Wearable Communication Research Articles

Printed textile metasurfaces for gain and directivity enhancement

Abstract Wearable printed electronics are of significant recent interest for use in on-body communication devices, including antennas that are readily integrated into textiles using additive manufacturing. Directly printing the device onto textile reduces the need for costly, time-intensive processing steps; however, textile substrates impose design and performance limitations given that the design must be compatible with on-body usage and must also remain below maximum safe radiation levels. Herein, we present a passive solution for improving the performance of a commercial off the shelf omnidirectional antenna using textile metasurfaces. A modular system was developed for gain enhancement and pattern shaping using three metasurface elements with a band stop resonance at 6 GHz, where reflection is used to enhance gain. The versatility of a wearable metasurface is demonstrated for two of the designs which also offer a band pass at 2.4 GHz. Radiation pattern measurements conducted in an anechoic chamber showed that the metasurface achieved a gain improvement of up to 7.2 dB. This methodology enables a wearable, low-profile, passive, and non-destructive system for the improvement of existing wearable communication devices.

Design and SAR Analysis of an AMC-Integrated Wearable Cavity-Backed SIW Antenna.

Wearable communication technologies necessitate antenna designs that harmonize ergonomic compatibility, reliable performance, and minimal interaction with human tissues. However, high specific absorption rate (SAR) levels, limited radiation efficiency, and challenges in integration with flexible materials have significantly constrained widespread deployment. To address these limitations, this manuscript introduces a novel wearable cavity-backed substrate-integrated waveguide (SIW) antenna augmented with artificial magnetic conductor (AMC) structures. The proposed architecture is meticulously engineered using diverse textile substrates, including cotton, jeans, and jute, to synergistically integrate SIW and AMC technologies, mitigating body-induced performance degradation while ensuring safety and high radiation efficiency. The proposed design demonstrates significant performance enhancements, achieving SAR reductions to 0.672 W/kg on the spine and 0.341 W/kg on the forelimb for the cotton substrate. Furthermore, the AMC-backed implementation attains ultra-low reflection coefficients, as low as -26.56 dB, alongside a gain improvement of up to 1.37 dB, culminating in a total gain of 7.09 dBi. The impedance bandwidth exceeds the ISM band specifications, spanning 150 MHz (2.3-2.45 GHz). The design maintains remarkable resilience and operational stability under varying conditions, including dynamic bending and proximity to human body models. By substantially suppressing back radiation, enhancing directional gain, and preserving impedance matching, the AMC integration optimally adapts the antenna to body-centric communication scenarios. This study uniquely investigates the dielectric and mechanical properties of textile substrates within the AMC-SIW configuration, emphasizing their practicality for wearable applications. This research sets a precedent for wearable antenna innovation, achieving an unprecedented balance of flexibility, safety, and electromagnetic performance while establishing a foundation for next-generation wearable systems.

Textile Antenna with Dual Bands and SAR Measurements for Wearable Communication

A novel dual-wideband textile antenna designed for wearable applications is introduced in this study. Embedding antennas into wearable devices requires a detailed analysis of the specific absorption rate (SAR) to ensure safety. To achieve this, SAR values were meticulously simulated and evaluated within a human voxel model, considering various body regions such as the left/right head and the abdominal region. The proposed antenna is a monopole design utilizing denim textile as the substrate material. The characterization of the denim textile substrate is carried out using two different methods. The first analysis included a DAC (Dielectric Assessment Kit), while a ring resonator technique was employed for the second examination. Operating within the frequency bands of (58.06%) 2.2–4 GHz and (61.43) 5.3–10 GHz, the antenna demonstrated flexibility in its dual-wideband capabilities. Extensive simulations and tests were conducted to assess the performance of the antenna in both flat and bent configurations. The SAR results obtained from these tests indicate that the antenna complies with safety standard limits when integrated with the human voxel model. This validation underscores the potential of the proposed antenna for seamless integration into wearable applications, offering a promising solution for future developments in this domain.

