The Many Different Wireless Charging Technologies – The Wireless Solution

The Many Different Wireless Charging Technologies

The Pi wireless charging cone next to a smartphone


Up until now we’ve perhaps misleadingly given the impression that only two different wireless charging technologies exist, and if you’re still new to wireless charging you may only be aware of one, inductive charging.


Man biting pencil in frustration

But there’s actually a whole host of different technologies each with unique benefits and uses.

Despite inductive charging dominating the consumer market, the playing field is becoming much more open, as startups are revealing exciting technologies that could shake up the way we think about wireless charging forever.

This will become increasingly important as we begin to see a shift

Now that Qi dominates the inductive charging market, its competition may come from different technologies that are continuing to change the way we think about wireless charging.

According to Digitimes research, Apple’s move to join the Wireless Power Consortium has:

“Pushed the member companies in the AFA (AirFuel Alliance) to exert efforts to develop magnetic resonance (MR) and other RF wireless charging solutions in order to win a new round of battle in the mid and long-distance wireless charging segment.”

Despite Qi finally triumphing in the inductive standards war, many still have qualms about its limitations, in particular, its lack of spatial freedom. With distance charging technologies gaining traction it might now be better to think of the wireless charging standards war in terms of “near-field” vs “far-field” instead of Qi vs PMA. Far field systems are also called “radiative” because they beam power over long distances, whereas near field systems simply use electromagnetic fields.

If inductive charging proves incapable of fully supplanting wired charging (although we don’t think it will), it may well be that long-range charging finishes the job that Qi set out to do.

Near Field / Non-Radiative


So what is so called “near field” charging? This can be defined as:

Charging that occurs within one wavelength of a transmitter coil.

The first example of this is no doubt a technology you've heard of before:


Inductive Coupling


Hand putting smartphone down upon blue CHOETECH charging pad


The most common form of near field charging is inductive charging and is the technology utilised in all of the products we currently sell in our store. It works by transferring power via the electromagnetic field generated by an AC current.

If aligned properly this electro-magnetic field can then generate an AC current in a receiver coil, which is then converted back into DC current via a rectifier.

While an inductive charger can power your phone wire free, magnetic induction requires two coils of similar sizes to be closely aligned, with a strong drop off in efficiency occurring the further away your phone’s coil is from the transmitter coil.

The bigger the coil the bigger the magnetic field, this is why inductive phone chargers have a range of around 1cm whereas EV chargers can inductively charge over several inches.

 It has many benefits including:

  • More convenient than a cable
  • Charging speeds comparable to wired charging at 15W
  • It is safer than a cable
  • It can be built into surfaces

Inductive provides more spatial freedom than a wired charger whilst maintaining a good level of efficiency.


Capacitive Coupling


Capacitive coupling diagram


There is another kind of near-field power transfer called capacitive coupling. This uses an electric field as opposed to a magnetic field to transfer power.

Capacitive coupling is not nearly as commercially popular as magnetic induction and is used predominantly in low power applications.

This is because electric fields are more volatile and have the potential to interact with objects, including people. There is however a Japanese company called Murata which claim to have built a capacitive coupling system that works for smartphones.


Mid Field / Non-Radiative


Resonant Coupling


Qi resonant charging demonstration


When an inductive charger creates a magnetic field, it’s omnidirectional. The advantage of magnetic resonance is that when two coils are tuned to the same frequency, they become strongly coupled. This funnels the magnetic field, offsetting some of the energy leakage over longer distances.

This frequency coupling isn’t as effective when the coils are closely aligned but can be effective in reducing energy wastage over mid-range distances of around 2cm. Whilst resonant is less efficient than inductive in optimal conditions, with an efficiency that continues to taper off over distance, it has several benefits over inductive charging:

  • Multiple device charging from one coil
  • Further charging distance
  • No need for coil alignment

The Airfuel Alliance are currently a big champion of resonant with their Airfuel Resonant technology (formerly Rezence), which they claim can charge devices from up to 50mm away, it is currently used to power the Dell 2-in-1 Latitude laptop and Chargifi’s public infrastructure charging.

