10.3390/s22030818 - 21 Jan 2022
Cited by 12 | Viewed by 2665
Abstract
This paper presents the design of an ultra high-frequency (UHF) radio frequency identification (RFID) sensor tag integrated into a textile yarn and manufactured using the E-Thread® technology. The temperature detection concept is based on the modification of the impedance matching between RFID [...] Read more.
This paper presents the design of an ultra high-frequency (UHF) radio frequency identification (RFID) sensor tag integrated into a textile yarn and manufactured using the E-Thread® technology. The temperature detection concept is based on the modification of the impedance matching between RFID tag’s antenna and the chip. This modification is created by the change in the resistance of a thermistor integrated within the tag system due to a temperature variation. Moreover, in order to obtain an environment independent detection, a differential approach is proposed that avoids the use of a pre-calibration phase by the use of a reference tag. Experimental characterization demonstrates the RFID sensor’s potential of detecting a temperature variation or a temperature threshold between 25 and 70 °C through the variation of the transmitted differential activation power. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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12 pages, 5334 KiB  
Communication
High-Efficiency Broadband Planar Array Antenna with Suspended Microstrip Slab for X-Band SAR Onboard Small Satellites
by Kyei Anim, Patrick Danuor, Seong-Ook Park and Young-Bae Jung
Sensors 2022, 22(1), 252; https://0-doi-org.brum.beds.ac.uk/10.3390/s22010252 - 30 Dec 2021
Cited by 10 | Viewed by 2675
Abstract
In this paper, a high efficiency broadband planar array antenna is developed at X-band for synthetic aperture radar (SAR) on small satellites. The antenna is based on a multi-layer element structure consisting of two dielectric substrates made of Taconic TLY-5 and three copper [...] Read more.
In this paper, a high efficiency broadband planar array antenna is developed at X-band for synthetic aperture radar (SAR) on small satellites. The antenna is based on a multi-layer element structure consisting of two dielectric substrates made of Taconic TLY-5 and three copper layers (i.e., the parasitic patch (top layer), the active patch (middle layer), and the ground plane (bottom layer)). The parasitic patch resides on the bottom surface of the upper TLY-5 substrate while the active patch is printed on the top surface of the lower substrate. A Rohacell foam material is sandwiched between the top layer and the middle layer to separate the two dielectric substrates in order to achieve high directivity, wideband, and to keep the antenna weight to a minimum as required by the SAR satellite application. To satisfy the required size of the antenna panel for the small SAR satellite, an asymmetric corporate feeding network (CFN) is designed to feed a 12 × 16 planar array antenna. However, it was determined that the first corporate feed junction at the center of the CFN, where higher amplitudes of the input signal are located, contributes significantly to the leaky wave emission, which degrades the radiation efficiency and increases the sidelobe level. Thus, a suspended microstrip slab, which is simply a wide and long microstrip line, is designed and positioned on the top layer directly above that feed junction to prevent the leaky waves from radiating. The experimental results of the antenna show good agreement with the simulated ones, achieving an impedance bandwidth of 12.4% from 9.01 to 10.20 GHz and a high gain above 28 dBi. The antenna efficiency estimated from the gain and directivity eclipses 51.34%. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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16 pages, 6190 KiB  
Communication
UHF RFID Conductive Fabric Tag Design Optimization
by Franck Kimetya Byondi and Youchung Chung
Sensors 2021, 21(16), 5380; https://0-doi-org.brum.beds.ac.uk/10.3390/s21165380 - 10 Aug 2021
Cited by 5 | Viewed by 2335
Abstract
This paper presents the design of a 920 MHz Ultra High Frequency (UHF) band radio frequency identification (RFID) conductive fabric tag antenna. The DC (Direct Current) resistance and impedance of the conductive fabric are measured by a DC multimeter and by a network [...] Read more.
