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The uBeam FAQ

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(I was going to post this on my own site. But more people might be interested here, since there's already a long uBeam thread. @Mods, feel free to move if this is the wrong forum.)

Version 1.11 - Last updated 2016-05-17

Disclaimer: The author is not affiliated with uBeam, or any uBeam competitor.

1. What is uBeam?

uBeam[1] is a hardware startup, founded in 2011 by Meredith Perry[2] and Nora Dweck[3]. uBeam aims to create "a world without wires", where almost all electronics are powered by uBeam's wireless ultrasound technology[1].

2. Why is uBeam controversial?

Wireless power has always been a dream of electrical engineers, ever since Nikola Tesla's experiments in the early 20th century[4]. However, it faces many serious obstacles. Many people have questioned whether uBeam can overcome these obstacles, and produce a commercially practical device.[5][6][7] This FAQ aims to answer some of those questions.

3. How much is known about uBeam?

Very little. uBeam has never shipped a product, and has never exhibited a prototype (unlike some competitors, who demonstrated their tech at CES 2015 [8][9]). uBeam has also never released basic technical specs, such as range, efficiency, and amount of power delivered. uBeam says they have a working prototype, but even uBeam investor Mark Cuban says he never saw it before investing[29].

4. Why is uBeam so secretive?

No one really knows. uBeam has said that "like all technology companies in the product development process, with critical intellectual property, at this time, we cannot release our full technical specifications to the public".[1] However, the accuracy of this explanation is questionable. uBeam competitor WiTricity, which is also pre-launch, has not only released technical specs but sells a demonstration kit for $995 [10]. Further, unlike most "stealth" startups (eg. [11]), uBeam has started a large-scale PR campaign, with over 750 Google News hits as of late 2015 [12]. uBeam's website says that "since uBeam owns the entire ultrasonic wireless power space from an IP perspective, the world will have to leverage uBeam’s technology", so the need for secrecy is unclear when uBeam feels they already have strong patent protection.

5. How intense is uBeam's ultrasound?

Very intense. A TechCrunch article says that uBeam "is still keeping some technical details such as the acoustic intensities involved under wraps"[13], but uBeam's patent applications describe intensities of "up to about 155 dB"[14]. The dB (decibel) scale can be deceptive, because it's a logarithmic scale, not a linear scale. Adding another 10 dB means the sound becomes ten times as loud. An 80 dB sound isn't twice as loud as a 40 dB sound; it's ten thousand times as loud.

Here are two graphs for illustration:

155 dB is incredibly loud. It's about five times louder than standing four feet away from a jet engine. It's about 300,000 times louder than using a jack hammer.[15] Humans can't normally hear ultrasound, but at that intensity, other problems start to arise (as this FAQ discusses later). The blog post at [6] describes a worker's experience with 155 dB ultrasound:

"The transducer was so loud, I could only use it after normal business hours, with a 24 hour advance email warning to everyone on the floor, putting signs on the lab doors, making foam earplugs available to everyone in my lab area, and making sure that no one was doing small animal work at the times when it would be on."

uBeam claims that it "operates at a frequency and power level broadly similar to that of other commercial systems such as Holosonic's "Audio Spotlight"" [1]. However, that seems fairly implausible. Holosonic's devices are widely described as operating in the 80-100 dB range[16][17], but that'd be much too weak to transmit power, as discussed in Question #9.

6. What is uBeam's range?

uBeam hasn't said. However, we can make some estimates from the physical properties of ultrasound.

Sound is a wave moving through a medium, like air or water. The molecules of the medium are constantly in motion. When this motion is random, we call it "heat" - hot objects have faster motion than cold ones. When the motion is organized in a wave pattern, we call it "sound".

As a sound wave moves outward from its source, the motion of the wave becomes less organized - some of the wave motion becomes random motion, or heat. This is called "attenuation". Attenuation is a different effect from sound "spreading out" as it travels - the sound energy is absorbed by the medium it travels through, in addition to spreading out more. Energy losses from spreading out increase with the square of the distance, while losses from attenuation increase exponentially with distance [18].

