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Aiming Wireless Power

We Explore PowerByProxi and Cota

Not long ago, we looked at wireless power. And we looked at some of the standards and conflicts underway as companies and technologies vie for best position. And it looked like a simple two-sided issue, with the eventual winner not yet clear.

Well, turns out there’s even more going on, some of it in places we rarely visit. I’ve run across two more wireless power stories, and they’re different from what we’ve seen and from each other. In an attempt to find a unifying theme as I bring them into the discussion, the common denominator seems to be their ability to “aim” their power at a device that needs charging.

Let’s back up, however, and start with a quick review.

  • Old school toothbrush wireless charging is “inductive” and requires extremely precise (mm-level) positioning to work.
  • New wireless approaches, called “resonant,” allow charging with much more positional forgiveness – several inches. Now you can mount a charging pad under a table or counter and place devices on the surface above for charging. You can extend this range using passive “repeaters.”
  • Some say there is no difference between “inductive” and “resonant” – that they’re the same thing, really – but there does seem to be a distinction that matters. New efforts are focused on resonant-style charging (although… well… wait for it… more on this in a minute).
  • The old inductive charging takes place at 200 kHz. New resonant charging is being developed in that frequency range.
  • New resonant systems are also being developed at 6.78 MHz.
  • There are various arguments about which frequency is better, including backwards compatibility with existing inductive systems and heating of nearby items (and there’s news there as well).

With these charging system, we have stations radiating fields that charge a device. But any given device will intercept only a part of the field. There is communication between charger and chargee, so power to the charger can be turned on or off to avoid wasting energy outright, but it’s otherwise not particularly selective in how it radiates (although shielding and system design restrict field leakage to some extent).

More selective charging

Well, while we weren’t looking, way around on the other side of the world, PowerByProxi has commercialized technology developed at the University of Auckland (where, they assert, the whole wireless power thing started over 20 years ago). They’ve been involved in a number of different wireless power efforts in the industrial arena – such as a gantry that used to be powered using a carbon brush – which generates nasty contaminating particles – that can now be powered cleanly using a wireless and carbonless approach.

But in the simple consumer-device-charging context, they have a finer-granularity technique. Instead of a single flat loop coil, they use an array of smaller helical coils. Exactly how big will vary by design (they license the technology to OEMs that build specific implementations). Through in-band communication, they will know when they’re in the presence of a device that needs to be charged. But they also sample the field anomalies caused by the presence of the device, and, from that, they can deduce the rough size and position of the device. And then they engage only the coils under (or close to) the device being charged. This can be adapted to accommodate multiple charging devices.


Figure 1. Single-loop charging pad (above) and PowerByProxi pad (below). “Energized” area shown in pink.

In the figure above, I’ve intentionally not shown the loop arrangement in the top pad – because I’m not exactly sure what it is. PowerByProxi asserts that these pads have “dead” spots (or at least “sweet” spots), but further discussions with WiTricity provided assurances that a good design will give uniform coverage. It’s that focus on “design” that suggests that this isn’t something you just slap together and call it good – there appears to be a fair bit of work in ensuring that the fields are where they should be. I’m not going to try to guess what that might mean.

But it’s clear from the bottom image that only the coils roughly under the device being charged are energized. This clearly restricts the field and saves power. And improves efficiency – something we really haven’t talked about much because each side has efficiency claims that are hard to sort through (or at least I haven’t sorted through them at this point).

The PowerByProxi approach also limits stray fields – which helps to mitigate the whole local heating thing. Especially since PowerByProxi uses the legacy 200-kHz frequency – at the request of their customers.

GHz charging

Meanwhile, from the far end of the geographical world, we’re going to travel way to the other end of the frequency range, zooming past 6.78 MHz all the way out to 2.4 GHz and a completely different concept called “Cota” from a company named Ossia. At its simplest, we’re talking about charging using RF signals. (PowerByProxi characterized the concept as being the same as RF energy harvesting, except that you’re generating the signal being harvested.) This technology extends the charging range to as much as 30 ft (10 m) – much farther than anything else we’ve seen.

The main difference here is that this is low-energy charging. It would take a very long time to charge a phone from scratch this way. The idea is, however, that, if stations using this technology are prevalent, then phones would mostly be charged all the time, and this provides a constant trickle-charge to keep them that way. The phone would rarely need a long charge. Unlike the other approaches, which require you to leave your phone on a pad, this can charge your phone while you talk on it or while it’s in your pocket.

