When Nikola Tesla developed alternating current electricity (the sort that flows from modern wall sockets) in the late 1800s, he never imagined that powerlines would someday come to crisscross the globe. He went on to devise devices that could transmit power wirelessly and dreamed of a global network that would supply machines everywhere with power and information.
"All railroads will be electrified," he said in a 1926 interview with the magazine "Collier's." "But "perhaps the most valuable application of wireless energy will be the propulsion of flying machines, which will carry no fuel."
Tesla was half right. Today's cellphone networks allow cable-free communication, but a worldwide web of wireless power remains elusive — and likely impossible in the form that he imagined. Nevertheless, companies such as the Massachusetts-based WiTricity and Israeli start-up Electron, as well as academic teams, continue to work toward a world with fewer wires, one that realizes specific aspects of Tesla's vision.
But to go mainstream, wireless charging will need international standards and more flexible implementations. Both are under way. Charging while parking will likely be coming to consumer vehicles in 2022, for instance. More versatile technology exists in the lab too. Standard wireless charging approaches work best between two objects at a fixed distance, but in April a Stanford team announced a system capable of efficiently transferring power to a moving device within arm's length — technology that could someday help cut power cords at home and on the road.
"This will attract a lot of interest from industry," says Younes Ra'di, a researcher at the City University of New York who has demonstrated the same technique independently of the Stanford group. This research "created a new direction in designing wireless power transfer that could help build a new generation of wireless power transfer systems."
Electromagnetic waves carry energy as well as information, so there's no theoretical reason that telecom companies couldn't beam power around like they do cat videos and music. But practical challenges abound. Long-range power-transfer experiments typically involve beams of microwaves focused tightly on a receiver — imagine charging a solar panel with a laser pointer — that don't scale well to millions of devices.
Over short distances, however, a different approach makes widespread wireless charging more practical. A magnetic field vibrating at one special frequency can make a nearby magnetic field wobble in response, much as belting out the right pitch can shatter a wineglass.
Through this effect, one magnetic coil can drive an electric current in a device attached to a partner coil, as a team of MIT researchers demonstrated in 2007, improving on ideas Tesla pioneered. The group spun off the technology into a start-up company in Watertown, Massachusetts, WiTricity, whose charging coils have since found their way into a laptop and electric vehicles.
The technique delivers high amounts of power with cablelike efficiency, but the link between the coils can be delicate. Disturbing the system changes the frequency of the magnetic vibration, breaking the wireless connection for such setups in general. "If you move the transmitter or receiver even a little bit, you lose the effect," Ra'di says. [A WiTricity spokesperson notes that the company has found alternative ways to compensate for this effect.]
"If you move the transmitter or receiver even a little bit, you lose the effect," Ra'di says.
In 2017 and 2018, two groups, one at Stanford University and another headed by Ra'di independently, stumbled upon similar workarounds. Inspired by a theoretical concept from optics, they set up the transmitter and receiver in such a way that the two units functioned together as one entity. When one side moves (changing the ideal vibration frequency), the shift provokes a near-instant reaction from its partner, explains Sid Assawaworrarit, one of the Stanford researchers.
This flexibility lets the system exploit physical laws to swiftly and automatically seek the most efficient frequency, no software or manual adjustments required. But it was a power hog. For every watt the groups pumped into the transmitter, only around a tenth of a watt reached the receiver.
Now the Stanford group has solved that problem too, according to research published in "Nature Electronics." A redesigned amplifier has let them transmit 10W (more than enough to charge a phone or tablet) over 2 ft with 92% efficiency. More significantly, they got the same performance at closer distances, as well as when Assawaworrarit swung one of the 2-ft-wide coils back and forth as fast as he could. He says that the system would transmit power even if one coil were zooming by at 200 mph, according to simulations.
Ra'di calls such performance "amazing," especially when compared with more rigid systems that work best at one single distance, or inefficient systems where most of the power is lost. "That's a really huge step forward," he says.
The transmitter effectively creates a similarly sized bubble of energy that can charge any coil-equipped device in range, and requires little power to maintain. These features lend themselves to a range of potential applications, from electrified highways to factories where mobile robots never need to stop and charge. Ra'di, for his part, imagines walking in the door at the end of the day and flopping onto the couch to charge his phone, rather than dashing to the wall to plug it in.
And the system could handle much more power using off-the-shelf parts, according to Assawaworrarit. A bigger challenge to scaling up would be the hassle of installing large enough coils. Filling a room with wireless energy, for instance, would require covering most of the floor.
Moreover, the road from the lab bench to the real world is long and winding, as Alex Gruzen, WiTricity's CEO knows all too well. He calls the adaptive charging approach "elegant" and applauds the groups' work as moving in a "great direction," but suggests that simpler solutions are already nearing commercialization — especially for electric cars.
Electric vehicles are becoming a major market, and keeping them charged will require installing tens of millions of charging stations collectively, worth nearly $50 billion by 2030 (up from about $5 billion today), according to a McKinsey & Co. report. Wireless parking places, if they work well with a variety of vehicles, are primed to be part of the gold rush. WiTricity's charging coils, which China chose for its national wireless standard in May, can reach parked electric sports cars and SUVs alike with clearance ranging from 4 in.–10 in., Gruzen says, without significantly adjusting their frequency.
Charging vehicles in motion is on the table with existing technology too, since the distance between a car's carriage and the road stays fairly constant. Fellow wireless charging company Qualcomm Halo, which WiTricity acquired last year, has built a 300-ft test track in France that can charge cars driving at highway speeds. And Israeli start-up Electreon is electrifying short stretches of road in Israel and Sweden.
Magnetic coils could allow wireless charging stations at home eventually, Gruzen agrees. But for now he's focused on rallying automakers around a single wireless standard that will allow for the proliferation of parking spots and road lanes that energize the vehicles above them.
Toyota licensed WiTricity technology back in 2011, and BMW launched one wireless charging option in Germany in 2018 for about $3,500 (a limited pilot program reached California last summer). Gruzen says other major automakers have committed to launching models with WiTricity technology in 2022. Tesla (the automaker) appears to have other plans, with a robotic "snake" plug in development since 2015.
If automakers can settle on one standard technology, omnipresent, automatic charging stations would let electric vehicles go farther on smaller batteries, reminiscent of Tesla's imagined fuel-free planes. Hands-free charging also will grow more essential if cars get more autonomous, since they won't be able to plug themselves in.
"It's just all about accelerating the deployment of electric vehicles, Gruzen says, "making them work in more and more places."
For the researchers developing the new adaptive technique, the technologies are complimentary: More resilient connections are just one more tool for expanding the situations where wireless power becomes feasible. Self-tuning systems could also charge multiple moving devices at once, Ra'di says, such as different phones in different pockets.
The current wireless charging market, which is limited to pads that create small charging surfaces, is expected to grow by 30% per year, reaching $27 billion by 2025. Whether future consumers would install additional infrastructure in return for larger charging areas remains to be seen.
Eventually, Ra'di imagines, power will fill the home alongside Wi-Fi — Tesla's 1926 vision of the world writ small. "In the future, research will go toward the direction of a small box in the corner," he says. "You don't have to stay a certain distance away; you just walk around and it will charge your phone."
Correction: This story has been updated to reflect that Toyota licensed WiTricity's technology in 2011.