This paper presents the design of a 920 MHz Ultra High Frequency (UHF) band radio frequency identification (RFID) conductive fabric tag antenna. The DC (Direct Current) resistance and impedance of the conductive fabric are measured by a DC multimeter and by a network analyzer at a UHF frequency band. The conductivities of the fabrics are calculated with their measured DC resistance and impedance values, respectively. The conductivities of the fabric are inserted into the CST simulation program to simulate the fabric tag antenna designs, and the results of the tag designs with two conductivities are compared. Two fabric UHF RFID tag antennas with a T-Matching structure, one with the name-tag size of 80 × 40 mm, and another with 40 × 23 are simulated and measured the characteristics of tag antennas. The simulated and measured results are compared by reflection coefficient S11, radar cross-section and reading range. The reading range of the 80 × 40 mm fabric tag antenna is about 4 m and 0.5 m for the 40 × 23 size tag. These fabric tags can be easily applied to an entrance control system as they can be attached to other fabrics and clothes. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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11 pages, 4383 KiB  
Communication
Extremely Low-Profile Monopolar Microstrip Antenna with Wide Bandwidth
by Youngseok Ha, Jae-il Jung, Sunghee Lee and Seongmin Pyo
Sensors 2021, 21(16), 5295; https://0-doi-org.brum.beds.ac.uk/10.3390/s21165295 - 05 Aug 2021
Cited by 2 | Viewed by 2410
Abstract
In this paper, we propose a new monopolar microstrip antenna for a high-speed moving swarm sensor network. The proposed antenna shows an extremely thin substrate thickness supported with an omni-directional radiation pattern and wide operation frequency bandwidth. First, to achieve the low-profile monopolar [...] Read more.
In this paper, we propose a new monopolar microstrip antenna for a high-speed moving swarm sensor network. The proposed antenna shows an extremely thin substrate thickness supported with an omni-directional radiation pattern and wide operation frequency bandwidth. First, to achieve the low-profile monopolar microstrip antenna, the symmetrical center feeding network and the gap-coupled six arrayed patches which form a hexagonal microstrip radiator were utilized. The partially loaded ground-slots under the top patches were employed to improve the radiation performance and adjust the impedance bandwidth. Second, to obtain the broad bandwidth of the low-profile monopolar microstrip antenna, the degenerated non-fundamental TM02 modes, that is, even and odd TM02 modes, were carefully analyzed. To verify the feasibility of the degenerated TM02 mode operation, the parametric study of the proposed antenna was theoretically investigated and implemented with the optimized parameter dimensions. Finally, the fabricated antenna showed a 0.254 mm-thick substrate and demonstrates 1.5-wavelength resonant monopolar radiation with broad impedance bandwidth of 855 MHz and its factional bandwidth of 15.24% at the resonant frequency of 5.57 GHz. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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14 pages, 3917 KiB  
Article
Compact Slotted Waveguide Antenna Array Using Staircase Model of Tapered Dielectric-Inset Guide for Shipboard Marine Radar
by Kyei Anim, Henry Abu Diawuo and Young-Bae Jung
Sensors 2021, 21(14), 4745; https://0-doi-org.brum.beds.ac.uk/10.3390/s21144745 - 12 Jul 2021
Cited by 5 | Viewed by 5141
Abstract
This paper presents a new configuration of a slotted waveguide antenna (SWA) array aimed at the X-band within the desired band of 9.38~9.44 GHz for shipboard marine radars. The SWA array, which typically consists of a slotted waveguide, a polarizing filter, and a [...] Read more.
This paper presents a new configuration of a slotted waveguide antenna (SWA) array aimed at the X-band within the desired band of 9.38~9.44 GHz for shipboard marine radars. The SWA array, which typically consists of a slotted waveguide, a polarizing filter, and a metal reflector, is widely employed in marine radar applications. Nonetheless, conventional slot array designs are weighty, mechanically complex, and geometrically large to obtain high performances, such as gain. These features of the conventional SWA are undesirable for the shipboard marine radar, where the antenna rotates at high angular speed for the beam scanning mechanism. The proposed SWA array herein reduces the conventional design’s size by 62% using a tapered dielectric-inset guide structure. It shows high gain performance (up to 30 dB) and obtains improvements in radiation efficiency (up to 80% in the numerical simulations) and weight due to the use of loss and low-density dielectric material. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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15 pages, 2331 KiB  
Article
Low-Cost Beamforming Concept for the Control of Radiation Patterns of Antenna Arrays Installed onto UAVs
by Leonardo C. dos Santos, Edson R. Schlosser and Marcos V. T. Heckler
Sensors 2021, 21(13), 4265; https://0-doi-org.brum.beds.ac.uk/10.3390/s21134265 - 22 Jun 2021
Cited by 1 | Viewed by 2634
Abstract
This paper presents a low-cost architecture that allows for beamforming with antenna arrays installed onto unmanned aerial vehicles (UAVs). Beam switching is proposed to improve the antenna gain towards the ground station with two three-element arrays installed below the wings of the UAV. [...] Read more.
