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Is Wireless Power Transfer Safe and Secure?

August 23, 2019 by Emily Gray-Fow

With a range of small-scale and large-scale wireless power platforms in their final phases of testing and deployment, the question remains: ‘How can wireless power be both economically viable and secure?’

In this article, we'll look at some of the different technologies poised to both pay for themselves and bring profit to shareholders. 


Profiting from Thin Air

Wireless power transfer has been around for many years, but because technology has only just begun to call for ubiquitous electricity, we haven’t seen much development in the area until recently,

Another major reason is that showing investors how they can profit from electricity (something that is easily accessed and widely available) has been an uphill battle.

Consider, for instance, that a lack of confidence from investors is one of the main reasons why Nikola Tesla’s Wardenclyffe Tower (artist’s impression below) didn’t become the first node in a global wireless power and information network. In fact, the idea that power would be beamed into the air—i.e free for the taking—put off major investors and caused the scheme to fail.


Wardenclyffe Tower

Nikola Tesla's Wardenclyffe Tower (artist's rendition). Image courtesy of Wikimedia Commons. 


In today’s world, however, there are multiple businesses proposing wireless power on a commercial basis. The variety of near-field and far-field transfer processes have led to a range of profit extraction suggestions. Whether or not we will ever see these proposals in action on a large-scale level depends very much on whether investors deem these suggestions viable, just like with Tesla’s plans from the last century.


Power In and Money Out?

Since power costs money, there are (quite understandably) concerns about how to monetise wireless power. Which methods can be used to have people to pay for power—and, on the other hand, which methods could be used to steal electricity?


Magnetic Induction

With near-field wireless power transmission, the power source needs to be close to a receiver. Think of today’s wireless chargers for small devices such as those that use inductive coupling to transfer power. The Qi standard is one of the better-known protocols for this type of charging, and the chances are that you’ll occasionally see wireless charging pads (pictured below) in places like public transport, fast-food restaurants, and so on.

Although most of the public places in which you’ll see Qi charging pads allow free access, the location of the pads themselves—plus the fact that the item being charged needs to be in direct contact with the pad—is what enables them to ‘pay for themselves’. After all, staff may well allow you to charge your phone for free in a fast-food restaurant, but they also know that hunger, thirst (and etiquette) mean you likely won’t sit there for around 30 minutes or more without buying a drink or some food.


A wireless charging pad that can be used to charge a smartphone. Image courtesy of Bigstock.


There are also proposals (and progress has already been made) to build induction power into road surfaces for EV charging. How acceptable this would be in cities, however, remains to be seen—but either way, the system of designated charging lanes on larger highways is likely in the next few years.

Induction charging systems are relatively straightforward and easy to hack. Though most people would never hand-wind their own induction coils, it’s possible with a little effort to move the receiving equipment from one gadget to another.

The Wireless Power Consortium is key in the development of Qi and other inductive power transmission standards. Currently, they’re working on a mid-range power standard for charging devices such as power tools; plus, they’re looking at establishing a high-powered (over 2kW) standard for kitchens.


Resonant Charging

Resonant charging works by tuning two electromagnetic coils to resonate at the same frequency. AirFuel is one of the front-runners. The concept of resonant power transfer offers some advantages over induction (such as not needing to have the coils exactly matched up). Instead of being limited to 5 mm distances (as is the case with induction), resonant charging also works up to 50 mm.


Radiofrequency Power Transmission for IoT and Personal Gadgets

There are several proposed schemes to enable wireless power transfer (WPT) for a selection of mobile devices, with the assumption that people will move between areas where wireless charging is available and will also want the charging process to be automated to some extent.

The IoT, edge computing, and the global penetration of personal devices all call for a more effective way to power devices than through wires alone. We may well see Wireless Energy Transfer Interfaces set up alongside our current infrastructure sooner rather than later.


Panoramic cityscape background with two smartphones.

Two smartphones close up with a panoramic cityscape background, which are surrounded by graphics that denote interconnected communications. Image courtesy of Pixabay.


The rollout of 5G, along with the relatively high-power requirements of the latest smartphones, has given RF power transmission a boost. There are proposals for developing a system whereby the smaller, more frequent 5G base stations are also used to transmit power, either on the same carrier wave (as Tesla planned for his global power and data network)—or otherwise through the use of orthogonal waves that would avoid the communications signals already being put out by the growing number of small 5G base stations.

Combining power transmission with the data network has some of the most promising potentials of any of the proposed power transmission schemes. There’s a very good chance that 6G will turn out to be ‘power and data’-based or simultaneous wireless information and power transfer-based (SWIPT).


What About the Licensing of Frequencies?

