Please note that this story is currently being rewritten to address a few issues brought to our attention by several of our sharp-eyed readers. It won't be ready for a day or two so, for the moment, I've written this prologue to help you view the origin story in perspective it was written from.
All of the issues boil down to Ossia's extremely ambitious claims for their technology, and its somewhat vague explanations about how they achieve them. This story was not unique—I routinely run into stories that both catch our interest and strain our credibility at the same time, forcing us to make the difficult call as to whether to ignore them or share them with you.
When the topic is compelling enough to warrant coverage, I try to frame the story in a skeptical but balanced manner that presents the company's claims while pointing out the places where they either fail to provide facts to substantiate them, or appear to have discovered an entirely new branch of physics. One good example is the story on the two companies claiming to be producing "Nuclear Diamond Batteries" that I posted a year ago. We had good fun with it and several readers shared their analysis of the physics involves with these most-likely fictional devices.
In the case of Ossia, several of its claims appeared to border on science fiction, so I was tempted to ignore the announcement but decided instead to learn what I could and share it with our readers. As a result, I asked a bunch of hard questions and Ossia replied at length with answers I duly included in the story, leaving readers to judge for themselves.
Unfortunately, I think that the company's willingness to supply actual written answers, however sketchy they were, caused be to be a bit too “fair and balanced,” and tone my skepticism down a bit too far. In addition, headline “New Wireless Power Tech Could Transform How We Charge Mobiles,” which was substituted for the original one, “Wireless Power System Approved by EU and UK Claims to Charge Mobile Devices Without Frying Users,” may have also added to the impression that I'd bought into the fantastic claims hook, line, and sinker.
Thankfully, I can always rely on the many readers who count on us to point out any problems they find in my stories. You have kept me honest and motivated to dig as deep as my deadlines permit for the past 30+ years, something I'm forever grateful for.
I'm incorporating a few of the insights I received from readers in the revised version of this story that I'm working on—and will have it posted as soon as I can.
Thanks again for your continued interest, support, and feedback,
Lee Goldberg
Ossia's Sept. 9, 2021 announcement that its Cota Real Wireless Power technology has passed both EU and UK regulatory assessments may change the way tablets, phones, and other mobile devices keep their batteries topped up. It may also free remote sensors used by IoT applications from the tyranny of limited-life batteries.
Doug Stovall, Ossia’s CEO, says that the approval of its system, which delivers power over-the-air (OTA), at a distance, across the US and EU, will pave the way for additional global approvals. In turn, a single version of a product that uses Cota power technology could be quickly approved for sale in many major markets.
If Ossia's ambitious performance claims can be demonstrated by the products in which its technology is licensed, Stoval's analysis is most likely correct. Nevertheless, some of those claims gave rise to a number of questions about how the system achieves its remarkable functionality and performance. Our questions, and Ossia's responses, are published later in this report.
Here's what we know at the moment:
Previously, the Cota system was only authorized for sale in the US by the FCC. This new approval certifies that the Cota system complies with the UK and European Union essential requirements and can be licensed and sold with the CE marking in Europe and the UKCA mark in the UK. In addition, the certification doesn’t have a distance limitation for delivery of wireless power OTA, and effectively delivers power over air without any distance limitation. As we'll see, this opens up the possibility for supporting multi-watt applications at one to two meters and milliwatt-level applications with ranges in the tens of meters.
The system mentioned in the company’s announcement operates in the 2.4-GHz band, also used by Wi-Fi, Bluetooth, and microwave ovens(!), but the material on its website focuses primarily on a second system being developed that operates in the 5.8-GHz band. I wasn't able to obtain power levels for the 2.4-GHz system but Ossia says the 5.8-GHz Cota system can deliver 2 to 3 W to a receiver at one meter from the transmitter, 1 W at two meters, and 10 to 50 mW at 10 meters. Since attenuation and other losses tend to be lower at 2.4 GHz, I suspect that the system with EU/GB approval may offer somewhat better performance.
