[HN Gopher] Spin-torque oscillators for WiFi band transmission a...
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Spin-torque oscillators for WiFi band transmission and energy
harvesting
Author : giuliomagnifico
Score : 77 points
Date : 2021-05-18 14:09 UTC (8 hours ago)
(HTM) web link (www.nature.com)
(TXT) w3m dump (www.nature.com)
| londons_explore wrote:
| Reading the abstract, my 'this isn't real science' detector went
| crazy...
|
| It's something about the fact they explained very basic things
| (series Vs parallel, battery-free), while also having a lot of
| words I didn't understand.
| WJW wrote:
| Eh, it's basically a new(-ish) way to make a small radio
| receiver but instead of converting the output power of the
| antenna into an input signal for an amplifier, they try to feed
| a small electric device with it. This is super possible and
| doesn't violate known physics in any way, but the amount of
| power you can transmit is minuscule. Still, it might be useful
| for some type of sensor where it is non desirable to have to
| replace the battery for some reason.
| amelius wrote:
| How would you handle payment for the energy and how would you
| make sure the energy ends up at the proper device and not at
| some man-in-the-middle?
| btown wrote:
| The energy to generate the 2.4GHz signal is already being
| lost; I don't believe that placing a spintronic device
| attenuates the signal in any meaningful way. In certain
| ways it's similar to tidal energy; one small tidal
| generator is not going to have any measurable effect on an
| ocean-scale system. The power absorbed is measured in
| _microwatts_ whereas the power consumption of a consumer
| router is measured in watts.
| MayeulC wrote:
| It isn't meant for energy delivery, but energy harvesting.
| Put a metal stick in place of the antenna, the same power
| is harvested, but dissipated away.
|
| I can see this useful for very low power devices. I don't
| have specific example in mind, but you can picture
| something like sensors embedded inside smart concrete high-
| rise buildings, that alert when crackling is found.
| cogman10 wrote:
| The problem is getting enough power to broadcast the sensor
| report. It means you have to run your sensors with a thimble
| of energy and store up remaining energy for a burst of
| reports (hope someone is listening :))
| tzs wrote:
| If you don't need much range (a couple feet, say), you can
| use ambient backscatter which doesn't need to store up
| energy for bursts.
|
| Here's a video about it from 2013 [1] showing some test
| devices. Here's an article about it [2].
|
| A bit later they extended this to make it work with off-
| the-shelf WiFi devices, so you could have a battery-free
| device that can communicate to ordinary WiFi devices [3].
| Still short range, but now you could make it so the reader
| is a commodity WiFi device like a smartphone, instead of a
| specialty device.
|
| Here are some other researchers who demonstrated a
| backscatter tag that diddled with Bluetooth Low Energy
| (BLE) instead of WiFi, and was correctly received by an
| iPad at over 9 m using the existing iOS Bluetooth stack
| with no modifications [4].
|
| And here is a battery-fee phone that communicates with a
| powered base station [5]. It works up to 30 ft away. The
| phone uses energy from ambient RF and small photodiodes.
|
| [1] https://www.youtube.com/watch?v=gX9cbxLSOkE
|
| [2] https://www.washington.edu/news/2013/08/13/wireless-
| devices-...
|
| [3]
| https://iotwifi.cs.washington.edu/files/wifiBackscatter.pdf
|
| [4] https://www.washington.edu/news/2017/07/05/first-
| battery-fre...
| ThrowawayR2 wrote:
| Products similar to that already exist, albeit not as low
| power as the device in the paper. For example, this
| passively powered UHF RFID tag has a moisture sensor built
| in: https://www.dipolerfid.com/RFID-Tags/Smartrac-Dogbone-
| Humidi...
| lefrancais wrote:
| There is this company [https://uwinloc.com] , I've been
| working for. However ,they are using 968MHz band to harvest
| energy, thus (lower freq = less loss due to distance). It
| works up to ~20m if the antenna are correctly "aligned".
| cptskippy wrote:
| > a burst of reports
|
| That assumes the device needs to be running constantly
| collecting data.
