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The most important variables to consider in the design of antennas for RFED applications and effective communications are low cost, low profile, and reduced size. The dipole antenna, often known as a dipole aerial, is the most basic and widely used type of antenna. Among other antennas, this is one of the most straightforward antenna layouts. It may be achieved by applying a sinusoidal voltage differential between two thin metallic rods. The dipole antenna is a particularly important type of RF antenna that is frequently used for radio transmission and reception. For many types of antennas, this antenna can be employed as a radiating or driving element. This Dipole antenna may be used in the radio frequency spectrum sections HF, VHF and UHF. The major advantage of a dipole antenna is that it can serve as both a broadcast transmitter and receiver. So, to obtain the most crucial factors, we'll design an antenna in COMSOL Multi Physics and display the results as Radiation patterns.

Ultra High Frequency Radio Frequency Identification (UHF RFID)-based sensing technology with antenna-integrated sensor tags offers a cost-effective solution for Internet of Things (IoT) applications. A multi-dimensional differential measurement technique for eliminating the effect of measurement setup, such as unknown mutual distance and orientation between the read/write device (RWD) and sensor tags, and line-of-sight obstruction, on acquiring information from multiple sensor tags simultaneously is proposed. The concept is based on 1) using a channel hopping mechanism to acquire multi-dimensional datasets and 2) conducting a dissimilarity analysis between offline and online datasets to extract sensor information. The differential measurement, which is activated by the channel hopping mechanism, mitigates the impact of the measurement setup, making the pattern of the multi-dimensional datasets tightly relate to the sensing state. A sensor tag for measuring the water filling level of polyvinyl chloride (PVC) pipes is designed and fabricated. Experiments show that the proposed method can accurately acquire information from three sensor tags simultaneously under different measurement setups. The performances using datasets of different dimensions are compared. Results reveal that using low-dimensional datasets can still be capable of getting accurate information from the sensor tags, implying that the acquisition time can be reduced.

A denture implanted UHF RFID tag antenna is proposed. The limitation on antenna size means that a low-loss and compact antenna including matching circuit is necessary to increase the tracking distance. To reduce the loss brought by reflection, a partially exposed folded dipole antenna with gamma matching is utilized. The denture implanted RFID tag is fabricated by using materials utilized in the exact denture such as metal wire and resin. Furthermore, the RFID operation properties of the denture implanted tag are evaluated by changing the parameters of antenna structure. Based on the measurement result, the new proposed structure reduce the reflection loss from the mismatch between RFID chip and small antenna, which provides enough energy for communication. Also, this proposed antenna structure provides a brand new idea for designing antenna in medium.

As a basic characteristic of sea clutter, the reflectivity of sea surface depends on many factors. Various universal empirical models of low precision have been developed to predict the reflectivity of sea surface. In this letter, a method is proposed to train specific predictors by big data learning, where the universal empirical models are embedded to the architecture of the generalized regression neural network (GRNN) to enhance the learning ability and efficiency. On the sea clutter database measured by an island-based UHF-band radar in the offshore waters of the Yellow sea of China at low grazing angle, the GRNN-based predictors of different structures are compared with other predictors. The results on the database show that the GRNN-based predictors behave better at learning efficiency, prediction precision, and robustness.

Wearable sensors demand flexible and concealable devices that can be seamlessly integrated with apparels and clothes. E-textile sensors and devices, built from specially functionalized fibers and yarns and constructed with embroidery and woven processes, provide an ideal solution for different wearable applications. In this article, we propose a textile-based, embroidered passive strain and displacement sensor functioned as a UHF RFID antenna that can be aesthetically integrated with garment fabrics. The antenna structure consists of a dipole arm and a coupling loop mounted with an RFID chip. The displacement between the loop and dipole arm will alter the impedance of the antenna and consequently modulate the backscattered signals from the RFID chip to the reader. The sensor is passive, i.e., no battery is needed on the sensor and the sensing information can be wirelessly retrieved by the reader from a few meters away. The structure is sensitive to strains and displacement caused by body movement. Our experiments demonstrate different applications for this sensor, i.e., when the sensor is embroidered on different locations on human body, such as breast, knees, and elbows, it can be used as a respiration monitor, gesture indicator, etc. to conveniently track and log various forms of body movements.

This article presents a novel miniaturized circularly polarized (CP) antenna based on periodically structured surfaces inspired by the vertical split-ring resonator (VSRR). The VSRR is considered as a magnetic dipole placed above the ground, which could excite strong boresight radiation with a reduced size. To enhance the aperture gain, multicapacitors and inductors (Multi-C&L) are loaded on the loop, which replace the single capacitive gap of the conventional split-ring resonator (SRR). Here an SRR-inspired periodic structure with a relatively uniform field distribution is achieved. The stepped impedance resonator (SIR) structure, as the unit cell of the SRR-inspired surface, is analyzed and investigated using the circuit models derived from the SRR. By cascading multiple high-value capacitors, a larger aperture with a uniform field distribution is obtained. Linearly polarized (LP) and CP antennas are studied. The proposed CP antenna is made of thin substrates and metallic screws, resulting in a negligible dielectric loss. It offers attractive features including a compact size, a low profile ( $0.191\lambda _{0} \times 0.191\lambda _{0} \times 0.032\lambda _{0}$ ), good radiation efficiency, novel working principle, flexible performance control, and a bandwidth well covering the 902–928 MHz UHF band, which is well situated for radio frequency identification (RFID) application.

