Maximum RF-DC Conversion Efficiency Research Articles

Investigation of a Circularly Polarized Metasurface Antenna for Hybrid Wireless Applications.

The increasing prevalence of the Internet of Things (IoT) as the primary networking infrastructure in a future society, driven by a strong focus on sustainability and data, is noteworthy. A significant concern associated with the widespread use of Internet of Things (IoT) devices is the insufficient availability of viable strategies for effectively sustaining their power supply and ensuring their uninterrupted functionality. The ability of RF energy-harvesting systems to externally replenish batteries serves as a primary driver for the development of these technologies. To effectively mitigate concerns related to wireless technology, it is imperative to adhere strictly to the mandated limitations on electromagnetic field emissions. A TA broadband polarization-reconfigurable Y-shaped monopole antenna that is improved with a SADEA-tuned smart metasurface is one technique that has been proposed in order to accomplish this goal. A Y-shaped printed monopole antenna is first taken into consideration. To comprehend the process of polarization reconfigurability transitioning from linear to circular polarization (CP), a BAR 50-02 V RF PIN Diode is employed to shorten one of the parasitic conducting strips to the ground plane. A SADEA-driven metasurface, which utilizes the artificial intelligence-driven surrogate model-assisted differential evolution for antenna synthesis, is devised and positioned beneath the radiator to optimize performance trade-offs while increasing the antenna's gain and bandwidth. The ultimate prototype achieves the following: an impedance bandwidth of 2.58 GHz (3.27-5.85 GHz, 48.45%); an axial bandwidth of 1.25 GHz (4.19-5.44 GHz, 25.96%); a peak gain exceeding 8.45 dBic; and when a highly efficient rectifier is integrated, the maximum RF-DC conversion efficiency of 73.82% and DC output of 5.44 V are obtained. Based on the results mentioned earlier, it is considered appropriate to supply power to intelligent sensors and reduce reliance on batteries via RF energy-harvesting mechanisms implemented in hybrid wireless applications.

A compact hybrid solar and electromagnetic energy harvester at 2.45 GHz microstrip rectenna

This paper presents a compact rectenna integrated with a packaged solar cell to convert a hybrid (solar + electromagnetic) energy to DC energy. The packaged solar cell used as the substrate is sandwiched between a meshed patch and a rectifying circuit. Based on particle swarm algorithm, the meshed patch with high transparency (96.2 % transmittance) is mounted on the surface of the solar cell. By using a copper rod, the high-efficient rectifying circuit is connected with the meshed patch through the solar cell. Due to the high-integrated hybrid energy harvester, the solar and radio frequency (RF) energies can be absorbed and converted to DC power separately or simultaneously. The measured maximum RF-DC conversion efficiency of the rectenna acquires 73 % under the input power of the antenna of 17 dBm, and the maximum DC power of 60.6 mW is generated when the solar cell is illuminated with standard global AM1.5 illumination conditions. The measured DC combining efficiency of 96.8 % is achieved from the hybrid solar rectenna, with the optimal load of 400 Ω. Furthermore, the design method is extended to harvesting ambient electromagnetic energy, and a low-power rectifying circuit with conversion efficiency of 59.6 % at input power of −10 dBm is designed.

Optimal Power Splitting of Wireless Information and Power Transmission Using a Novel Dual-Channel Rectenna

Traditionally, the signal power is divided equally between dual functions in wireless information and power transmission (WIPT), which, intuitively, is not an optimal solution since the power sensitivities for communication and charging node pose different constraints for signals. To address this challenge, a two-channel rectenna with an asymmetrical coupler feeding network (ACFN) has been proposed for WIPT under the power-splitting and time-sharing (PS and TS) schemes. The proposed two-port rectenna consists of a receiving antenna integrated with ACFN where one output port is connected to a rectifying circuit, whereas the other is used for information recovery. Different from the conventional PS scheme with equal division, the proposed rectenna can adjust ratios of power at two outputs. That is, routing high power to the radio frequency (RF)-dc port, and transferring low power but of a sufficient signal-to-noise-ratio (SNR) to the port being used for signal demodulation/decoding. As a result, the simulated/measured maximum RF-dc conversion efficiency of the rectenna can reach up to 73.9%/70.4% for quadrature phase shift keying (QPSK) modulated signals and 63.9%/60.7% for continuous wave (CW) signals. In addition, good isolation between the two output ports ensures low interference against information decoding.

Multiband Ambient RF Energy Harvester with High Gain Wideband Circularly Polarized Antenna toward Self-Powered Wireless Sensors.

