It’s a century old idea, but wireless electricity is finally coming into its own. Drew Turney learns about the horizons, limits and products you’ll use wire-free in the near future.
We’ve all seen the horror movie with the heroine locked in a cupboard with a killer in the house, desperately trying to call the police while her phone runs out of charge.
Imagine how different the world would be with electrical power delivered not through wall sockets or limited batteries but through the very air, keeping our devices, appliances and machinery charged as we use them? As any science geek will tell you, it’s not a new idea. During the early days of electrical power in the 1900s several names were experimenting with it.
The most famous was Nikola Tesla, who built inductive and capacitive coupling using spark-excited radio frequency resonant transformers – that’s the Tesla coil to the rest of us. His successful public demonstrations lighting Geissler tubes (the precursor to neon lighting) and incandescent bulbs using wireless power inspired greater ambitions.
One of his ambitions was a network of balloons, nine kilometres up, transmitting electricity over vast distances wirelessly from suspended electrodes. But Tesla’s best-known effort is Wardenclyffe Tower, a 187 foot tall wireless transmission station on Long Island, New York, intended to transmit information – 80 years before the Internet – as well as power.
While Edison supposedly destroyed Tesla’s advances with litigation and industrial espionage, funding for Wardenclyffe Tower ran out and it was demolished in 1917.
But Tesla and his peers were still onto something – he might simply have been thinking on too grand a scale. If you’ve ever seen a Tesla coil on YouTube you’ll wonder how a machine throwing electrical arcs in all directions can possibly be safe (it’s not – see ‘Is wireless power safe?’)
The new wireless
But thanks to the work done all those years ago, wireless power transfer is all around us today. Your cordless electric toothbrush and induction stove both work using magnetic induction, the creation of an electrical force when a conducting material interacts with a magnetic field.
The alternative magnetic field in a coil in the charging station generates a current in another coil in the toothbrush, which charges the battery. In an induction stove a coil under the cooking plate receives an alternating current, which magnetises the pot, creating movement in the contents and heating them without transferring thermal energy like a glowing red electrical coil or gas flame does.
After that the next frontier in wireless electricity is distance. If a device only receives a charge by being so close to the coil you can’t move it around, wireless power kind of defeats the purpose (although in some circumstances it’s about safety – as it’s kept near water, an electric toothbrush is encased mostly fully in non-conductive plastic).
One of the answers to separating the two coils any distance offered by science is magnetic resonance, where the transmitting and receiving coils resonate with the same wave frequency. When you achieve that, you get was wireless power transfer provider WiTricity’s Sanjay Gupta calls ‘spatial freedom’.
To illustrate, he talks about the way an opera singer can shatter a wine glass from across a packed venue. The sound waves from the singer’s voice match the frequency of movement of air molecules around the glass, causing them to vibrate so much it’s not much different from hitting the glass with a hammer. As long as the frequencies match, the distance is theoretically immaterial.
Plus, as WiTricity told CNN online, it’s much safer than the old days of Tesla coils sending huge sparks of static arcs everywhere because transmitters put magnetic fields – not electricity itself – into the air.
Where do you get it?
We’ve seen the first generation of magnetic induction charging products of our age already, in the mobile device charging pads you rest your phone or tablet on to recharge them.
Where your toothbrush or electric kitchen knife charger generates magnetic fields in the coils in a specific direction, your phone is charged without having to be so precisely aligned to the field because the resonant frequency in the base station matches that of the charging apparatus of your device. Theoretically, you’d be able to leave your phone across the room and it would still charge.
Another recent application we’ve seen is in electric vehicles. As long ago as 2011 New Zealand start-up HaloIPT (now part of Qualcomm) introduced charging pads for electric vehicles using resonance technology like that in mobile charging pads.
Today the tech can be hard wired in, with a coil right in the floor of your garage or in city parking spaces, where the few inches of concrete or asphalt and the half metre or so between the floor and the underside of the car is no real impediment.
Other new uses and applications are appearing as the field expands. A new system developed at The Korea Advanced Institute of Science and Technology will charge devices from any distance and direction as long as they’re in range of a transmitter, much like wi-fi keeps mobile devices connected to the internet now.
An even more exciting system from the University of Washington uses the wi-fi signal itself to power devices. The computer engineers behind the research into what’s been called PoWiFi (power over wi-fi) found that the ambient wi-fi signals from a router came close to the minimum requirements to keep certain low powered devices alive.
By harnessing wi-fi signals not used for data transmission, PoWiFi sends a resonant frequency signal that generates a charge in a coil the same way described above – and all without degrading the data transmission and speed because it’s using snippets of data ‘downtime’ (where there’s not a lot of packet transmission) to send the signals.