|
| What if a circuit passively charges a capacitor that once
| full powers up the device just long enough to take a
| reading and transmit it? This wouldn't be viable for things
| like air monitors where the sensors need to warm up for
| minutes, but it seems like it would be ideal for
| temperature sensors which can be influenced by the waste
| heat of the device.
| gabrielblack wrote:
| If someone reading the post here is thinking that will be
| possible give power to "small devices" using WIFI, that is not
| and will not be impossible. We are talking about few micro
| amperes when a coin cell battery can deliver 220.000 micro
| amperes, as paragon. There are some niche applications in micro
| ampere range, but in that cases there are some reliable and more
| stable solution, like cesium batteries. Dave of EEVBlog has a
| mission, debunk this wireless energy affirmation, explaining why
| it's simply impossible, for example:
| https://www.youtube.com/watch?v=P8s3Xjeg0sk
|
| Moreover the power is related to the distance to the wifi source
| and the presence of an active WIFI obviously doing this kind of
| solution at least impractical even for ultra low power
| consumption applications. An Apple tag uses a coin battery and I
| think will use that solution for a veeeeery long time.
| sigstoat wrote:
| this didn't claim to have anything to do with "common user"s.
| energy harvesting/storage for IoT-type nodes is of huge
| interest, with lots of work being done on it.
|
| > Dave of EEVBlog has a mission
|
| and i don't think he'd appreciate your "contribution" here to
| that mission.
| gabrielblack wrote:
| I wrote it fast, I rewrote it. My point is that the title is
| misleading and suggest you can use WIFI radiation as power
| source to do something useful in the near future in consumer
| electronics. You simply will not.
| sigstoat wrote:
| you're the one who hallucinated "consumer" into all of
| this. nobody said that. it wasn't in the title. this isn't
| a consumer electronics forum.
|
| as the abstract of the article points out, it's for energy
| harvesting applications. which have been demonstrated as
| being perfectly useful with microwatt collection rates.
| gabrielblack wrote:
| The administrators changed the title of this article for
| a reason. Moreover, that device is intended to be
| installed very close to the "consumer", that is useful in
| medical application, for example, where is no advisable
| to install the battery in a device to be implanted in the
| body. So you can install the emitter , transmitter,
| whatever you want call it on the skin. And WIFI is total
| bullshit. The say "WIFI frequency" aka 2.4 GHZ because as
| we all known is the deregulated frequency reserved for
| consumer application. So, IMHO the researcher shouldn't
| have used that term, is confusing ! From there to say
| that the experiment involve the problem of powering
| cordless devices in the sense of electronic gadget is
| complete misunderstanding of the sense of that research.
| Man , science is not an opinion.
| sigstoat wrote:
| it kind of looks like you're having a rough day. i hope
| you feel better.
| gabrielblack wrote:
| Simply I don't like fake news.
| gabrielblack wrote:
| The title of this article was changed, by the administrators I
| guess, I think it's good in times where someone think opinions
| are more relevant then science.
| giuliomagnifico wrote:
| Maybe he's right but his video is from "jan 2010", maybe in 11
| years some improvements are been made... and this research
| doesn't talk about "power a smartphone" but a very very small
| device.
| gabrielblack wrote:
| look it's science , if you know electronic 101 and pay
| attention watching Dave's video, you could understand why.
| And yes, the power available was in microwatt range 10 years
| ago, too.
| detaro wrote:
| And you shouldn't jump to conclusions and shout
| "alternative science!!!" before looking at least at the
| order of magnitude discussed.
| gabrielblack wrote:
| the title is misleading , you should specify microwatt
| detaro wrote:
| A scientific paper should have to specify in the title
| that it's staying in the (in the field) obvious physical
| limits of what's possible?
| gabrielblack wrote:
| I think titles that are clickbaits should be avoided,
| titles like "eternal youth found" referring to article
| with: "eating apple seeds for 10 years you can gain up to
| 10 microsenconds lifespan".
| detaro wrote:
| So you provide a video of Dave showing the math that you can
| get only microwatts out of radio waves to debunk something that
| ... claims to provide power in the microwatts range?
