Textiles have been concomitant of human civilization for thousands of years. With the advances in chemistry and materials, integrating textiles with energy harvesters will provide a sustainable, environmentally friendly, pervasive, and wearable energy solution for distributed on-body electronics in the era of Internet of Things. This article comprehensively and thoughtfully reviews research activities regarding the utilization of smart textiles for harvesting energy from renewable energy sources on the human body and its surroundings. Specifically, we start with a brief introduction to contextualize the significance of smart textiles in light of the emerging energy crisis, environmental pollution, and public health. Next, we systematically review smart textiles according to their abilities to harvest biomechanical energy, body heat energy, biochemical energy, solar energy as well as hybrid forms of energy. Finally, we provide a critical analysis of smart textiles and insights into remaining challenges and future directions. With worldwide efforts, innovations in chemistry and materials elaborated in this review will push forward the frontiers of smart textiles, which will soon revolutionize our lives in the era of Internet of Things.

Smart Textiles for Electricity Generation.

Wearable devices are drawing increasing attention in both academia and industry in that they can offer unprecedented information related to human health in real-time and human–machine interactions, which is expected to enable a paradigm shift in the digital world. For this shift to occur, green and sustainable energy technology for powering flexible wearable devices is a roadblock. This paper is dedicated to reviewing cutting-edge wearable power generation methodologies, for which we discuss their pros and cons, underlying physics, and general design/evaluation criteria. Sensor types, materials, processing technology, power consumption, and methods of testing the stretchability and flexibility of wearable devices are also summarized. Based on application scenarios in healthcare, industrial inspection, structural monitoring, armed forces and consumer electronics, an integrated system architecture of wearable, flexible systems is presented. Finally, future perspectives of wearable technologies are outlined by covering the aspects of all-in-one printable wearable electronics, fiber and textile electronics, self-powered self-awareness wearable systems, hybrid-integrated Systems on a Chip (SoC) for flexible electronics, and Internet of Things (IoT)-enabled self-contained systems towards full life cycle monitoring.

Power generation for wearable systems

The field of flexible antennas is witnessing an exponential growth due to the demand for wearable devices, Internet of Things (IoT) framework, point of care devices, personalized medicine platform, 5G technology, wireless sensor networks, and communication devices with a smaller form factor to name a few. The choice of non-rigid antennas is application specific and depends on the type of substrate, materials used, processing techniques, antenna performance, and the surrounding environment. There are numerous design innovations, new materials and material properties, intriguing fabrication methods, and niche applications. This review article focuses on the need for flexible antennas, materials, and processes used for fabricating the antennas, various material properties influencing antenna performance, and specific biomedical applications accompanied by the design considerations. After a comprehensive treatment of the above-mentioned topics, the article will focus on inherent challenges and future prospects of flexible antennas. Finally, an insight into the application of flexible antenna on future wireless solutions is discussed.

Flexible Antennas: A Review.

Diversiform sensors and sensing systems driven by triboelectric and piezoelectric nanogenerators

This review paper summarizes various approaches developed in the literature for antenna sensors with an emphasis on flexible solutions. The survey helps to recognize the limitations and advantages of this technology. Furthermore, it offers an overview of the main points for the development and design of flexible antenna sensors from the selection of the materials to the framing of the antenna including the different scenario applications. With regard to wearable antenna sensors deployment, a review of the textile materials that have been employed is also presented. Several examples related to human body applications of flexible antenna sensors such as the detection of NaCl and sugar solutions, blood and bodily variables such as temperature, strain, and finger postures are also presented. Future investigation directions and research challenges are proposed.

https://www.mdpi.com/1996-1944/13/17/3781/pdf

A Review of Flexible Wearable Antenna Sensors: Design, Fabrication Methods, and Applications

Millimeter-wave (mmWave) bands, a key part of future 5G networks, represent a potential channel for RF energy harvesting, where the high-gain antenna arrays offer improved end-to-end efficiency compared with sub-6-GHz networks. This article presents a broadband mmWave rectenna, the first rectenna realized on a flexible textile substrate for wearable applications. The proposed novel antenna’s bandwidth extends from 23 to 40 GHz, with a minimum radiation efficiency of 67% up to 30 GHz, over 3-dB improvement compared with a standard patch. A stable gain of more than 8 dB is achieved based on a textile reflector plane. The antenna is directly connected to a textile-based microstrip voltage doubler rectifier utilizing commercial Schottky diodes. The rectifier is matched to the antenna using a tapered line feed for high-impedance matching, achieving broadband high voltage sensitivity. The rectifier has a peak RF–dc efficiency of 12% and a 9.5-dBm 1-V sensitivity from 23 to 24.25 GHz. The integrated rectenna is demonstrated with more than 1.3-V dc output from 12 dBm of mmWave wireless power across a 28% fractional bandwidth from 20 to 26.5 GHz, a 15% half-power fractional bandwidth, and a peak output of 6.5 V from 20 dBm at 24 GHz.

