Magnetic fields provide a new way to communicate wirelessly | Hacker News Reader

Magnetic fields provide a new way to communicate wirelessly

jacobsschool.ucsd.edu

68 pointsghosh21 comments

If this is as "ultra low power" as I think it is, I imagine it could be used by all kinds of implants, especially critical ones like pace makers, to extract information about their functionality.

So magnetic waves? Shouldn't those be called "electromagnetic waves"? What's new here? Just that they use a frequency that is transmitted well through the body?

A wire is an electric field with an electromagnetic field in the vacuum surrounding it. Chances are the same principle applies here: you'd have a magnetic wave in your tissues with a weak electromagnetic field around you. I'd assume that the "magnetic field" would be similar to (or the same as) the field present in ferromagnetic materials.

Remember electromagnetism isn't really a "thing:" it is not a distinct field, rather its two fields that interact with each other. The electric field and magnetic field are still distinct.

"The electric field and magnetic field are still distinct." This is not entirely true. In general it depends on your intertial frame what fields you see.

See for example: https://en.wikipedia.org/wiki/Classical_electromagnetism_and... and https://en.wikipedia.org/wiki/Moving_magnet_and_conductor_pr...

I think they may use near field rather than radiation for communication.

Yes, this is definitely near-field stuff. It can also be done with electric potential!

At first glance it looks like they are turning the body into a giant transformer. I'd be curious to see the effect on SNR as the demonstrator moves his hands closer together, reducing the "air gap".

This assumes that the body is magnetically conducting. The article implies this, too, with the statements about increased privacy and the claim of employing the body as a communication medium (versus simply having it transparent, which would still be better than its absorption of waves in the GHz range). Can anyone point out numbers and the involved mechanisms? I'd say for static fields the only mechanism would be the iron in the blood, and for dynamic fields possibly the conductivity through ions, but I'm unsure if the latter would even help, as electric conductivity is something that designers usually try to avoid in magnetic cores.

They're not. This is playing with skin capacitance. Similar to how you can work as a pretty good antenna for a TV if you put your finger on the socket.

> Researchers noted that a limitation of this technique is that magnetic fields require circular geometries in order to propagate through the human body. Devices like smart watches, headbands and belts will all work well using magnetic field human body communication, but not a small patch that is stuck on the chest and used to measure heart rate, for example. As long as the wearable application can wrap around a part of the body, it should work just fine with this technique, researchers explained.

Wait, so how do you get the data anywhere useful? At some point to connect to a phone or whatever it'll have to bridge to Bluetooth or equivalent anyway.

The phone could use a transmitter with circular geometry - a wire loop, for instance. It could be part of the case; I assume the magnetic field is unaffected by human touch, unlike the iPhone 4's antenna infamously did: http://www.wired.com/2010/06/iphone-4-loses-reception-when-a...

I seem to recall Microsoft toying with the idea of sending data as electric pulses through the human body. One silly example was a shoe that would send your business card when you shook hands with someone.

A better (pdf) article on the subject: http://embc.embs.org/files/2013/3185_FI.pdf

Fukuro Koshiji, Nanako Yuyama, and Kohji Koshiji, Transmission Characteristics of Body Area Communication Using Electromagnetic Resonance Coupling

A study by Park (from UCSD) will be published, but it's not avaiable for download and the abstract isn't very helpful.

“In the future, people are going to be wearing more electronics..."

Are they though?

I have a phone and a smartwatch on right now. I could also see some kind of mini-wearable like a pendant or bracelet or cufflink that could change colors for priority notifications or other user defined events. Heck, I could see something built, tastefully, into the frames of my glasses as well.

As long as its convenient, useful, and easy to use, people will be on board.

As a side note, I stopped wearing my Moto 360 for a week due to being too lazy to unpack my charger from a recent trip. I was driven half-crazy by having to pull out my phone all the time for basic notifications or to check the time. Once people get a taste of wearables they'll love them.

Further, that smartphone has nearly a billion transistors. By that metric, we will see wearable electronics grow geometrically.

Humans and large livestock (and maybe even pets) will have health monitoring devices embedded into their bodies in the near future. The devices will save the insurance companies money. Savings on insurance premiums will be the incentive to encourage mass adoption by citizens and owners of livestock.

Humans, ie. large livestock, will have monitoring embedded into their bodies in the near future -- not just for health reasons.

If we can think of it, governments can push it as a formal requirement -- one step at a time.

Is this not essentially the same tech as the antenna-mice from yesterday? Just a longer wavelength for a bigger sack of mostly water?

> In their experiments, researchers demonstrated that the magnetic communication link works well on the body, but they did not test the technique’s power consumption.

Isn't total power/bit transmitted the most interesting point? Magnetic path loss in biological tissue is very well understood, see MRI. I don't understand how this is Ph.D. level work.

It is a relatively novel method for transmitting signals through the body with applications to body sensors, medical devices and ubiquitous computing. People have gotten PHD's on a lot less. Who are you to say it isn't worthy?

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