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 article presents the deployment and experimentation architecture of the Aveiro Tech City Living Lab (ATCLL) in Aveiro, Portugal. This platform comprises a large number of Internet-of-things (IoT) devices with communication, sensing and computing capabilities. The communication infrastructure, built on fiber and Millimeter-wave (mmWave) links, integrates a communication network with radio terminals (WiFi, ITS-G5, C-V2X, 5G and LoRa(WAN)), multiprotocol, spread throughout 44 connected points of access in the city. Additionally, public transportation has also been equipped with communication and sensing units. All these points combine and interconnect a set of sensors, such as mobility (radars, light detection and rangings (LiDARs), video cameras) and environmental sensors. Combining edge computing and cloud management to deploy the services and manage the platform, and a data platform to gather and process the data, the living lab supports a wide range of services and applications: IoT, intelligent transport systems (ITSs) and assisted driving, environmental monitoring, emergency and safety, among others. This article describes the architecture, implementation and deployment to make the overall platform to work and integrate researchers and citizens. Moreover, it showcases some examples of the performance metrics achieved in the city infrastructure, the data that can be collected, visualized and used to build services and applications to the cities, and, finally, different use cases in the mobility and safety scenarios.

In this article, it is provided a comprehensive survey on the most relevant research in the area of detection, classification and location of partial discharge (PD) sources using the radiometric or ultra high frequency (UHF) method, focusing mainly on the works related to the use of antennas. To the best of the authors knowledge, this is the first review paper that focuses on the application of antennas based on UHF method in the complete diagnosis of PD. Specifically, it is first presented the main contributions to the development and optimization of UHF sensors for application in the detection of PD sources. Second, articles that used the UHF method to identify different types of PD in high voltage equipment are described. Finally, the main contributions regarding the location of sources of defects using the radiometric method are presented. Summary of works in the area of UHF detection sensors, PD classification and PD location, with their respective contributions, are shown. Finally, research trends, challenging and open issues are discussed. The purpose of this article is to provide important information about the complete diagnosis of PD, which could be used to guide the development of more efficient techniques in this research area.

Real-time frequency agility is one of the key limitations of current all-digital transmitters (ADTs). In this paper, to address this problem, an ADT based on direct-RF generation is proposed and implemented in a field-programmable gate array (FPGA). To achieve this, the pulse encoding is performed after the digital upconversion, which presents challenges in the pulse encoder implementation. However, the proposed design considerably improves the frequency agility when compared with current state-of-the-art approaches. Two different pulse encoders were designed in this paper, one is based on pulsewidth modulation (PWM) and the other on delta-sigma modulation (ΔΣM). These units are implemented with high parallelization to achieve the required equivalent sampling rates. The proposed design enables the implementation of all-digital RF transmitters in FPGA with a widely tunable carrier frequency. In this paper, a variation from 0.1 up to 6 GHz of carrier frequency, with a maximum frequency resolution of 1.5625 MHz, is demonstrated. Measurement results in terms of signal-to-noise ratio (SNR) and error-vector magnitude are presented and discussed. In the case of the PWM, maximum SNRs of 39 and 36 dB were obtained for a 5 and 10 MBd of symbol rates (SRs). In the case of ΔΣM, maximum SNRs of 38 and 35 dB were obtained for 20 and 40 MBd of the SR.

Passive RF identification (RFID) readers transmit a continuous wave (CW) powering signal to remotely power up batteryless transponders, while simultaneously receiving a backscattered signal at the same frequency [1]. To separate the transmitter and receiver paths, readers use either a bistatic or monostatic antenna configuration. The first configuration employs two separate antennas, one to transmit and one to receive; in the second, the transmitter and receiver share a common antenna by means of a coupler or circulator. Both cases, however, suffer from poor transmitter-to-receiver isolation: strong CW signals can leak into the receiver, degrading its sensitivity to the weak transponder backscattered signals. Receiver sensitivity degradation occurs due to the leaked local oscillator (LO) phase noise [1] and also to the saturation of the front end caused by strong CW leakage. This requires high-dynamic-range capability in the RF stage [the low-noise amplifier (LNA) and mixer] as well as in the baseband stage [the amplifiers and analog-to-digital converters (ADCs)].