Yeah… I know. Some of you cringed at the thought of charging waves being aimed at or near your pocket. There’s probably room for marketing abuse here (hopefully folks are above that), but safety has to be an explicit consideration for any of these technologies. And, in fact, if you talk to some of the other folks in this space, there’s concern about how much power has to be radiated – and how much people would be exposed to – if the near-field approaches discussed so far were simply to juice up harder so they could charge farther-away things.

Which is why the Cota approach is low power. In fact, by design, the power is no higher than what the phone itself would radiate when in use. They’re working with the FCC to demonstrate that there is no issue here. (The 2.4-GHz band, like the 6.78-MHz band, is an industrial-scientific-medical (ISM) band, but that just means you don’t need a license. You still have to get FCC – and EC etc. – blessing for interference and such.)

But there’s more to this story than simply radiating out some huge low-power field – because that’s not how it works. It’s more subtle than that – especially due to the presence of obstacles. With the near-field approaches, where you put the charging device on a pad, the device is still pretty close to the charger, so obstacles aren’t an issue (unless you consider, say, the countertop to be an obstacle – and the field goes right through it). But obstacles interfere with RF, and you can’t clear a 30’ space to provide for charging. Within such a radius you would expect to find tables and chairs and counters and oddly-shaped obstructions – and people. The obstructions might (or might not) stay in place, but the people won’t.

So here comes the tricky bit. The phone itself emits a chirp that the charger can detect. The charger has on the order of 10,000 small antennas, and each antenna measures the chirp. For the chirp to arrive at these antennas, it’s going to be blocked by obstructions and reflected by walls and other obstructions. So the chirp will arrive at the charger via a complex set of multi-paths.

Each antenna “remembers” the timing of the signal it receives (which may be the sum of several multi-paths). When charging, then, each antenna sends out a higher-power charging signal that exactly reverses this path and the timing it detected. The idea (which to me seems like beamforming, but apparently there is some nuance such that, strictly speaking, it isn’t) is that the transmitted charging signals reverse the various paths of the chirp and arrive together “in focus” at the phone.


Figure 2. Cota’s RF focusing approach (Image courtesy Ossia)

This is why they use the high frequency. The precision with which they can focus depends on the wavelength. At 2 MHz, it’s 300 feet – not so precise. At 2 GHz, it’s 5 inches. They see 2.4 GHz both as a “Goldilocks” frequency (higher and the antenna window gets smaller) and as a space-saver because it allows them to make use of the existing Bluetooth antenna.

If you think that’s complex, well, we’re not done yet. Using a single chirp to establish a longer-term charging relationship works only if nobody moves. Last Starbucks I saw, there was lots of movement. So this chirp/charge process happens 100 times per second. Each time, it re-measures the environment and sends another “power packet.” (My term, not theirs.)

There’s also an issue of materials to contend with. Some materials reflect at this frequency; some don’t. If the environment is very transmissive, then very little of the chirp will be received by the charger, and the system will decline to respond with a power packet. There’s also a conversation with the device to be charged, and if it says, “I’m fully charged, thank you,” then no power packet will be sent.

Cota is currently being evaluated by manufacturers for embedding into systems. They even envision Cota-enabled batteries. They say this is a long process, so it will be some time before we know whether it gets picked up.

So there you go. Two completely different ways of implementing wireless power. On the one hand, seems like a lot of engineering going into a specialized space. Then again, the implications are enormous. The Ossia folks imagine a future generation of kids that won’t understand the concept of a phone charger – they’ll be accustomed to things being charged automatically and transparently as they walk around. Of course, this now means at least three mutually-incompatible systems duking it out, and it may get messy before it all settles out.


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15 thoughts on “Aiming Wireless Power”

  1. Nice article, Bryon. I enjoyed speaking with you for this article, and appreciate the opportunity to share more about our Cota solution with your readers. As you talk about trickle charging in your piece, I thought it would be worth a bit more detail here for your readers to understand how trickle charging works with respect to the Cota technology. Trickle charge is typically around 10mW of power, or 1/500 what an iPhone needs to charge using a traditional wired charger. Our Cota technology is approximately 200x that of trickle charging, or 30 percent of what a normal charger emits, while Qi chargers work at around 50 percent capacity. Currently, we have not seen any articles where Qi-based technology is described as trickle charge. We consider one percent of normal charging to be trickle charge.