The ability to detect abnormalities in infrastructure automatically and remotely with a small number of sensors would greatly contribute to efficient and timely infrastructure inspection. Here, we propose a passive sensor that can be installed by painting. The painted waveguide-based sensor detects abnormalities in infrastructure from abnormality-induced changes in the resonance frequency of electromagnetic waves resonating inside the sensor. In this paper, the principle of detecting loose bolts with the painted waveguide-based sensor is demonstrated by simulation and experiment. The sensor is designed and fabricated as a resonator with resonance frequencies from 100 kHz to 2.5 GHz, which includes the UHF radio-frequency identification band, and the measurement frequency was set within this range. The fabricated sensor is capable of detecting not only a single loose bolt but also two or more loose bolts on the waveguide of the sensor to monitor.

Radio technologies are appealing for unobtrusive and remote monitoring of human activities. Radar-based human activity recognition proves to be a success, for example, Project Soli developed by Google. However, it is expensive to scale up for multiuser environments. In this article, we propose a solution—the HoloTag system—which circumvents the multichannel-radar scaling problem through the use of a quasivirtual ultralow-cost UHF RFID array over which a holographic projection of its environment is measured and used to both localize and monitor the health of several targets. The method is first described in detail, before the image reconstruction process, employing known beamforming algorithms—Delay & Sum, and Capon—is shown and its scaling properties simulated. Then, the idiosyncrasies of the implementation of HoloTag using low-cost off-the-shelf hardware are explained, before its ability to simultaneously measure the breathing rates and positions of multiple real and synthetic targets with accuracies of better than 0.8 bpm and 20 cm is demonstrated.

HFCT method is a common detection technology for partial discharge (PD) in transformer. However, it suffers a lot from electromagnetic interference in field applications because conventional detection band of it is relatively low, usually in HF band. In this paper, a HFCT, which frequency response includes the whole of the VHF band and extends up to 500 MHz in the UHF band, is adopted to improve the anti-interference capacity of HFCT method. And we make a full investigation on the detection characteristics of HFCT method in UHF band based on an actual 220 kV transformer with complete internal structures. Four typical defects model is established as PD sources, additionally, conventional methods are also adopted in the experiment to make comparison with HFCT method in UHF band. The experiment results indicate that HFCT method can detect PD effectively in UHF band, and the detection sensitivity of it is no less than that of conventional methods. The results confirm the effectiveness of HFCT method in UHF band, therefore, the problem of low anti-interference capacity of conventional HFCT method that detects PD in HF band can be overcome. It offers a new effective and practical solution for transformer field monitoring of PD, especially for the transformers to which internal antenna UHF method can't be applied due to the lack of dielectric window.

A novel ultrahigh frequency (UHF)/ultrawideband (UWB) hybrid radio frequency identification (RFID) tag is reported for object-specific remote vital-sign monitoring application. The tag achieves a record energy-harvesting sensitivity at the UHF band by codesigning a meander dipole antenna and a passive rectifier. The especially high quality-factor makes the frontend sensitive to near-field motions such as heartbeats and respiration in a wearable setting. The custom CMOS integrated circuit (IC) of approximately 1- $\mu \text{W}$ power consumption builds around a low-power UWB transmitter and converts the variations in the supply voltage to the impulse repetition rate. The tag consisting of the IC and UHF/UWB antennas requires no other discrete components and features a size of 4.2 cm $\times2.9$ cm and a weight of 0.93 g. A long-distance experiment verifies that the tag can be wirelessly powered up at 51 m from a 4-W effective-isotropic-radiation-power UHF transmitter. Remote vital-sign monitoring is validated on a human subject, in which the UHF power source is placed 2 m away from the subject with a power emission of less than 20 dBm. This work proposes a first-of-its-kind remote vital-sign monitoring solution based on a passively powered noncontact wearable tag. The design of the far-field energy-harvesting frontend with a record sensitivity serves as a reference for future works on battery-free remote sensors.

One of the major challenges faced by passive on-body wireless Internet of Things (IoT) sensors is the absorption of radiated power by tissues in the human body. We present a battery-less, wearable knitted Ultra High Frequency (UHF, 902-928 MHz) Radio Frequency Identification (RFID) compression sensor (Bellypatch) antenna and show its applicability as an on-body respiratory monitor. The antenna radiation efficiency is satisfactory in both free-space and on-body operations. We extract RF (Radio Frequency) sheet resistance values of three knitted silver-coated nylon fabric candidates at 913 MHz. The best type of fabric is selected based on the extracted RF sheet resistance. Simulated and measured performance of the antenna confirm suitability for on-body applications. The proposed Bellypatch antenna is used to measure the breathing activity of a programmable infant patient emulator mannequin (SimBaby) and a human subject. The antenna is highly sensitive to respiratory compression and relaxation. Fluctuations in the backscatter power level/Received Signal Strength Indicator (RSSI) in both cases range from 6 dB to 15 dB. The improved on-body read range of the proposed sensor antenna is 5.8 m, about 10 times higher than its predecessor wearable knitted strain sensing Bellyband antenna (0.6 m). The maximum simulated Specific Absorption Rate (SAR) on a human torso model is 0.25 W/kg, lower than the maximum allowable limit of 1.6 W/kg.

In this paper, a novel compact broadband antenna at UHF frequencies is presented with canonical shapes. Hemispherical, conical and cylindrical shapes have all been considered for antenna configuration. The designed antenna provides an instantaneous frequency range from 370 to 5,000 MHz with omnidirectional characteristics. The antenna was simulated in CST Microwave Studio, fabricated and evaluated; the results are presented. The simulated and measurement results are in good agreement. The antenna has voltage standing wave ratio (VSWR) ≤ 1.9:1 in 400–570 MHz, 2,530–3,740 MHz and 4,180–4,620 MHz; it has VSWR ≤ 3:1 over the operating frequency range 370–5,000 MHz and the measured gain varies from -0.6 to 4.5 dBi over the frequency band. The concept of canonical-shaped antenna elements and the incorporation of triple sleeves resulted in a reduction of the length of the antenna by 62% compared to the length of a half-wave dipole antenna designed at the lowest frequency. The antenna can be used for trans-receiving applications in wireless communication.