Ossia is making several unique claims that appear to push the state of the art for wireless power, which we'll try to clarify here. For one thing, the company claims that its Cota system is the first RF-based non-line-of-sight, wireless-power technology, at-a-distance product to receive EU/UK Type Examination Certificates.
Electronic Design has covered several "long distance" wireless-power systems, including GuRu and Powercast, so we were a bit skeptical about the claim about being “first-of-type.” However, when we took a closer look, it turns out that while Powercast does transmit power via non-line-of-sight, the power levels it supports are much lower. And, while GuRu's system does transmit multi-watt power levels (enough power to make me nervous), it relies on line-of sight-transmission, as shown in the video below, with the transmitter often located in the ceiling, over a desk, or conference room table.
Conclusion: I'm not sure whether there’s another wireless power-technology that offers both capabilities, but it’s almost certainly the only one (at the moment) to receive EU approval.
In fact, it was those concerns about many of these technologies having the potential to turn a living room or boardroom into a walk-in microwave oven that made me even more interested in Ossia's technology.
A Friendly Q&A
Since Ossia's release was focused on the certification of its technology, it was understandably light on the technical details behind the system. We sought those details on the company website, which provided some interesting information on what the system was intended to do, but still did not provide many details about how it did them. Here are some of the most notable claims we found:
- Ossia’s patented RF smart antenna technology automatically keeps multiple devices charged without any user intervention, enabling an efficient and truly wire-free, powered-up world that’s always on and always connected.
- The Cota Power Receiver, embedded into any device, initiates the “conversation” by sending a beacon signal (see diagram below) to find a Cota Power Transmitter. The transmitter then sends power back in the same exact paths. This “conversation” between device and transmitter occurs 100 times per second, enabling it to send power safely to devices at a distance while they’re in motion. All your Cota-enabled devices will receive power simultaneously.
- Cota Real Wireless Power delivers meaningful power to devices at a distance while meeting all of the FCC’s stringent specific absorption rate (SAR) requirements for safety.
- The Cota technology is designed to be inherently safe and avoids any potential obstructions. This means the Cota certification doesn’t need an “exclusion zone” in front of the transmitter, nor does it need sensors to shut the system off when it detects movement.
These claims naturally raised a bunch of questions, which CEO Doug Stovall dutifully answered. While not complete, they do provide a few insights about how their system implements safety and performance functions, such as non-line-of-sight transmission, receiver tracking, and detection of living things in its transmission path to avoid cooking its users:
Is the 5.8-GHz power beam modulated or just a pure carrier?
The Cota power transmitter uses a pure carrier (continuous wave or CW) for wireless-power transmission. It is important to note that the EU/UK regulatory approval is for Ossia’s Cota 2.4-GHz system.
How does the receiver rectify the RF into useful power?
The receiver utilizes high-efficiency rectifier diodes to convert the RF signal to dc power. Once converted, buck/boost regulators are used to provide stable, low-noise dc power to the battery or device.
There’s at least one other company claiming to provide these levels of power.
Although other companies have adopted the term “wireless power,” Cota technology cannot be compared to their technology. For electronic gadgets to be available round-the-clock, they need uninterrupted power. It’s important to illustrate the core differences in technologies between these companies.
At Ossia, we classify most solutions as “wireless charging,” not wireless power. Wireless charging is typically a near-field (very close range, either pad changing or millimeters away) that charges the existing battery in a device; the common example of this is pad charging with a mobile phone. Wireless power changes the paradigm of how power is delivered, whether it’s through a device’s battery or the invention of battery-less devices that are receiving power over-the-air, at a distance.
Cota Real Wireless Power technology uses reciprocal RF. Cota technology is not based on radar principles of beamforming or communication methods, such as MIMO. This gives Cota technology unique differentiators such as tracking moving devices, delivering power non-line-of-sight, and inherent safety features that are easily demonstrated as unmatched in the industry.
