Wireless Power: From Small to Big
In the modern environment we are living surrounded by invisible flows of energy generated by wireless networks. Wireless power is ubiquitous: it is generated by mobile base stations, home Wi-Fi, mobile phones, terrestrial and satellite TV and radio. Huge amount of energy is spent powering transmission of the wireless signal but could that energy be recovered in a meaningful way?
Dr Paul Mitcheson and his colleagues from Imperial College London wanted to find an answer. They conducted a city-wide RF spectral survey outside all of the 270 London Underground stations and the analysis of the results showed that in London DTV, GSM900, GSM1800 and 3G are the highest contributors. The results were published on http://www.londonrfsurvey.org/. The team from Imperial College also fabricated single multiband rectennas, rectifying antennas used to convert microwave energy into direct current electricity. Based on the spectral survey and the harvesters’ performance, it was shown that more than 220 of the surveyed locations were suitable for ambient RF energy harvesting using the far field rectennas. The amount of energy that could be harvested that way is tiny but it could still be practically useful.
The far field RF energy harvesting inspired researchers at the University of Tokyo to look for applications in agriculture. Researchers from the group of Professor by Yoshihiro Kawahara decided to help farmers save water when watering crops. They built a prototype of a moisture sensor and a rectenna printed on paper and powered by radio waves in the air. The device called SenSprout, developed from the University of Tokyo, gives real-time measures of soil moisture to make irrigation more efficient. SenSprout was presented at the Techno-Frontier 2013 EXPO where students from Professor Kawahara’s group were interviewed by the UK’s Energy Harvesting SIG. The interview is now available on YouTube. The SenSprout project demonstrated that an RF energy harvester could be fabricated using conductive printing but the technology would only work in the presence of sufficient ambient RF power, which is likely to be the case in the urban rather than rural areas as was shown by the London RF Survey conducted by Imperial College.
Another wireless power application, wireless charging, could find its way to the market much faster. An alternative to the far field technology for ambient RF energy harvesting is near field inductive power transfer. It is already used to charge various electronic devices including mobile phones. The market for wireless charging will grow even bigger as electric cars become more and more popular. Dr Manuel Pinuela who used to work with Dr Paul Mitcheson at Imperial College is now at Drayson Racing Technologies, a leading UK motorsport company, where he continues his work on wireless charging. Dr Pinuela will give a talk on Accelerating Innovation in Wireless Power Transfer through Motorsport at the 3rd UK-Japan Energy Harvesting Workshop, which will take place on the 6th of December 2013 at the Royal Society, London. The event offers a great networking opportunity and exciting presentations from Japan, including NTT Data Institute of Management Consulting, National Institute of Advanced Industrial Science and Technology, Lapis Semiconductor and the University of Tokyo. Drayson Racing Technologies, Perpetuum, Thhink Wireless and European Thermodynamics will represent the UK.
The full agenda and registration are available at http://tinyurl.com/lo988m8 .