The current research is dedicated to the experimental study of wireless power transfer and RF-to-DC conversion efficiency using waveforms with a high Peak-to-Average Power Ratio (PAPR). Three devices: a classical voltage doubler circuits with and without matching network and a commercially available energy harvesting device - Powercast P2110B are selected for the study. The use of a software-defined radio (SDR) for generation of sub-GHz signals allows to achieve high accuracy and customization of waveforms. The analysis of RF-to-DC conversion efficiency is based on the results of measurements of the input average power and DC voltage in laboratory conditions. The impact of the PAPR level and input average power level on the RF-to-DC conversion efficiency is investigated. Moreover, the results of RF-to-DC conversion for high PAPR signals are compared to the case when a low PAPR single-carrier waveform is used.

Possibilities of far field wireless power transfer (WPT) for creation of energy autonomous sensor nodes employing LoRaWAN technology for radio communications are explored in this study. WPT experiments were performed using continuous wave signal generator followed by amplifier at the transmitter side and RF-DC converters with different parameters at the receiver side. Two pairs of antennas with different gain and directivity were used. According to the experimental results it is possible to accumulate sufficient electrical energy to perform data transmissions at regular time intervals of several seconds. However, the energy requirements of sensor node depend strongly on operation mode of LoRa communication module together with supplementary circuit. Therefore, careful configuration of sensor nodes is required to achieve acceptable performance of wireless sensor network (WSN). Because of specific propagation of electromagnetic radiation in indoor environment there are locations with minimum available power even close to the transmitter. Consequently, installation of sensor nodes in closed areas requires knowledge of electromagnetic field distribution around transmitter.

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%.

This paper is dedicated to the experimental study of the impact of multi-tone signal with a high peak-to-average power ratio (PAPR) on the performance of wireless power transfer (WPT) using a single stage Cockcroft-Walton voltage multiplier with HSMS-285C diodes. The study is done using unlicensed sub-GHz frequencies 863 - 868 MHz in a laboratory under real-life conditions. Two types of design of radio frequency (RF) energy harvesting device (with and without matching network) are used to demonstrate PAPR impact on WPT performance. Eight sub-carriers summed in-phase are used to produce a multi-tone signal with a high PAPR level. For WPT results comparison, a single-tone signal with the same average power is exploited. For the experimental implementation of WPT, pairs of directional (LP0410 Log Periodic PCB) and omnidirectional (VERT900) antennas are used. Moreover, during the experiments the distance between transmitting and receiving antennas is being changed up to 3.2m. The main objective of the experiment is to find conditions when multi-tone signal with a high PAPR provides substantially higher output power compared to single-tone signal. The experimental measurement process includes evaluating the average power at the RF rectifier circuit output for different signals, distances, antennas, and RF-DC converter circuit designs. Furthermore, an additional WPT experiment is performed and the analysis of channel characteristics in the frequency range of interest is done to investigate the reason of the difference between the harvested power using single-tone and multi-tone signals.

This paper presents a chaotic communication system based on a modified Chua’s circuit. The proposed system can be classified as chaos shift keying (CSK) based on chaotic synchronization phenomena. The mathematical model of the modified Chua’s circuit is based on a system of four differential equations. A linear feedback is used for chaotic synchronization implementation. One driving chaotic oscillator in the transmitter and two responding oscillators in the receiver are employed for data transmission. The paper presents not only the concept of a new chaotic communication system but also addresses the stability of the chaotic synchronization with different initial conditions in responding and driving chaotic oscillators. To validate the proposed concept of the advanced CSK system, simulation in MATLAB/Simulink environment is employed.

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.