RF energy harvesters for wireless sensors, state of the art, future prospects and challenges: a review

The power consumption of portable gadgets, implantable medical devices (IMDs) and wireless sensor nodes (WSNs) has reduced significantly with the ongoing progression in low-power electronics and the swift advancement in nano and microfabrication. Energy harvesting techniques that extract and convert ambient energy into electrical power have been favored to operate such low-power devices as an alternative to batteries. Due to the expanded availability of radio frequency (RF) energy residue in the surroundings, radio frequency energy harvesters (RFEHs) for low-power devices have garnered notable attention in recent times. This work establishes a review study of RFEHs developed for the utilization of low-power devices. From the modest single band to the complex multiband circuitry, the work reviews state of the art of required circuitry for RFEH that contains a receiving antenna, impedance matching circuit, and an AC-DC rectifier. Furthermore, the advantages and disadvantages associated with various circuit architectures are comprehensively discussed. Moreover, the reported receiving antenna, impedance matching circuit, and an AC-DC rectifier are also compared to draw conclusions towards their implementations in RFEHs for sensors and biomedical devices applications

Architecture of an efficient dual band 1.8/2.5 GHz rectenna for RF energy harvesting

This paper presents a highly efficient rectenna of RF energy harvesting systems operating at 1.8 GHz and 2.5 GHz bands for battery-less sensor application. The antenna is designed by CST-MWS. The Schottky diode used for rectifying circuit is HSMS 286B in which designed by Agilent ADS. The key finding of the paper is that the simulated DC output voltage of the rectenna is 1.35 V for low input power of -25 dBm at a high resistance load of 1M Ω. Correspondingly, the RF-DC conversion efficiency of the rectification process is 59.51% and 45.75% at 1.8 GHz and 2.5 GHz, which are high efficiency and much better compared to literature respectively. The rectenna is capable to produce 1.8 V from an input power of -20 dBm. Thus, the proposed RF energy harvesting system offers a promising solution designed for efficient functionality at a low power level of RF energy in the dual band

Design of Processing Circuitry for an RF Energy Harvester

Significant advancements in technology and the use of low power sensors in both commercial and industrial applications have made it essential to develop wireless solutions for low power devices. Once such solution, which has generated attention in university and R&D environments, is radio frequency (RF) energy harvesting. RF energy harvesting seeks to capture ambient RF energy by means of an antenna and convert this energy to useable DC power. The presence of ambient RF energy in the environment is a result of numerous high-frequency technologies including Wi-Fi, cell phones, microwave ovens, and radio broadcasting, as well as many others. The intention of this thesis is to design the processing circuitry necessary to convert a received RF signal into useable DC power, with the ability to charge a Lithium-Ion battery. The design presented here was performed to process an RF energy signal received from an antenna that targets both the 2.4GHz and 5GHz Wi-Fi bands. The final design consists of two bandpass filters (one for each Wi-FI band) two two-stage voltage doubler circuits (one for each Wi-Fi band), and a boost converter that is designed to achieve an output voltage of 3.2V in order to charge a Lithium-Ion battery. Testing of the RF energy harvester in an environment with ambient 2.4GHz Wi-Fi signals and a 470μF capacitor connected at the output demonstrates the circuit’s ability to harvest a measureable amount of energy. While the maximum measured voltage of 50mV does not meet the design specification of 3.2V, the circuit demonstrates proof-of-concept. Additional design improvements are necessary to make it a viable solution for charging a battery

Rectenna Systems for RF Energy Harvesting and Wireless Power Transfer

With the rapid development of the wireless systems and demands of low-power integrated electronic circuits, various research trends have tended to study the feasibility of powering these circuits by harvesting free energy from ambient electromagnetic space or by using dedicated RF source. Wireless power transmission (WPT) technology was first pursued by Tesla over a century ago. However, it faced several challenges for deployment in real applications. Recently, energy harvesting and WPT technologies have received much attention as a clean and renewable power source. Rectenna (rectifying antenna) system can be used for remotely charging batteries in several sensor networks at internet of things (IoT) applications as commonly used in smart buildings, implanted medical devices and automotive applications. Rectenna, which is used to convert from RF energy to usable DC electrical energy, is mainly a combination between a receiving antenna and a rectifier circuit. This chapter will present several designs for single and multiband rectennas with different characteristics for energy harvesting applications. Single and multiband antennas as well as rectifier circuits with matching networks are introduced for complete successful rectenna circuit models. At the end of the chapter, a dual-band rectenna example is introduced with a detailed description for each section of the rectenna