    It’s also worth noting that wired chargers consume energy continuously, even after the device they are connected to is fully charged (stand by), and while plugged into an electrical socket without a device connected, sometimes called “vampire” state. In contrast, when not delivering power to any devices, the Cota system goes into hibernation and consumes miniscule amounts of energy, thereby being a more energy efficient solution as well. I hope this helps clarify how trickle charge works with the Cota system, but if readers have any further questions I invite them to let us know via our Facebook page or Twitter. We look forward to answering any questions and sharing further facts to break down the myths and dispel any doubts that truly wireless power has actually arrived.

    -Hatem Zeine, Inventor of Cota

  2. As a child we put Chlordane in a small wall heater to disperse it into the air to kill all insects. It was declared safe, and widely used since it was effective for killing a LOT of pests. It also turned out that breathing it, was REALLY bad for you, and the substance was banned from sale for most uses in the US around 1983, and all uses in 1988. Many buildings in use prior to 1988 will continue to emit Chlordane used for termite control, at very high levels for the life of the building. Not just cancers, but other life altering poor health issues that widely affect our generation, that are nearly non-existant in previous populations. http://en.wikipedia.org/wiki/Chlordane

    We are still learning what is “safe”, dispite high claims from lobbists that their questionable practices and products are really irrevokably provable as “really safe forever”.

    Studies linking EMF exposure to disruption of biological processes continue to trickle in, as do biased industry supported studies refuting other studies that impact the economics of EMF practices and products. Again we have studies, that connect not only cancers, but other life altering poor health issues that widely affect our generation, that are nearly non-existant in previous populations where high steady EMF exposures were non-existant. http://www.emfcenter.com/emffaqs.htm

    I’m certain there are a number of Chlordane industry folks that are indifferent to the impact that their industry had on the lives of many people …. as well as those struggling to accept the negative impact they made on so many people.

    When the EMF health studies are done, and finally conclusive, there may again be people in many other industries may also struggle with similar life altering impacts from EMF fields and products.

  3. # TotallyLost

    I notice that the only source you cite for the problems of EMF is a man who has build a very healthy living in “countering” these effects.

    You also say that studies on EMF “are trickling in”. The World Health Organisation – not as far as I know dominated by people with a vested interest in EMF, says in a long document http://www.who.int/peh-emf/about/WhatisEMF/en/

    “In the area of biological effects and medical applications of non-ionizing radiation approximately 25,000 articles have been published over the past 30 years. Despite the feeling of some people that more research needs to be done, scientific knowledge in this area is now more extensive than for most chemicals. Based on a recent in-depth review of the scientific literature, the WHO concluded that current evidence does not confirm the existence of any health consequences from exposure to low level electromagnetic fields. However, some gaps in knowledge about biological effects exist and need further research.”

    The WHO then goes on to propose further studies to fill these gaps, as a part of its International EMF project.

    25,000 articles is a trickle?

    You also, in your last sentence, appear to presume that the results of the further studies are going to be anti-EMF.

    I would have thought that you, as an engineer, would have looked at evidence more thoroughly rather than spreading Fear Uncertainty and Doubt.

    There are enough people out there, who don’t have your training, that are trying to build a case against science and technology. Please don’t feed them

  4. Hatem – Thanks for the clarification on “trickling.” I had always thought of “trickling” in a more qualitative way, where systems more or less stay charged or never reach much of a discharge level due to constant input. As contrasted with the charge-discharge-recharge model. Interesting to learn that it’s actually a quantitative definition. My use of the term was intended in the qualitative, not quantitative, sense.

  5. #Selwood

    The lack of controlled long term exposure and risk studies, leaves lots of questions unanswered, so that things are not nearly as consulsive as might appear.

    There were similar attacks on those concerned about chemcial exposures several decades ago, and in the end the high risk chemicals were removed after proven to be dangerous.

    What we do know, is that the epidemiological evidence indicates power-frequency magnetic fields create a small absolute raised risk of leukaemia in children, but not in adults. To the parents of these children, that’s significant.

    In fact, even when the risks are tiny for chemical or other factors, once factored into a world wide population, the tiny statistics are significant numbers of real people, even when only 1 in 10,000 people are affected.