This paper presents a compact and largely digital UHF EPC Gen2-compatible RFID implemented using digital IP blocks that are easily portable. This is the first demonstration of a digital Gen2-compatible RFID tag chip with an area of $125{\mu }\text{m} \times 245{\mu }\text{m}$ and −2 dBm sensitivity operating in the 860–960MHz band. It is enabled by a) largely standard cell-based digital implementation using dual-phase RF-only logic approach, b) near-threshold voltage operation, and c) elimination of area intensive, complex, and less scalable rectifiers, storage capacitors, and power management units used in conventional RFID tags. In this demonstration, all but six cells were directly used from the standard cell library provided by the foundry. This makes it suitable for cost-sensitive applications, and as embedded RFIDs for tagging counterfeit Integrated Circuits (ICs).

Localized electric field strength in high-voltage (HV) equipment results in electrical discharges which radiate electromagnetic waves in ultrahigh frequency (UHF) range of 0.3-3 GHz. Due to the large antenna dimensions in UHF regime and lack of radome, existing UHF sensors have limited use in HV equipment for online partial discharge (PD) detection. In this work, we present the design and experimental verification of a UHF antenna with relatively small aperture and radome for PD detection. The proposed UHF sensor is a compact conical monopole with ground plane and protective radome. The monopole shape was optimized for broadband operation and directional radiation pattern using electromagnetic simulations. A cylindrical radome transparent to electromagnetic waves was designed without perturbing the radiation characteristics of the optimized UHF antenna. The 130 mm diameter fabricated sensor has directional radiation pattern, UHF bandwidth of 0.5 – 3 GHz and compact radome of 150 mm diameter. PD signals gathered for three defects in gas insulated test cells indicate better detection capability and sensitivity for the proposed UHF sensor than the reference sensor.The improved performance of the proposed sensor suggest that it could be used for PD detection in HV equipment such as gas insulated switch gear and transmission line.

In this paper, the shielded open-circuited probe operating in the wide frequency range from 75MHz to 2GHz is proposed. The probe is made of an SubMiniature version A (SMA) flange connector. The central rod of the SMA connector emerges from a coaxial transition in the flange and shielded by four rods. The robe design allows us to calculate of the probe reflection coefficient S11 used simple analytical transmission line model (TEM wave mode), the parameters of which were calibrated on a set of substances with a known frequency spectrum of permittivity. The refractive index (RI) and normalized attenuation coefficient (NAC) retrieval technique is based on solving the inverse problem of minimizing the residual norm between measured and calculated frequency spectra of reflection coefficient S11. After calibration, the root-mean-square error (determination coefficient) between the measured and calculated module and phase of the reflection coefficient S11 for the sets of calibration media air, distilled water, butanol, pure ice, water solution with NaCl of salinity of 8.9% do not exceed 0.26dB (0.995) and 0.03 rad (0.999), respectively, in the frequency range from 75MHz to 2GHz. The root-mean-square error (determination coefficient) between the measured RI and NAC spectra for four soil cover samples (variation of the clay fraction from 10.5 g/g to 47.6 g/g) using the proposed probe and a precision coaxial cell not exceeds 0.109 (0.993) and 0.057 (0.986), respectively, in the frequency range from 75 MHz to 2 GHz. As a result, it is experimentally shown that RI и NAC can be measured by the proposed non-precision probe with an error comparable to the precision coaxial cell.

Ultrahigh frequency radio-frequency identification (UHF RFID) tags have shown enormous potential in wearable applications for sensing human vital signs. However, the integration of UHF RFID tags in clothing to achieve machine washability remains a challenge. In this study, we investigated different ways of protecting wearable UHF RFID tags with electro-textile antennas against repeated washing. We replaced the antennas of commercial UHF RFID tags with the antennas made from a silver-coated fabric. Twenty-three types of methods, including five integrated circuit (IC)-protection methods and seven fixation/cover methods, were compared, with each having ten identical samples. The 230 samples underwent 20 cycles of machine washing and drying, and the changes in received signal strength indicator (RSSI) and the number of failed tags after washing were recorded and analyzed statistically. We found that 1) water penetration does not have a negative impact on tag functionality, therefore, being waterproof is not a requirement for the coating material; 2) heat-bond hem taping is the most efficient IC protection method; 3) heat and high pressure is effective to improve tag endurance; and 4) fusible interlinings and ironing, used in traditional garment production, can be effective.

UHF RFID reader suffers from a strong transmitter (Tx) leakage signal coupled to a receiver (Rx), especially for an area-compact single-antenna implementation. Then, several Tx leakage cancellation schemes have been developed not to saturate the Rx and to minimize the performance degradation. This brief proposes a UHF RFID reader Rx with a low noise performance and a fast settling time by employing a digitally controlled leakage cancellation method in both passive and active realizations. A digitally-controlled passive vector reflector enhances the Tx to Rx isolation ratio by providing the optimum load impedance. An active anti-leakage feedback loop adaptively tracks the time-varying leakage and generate the phase-inverted leakage replica to suppress the leakage. The prototype chip is fabricated in a CMOS 55 nm process and the area of the chip is 2.1 mm $\times1.8$ mm. The passive leakage cancellation (PLC) with a vector reflector endures the 1 dBm leakage with a low Rx noise figure of 12.5 dB and 35.7 mW power consumption. The active leakage cancellation (ALC) with an anti-leakage feedback loop covers 6 dBm leakage with a fast settling time of $4.6~\mu \text{s}$ and 58 mW power consumption.