Generally, attenuation is stronger at higher frequencies. Here's a graph of sound attenuation in air [19]:

uBeam claims that their system "will not affect pets or animals"[1]. Some common animals, such as cats and mice, can hear frequencies up to 80 kHz[20]. To be safely above the hearing threshold of most animals, uBeam would have to operate around 100 kHz. However, attenuation in air is strong at these high frequencies. According to [19], the attenuation at 100 kHz would be about 3-4 dB per meter. If we assume that the transmitter is 100% efficient, the receiver is 100% efficient, the beam is 100% straight, the receiver is perpendicular to the beam, there are no obstacles between the receiver and transmitter (discussed in Question #8), and there are no nonlinear effects (discussed in Question #10), uBeam will still be only about 20% efficient at a distance of 2 meters (6-7 feet). An iPhone charger delivers 5 watts [21], so the uBeam transmitter would have to draw 25 watts at 2 meters away, even given the previous unrealistic assumptions. Since attenuation increases exponentially - ~125 watts would be needed at 4 meters, ~625 watts at 6 meters, and so on - it's clear that uBeam wouldn't be practical beyond about 1.5 meters/5 feet. uBeam themselves don't appear to dispute this, saying that "ultrasound levels decay very rapidly beyond a few meters"[1].

7. Is ultrasound safe?

That's not really the right question. The real question is, "what level of ultrasound is safe"?

A fundamental principle of toxicology is "the dose makes the poison".[22] At a low enough level, everything is safe. The element selenium is poisonous, but in trace amounts it's essential to human life[23]. On the other hand, too much of anything will hurt, even oxygen[24] and water[25].

uBeam says that "ultrasound is all around us in our day-to-day lives in car parking sensors, fluorescent lighting, directional speakers, automatic door sensors, and alarm systems"[1]. uBeam investor Mark Suster adds that "[ultrasound] is just an inaudible soundwave being transferred – as in the kind also used for women during pregnancy. It also happens to be how your car likely tells the distance to objects when you park or if you have a side assist whether you can change lanes safely"[26]. That's perfectly true. However, those applications involve lower levels of ultrasound. At higher levels, ultrasound is also used to destroy tissue during surgery[27], and can artificially cause infertility[28].

[30] discusses the limits that different agencies have proposed on human exposure to ultrasound. These limits are summarized in this table:

The highest level listed is 115 dB, which is ten thousand times less than the highest uBeam level of 155 dB (from Question #5). In 2003, the US's OSHA broke from international standards, and voted to raise their exposure limits to 145 dB (ten times less than 155 dB), when "there is no possibility that the ultrasound can couple with the body by touching water or some other medium"[31]. The meaning of this phrasing is unclear[31], and an independent 2005 review recommended that "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."[31]. [30] takes the position (in section 4.2.1) that 110 dB may be exceeded in a work environment, but only if the intensity can't be feasibly reduced, all workers have ear protection, and the intensity level is still kept below 137 dB, about 1.5% of 155 dB.

uBeam claims that the "air coupled ultrasound method used by uBeam cannot, even if focused directly on a person for a continuous period, cause any noticeable heating."[1] But for sound levels of 165 dB, which would be needed for larger appliances (Question #9) or longer ranges (Question #6), the literature reports that "local heating in the crevices between fingers caused burns almost instantly at these levels. Painful heating occurred after several seconds of exposure of broader surfaces such as the palm of the hand." ([30], citing [32]). Skin heating has been observed at levels as low as 140 dB, roughly 3% of the stated highest uBeam level of 155 dB ([30], citing [33]).

