A literature of the Academic papers regarding harvesting ambient Radio Frequency (RF) energy shows that there are a number of potential application extant if harvested in sufficient amounts and with practically sized apparatuses. This RF (Radio Frequency) energy lends itself to a wide range of potential uses including, but not limited to, recharging personal and business usage to recharge communication apparatuses , . The greatest amount of the Academic papers reviewed look at this RF energy source as a method of employing battery-less, low-energy devices without the further complications presently inherent in solar power that is only effective in daylight situations. , , . The research available went beyond the feasibility of RF energy and included a number of prototype devices. , . There were sources that specifically looked at the most efficient antennas , , and software. .
This Literature Review shows that recent advance have taken RF energy harvesting far beyond the possibility range of “can it be done,” and now it is only a matter of the best way to utilize this established energy source.
An Experimental Evaluation of Surrounding RF Energy Harvesting Devices studied RF harvesting devices tested in an urban area. After optimization D. Bouchouicha, M. Latrach, F. Dupont, and L. Ventura were able to harvest sufficient RF energy to power some low power devices like wireless sensors and to trickle charge a rechargeable micro-battery or super-capacitor. They focused on ambient RF energy from commercial RF broadcasting stations GSM1800 and Wi-Fi (2.45GHz) as the energy sources. Although they conducted this study in an urban area, they were seeking an answer to how RF energy could be applied to remote locations where there was little or no solar or wind power available.
After testing a variety of RF energy harvesting devices, they found that they received the best results from a spiral antenna. The study presented results from an outdoor location close to a mobile phone base station They measured the surrounding RF power density in broadband (GHz-3.5GHz) is in the order of -12dBm/m² (63μW/m²). The RF density power at its maximum measured in at a 1.8 GHz-1.9GHz frequency band, at - 14dBm/m². To allow for this, they designed and simulated two rectifiers at 1.85GHz and 2.45 GHz.,
In An Experimental Evaluation of Surrounding RF Energy Harvesting Devices D. Bouchouicha, M. Latrach, F. Dupont, and L. Ventura concluded urban RF power density contained very low DC energy. Even when they worked with a large wide frequency band, they still had trouble detection significantly stronger amounts of this energy. They found that the harvested energy was not sufficient to supply continuously an electronic application. Never the less, they did recover enough of this energy to warrant storage for later utilization. “The DC power recovered by a rectenna (1.8GHz-1.9GHz) near a base station on 100m of distance was about a 0.5pW to100nW with average around 3.5nW.”
Prototype Implementation of Ambient RF Energy: Harvesting Wireless Sensor Networks by Hiroshi Nishimoto, Yoshihiro Kawahara, and Tohru Asami of the Graduate School of Information Science and Technology at The University of Tokyo, Japan examines energy harvesting as a method to deploy wireless sensor networks (WSNs). They turn to this method to avoid the limitations enforced by utilization of solar power. Since solar power is not available at night, they looked at the possibility that RF energy harvesting from TV broadcasts airwaves to serve as the sources that would generate sufficient energy in order to power wireless sensor nodes. In the initial stages, the utilized the output of a rectenna that they monitored continuously for seven. This initial monitoring permitted them to determine that RF energy was always available.
The second phase was to develop a RF energy harvesting WSN prototype to determine if it was possible to harvest sufficient RF energy to power a WSN. After setting a duty cycle determination method and verifying the validity of this method, they determined their system was effective for long period measurement applications not requiring high power consumption.
Vlad Marian, Bruno Allard, Christian Vollaire, and Jacques Verdier determined in Strategy for Microwave Energy Harvesting from Ambient Field or a Feeding Source that harvesting energy from RF sources was possible; however, the applications were limited due to the narrow efficiency range. They designed and used a switch to extend this power range to achieve an acceptable efficiency. This configuration also protected their most sensitive circuit from excessive input voltage. Although they found room for improvement, their design featured an advancement that employed a reconfigurable receiver fabricated from low cost SMD technologies or integrated on a single chip. .
Ambient Electromagnetic Wireless Energy Harvesting Using Multiband Planar Antenna looks at the application of Ambient Electromagnetic energy (EM) harvesting a and how the energy harvesting method can be advanced by using a harvester that simultaneously utilizes different ambient EM frequencies. In this study, they employed a Wireless EM harvester constructed with a Printed Circuit Board (PCB) a planer antenna and a RF to DC circuit. The impedance masking for this device used schottky diodes and passive components. The harvester’s open circuit voltage increased when optimally moved from a single signal at 1.8 GHz to one where it could receive 1.8 GHz and 1 GHz simultaneously.