A compact tri-notched flexible UWB antenna based on an inkjet-printable and plasma-activated silver nano ink

The rapid development of ultrawideband (UWB) communication systems has resulted in increasing performance requirements for the antenna system. In addition to a wide bandwidth, fast propagation rates and compact dimensions, flexibility, wearability or portability are also desirable for UWB antennas, as are excellent notch characteristics. Although progress has been made in the development of flexible/wearable antennas desired notch properties are still rather limited. Moreover, most presently available flexible UWB antennas are fabricated using environmentally not attractive subtractive etching-based processes. The usage of facile additive sustainably inkjet printing processes also utilizing low temperature plasma-activated conductive inks is rarely reported. In addition, the currently used tri-notched flexible UWB antenna designs have a relatively large footprint, which poses difficulties when integrated into miniaturized and compact communication devices. In this work, a silver nano ink is used to fabricate the antenna via inkjet printing and an efficient plasma sintering procedure. For the targeted UWB applications miniaturized tri-notched flexible antenna is realized on a flexible polyethylene terephthalate (PET) substrate with a compact size of 17.6 mm × 16 mm × 0.12 mm. The antenna operates in the UWB frequency band (2.9–10.61 GHz), and can shield interferences from WiMAX (3.3–3.6 GHz), WLAN (5.150–5.825 GHz) and X-uplink (7.9–8.4 GHz) bands, as well as exhibits a certain of bendability. Three nested "C" slots of different sizes were adopted to achieve notch features. The simulation and test results demonstrate that the proposed antenna can generate signal radiation in the desired UWB frequency band while retaining the desired notch properties and having acceptable SAR values on-body, making it a viable candidate for usage in flexible or wearable communication transmission devices. The research provides a facile and highly efficient method for fabricating flexible/wearable UWB antennas, that is, the effective combination of inkjet printing processing, flexible substrates, low temperature-activated conductive ink and antenna structure design.

Human electromagnetic field exposure in wearable communications systems: A review

While wearable technologies have taken essential parts of our daily lives, concerns on human health are often overseen. Mainly due to extreme proximity or direct physical contact to human skin, wearable communications devices are prone to cause higher levels of electromagnetic field (EMF) exposure at human skin surface than any other type of wireless technologies. Nevertheless, while focusing on theoretical aspects of human EMF exposure in wearable communications, prior work paid little to no attention on exact exposure levels generated by commercial wearable devices that are already widely used by public consumers. In this context, this paper provides an extensive review of SAR from various commercial wearable devices that are currently sold in the market, as well as the analytical framework and the current measurement methodologies for standard compliance tests. To extend the discussion to general wearable communications, this paper presents simulation results adopting representative antenna patterns, which leads to suggestion of separation distances to keep the current safety guidelines. In particular, considering the increasing interest in millimeter wave (mmW), this paper sheds light on EMF exposure evaluated at 60 GHz and compares to results from 2.4 GHz.

Wearable microstrip patch antenna with low SAR for WBAN applications

The development of intelligent textile systems to raise the degree of protection for the wearer has revealed the need for wearable communication devices and motivated research in textile antennas. In this paper, a new fully textile microstrip patch antenna is designed for a central frequency of 5.8 GHz. a substrate made of polyester and cotton with a dissipation factor of tan = 0.02 and a dielectric constant of 1.6 was employed. Thanks to its high conductivity (0.02 Ohm/cm), the Stick E shield was chosen as a conductor material. The CST simulator version 2018 is used to simulate the suggested conception, and measured by Vector Network Analyzer Master MS2026C, the HFSS software was employed as a comparative tool. For wearable situations in the free medium and on the human body, promising results from simulation and experimental studies are presented. The suggested antenna might possibly be connected to the human body, requiring the calculation of the specific absorption ratio (SAR).Thus, the proposed antenna design permits to attain 0.087 W/kg for 1 g. SAR and 0.0321 W/kg for 10 g. Experimental and numerical results demonstrate excellent performance regarding return loss, VSWR. Finally, our results indicate that the suggested antenna performs as intended when situated within the vicinity of the human body, making it a good candidate for application in wearable technologies.