Bushings are essential components in a power transformer where incipient partial discharge (PD) activities and its detection and diagnosis cannot be ignorant. In this paper, an oil-impregnated paper (OIP) bushing is modeled to investigate that the oil gaps between the flange and condenser body in a typical OIP bushing provide a feasible path to trace the electromagnetic signal. As a non-destructive method, UHF (Ultra High Frequency) is proposed to detect 4 typical inside and outside PD defects of 110 kV bushings. To analyze the parameters of different defects, not only phase-resolved partial discharge (PRPD) is presented, but also 16 detailed time-domain and frequency-domain parameters of UHF signal are involved. Then feature extraction and selection are conducted through comparative principal component analysis (PCA) and extremely randomized trees (ET) algorithms. It is revealed that the selected features are representative and ET greatly reduces the amount of data whilst ensuring high accuracy. Fault diagnosis for bushing is finally achieved via support vector machine (SVM) with the selected features. The presented work of bushing PD detection based on UHF sensors provides a complete solution for the bushing diagnosis in potential field application and maintenance.

UHF RFID tags need to be attached or embedded into various objects. Unlike traditional free-standing antennas, UHF antenna shapes and form factors may vary significantly. There have been no systematic methods that facilitate the design practice of antenna with unconventional shapes. In this paper, using the geometries of 26 English letters (in capital) as examples, we explore the general methodology of shape-specific antenna design. More specifically, we show that 26 letter geometries can be categorized into 9 groups, and the antennas in each group can be divided and conquered into standard baseline geometries. Through prototypes and measurements, we demonstrate that each letter-shaped antenna, although exhibiting different gains and radiations, can achieve satisfactory performance, as compared to standard UHF dipole antennas. Specifically, letters “M” and “J” achieve the longest reading range of more than 20 meters with a good radiation pattern, which is comparable or even better than many commercial UHF RFID tags.

This letter presents a simple, lightweight, and ultrawideband, the very high frequency/ultrahigh frequency (VHF/UHF) open-sleeve dipole antenna array for airborne ice measuring radar. The proposed antenna array achieves a wide bandwidth of 300 MHz via mutual coupling from neighboring excited elements. A hollow aluminum tube is used for both dipole and parasitic elements to minimize the antenna's weight. The simulation results show that to achieve a bandwidth of 300 MHz with a peak realized gain up to 12 dBi in the frequency range from 170 to 470 MHz, the length of the dipole ( L dip) and parasitic elements ( L para) of elements 1 and 4 of the four-element antenna array need to be 670 mm and 200 mm, respectively. At the same time, elements 2 and 3 require an L dip of 640 mm and L para of 180 mm. Based on these dimensions, a four-element antenna array is fabricated and tested. The measured antenna performance results show a good agreement with the simulated results.

A slim and semi-flexible UHF RFID tag antenna, which has a compact dimension of 40 mm $\times $ 5 mm $\times $ 3.2 mm ( $0.1221\lambda \times 0.0153\lambda \times 0.0098\lambda $ ), is proposed for tagging on metallic industrial tools with a narrow footprint. For a metal-mountable tag antenna, the unwanted electromagnetic antenna-metal interaction can deteriorate the tag read performances and it is particularly pronounced when the tag is attached to a narrow industrial tool. To achieve a size-reduction, the proposed tag is made of an inlay comprising a very compact 3-layer structure with two radiating patches. The currents on the top and middle patches can be made in phase for enhancing the radiated fields. Digital serrations, inductive stubs, and open slots loading have been studied for optimizing the antenna resonant frequency efficiently. With the use of the tuning mechanisms, when being tested on a narrow-body metal tool, the antenna impedance can be fully matched with the RFID microchip impedance, resulting in a good power transmission coefficient of ~ 1. Despite its compactness, the proposed tag antenna is readable from 11.0 m with an EIRP of 4W. To the best of our knowledge, the proposed tag antenna has a much better aspect ratio between its read distance and tag volume than most of the commercially available on-metal tags and it can be used for tagging on narrow metallic surfaces.

Ultra-high frequency (UHF) radio frequency identification (RFID) tags with an antenna made of a highly flexible graphene assembly film (GAF) is presented. The superb electrical conductivity (∼1.6 × 106 S m−1) of the GAF results in the tag to reach reading range of ∼12 m, which is comparable to that of the commercially available metallic counterparts. The performance of the GAF-based RFID tags under mechanical bending and stretching is experimentally evaluated, which demonstrates excellent mechanical stability of the GAF tag than that of metallic tags. Additionally, substrate stability tests are also conducted. The GAF-based UHF RFID tags can thus lead to numerous applications in information exchange, tracking and tracing as well as the Internet of Things (IoT).

Power transformer is one of the most important high voltage apparatus in any power system network. The life span of such apparatus commonly relies upon its insulation condition. The primary reason for an insulation breakdown is partial discharge. Partial discharges (PDs) are electrical discharges that happen in the insulation system of the transformers. Occurrence of PDs results in deterioration of the transformer insulation system. Hence, measuring and detecting the PD at an initial stage is necessary to avoid complete breakdown of the transformer. Currently, various PD detection and measurement methods, such as, electrical, chemical, acoustic, UHF and optical methods are being used for PD monitoring in power transformers. The conventional PD monitoring techniques like electrical or chemical have some limitations. The optical Fiber Bragg Grating (FBG) Sensor has been used as a PD sensor for PD monitoring in the power transformer to overcome these issues. This paper presents a review of FBG sensors’ application as a sensor for PD monitoring in an oil-filled power transformer. The challenges and future prospects in this area are also discussed.