Moreover, even if true, this claim by uBeam might not be relevant. As intensity increases, the first biological effect of ultrasound isn't skin heating, but a subjective "ultrasound sickness" which "involv[es] manifestations of nausea, headache, tinnitus, pain, dizziness, and fatigue".[30] Exposure limits in the 110-115 dB range exist in part to prevent this "ultrasound sickness"[30][31]. This effect isn't thought to cause serious harm, but is still concerning for what's essentially a luxury product, especially if it affects innocent bystanders. A more serious, though less certain, concern is permanent hearing loss, which the literature review at [35] discusses: "For ultrasonic components 20 kHz and above, DRCs [Damage Risk Criteria] were specified to avoid hearing damage in the audible (lower) frequencies. Such damage would take the form of Temporary Threshold Shift on a daily basis, possibly leading to permanent NIHL [Noise Induced Hearing Loss] over years of occupational exposure. However, the maximum acceptable one-third-octave band levels of 105-115 dB had been demonstrated to produce no hearing deficit. Without information to suggest that the band levels are over-protective, there seems little reason to relax the DRCs."

Anecdotally, [6] also reports other effects at 155 dB: "Human keratinocytes become damaged in a way that’s incompatible with life in a matter of minutes due to mechanical stress. You should care about this because keratinocytes are the most plentiful type of cell in your skin, and they produce keratin, a structural protein that helps hold all your insides together. They’re strong little bastards, and if they’re hurt by ultrasound, you can bet that less structurally focused cells will suffer too. Mechanical damage... think of a scrape, just larger. Like large swaths of your skin. I don’t want to even contemplate eyeball damage."

uBeam's design uses a focused beam system with active receiver tracking[1], which lowers human exposure to ultrasound. However, this safety system will fail sometimes, and even when it doesn't, some amount of sound will always "leak out" of the beam into surrounding air. It's likely that regulators don't even know what failure and leakage rates would be acceptable, as historically "such high sound-pressure levels [between 145 and 155 dB] have never been encountered in either commercial or industrial applications."[30]. As of 2001, high-power ultrasound in air was so rare that there might have only been a few hundred workers exposed to it in the entire UK ([35], pg. 48). If uBeam became popular, this blank spot on the regulatory map would get filled in fast.

uBeam also claims that "the power levels beamed are more than 50 times lower than the lowest ultrasound imaging exposure limits set by the FDA for medical imaging"[1]. It's unclear what this refers to, as the uBeam website cites no source[1]. Nevertheless, it's likely to be irrelevant. Medical imaging is done on human tissue, which is mostly water. Water is roughly 800 times denser than air, and its characteristics as a sound medium are totally different. In particular, most medical ultrasound uses frequencies in the megahertz range ([34], table 3.2), which are so high that air becomes basically opaque due to extremely strong attenuation[34]. Sound in water doesn't even use the same intensity scale as sound in air; a 67 dB noise in water is considered barely audible[36], while in air 67 dB would be as loud as an electric mixer[15].

8. How convenient would uBeam be?

Not very. Unlike WiFi, which uses radio, uBeam's ultrasound can't penetrate obstacles. It requires a continuous line-of-sight between the transmitter and receiver. uBeam themselves say that "uBeam’s system functions only in the “line of sight”", and ultrasound "[does] not penetrate walls, doors, or windows"[1]. But more importantly, it doesn't penetrate clothes, bags, furniture, or fingers. This severely limits its potential.

According to uBeam, when their first product launches, the receiver will be on the outside of a phone case[1]. When not being used, a smartphone is usually in a purse, bag, pocket, or other container, and any container obscures the receiver's line-of-sight. When a phone is being used, its back (and hence the uBeam receiver) is usually pointed down, facing the floor, and partially covered by the user's hands. Looking at stock photos from Google Images:

Ignoring the hands problem, putting transmitters in the floor (facing the phone) means running new wires across it, and transmitters would inevitably get stepped on, especially in public places. Putting transmitters in the lower wall avoids the stepping problem, but the signal will likely get blocked by legs, bags and furniture. For example, this is a stock photo of a coffee shop:

