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The uBeam FAQ

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PaulReynolds:

--- Quote from: StillTrying on January 16, 2019, 11:25:04 am ---
--- Quote from: PaulReynolds on January 16, 2019, 08:48:55 am ---I expanded that post to a blog, for those interested:
https://liesandstartuppr.blogspot.com/2019/01/more-ubeam-at-ces-2019-macworld.html
--- End quote ---

 :)
I watched the blue-white RX LEDs coming on 2 or 3 times in the video, with superbright LEDs that amount of light could be as low as 25-30mW.

In this thread somewhere Howardlong and me have both tried to create subharmonics in the air by mixing 2 40kHzs 1 or 2kHz apart, and neither of us could hear anything for some reason, I checked with a very close EMC that they were mixing, there seems to be more to it than just 2 cleanly mixed 40kHzs.


--- End quote ---

I was being very generous to uBeam with a 100mW estimate in the post, trying to be as "best case" as I can. It most likely is closer to what you are suggesting at 25mW.

Subharmonics are different than nonlinear sound generation. Subharmonics are when there's a nonlinearity in the system and the system itself generates a lower frequency from a single frequency source and creates an integer division of the fundamental frequency. The eardrum is a good example of this, at round about 110 to 120 dB the ear stops responding linearly (specifically, the restoring force on the eardrum goes asymmetric), and the first subharmonic starts appearing at 30 to 40dB lower (1/2 freq), and then at 130 to 140 dB the second subharmonic (1/4 freq)starts appearing around 60-70dB lower (from memory, need to reread the papers to confirm). There are a few studies covering this, so the dataset is fairly limited - it's utterly unethical to perform such experiments on people for a start, and it's a tricky setup to get right.

Paper on subharmonics in the ear
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3387311/

Parametric sound is where the inherent nonlinearity of the air is used to generate sound at a location, and uses high frequency sound to ensure the array is larger than the wavelength so steering and directionality is straightforward. It needs to be 110dB+ for that to happen IIRC in theory, 130dB+ in practice, but you lose at least 60dB in what you hear, so I doubt with a regular source you would have much luck. In theory you can generate any frequency you want, not just an integer division of the fundamental.

https://en.wikipedia.org/wiki/Sound_from_ultrasound
https://www.holosonics.com/fundamental-limitations-of-loudspeaker-directivity

BTW in looking up a link on nonlinear sound I found this Kickstarter backed project that resulted in a 98 element array transmitter using Murata style devices that probably puts out a similar amount of power to the uBeam transmitter. For $250 $500 inc amp.

https://www.soundlazer.com/shop/

sdpkom:

--- Quote from: StillTrying on January 16, 2019, 11:25:04 am ---

--- Quote from: EEVblog on January 14, 2019, 11:06:00 pm ---So what is this "Burst circuit"?
--- End quote ---

I dunno, a guess is it's something to do with powering 4 receivers at the same time.

--- End quote ---

Maybe it's better to start with powering just one receiver, for part of the time, ehh....?

EEVblog:

--- Quote from: PaulReynolds on January 15, 2019, 09:16:25 pm ---Macvoices video of uBeam floor demo at CES



--- End quote ---

So they had a "public" stand with a demo but it's not their "real" latest demo which you have to be invited to their private suite to see?
What company does this if they don't have something to hide? CES is where you show off your latest stuff and wow the media.
Of course, we know the answer  ;D

EEVblog:
Whatever happened to these transducers?

Fungus:

--- Quote from: mikeselectricstuff on January 15, 2019, 10:49:03 pm ---"I wouldn't be doing my job if I didn't ask about safety"
..and power transferred, cost, efficiency... ?
Thought not. Typical clueless idiot journalism

--- End quote ---

You'd think there'd be one journalist at that show with camera and a clue, but nooooo.

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