UBeam's Meredith Perry shows her wireless charging technology really works
The picture shows a 32 x 32 array of small ultrasonic emitters.   So that&#x27;s 1024 emitters.  The framed area is about 200mm square, so each emitter has a diameter of about 6mm. That&#x27;s unusually small; typical diameters are 9mm to 20mm.  I haven&#x27;t been able to find the source of that transducer, but a similar one 9mm across is here.[1]<p>That one can deliver 112dB sound pressure at 30cm range. 1000 of those would deliver 142dB at 40KHz. (10x = 10dB).  If they&#x27;re all wired to one amp, you get a straight beam.  The demo indicates they&#x27;re only getting a straight beam; steering the beam requires electronics behind each transducer. Quite possible, but runs up the cost.  If they wire up the transducers in rings and drive them with slightly different phases, they can tighten up the beam focus. Since the receiver is smaller than the transmitter, focusing would help.
Frequency is probably around 40KHz; if you go higher, losses in air go way up.<p>I haven&#x27;t worked out the drive power for this thing, but it&#x27;s probably a few watts per transducer, or a few kilowatts for the whole array.<p>So they have a 142dBA 40Khz beam about 200mm square.  They ought to be able to do some
short-range charging with it.<p>Notes:<p>* That&#x27;s a high-powered ultrasonic beam. Is it hazardous?  Most of the literature on ultrasonic safety involves energy coupled directly to skin, as with ultrasonic scanning,
where there&#x27;s a gel to improve transmission.  Generating high energy in air is rarely done. 
It&#x27;s certainly going to heat up anything in the beam.  The safety issue is a big deal.  All that energy has to go somewhere.<p>* How far can they project this?  At 40KHz, meters, maybe tens of meters.[2] 
Attenuation gets much worse with frequency, so this thing probably works in the low ultrasonic range. Early PR from UBeam talked about megahertz ultrasound, but the range would be a few millimeters up there.<p>* Efficiency is terrible.  Kilowatts in, watts out.<p>* That array of transducers isn&#x27;t cheap. Those things are usually a few dollars each. But in quantity, that could come down.<p>So the demo they did, at under 1m range, is possible, but doesn&#x27;t mean it&#x27;s a useful technology.<p>[1] <a href="https:&#x2F;&#x2F;www.americanpiezo.com&#x2F;images&#x2F;stories&#x2F;content_images&#x2F;pdf&#x2F;apc_10-3005.pdf" rel="nofollow">https:&#x2F;&#x2F;www.americanpiezo.com&#x2F;images&#x2F;stories&#x2F;content_images&#x2F;...</a>
[2] <a href="http:&#x2F;&#x2F;www.kayelaby.npl.co.uk&#x2F;general_physics&#x2F;2_4&#x2F;2_4_1.html" rel="nofollow">http:&#x2F;&#x2F;www.kayelaby.npl.co.uk&#x2F;general_physics&#x2F;2_4&#x2F;2_4_1.html</a>