This paper presents a low-cost architecture that allows for beamforming with antenna arrays installed onto unmanned aerial vehicles (UAVs). Beam switching is proposed to improve the antenna gain towards the ground station with two three-element arrays installed below the wings of the UAV. The electromagnetic modeling of the complete structure (UAV and integrated antennas) was performed with commercial electromagnetic simulator Ansys HFSS. The radiation patterns were synthesized with particle swarm optimization (PSO). By employing lumped surface-mount device (SMD) components and switches, the design of the feeder to deliver proper excitation coefficients to the antennas is presented, and its performance was assessed by simulations. The proposed approach is demonstrated to be very effective with low-cost production. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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11 pages, 8303 KiB  
Communication
High-Gain Millimeter-Wave Patch Array Antenna for Unmanned Aerial Vehicle Application
by Kyei Anim, Jung-Nam Lee and Young-Bae Jung
Sensors 2021, 21(11), 3914; https://0-doi-org.brum.beds.ac.uk/10.3390/s21113914 - 06 Jun 2021
Cited by 9 | Viewed by 3235
Abstract
A high-gain millimeter-wave patch array antenna is presented for unmanned aerial vehicles (UAVs). For the large-scale patch array antenna, microstrip lines and higher-mode surface wave radiations contribute enormously to the antenna loss, especially at the millimeter-wave band. Here, the element of a large [...] Read more.
A high-gain millimeter-wave patch array antenna is presented for unmanned aerial vehicles (UAVs). For the large-scale patch array antenna, microstrip lines and higher-mode surface wave radiations contribute enormously to the antenna loss, especially at the millimeter-wave band. Here, the element of a large patch array antenna is implemented with a substrate integrated waveguide (SIW) cavity-backed patch fed by the aperture-coupled feeding (ACF) structure. However, in this case, a large coupling aperture is used to create strongly bound waves, which maximizes the coupling level between the patch and the feedline. This approach helps to improve antenna gain, but at the same time leads to a significant level of back radiation due to the microstrip feedline and unwanted surface-wave radiation, especially for the large patch arrays. Using the SIW cavity-backed patch and stripline feedline of the ACF in the element design, therefore, provides a solution to this problem. Thus, a full-corporate feed 32 × 32 array antenna achieves realized gain of 30.71–32.8 dBi with radiation efficiency above 52% within the operational band of 25.43–26.91 GHz. The fabricated antenna also retains being lightweight, which is desirable for UAVs, because it has no metal plate at the backside to support the antenna. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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17 pages, 10257 KiB  
Article
Compact Design of Annular-Microstrip-Fed mmW Antenna Arrays
by Shu-Dong Lin, Shi Pu, Chen Wang and Hai-Yang Ren
Sensors 2021, 21(11), 3695; https://0-doi-org.brum.beds.ac.uk/10.3390/s21113695 - 26 May 2021
Cited by 2 | Viewed by 2293
Abstract
In this paper, a series of four novel microstrip antenna array designs based on different annular-microstrip feeding lines at 60-GHz millimeter wave (mmW) band are proposed, aiming at the potential usage of the mmW coverage antenna with multi-directional property. As the feeding network, [...] Read more.
In this paper, a series of four novel microstrip antenna array designs based on different annular-microstrip feeding lines at 60-GHz millimeter wave (mmW) band are proposed, aiming at the potential usage of the mmW coverage antenna with multi-directional property. As the feeding network, the annular contour microstrip lines are employed to connect the patch units so as to form a more compact array. Our first design is to use an outer contour annular microstrip line to connect four-direction linear arrays composed of 1 × 3 rectangular patches, thus the gain of 8.4 dBi and bandwidth of over 300 MHz are obtained. Our second design is to apply the two-direction pitchfork-shaped array each made up of two same linear arrays as the above, therefore the gain of 9.65 dBi and bandwidth of around 250 MHz are achieved. Our third design is to employ dual (inner and outer contour) annular-microstrip feeding lines to interconnect the above four-direction linear arrays, while our fourth design is to bring bridged annular-microstrip feeding lines, both of which can realize the goal of multi-directional radiation characteristic and higher gain of over 10 dBi. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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11 pages, 5628 KiB  
Communication
Design of an Optical Transparent Absorber and Defect Diagnostics Analysis Based on Near-Field Measurement
by In-Gon Lee, Young-Joon Yoon, Kwang-Sik Choi and Ic-Pyo Hong
Sensors 2021, 21(9), 3076; https://0-doi-org.brum.beds.ac.uk/10.3390/s21093076 - 28 Apr 2021
Cited by 7 | Viewed by 1880
Abstract
To reduce the electromagnetic wave interference caused by cavity resonance or electromagnetic wave leakage, herein, an optical transparent radar absorbing structure (RAS) was designed using transparent conductive oxides (TCOs) with a high optical transmittance and electrical conductivity, and a procedure was proposed for [...] Read more.