The left wall, and probably also the back wall, is obscured by chairs, tables, legs, and bags. The lower right wall has a clear line-of-sight, but is too far away from most tables, given the range limits discussed in Question #5 (this room is likely about 22 ft/7 m across). The upper walls and ceiling have a clear line-of-sight, but putting transmitters there requires turning phones so their back side faces up, making a phone very annoying to use during charging.

uBeam hasn't said if a single transmitter can support more than one receiver. However, a very large number would be needed to cover a significant area. A single WiFi transmitter can connect about fifty devices[37], and can cover many rooms by itself. If attached to the wall, one uBeam transmitter with a 2 meter range (Question #5) could cover about 6 square meters (~65 square feet).[38] Hence, assuming perfect geometry, one would need about 20 transmitters to cover a 120 square meter house. An average US grocery store is about 46,000 square feet [39], and would need about 700 transmitters.

9. How much power can uBeam deliver?

uBeam hasn't said, but again, we can guess based on physics.

At uBeam's assumed maximum intensity of 155 dB (from Question #5), sound has a power density of about 0.3 watts per square centimeter[6][40]. Apple's iPhone 6, a typical smartphone, has a height of 13.8 cm and a width of 6.7 cm [41], for a total surface area of 92.46 cm^2, which is realistically about 90 (to account for rounded corners, edges, etc). Hence, under ideal conditions - receiver right next to transmitter, all parts are 100% efficient, no obstacles - uBeam's total power will be about 90 * 0.3 = 27 watts. That's definitely enough to charge the phone, since a standard iPhone charger draws 5 watts[21]. So, under very good conditions, ultrasound will charge an iPhone at the sound intensity uBeam describes.

However, there are several limitations. The first, already discussed in Question #5, is range. At 100 kHz, sound intensity drops by about a factor of 5 every two meters. Two meters away, uBeam will only deliver 5.2 watts, about the same as the iPhone charger. At four meters (13 feet), uBeam will deliver 1.08 watts, which is close to useless.

The second limitation is that uBeam can't use a less intense beam to address the safety concerns in Question #7. At 140 dB, the lowest limit of skin heating, uBeam will only deliver 0.85 watts - not enough to keep a phone charged. At 115 dB, a standard international safety limit, uBeam delivers a negligible 2.7 milliwatts.

The third limitation is that this calculation assumes 100% efficiency. If the transmitter is inefficient, one can just feed it more power (if one doesn't mind the electric bill). But if the receiver is inefficient, the power can't be increased without sending more than 155 dB of sound, which is intense enough. uBeam hasn't released efficiency numbers, but if the receiver is (say) 30% efficient, that would reduce the maximum power to 8.1 watts.

The fourth limitation is that 27 watts assumes the phone is perpendicular to the beam. The "effective area" (receiver area facing the beam) is proportional to sin(theta), where theta is the angle between the beam and receiver. At a 90 degree angle (perpendicular), one gets 100% power; at a 45 degree angle, one gets 70%; at a 30 degree angle, 50%; and at a 15 degree angle, just 26%.

The fifth limitation is that we assumed no "beam spread"; ie., the beam is perfectly parallel, and perfectly focused on the receiver. If part of the beam misses the receiver, that energy is lost.

The sixth limitation is that this calculation assumes no obstacles. From Question #8, under realistic conditions, one's hand will cover part of the phone while one is using it. If (a big if) the uBeam transmitter can intelligently avoid fingers for safety reasons, they're still obstacles that lower the power available. If one's hand covers half of the back, that reduces the power by 50%. (Another thing, that hasn't been mentioned yet, is that phones take a lot of abuse - they get dropped, scratched, abraded, and so on, for years at a time. Since uBeam hasn't released a prototype, it's unclear how well an ultrasonic receiver can take this wear and tear without breaking.)