|
| The "charge a phone" thing is obviously bunk, but that's not
| what's discussed here.
| gabrielblack wrote:
| Show me applications in microwatt range to justify the
| "usable", moreover you need a wifi. Why someone should use
| that instead of a solar cell, like the one on calculators ?
| gabrielblack wrote:
| errata corrige: ... that is not and will not be possible.
| agumonkey wrote:
| I wonder if these could also improve bandwidth for other devices
| since the absorbed waves won't bounce / interfere with actual
| signals.
| dr_orpheus wrote:
| Really not sure what they are trying to get at here, but their
| "usable energy" is on the pico-watt to micro-watt scale. It looks
| more and more like one of those "free energy" type devices.
|
| Edit: Yes I understand that there is energy in RF signals, I am
| just questioning the actual practicality and claim that they can
| get usable energy from this. For a 200 mW (23 dBm) WiFi
| transmitter the free space loss at about 6 inches is 23 dB at
| which point you would have the same 0 dBm input that they used in
| the experiment. I have not included any antenna gain as they did
| not include the antenna gain from their microstrip patch antenna
| in their experiment, just the 0 dBm power input number.
| sigstoat wrote:
| > their "usable energy" is on the pico-watt to micro-watt scale
|
| devices which have long-term average power consumptions of
| micro-watts are perfectly reasonable. it's how some BLE sensors
| can run for years off a single coin cell battery.
|
| you'd need some energy harvesting circuitry and something low-
| leakage to build it up in, but that's doable. more expensive
| than just stuffing a coin cell into the circuit, though.
|
| > It looks more and more like one of those "free energy" type
| devices.
|
| it's perfectly well understood that there's energy in RF. just
| very very little of it, as you note.
|
| that's qualitatively different from the claims of most free
| energy devices.
| giuliomagnifico wrote:
| The device can receive:
|
| > For the condition of synchronization of four oscillators at
| 2.4 GHz with Idc,sync = 3 mA (1.2 mA) for the parallel (series)
| configuration
|
| That's very low but I think a first step in order to power
| small biometric implants, for example some kind of pacemakers.
| It's very frustrating have a surgical operation to change the
| battery every 10/15 years.
| nycdotnet wrote:
| Would be an ironic way to power a pacemaker as you'd be asked
| to start standing near the microwave.
| giuliomagnifico wrote:
| Ahah that's true, because some pacemakers send datas to the
| receiver/hospital through 2.4ghz band, so it can have
| interferences. But mine was only an example because my
| father has one of those device into his body and sooner or
| later it will need a "battery swap". Maybe not a pacemaker
| but to power a small temperature sensor, or something
| similar, it will be useful, send datas and get energy,
| quite nice and futuristic!
| dr_orpheus wrote:
| The current you refer to there is not the power that is being
| generated though, it seems to be an input in to the STO
| devices.
|
| > The STOs are connected in parallel (Fig. 1a) or in series
| (Fig. 1b) configuration, stimulated by a single dc source.
| For the parallel connection, at the dc bias (Idc) value of
| 1.5 mA
|
| Fig 2c and d shows the total output power which maxes out at
| 0.85 uW. Maybe this is enough to run a pacemaker or something
| small, I don't actually know. Fig 6 shows the rectification
| of the signal in to a voltage that can turn on an LED. The
| dc-dc converter puts it in the ~3V range. Assuming the dc-dc
| converter is near 100% efficiency (some are pretty damn good)
| this is a current of only 0.28 uA.
|
| Its a novel way, but they talk about in their own paper that
| it is not a new more efficient way to convert RF energy to DC
| energy
|
| > in the range of 1.65-2.8 GHz at Prf = 0 dBm and zero dc
| bias ac to dc conversion efficiency of ~6% at Prf = -20 dBm.
| This is higher than the reported values for STOs53,55 but
| less than the recent reports of power conversion efficiency
| of 40% and 40-70% at an input rf power ~0 dBm for MoS2-based
| flexible rectenna and state-of-the-art Si and GaAs
| rectifiers56
| PragmaticPulp wrote:
| Energy harvesting is real, but the amount of energy that can be
| harvested from stray WiFi signals is vanishingly small. Even with
| a hypothetical 100% efficient collector, stray WiFi energy
| wouldn't be able to power much at all in a small device.
