Though it has been around for over a hundred years, the idea of wireless electricity has been gathering momentum recently. Now, even the defence community is looking to revolutionise this technology for battlefield use.
By Chris Sheehan
The idea of transmitting power without the need of wires has been around for over a century, with Nikola Tesla’s revolutionary ideas and experiments being some of the most well known early attempts. Since then the concept has continued to develop, with the Haier Group debuting the world’s first completely wireless LCD television at the 2010 Consumer Electronics Show and a fully integrated wireless power receiver being demonstrated in CMOS (Complementary Metal-Oxide-Semiconductor) process just last year.
The technological prospects of the technology go far beyond consumer electronic. The Defense Sciences Office (DSO) of the Defense Advanced Research Projects Agency (DARPA) in the United States are interested in the technology, with the aim of reducing the weight of batteries which soldiers have to carry in order to power the vast array of electronic equipment which they carry.
Long range wireless technologies are also currently under development which could assist in disaster relief situations, with a long term ambition of placing a solar plant in space which beams the generated power back down the earth.
Near field wireless energy transfer utilises electromagnetic induction to power electronic devices. This kind of technology would be useful for snack-charging, where devices such as mobile phones could benefit from a small boost by simply placing then on a table.
This technology has also been in the news a lot over the past couple of weeks, with Toshiba announcing new enhancements to its power transmitter / receiver chipset, now supporting five watt wireless power transfer.
IDT (Integrated Device Technology, Inc) has introduced the industry’s first Qi-compliant, single-chip five volt wireless power transmitter solution. This equates to up to eight watts when pairing with an IDT wireless power receiver. This development allows USB-powered wireless charging bases with 75 per cent fewer integrated circuits than competing solutions.
WiTricity Corp. has also made a breakthrough announcement this week, introducing the world’s first system for wireless charging of consumer devices, such as the iPhone 5, using the company’s patented highly resonant wireless power transfer technology. The WiTricity system has been show to charge gadgets over distances of several metres at powers ranging from a few milliwatts to kilowatts. Power can also be transferred through a variety of ‘magnetically transparent’ materials, such as wood, granite, plastic and glass. The magnetic near field can also ‘wrap around’ some metallic objects in order to transfer power.
Japanese automaker, Toyota, has signed an agreement to licence the intellectual property of WiTricity Corp. This will mean that instead of plugging in vehicles, they only need to park over small fifty centimetre square charging pad.
Toyota has also been in partnership with Duke University, who have been looking at the potential benefits of metamaterials within wireless energy transfer. With funding from Toyota, they have designed and tested a ‘superlens’ which can focus both non-propagating near and far field waves. This allows for the transfer of power of distances much larger than the size of the transmitter and receiver. ‘This is important because if this technology is to become a part of everyday life, it must conform to the dimensions of today’s pocket-sized mobile electronics’ says Yaroslav Urzhumov, assistant research professor of electrical and computer engineering at Duke University.
Last year South Korea switched on a twelve kilometre stretch of road which can recharge electric vehicles as they drive over it. This will mean that vehicles fitted with compatible equipment will not need to stop to recharge and can be fitted with smaller batteries. Two public buses are already using the technology and there are plans to add ten more by 2015.
Aerostats and Lasers
The future, however, is in far-field energy transfer. Utilising electromagnetic radiation, the technology can be used to power devices over large distances.
This technology has been highlighted for its potential uses within disaster relief situations. Stephen Blank, of the New York Institute of Technology, has proposed using aerostats – military-grade balloons historically used for surveillance – and lasers to wirelessly transfer power into otherwise unreachable areas. He plans to send a laser up to an aerostat via a fibre-optic cable, then beaming through the air to a distant aerostat. This high energy light would then be converted into electricity before streaming back to earth via a tether.
According to Blank, this technology could be used to send hundreds of kilowatts of power over several hundred kilometres. One case study which he put forward was the recent natural disaster in the Philippines, when typhoon Hiyan struck. As described by Blank, ‘You could have an aircraft carrier off the coast of the Philippines, with its nuclear generator, beaming power where it’s needed.’
Wireless Power in Battlefield
It is estimated that troops on single day missions currently carry two to five kilograms of battery weight, and this weight is expected to increase as we continue to equip them with more portable electronics.
As the size of batteries decreases they tend to get less efficient, providing a lower energy-to-weight ratio. In the past, cable-linked power management systems have been considered, however these proved to be cumbersome, limiting the soldier’s mobility. A wireless solution would provide the benefits of a higher energy-to-weight efficiency, without reducing the missions flexibility.
DARPA announced in 2011 that it wants to deploy wireless charging hubs in the battlefield. They would like is a single, physically separate power source, which can charge multiple devices simultaneously. This could be a high-energy fuel cell or rechargeable battery, to be carried by a single soldier, which powers the equipment of other troops at a distance of up to five metres without the need for wires. Similar equipment could then be fitted to vehicles to recharge the battery pack when they are in close enough proximity. In order to achieve these goals, the US army allocated $5-$6 million to advance these technologies in 2012.
Orbiting Solar Panel
According to Reza Zekavat of Michigan Technology University, wireless power is at its most advanced in Japan.5 The Japanese government is prepared to spend $21 billion with the aim of placing one gigawatt of solar generating capacity into space within the next thirty years. The Space Solar Power Systems (SSPS) project would be positioned 36,000 kilometres above the earth in a geostationary orbit, where it would transmit power back to earth via laser beam. This is often seen as the ‘ultimate goal’ in wireless power.
In 2009 Mitsubishi and other Japanese companies have signed up to assist with the four kilometres of solar panels. While it is possible that these will be made from the superefficient variant made by US-based Spectrolab, it is more likely that the solar panels will be domestically sourced.
If launched, the system will benefit from never passing out of sunlight. Furthermore, with no atmosphere to transition through and no interference, solar panels in space are eight to ten times more efficient at converting solar power into electricity then Earth-based systems. The system will however only produce enough power for 300,000 – less than one per cent – of Japanese homes for a cost of $21 billion.
Projects such as this are venturing into uncharted territory, with which comes the possibility of unforeseen risks. While the power station will not have the intensity to cause any damage, it does raise the issue of the potential future militarisation of space. Even with this threat aside, research will need to be undertaken to better understand how this beam will interfere with other wireless power transfers, such as radio broadcast signals and mobile telephone communications.
Towards Realisation
Wireless power has the potential assist in various situations where wires would be impractical. On an individual level it would assist with decluttering, since multiple devices could be powered through a single induction transmitter. Furthermore, battery life would no longer be such an issue and so devices could be made smaller and lighter. As the technology progresses, power cables could be removed from buildings all together. This would have benefit of every device behaving as if it had infinite battery life, and additional lighting could be installed without the need for an electrician.
The main issue facing wireless energy transfer is its efficiency, which deteriorates rapidly as the distance between the transmitter and receiver increase. Low levels of efficiency results in increased cost and slower charging. Optimists however predict that over time this technology will catch-up with current copper wires, becoming just as – if not more – efficient.
Note
 [1].       Hal Hodson, ‘Send wireless power long range with lasers and balloons’, New Scientist, 6 December 2013
Second photo: Wireless Power Transfer picture courtesy of Guy Lipworth, Graduate researcher at Duke University