This paper as an author contribution introduces the implementation of the new aspects in the modernization of the ships Radio Direction Finders (RDF) and their modern principles and applications for shipborne and coastal navigation surveillance systems. The origin RDF receivers with the antenna installed onboard ships or aircraft were designed to identify radio sources that provide bearing the Direction Finding (DF) signals. The radio DF system or sometimes simply known as the DF technique is de facto a basic principle of measuring the direction of signals for determination of the ship's position. The position of a particular ship in coastal navigation can be obtained by two or more measurements of certain radio sources received from different unspecified locations of transmitters on the coast. In the past, the RDF devices were widely used as a radio navigation system for aircraft, vehicles, and ships in particular. However, the newly developed RDF devices can be used today as an alternative to the Radio – Automatic Identification System (R-AIS), Satellite – Automatic Identification System (S-AIS), Long Range Identification and Tracking (LRIT), radars, GNSS receivers, and another current tracking and positioning systems of ships. The development of a modern shipborne RDF for new positioning and surveillance applications, such as Search and Rescue (SAR), Man over board (MOB), ships navigation and collision avoidance, offshore applications, detection of research buoys and for costal vessels traffic control and management is described in this paper.

The near-field ultrahigh-frequency (UHF) quadruple-loop antenna (QLA) with uniform field distribution for item-level tagging is proposed. The proposed antenna consists of quadruple fan-shaped small loops and the middle feeding lines of each loop located at the top and bottom of the substrate using vias. The currents flowing through feeding lines are cancelled due to opposite directional currents (ODCs), and the proposed QLA operates as one large loop electrically. From this configuration, the proposed antenna achieves more uniform field distribution and a precise interrogation zone than conventional loop antennas. Compared to the conventional loop antennas with different sizes, the proposed antenna using the uniform field distribution achieves a interrogation zone of 40 × 40 mm $^2$ at up to approximately 50 mm.

Laser texturing has been carried out on the surface of the silicone nano‐micro composites to achieve super hydrophobic properties, and water droplet‐initiated Corona discharge studies were carried out. The Corona inception voltage (CIV) exhibits considerable enhancement with increase in the nano filler content under DC voltage compared with AC voltage. The corona inception voltage is high with the textured surface and is found to have direct correlation with contact angle of the composite specimen. The Corona inception voltage was measured using Ultra‐high frequency (UHF) and fluorescent fibre techniques. It is observed that the fluorescent fibre technique is more sensitive in identifying discharges. Frequency domain analysis of UHF signal shows a dominant frequency at 1 GHz and for fluorescent signal, the spectral content is in the range of DC to 10 MHz. The rise time and pulse width of the UHF signal increases with the increase in the nano filler in composite material. The energy content of UHF/fluorescent signal due to discharges shows similar trend with its increase in energy with variation in its magnitude of the signal formed. The pulse width of fluorescent signal formed due to water droplet‐initiated discharges under AC and DC voltage is almost the same, and with the textured specimen it is quite low than the non‐textured material.

A novel miniaturized dipole antenna design incorporating triple sleeves and shorting load leading to enhanced bandwidth is proposed in the present work. The Triple Sleeve Dipole Antenna with Shorti...

A distilled water dielectric resonator antenna (DRA) with a wide frequency-tuning range and high efficiency is presented in this article. It consists of a water resonator and a ground plane with a wideband bowtie feeding slot. The water resonator, having tunable dimensions, is employed to achieve frequency-reconfigurable characteristics. Mechanical switches and a microfluid pump are integrated to control the tuning process. The water DRA, with and without the liquid control system, is designed with a simulation tool and then fabricated and measured to validate the antenna's performance. It is demonstrated that the antenna exhibits high total efficiency (g80%) across a wide frequency-tuning range from 168 to 474 MHz (for S11, -10 dB) with a very compact volume of 278 t 278 t 131 mm3 (0.155l t 0.155l t 0.073l at 168 MHz). Compared with traditional reconfigurable antennas, this design provides a wider frequency-tuning range, a more compact size, and a higher degree of design freedom. It is therefore a promising candidate for very high-frequency (VHF) and ultrahigh-frequency (UHF) applications.

The motivation of this paper increases the bandwidth of power amplifier to multioctave by matching circuit, which consists of ferrite balun, 4:1 transformers and RC network feedback to make atrade-...

A deployable log periodic dipole antenna (DLPDA) is proposed. The antenna consists of pairs of collapsible steel tape springs (as the dipoles), a novel stretchable zigzag double-sided parallel stripline (ZDPS) (as the boom), and a coplanar waveguide on one side of the parallel striplines to guide the electromagnetic wave from the backend to the frontend. As a result, the proposed antenna becomes foldable and can be stored in a small volume prior to deployment. A design guideline for the DLPDA is given based on the simplified circuit model. Furthermore, the ZDPS, which is found as a slow wave structure, has been studied. The empirical equations are derived to obtain its characteristic impedance and propagation constant, which are the key parameters for the design guideline. One prototype of the DLPDA has been fabricated and tested. The deployment mechanism of the prototype has been successfully demonstrated using compressed air in a lab. The prototype has a stowed volume of < 2000 cm3, which is only 2% of the volume in fully deployed state.

To date, CubeSat radars and imagers have been limited to operations beyond S-band due to the challenges associated with the design of wideband, compact, low-frequency antennas. Concurrently, the frequencies at VHF/UHF bands can image through clouds and foliage, and are very attractive for ice, water and biomass sensing. There is thus a need to develop wideband antennas that can operate at VHF/UHF bands which are low cost, light-weight, and packable. In this paper, we present a CubeSat deployable Tightly Coupled Dipole Array (TCDA) that achieves VSWR

Radio frequency identification (RFID) is a rapidly developing technology, and RFID sensors have become important components in many common technology applications. The passive ultra-high frequency (UHF) tags used in RFID sensors have a higher data transfer rate and longer read range and usually come in unique small and portable application designs. However, these tags suffer from significant frequency interference when mounted on metallic materials or placed near liquid surfaces. This paper presents the recent advancements made in passive UHF-RFID tag designs proposed to resolve the interference problems. We focus on those designs that are intended to improve antenna read range as well as scalability designs for miniaturized applications.