To reduce the electromagnetic wave interference caused by cavity resonance or electromagnetic wave leakage, herein, an optical transparent radar absorbing structure (RAS) was designed using transparent conductive oxides (TCOs) with a high optical transmittance and electrical conductivity, and a procedure was proposed for detecting possible defects in the fabrication and operation and for assessing the influence of the defects on the electromagnetic performance. To detect locally occurring defects in planar and three-dimensional absorbing structures, a measurement system based on an open-ended near-field antenna capable of producing small beam spots at a close distance was constructed. Moreover, the reflection characteristics of the transparent RAS were derived from a simplified multiple reflection equation, and the derived results were compared with the analysis results of an equivalent circuit model to predict the surface resistance of the TCO coating layer, based on which the presence of defects could be confirmed. By using the experimental results, the predicted surface resistance results of the coating layer and the results measured using a non-contact sheet resistance meter were compared and were found to correspond, thereby confirming the effectiveness of the proposed defect detection method. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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10 pages, 3716 KiB  
Communication
Long-Range UHF RFID Tag for Automotive License Plate
by Youchung Chung and Teklebrhan H. Berhe
Sensors 2021, 21(7), 2521; https://0-doi-org.brum.beds.ac.uk/10.3390/s21072521 - 04 Apr 2021
Cited by 8 | Viewed by 2783
Abstract
In this paper, various locations of an Ultra High Frequency (UHF) Radio Frequency Identification (RFID) tag on automotive license plates have been considered based on the radiation pattern of the tag antenna. A small, 130 × 50 mm, passive loop antenna type UHF [...] Read more.
In this paper, various locations of an Ultra High Frequency (UHF) Radio Frequency Identification (RFID) tag on automotive license plates have been considered based on the radiation pattern of the tag antenna. A small, 130 × 50 mm, passive loop antenna type UHF RFID tag for an automotive license plate was simulated with an EM simulation CST program. It was designed to have a larger back-lobe radiation pattern since the front side of the tag faces the back side of the plate holder to protect the tag antenna from bugs and dust when the automobile runs. The tag was attached to the side of a license plate holder with a dimension of 520 × 110 mm, the typical size of the standard license plate. The reflection coefficient of the tag antenna is −21 dB at 920 MHz, and the gain of the tag antenna is 6.29 dBi at the back-lobe. The reading range of the tag antenna with the plate holder, which was measured in an open field, is about 10.3 m, and the reading range of the tag installed on the bumper from the front of the vehicle is 9.4 m. The tag antenna is small enough to apply to a real automobile, and it is applicable because it uses the back-lobe pattern, so it does not require an extra device for protection from damage. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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14 pages, 3965 KiB  
Article
3D Printed Long-Range Cavity Structure UHF RFID Tag Antenna with Painting Conductive Ink on Convex Surface
by Franck Kimetya Byondi and Youchung Chung
Sensors 2021, 21(4), 1408; https://0-doi-org.brum.beds.ac.uk/10.3390/s21041408 - 18 Feb 2021
Cited by 2 | Viewed by 2966
Abstract
In this paper, we describe a long-range convex cavity-type passive ultra-high-frequency (UHF) radio frequency identification (RFID) tag to use on various metal and non-metal surfaces, for IoT sensor energy harvesting. The tag antenna is built on the 3D printed cavity structure with polylactic [...] Read more.