Finally, all of these limitations "stack" - each one adds to the others. If the transmitter is two feet away, and the beam power is reduced to 152 dB for safety reasons, and the receiver is only 50% efficient, and the phone is at a 30-degree angle, and half of the beam misses the phone, and fingers cover half the phone's back... each effect reduces the power by 50%, for a combined total of 63/64 = 98.4%, and a final power of ~0.4 watts. By itself, each problem would be manageable, but together they make charging impractical.

uBeam's website also describes uBeam powering other electronics, such as "hearing aids, tablets, sensors, light bulbs, computers, and flat screen TVs"[1]. Some of these use less power than smartphones, but others use far more. A typical large, flat-screen TV (eg. [42]) will draw about 60 watts. Since a TV is usually mounted in one place, some of the limitations get easier, but not all - if the TV is two feet (60 cm) from the wall, and the receiver is 40% efficient, that's still about 80% losses. To transmit 300 watts at 0.3 W/cm^2, one has to have a 1,000 cm^2 transmitter, a bit over a foot on each side (31.6 cm). One could make the transmitter smaller (100 cm^2, or 4 inches/10 cm across) by increasing the intensity to 165 dB, a level that causes burns "almost instantly" (from Question #7), but that seems unwise. Since most power outlets are near the floor, and the TV probably isn't, one would still have to run a cord to the transmitter. And uBeam takes 240 watts of electricity, about a dozen light bulbs' worth, and dumps it into the air for no real reason. That's not good for the environment. Or the power bill. Or the air conditioning - all that heat makes the room hotter.

10. What are nonlinear effects?

According to [6], air becomes a nonlinear medium in an intense ultrasound beam, which causes additional problems. Since [6] is only a blog post, it's not really a reliable source, but the discussion is included for completeness. More reliable sources here would be welcomed. [6] says:

"If you’re in a room with a focused ultrasound beam, and that beam is strong enough, the medium through which it’s traveling (air in uBeam’s case) becomes nonlinear, the oscillations of which causes beams of widely ranging frequencies to be generated, and because they have different wave propagation speeds due to dispersion, they don’t focus, and instead propagate in all different directions. Air becomes a dispersive medium at frequencies greater than 28 kHz thanks to the presence of CO2. These propagating beams are hard to predict and control, and given that they’re going to be at lower frequencies than the original beam (because physics), they will probably drop into the audible human range (upper bound is around 23 kHz) and will be at the very least annoying as hell. Factors that influence this phenomenon is [sic] air temperature, pressure, altitude, CO2 concentration... controlling this is well-nigh impossible."

(Note: Former uBeam engineer Paul Reynolds has written a detailed explanation of non-linearity here.)

11. Has anyone done due diligence on uBeam?

As of October 2015, uBeam has received $23 million in funding from 37 investors [2]. For some of them, the level of due diligence is questionable - Mark Cuban invested without seeing uBeam's claimed prototype, and Marissa Meyer invested after just a 15-minute meeting [29]. But despite that, it's probably safe to assume that, with 37 investors, a few have done some due diligence. In particular, Mark Suster says he investigated many of uBeam's claims[26].

Unfortunately, in the world we live in, receiving VC funding doesn't show a company's science is sound. Famously, even BlackLight Power has received tens of millions in funding - BlackLight claimed it could get energy from putting hydrogen atoms into a state below the ground state, which is prohibited by freshman quantum mechanics [43]. Not surprisingly, BlackLight Power has failed to ship a product since it was started in 1991 [43].

Even more worringly, the quantum computing company D-Wave has received over $100 million in funding [44]. Its investors included Goldman Sachs, Draper Fisher Jurvetson, the CIA, and Jeff Bezos [45], and its customers include Google, NASA, and Lockheed Martin [46]. But in 2013, quantum computing professor Scott Aaronson reported that a team lead by Matthias Troyer proved D-Wave's $20 million computer was no faster than a laptop [47]. D-Wave's computer outperformed off-the-shelf software by focusing on one particular subproblem, but when a laptop's software was focused in the same way, it ran faster than D-Wave's machine.