Cube Satellites, aka CubeSats, are a class of nano satellites that have gained popularity recently, especially for those that consider CubeSats as an emerging alternative to conventional satellites for space programs. This is because they are cost-effective, and they can be built using commercial off-the-shelf components. Moreover, CubeSats can communicate with each other in space and ground stations to carry out many functions such as remote sensing (e.g., land imaging, education), space research, wide area measurements and deep space communications. Consequently, communications between CubeSats and ground stations is critical. Any antenna design for a CubeSat needs to meet size and weight restrictions while yielding good antenna radiation performance. To date, a limited number of works have surveyed, compared and categorised the proposed antenna designs for CubeSats based on their operating frequency bands. To this end, this paper contributes to the literature by focusing on different antenna types with different operating frequency bands that are proposed for CubeSat applications. This paper reviews 48 antenna designs, which include 18 patch antennas, 5 slot antennas, 4 dipole and monopole antennas, 3 reflector antennas, 3 reflectarray antennas, 5 helical antennas, 2 metasurface antennas and 3 millimeter and sub-millimeter wave antennas. The current CubeSat antenna design challenges and design techniques to address these challenges are discussed. In addition, we classify these antennas according to their operating frequency bands, e.g., VHF, UHF, L, S, C, X, Ku, K/Ka, W and mm/sub-mm wave bands and provide an extensive qualitative comparison in terms of their size, −10 dB bandwidths, gains, reflection coefficients, and deployability. The suitability of different antenna types for different applications as well as the future trends for CubeSat antennas are also presented.

Antena yang bekerja pada band UHF , banyak jenisnya antara lain : antena dipole 1/2l, antena Yagi-Uda array, antena log periodik dan sebagainya. Antena jenis ini, dimensi fisiknya disesuaikan dengan panjang gelombang. Semakin tinggi frekuensi kerja, semakin pendek panjang gelombangnya, sehingga semakin pendek pula panjang fisik antenna tersebut. Antena bow tie juga sering digunakan sebagai antena penerima TV , selain cukup mudah pembuatannya, sederhana dan gainnya cukup besar. Pada penelitian ini, antena yang disain adalah antena jenis bow tie (kupu-kupu) yang bekerja pada frekuensi UHF yaitu 750 Mhz, disusun secara array, selanjutnya dicatu dengan balun 4:1 (impedansi antena 300 ? ke 75 ?), menggunakan balun toroida dengan inti udara, agar bisa matching dengan impedansi kabel koaxial 75 ?. Bahan antena dari alumunium(solid). Adapun tempat penelitian dilaksanakan di laboratorium Telekomunikasi Polinema. Hasil Pengujian antena pada frekuensi kerja yakni 750 Mhz, menunjukkan bahwa nilai RL (retrun loss) : - 11 dB, koefisien pantul ? = 0,282 dan besarnya nilai VSWR = 1,786 . Sedang untuk pengukuran gain tertinggi terjadi pada frekuensi : 567,25 Mhz (kanal 33) yakni 10,45 dB, dan gain rata-rata antena adalah 3,19 dB. Karena harga VSWR lebih kecil dari 2, maka dapat dikatakan bahwa antena bow tie masih cukup layak atau bagus , telah memenuhi kreteria dari suatu parameter antena.

PURPOSE To introduce and investigate a method for free-breathing three-dimensional (3D) B1+ mapping of the human body at ultrahigh field (UHF), which can be used to generate homogenous flip angle (FA) distributions in the human body at UHF. METHODS A 3D relative B1+ mapping sequence with a radial phase-encoding (RPE) k-space trajectory was developed and applied in 11 healthy subjects at 7T. An RPE-based actual flip angle mapping method was applied with a dedicated B1+ shim setting to calibrate the relative B1+ maps yielding absolute B1+ maps of the individual transmit channels. The method was evaluated in a motion phantom and by multidimensional in vivo measurements. Additionally, 3D gradient echo scans with and without static phase-only B1+ shims were used to qualitatively validate B1+ shim predictions. RESULTS The phantom validation revealed good agreement for B1+ maps between dynamic measurement and static reference acquisition. The proposed 3D method was successfully validated in vivo by comparing magnitude and phase distributions with a 2D Cartesian reference. 3D B1+ maps free from visible motion artifacts were successfully acquired for 11 subjects with body mass indexes ranging from 19 kg/m2 to 34 kg/m2 . 3D respiration-resolved absolute B1+ maps indicated FA differences between inhalation and exhalation up to 15% for one channel and up to 24% for combined channels for shallow breathing. CONCLUSION The proposed method provides respiration-resolved absolute 3D B1+ maps of the human body at UHF, which enables the investigation and development of 3D B1+ shimming and parallel transmission methods to further enhance body imaging at UHF.

We present a passive ultra-high frequency (UHF) radiofrequency identification (RFID)-based strain sensor, which is designed for simple and efficient body movement monitoring. This RFID platform is fabricated from electro-textile materials and can thus be seamlessly integrated into our everyday clothing. The sensor platform has an integrated reference tag, in order to avoid the effects of reflections or external disturbances on the sensor tag performance. This sensor platform prototype has an on-body read range of 1 meter in a normal office environment with an off-the-shelf RFID reader. The wireless performance of the sensor tag has a significant change caused by arm elongation. Thus, the sensor functionality can be based on variation of the sensor tag’s backscattered power percentage ( $\Delta {P}{\%}$ ). Based on the preliminary results achieved in this study, this passive and cost-effective sensor platform could be an efficient future way to turn human gestures into inputs for digital devices.

Textile-based antennas that can be embroidered directly onto cloth fabrics have shown great potentials for wearable applications. However, the performance of the embroidered antennas is significantly affected by the materials used, as well as the antenna’s geometrical variations and deformations caused by human activities. In this article, we analyze several factors that affect the performance of embroidered antennas, including the choice of geometry, the bending and elongation of fabric substrate, as well as the resistivity of the yarns used for embroidery. Modeling, simulation, and measurement results have verified our analysis and demonstrated that slotted-patch UHF RFID antennas fabricated with low resistance yarns are more sensitive to geometrical variations, such as bending and curving, while meander line dipole (MLD) antennas are more sensitive to stretching and elongation. RFID tags equipped with these embroidered antennas can be utilized as battery-less passive deformation sensors for human movements.

