Radio frequency (RF) energy harvesting and wireless power transmission (WPT) technologies —both near-field and far-field—have attracted significant interest for wireless applications and RFID systems. We already utilize near-field WPT products in our life and it is expected that RF EH and far-field WPT systems can drive the future low-power wireless systems. In this article, we initially present a brief historical overview of these technologies. The main technical challenges of rectennas and WPT transmitters are discussed. Furthermore, this paper presents the recent advances on the development of these technologies, including the possibility of powering RFID systems through the millimeter wave power from 5G networks, the trends in flexible rectennas design and the technological developments on the simultaneous wireless information and power transfer (SWIPT).

This paper presents a holistic and authoritative review of the role of microwave technologies in enabling a new generation of wearable devices. A human-centric Internet of Things (IoT) covering remote healthcare, distributed sensing, and consumer electronics, calls for high-performance wearable devices integrated into clothing, which require interdisciplinary research efforts to emerge. Microwaves, the “interconnect” of wireless networks, can enable, rather than solely connect, the next generation of autonomous, sustainable, and wearable-friendly electronics. First, enabling technologies including wireless power transmission and RF energy harvesting, backscattering and passive communication, RFID, and electromagnetic sensing are reviewed. We then discuss the key integration platforms, covering smart fabrics and electronic textiles, additive manufacturing, printed electronics, natively-flexible and organic RF semiconductors, and fully-integrated CMOS systems, where opportunities for hybrid integration are highlighted. The emerging research trends, from mmWave 6G, RF sensing and imaging, to healthcare applications including neural implants, drug delivery, and safety upon exposure to microwaves are re-visited and discussed, presenting a future roadmap for interdisciplinary research towards sustainable and reliable next-generation wearables.

In this work, a flexible and extensive digital platform for Smart Homes is presented, exploiting the most advanced technologies of the Internet of Things, such as Radio Frequency Identification, wearable electronics, Wireless Sensor Networks, and Artificial Intelligence. Thus, the main novelty of the paper is the system-level description of the platform flexibility allowing the interoperability of different smart devices. This research was developed within the framework of the operative project HABITAT (Home Assistance Based on the Internet of Things for the Autonomy of Everybody), aiming at developing smart devices to support elderly people both in their own houses and in retirement homes, and embedding them in everyday life objects, thus reducing the expenses for healthcare due to the lower need for personal assistance, and providing a better life quality to the elderly users.

In this article, we describe a customized 2.45-GHz radio frequency identification (RFID) reader designed to simultaneously perform 3-D tracking of multiple tagged entities (objects or people), static or dynamic, in harsh electromagnetic indoor environments. This is obtained by a bi-dimensional electronic beam-steering, implementing the monopulse radar concept simultaneously in the elevation and azimuth directions, with tags-reader distance estimation based on received signal strength indicator (RSSI) measurements. Experimental results show that the system is able to perform a tri-dimensional scanning of a monitored room with decimeter-accuracy over the three reference axes. The RF front end is designed to be lightweight, thin, and compact in such a way that it is portable and embeddable in domestic objects. For this purpose, a multi-layer solution is adopted with a 2-D patch antenna array aperture coupled with the RF front end. 3-D localization data are computed onboard by means of a seamless connection of the RF front end with a low-power microcontroller, which is able to store tags 3-D localization data over a multi-hour time frame. A useful method to remotely control the whole system is presented, using a Raspberry Pi 3B, directly connecting the reader with a flexible and extensive digital platform for Smart Homes. The presented architecture is experimentally demonstrated to perform a reliable fall detection of tagged people in indoor environments.

This paper discusses the electromagnetic compatibility and interference aspects related to wireless power transfer (WPT) systems for wearable and implantable devices. The cases of a near-field (reactive) link for recharging a pacemaker and a far-field (radiative) link for wearable devices are considered. For the first case a design approach, able to perform efficient energy transfer under the safety regulations constraints of medical devices is proposed. In the second case, a rigorous methodology is proposed to predict the transferred energy to a worn device able to account for interferences due to the human body or any other wireless system located close to the worn device. An implementation of grounded worn rectennas in the presence of unconventional radio channels is presented.

This work proposes the design and implementation of a wearable rectifying filtenna (filtering antenna) which is activated and powered wirelessly, to detect the presence of ethanol solutions. The system is implemented on a Rogers RT/Duroid 5880 substrate ( $\varepsilon _{r} =2.2$ and thickness: 0.508 mm), whose flexibility facilitates the system wearability. The fluid detection is performed by a resonant stub embedding a microfluidic channel on its end, which resonates as an open circuit at 2.45 GHz when the channel is filled with the ethanol solution and undergoes a dramatic shift on its input impedance behavior when the channel is filled with water or when it is empty. The system is powered wirelessly by means of a 2.45-GHz narrowband antenna, and the frequency selection is performed by a second-order open-end coupled-line filter whose one end is loaded with the resonant stub. The filtenna RF signal is transduced by a full-wave rectifier exploiting low-threshold voltage diodes, and fluid detection is read out through different values of dc-output voltages, allowing an immediate response. The system is designed and optimized by means of full-wave/nonlinear co-simulations and the realized prototype is measured to confirm a safe detection of the tested solution.