A Novel Elastic Conductive Yarn for Smart Textile Applications

Conductive yarns are crucial for electrical connections in electronic textiles. Challenges in conductive and elastic properties of conductive yarns, their durability, and compatibility with existing manufacturing processes limit mass production and affordability of conductive yarn. This work investigates elastic, shell‐conductive, and noncorrosive electroconductive yarns for textile‐based wearable electronics. The existing textile manufacturing processes (plaiting, coiling, and twisting) are used to fabricate elastic conductive yarn (ECY) using different blend ratios of stainless steel conductive yarn and elastomeric yarn. The ECY samples are inspected for structural uniformity, conductive coverage, ability to be woven, thickness, and extensibility. The most promising ECY exhibits a breaking force of 10.87 N, a tenacity of 2.04 cN tex−1, and an elongation at break of 61.1%, suitable for integration into e‐textiles where elasticity is required. The ECY with a conductive coverage of 85.36% provides better electrical connection points, while a thickness of 0.69 mm and linear density of 534 tex make it compatible with traditional textile manufacturing equipment. Findings demonstrate that the fabrication method and input parameters significantly impact the properties of ECY, including their elasticity and conductive coverage. Utilizing ECYs in fabric circuit boards can enable improved smart wearables for sustainable and modular integration of electronic components.

Sistem Komunikasi Wearable Yang Menerapkan PCB Fleksibel

The rapid adaptation of Wearable Communication technology to be applied in various fields has shown a remarkable development profile over the past decade. In this research project, a prototype wearable device operating at a frequency of 2.4 GHz was developed using rice husk fiber composite material to construct a flexible PCB Board as a circuit path and shield for IoT component modules and practically tested. This wearable device is designed to transfer video and image streaming data in indoor and outdoor scopes. The sensing object or location captured using the wearable device placed on the user's shirt is connected to an access point and will send the data to a registered server or authorized receiving station. The first trials of the fabricated wearable devices have shown excellent data transmission conducted in two different environments. The maximum communication range between the wearable device and the access point was 87 meters in the indoor test while in the outdoor test the maximum communication distance was 60 meters. During the communication range, the transmission quality degraded so that the sending signal strength during the indoor test was 398 kb/s and the outdoor test was 299 kb/s.

Multiband and Low-Specific-Absorption-Rate Wearable Antenna With Low Profile Based on Highly Conductive Graphene Assembled Film

A flexible tri-band antenna with low profile and low specific absorption rate (SAR) based on highly conductive graphene assembled film (GAF) is proposed. The antenna incorporates GAF with polydimethylsiloxane (PDMS) to provide the flexibility for wearable applications. To reduce the effect of backward radiation on human body, a new multi-band artificial magnetic conductor (AMC) reflector is proposed, which consists of several circular patches. The measured operating bandwidths of GAF antenna include 2.26-2.46 GHz (WiFi band), 3.52-3.68 GHz (5G n77 band) and 4.94-5.26 GHz (5G WLAN band). Correspondingly, the realized gain varies from 5.7-7.9 dBi. The proposed GAF antenna shows good flexibility and radiation stability when loaded on human body. The simulated SAR peak value is 0.51 W/kg at 2.36 GHz, 0.61 W/kg at 3.6 GHz and 0.562 W/kg at 5.1 GHz when the tissue is 1 g, which meets the international standard. All results demonstrate that the proposed flexible GAF tri-band antenna is suitable for integrating in wireless wearable communication system.