This contribution is the first part of a two-part series which deals with proposing a new type of UHF probe to overcome problems of UHF partial discharge (PD) measurement in power transformers. In the first part, the main obstacles of using the UHF technique in power transformers including problems of installation, unfeasibility of calibration, low sensitivity, etc. are addressed. Moreover, a new type of UHF sensor called the “Turret-Electrode” antenna is presented to deal with the above obstacles. In the new antenna, the transformer turrets employed as the housing of open waveguide antenna (horn antenna with zero flare angle), while an electrode inside of the turret is designed to capture the electromagnetic (EM) waves produced by the PD signals inside of the transformer tank. The significant characteristics of the proposed antenna are investigated in detail and a prototype of the antenna is investigated via practical measurements. The results show the antenna parameters are quite appropriate for online PD measurement. The second part of the paper shows how the proposed antenna can resolve the problems pertaining to the UHF PD measurement in power transformers.

This article details the use of an acceleration measuring system which can transmit in real-time sensor data through UHF RFID to a computer. Existing methods of real-time transmission of sensor data rely on power-intensive Bluetooth or Wi-Fi technologies which result in devices that require large bulky batteries, this causes the overall device size to be high and thus can potentially cause issue during use. By harnessing status flags within a specific UHF RFID chip and custom reader software conforming to the EPC GEN2 standard, continuous streaming data rates of 5.2KBps were achievable. These enhanced data rates were shown to be reliable up to a range of 2.4M with above 99.99% data integrity. The power consumption of this methodology was found to be below 2mW during full power continuous transmission. In summary this article outlines and lays the foundation for the use of UHF RFID to deliver sub-2mW low latency, high reliability streaming methods within the domain of on body transmission.

A compact wearable dual-band quasi-Yagi RFID-reader antenna is designed for being incorporated into a smart glove. The antenna dual-band capability allows the integration of both the RFID reader at UHF band and a wireless data link at 2.4 GHz, into a single compact and wearable device. Dipole and loop antennas are combined into a quasi-Yagi structure to be placed on a hand back, in order to detect tagged objects close to the hand palm and fingers, during the operator normal activities. The dual-band driven element consists of a rectangular-shaped folded dipole (resonating at the ETSI UHF RFID band, 865–868 MHz) and a rhombus-shaped folded dipole (resonating at the WLAN band, 2400–2485 MHz). A few parasitic elements (reflector and directors) are included to focus the field in the required direction, namely out of the worker’s hand. A prototype of the proposed textile antenna is developed on a stretchable fabric and its performance is measured in terms of read range and near-field distribution, at 868 MHz, and radiation pattern and gain at 2.45 GHz.

In this article, broadband gallium nitride (GaN) high-electron-mobility transistor (HEMT) power amplifier with shunt-feedback and push–pull technique is presented. Shunt-feedback and push–pull realization provide the robust broad bandwidth covering very high frequency and low-frequency ultra high frequency (UHF) bands. The benefit due to the feedback presented in the form of shunt–shunt network on power amplifier module provides the linear and broadband frequency amplification. The push–pull topology provides enhanced efficiency and high power generation along with the cancellation of the second-order distortions and thus helps to compensate for the efficiency degradation from the feedback. These techniques are realized with the help of in-house designed GaN HEMT transistor, which provides high power, good efficiency, and high reliability (bandgap). The prototype was realized in 0.25- $\mu$ m GaN HEMT, operates from 30 to 520 MHz, and dissipates 650 mA of quiescent current from 28-V supply. The power amplifier delivered a saturated output power of >43 dBm and 40% power added efficiency at 20 W output power. The linearity of the amplifier was characterized by the two-tone injection test. The measurement result shows that the third-order intermodulation distortion tones are below $-$ 35 dBc at 35 dBm output power.

Capacitive loading due to human tissue can lead to low efficiency for implantable Passive Radio Frequency Identification (RFID) antennas. The presented passive UHF antenna sensor provides read distances above 0.5 meters (within a body phantom) by utilizing a convoluted half-wave dipole design. It is able to detect simulated early to mature Candida albicans biofilm growth when mounted upon a voice prosthesis (up to a $30~\mu \text{m}$ biofilm thickness). Depending on the propagation frequency of interest, as early 4-hour growth (5 to $10~\mu \text{m}$ biofilm thickness) equivalent could be detected and before any device failure could occur due to the colonization. This was accomplished by utilising thin layers of polyurethane to decouple the saliva from the presented UHF sensor (biofilm growth is known to increase layer hydrophobicity). This presented sensor has better functionality within the U.S. UHF frequency band as it detects changes above $5~\mu \text{m}$ . If there is a need for implantation within additional tissues with variable dielectric properties, a shunt capacitance of 2.6 pF could allow the system functionality within the permittivity range of 21 to 58. Allowing for immediate medical intervention before medical prosthesis failure.

A fully integrated passive ultrahigh-frequency (UHF) RF identification (RFID) tag integrated circuit (IC) based on Chinese UHF RFID standard (GJB 7377.1) is proposed. An optimized voltage multiplier with threshold compensation and leakage current suppression is designed to improve the RF-DC power conversion efficiency, which is more than 58% for different load current. A system clock constraint condition and proposed digital baseband (BB) algorithm instead of clock calibration is introduced to ensure correct demodulation of the forward link from reader to tag and back link frequency (BLF) tolerance from tag to reader. Moreover, a 2Kb multi-time programmable (MTP) non-volatile memory (NVM) in standard CMOS process without any additional masks and process modification is designed and implemented to significantly save the manufacture cost of the chip. The proposed RFID tag IC is fabricated using a $0.13-\mu \text{m}$ one-poly-five-metal (1P5M) standard CMOS process with an area of $620\times 660\,\,\mu \text{m}^{2}$ and a power consumption of 4.8 $\mu \text{W}$ and 11.5 $\mu \text{W}$ for reading and writing operations, respectively. The tag with antenna gain of 2 dBi shows successful reading detection at distances up to 17 m in the case of 4 W Equivalent Isotropically Radiated Power (EIRP) from reader.