The Wireless Power Consortium has also built resonant into all Qi devices from the 1.2 specification onwards. However, it’s use is limited, with the main example being the public charging solution provided by Aircharge.

In addition, there are a few companies with patents in the field of resonant charging who license their technology to other brands. These include the likes of WiTricityMojo Mobility and WiPower by Qualcomm.

WiTricity in particular was the company that really brought Resonant to the mainstream after being setup with help from the MIT researchers who discovered a commercial use for resonant technology. WiTricity offer a development kit for start-ups which helps companies take their technology and integrate it into a whole range of devices, from automotive solutions to implantable medical devices.

If you’d like to read more about resonant charging which we strongly believe has untapped potential, please check out our article on Resonant.


Shaping Resonant Coupling 


Pi Charging cone in use on a desk by lots of people


A recent and exciting development in the world of wireless charging is a technology called Pi.

This product allows for resonant charging from up to 1 foot of distance in any orientation. This became possible after an MIT student named Lixin discovered a mathematical breakthrough that enabled the shaping of magnetic fields in real time.

You can even read the original scientific paper that takes you through the how the technology is possible.

Their commercial product, the "Pi Cone", will constantly shape a magnetic field to perfectly align with the angle of any Pi-enabled devices in its radius. It can do this with multiple devices with a power transfer that is comparable to inductive charging over short distances but drops off the further you take your phone away.

The company won at TechCrunch Disrupt SF in 2017 and as of December 2017 have secured almost $12 million in series A investments.

Pi seems like a promising technology as it doesn’t claim the extraordinary, it is merely a smart extension of resonant technology that improves the efficiency and increases the number of chargeable devices in the mid-field range.

However, we are yet to hear from Pi in 2018 so they may be having trouble translating the technology into a commercial product.



Far Field / Radiative


Despite the possibilities created by resonant charging, it’s efficiency can be a strong deterrent, and while it does provide more spatial freedom than inductive, its ability to charge over distance is far less than some of the emerging “far field” technologies.

As we’ve become more dependent on our smartphones there has also been a huge interest in the development of far-field power transmission. This is because the possibility it creates of a constant stream of charge wherever we go. The major drawback however is that these technologies have various issues that are hard to overcome including:

  • Safety issues
  • Poor efficiency
  • Poor power transfer

Nevertheless here’s a look at some of these pretty fascinating far field technologies.




Strobe lights all over a dark room


Laser wireless charging functions by converting electromagnetic radiation from a transmitter coil into a wavelength closer to the visible region of the spectrum and focusing it, this is also known as “power beaming” and it sounds pretty darn cool if you ask us.

The laser beams are then captured on a receiver and turned into current by tiny photo-voltaic cells. The advantage of this is the ability to carry large amounts of power over great distances, but one big downside is that if the line of sight is obscured no transmission can occur.

One of the main proponents of this currently is an Israeli company called Wi-Charge, whose technology works by directing infrared lasers using a rotating transmitter in the ceiling which turns to constantly provide a clear line of sight to your device.

The technology is FDA approved and according to Wi-Charge can provide power over distances of up to 250 square feet. Whether it will be able to provide enough power to be a suitable system for charging our smartphones remains to be seen, but according to EEV Blog the end to end efficiency may prevent it ever being a complete charging solution.

Here’s Linus Tech Tips trying out a demo:





A blue radio frequency wave


RF or Radio Frequency is a far field radiative charging technology that has had multiple proponents over the last few years, and is even part of the Airfuel standard (Airfuel RF). 

RF transmits electronic waves at radio frequencies to a receiver which then converts these waves back into usable energy.




Energous WATTUP technology


Energous are a member of the Airfuel Alliance and are perhaps the most high profile RF wireless charging technology, mainly owing to the huge backing they’v received from investors.

Having had both mid-field and far-field prototypes approved by the FCC, their product could prove a convenient home solution for charging if it works. This showcase at CES 2018 indicates how it could be used to power all the PC accessories around your computer thanks to a transmitter built into the monitor.

However, despite various series of investments over many years Energous still don’t seem close to commercial production, leading many to speculate that their product is pretty much a sunk cost at this point. For instance, short seller Chris Brown has gone as far calling Energous a “worthless equity”.