In this paper, we describe a long-range convex cavity-type passive ultra-high-frequency (UHF) radio frequency identification (RFID) tag to use on various metal and non-metal surfaces, for IoT sensor energy harvesting. The tag antenna is built on the 3D printed cavity structure with polylactic acid (PLA) plastic and painted with the conductive ink on the 1 mm protruding area (convex) of inner surface and the side-walls of the cavity structure to form a cavity structure. The tag is designed to operate in the UHF band (840–960 MHz). This long-range cavity tag antenna (CTA) works at both 920 MHz and 915 MHz UHF RFID frequencies. It provides a linear polarized (LP) frontal reading range of 35 m and side reading range above 15 m when mounted on either metal or non-metal objects. We describe the antenna characteristics, structure, modeling, simulation, and experimental results. A mathematical reading range also was calculated and compared with experimental data. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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Review

Jump to: Research, Other

17 pages, 6714 KiB  
Review
A SSTDR Methodology, Implementations, and Challenges
by Samuel Kingston, Evan Benoit, Ayobami S. Edun, Farhad Elyasichamazkoti, Dawn E. Sweeney, Joel B. Harley, Paul K. Kuhn and Cynthia M. Furse
Sensors 2021, 21(16), 5268; https://0-doi-org.brum.beds.ac.uk/10.3390/s21165268 - 04 Aug 2021
Cited by 13 | Viewed by 4721
Abstract
Sequence time-domain reflectometry (STDR) and spread spectrum time-domain reflectometry (SSTDR) detect, locate, and diagnose faults in live (energized) electrical systems. In this paper, we survey the present SSTDR literature for discussions on theory, algorithms used in its analysis, and its more prominent implementations [...] Read more.
Sequence time-domain reflectometry (STDR) and spread spectrum time-domain reflectometry (SSTDR) detect, locate, and diagnose faults in live (energized) electrical systems. In this paper, we survey the present SSTDR literature for discussions on theory, algorithms used in its analysis, and its more prominent implementations and applications. Our review includes both scientific litera-ture and selected patents. We also discuss future applications of SSTDR. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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38 pages, 2775 KiB  
Review
Review of Recent Microwave Planar Resonator-Based Sensors: Techniques of Complex Permittivity Extraction, Applications, Open Challenges and Future Research Directions
by Rammah Ali Alahnomi, Zahriladha Zakaria, Zulkalnain Mohd Yussof, Ayman Abdulhadi Althuwayb, Ammar Alhegazi, Hussein Alsariera and Norhanani Abd Rahman
Sensors 2021, 21(7), 2267; https://0-doi-org.brum.beds.ac.uk/10.3390/s21072267 - 24 Mar 2021
Cited by 76 | Viewed by 8272
Abstract
Recent developments in the field of microwave planar sensors have led to a renewed interest in industrial, chemical, biological and medical applications that are capable of performing real-time and non-invasive measurement of material properties. Among the plausible advantages of microwave planar sensors is [...] Read more.
Recent developments in the field of microwave planar sensors have led to a renewed interest in industrial, chemical, biological and medical applications that are capable of performing real-time and non-invasive measurement of material properties. Among the plausible advantages of microwave planar sensors is that they have a compact size, a low cost and the ease of fabrication and integration compared to prevailing sensors. However, some of their main drawbacks can be considered that restrict their usage and limit the range of applications such as their sensitivity and selectivity. The development of high-sensitivity microwave planar sensors is required for highly accurate complex permittivity measurements to monitor the small variations among different material samples. Therefore, the purpose of this paper is to review recent research on the development of microwave planar sensors and further challenges of their sensitivity and selectivity. Furthermore, the techniques of the complex permittivity extraction (real and imaginary parts) are discussed based on the different approaches of mathematical models. The outcomes of this review may facilitate improvements of and an alternative solution for the enhancement of microwave planar sensors’ normalized sensitivity for material characterization, especially in biochemical and beverage industry applications. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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Other

Jump to: Research, Review

23 pages, 9615 KiB  
Technical Note
A Novel Electrically Small Ground-Penetrating Radar Patch Antenna with a Parasitic Ring for Respiration Detection
by Di Shi, Taimur Aftab, Gunnar Gidion, Fatma Sayed and Leonhard M. Reindl
Sensors 2021, 21(6), 1930; https://0-doi-org.brum.beds.ac.uk/10.3390/s21061930 - 10 Mar 2021
Cited by 9 | Viewed by 3122
Abstract
An electrically small patch antenna with a low-cost high-permittivity ceramic substrate material for use in a ground-penetrating radar is proposed in this work. The antenna is based on a commercial ceramic 915 MHz patch antenna with a size of 25 × 25 × [...] Read more.
