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"uBeam could be vaporware" You don't say? Seriously — uBeam's claims were always ridiculous. Anybody with any kind of engineering background should be able to

by jwr 10y ago

"uBeam could be vaporware" You don't say? Seriously — uBeam's claims were always ridiculous. Anybody with any kind of engineering background should be able to feel it instinctively, and be convinced after spending a couple of minutes with pen and paper.

petra 10y ago
I'm not deeply into the details, but doesn't it depend on how focused the ultrasonic beam is if you can fully protect the beam from hitting people by some smart and rapid sensing ?
- wiredfool 10y ago
  From what I understand, uBeam's low power demo `works` because they're still (mostly) in the linear range. As you scale it up, you run into a couple of nonlinearities that form an upper limit of the power density and distance. 1) You can't run sound at over 1 atm of overpressure, because the troughs can't get to negative pressure. This limits the amount of power that you can physically get into a region using sound pressure. 2) Dispersion is a nonlinear effect that changes the frequency distribution of the sound, which has the effect of reducing the focus effect at greater range. (Also, affects the absorption losses). 3) Even in fully linear systems, phased arrays don't focus all the energy into one area, they have significant side lobes. You can monkey with the shapes and intensities, but TNSTAAFL. The SPL that they're talking about is in the range of jet engines at close range. Yeah, it's ultrasonic, and yeah, it's focused. But I don't want to get anywhere near the thing. The world is nicely linear, until it's not. You have to know where the simplifying assumptions end.
- daxorid 10y ago
  If you have to develop 100% accurate human detection and avoidance systems in order to avoid catastrophic tissue damage for users of a mild convenience, maybe you should pack it in. Some things are worth the risk. Spaceflight, experimental cancer research, assassination of despots, hazardous waste storage technologies. Sometimes you really do need to crack a few eggs to advance humanity. But the 'advance' we're talking about here is the trivial convenience of not plugging in your phone.
  - benologist 10y ago
    This technology starts with phone charging, where it ends may be quite a distance from there. We've also quite literally had to develop as close as we can get to 100% safe ways of pretty much everything complicated we do, from surgery to driving to toasting bread.
  - deleted 10y ago
    [deleted]
aurizon 10y ago
I agree with you. There was a cascade of low efficiency stages. Making UHF sound in electrical form - a wave train - into a speaker or transducer to couple to the air = overall efficiency of 3-4%. Beam into the air as well focussed as possible - 10 feet away, less than 25% there. Turn that sound into electricity with another transducer with 3-4% efficiency = over all under 1%. So a honking great ultrasonic horn using 10,000 watts of power will transmit around 10 watts of usable power. The whole area will become an ultrasound cooker(you dare not walk through the beam = dead and cooked if you stayed for long, blood clots in a second or less. and for a large area bats will hate it and dogs howl

by jwr 10y ago

petra 10y ago

I'm not deeply into the details, but doesn't it depend on how focused the ultrasonic beam is if you can fully protect the beam from hitting people by some smart and rapid sensing ?

wiredfool 10y ago
From what I understand, uBeam's low power demo `works` because they're still (mostly) in the linear range. As you scale it up, you run into a couple of nonlinearities that form an upper limit of the power density and distance. 1) You can't run sound at over 1 atm of overpressure, because the troughs can't get to negative pressure. This limits the amount of power that you can physically get into a region using sound pressure. 2) Dispersion is a nonlinear effect that changes the frequency distribution of the sound, which has the effect of reducing the focus effect at greater range. (Also, affects the absorption losses). 3) Even in fully linear systems, phased arrays don't focus all the energy into one area, they have significant side lobes. You can monkey with the shapes and intensities, but TNSTAAFL. The SPL that they're talking about is in the range of jet engines at close range. Yeah, it's ultrasonic, and yeah, it's focused. But I don't want to get anywhere near the thing. The world is nicely linear, until it's not. You have to know where the simplifying assumptions end.
daxorid 10y ago
If you have to develop 100% accurate human detection and avoidance systems in order to avoid catastrophic tissue damage for users of a mild convenience, maybe you should pack it in. Some things are worth the risk. Spaceflight, experimental cancer research, assassination of despots, hazardous waste storage technologies. Sometimes you really do need to crack a few eggs to advance humanity. But the 'advance' we're talking about here is the trivial convenience of not plugging in your phone.
- benologist 10y ago
  This technology starts with phone charging, where it ends may be quite a distance from there. We've also quite literally had to develop as close as we can get to 100% safe ways of pretty much everything complicated we do, from surgery to driving to toasting bread.
- deleted 10y ago
  [deleted]

aurizon 10y ago

I agree with you. There was a cascade of low efficiency stages. Making UHF sound in electrical form - a wave train - into a speaker or transducer to couple to the air = overall efficiency of 3-4%. Beam into the air as well focussed as possible - 10 feet away, less than 25% there. Turn that sound into electricity with another transducer with 3-4% efficiency = over all under 1%. So a honking great ultrasonic horn using 10,000 watts of power will transmit around 10 watts of usable power. The whole area will become an ultrasound cooker(you dare not walk through the beam = dead and cooked if you stayed for long, blood clots in a second or less. and for a large area bats will hate it and dogs howl