

Engineer invents safe way to transfer energy to medical chips in the body - givan
http://news.stanford.edu/news/2014/may/electronic-wireless-transfer-051914.html

======
phasetransition
Caveat - It has been more than decade since I worked in an optics lab, and I
haven't looked behind the pay wall at the paper.

\---

-I'm pretty sure this works in a way analogous to "frustrated total internal reflection," which powers many fingerprint readers. (look up total internal reflection on Wikipedia)

-By placing three mediums with different impedances in sequence, you can promote an "evanescent" (non-propagating) nearfield wave to partially couple into the the third medium.

-The wave will propagate in the third medium if it has the correct impedance relationship to the other two, and if it supports a propagation mode of the incident wave. In this case it appears that the skin is being used as the third medium, based on the wording in the promo blurb from Stanford.

------
jcr
Paper" "Wireless power transfer to deep-tissue microimplants" from "
_Proceedings of the National Academy of Sciences_ " (PNAS) is pay-walled here:

[http://www.pnas.org/content/early/2014/05/14/1403002111](http://www.pnas.org/content/early/2014/05/14/1403002111)

------
programmer_dude
Summary:-

Far-field electromagnetic waves are reflected/absorbed by the body therefore
are not useful for energy transfer. Near-field waves do not reach far enough
to be useful (1/r^3 law). The discovery: Mid-field waves, waves which
propagate well in biological tissue.

~~~
msandford
The near field 1/r^3 is defined by r and the starting point for how you define
r is the radius of the coil used to generate the magnetic field. The average
human body isn't much more than a foot thick. Putting a 12" diameter and thus
6" radius coil in a bit of padding and wearing it like a backpack isn't out of
the question especially if it's only for a few hours to charge up every day.
Or built in to your bed.

That's not to say that what's been discovered here isn't a lot better than a
big-ass coil. Just that the idea you couldn't get wireless power into the body
is wrong. People have been using subdermal inductive charging for insulin
pumps for years.

~~~
programmer_dude
>Just that the idea you couldn't get wireless power into the body is wrong.

Agreed! But like you said this might make this thing a little less unwieldy.

~~~
msandford
Yeah I guess I was disagreeing with the notion in the article that the
researcher "invented" a way to get wireless power into the body. That's
already done. It works. It's not great, but it works. So what was cooked up
was a huge improvement, not the original invention.

------
tinco
Slightly off-topic, but are humans the only animal that communicate
electromagnetically? There's a bunch of obvious advantages to it, and there
are already animals that can generate sufficient current. Is it because you
can't build antennae from organic material?

~~~
Stwerp
To be fair, any animals that use body language (i.e. dogs wagging tails) or
sight are communicating electromagnetically (reflected light) in the same we
humans communicate electromagnetically. We're not generating our own EM
signals, but using tools.

I had a discussion about this a while ago with a friend. There's a really
interesting video of a HAM guy who has built a system such that he yells into
a microphone which then uses the audio energy to generate an RF pulse that
travels out the antenna. All RF energy is generated by the vocal energy. By
yelling in pulses, Morse (or whatever) coding can be generated. I think he had
used to the communicate between Massachusetts and somewhere in Florida.

Our conclusion as to why don't animals communicate with their own RF energy
was your answer that you can't build good antennas from organic material.
Evolutionarily, though, it seems like a great advantage!

~~~
kasbah
>There's a really interesting video of a HAM guy who has built a system such
that he yells into a microphone which then uses the audio energy to generate
an RF pulse that travels out the antenna.

Fascinating, would love to see that in some distopian sci-fi story. Link for
those that are curious: [http://hackaday.com/2013/11/26/amateur-radio-
transmits-1000-...](http://hackaday.com/2013/11/26/amateur-radio-
transmits-1000-miles-on-voice-power/)

------
Gertig
This is the future of "Wearables"! Combining them with implants to provide
truly valuable data about your body and allowing them to deliver targeted
medical treatment. So very exciting.

~~~
Phlarp
Conveniently packaging data regarding heart, liver and kidney function to be
easily parsed and stored by advertisers/insurance/NSA

------
shinryuu
One step closer towards the borg :)

~~~
BugBrother
A very, very EMP-sensitive borg.

