6 ms·

Bye-Bye, Batteries - Radio Waves as a Low-Power Source

42 points by donohoe 16y ago

Groxx 16y ago
important bit: simple processing & sound using ambient radio waves in a construction hat. Which is very cool. Other cited uses cover small temperature sensors and possibly replacing AAA battery powered devices. Add in a healthy dose of sparkly-futurist-hope (devices that run FOR EVAR), and some actual data on another experimental device: >The device collects enough power to produce about 50 microwatts of DC power, Dr. Smith said. That is enough for many sensing and computing jobs, said Professor Otis. The power consumption of a typical solar-powered calculator, for example, is only about 5 microwatts, he said, and that of a typical digital thermometer with a liquid crystal display is one microwatt. Didn't see anything on the size of the "device", but that's still pretty cool.
sasmith 16y ago
Should I be considering this differently from solar? They're both harvesting ambient EM radiation; and the energy density of solar is much higher. I guess that radio goes through walls and never sleeps, so that's a plus. Anyway, I thought that the mentioning of a solar calculator was quite appropriate and warranted further discussion.
- sliverstorm 16y ago
  It sounds like the device on the hard hat is more like a passive RFID chip; It's hard to be sure, but the article says all the dangerous equipment has transmitters of their own. Of course, the effective difference between the passive RFID chip and a device that simply consumes ambient radio-spectrum EM radiation is small, mostly a paradigm change. Your initial question begets an interesting question- since light is EM radiation, just like radio waves, shouldn't we be able to pick up light with an antenna? If we can figure that out, we can forget about solar cells with their sad efficiency levels. edit: with some quick research, the answer is obvious; while it seems extremely weird to imagine, light can be absorbed by an antenna- and the first and foremost reason this isn't being done already is because the appropriate antenna would be ~700 nanometers long.
  - kragen 16y ago
    You can absorb EM radiation just fine with an antenna that's "too long". It's when it's too short that you run into problems. 500nm-wavelength light oscillates at about 600 terahertz, with a period of about 1.7 femtoseconds. If you want to rectify that and turn it into DC current so you can run current semiconductor devices, you need a diode that can switch on once and off once in that period of time. So your forward recovery time plus your reverse recovery time needs to total less than 1.7 femtoseconds. Among other things, I think this implies that the depletion region in the diode needs to be less than 0.9 femtoseconds in width --- at the electron drift velocity of the semiconductor, which I think is typically around 12 orders of magnitude less than c, although in silicon it can be as high as only three orders of magnitude less than c. Which means that your depletion region needs to be 3 orders of magnitude smaller than the wavelength. Unfortunately the wavelength we're talking about here, at around 1000nm, is only four orders of magnitude bigger than a smallish atom, at 0.1nm. So you're pushing up against the bounds of possibility here with an insulating depletion region of a few atoms in thickness. Forward and reverse recovery times for silicon diodes vary widely. Typical values for discrete components are measured in the tens to hundreds of nanoseconds. Schottky diodes bring that down to tenths of nanoseconds. One nanosecond is one million femtoseconds, so that's still five orders of magnitude too slow. Anyway, I don't know anything about this stuff, really.
