The paper presents a computationally efficient and accurate numerical approach to evaluating RF–DC power conversion efficiency (PCE) for energy harvesting circuits in the case of multi-tone power-carrying signal with periodic envelopes. This type of signal has recently received considerable attention in the literature. It has been shown that their use may result in a higher PCE than the conventional sine wave signal for low to medium input power levels. This reason motivated the authors to develop a fast and accurate two-frequency harmonic balance method (2F-HB), as fast PCE calculation might appreciably expedite the converter circuit optimization process. In order to demonstrate the computational efficiency of the 2F-HB, a comparative study is performed. The results of this study show that the 2F-HB significantly outperforms such extensively used methods as the transient analysis (TA), the harmonic balance method (HB), and the multidimensional harmonic balance method (MHB). The method also outperforms the commercially available non-linear circuit simulator Keysight ADS employing both HB and MHB. Furthermore, the proposed method can be readily integrated into commonly used commercially available non-linear circuit simulation software, including the Keysight ADS, Ansys HFSS, just to name a few—minor modifications are required. In addition, to increase the correctness and reliability of the proposed method, the influence of PCB is considered by calculating Y parameters of its 3D model. The widely employed voltage doubler-based RF–DC converter for energy harvesting and wireless power transfer (WPT) in sub-GHz diapason is chosen to validate the proposed method experimentally. This RF–DC converter is chosen for its simplicity and capability to provide sufficiently high PCE. The measurements of the PCE for a voltage doubler prototype employing different multi-tone waveform signals were performed in laboratory conditions. Various combinations of the matching circuit element values were considered to find the optimal one in both—theoretical model and experimental prototype. The measured PCE is in very good agreement with the PCE calculated numerically, which attests to the validity of the proposed approach. The proposed PCE estimation method is not limited to one selected RF–DC conversion circuit and can also be applied to other circuits and frequency bands. The comparison of the PCE obtained by means of the proposed approach and the measured one shows very good agreement between them. The PCE estimation error reaches as low as 0.37%, and the maximal estimation error is 32.65%.

With the rapid development of the Internet of Things (IoT) and wireless sensor networks (WSN), the modern world requires advanced solutions for the wireless powering of low-power autonomous devices. The present study addresses the wireless power transfer (WPT) efficiency problem by exploiting a multi-hop concept-based technique to increase the received power at the end sensor node (ESN). The current work adopts efficient multi-hop technology from the communications field to examine its impact on WPT performance. The investigation involves power transfer modeling and experimental measurements in a sub-GHz frequency range, chosen for being capable of providing a greater distance to transmit power. The paper proposes a multi-hop (MH) WPT concept based on signal amplification and demonstrates the fabricated multi-hop node (MHN) prototype. The experimental verification of the MHN is performed in the laboratory environment. The present paper examines two WPT scenarios: line-of-sight (LoS) and non-line-of-sight (NLoS). The turn-on angle of 90 degrees on MHN is used for the NLoS case. The received power and RF-DC converted voltage on the ESN are measured for all investigated scenarios. Moreover, the paper proposes an efficient simulation approach for the performance evaluation of MH WPT technology, providing an opportunity to analyze and optimize wireless sensor nodes’ spatial distribution to increase the received power.

This paper is devoted to studying multi-hop wireless power transfer (WPT), which is especially applicable in autonomous wireless sensor networks. The main objective of the current work is to investigate the possibility of increasing the efficiency of WPT using a multi-hop transmission approach. The study describes the main limitations of the multi-hop RF energy transmission, analyses the possible technical solution of a multi-hop sensor node, and evaluates the performance of multi-hop WPT compared to the classical technique. The research combines RF signal transmission simulations and experimental studies. Multi-hop WPT analysis is made for the sub-GHz frequency band and two wireless nodes. Friis approximation of point-to-point signal propagation is used for simulating the multi-hop energy transmission in free space, while the method of Shooting and Bouncing Ray is used for multichannel propagation simulation. Current work expands the WPT applications by providing an approach to increase the distance of RF energy transmission for the wireless sensor nodes in the areas with lower coverage.

This research is devoted to an experimental study on radiofrequency (RF) wireless power transfer (WPT) employing multi-hop technology. A special multi-hop node (MHN) that uses GHz radio waves has been developed for the study. The multi-hop node design is based on Yagi-Uda antennas, a voltage doubler-based RF-DC converter, a two-stage amplifier and a capacitor for energy storage. The experimental study is performed in laboratory conditions emulating a real-life environment with line-of-sight propagation with 27 dBm transmitted power and a 3.8-6.5 m distance range. The experimental setup comprises a transmitter, a multi-hop node, an edge node equipped with a voltage-doubler-based RF-DC converter, as well as measurement equipment. The wireless power transfer efficiency measurements for direct (without the multi-hop node) power transfer scenarios are also performed to evaluate the efficiency of the multi-hop-based WPT. The edge node received averaged power in both cases and RF-DC converted voltage is measured and analyzed.

This paper reports the results of an experimental study of simultaneous information and power transfer using frequency modulated signal. The research is done in two phases: the first one is RF-DC conversion efficiency study, the second one - WPT performance study, where the impact of the distance between the receiving and transmitting antennas, as well as the type of antenna on the efficiency of wireless power transfer is examined. Two transmit/receive scenarios were considered: with omnidirectional and log-periodic antennas to ascertain how the antenna radiation pattern affects the efficiency of the entire system. In all scenarios, the wireless power transfer system employs identical receiving and transmitting antennas. The power of the incoming electromagnetic wave received by the receiving antenna is converted to DC utilizing a simple Schottky diode voltage doubler-based RF-DC converter.

The goal of this study is to investigate the impact of waveforms on the RF-DC power conversion efficiency for several designs of energy harvesting circuits, as the RF -DC conversion is a crucial part of the RF wireless power transfer (WPT). The efficiency of two simplest and most commonly used energy harvesting circuit topologies, namely, a voltage doubler and single diode rectifier is analyzed. Both considered topologies include matching networks designed for the sub gigahertz frequency band 863–865 MHz. The impact of different powering signal waveforms including a sine wave, and multi-tone signals with different values of peak-to-average power ratio (P APR) on the circuit is examined. The analysis of the single diode rectifier is performed by means of a fast theoretical model exploiting a two dimensional version of the well-established Harmonic Balance method. The results obtained using the model are verified experimentally. Additionally, the PCE obtained for the single diode rectifier is compared with the measured one of the voltage doubler circuit, to find the most optimal signal and circuit combinations.