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Author Topic: Bye-Bye Batteries: Radio Waves as a Low-Power Source  (Read 3712 times)

Fansome

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Bye-Bye Batteries: Radio Waves as a Low-Power Source
« on: July 18, 2010, 0359 UTC »
http://www.nytimes.com/2010/07/18/business/18novel.html?hpw

The New York Times

July 16, 2010
Bye-Bye Batteries: Radio Waves as a Low-Power Source
By ANNE EISENBERG

MATT REYNOLDS, an assistant professor in the electrical and computer engineering department at Duke University, wears other hats, too — including that of co-founder of two companies. These days, his interest is in a real hat now in prototype: a hard hat with a tiny microprocessor and beeper that sound a warning when dangerous equipment is nearby on a construction site.

What’s unusual, however, is that the hat’s beeper and microprocessor work without batteries. They use so little power that they can harvest all they need from radio waves in the air.

The waves come from wireless network transmitters on backhoes and bulldozers, installed to keep track of their locations. The microprocessor monitors the strength and direction of the radio signal from the construction equipment to determine if the hat’s wearer is too close.

Dr. Reynolds designed this low-power hat, called the SmartHat, with Jochen Teizer, an assistant professor in the school of civil and environmental engineering at Georgia Tech. They are among several people devising devices and systems that consume so little power that it can be drawn from ambient radio waves, reducing or even eliminating the need for batteries. Their work has been funded in part by the National Science Foundation.

Powercast, based in Pittsburgh, sells radio wave transmitters and receivers that use those waves to power wireless sensors and other devices. The sensors, for example, monitor room temperature in automatic systems that control heating and air-conditioning in office buildings, said Harry Ostaffe, director of marketing and business development.

The company recently introduced a receiver for charging battery-free wireless sensors, the P2110 Powerharvester Receiver, and demonstrated it in modules that sense temperature, light level and humidity data, he said. The modules include microcontrollers from Microchip Technology, in Chandler, Ariz.

Until recently, the use of radio waves to power wireless electronic devices was largely untapped because the waves dilute quickly as they spread, said Joshua R. Smith, a principal engineer at Intel’s research center in Seattle and an affiliate professor at the University of Washington.

“That’s changing,” said Dr. Smith, who explores the use of electromagnetic radiation. “Silicon technology has advanced to the point where even tiny amounts of energy can do useful work.”

Two types of research groups are extending the boundaries of low-power wireless devices, said Brian Otis, an assistant professor of electrical engineering at the University of Washington. Some researchers are working to reduce the power required by the devices; others are learning how to harvest power from the environment. “One day,” Professor Otis said, “those two camps will meet, and then we will have devices that can run indefinitely.”

Professor Otis, who designs and deploys integrated circuits for wireless sensing, is in the first group. Dr. Smith of Intel is one of the harvesters, gathering radio power that is now going to waste. And there are plenty of radio waves in the air to provide fodder for him as they spread from Wi-Fi transmitters, cellphone antennas, TV towers and radio stations.

Some of the waves travel to living-room televisions, for example. But others, which would otherwise be wasted as they rise through the atmosphere into space or are absorbed in the ground, can be exploited, he said. “Ambient radio waves,” he said, “can already provide enough energy to substitute for AAA batteries in some calculators, temperature and humidity sensors, and clocks.”

At Intel, Dr. Smith, working with the researcher Alanson Sample of the University of Washington, created an electronic “harvester” of ambient radio waves. It collects enough energy from a TV station broadcasting about 2.5 miles from the lab to run a temperature and humidity sensor.

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.

DR. SMITH and his colleagues have built a second device, powered by radio waves, that collects signals from an outdoor weather station and transmits them to an indoor display. The unit can accumulate enough energy to send an updated temperature every five seconds.

Dr. Reynolds of Duke has long been interested in electronics and wireless equipment. One company he helped found, Zensi, developed a system to sense the amount of electricity used by home appliances; Zensi was bought by Belkin, an electronics concern.

Many electronic devices are limited by batteries that fade away or can’t survive temperature extremes, he said. But, he added, “we are on the cusp of an explosion in small wireless devices” than can run on alternatives to battery power. “Devices like this can live on and on,” he said.


cmradio

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #1 on: July 19, 2010, 0109 UTC »
Mythbusters did something related on a recap episode, only from nearby HV hydro wires.... the RF idea seems FAR more efficient.

Peace!

Offline Token

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #2 on: July 19, 2010, 0140 UTC »
Nice to see this starting to be used regularly at something other than the lab level.  This has been a dream of Sci-Fi writers for decades, "power satellites beaming energy to the surface" etc.  And 35 years ago a working model was demonstrated in one of my classes...and was far from new at that time.  It can be argued that crystal radios have been doing this for over a century.

25 years ago, for one of the family day displays at work, we set up an LED powered by RF energy alone.

Of course, the thing to remember is that this will never be applicable to anything but devices with very small current draw; fortunately technology is always pushing what can be done on very small current sources.  The amount of energy that can be recovered is always going to be limited by two things, the RF power density and the capture area of the device being powered.  No matter what magic can be done with antenna design the amount of energy recovered can never be more than the amount of energy illuminating the surface area of the device, physics is physics, after all.  The smaller the device the less energy that can potentially be recovered.
T!
Mojave Desert, California USA

Fansome

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #3 on: July 19, 2010, 0300 UTC »
Actually, this concept is in widespread use already. RFID tags using "backscatter" tecehnology need no batteries. They capture the energy from the broadcast antenna, and use it as power to return a signal with digital information. These tags are used throughout the toll industry, as well as in other applications, such as theft prevention. However, the tags don't retain power for any length of time; they are only active when in the antenna's field. The developments mentioned here would be a step beyond that.

Offline SW-J

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #4 on: July 19, 2010, 0314 UTC »
Nice to see this starting to be used regularly at something other than the lab level.  This has been a dream of Sci-Fi writers for decades, "power satellites beaming energy to the surface" etc.  ...


Kinda like the 'sun' does ... what goes around comes around ...

And, of course, one even has to be careful of what 'ol sol dishes out too, like, UV rays ...
o Icom IC-756ProII, ProIII, Alinco DX-70, Kenwood TS-680s
o WinRadio G303e, Degen/Kaito 1103/DE1103, