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Near-field radiative Wireless Power Transfer (WPT)has the advantage of high-power WPT. In this paper, an all textile high-power WPT receiver is realized for the first time, using an embroidered coil and a printed tuning capacitor on a textile substrate. The proposed coil is demonstrated receiving over 3 W DC power at 6.78 MHz with a 23% end-to-end efficiency. A low Specific Absorption Rate (SAR) of 0.37 W/kg is observed, through full-wave simulation, for up to 10 W high frequency input to the on-body coil, demonstrating its suitability for wearable applications.

While a range of Simultaneous Wireless Information and Power Transfer (SWIPT) rectennas were proposed for wearables, the human-proximity effects on a complex-conjugate matching network-free rectenna remain mostly unknown. This paper reports for the first time the impact of human proximity on a complex conjugate rectenna's impedance. The impedance of a dual-mode SWIPT microstrip/dipole rectenna is measured experimentally for varying separation from the body and on different body positions. The measured input impedance is used to simulate the rectifier's RF-to-DC efficiency using a non-linear model showing the effects of the power level, load, and frequency on the DC output for different on-body impedances.

While far-field wireless power transfer (WPT)promises a long range of operation, it falls short on the DC powerwhich can be provided. On the other, hand resonant near-fieldWPT suffers from a short wireless range. In this work, a dual mode high/low-power near/far-field rectenna is demonstrated for the first time based on a flexible rectifier and a textile antenna. Based on a high-efficiency single-series rectifier, the far-field rectenna achieves a peak efficiency of 42.7% from an ultra low power density of 0.43 μW/cm2, with a 1 V DC output from4 μW/cm2. A high-power 6.78 MHz bridge rectifier is designed and implemented on a flexible textile-based substrate with a10 dB return loss for inputs above 15 dBm. As a near-field receiver, the antenna could receive 3.75 W DC power at 5 cm from the transmitting coil, with an end-to-end efficiency of 30%inclusive of rectifier, coils, and power amplifier losses. Based on the proposed dual-mode antenna, textile-based wearables could be wirelessly powered dynamically using resonant near-field and radiative near-field WPT.

While millimeter-wave (mmWave) technologies are often associated with costly applications using large arrays, several inexpensive implementations promise mmWave connectivity closer to the user in Body Area Networks (BANs) applications. Here, we evaluate the potential for multi-mode mmWave links for information and power transfer applications. The co-existence of off-body radiative and on-body wave-guiding mechanisms is experimentally investigated based on state-of-the-art transmission lines and antennas. First, a body-to-body link with at least -50 dB channel gain is demonstrated based on wide-beam microstrip and reflector-backed broadband antennas. Co-existence is then studied experimentally by measuring the coupling between the off-body communication/power transfer antenna and a wearable Single Wire Transmission Line (SWTL), with an ultra-low on-body attenuation of below -0.8 dB/cm around 28 GHz. Less than -40 dB coupling is demonstrated for clearances as low as 1 cm between the antenna and SWTL. The measured results indicate that co-located textile-based antennas and transmission lines can enable multi-mode high-performance body-centric mmWave networks, and highlight the need for interference-countering mechanisms in future high-density BANs.

There has been significant innovation in the domain of Internet of Things (IoT) as nowadays wireless data transmission is playing an essential role in various organizations like agriculture, defence, transportation, etc. Batteries are the most common option to power wireless devices. However, using batteries to power IoT devices has drawbacks including the cost and disruption of frequent battery replacement, and environmental concerns about battery disposal. Solar energy harvesting is a promising solution for long-term operation applications. However, solar energy harvesting varies drastically over location and time. Due to fluctuating weather conditions and the environmental effects on PV surface condition, output could be reduced and become insufficient. Environmental conditions including temperature, wind, solar irradiance, humidity, tilt angle and the dust accumulated over time on the photovoltaic (PV) module surface affects the amount of energy harvested. To address this issue, a novel solution is required to autonomously predict the harvested energy and plan the IoT device tasks accordingly, to enhance its performance and lifetime. Using Machine Learning (ML) algorithms could make it possible to predict how much energy can be harvested using weather forecast data. This research is ongoing, and aims to apply ML algorithms on historical weather data including environmental factors to generate solar energy predictions for IoT device energy budget planning.

Textile-based antennas are typically realized using conductive fabrics adhered to thick non-woven fabrics such as felt, which are not suited for additive manufacturing due to their roughness. This paper presents screen printing on thin and breathable polyurethane films as a method for realizing e-textile antennas without altering the feel of the fabric, demonstrated through a microstrip antenna on standard felt fabric. The fabricated proximity-coupled patch maintains at least 100 MHz (4\%) bandwidth from 2.46 to 2.56~GHz regardless of bending and human proximity, 6.6~dBi measured gain, and 69\% radiation efficiency. The robustness of the proposed antenna is demonstrated, for the first time, through the measured radiation properties, showing that the antenna maintains its peak gain and radiation patterns after more than 10,000 bending cycles.

The broad spectrum available at millimeter-wave (mmWave) bands has attracted significant interest for a breadth of applications, with 5G communications being the main commercial drive for mmWave networks. Wireless power transmission and harvesting at mmWave bands have attracted significant attention due to the potential for minimizing the harvesting antenna size, allowing for more compact rectennas. For a fixed antenna size, the received power increases with frequency. Nevertheless, several challenges lie in realizing high efficiency antennas and rectifiers at mmWave bands. This paper reviews the recent advances in mmWave rectenna design at a component- and system-level. Low-cost antennas and components for mmWave power harvesting, such as high efficiency scalable rectifiers on polymers and high radiation efficiency antennas on textiles, are reviewed. Both the antenna and rectifier can be realized using low-cost fabrication methods such as additively-manufactured circuits and packages, in addition to digital integrated circuits (ICs) for the rectifiers. Finally, this paper provides an overview of future antenna design challenges and research directions for mmWave power harvesting.

Wireless power transfer (WPT) and Radio Frequency (RF) energy harvesting (EH) are increasingly seen as an enabling technology for power-autonomous Internet of Things (IoT) [1, 2]. RFEH and WPT are a particularly attractive power source for flexible, printed, and e-textile systems due to their compatibility with standard fabrication processes, abolishing the need for specific materials and transducers. This work provides an overview on flexible WPT at multiple frequencies (6.78 MHz to 26 GHz) and techniques from near-field WPT to Millimetre-wave WPT and RFEH.