Battery-free self-powered sensor harvests magnetic energy | Hacker News Reader

Battery-free self-powered sensor harvests magnetic energy

news.mit.edu

101 pointsgeox41 comments

Interesting that this comes on the same day as another HN submission on the Beverly Clock which powers itself via volume flux (due to tempreture | pressure changes) of a sealed mass of air.

https://news.ycombinator.com/item?id=39084732

The magnetic flux near powered equipment is relatively high - one wonders if this can be pushed to power a sensor from diurnal flux - the daily pulse of a earths magnetic field at any fixed location, the measurement of which can be used for resource mapping:

https://www.ga.gov.au/scientific-topics/disciplines/geophysi...

> one wonders if this can be pushed to power a sensor from diurnal flux

Get the backs of your envelopes ready, this sounds like a Fermi problem. From a quick reading of geomagnetic k-index data let's estimate the short time average flux change at 1 millitesla per three hours. That would give a maximum energy budget of 7e-5 watts per cubic metre (from dB²/2mu_0), so you're looking at picowatts of power for anything handheld.

(If anyone wants to refine this upper bound I'd be pleased.)

Of course smarter people than me have spent more than 30 seconds thinking about this and may have better answers, see e.g. https://physics.aps.org/articles/v9/91 and https://physics.stackexchange.com/questions/65082/can-the-ea...

Nice to see somebody take the challenge.

Ballpark you're pretty much on the money .. although the standard geophysical unit for measure surface magnetic flux in surveying is the nanotesla .. with 3 axis measurements taken ten times a second at each wingtip and tail of an aircraft travelling 70m/s some 80m above the ground.

Similar but different for "long soak" fixed position magnetotelluric mapping where the field moves about the instrument rather than grid survey where the aircraft moves through the field.

https://www.ga.gov.au/scientific-topics/disciplines/geophysi...

This is related to the power question - it's all sensors moving through fields. Creating images from all that raw data is another ball of (fun) wax.

And 3 days after another HN submission on a self-powered sensor that harvest energy from soil microbes.

https://news.ycombinator.com/item?id=39046697

Are they omitting the fact that there are side effects? There is no free energy. So the energy they consume from the environment will either attenuate useful radio signals or will cause impedance in wires. It's not new anyway, you can listen to radio without any batteries by harnessing the energy from radio waves.

There are always side effects, some energy of the magnetic field will dissipate anyway in pieces of metal nearby like housings, screws, rebar in the walls etc.

I think the interesting parts here are:

- it absorbs energy and stores them in capacitors until fully charged

- once on, it attempts to activate sensors in such a way it does not need to go offline.. which seems to include "higher power" sensors that will probably have less frequent measurements taken due to the power requirement

- the design explanation seems to indicate it would work well with any low power sensor, it is supposed to "learn" how much power a sensor needs to take a measurement.

So this isn't (to me) interesting because it's a self-powered sensor, but because it's an auto-starting sensor controller that can make best effort measurements from radio waves, and it's not necessarily fixed to specific sensors (presumably any sensor that doesn't exceed it's capacitors, less the power required to switch back to harvest mode)

Generally these energy harvesting devices harvest such little energy than any effect is negligible. Like leaving a drinking glass in the rain and working out how that will affect the water table.

Passive spying device that required no power:

https://en.wikipedia.org/wiki/The_Thing_(listening_device)

One of my favourite gadgets of history and a worthy link, technically it required external power, an illuminating external radio signal which is modified by local audio signals and rebrodcast in changed form.

Would something like this still work today? I assumed that sensitive locations would have shields in place to prevent potential bugs from transmitting information.

Then again, this would also make cell phones and wifi inoperable, so maybe that is considered too high of a cost vs being diligent in monitoring for devices.

It's pretty standard (as in, there are literally standards for it) to have shielding around air-gapped systems and rooms. TEMPEST is a good reference point.

Up until recently the standards were tested once then done. After that people were free to drill holes or alter things to bypass the standards.

Now they perform checks periodically so this happens less.

Making WiFi and cell phones inoperable within secure facilities is a feature - only cleared comms units should work, and even those should be able to be shut down.

For interest, see:

Rare Shot of POTUS Inside a Sensitive Compartmented Info Facility https://news.ycombinator.com/item?id=39050756

SCIF and Radio Frequency Secured Facility Design https://news.ycombinator.com/item?id=35729283

Similar system already exists as a product. Wireless microchip that is powered by energy harvesting https://www.onio.com/

Have you actually used these / seen them in use?

Those devices really struggle to find any market fit. If your device really uses this little power, it's almost always easier to just use a small button cell battery which then easily lasts 10+ years.

Interesting company.

NFC and RFID use radio energy and have been around for a while. There are a few variations of chips harvesting energy from other sources. Including body heat, movement, ambient light (even electrical light), and other sources of energy. Magnetic energy of course make sense. After all that's how most generators work. Doing that without mechanical parts is interesting.