Red InGaN Micro-LEDs on Silicon Substrates: Potential for Multicolor Display and Wavelength Division Multiplexing Visible Light Communication

Red micro light-emitting diodes (micro-LEDs) on silicon substrates are crucial for the realization of large-scale, high-quality, low-cost micro-LED displays, and are also beneficial for high-speed visible light communication (VLC). In this letter, micro-LEDs with different sizes were fabricated. The maximum light output power density of the 20 μm pixel can reach 3.36 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which is 14 times higher than that of the largest pixel (150 μm). By adjusting the pixel size and injection current, a direct color shift from red to green can be observed. Moreover, multicolor emission with uniform brightness can be realized by adjusting duty cycle, which has broad application prospect in monolithic, multicolor displays. Despite the significant blue shift phenomenon, the peak wavelength of all pixels is still greater than 630 nm at the current density of 100 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which means that red light can be emitted in a large current density range to meet various application scenarios requiring different driving conditions. We have realized red, yellow and green micro-LED transmitters on Si substrate by changing the driving current density and modulation bandwidth up to 533.15 MHz is achieved when emitting green light. This is the report of red-emission micro-LEDs on Si substrates for visible light communication for the first time. And we proposed a proof-of-concept monolithic, multicolor wavelength division multiplexing scheme that achieved a total allowable transmission data rate of 2.35 Gbps. Such micro-LED is expected to be applied in multicolor displays, high-speed multi-channel VLC, color-tunable light sources, etc. In particular, due to its high integration and miniaturization, it is expected to be used in future practical application scenarios such as wearable communication devices and smartwatches.

Circularly polarized metamaterial Antenna in energy harvesting wearable communication systems

When battery powered sensors are spread out in places that are sometimes hard to reach, sustaining them become difficult. Therefore, to develop this technology on a large scale such as in the internet of things (IoT) scenario, it is necessary to figure out how to power them. The proffered solution in this work, is to get energy from the environment using energy harvesting Antennas. This work presents a wearable circular polarized efficient receiving and transmitting sensors for medical, IoT, and communication systems at the frequency range of WLAN, and GSM from 900 MHz up to 6 GHz. Using a cascaded system block of a circularly polarized Antenna, a rectifier and t-matching network, the design was successfully simulated. A DC charging voltage of 2.8V was achieved to power-up batteries of the wearable and IoT sensors. The major contribution of this work is the tri-band Antenna system which is able to harvest reflected Wi-Fi frequencies and also GSM frequencies combined in a miniaturized manner. This innovative configuration is a step forward in building devices with over 80% duty cycle.

Circularly polarized metamaterial Antenna in energy harvesting wearable communication systems

When battery powered sensors are spread out in places that are sometimes hard to reach, sustaining them become difficult. Therefore, to develop this technology on a large scale such as in the internet of things (IoT) scenario, it is necessary to figure out how to power them. The proffered solution in this work, is to get energy from the environment using energy harvesting Antennas. This work presents a wearable circular polarized efficient receiving and transmitting sensors for medical, IoT, and communication systems at the frequency range of WLAN, and GSM from 900 MHz up to 6 GHz. Using a cascaded system block of a circularly polarized Antenna, a rectifier and t-matching network, the design was successfully simulated. A DC charging voltage of 2.8V was achieved to power-up batteries of the wearable and IoT sensors. The major contribution of this work is the tri-band Antenna system which is able to harvest reflected Wi-Fi frequencies and also GSM frequencies combined in a miniaturized manner. This innovative configuration is a step forward in building devices with over 80% duty cycle.

A monopole antenna with cotton fabric material for wearable applications

A monopole antenna operated at 2.45 GHz and embedded with artificial magnetic conductor (AMC) for wearable communication systems is investigated in this article. The proposed antenna is composed of a metalized loop radiator with a coplanar waveguide microstrip feedline which is affixed on a cotton fabric material substrate. As well, a cotton-based AMC surface is utilized to eliminate the body’s absorbed radiation and enhance the gain of the antenna. It is composed of 5 × 5 array unit cells etched with I-shaped slots. Using this configuration, simulations show that the specific absorption rate (SAR) level was significantly reduced. Considering flat and rounded body parts, it was found that the SAR values averaged over 10 g at a distance of 1 mm away from the tissues model were only 0.18 W/kg and 0.371 W/kg, respectively. Additionally, the antenna gain was improved up to 7.2 dBi with an average radiation efficiency of 72%. Detailed analysis with experimental measurements of the cotton-based antenna for different operation scenarios is introduced. The measured data show a good correlation with the electromagnetic simulation results.