In this work toward a sustainable operation of a self-powered wireless sensor, we investigated a multiband Wi-Fi/3G/4G/5G energy harvester based on a novel wideband circularly polarized antenna, a quadplexer, and rectifiers at four corresponding bands. This proposed antenna consisted of four sequentially rotated dual-dipoles, fed by a hybrid feeding network with equal amplitude and an incremental 90° phase delay. The feeding network was composed of three Wilkinson power dividers and Schiffman phase shifters. Based on the sequential rotation method, the antenna obtained a −10 dB reflection coefficient bandwidth of 71.2% from 1.4 GHz to 2.95 GHz and a 3 dB axial ratio (AR) bandwidth of 63.6%, from 1.5 GHz to 2.9 GHz. In addition, this antenna gain was higher than 6 dBi in a wide bandwidth from 1.65 GHz to 2.8 GHz, whereas the peak gain was 9.9 dBi. The quad-band rectifier yielded the maximum AC–DC conversion efficiency of 1.8 GHz and was 60% at −1 dBm input power, 2.1 GHz was 55% at 0 dBm, 2.45 GHz was 55% at −1 dBm, and 2.6 GHz was 54% at 0.5 dBm, respectively. The maximum RF–DC conversion efficiency using the wideband circularly polarized antenna was 27%, 26%, 25.5%, and 27.5% at −6 dBm of input power, respectively.

Metamaterial-Integrated High-Gain Rectenna for RF Sensing and Energy Harvesting Applications.

This paper presents a metamaterial (MTM)-integrated high-gain rectenna for RF sensing and energy harvesting applications that operates at 2.45 GHz, an industry, science, medicine (ISM) band. The novel MTM superstrate approach with a three-layered integration method is firstly introduced for rectenna applications. The integrated rectenna consists of three layers, where the first layer is an MTM superstrate consisting of four-by-four MTM unit cell arrays, the second layer a patch antenna, and the third layer a rectifier circuit. By integrating the MTM superstrate on top of the patch antenna, the gain of the antenna is enhanced, owing to its beam focusing capability of the MTM superstrate. This induces the increase of the captured RF power at the rectifier input, resulting in high-output DC power and high entire end-to-end efficiency. A parametric analysis is performed in order to optimize the near-zero property of the MTM unit cell. In addition, the effects of the number of MTM unit cells on the performance of the integrated rectenna are studied. A prototype MTM-integrated rectenna, which is designed on an RO5880 substrate, is fabricated and characterized. The measured gain of the MTM-integrated rectenna is 11.87 dB. It shows a gain improvement of 6.12 dB compared to a counterpart patch antenna without an MTM superstrate and a maximum RF–DC conversion efficiency of 78.9% at an input RF power of 9 dBm. This results in the improvement of the RF–DC efficiency from 39.2% to 78.9% and the increase of the output DC power from 0.7 mW to 6.27 mW (a factor of 8.96 improvements). The demonstrated MTM-integrated rectenna has shown outstanding performance compared to other previously reported work. We emphasize that the demonstrated MTM-integrated rectenna has a low design complexity compared with other work, as the MTM superstrate layer is integrated on top of the simple patch antenna and rectifier circuit. In addition, the number of MTM units can be determined depending on applications. It is highly envisioned that the demonstrated MTM-integrated rectenna will provide new possibilities for practical energy harvesting applications with improved antenna gain and efficiency in various IoT environments.

Second Harmonic Exploitation for High-Efficiency Wireless Power Transfer Using Duplexing Rectenna

In this article, a novel duplexing rectenna with harmonic feedback capability is proposed for efficient wireless power transfer (WPT) applications. The proposed duplexing rectenna can harvest the incoming radio frequency (RF) energy efficiently and also make use of an inherent harmonic signal, which is sent back to the RF transmitter (Tx) for positioning in order to guide the radiation patterns from Tx antenna array for optimum WPT. A novel duplexing dipole antenna is designed based on the top loading and capacitive gap effects. It is used to receive RF power at fundamental frequency 0.915 GHz and transmit the second harmonic signals at 1.83 GHz as a feedback. Experimental validation of a complete WPT system with beam-scanning capability has been carried out. It is shown that the fabricated rectifier has realized a maximum RF-dc conversion efficiency of 71% (at 15-dBm input power) and a measured peak second harmonic power of −1 dBm. Thus, the proposed duplexing rectenna can form a closed-loop system by providing its location information for efficient WPT applications.

A Novel Class-C Rectifier With High Efficiency for Wireless Power Transmission

In this letter, a compact Class-C rectifier with high efficiency based on a novel structure was proposed for wireless power transmission (WPT). This structure is connected to the rectifying diode in parallel. It presents infinite impedance at the output port at the fundamental frequency for impedance matching and zero impedance at the high harmonic frequencies. An open-end 12th wavelength microstrip line and a short-end quarter wavelength microstrip line are applied in this design. For fabricated, a radio frequency (RF) rectifier operating at 2.45 GHz was designed and tested. The measurement results show that the maximum RF-dc conversion efficiency is 82.7% at 25 dBm. Moreover, the proposed rectifier is compact with the size of 0.35λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> × 0.13λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> .