The licence-free 2.45 GHz ISM (Industrial, Scientific and Medical) band is just one option that has been mooted. The ISM radio bands are set aside as licence-free bandwidth for the titular use of industrial, scientific, and medical applications. The said bandwidth has been used for communication technologies like WLAN and Bluetooth in the past, and thanks to the potential for mixed-use rectennas and SWIPT, there’s also no reason not to use it for power transfer within a 5-to-10 m radius of a base station.

Current laws limit the amount of power that can be transmitted over-the-air (OTA), with the FCC (Federal Communications Commission) having recently licensed the first ‘power at a distance’ product (Energous’s WattUp), which has an effective radius of 3 ft. This is a big leap forward, as current regulations for power via RF communications signals limit transmissions to 1W—nothing even close to a practical level, even for portable gadgets.

In the U.S., the FCC is more likely to allow transmission of any level of power, so long as it can be carried out safely. Regulations will vary from country to country and may take a long time to align in some parts of the world.


Directional vs Broadcast RF Power

The distance of which RF OTA power can be transmitted varies greatly depending on whether the signals are broadcast, or if part of the directional beam that tracks the device is charging. Directional power broadcasts at least triple the effective distance of power signals, but it also requires a lot more in the way of software and hardware to manage access.

Directional power broadcasts can also interfere with each other, limiting the number of devices that can receive power on a certain frequency. None of this is insurmountable, and directional beams would also save power when compared to an ‘always-on’ broadcast model. Which system we end up with, or whether we end up with a mixture of systems, remains to be seen.


City graphic of connectivity

A concept image of a wireless communication network along a cityscape. Image courtesy of Bigstock.


So How Practical is RF as a Power Source?

Current Wi-Fi routers don’t broadcast continuously, making them poor sources of wireless power in their unmodified state. Vamsi Talla at the University of Washington has been working on this problem with a few fellow researchers.

Imagine if every public Wi-Fi router and mobile phone antenna were broadcasting power with a 5-to-12 m radius. It's estimated that the 5G network will use around 400 times as many base stations as the current 4G network, though these will use less power than 4G towers. It’s not a massive assumption to anticipate that we’ll be near a base station a lot more often once 5G has been rolled out everywhere—though, in the near future, 15 ft is more likely than 15 m.

Also, it is unlikely that we’ll see the end of popular battery use with the adoption of this new technology. Rather, we’ll carry devices that automatically top themselves up when they’re near a compatible power source. Software handshakes can also be used to mitigate who has access to each charging station to prevent unauthorised use.

Being able to limit access is an essential part of the technology—not just to prevent those who haven’t paid from accessing free power—but to ensure that charging signals don’t interfere with themselves or other signals. Preventing interference is another issue that would be easier to mitigate if power and communications were transmitted from the same box.


Higher Power Applications for RF Power Transmission

Due to regulations on how much power can be transmitted OTA, we’re unlikely to see substantially high-power wireless energy transfer in the near future.

This doesn’t mean that Nikola Tesla’s dream is dead. There is ongoing research into transferring energy over longer distances at infrastructure/power grid levels of energy. Viziv Technologies has a test tower in Texas, and the company’s actively researching the technology (which uses Zenick waves) in the interest of building a test network in the Middle East. 

Such a system would likely transmit energy between power plants and electrical sub-stations with no appreciable difference for individual customers. Frequency-hopping (or perhaps another method) would be needed to prevent thieves, and there are many other hurdles to overcome before this technology becomes a realistic prospect.


NASA solar satellite

NASA solar satellite (artist's rendition). Image courtesy of NASA. 


Space-Based Power

There are various schemes proposed to enable the transmission of power from solar satellites to either planet-based receivers or other space-based platforms. Using highly directional laser or microwave beams would be the only way to make the technology practical. It would also make it extremely difficult to steal power.

Projects have been suggested for a future Mars colony, and for laser propulsion of spacecraft using solar sails, as well as simple solar power generation. All of these ideas focus on the distant future, however: they remain largely theoretical for the time being.


What the Future Holds for Over-the-Air Power 

Rapidly growing requirements for the powering of gadgets, sensors, and other low-power items mean that mid-range wireless power transfer is likely to become a commercial reality sometime in the next 10 years. Regulatory bodies have already been shown willing to work with companies to make the technology a reality, and OTA power would reduce the costs and hassle associated with keeping an increasing array of devices working on a day-to-day basis. 

Ultimately, while perhaps 6G or 7G will solve the said communications challenges by each having a built-in power transmission component, for now, the question of how these technologies will evolve in practice remains to be seen. Still, it’s clear from the points raised that the future of wireless transmission and power solutions are promising to say the least.

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