The Cota Technology is the only wireless-power technology certified for use in the EU/UK at unlimited distance. In the US, Cota Technology is the only wireless-power technology that delivers the highest level of RF power without requiring a motion detector of an exclusion zone, requiring the system to trigger off when humans are near.
RF at 2.4 GHz, and especially at 5.8 MHz does not have very good range without additional technical wizardry, such as beamfocusing/beamsteering. What technology(s) do they use, and how much power can it deliver at 2 m, 5 m, 10 m, and further distances? What’s the maximum practical range for charging lower-power devices?
The prototype 5.8-GHz Cota system can deliver 2 to 3 W to a receiver at 1 m, 1 W at 2 m, and 10 to 50 mW at 10 m.
The Cota 5.8-GHz system allows for higher power delivery with smaller antenna sizes. This system enables higher efficiencies because of the shorter wavelength, allowing higher antenna gain that leads to significantly higher received power, providing a better user experience to charge a device.
Either at 5.8 GHz or 2.4 GHz, it’s possible to design devices with different sizes and shapes of receive antennas to deliver more power. Cota 5.8 GHz enables higher efficiencies because of the smaller wavelength, allowing higher antenna gain for a given Cota transmitter and receiver size. This makes possible significantly higher received power and/or the use of smaller-size transmitters.
Your website mentions multipath transmission. I’m not sure if multipath works well at those frequencies, but if it does, how lossy is it?
Just like Wi-Fi, the farther you move away from the transmitter, the less data bandwidth you receive. There is path loss through reflectivity. However, Cota is the only technology that can use reflective paths, allowing for non-line-of-sight power delivery.
Uniquely to any other wireless-power technology on the market, Cota can delivery power without needing line-of-sight between the transmitter and receiver. Non-line-of-sight power delivery depends on the lengths of the paths being traveled.
When the line-of-sight is obscured, the system will utilize other reflective paths that will be (by definition) longer than the line-of-sight. These path lengths can be multiple times longer than the line-of-sight distance in the close-in range (a few meters), reducing to only fractionally higher for longer ranges (5m to 10m+).
The Cota technology operates as follows:
- The receiver (Rx) has at least one antenna of the power frequency, and the transmitter (Tx) has hundreds of antennas polarized both horizontally and vertically. All of the antennas in the system are transceivers (have transmitter and receiver capability).
- The receiver device sends out a “beacon signal”—a short (tens of microseconds), low-power (around 5 mW) signal—encoding the device's ID.
- This beacon is scattered around the environment reflecting and refracting, with some of the signal landing on the transmitters’ hundreds of antennas (whether line-of-sight or otherwise), all of which are in “phase detect mode,” establishing the phase of each antenna.
- To power the device, every antenna emits the complex-conjugate signal of the detected phase (i.e., the negative of the detected phase). This will create a retrodirective signal that travels back to the receiver device, taking every possible path available (the same paths that were taken by the beacon). This step requires ZERO computing, meaning it can be performed by the antenna's own local circuitry in less than 1 μs. It reduces the complexity of the system implementation, while ensuring reliability. The various paths taken by the retrodirective power signals are constructively combined (i.e., they arrive at the receiver device in phase with each other) such that the maximum power possible is delivered.
- The beacon is repeated at appropriate intervals to ensure the device always updates the phases across the Tx array so that the power is always focused on the intended receiver device.
- The retrodirective technique has been proven mathematically to achieve the highest link possible between any two sets of antennas. No other technique such as beamforming, genetic algorithm, or AI can achieve greater than "mathematical maximum proof" link.
Cota makes use of all available paths (direct and reflection) to deliver maximum power to the receiver. Cota technology’s complex conjugate retrodirectivity is an implementation of the Maximum Power Transfer Theorem in engineering and physics. Therefore, the system does not select an individual beam or path, but instead makes use of all clear paths that exist.
How many receivers can a base station support? How much total power can it deliver?