A wireless sensor doesn't need a lot of power. With multiple possible ways to power them, somebody is likely to stumble on a way to mass produce them cheaply eventually.

This company creates sensors for monitoring power-grid lines which are powered from line induction:

https://www.gridsentry.us/

I'm sure this is a completely dumb idea. But I want wireless Christmas lights. Individual little clip-on LEDs powered by ambient RF like wifi background, the ambient field from a home's wiring, or an "antenna" that you snake up the trunk of the tree to emit a field. Then you just clip on the lights where you want them. I'm not knowledgeable enough in electronics to know if this is even possible.

It would be cool to just have one off LEDs like this to stick around. If they ever light up, get scared!

Yes look at onio.com they developed a frequency energy harvesting microcontroller

Tesla coil trunk, fluorescent bulbs as lights? Could work, might kill you somewhere along the line.

It's possible, but in the worst way.

The idea you have in your head, is not possible. A single LED (like one tiny bulb, not a string) hanging on your evergreen shrub is going to consume about 1000x more energy than what could be expected to be available floating around the local airwaves. So - impossible.

But of course you could just increase the energy in the airwaves by 1000x, give the middle finger to the FCC, and risk having to take out a loan to cover your energy bill.

Or you could go for inductive coupling, which actually would be viable and has been demonstrated as "wireless energy" ad-nauseam for the last 120 years. You would just have to deal with extremely finicky LED alignment to get power from the very difficult to engineer and extremely power inefficient source coil which will bathe your front yard in a rapidly oscillating magnetic field. Again pissing off the FCC and super charging your energy usage.

Or you can just plug in your lights.

You can do that with microwave oven. It would need some adjustments..

In an outdoor context one could also harvest another abundant energy source. I think this is actually sort of interesting. A swarm of individual lights could each be pulsed randomly at a very low duty cycle and the effect might still be usable.

Sadly, I expected that to be the answer. Oh well, I can dream! Thanks for your helpful follow-up.

The other solutions are right in that you'd need some high power transmission to be practical

but

if you harness solar power during the day and use battery power at night, you could drive some, but not many, bulbs. More photovoltaics and parallel batteries would be needed to scale. But, it would be able to amplify the RF signal and effectively drive the bulbs by radio. I would recommend driving a near-field radio and not off of WiFi if you're going for any aesthetic effect. You could even drive it with the ambient audio (there are some integrated devices already like this, but wired).

There are solar powered christmas lights. That seems more much more practical.

Looking at the first picture in the abstract of their paper: https://ieeexplore.ieee.org/document/10341273

It looks like they are putting a secondary winding around an AC wire. Sounds a bit underwhelming ...

" a clampable, split-core current transformer (CT) magnetic energy harvester"

It's exactly the same as the Efergy gadget I use to measure how much power my house is using. Nothing new in that at all. The innovations (if there are any) are in the control system and it's ability to reliably start up when it has enough charge.

They already have self-powered GPS but it can only muster enough power to ping once a day right now.

https://news.ycombinator.com/item?id=38086227

From being clipped to things carrying electricity, at least in the example they gave.

Nice for not requiring a soldered connection, meaning you can add it as an after thought.

Energy harvesting is useful where the power need is very low and changing batteries is inconvenient and/or expensive. So it makes sense where you need to deploy a large network of low power sensors. But ordinary batteries or mains power should be the default choice for most applications.

Smart wall light switches are another place where they are beneficial (in places where you do not have the neutral)

> such a sensor could be embedded in a hard-to-reach place, like inside the inner workings of a ship’s engine.

the "inner workings of a ship's engine" is a Faraday cage, no?

full of accelerating pieces of iron...

edit: TFA says meant to be attached to a wire, so maybe attached to connections coming from an alternator.

Kind of hilarious how they don't mention the core need (and source of funding?) of these types of devices... spies

It really isn’t the core need. The core need is industrial settings where you want to be able to fit and forget a sensor and have it alert you to problems or provide a stream of data for diagnostic monitoring.

Can it be used for spying? Maybe, assuming audio surveillance that’s a large power requirement though, so seems unlikely for the foreseeable.

Source: I did my PhD in energy harvesting

I find the pro/con for this solution in an industrial environment interesting:

- adding yet another power/data line for a sensor is expensive, possibly requiring equipment to be shutdown, new mounting points to be drilled, etc.

- trying to find an accessible current carrying wire that isn't further enclosed in a ferrous enclosure that would block RF.

It reminds me of the time my boss suggested using inductive power for a camera in a dairy barn. It's a wet and difficult environment where urine, salt, water, temperature swings were common. How were we going to get the power to the inductive coil? Ah, yeah.

MIT press release = BULLSHIT

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