River discharge measurement is of great significance, and as such, many methods and measuring instruments have been developed by many hydrologic researchers. However, most commonly used measuring instruments must be in contact with the water and are difficult to place and maintain. In this letter, a noncontact measurement method is proposed using ultrahigh- frequency (UHF) radar. The index-velocity method is employed to calculate the mean cross-sectional velocity, and the water-surface velocities on the cross section detected by the UHF radar are used to select the optimum index velocity. A field experiment was conducted in the Hanjiang River at Xiantao, Hubei, China, from March to July 2018. Data from March to June were processed for selecting the optimum index velocity, and the maximum water-surface velocity of the cross section was proven to be optimal. The fit relationship between the mean cross-sectional velocity and the index velocity was used to estimate the mean cross-sectional velocities and river discharges for June to July. The results were compared with those provided by the Hubei Xiantao hydrologic station, and the errors were mostly within ±5%. This confirms that the UHF radar can be used to accurately, automatically, and continuously measure river discharge.

Advances in the dynamic response of welding power sources have allowed the use of pulsed current at frequencies above 20 kHz. However, the effects of pulsing the welding current at these high-frequency levels are not well known, especially those associated with the voltaic arc. Thus, the aim of this study was to carry out experimental research on a pulsating welding current at ultra-high frequencies focusing on two important voltaic arc parameters in gas tungsten arc welding processes: arc voltage and arc stagnation pressure. The tests were performed with a welding current pulsed at frequencies of 20 to 80 kHz and amplitudes of 0 to 50 A. The results indicated that pulsing the current at ultra-high frequencies leads to a reduction in the average arc voltage, increasing the stagnation pressure and the arc constriction. Regarding the weld bead dimensional aspects, greater values of width and penetration were obtained when the high-frequency current pulsation was applied.

A novel compact isolation circuit (IC) is proposed for the ultracompact and wideband UHF Marchand balun topology, and exact design formulas are presented for arbitrary coupling coefficients and impedance-transforming termination impedances. The wideband Marchand balun mainly consists of two identical coupled transmission-line sections which are far shorter than 90° long, connecting segment, two or three lumped elements and the proposed IC. The novel IC features −180° phase delay between two balanced ports, and makes the ultracompact implementation possible, which is quite different from the conventional ones with 180° phase delays between two balanced ports. In addition, due to the −180° phase delays, excellent isolation performance and excellent phase responses can be performed. For the proof-of-concept demonstrations, one prototype with each coupled-line section being only 20° long and the half IC being only 20° long is tested at 700 MHz. The measured frequency responses are in good agreement with the predicted ones with the performance of the 10-dB return loss bandwidth of 40% and −15 dB isolation bandwidth of 121.4%. In terms of sizes versus bandwidths, the fabricated Marchand balun can be regarded as the best and the smallest ever recorded, based on the low-cost microstrip technology.

This investigation primarily promotes a ultra-high frequency radiofrequency identification (RFID) tag antenna for complex environment applications of smart card in free space and near body scenarios. It also considers other high dielectric materials such as water and metallic objects. A dual dipole antenna with T-match structure is chosen due to the advantage of providing high resilience towards change in impedance of high dielectrics, and to ensure the reception of maximum signals at the blind spots of the antenna. The proposed geometry facilitates placement of other off-the-shelf high and low-frequency antennas on the card, enabling more features, higher performance, and minimum field interaction between different frequencies. A presented RLC equivalent circuit model estimates the impact of body layers on antenna impedance. A high read range of 7.7 m in free space, 5.2 m near body and 2.8 m at the blind spots is obtained. The novelty is shown by testing the antenna near metals and water, achieving high read range without any design modifications. The proposed tag aims to provide new RFID applications that demand small size, less volume, low cost and multifunctionality over various constraints while showing good agreement with sensitivity, impedance matching and the read range.

Radar sounding is a powerful tool for constraining subglacial conditions, which influence the mass balance of polar ice sheets and their contributions to global sea-level rise. A satellite-based radar sounder, such as those successfully demonstrated at Mars, would offer unprecedented spatial and temporal coverage of the subsurface. However, airborne sounding studies suggest that poorly constrained radar scattering in polar firn may produce performance-limiting clutter for terrestrial orbital sounders. We develop glaciologically constrained electromagnetic models of radar interactions in firn, test them against in situ data and multifrequency airborne radar observations, and apply the only model we find to be consistent with observation to assess the implications of firn clutter for orbital sounder system design. Our results show that in the very high-frequency (VHF) and ultrahigh-frequency (UHF) bands, radar interactions in the firn are dominated by quasi-specular reflections at the interfaces between layers of different densities and that off-nadir backscatter is likely the result of small-scale roughness in the subsurface density profiles. As a result, high frequency (HF) or low VHF center frequencies offer a significant advantage in near-surface clutter suppression compared to the UHF band. However, the noise power is the dominant constraint in all bands, so the near-surface clutter primarily constrains the extent to which the transmit power, pulselength, or antenna gain can be engineered to improve the signal-to-noise ratio. Our analysis suggests that the deep interior of terrestrial ice sheets is a difficult target for orbital sounding, which may require optimizations in azimuth processing and cross-track clutter suppression which complement existing requirements for sounding at the margins.