3 ms·

I don't know a lot about specific engineering details, but a jet engine (turbofan) produces about 1 kw of sound energy [1]. A cell phone has about 75 sq. cm of

I don't know a lot about specific engineering details, but a jet engine (turbofan) produces about 1 kw of sound energy [1]. A cell phone has about 75 sq. cm of area on one side. Thus, with perfect efficiency and spherical propagation, the available power to the phone for a user about 3m away would be about 0.2 watt. However, I'm skeptical that they can actually create a kilowatt of sound energy, and while you can focus the power (certainly you could do something more efficient than fully-spherical propagation), you're also going to have significant losses. All this for a charging rate that's about 1/5 of what you get from a 1 amp USB charger. [1] https://en.wikipedia.org/wiki/Acoustic_power#Table_of_selected_sound_sources https://en.wikipedia.org/wiki/Acoustic_power#Table_of_select...

xgbi 12y ago
Unless they are beamforming, which is highly unprobable, I think you're right.
- sp332 12y ago
  You can do beamforming with ultrasound. http://www.ted.com/talks/woody_norris_invents_amazing_things http://www.ted.com/talks/woody_norris_invents_amazing_things The demo device was flat, like the one shown in the article.
- timdierks 12y ago
  Beamforming would be cool and might actually allow this to work, although I don't know with what efficiency. That said, the tech just to locate the phones in space to allow the beamforming would be a significant accomplishment itself. But forming the beam or multiple beams to charge multiple devices is probably quite feasible.
  - wlesieutre 12y ago
    A possibly effective option would be sweeping the beam around and having the phone report when it hits. That should be easier than trying to accurately locate the phone first so that you can aim a beam at it. If you can also make a reasonable initial guess of it's location (to within a few degrees) you could narrow down the guess and check search area considerably.
- leeoniya 12y ago
  http://en.wikipedia.org/wiki/Long_Range_Acoustic_Device http://en.wikipedia.org/wiki/Long_Range_Acoustic_Device http://science.howstuffworks.com/lrad.htm/printable http://science.howstuffworks.com/lrad.htm/printable
- zheshishei 12y ago
  The NPR article[1] gives some more information on what it is. Apparently, it's ultrasonic piezoelectric charging. My guess is that it's using a resonance frequency approach to vibrate the crystals. 1: http://www.npr.org/2011/08/23/139854129/young-entrepreneur-has-a-better-idea-now-what http://www.npr.org/2011/08/23/139854129/young-entrepreneur-h...

xgbi 12y ago

Unless they are beamforming, which is highly unprobable, I think you're right.

sp332 12y ago
You can do beamforming with ultrasound. http://www.ted.com/talks/woody_norris_invents_amazing_things http://www.ted.com/talks/woody_norris_invents_amazing_things The demo device was flat, like the one shown in the article.
timdierks 12y ago
Beamforming would be cool and might actually allow this to work, although I don't know with what efficiency. That said, the tech just to locate the phones in space to allow the beamforming would be a significant accomplishment itself. But forming the beam or multiple beams to charge multiple devices is probably quite feasible.
- wlesieutre 12y ago
  A possibly effective option would be sweeping the beam around and having the phone report when it hits. That should be easier than trying to accurately locate the phone first so that you can aim a beam at it. If you can also make a reasonable initial guess of it's location (to within a few degrees) you could narrow down the guess and check search area considerably.
leeoniya 12y ago
http://en.wikipedia.org/wiki/Long_Range_Acoustic_Device http://en.wikipedia.org/wiki/Long_Range_Acoustic_Device http://science.howstuffworks.com/lrad.htm/printable http://science.howstuffworks.com/lrad.htm/printable
zheshishei 12y ago
The NPR article[1] gives some more information on what it is. Apparently, it's ultrasonic piezoelectric charging. My guess is that it's using a resonance frequency approach to vibrate the crystals. 1: http://www.npr.org/2011/08/23/139854129/young-entrepreneur-has-a-better-idea-now-what http://www.npr.org/2011/08/23/139854129/young-entrepreneur-h...