12. Who are uBeam's competitors?

uBeam claims they have no real competitors; their website states that "[ultrasound] is the only type of energy that can safely and reliably transmit energy wirelessly; thus it's the only type of energy that can be used for over-distance wireless power transmission."[1]. However, this isn't very plausible. The companies WiTricity and Energous, among others, also say they've solved the wireless energy problem. Unlike uBeam, both WiTricity and Energous have shown prototypes at CES 2015 [8][9], where "dozens of companies [were] demonstrating wireless power devices"[48].

WiTricity was founded in 2007 at MIT[48]. They deliver wireless power through magnetic resonance technology, and in 2013 published a booklet describing the technical details and physics behind their device [49]. They sell a demonstration kit for $995 [10], and plan to start shipping in 2016 by integrating wireless charging technology into laptops [4]. uBeam's website says that magnetic resonance "require [sic] gigantic transmitters and receivers" [1], but WiTricity has demonstrated powering a light bulb from seven feet away with much smaller coils [48], and their slide decks say their coils are compact enough to fit inside a phone[50].

Energous is a publicly traded company (stock symbol WATT). Their website describes a charging technology called WattUp, which transmits power via radio waves[51]. Energous's website says that each WattUp transmitter can reach a range of 15 feet, and charge 12 devices at once[51]. Energous has signed a partnership agreement with a "tier one consumer electronics company"[52], likely Apple or Samsung[53], to include its technology in cellphones. uBeam's website claims that "RF [radio] and microwaves also both require impractically large transmitters and receivers to send power over distances greater than a meter"[1], but this appears to have been proven false by Energous's CES demonstration[8].

(Note: Electrical engineer Paul Reynolds has since given some reasons to be skeptical of Energous.)

WiTricity, Energous, and the other companies in wireless power all have their own technical problems. It's unclear if any of them will succeed in the market. However, they are in many ways further along than uBeam, and it's misleading for uBeam to dismiss their technologies as impossible. It's doubly misleading when uBeam director Mark Suster [54] wrote a long, emotional essay declaring that some startup founders were "backbenchers [who] never do anything. They get to sit in the back of the room, snicker, criticize and yet enjoy the benefits of our efforts. They aren’t just free riders – they are negative with no personal ideas for how to make things better", because they had dismissed uBeam's technology as impossible [55].

What is clear is that USB Type-C, a new charging cable, is being adopted fast. It can deliver 100 watts of power, twenty times more than an iPhone charger [21], and enough to power laptops and other electronics [56]. Apple and Google are both using it [56], and faster charging will reduce the need for wireless power of all kinds.

13. So what? Who cares?

Thousands of startups have technical problems. Why uBeam? Why make this FAQ?

Investors have given uBeam over $23 million [2]. But that's not a big problem. It's their money, they can spend it how they want, and they can afford to lose it.

It's likely that uBeam's product will fail, if it ever launches. But that's not a problem either. Plenty of other companies take unlikely chances (eg. [11]), and on the whole, we're better off for it. We can't succeed without failures along the way.

The problem is that uBeam's CEO, Meredith Perry, has turned the wireless power industry into a vehicle for her own self-promotion. uBeam, which has never demoed a prototype, lead Forbes to proclaim "Is this woman the next Elon Musk?"[29], among hundreds of other press hits [12]. uBeam constantly stresses their need for secrecy, to avoid discussing any technical details [1][55], while at the same time doing photoshoots for fashion magazines that say Meredith Perry "is the real-life version of Tony Stark"[57]. When someone else in the ultrasound industry criticized uBeam [7], uBeam director Mark Suster didn't show his math was wrong, even when it was. His rebuttal had not a single number, no diagrams, no graphs, no references to the literature on ultrasound. Instead, it sounded like the victim of a personality cult[55]:

"Meredith Perry is 25. She has withstood 2+ years of backbenchers questioning what she’s working on. My experiences with her have been amazing. She never lost enthusiasm for her pursuit. She never lost confidence in the team’s ability to innovate and execute. She never got distracted from her core mission. She has never given up despite setbacks. The determination, grit & pluck are inspirational. I wish I had 20% of her confidence, focus and leadership skills at 25."