A Compact High-Efficiency Rectifier With a Simple Harmonic Suppression Structure

In this letter, a compact high-efficiency radio frequency (RF) rectifier based on a series harmonic suppression structure is proposed for wireless power transmission (WPT). The proposed structure removes the cascading bandpass between the RF source and the diode, and the dc-pass filter between the diode and the dc load, simultaneously. The harmonic suppression structure consists only of a short-ended eighth-wavelength microstrip line, which shows an inductive impedance to compensate the rectifying diode's capacitive impedance at fundamental frequency and changes to open circuit to reflect the second harmonic for rectifying again. Two Schottky diodes are used in this design for voltage-doubling rectifying. For fabrication, a rectifier operating at 2.45 GHz was designed, fabricated, and tested. The measurement results show that the maximum RF-dc conversion efficiency is over 80% at 25 dBm. Meanwhile, the fabricated rectifying is compact with 20 mm $\times \,\,{5}$ mm.

Highly Efficient 2.4 and 5.8 GHz Dual-Band Rectenna for Energy Harvesting Applications

In this letter, highly efficient dual-band rectenna at 2.4 and 5.8 GHz for energy harvesting is presented. A new sickle-shaped antenna is designed to operate at both frequencies. Rectenna shows the maximum RF–DC conversion efficiency of 63% and 54.8% at 2.4 and 5.8 GHz, respectively. The impact of matching network and output filter on RF–DC conversion efficiency at both frequencies is analyzed. The output dc voltage of 3 and 2.6 V is measured for 2.4 and 5.8 GHz correspondingly at a 600 Ω load resistance. The rectenna can be utilized for various low-power applications.

High-Efficiency Broadband Rectifier With Wide Ranges of Input Power and Output Load Based on Branch-Line Coupler

In this work, a novel rectifier based on a branch-line coupler is proposed to operate within wide ranges of input power, operating frequency and output load. In the proposed topology, two output ports of the coupler are connected with two identical sub-rectifiers and the isolation port is directly connected to the ground. The input impedance of the two sub-rectifiers varies with different input power, operating frequency and output load, which leads to impedance mismatching. By using the branch-line coupler with grounded isolation port, the power reflected from the two sub-rectifiers can be partially re-injected back to the sub-rectifiers. Thus, the power can be reused and the RF-dc conversion efficiency can be improved. Theoretical analysis and performance comparison are carried out. The results indicate that the proposed topology is able to realize high efficiency with wide input power, frequency and load dynamic ranges. For validation, a rectifier working at 2.45 GHz is designed. The fabricated rectifier circuit demonstrates a maximum RF-dc conversion efficiency of 80.8%. The measured efficiency remains over 70% with the input power from 10 dBm to 18.6 dBm and the operating frequency from 2.08 to 2.58 GHz.

Development of 24GHz Rectenna for Receiving and Rectifying Modulated Waves

In this paper, we show experimental results of RF-DC conversion with modulated 24GHz waves. We have already developed class-F MMIC rectenna with resonators for higher harmonics at no modulated 24GHz microwave for RF energy transfer. Dimensions of the MMIC rectifying circuit is 1 mm × 3 mm on GaAs. Maximum RF-DC conversion efficiency is measured 47.9% for a 210 mW microwave input of 24 GHz with a 120 Ω load. The class-F rectenna is based on a single shunt full-wave rectifier. For future application of a simultaneous energy and information transfer system or an energy harvesting from broadcasting waves, input microwave will be modulated. In this paper, we show an experimental result of RF-DC conversion of the class-F rectenna with 24GHz waves modulated by 16QAM as 1st modulation and OFDM as 2nd modulation.

5.8-GHz Integrated Differential Rectenna Unit Using Both-Sided MIC Technology With Design Flexibility

A 5.8-GHz integrated differential rectifying antenna (rectenna) unit with design flexibility is proposed, and its performance is confirmed experimentally. It positively uses both-sided microwave integrated circuit (MIC) technology, and its antenna feed circuit includes filters which suppress 2nd harmonic. This proposed rectenna unit is a very simple, compact and novel configuration. It operates in a differential mode, and effectively integrates an antenna array with a rectifying circuit. Its configuration provides the pragmatically advantages such as antenna array design flexibility and rectenna unit extensibility. Herein, the behavior of the rectenna unit was successfully confirmed under low radio frequency (RF) power density. Maximum RF-DC conversion efficiency at 5.8 GHz of Industry-Science-Medical (ISM) band was approximately 27% with the load resistance of 390 Ω when the received power density (PD) was 0.031 W/m2.

Design of high efficiency RF-DC conversion circuit using novel termination networks for RF energy harvesting system

In this letter, a high efficiency RF-DC conversion circuit for RF energy harvesting system (EHS) is proposed.The proposed circuit consists of Villard voltage doubler, the input and output termination networks which can suppress the unwanted RF signals produced by Schottky diodes. The fabricated circuit operating at 2.45 GHz has a maximum RF-DC conversion efficiency of 83.37% and output voltage of 11.30 V at an input RF power of 140 mW. The proposed circuit has an advantage of simple design which helps to reduce the design cost of EHSs. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2330–2335, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27087