    - sliverstorm 16y ago
      Seems like it'd be easier to just drive a 600 terahertz motor, if such a motor can be made, and use that to drive a good old fashioned 60hz generator. The silicon would be a much nicer solution though. Thank you for the details on the diodes, I forgot about that part. You're probably right on the diodes being the hold-up.
      - kragen 16y ago
        Now that's an interesting idea. The light contains an oscillating magnetic field that you could use directly to spin a permanent magnet, if you had one that was small enough. (Any atomic nucleus would do, but you can't connect a shaft to it.) Maybe you could build a multipole nanomotor so that the rotor itself doesn't have to spin at 600THz; if you have 100 poles, which is not that far out of what people commonly do with macroscopic stepper motors, then you could get the rotation down to only 6THz. (But then you're only potentially absorbing light at the rim of this rotor.) Gearing that down to 60Hz at the nanoscale — without losing most of the energy to friction — could still be a significant challenge. I don't know of any hundred-billion-to-one gearboxes. The basic difficulty with the nanomotor approach, I think, is that electrons are lighter than nuclei, so it's easier to get them to oscillate over useful distances in any particular frequency range, and this is especially tricky in the terahertz to petahertz frequency range. A nucleus, under the influence of the same electrical field as an electron, will accelerate about three or four orders of magnitude more slowly. Ultimately this should be a scale advantage for mechanical computation, since it means you can localize an atom to a much smaller region, given a certain momentum uncertainty, than an electron. The atom can't tunnel as far, so it can store a bit reliably in a much smaller region. I don't think we're there yet.
typedef_void 16y ago
Didn't Tesla claim to have developed wireless power a long time ago. Those more familiar with Tesla/Physics ... is this the same technology?
- retube 16y ago
  The technology in the linked article would appear, at least superficially, to be similar to RFID. Although one difference might be that RFID works at a fixed frequency (to match the harmonic frequency of the receiving radio circuit) whereas this apparently works with "ambient" radio, implying a broad spectrum of frequencies, which is quite clever. Either way, the broadcast signal is losing power at a rate proportional 1/d^2. So these devices necessarily have to work at very low power. What Tesla did - or is supposed to have done - was to figure out how to transmit power without the 1/d^2 loss. I.e, much like a collimated laser beam, he could transmit power over large distances and power high current devices.
  - Rhapso 16y ago
    It is interesting, that we are only now scratching on the surface of what Tesla did 100 years ago.
    - tomjen3 16y ago
      There is no kidding that he was off the charts brilliant, but he was also - especially towards the end - insane. That is why it is so hard to figure out what Tesla actually did or didn't do.
- code_duck 16y ago
  He had dramatic ideas for free, wireless power transmission for everyone. His wealthy backer (was it JP Morgan?) said he couldn't see the profit angle in that and wasn't interested, saying something like "Where do you attach the meter?". Not exact quotes, but the source is my print version of : http://books.google.com/books?id=40NzjS5FunkC&printsec=frontcover&ei=ECRDTLqMC5SksQPgzKiXDA&#38 http://books.google.com/books?id=40NzjS5FunkC&printsec=f...;
- 16y ago