But at least Suster is an investor, so he's supposed to be biased. The same can't be said for the tech press:

"It's not a stretch to imagine a time in the not-too-distant future when Meredith Perry gets a Nobel Prize."[58]

"Perry and her potentially world-changing startup are a breath of fresh air -- for women, New Yorkers and entrepreneurs everywhere. For being only 22, Perry is unbelievably driven. Her impressive list of investors (Google's Marissa Mayer, Andreessen Horowitz, and FF Angel etc) must think so too. She knew nothing about electrical engineering when she started working on uBeam. Still, she built a working prototype merely by conducting research on Google and Wikipedia. (...) New York needs more hardware and tech companies like uBeam. Women in tech should be more like Perry."[59]

"Obviously [Perry's] ability to do power transmission wirelessly through sound was something that was fundamentally new."[60], quoting investor Scott Nolan

Of course, Perry didn't really invent ultrasonic power transmission. There have been patents in the area since at least 2003:

"A method and apparatus for converting electrical power from a wall outlet to electronically focused ultrasound, and converting the electronically focused ultrasound back to electrical power at a compatible receiving device is provided. The compatible receiving device may be cell phone, PDA, or a notebook computer or other suitable devices. (...) A power unit is provided in which it electronically scans the available space looking for a compatible receiving device (a cell phone, a PDA, or a notebook computer outfitted with the embodiment of this invention). Once the compatible receiving device is located, the power unit focuses its beam on the compatible receiving device, thereby delivering power thereto." [61]

There's nothing wrong with fame, just like there's nothing wrong with making money. But if one makes money by selling gadgets that can't do what they say they can, that's called "fraud". The same principle applies here.

14. Are additions/corrections welcome?

All suggestions, additions, corrections and comments are appreciated. However, please provide sources, especially for any controversial claims.


