Many years back I have seen an interesting project about ultrasound used as
a directional speaker. Quick google search shows this:

http://www.ultrasonic-audio.com/products/acouspade.html

The idea is that ultrasound is used to carry the audio signal to your ears.
And as ultrasound is not as easily spreading than in the hearing range, you
can focus the sound to certain area - you step away few meters and cannot
hear the audio content anymore.

Anyways, what I was thinking is even if you cannot directly hear
ultrasound, it still must be receipted by your body.

Tamas



On Wed, Jul 29, 2015 at 8:15 PM, Harold Hallikainen <harold@hallikainen.org=
>
wrote:

>
> > I may be wrong, but I feel dirty for bringing this filth onto the
> piclist.
> >
> > What do you all think of this "wireless charging technology"?
> >
> > http://www.businessinsider.com/startup-ubeams-10-million-debate-2014-11
> > http://fortune.com/2014/12/30/meredith-perry-ubeam/
> >
> > So many things about these sensationalist writings seem off. Thoughts?
>
> Thus far, I'm not a believer. The power, of course, spreads over an area
> that increases with the square of the radius. As you move away, the power
> drops off pretty quickly. So, to get any power at the receiver, you have
> to transmit quite a bit of power which I don't think is that safe. They
> keep saying it's safe because it's used in medical imaging. A quick searc=
h
> does not reveal how much power medical ultrasound imaging systems use, bu=
t
> I suspect it's fairly low. One thing that surprised me is the frequencies=
:
> 2MHz to 15MHz. I wonder what absorbtion of air is at these frequencies.
>
> Anyway, thus far, I'm not a believer in the technology.
>
> Harold
>
>
>
>
>
> --
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> Not sent from an iPhone.
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--=20
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