The future is wireless power, or so say a thousand press releases in my spam folder, and with very few exceptions every single system of wireless power delivery has fallen flat on its face. Except for a few niche cases – RFID tags, Wacom tablets and the S Pen, and the Qi inductive power mats for cell phones – the future of wireless power hardly looks bright, and in some cases seems downright dangerous. No one seems to grasp that wireless power transfer is much more inefficient than using a wire, and the inverse square law only makes everything worse.

Now there’s a new wireless power technology that’s a strange mix of running in stealth mode and sending press releases to every tech outlet on the planet. It’s called uBeam. This company says it will deliver wireless power to the world, but it’s not doing it with giant Tesla-inspired towers of power, radios beamed directly at devices, induction, magnetic resonance, or even light. uBeam transmits power via sound, specifically high intensity ultrasound. uBeam has never demonstrated a prototype, has never released any technical specs, and even some high-profile investors that include [Mark Cuban] have not seen the uBeam working. Despite running in a ‘stealth mode’, it has garnered a lot of press, and has been featured on TechCrunch dozens of times. This may just be a consequence of CrunchFunds’s investment in uBeam, but there’s still more Google News results for a technology that hasn’t even been demonstrated than a reasonable person would expect.

In what is perhaps the greatest breakdown ever posted on the EEVForums, [georgesmith] goes over what uBeam is, how the technology doesn’t make sense, and how far you can take a business before engineers start to say, ‘put up or shut up.’ [georgesmith]’s research goes over just some of what makes uBeam impractical, but digging even further reveals how insane uBeam actually is.

The Basic Tech Breakdown

The core technology, and the core criticism of uBeam is that it uses sound to transmit power. All speakers turn power into sound, and microphones operate on the reverse principle. Speakers and microphones can both be called transducers, and this is exactly what uBeam is using to transmit power wirelessly. Of course a gigantic speaker blaring a very, very loud sine wave would be far more annoying than a simple cable to charge your phone, so uBeam is using ultrasound – sound too high for humans, cats, dogs, mice, and even bats to hear.

In the TechCrunch technical teardown of uBeam, we get a small glimpse of what it takes to transmit power via ultrasound. The uBeam team, headed up by [Meredith Perry] created a, “novel high-powered ultrasonic transducer” that is the, “thinnest, most powerful, most complex, and most intelligent … in the world.”

This ultrasonic transmitter is mounted on a room’s wall, converts data and energy into ultrasound, and broadcasts it directly to devices requesting power. This includes cell phones, tablets, laptops, appliances. Of course, all of these devices will be equipped with ultrasonic power receivers, all based on uBeam IP. The promise of beamed wireless power is deafening, and if you’re an investor putting this technology in millions of devices sounds like a great idea.

The Problems With The Tech

Of course uBeam and its investors contend the technology is safe and even innocuous, but is it? I’m completely unable to find any media that will report on the frequency or intensity of the ultrasound used in uBeam. Patents, on the other hand, actually give us information. uBeam will transmit at about 120 kHz, with an intensity of about 155dB. To put the frequency in perspective, humans can hear up to about 20kHz, dogs up to about 60kHz, cats up to about 80kHz, and bats up to about 115kHz. The frequency of uBeam is higher than nearly all land-based animals. The intensity, however, is impressive. The intensity of a jet engine at 100 feet is cited at 140dB. A 12 gauge shotgun blast can be as loud as 165dB, albeit for an instance. OSHA guidelines for sound protection cite 145dB as the loudest recommended exposure with hearing protection, although this is frequency dependant.

The difference between the intensity of uBeam and OSHA guidelines is not small; it’s only 10dB. uBeam operates at 155dB and OSHA guidelines have a limit at 145dB. Decibels are logarithmic, though, and an increase of just 3dB is a doubling of intensity. uBeam is actually 10 times louder than OSHA guidelines, and a 2005 review of ultrasound exposure limits recommended, “sound pressure levels should be less than 110 dB above 25 kHz, regardless of the exposure duration, to prevent the undesirable subjective effects of ultrasound.”

This is the fundamental problem of uBeam. Simply by virtue of a lack of research into very high intensity ultrasound, all arguments about uBeam eventually devolve into appeals to ignorance countering appeals to authority. Personally, I quite enjoy the arguments presented by both uBeam, its investors, and its detractors. It’s an amazing rhetorical rigamarole.

The Insanity Of The Tech

Ultrasound exposure limits and questions of how safe the uBeam system are interesting, but to realize the pure insanity of this wireless power system, you only need to look into the patents and a little bit of physics.

Anyone who has ever lived in an apartment will tell you sound absorption is related to frequency. If you’ve ever had the displeasure of having a neighbor with a large subwoofer, you know higher frequency sound is absorbed at a higher rate than lower frequency sound. This trend continues into ultrasound territory, where sound at a frequency of 100kHz will be attenuated 3-4dB (effectively halved in power) for every meter of air it passes through.

You are not reading the last paragraph incorrectly. Because decibels are a logarithmic scale, a decrease of 3dB is half the power. With the uBeam system, being just one meter away from the transmitter will bring the power down by half. Being two meters away will bring the power down to a quarter of what it was at the source. Being three meters away will reduce the power received by any device to an eighth of the transmitters original output, and bring it down to nearly OSHA-approved levels.

The incredible attenuation of ultrasonics is the nearly insurmountable problem of uBeam, but luckily the patents tell us how the uBeam team plans to combat it. They’re using dozens of power transmitters per location; a transmitter every two feet, blaring ultrasonics. It’s not dangerous, though: these transducers will be focused directly on a compatible uBeam device with a “mechanical steering component“. Yes, each transmitter will be mounted to an electromechanical linkage so the transmitter is pointed directly at the device it is powering. If you’re wondering, yes, this means a transmitter is required for each device being powered.

Consider a Starbucks. In a small Starbucks, you might find 10 people, sitting on their MacBooks, working on the next Great American Novel, or their screenplay, or just on tumblr. Each of these 10 people will require their own ultrasonic power transmitter, and it will need to be within a few feet of each machine. In the ceiling, or perhaps mounted on the wall, will be an ultrasonic power transmitter that contains motors to ensure each MacBook can charge wirelessly. This is a vision of the near future; Starbucks may be lining up a deal to put this in their stores. It’s also absolutely insane. For something that claims to be as easy as WiFi to install, look at the differences: WiFi merely requires a single router to be installed anywhere in the store. uBeam would require a dozen transmitters, each of with include mechanical steering for their transducers. uBeam would require everyone to buy an ultrasonic power receiver for each device.

Unlike [georgesmith]’s teardown of uBeam, we’re going to stop short of calling it a fraud. It has not been demonstrated to the public, and although it is impractical that does not make it impossible. Consider this, though: you can buy a 10-pack of outlets that include a USB charging port for $200. Including installation, it would cost Starbucks a minimum of $22 Million dollars to outfit each of its stores with USB charging ports, assuming an installation cost of $800. This would be more convenient – and cheaper – than any wireless power scheme, be it RF, inductive, or ultrasonic. Curiously, investors are glomming on to a system that is less convenient, more expensive, and uses fundamentally unproven technology. It’s a curious case indeed.