42 points by donohoe 16y ago

Groxx 16y ago

important bit: simple processing & sound using ambient radio waves in a construction hat. Which is very cool. Other cited uses cover small temperature sensors and possibly replacing AAA battery powered devices. Add in a healthy dose of sparkly-futurist-hope (devices that run FOR EVAR), and some actual data on another experimental device: >The device collects enough power to produce about 50 microwatts of DC power, Dr. Smith said. That is enough for many sensing and computing jobs, said Professor Otis. The power consumption of a typical solar-powered calculator, for example, is only about 5 microwatts, he said, and that of a typical digital thermometer with a liquid crystal display is one microwatt. Didn't see anything on the size of the "device", but that's still pretty cool.

sasmith 16y ago

Should I be considering this differently from solar? They're both harvesting ambient EM radiation; and the energy density of solar is much higher. I guess that radio goes through walls and never sleeps, so that's a plus. Anyway, I thought that the mentioning of a solar calculator was quite appropriate and warranted further discussion.

sliverstorm 16y ago
It sounds like the device on the hard hat is more like a passive RFID chip; It's hard to be sure, but the article says all the dangerous equipment has transmitters of their own. Of course, the effective difference between the passive RFID chip and a device that simply consumes ambient radio-spectrum EM radiation is small, mostly a paradigm change. Your initial question begets an interesting question- since light is EM radiation, just like radio waves, shouldn't we be able to pick up light with an antenna? If we can figure that out, we can forget about solar cells with their sad efficiency levels. edit: with some quick research, the answer is obvious; while it seems extremely weird to imagine, light can be absorbed by an antenna- and the first and foremost reason this isn't being done already is because the appropriate antenna would be ~700 nanometers long.
- kragen 16y ago
  You can absorb EM radiation just fine with an antenna that's "too long". It's when it's too short that you run into problems. 500nm-wavelength light oscillates at about 600 terahertz, with a period of about 1.7 femtoseconds. If you want to rectify that and turn it into DC current so you can run current semiconductor devices, you need a diode that can switch on once and off once in that period of time. So your forward recovery time plus your reverse recovery time needs to total less than 1.7 femtoseconds. Among other things, I think this implies that the depletion region in the diode needs to be less than 0.9 femtoseconds in width --- at the electron drift velocity of the semiconductor, which I think is typically around 12 orders of magnitude less than c, although in silicon it can be as high as only three orders of magnitude less than c. Which means that your depletion region needs to be 3 orders of magnitude smaller than the wavelength. Unfortunately the wavelength we're talking about here, at around 1000nm, is only four orders of magnitude bigger than a smallish atom, at 0.1nm. So you're pushing up against the bounds of possibility here with an insulating depletion region of a few atoms in thickness. Forward and reverse recovery times for silicon diodes vary widely. Typical values for discrete components are measured in the tens to hundreds of nanoseconds. Schottky diodes bring that down to tenths of nanoseconds. One nanosecond is one million femtoseconds, so that's still five orders of magnitude too slow. Anyway, I don't know anything about this stuff, really.
  - sliverstorm 16y ago
    Seems like it'd be easier to just drive a 600 terahertz motor, if such a motor can be made, and use that to drive a good old fashioned 60hz generator. The silicon would be a much nicer solution though. Thank you for the details on the diodes, I forgot about that part. You're probably right on the diodes being the hold-up.
    - kragen 16y ago
      Now that's an interesting idea. The light contains an oscillating magnetic field that you could use directly to spin a permanent magnet, if you had one that was small enough. (Any atomic nucleus would do, but you can't connect a shaft to it.) Maybe you could build a multipole nanomotor so that the rotor itself doesn't have to spin at 600THz; if you have 100 poles, which is not that far out of what people commonly do with macroscopic stepper motors, then you could get the rotation down to only 6THz. (But then you're only potentially absorbing light at the rim of this rotor.) Gearing that down to 60Hz at the nanoscale — without losing most of the energy to friction — could still be a significant challenge. I don't know of any hundred-billion-to-one gearboxes. The basic difficulty with the nanomotor approach, I think, is that electrons are lighter than nuclei, so it's easier to get them to oscillate over useful distances in any particular frequency range, and this is especially tricky in the terahertz to petahertz frequency range. A nucleus, under the influence of the same electrical field as an electron, will accelerate about three or four orders of magnitude more slowly. Ultimately this should be a scale advantage for mechanical computation, since it means you can localize an atom to a much smaller region, given a certain momentum uncertainty, than an electron. The atom can't tunnel as far, so it can store a bit reliably in a much smaller region. I don't think we're there yet.

typedef_void 16y ago

Didn't Tesla claim to have developed wireless power a long time ago. Those more familiar with Tesla/Physics ... is this the same technology?

retube 16y ago
The technology in the linked article would appear, at least superficially, to be similar to RFID. Although one difference might be that RFID works at a fixed frequency (to match the harmonic frequency of the receiving radio circuit) whereas this apparently works with "ambient" radio, implying a broad spectrum of frequencies, which is quite clever. Either way, the broadcast signal is losing power at a rate proportional 1/d^2. So these devices necessarily have to work at very low power. What Tesla did - or is supposed to have done - was to figure out how to transmit power without the 1/d^2 loss. I.e, much like a collimated laser beam, he could transmit power over large distances and power high current devices.
- Rhapso 16y ago
  It is interesting, that we are only now scratching on the surface of what Tesla did 100 years ago.
  - tomjen3 16y ago
    There is no kidding that he was off the charts brilliant, but he was also - especially towards the end - insane. That is why it is so hard to figure out what Tesla actually did or didn't do.
code_duck 16y ago
He had dramatic ideas for free, wireless power transmission for everyone. His wealthy backer (was it JP Morgan?) said he couldn't see the profit angle in that and wasn't interested, saying something like "Where do you attach the meter?". Not exact quotes, but the source is my print version of : http://books.google.com/books?id=40NzjS5FunkC&printsec=frontcover&ei=ECRDTLqMC5SksQPgzKiXDA&#38 http://books.google.com/books?id=40NzjS5FunkC&printsec=f...;
16y ago