Energy Harvesting from Ambient RF Sources is a feasibility study by Shoichi Kitazawa, Hiroshi Ban, and Kiyoshi Kobayashi that explores energy harvesting from ambient RF sources by calculating the power spectrum density and received power in a suburban location. It confirmed that it is possible and identified low received power from ambient RF sources as one of the difficulties encountered. They employed an 800 MHz mobile telephone base station averaged 13dB stronger than Digital Television broadcasting. Their study showed that “a 1.0 F electric double layer capacitor can be charged up to 320 mV in 3900 minutes at common suburban area.”
Ambient RF Energy Harvesting from DTV Stations looks specifically at DTV stations place in the framework of RF energy harvesting to that end S. Keyrouz, H. J. Vissery, and A. G. Tijhuis of the Eindhoven University of Technology, examined the antenna and rectifier parts of a RF harvester and used a Yagi-Uda antenna to harvest RF energy from DTV signals. They showed that “cascading 12 rectifiers will not only maximize the output voltage but also will reduce the impedance from Zin = 78:437 - j1197:47 (for a single rectifier) to Zin = 21:51 - j102:78 (for a 12 stage rectifier).”
Gudan, Kenneth; Chemishkian, Sergey; Hull, Jonathan J; Reynolds,, Matthew S; and. Thomas, Stewart; conducted a feasibility study entitled the Feasibility of Wireless Sensors using Ambient 2.4GHz RF Energy. In this study they presented a new apparatus to prove the feasibility of using RF energy to power ultra-low-power sensors and microcontrollers using a Bluetooth Low Energy (BLE) or other such ultra-low power uplink. To do this, they summed and averaged data from both a fast wide-band spectrum analyzer and a slower frequency-selective spectrum analyzer in a typical office environment. The processed data from this study indicated that it was feasible to capture ambient RF energy in the “2.4GHz ISM band is feasible with a sufficiently patient duty cycle.” .
In Energy Harvesting from Ambient Electromagnetic Wave Using Human Body as Antenna, J.H. Hwang, C.H. Hyoung, K.H. Park and Y.T. Kim investigate the feasibility of using the human body as the antenna to harvest low-frequency band ambient electromagnetic waves. They begin by noting the difficulties posed by the inconvenient size of the spiral antenna used in a 1 to 3 GHz range and the smaller, but still impracticable antenna developed for the 300 MHz range. They noted that the lower frequencies under 30MHz were less regulated than the higher frequencies and concluded that it might be possible use the human body to harvest low-frequency ambient electromagnets waves. They compared the results of using a high frequency general antenna to the results obtained from using the human body as a low-frequency band antenna. After comparing the data they surmised that their “method was able to harvest much higher power without a general antenna. The harvesting might increase even more if we use a rectifier circuit operating over a wide-frequency band.”
Aaron N. Parks, Alanson P. Sample, Yi Zhao, Joshua R. Smith from the Electrical Engineering and Computer Science and Engineering Departments of the University of Washington, Seattle, looked at ambient RF energy harvesting to combat the need for a battery that limits spaces and increases costs in many devices. They constructed a prototype that measured and transmitted light and temperature levels. Subsequently they reported their findings in A Wireless Sensing Platform Utilizing Ambient RF Energy in which they concluded, “The minimal RF input power required for sensor node operation was -18 dBm (15.8 W). Using a 6 dBi receive antenna, the most sensitive RF harvester was shown to operate at a distance of 10.4 km from a 1 MW UHF
Television broadcast transmitter, and over 200 m from a cellular base transceiver station.”
In An Investigation of Ambient Radio Frequency as a Candidate for Energy Harvesting Rahim, Hassan, Malek, Junta, and Jamlos, conducted a feasibility study to determine the potential to harvest ambient RF from the GSM telecommunication tower and convert it into electrical energy for very low power device usage. They used a normal mode helical rectenna instead of a microstrip patch antenna array to avoid size related problems. Their results showed that a voltage of 0.3V is generated at the distance of 2.5 meters having a -10dBm input power. These findings permitted them to conclude this source of RF was a suitable candidate for RF energy harvesting.
