One of the most prominent approaches to pulling electricity from thin air clearly gives a nod to the venerable crystal radio. It harvests energy, not surprisingly, from radio waves.
At the University of Bedfordshire’s Centre for Wireless Research in Luton, UK a trio of bright people have been working on a radio-wave-harvesting solution they believe will one day not only reduce consumer reliance on batteries and AC power, but will also reduce the impact on our environment.We spoke with Ben Allen, who heads up the team, to find out more. Allen and his associates gained international attention back in February when they announced they’d developed the technology and had filed a patent application for radio wave harvesting. Some wags suggested it was a world’s first, though Allen’s group is but one of many worldwide looking into the very same prospects. Indeed, noted Serbian-American scientist and certified brainiac Nikola Tesla demonstrated the phenomenon of wireless energy transmission more than a century ago. Nevertheless, Allen and his team have taken the technology to a point few others have.According to Allen, the team’s proposed solution focuses on the frequency band “which is around 1MHz and is sometimes called the ‘AM band’. It doesn’t have to be these signals that we harvest energy from, but we’ve been focusing on medium waves as we believe they have advantages compared to high-frequency waves.”At the heart of the concept is an antenna – an antenna Allen likens to a windmill. “The (radio) wave induces a current into the antenna, which we convert to DC and apply to the device requiring power. The bigger the antenna, the more power is available. The antenna is like a windmill — the bigger the windmill, the more power is available.”
Allen is also quick to boast that the technology can be retrofitted to existing devices and is comparatively compact. As for concerns that widespread radio wave harvesting might eventually vacuum up so much energy that nothing is left, Allen again plays the windmill card. “We use antennas that are very small and have a negligible effect on the signals – a bit like the effect a child’s windmill has on the wind. If we had a very large device then it would be difficult to receive a signal behind it, just like the shortage of wind behind a large wind generator.”The obvious upside is the constancy of the harvested source. As Allen explains, radio wave harvesting does not depend on sunlight or wind. Nor does it rely on heat differential (the concept behind thermoelectric energy harvesting, discussed later in this article). Radio waves are always out there, more so in metropolitan areas. Moreover, says Allen, “In principal, it operates well in rural locations and the radio waves should have relatively good penetration into buildings compared to those at higher frequencies.”
“The (radio) wave induces a current into the antenna, which we convert to DC and apply to the device requiring power. The bigger the antenna, the more power is available. The antenna is like a windmill — the bigger the windmill, the more power is available.”
Radio waves don’t pack a ton of harvestable juice, so Allen and his team are currently targeting ultra-low power devices – products such as wireless sensor network nodes that only occasionally execute power-demanding actions and otherwise remain in wait mode. Future candidates include remote controls and clocks.
“Some applications will require rechargeable batteries to help with energy supply, but (even they will be) charged from harvested energy,” Allen says. “This would limit the life of any device and eventually the battery will degrade and need replacing. This may be after a few years, but does vary due to battery technology, temperature and charge cycle.”
Still, high-drain current-gobblers such as tablets and flashlights may never be part of the picture. And if they are – and we’re looking way down the road here – radio wave harvesting almost certainly won’t be the only power source. Picture a rechargeable battery that depends on “regular” recharging but is potentially also topped up by an amalgamation of energy harvesting alternatives, and you begin to get an idea what the future might hold.