/pdf/broadband-millimeter-wave-textile-based-flexible-rectenna-wdhlo2c51n.pdf

Broadband Millimeter-Wave Textile-Based Flexible Rectenna for Wearable Energy Harvesting

Radio-frequency (RF) energy harvesting (RFEH) and radiative wireless power transfer (WPT) have attracted significant interest as methods of enabling battery-free sustainable wireless networks. Rectifying antennas (rectennas) are the cornerstone of WPT and RFEH systems and critically affect the amount of dc power delivered to the load. The antenna element of the rectenna directly impacts the radiation-to-ac harvesting efficiency, which can vary the harvested power by orders of magnitude. In this article, antenna designs employed in WPT and ambient RFEH applications are reviewed. Reported rectennas are categorized based on two main criteria: the antenna-rectifier impedance bandwidth and the antenna's radiation properties. For each criterion, the figure of merit (FoM) is identified for different applications and reviewed comparatively.

/pdf/rectennas-for-radio-frequency-energy-harvesting-and-wireless-23tnrq8gp6.pdf

Rectennas for Radio-Frequency Energy Harvesting and Wireless Power Transfer: A Review of Antenna Design [Antenna Applications Corner]

Textile-based triboelectric nanogenerator with alternating positive and negative freestanding grating structure

Despite the recent advances in textile antennas, in complete systems such as a rectenna, the efficiency of fully textile solutions has been over 46% lower than hybrid textile/rigid implementations. This article presents a fully textile rectenna for ultralow-power sub- $\mu \text{W}$ /cm2 applications. A dual-polarized omnidirectional low-profile textile antenna is presented. The rectenna is based on a compact inductively matched rectifier. The textile-based rectifier occupies 0.22 cm2 and achieves a state-of-the-art power conversion efficiency (PCE) of 41.8% at −20 dBm, at 820 MHz, despite its lossy substrate. A triple-band rectifier is then designed and fabricated to show the scalability of the matching approach. The rectifier is characterized using a new figure of merit “average PCE” over a time period while charging a capacitor. Time-varying S-parameters are used to quantify the impact of the capacitor’s charge on the impedance matching. The rectifier directly charges a 1.32 mF capacitor up to 1 V in 0.41 and 4.5 s from 10 and 0 dBm, respectively. Wireless testing of the proposed rectenna demonstrates over 50% and 40% (PCE) below $1~\mu \text{W}$ /cm2 in space and on-body, respectively. The rectenna efficiently receives power from mismatched polarization and with a 360° half-power beamwidth.

/pdf/omnidirectional-dual-polarized-low-profile-textile-rectenna-2szp2rqox9.pdf

Omnidirectional Dual-Polarized Low-Profile Textile Rectenna With Over 50% Efficiency for Sub- μ W/cm 2 Wearable Power Harvesting

This article presents a textile antenna for dual-band simultaneous wireless information and power transfer (SWIPT) The antenna operates as a 24 GHz off-body communications antenna and a sub-1 GHz (785–875 MHz) broad-beam rectenna Incorporated within the broadside microstrip antenna is a high-impedance rectenna for sub-1 GHz power harvesting Utilizing antenna-rectifier co-design, the rectenna eliminates the rectifier matching network The textile antenna is fabricated on a felt substrate and utilizes conductive fabrics for the antenna At 24 GHz, the antenna achieves a realized gain of 72 dBi on a body phantom and a minimum radiation efficiency of 63%, with and without the rectifier The rectenna achieves a best-in-class RF to dc efficiency of 62% from 08 $\mu \text{W}$ /cm2, representing over 25% improvement over state-of-the-art textile rectennas and demonstrating that SWIPT does not detrimentally affect the energy harvesting or communications performance The antenna/rectenna occupies an electrically small area of $0213\times 019\,\,\lambda ^{2}_{0}$  This antenna is the first dual-band, dual-mode antenna demonstrated on textiles for SWIPT applications and the first dual-band matching network-free SWIPT rectenna

/pdf/dual-band-dual-mode-textile-antenna-rectenna-for-4tm8b9rl7u.pdf

Mahmoud Wagih

Papers

Broadband Millimeter-Wave Textile-Based Flexible Rectenna for Wearable Energy Harvesting

Rectennas for Radio-Frequency Energy Harvesting and Wireless Power Transfer: A Review of Antenna Design [Antenna Applications Corner]

Textile-based triboelectric nanogenerator with alternating positive and negative freestanding grating structure

Omnidirectional Dual-Polarized Low-Profile Textile Rectenna With Over 50% Efficiency for Sub- μ W/cm 2 Wearable Power Harvesting

Dual-Band Dual-Mode Textile Antenna/Rectenna for Simultaneous Wireless Information and Power Transfer (SWIPT)