E-WEHP: A Batteryless Embedded Sensor-Platform Wirelessly Powered from Ambient Digital-TV Signals by Rushi J. Vyas, Benjamin B. Cook, Yoshihiro Kawahara, and Manos M. Tentzeris, presented the embedded wireless energy-harvesting prototype (E-WEHP). E-WEHP is an embedded sensor-platform capable of receiving power wirelessly from ambient digital-TV signals at a distance of over 6.3 km from the TV broadcast source. They constructed a prototype that used “an optimized log-periodic antenna with peak gain of 7.3 dBi” ”an RF-dc charge-pump circuit with carrier RF-dc sensitivity of 14.6 dBm 4.67, W sensing peripherals on a 16-bit PIC24F microcontroller” . It used “TV signals with peak carrier levels of 7 dBm 0 W and channel power levels of 8.99 dBm 126.2 W at 6.3 km from the source” By using a RF-dc charge-pump with single-carrier RF-dc sensitivities of 18.86 dBm 13 W,” . They were able to draw power from “lower levels of ATSC standard-based wireless TV signals with channel power levels of 40.55 mW 13.92 dBm and carrier levels of 0.063 W 42 dBm” sufficient to power a 16-bit PIC24F microcontroller..
Ambient RF Energy Harvesting in Urban and Semi-Urban Environments reports how Manuel Piñuela, Paul D. Mitcheson, and Stepan Lucyszyn conducted a citywide scan of London, UK. To do this they used a spectral survey to locate sites for four harvesters “designed to cover four frequency bands from the largest RF contributors (DTV, GSM900, GSM1800, and 3G) within the ultrahigh frequency (0.3–3 GHz) part of the frequency spectrum.” In particular, they looked at 270 underground station locations as prime energy sources. They then deployed four energy harvesters and tested to see the most efficient configuration. Using the data produced from this study, they concluded, “(semi-)urban environments, especially when the antenna can be absorbed into background features” .
Ambient RF Energy Harvesting Sensor Device with Capacitor-Leakage-Aware Duty Cycle Control by Ryo Shigeta, Tatsuya Sasaki, Duong Minh Quan, Yoshihiro Kawahara, Rushi J. Vyas, Manos M. Tentzeris, and Tohru Asami, presented a software control method to increase the sensing rate of wireless sensor networks. This software addressed the problem of repeated charges and discharges associated with a WSN node. Testing involved a weeklong, real time, operational study that determined that the software was effective to reduce leakage loss and enabling the system to operate more reliably and effectively.
Antennas and Circuits for Ambient RF Energy Harvesting in Wireless Body Area Networks identifies the opportunities to harvest RF energy with power density measurements from 350 MHz to 3 GHz tested in field trials. In order to do this the researchers used the NARDA-SMR spectrum analyzer with a measuring antenna, a proposed dual-band band printed antenna operating at GSM bands (900/1800) which increases gains of 1.8-2.06 dBi and efficiency 77.6840/0. This paper also addressed RF energy harvesting circuit design guidelines and textiles for wearable antenna. Additional topics include guidelines for circuit design to harvest energy from a wireless body area network (WBAN) sustained by a TX91501 “Powereast RF dedicated transmitter and a five-stage Dickson voltage multiplier responsible for harvesting the RF energy. The IRIS motes, considered can perpetually operate if the RF received power attains at least -10 dBm.”
A Self-sustaining, Autonomous, Wireless-Sensor Beacon Powered from Long-Range, Ambient, RF Energy examined a wireless energy harvesting prototype (WEH) test setup and determined that it was a novel and successful “embedded sensing and wireless relay platform that can power and sustain itself using long range digital TV signals at distance of 6.5 km .” .
Feasibility Study on Ambient RF Energy Harvesting for Wireless Sensor Network studied the feasibility of generating sufficient energy to power a wireless sensor in urban Singapore and determine if emerging wireless power can integrate with RF energy harvesting. They based their computations upon the ambient RF power density on the GSM 900 and 1800 bands existing in Nanyang Polytechnic of Singapore. In their concussion, they found “A potential voltage of about 0.5 V can be harvested at the School of Engineering Nanyang Polytechnic. With this, the harvested energy can potentially power on a low power wireless sensor network.”
Ambient Backscatter: Wireless Communication Out of Thin Air introduces ambient backscatter. This is communication between computers using TV signals along with other ambient RF sources as power communication. One broadcast tower generally sends out a range of multi-directional signals in order for their signal to reach their intended customer recipients. The signals that are not absorbed by recipient devices remain as the ambient backscatter within that tower’s broadcast range. RF power harvesting utilizes this ambient backscatter to detour around the entire problem of the hard to maintain, expensive batteries and other costly infrastructure used by RFID and NFC and the unavailability of solar energy at night. This makes it possible to develop new applications that would otherwise be impractical with other systems due to the limitations of solar energy and the wasteful and larger scale equipment they need. One of the important features is as long as there are RF signals pervasive devices can enjoy unrestricted communication .