A compact low-power EM energy harvester using electrically small loop resonator

Electromagnetic (EM) energy harvester is a combination of an antenna or EM collector and a rectifier circuit. It is a concept that has seen applications in a variety of areas, as its essential purpose is to harvest and reuse the ambient microwave power. Compact system solutions for EM energy harvesting are presented and investigated in this work. The objective of this work is to reduce the size of the EM harvesters and simplify the fabrication process. A new approach to design a compact EM energy harvester which based on the concept of an electrically small square-loop collector, is proposed. Coplanar waveguide (CPW) transmission lines are utilized to build the half-wave rectifier. The input impedance of the rectifier is designed to be equaled to the conjugate of the impedance of the square-loop collector at the operating frequency. This method not only reduces the mismatch loss, but also reduces the overall size and simplifies the complexity of the system. The efficiency and the DC output power of the design are examined with respect to the power density on the EM harvester surface. Measurements demonstrate that the system is efficient to harvest EM energy in a low power density environment and generate a reasonable DC power. The proposed EM energy harvester is compact, easy to fabricate and integrate into other devices, and suitable for different energy harvesting applications. The mechanical flexibility of the proposed compact EM energy harvester is also discussed. The EM energy harvester is redesigned and fabricated on a thin flexible substrate. The performances are measured with respect to frequency in both planar and curvature configurations. The results show that the operating frequencies for both planar and curvature configurations do not vary. Furthermore, the output power of the two configurations at the operating frequency are very close to each other. The proposed flexible EM energy harvester requires a simpler fabrication process and a smaller size when compared to the previous work reported in the literature for EM energy harvesting at 2.45 GHz. A single element of EM energy harvester is insufficient for powering common devices. Therefore, two low-cost techniques are proposed and used to increase the capability of the system. In the first method, a parabolic reflector is designed, fabricated and placed behind the system to reflect the beam of parallel rays and concentrates the radiation power at the harvester surface. An alternate technique to boost the output DC power is based on using multi-square-loop collectors. Instead of using a rectifier circuit for each loop collector, multi collectors are combined before feeding into a single rectifier circuit. The experimental results show that these two techniques have significant improvement in the DC output power. The parabolic reflector technique can improve the DC output power by 35%, while in the case of the multi collectors technique, 4 times higher DC output power can be achieved

Radio frequency energy harvesting for autonomous systems

A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements for the degree of Doctor of PhilosophyRadio Frequency Energy Harvesting (RFEH) is a technology which enables wireless power delivery to multiple devices from a single energy source. The main components of this technology are the antenna and the rectifying circuitry that converts the RF signal into DC power. The devices which are using Radio Frequency (RF) power may be integrated into Wireless Sensor Networks (WSN), Radio Frequency Identification (RFID), biomedical implants, Internet of Things (IoT), Unmanned Aerial Vehicles (UAVs), smart meters, telemetry systems and may even be used to charge mobile phones. Aside from autonomous systems such as WSNs and RFID, the multi-billion portable electronics market – from GSM phones to MP3 players – would be an attractive application for RF energy harvesting if the power requirements are met. To investigate the potential for ambient RFEH, several RF site surveys were conducted around London. Using the results from these surveys, various harvesters were designed and tested for different frequency bands from the RF sources with the highest power density within the Medium Wave (MW), ultra- and super-high (UHF and SHF) frequency spectrum. Prototypes were fabricated and tested for each of the bands and proved that a large urban area around Brookmans park radio centre is suitable location for harvesting ambient RF energy. Although the RFEH offers very good efficiency performance, if a single antenna is considered, the maximum power delivered is generally not enough to power all the elements of an autonomous system. In this thesis we present techniques for optimising the power efficiency of the RFEH device under demanding conditions such as ultra-low power densities, arbitrary polarisation and diverse load impedances. Subsequently, an energy harvesting ferrite rod rectenna is designed to power up a wireless sensor and its transmitter, generating dedicated Medium Wave (MW) signals in an indoor environment. Harvested power management, application scenarios and practical results are also presented

A Sensitive Triple-Band Rectifier for Energy Harvesting Applications

(c) 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.[EN] This paper presents a novel sensitive triple-band power rectifier for RF energy harvesting systems. The proposed rectifier can simultaneously harvest RF energy from GSM-900, GSM-1800, and Wi-Fi-2450 bands at relatively low and medium ambient power densities. Previously, a few multi-band rectennas have been reached a stable conversion efficiency overall frequency bands of interest because of the nonlinearity and the distinct input impedance of the rectifying circuit at these frequencies. The originality of this paper is on the improved impedance matching technique that enhances the efficiency and performance of the rectifier. The proposed high-efficiency triple-band rectifier consists of three parallel branches. Each branch comprises an input matching circuit designed to provide maximum RF power transferred to rectifying diodes, a single voltage doubler using Schottky diode HSMS-2852, and a DC-pass filter to smooth the DC output voltage. A prototype of the proposed rectifier circuit is fabricated and tested to verify its performance against the simulation results. With an optimum load resistance of 3.8 k at -10 dBm input power level, the measured RF to DC conversion efficiency achieves 33.7%, 21.8%, and 20% at 0.9, 1.8 and 2.45 GHz respectively. The efficiency is above 46.5 % overall bands of interest under 0 dBm input powerThis work was supported in part by the EMMAG Program, 2014, funded by the European Commission.Tafekirt, H.; Pelegri-Sebastia, J.; Bouajaj, A.; Reda, BM. (2020). A Sensitive Triple-Band Rectifier for Energy Harvesting Applications. IEEE Access. 8:73659-73664. https://doi.org/10.1109/ACCESS.2020.2986797S7365973664