Digitally Controlled Tunable Fabric Microwave Filter Based on Organic Electrochemical Transistors

AbstractA microwave filter is important to determine the performance of a wearable communication system. However, the materials used in existing microwave filters require sophisticated and expensive fabrication processes. Moreover, they are not compatible with flexible and wearable platforms. In this study, a novel strategy for realizing a tunable fabric microwave filter (TFMF) by taking advantage of the spoof surface plasmon polariton (SSPP) structure and using organic electrochemical transistors (OECTs) is presented, which are lightweight and exhibit excellent mechanical flexibility and deformability. The TFMF is manufactured using fabric materials, and the OECT is printed to serve as a state‐changing material. The developed TFMF exhibits excellent flexibility, high planar integration and improved wearing comfort. Furthermore, the operating frequency of the TFMF with well‐designed gradient structures and multi‐state dispersion characteristics can be effectively tuned by applying different voltage sequences. To the best of the authors’ knowledge, this is the first tunable microwave filter designed for use in wearable systems. The measurements of scattering parameters and data transmission with a communication system based on the TFMF demonstrate a feasible pathway for enhancing the performance of wearable wireless communication systems.

CONFORMAL PLANAR ANTENNA WITH DGS FOR 5G WEARABLE COMMUNICATIONS

Future wireless communication systems will have data support, broadband connectivity, and extremely high reliability built in. Conformal antennas are used in a wide range of applications due to their high gain, small size, excellent radiation efficiency, and broad bandwidth. With this goal in mind, we propose the design of a conformal antenna and evaluate its performance. The conformal design makes use of traditional patch antennas with faulty ground construction. The conformal antenna is designed and simulated using the finite difference time domain. The substrate is made of the dielectric FR-4. The simulation results and goal parameters agree. The antenna is 14.59 &amp;times; 18.79 mm in length and 0.8 mm in thickness. The resonance frequency is 4.6 GHz. The effective bandwidth for these results extends from 3.5 GHz to 5.5 GHz, with a better return loss of less than -20 dB attained and measurements done to validate the design's compatibility. Furthermore, a specific absorption rate (SAR) assessment is performed to ensure that electromagnetic field exposure stays within the acceptable limits.

Machine-Learning Assisted Handwriting Recognition Using Graphene Oxide-Based Hydrogel.

Machine-learning assisted handwriting recognition is crucial for development of next-generation biometric technologies. However, most of the currently reported handwriting recognition systems are lacking in flexible sensing and machine learning capabilities, both of which are essential for implementation of intelligent systems. Herein, assisted by machine learning, we develop a new handwriting recognition system, which can be applied as both a recognizer for written texts and an encryptor for confidential information. This flexible and intelligent handwriting recognition system combines a printed circuit board with graphene oxide-based hydrogel sensors. It offers fast response and good sensitivity and allows high-precision recognition of handwritten content from a single letter to words and signatures. By analyzing 690 acquired handwritten signatures obtained from seven participants, we successfully demonstrate a fast recognition time (less than 1 s) and a high recognition rate (∼91.30%). Our developed handwriting recognition system has great potential in advanced human-machine interactions, wearable communication devices, soft robotics manipulators, and augmented virtual reality.

Disease Prediction in Edge Computing: A Privacy-Preserving Technique for PHI Collection and Analysis

Edge computing has garnered significant attention in recent years, as it enables the extension of cloud resources to the network edge. This enables the user to utilize virtually enhanced resources in terms of storage and computation at a lower cost. The edge-computing-assisted wireless wearable communication (EWWC) technology is a prime candidate for e-health edge applications to collect personal health information, which leads to disease learning and prediction. Ensuring privacy and efficiency of such a system in EWWC is extremely important. In this article, we introduce an efficient and privacy-preserving disease prediction scheme. We use the randomizable signature and matrices encryption technique to achieve identity protection and data privacy. The experimental analysis shows that our solution outperforms the existing solution in terms of computational costs and communication overhead. At the same time, it is able to provide data privacy, prediction model security, user identity protection, mendacious data traceability, and model verifiability. We also analyze potential future research directions related to this emerging area.