[1] Perry, Meredith. A new age of power. Retrieved October 11, 2015, from
[2] uBeam. Retrieved October 11, 2015, from
[3] Borison, Rebecca. (2014, August 22). 2 Women Who Were College Roommates Founded uBeam, One Of Tech's Hottest Startups - And Promptly Sued Each Other. Retrieved October 11, 2015, from
[4] Mims, Christopher. (2015, October 5). Soon, Power Will Be Delivered to Your Device by Air. Retrieved October 11, 2015, from
[5] Jones, Dave. (2014, August 7). UBeam Ultrasonic Wireless Charging – A Familiar Fish Smell. Retrieved October 11, 2015, from
[6] Boer, Miriam. (2014, November 3). Ultrasound, thermodynamics, and robot overlords. Retrieved October 11, 2015, from
[7] Rogers, Danny. (2014, October 31). How putting $10M into UBeam illustrates everything that is wrong with tech investing today. Retrieved October 11, 2015, from
[8] Energous Corporation Demonstrates Wire-free Charging during CES In a Future Home Environment. (2015, January 5). Retrieved October 11, 2015, from
[9] Ewalt, David. (2015, January 8). WiTricity’s wireless power connects at CES. Retrieved October 11, 2015, from
[10] Prodigy - WiTricity Corporation. Retrieved October 11, 2015, from
[11] Stone, Maddie. (2015, August 26). A Startup With No Website Just Announced a Major Fusion Breakthrough. Retrieved October 11, 2015, from
[12] Personal search on for "uBeam" "perry", conducted October 11, 2015. The term "perry" was included to avoid extraneous hits.
[13] Constine, Josh. (2015, October 8). UBeam Finally Reveals The Secret Of How Its Wireless Charging Phone Case Works Safely. Retrieved October 11, 2015, from
[14] Perry, Meredith. (2012, November 29). Patent Application US20120299540 A1 - Sender communications for wireless power transfer. Retrieved October 11, 2015, from
[15] Examples taken from Of course, these numbers are only approximate. More reliable sources appreciated.
[18] More reliable sources would be appreciated here, if any are online.
[19] Engineering Acoustics/Outdoor Sound Propagation. Retrieved October 11, 2015, from
[21] Bonnington, Christina. (2013, December 18). Choose the Right Charger and Power Your Gadgets Properly. Retrieved October 11, 2015, from
[23] Selenium. Retrieved October 11, 2015, from
[24] Jenkinson, S.G., Oxygen toxicity. New Horiz, 1993. 1(4): p. 504-11. Retrieved October 11, 2015, from
[25] DiLonardo, Mary Jo. (2014, August 14). When You Drink Too Much Water Too Fast, What Can Happen? Retrieved October 11, 2015, from
[26] Suster, Mark. (2014, October 30). The Audacious Plan to Make Electricity as Easy as WiFi. Retrieved October 11, 2015, from
[27] MR-Guided Focused Ultrasound Surgery (MR-gFUS). Retrieved October 11, 2015, from
[28] Therapeutic ultrasound as a potential male contraceptive: power, frequency and temperature required to deplete rat testes of meiotic cells and epididymides of sperm determined using a commercially available system. James K Tsuruta, Paul A Dayton, Caterina M Gallippi, Michael G O’Rand, Michael A Streicker, Ryan C Gessner, Thomas S Gregory, Erick JR Silva, Katherine G Hamil, Glenda J Moser and David C Sokal. Reproductive Biology and Endocrinology 2012, 10:7 doi:10.1186/1477-7827-10-7. Retrieved October 11, 2015, from
[29] Roberts, Daniel. (2015, July 29). Is this woman the next Elon Musk? Retrieved October 11, 2015, from
[30] Guidelines for the Safe Use of Ultrasound: Part II. (2008, September 15). Retrieved October 11, 2015, from
[31] Howard, C., Hansen, C., & Zander, A. (2004, September 8). A review of current airborne ultrasound exposure limits. Journal of Occupational Health and Safety - Australia and New Zealand 01/2005; 21(3):253-257. Retrieved October 11, 2015, from
[32] Allen, C.H., Frings, H., Rudnick, I. (1948). "Some Biological Effects of Intense High Frequency Airborne Sound." J. Acoust. Soc. Am., vol. 20, pp. 62-65. Retrieved October 11, 2015, from
[33] Acton, W.I. (1974). "The Effects of Industrial Airborne Ultrasound on Humans." Ultrasonics, May, pp. 124-128. Retrieved October 11, 2015, from
[34] Health Effects of Exposure to Ultrasound and Infrasound: Report of the Independent Advisory Group on Non-ionising Radiation. London; Chilton, Didcot: Health Protection Agency; Centre for Radiation, Chemical and Environmental Hazards, 2010. Retrieved October 11, 2015, from
[35] Lawton, B.W. (2001) Damage to human hearing by airborne sound of very high frequency or ultrasonic frequency, London, Health & Safety Executive, 77pp. Retrieved October 11, 2015, from
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[37] More precise sources appreciated.
[38] Area covered = pi * r^2 / 2, since the transmitter's line-of-sight forms a semicircle. r = 2 meters, so area = 3.14159 * 4 / 2 ~= 6.28318 m^2. Rounded down to 6 because this ignores 3D effects; if the transmitter and receiver are at different heights, that adds extra distance.
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[40] Calculation in [6] double-checked, via
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Crikey. And the detailed post of the day award goes to georgesmith!  :-+

I'll throw in a lifetime achievement award nomination. Maybe the Wikinazis would even allow it on their holy Wikipedia!


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