One of the obvious applications of bundling electrical power in with data transmission is in the exploding Internet of Things world, freeing millions of new devices loaded with sensors from the shackles of outlet power or on-board batteries.
Researchers at London’s Imperial College have developed a system where drones need never land, hovering over a resonant magnetic field generated from a base station on the ground to recharge while still in flight.
It’s only early days, with the drone needing to hover within four inches of the charger. But as a proof of concept it’s inspiring big plans, including charging over the magnetic field generated by power lines, fleets of charging drones that charge other drones or, resurrecting one of Tesla’s outlandish ideas, sky-high charging stations connected to balloons – even on other planets to charge devices like the Curiosity rover on Mars.
All of which leads to an inevitable question – how far can we take wireless electricity? If we can generate a magnetic field large enough to resonate with a distant receiver, can we power large, energy-thirsty tools wirelessly like clothes dryers or robots, maybe even factories, buildings or a whole city?
Maybe an airline could park planes on the tarmac on top of giant coils in the concrete, or we could embed them in the foundation of every new skyscraper to completely meet the power needs inside.
Absolutely – in theory.
Before we get ahead of ourselves, let’s not forget that haven’t abandoned voice transmission through wires in the developed world because the infrastructure is a century old and works perfectly well.
The same infrastructure already exists to deliver electricity to your house or workplace, and the upheaval and cost in retrofitting our entire society to adopt wireless electricity would be steep (to say nothing of intrusive and time consuming). Wires do a perfectly fine job transferring energy very efficiently right to your door.
The real gap where wireless electricity can take off, according to WiTricity, is in the last little stretch to your device, an interesting parallel with the last mile problem that’s dogged internet data transmission to the masses for years. Just like high speed data, getting electricity to your street corner or building is easy. Unshackling you from power outlets all throughout your home or work is a different problem.
WiTricity’s Sanjay Gupta sees his business as disrupting the wall socket. One of the company’s visions (it’s active in several industrial sectors) is for everything from stationary devices like TVs to on-the-go tools like your iPad, phone and even PC mice and keyboards to be powered by a resonant magnetic field enveloping your house.
“[We] have this fundamental desire to get un-tethered,” Gupta says. The problem we need to solve is not to make all energy transfer wireless, it’s to change the experience of plugging things in.”
Is wireless power safe?
As the Wikipedia page on Tesla coils puts it, ‘large systems can deliver higher energy, potentially lethal, repetitive high-voltage capacitor discharges from their top terminals’. A large coil can generate up to half a million volts, and as any museum tour guide that operates a Tesla coil will tell you, the arcs will destroy electronic equipment, coils can catch fire if they’re run for too long and they’re usually housed inside a Faraday cage (the same thing that stops microwaves leaking out of your microwave oven).
Today, consumer applications of wireless power like device charging pads aren’t enough to hurt you, but you wouldn’t want anything as obtrusive, loud or dangerous as a Tesla coil on top of your house, hissing away and throwing electrical arcs all over the yard.
But in a world where the electromagnetic fields generated by mobile phones still concern some people, should we be worried about our houses or workplaces enveloped in a sea of magnetic fields?
So far, wireless energy is a low power proposition. It’s enough to charge your mobile or iPad over time, but energy intensive applications like games and streaming video will still deplete the battery faster than low powered wireless energy can charge it. The consumer applications offered by WiTricity, according to CTO Sanjay Gupta, are lower powered than even a mobile, so the magnetic fields aren’t strong enough to be absorbed into the human body.
But powering every device in the living room, office or a whole city building constantly would need a much more powerful signal, and that can become a problem. Even though the effects of electromagnetic fields on human health is a contentious issue, few argue that there are indeed effects.
To Ha Pham N, a PhD and lecturer at the University of Technology, Sydney’s school of electrical, mechanical and mechatronic systems, the answer isn’t stronger magnetic fields, it’s more efficiency in devices to harvest the magnetic fields that generate electricity. “It is actually about design,” he says “In the future we need technology that requires very low power because our body has a limit. If we exceed that limit then [wireless power] will become dangerous.”
If mobile phones are indeed dangerous (conspiracy theorists wait for the day when years of lobbying records and manufacturer cover-ups are reveals), then the kind of magnetic fields we’ll need to run higher-powered devices wirelessly won’t be as safe as we’d like.
But even then, it’s a matter of successful systems design. “As long as there is no living body in the strong field it’s okay,” says Dr Pham. “A good product will make sure that the living bodies are kept away from that.
“A good example is wireless vehicle charging – you’re not supposed to lie under your car in the middle of the magnetic field charging it, so when the floor is safe – for example using sensor technology – it can be a little higher powered.”