An electrically small patch antenna with a low-cost high-permittivity ceramic substrate material for use in a ground-penetrating radar is proposed in this work. The antenna is based on a commercial ceramic 915 MHz patch antenna with a size of 25 × 25 × 4 mm3 and a weight of 12.9 g. The influences of the main geometric parameters on the antenna’s electromagnetic characteristics were comprehensively studied. Three bandwidth improvement techniques were sequentially applied to optimize the antenna: tuning the key geometric parameters, adding cuts on the edges, and adding parasitic radiators. The designed antenna operates at around 1.3 GHz and has more than 40 MHz continuous −3 dB bandwidth. In comparison to the original antenna, the −3 and −6 dB fractional bandwidth is improved by 1.8 times and 4 times, respectively. Two antennas of the proposed design together with a customized radar were installed on an unmanned aerial vehicle (UAV) for a quick search for survivors after earthquakes or gas explosions without exposing the rescue staff to the uncertain dangers of moving on the debris. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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11 pages, 2513 KiB  
Letter
Novel Resonance-Based Wireless Power Transfer Using Mixed Coupling
by SangWook Park and Seungyoung Ahn
Sensors 2020, 20(24), 7277; https://0-doi-org.brum.beds.ac.uk/10.3390/s20247277 - 18 Dec 2020
Cited by 2 | Viewed by 3891
Abstract
This study presents an equivalent circuit model for the analysis of wireless power transfer (WPT) through both electric and magnetic couplings using merely a resonant coupler. Moreover, the frequency split phenomenon, which occurs when transmitting couplers are near receiving couplers, is explained. This [...] Read more.
This study presents an equivalent circuit model for the analysis of wireless power transfer (WPT) through both electric and magnetic couplings using merely a resonant coupler. Moreover, the frequency split phenomenon, which occurs when transmitting couplers are near receiving couplers, is explained. This phenomenon was analyzed using simple circuit models derived via a mode decomposition technique. To verify the proposed method, a resonant coupler using mixed coupling was designed and its efficiency was compared with the result obtained using a commercial electromagnetic solver. The results of this study are expected to aid in designing various WPT couplers or sensor antennas by selecting electric, magnetic, or mixed couplings. Furthermore, the results of this study are expected to be applied to technologies that sense objects, or simultaneously transmit and receive information and power wirelessly. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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10 pages, 3429 KiB  
Letter
Design of a Miniaturized Rectangular Multiturn Loop Antenna for Shielding Effectiveness Measurement
by Sangwoon Youn, Tae Heung Lim, Eunjung Kang, Dae Heon Lee, Ki Baek Kim and Hosung Choo
Sensors 2020, 20(11), 3178; https://0-doi-org.brum.beds.ac.uk/10.3390/s20113178 - 03 Jun 2020
Cited by 3 | Viewed by 3939
Abstract
This paper proposes a novel miniaturized rectangular loop antenna sensor consisting of a multiturn wire and a cuboid ferrite core. The lateral surface of the ferrite core is tightly wound by the multiturn wire. To verify its feasibility, the antenna sensor is fabricated, [...] Read more.
This paper proposes a novel miniaturized rectangular loop antenna sensor consisting of a multiturn wire and a cuboid ferrite core. The lateral surface of the ferrite core is tightly wound by the multiturn wire. To verify its feasibility, the antenna sensor is fabricated, and the antenna factor (AF) levels are measured using the three-antenna method from the very low frequency (VLF) to the high-frequency (HF) bands. The measured AF levels are 31.8 dB (with a covering plastic case) and 33.1 dB (without a covering plastic case) at 30 kHz. In addition, the proposed antenna is employed in the shielding effectiveness measurement of a small commercial cabinet to observe its suitability for shielding effectiveness (SE) measurement of small shielding enclosures. The SE values averaged over the frequency range from 10 kHz to 3 MHz are 4.1 dB and 12 dB in the horizontal and vertical polarizations, respectively. Full article
(This article belongs to the Special Issue RF Sensors: Design, Optimization and Applications)
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