|
| Practically speaking, sticking a tiny solar panel on a device
| would collect more energy unless the device is completely in the
| dark.
| zamadatix wrote:
| For an idea of exactly how small the FCC limits maximum
| transmitter output power (as fed into the antenna) for the band
| to 1 Watt. I.e. the low numbers in the results are expectations
| not early previews for much larger numbers in the future.
| jandrese wrote:
| In practice even high power WiFi APs tend to top out around
| 300mW. Multiply by free space power loss and the
| inefficiencies of the system and the total available power is
| approximately bupkis.
|
| Those tiny solar cells that power cheap calculators are a far
| more practical solution.
| gabrielblack wrote:
| Exactly, moreover they speak about WIFI band, but in the
| experiment they didn't use an Access Point but a signal
| generator with the test device at * 2.5cm (0.9 inch) * from the
| antenna, if I've understood: "For the energy harvesting, we
| used the 2.45 GHz resonant patch antenna with a return loss of
| more than -35 dB at 2.45 GHz and a gain of 7 dBi. The antenna
| is fed by the signal generator at 0 dBm. The antenna is placed
| at ~2.5 cm away from the MTJ array". Let's try to measure at
| 2.5 meters. That is a laboratory experiment not intended to
| prove that you can give power to something moving around. They
| speak about neuromorphic computing: I know there are devices
| implanted int the brain of blind people receiving power from a
| radio device installed very not inside the cranium but at the
| outside, on the skin. That kind of application is more
| credible.
| gabrielblack wrote:
| And WIFI is total bullshit. They say "WIFI frequency" aka 2.4
| GHZ because, as we all know, that is the deregulated frequency
| reserved for consumer application. So, IMHO the researcher
| shouldn't have used that term, is confusing ! From there to say
| that the experiment involve the problem of powering cordless
| devices in the sense of electronic gadget with an access point
| is a complete misunderstanding of the sense of that research.
| They intend to power something very close to the emitter in
| medical/niche applications with a dedicated emitter. This is an
| important clarification because WIFI data transmission
| delivered power is NOT constant and too weak, differently from
| the one from a signal generator near the device.
| gabrielblack wrote:
| Some conspiracy theorist freak want transform a legitimate
| scientific paper in some kind of proof of alien technology
| existance, maybe ! :-)
| idiotfinder wrote:
| idiot found!
| woeirua wrote:
| This is a big deal for IoT, and ubiquitous sensing. It's not
| there yet, but you can see that a few years down the road we
| might be able to power very simple sensors via existing wireless
| networks (for free). That will allow us to put sensors on
| everything.
| raverbashing wrote:
| Or maybe just convert the ubiquitous 50Hz/60Hz power line signal?
|
| Or a small solar cell? (like many calculators?)
|
| Probably more efficient. But less hype worthy.
| grae_QED wrote:
| So they're using low to medium energy microwaves to power
| devices? Well if anyone doesn't buy that they can always try and
| sell it as a heater [1].
|
| [1] https://www.youtube.com/embed/Di3fPj0pUbQ
| dang wrote:
| We changed the title from "First steps to converting 2.4GHz WiFi
| into usable energy to power small devices", which is not a good
| rewrite because it's impossible to quickly determine whether it's
| accurate, and because it doesn't use representative language from
| the article itself.
|
| I've taken a crack at shortening the article's own title to fit
| HN's 80 char limit. Since I have zero idea what a "spin-torque
| oscillator" is, I probably got this wrong. If anyone can suggest
| a more accurate and neutral title, we can change it again.
| gabrielblack wrote:
| Yeah, exactly the point I was try to explain being bullied for.
| giuliomagnifico wrote:
| Thanks for the correction! It's difficult to write an short
| title that can explain easily a scientific paper, and I failed
| =]
| airbreather wrote:
| Meanwhile I can make a loop antenna on a banana box and tune to
| 880 6PR local am station and collect a few volts with enough
| drive for a loudspeaker (via a tx), light a dim led continuously
| or store up in a cap to make a burst of 2.4ghz data now and then.