    The negative research is FUD?? It’s only ment to feed the anti-science and Technology goofballs?? Are you so arrogant, as to suggest peer presure sensorship of negative results by industry professionals?

    research results: Cell phones and brain tumors: a review including the long-term epidemiologic data
    “The results indicate that using a cell phone for ?10 years approximately doubles the risk of being diagnosed with a brain tumor on the same (“ipsilateral”) side of the head as that preferred for cell phone use. The data achieve statistical significance for glioma and acoustic neuroma but not for meningioma.”

    research results: Non-thermal activation of the hsp27/p38MAPK stress pathway by mobile phone radiation in human endothelial cells: Molecular mechanism for cancer- and blood-brain barrier-related effects
    “Changes in the overall pattern of protein phosphorylation suggest that mobile phone radiation activates a variety of cellular signal transduction pathways, among them the hsp27/p38MAPK stress response pathway. Based on the known functions of hsp27, we put forward the hypothesis that mobile phone radiation-induced activation of hsp27 may (i) facilitate the development of brain cancer by inhibiting the cytochrome c/caspase-3 apoptotic pathway and (ii) cause an increase in blood-brain barrier permeability through stabilization of endothelial cell stress fibers. We postulate that these events, when occurring repeatedly over a long period of time, might become a health hazard because of the possible accumulation of brain tissue damage. Furthermore, our hypothesis suggests that other brain damaging factors may co-participate in mobile phone radiation-induced effects.”

    research results:Exposure to cell phone radiation up-regulates apoptosis genes in primary cultures of neurons and astrocytes
    “The results show that even relatively short-term exposure to cell phone radiofrequency emissions can up-regulate elements of apoptotic pathways in cells derived from the brain, and that neurons appear to be more sensitive to this effect than astrocytes.”

    research results:Long-term use of cellular phones and brain tumours: increased risk associated with use for ?10 years
    “Conclusions: Results from present studies on use of mobile phones for ?10 years give a consistent pattern of increased risk for acoustic neuroma and glioma. The risk is highest for ipsilateral exposure.”

    research results:Mobile Phone Use and the Risk of Acoustic Neuroma
    “Conclusions: Our findings do not indicate an increased risk of acoustic neuroma related to short-term mobile phone use after a short latency period. However, our data suggest an increased risk of acoustic neuroma associated with mobile phone use of at least 10 years’ duration.”

    research results:Association between number of cell phone contracts and brain tumor incidence in nineteen U.S. States
    “The effect of cell phone subscriptions was significant (P = 0.017), and independent of the effect of mean family income (P = 0.894), population (P = 0.003) and age (0.499). The very linear relationship between cell phone usage and brain tumor incidence is disturbing and certainly needs further epidemiological evaluation. In the meantime, it would be prudent to limit exposure to all sources of electro-magnetic radiation.”

  6. # TotallyLost

    OK Where are your citations?. I am sure that these studies are genuine, but unless you give me the details that allow me to read them they are meaningless.

  7. Presenting the results as excerpts makes for pretty searchable…ah, lulz.
    (letter to the editor, not article; sorry) is nice, but having “Non-thermal activation of…[blah blah hsp27/p38MAPK stress pathway word journey]” repeat around like a Thompson Catalog did. One that says Leszczynski (love the clear, plainly impossible recommendations) more than Smalley.

    El Reg is slacking on the coverage of this, maybe Vox has the latest electronic lab health notes, following up from the No Entry, Laser In Use Thing Turns Out To Be 400W series?

    hsp27; if it matters, you gotta knock out that pathwayhttp://www.molecular-cancer.com/content/11/1/20… (Then TMZ autophagy can brighten your day. (Hoping I can stick with the E! show as the worst available variant.) Or wipe it for rebuilding, separate article, whatevs.) Meanwhile, have a curryhttp://www.ncbi.nlm.nih.gov/pubmed/23494802… or say, a Brandy Alexander with 2 whole nutmegs crushed in it. Always follow your curcurminoid doctors’ advice. Do not begin one of those 30-mile maniac mud runs with a brandy alexander in hand. Mid-course. And on…

    It would seem nice to not have 50W radiating out of every likely carrier in a room; coffeemaker, game console, nanocell, stereo, grocery aisle, farm stand etc. even if I can look for heat stress factors easily. Looks like it’s 3-10ish for now (ca. 1W at device to charge.)

    May your omni treadmills be anechoic and keep you from the dangerous effects of the Higgs Field.

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