8. How convenient would uBeam be?

9. How much power can uBeam deliver?

10. What are nonlinear effects?

11. Has anyone done due diligence on uBeam?

12. Who are uBeam's competitors?

13. So what? Who cares?

14. Are additions/corrections welcome?

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