|
| Ok, it's the size of a banana box, but it is 24/7 dependable and
| a relatively decent amount of power compared to picowatts.
| crimandnakatoya wrote:
| Isn't that sort of like stealing power? Wouldn't the station
| need to broadcast with more energy to reach any listeners
| "behind" your antenna-siphon? And isn't the energy transfer
| extremely inefficient?
|
| It kind of sounds like the apocryphal tales of farmers who
| would lay big loops of cabling underneath HV lines to power
| their electric fences.
| TheOtherHobbes wrote:
| 1. No, because the power has already been transmitted. There
| would be problems if there were billions of these devices
| around a transmitter, because that would affect the loading.
| But one isn't going to make a difference.
|
| 2. Potentially yes, but the actual shadow is tiny. And
| transmitter powers are fixed and limited anyway.
|
| 3. Yes, of course. So is any form of undirected radio
| transmission.
|
| 4. This actually works. Kind of. You need to run the line
| parallel _or_ build a resonant mix of L and C at 60Hz (or
| 50Hz.) You can also do things like power fluorescent tubes by
| induction.
|
| https://www.trendhunter.com/trends/magnetic-field-
| fluorescen...
|
| The problem is the voltage/current is very hard to control,
| and the whole point of electric fences is that they're not
| lethal. You'll get _something_ out of a resonant circuit, but
| if you 're not a qualified electrical engineer it won't be
| the clean 110/60 or 220/50 needed for an electric fence.
| TeMPOraL wrote:
| 'TheOtherHobbes offered a detailed reply, but I'd like to add
| a useful mental model for such questions. Like all other EM
| radiation, radio waves are just _light_. They diffuse a bit
| differently than visible light due to _much_ longer
| wavelengths, and different materials are transparent /opaque
| to them, but to a first approximation, you can view the
| transmitting antenna as a lightbulb, and the receivers as
| opaque and weakly-reflective objects.
|
| Your questions are thus similar to asking, "If you put a tiny
| solar cell on a glass table, wouldn't that steal light from
| the lightbulb? Wouldn't we need a more powerful lightbulb to
| illuminate the room? Isn't this energy transfer extremely
| inefficient?". Yes - it consumes some power; no - it casts a
| tiny shadow, and enough light is scattered around that you
| won't see the difference; yes, if the only reason you turned
| the lightbulb on is to power that solar cell, it's _very_
| inefficient.
| abricot wrote:
| In Denmark the government have allowed people who live along
| some of the largest underground powerlines to install
| geothermal equipment to heat their houses.
| johntb86 wrote:
| That might actually save the utility companies some power
| usage - the resistance of a material increases with
| temperature and the homeowners would be reducing the
| temperature of the ground.
| sigstoat wrote:
| seems like that's a win for both parties? the transmission
| line heating is a waste product, which increases
| resistance, which increases the waste. so if folks are
| willing to pump the heat out and productively use it,
| that's great.
| gus_massa wrote:
| It's very interesting. Do you have a link about this?
|
| Anyway, this is very different.
|
| In an electric wire part of the energy is always
| transformed into heat and wasted, so it's nice is someone
| can use it.
|
| In this device, they add something to absorb part of the
| energy that otherwise would have traveled to your neighbor,
| so the transition tower must increase (slightly) the energy
| used.
|
| It's like digging a hole and replacing a part of the high
| voltage cable with a device that makes more heat on purpose
| to heat your home.
| hinkley wrote:
| You better be really, really sure the person who comes out
| to mark the utilities before you dig has the correct
| coordinates...
| alex_young wrote:
| Seems possible if a crystal radio is possible.
|
| https://en.m.wikipedia.org/wiki/Crystal_radio
| hungryforcodes wrote:
| Not to play the old man card, but I remember building them when
| I was younger -- and they worked for sure! You could tune in
| and listen to all sorts of broadcasts, no battery required at
| all.
| UI_at_80x24 wrote:
| Same here. I'm now an Amateur Radio operator. I wonder if
| there's a connection.
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