This depends on many variables, including power consumption, distance, transmitter/receiver design, and operating frequency. The 2.4-GHz RDK 2.0 wirelessly delivers power from a Cota transmitter to up to 200 Cota receivers in synchronous power delivery or tone power schedule mode, and up to 1,000 Cota receivers in asynchronous power delivery or anytime beacon mode. Power and distance depend on several factors, including form-factor of transmitter and current environment.
With conditions, such as a larger aperture, Cota transmitter has the capability to send more power at longer distances. Similarly, if you change frequencies, the ratio of power over distance increases. Highly reflective room will yield better performance.
Are there any potential biological hazards of constant exposure to that level of 5.8-GHz RF? And if so, does your product do anything to mitigate them? The site hints at routing the beams around living things.
Cota technology is Federal Communications Commission (FCC) Part 15 and Part 18 compliant. Cota technology has a unique inherent capability to transfer power by avoiding people and pets, and it’s the first of its kind to meet FCC safety exposure standards in a dynamic environment.
The important part of Part 18 is that any approved equipment must comply with the RF exposure and out-of-band emissions requirements, irrespective of the power output.
Our existing granted authorization is approved to emit approximately 5 W, which is a modest amount of power. As has already been demonstrated for the granted authorization, the device meets the RF exposure standards with the existing 1-m distance limit. Ossia’s test lab, UL, provided evidence that the potential RF exposure levels only become lower with increased distance, so we don’t see power levels as an issue in our current request.
How does it do that?
The Cota system is the first certified system that does not require a motion detector or an exclusion zone—that is, it’s the only wireless-power system certified as safe to use when organic lives are present in the charging area. It has the highest level of radio-frequency power delivered for a certified system, which means that devices will receive meaningful levels of over-the-air power.
Cota technology allows for precise control over the flow of wireless power for the power receiver devices; importantly, for safety, as Cota power does not expose users to any amount of radiation; secure because it can control unauthorized devices from drawing power from the Cota system. Cota technology is based on physics, with safety inherently built right in.
Is this always possible, and what does the transmitter do if it's not?
The Cota technology's multi-path functionality allows it to send power continuously and safely when needed. Cota technology is safe and efficient during its operation, cognizant of the environment or location of the Cota receiver devices that are receiving power. With Cota technology’s ability to remotely power a device, no scanning or triangulation is required. Cota components can seamlessly power devices in movement and in varying environments.
Cota technology’s inherent intelligence ensures that power is not transmitted unless power is required and until the devices are within range. When your power receiver device is completely charged or when your devices are not being charged, the power transmitter either sleeps/hibernates or powers the dozens of other small wireless appliances that might require charging, such as remote controls, clocks, keyboards, smoke detectors, and so on.
What is the (very) rough price range of the BOM for the transmitter and receiver devices? Is there a development kit available?
Ossia’s business model is to license the Cota technology platform to third parties for integration into their own products and product lines. As Ossia works with each customer to integrate the Cota technology, we work with them on materials, etc. BOM can be reduced in the receiver by taking advantage of existing components already in the device. Also, with volumes, the BOM is reduced significantly.
Conclusions
Although Ossia was remarkably more forthcoming than many of the companies we report on, some of their answers were unclear or incomplete. Some of this is quite understandable since Ossia needs to protect the unique IP behind its technologies from the prying eyes of competitors. Nevertheless, it should be possible to provide a broad explanation of how they achieve at least some of their ambitious claims in clear, commonly used technical terms while still protecting their IP.
Among the issues of highest interest would be clarifications of the terms “reciprocal RF” and “retrodirective.” They are used to describe some of the techniques used by the Cota system to locate a client device, direct wireless power to it, and avoid irradiating the user in the process.
Unfortunately, there wasn’t enough time to pose follow-up questions ahead of the Sept. 8 news deadline, so we went with what we had and will try to give you an update later. In the meantime, I’d welcome any comments or insights on this unique technology that our RF-savvy readers would care to share with the rest of us.
I look forward to hearing from you at lgoldberg@green-electronics(dot)com.