Ossia COTA technology


Ossia has demonstrated a slightly more concrete RF product with its Cota technology, which has appears to have the ability to navigate its way around objects to reach its charging destination. Other far field technologies, in particular Wi-Charge, require line of site to achieve charge.   

It achieves this by initially sending out an omni-directional low power beacon signal from the receiver, which is used by the transmitter to decode the receiver’s location. According to Ossia, the transmitter can then power beam back RF waves, bouncing these beams off walls if necessary. The entire process is then repeated 100 times per second to track moving receivers.  

The product uses a black cylinder roughly the size of a recycling bin to deliver power to receivers that can be made small enough to fit within a AAA battery and can charge multiple receivers at any orientation.

The Cota technology certainly has come up with an ingenious way to beam RF waves effectively to a mobile device and as a result has won the CES innovation award three years in a row. But once again this comes with all the expected caveats – whilst the technology has proven it can light up the charging icon on your phone, whether it will charge devices from a commercial product at an efficiency level that would make it desirable remains to be seen.  




Powercast Powerspot transmitter


Another company called Powercast, attracted a lot of attention at CES 2018 with its Powerspot technology.

In the video below LEDs being charged by the Powerspot show just how far its RF waves can reach, with an upper limit of up to 80 feet away, although this would only be a a very low power charge for sensors and other small electronics.  Powercast have suggested they may release commercial products within 2018 if they receive support from enough brands to bake their technology into popular gadgets.



The good thing about Powerspot is that the technology is geared towards trickle charging low power devices, and this feels like a more fitting use of RF power beaming. Powerspot only transfers 1 watt of power at a time so is limited to charging devices like headphones, remotes and game controllers. Although the transfer efficiency is not high, if a trickle charge is left on constantly it provides a neat solution for keeping these peripherals topped up.

Unfortunately, Powerspot is not designed with smartphones in mind - sorry to burst your bubble. But if Powercast are to be believed, they claim they may have a product ready to ship by late 2018, providing they can get device makers to bake the technology in with their products.  




uBeam diagram


Another far-field technology shrouded in controversy is uBeam, a startup that claimed it could deliver efficient wireless power via ultrasound – the same technology used to image unborn babies.

Founded by Meredith Perry in 2011 whilst she was an undergraduate student at the University of Pennsylvania, uBeam claimed it could develop a technology that transfers power by converting electromagnetic radiation into ultrasonic waves, sound waves that travel at a higher frequency than can be heard by humans.

Perry has been hailed as one of the greatest young innovators in technology and Ubeam has received serious upfront investments after its initial launch, gaining over $20m worth of investments in its series B round alone and backing from high profile investors including Mark Cuban and former Yahoo Chief Exec Marissa Mayer.

However, there have been several major flaws leveled at uBeam:

  • That it can't transfer a substantial level of power
  • That it can't reach acceptable levels of efficiency.
  • That it requires a direct line of sight between the transmitter and receiver.

Many, including an ex uBeam engineer who has published an outspoken blog on the subject, have criticised uBeam’s practicality.

And these criticisms could finally have caught up with uBeam: in September 2018 Meredith Perry stepped down from her role as CEO, most likely indicating that uBeam have and will struggle to ever build a commercial product.


What Should We Think of All This?


While it could just be a matter of time before everyone converts to inductive charging, those who romanticise about the idea of "true wireless charging" have turned their attention to startups that are creating new far-field technologies. 

The problem is that many of these startups have been known to make wild claims about the capabilities of their technology, in hopes of generating upfront investments. What makes this worse is that many high-profile investors are willing to jump on the hype train of these startups without actually knowing whether they can produce the results.  

We here at The Wireless Solution know that wireless is the future and that ubiquity is coming, but just when and how might still be a matter of debate. Whatever the case, we feel it’s important to remember that the process will happen in its own time, we are simply grateful to be able to cheer from the side-lines as more of these amazing technologies come to fruition.


Girl cheerleading


We also think that regardless of what lies ahead, inductive charging does a pretty darn good job of keeping your phone juiced up, so be sure to check out our store for all the latest inductive chargers on the market.


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