On the Design and Performance Analysis of Flexible Planar Monopole Ultra-Wideband Antennas for Wearable Wireless Applications

With the promising developments in wearable communication technology, attention towards flexible electronics is increasing day-by-day. This study presents flexible low-profile ultra-wideband (UWB) antennas for wearable applications. The antenna comprised of a modified dewdrop-inspired radiator and a defected ground plane and has an impedance bandwidth of 3.1–10.6 GHz. The antenna flexibility is investigated using four different substrates (polyester, polyamide, denim, and Teslin) and tested on a cotton shirt and a high-end Res-Q jacket to evaluate their performance stability for body-worn applications. The fabricated planar dewdrop-shaped radiator (PDSR) antennas have a radiation efficiency of &gt;90%, a gain of &gt;4 dBi, and a group delay variation of fewer than 0.5 ns. The antenna conformability is measured by placing the fabricated antennas on various curved and nonplanar parts of the human body. The aforementioned antennas offer better flexibility for different bent conditions. The specific absorption rate (SAR) of the designed antennas is investigated to determine their wearability, and values are found to be less than 0.2 W/Kg. Also, the received signal strength (RSS) is discussed in order to analyze signal attenuation, and the performance analysis of the antennas is compared.

Stretchable thin film inductors for wireless sensing in wearable electronic devices

The unique soft and elastic nature of stretchable electronics has potential to advance wearable devices as human-machine interfaces. The integration of wireless power and data communication technology into stretchable electronics, which could be realised by inductive coupling and oscillator circuits, is key to achieve continuous monitoring of body signals with minimally invasive devices. As one of the main components for inductive coupling and oscillator circuits, the development of stretchable inductors is therefore compelling. The most common strategy to fabricate stretchable inductors is to add periodic waves to a spiral conductor, which provides mechanical robustness but inevitably increases resistance. In this work, we introduce a method to fabricate stretchable inductors, which relies on creating a wrinkled thin film inductor on a polystyrene substrate, functionalizing the inductor surface with an adhesive layer, and then transferring the structure onto a polydimethylsiloxane (PDMS) elastomer. Contrary to inductors created through the addition of periodic wave patterns, the wrinkled inductor features low resistance while providing high stretchability. The wrinkled inductors fabricated using this approach exhibited 30% decrease in resistance compared to their flat counterparts of the same size and geometry. Resistance and inductance under uniaxial stretching remained unchanged up to 45% strain, revealing exceptional electrical and mechanical stability. The strong chemical bonding between the functionalized wrinkled inductor and the PDMS elastomer contributes to the robustness and long-term stability of the device. This method provides an added advantage of miniaturization of the stretchable inductor, as it is shrunk to 16% of its original size during the wrinkling process. This technology has potential for building high performance stretchable inductors for stretchable wireless electronic devices and can eventually benefit the design of electronics for implants, health care monitoring and wearable communication.

Triple Band Textile Array Antenna with Enhanced Gain and Low SAR for Off Body Communication Applications

A triple band wearable microstrip patch antenna array has been designed and analyzed in this work. The designed antenna can be operated in ISM, LAES and X-Band with moderate average gain of 4.2 dB. The antenna gain has been improved by constructing array structure of 1X2 and 1X4 with good impedance feeding by quarter wave transformer. The proposed array antennas are providing moderate gain of 5.7 dB (1X2) and 8.3 dB (1X4) with efficiency more than 90% in the operating bands. The antenna model and the array has been constructed on wearable substrate with conductive textile as radiating element in the design for off body wearable communication applications. SAR analysis also providing acceptable values below 1.6 w/kg at triple operating bands with body placement experimentation.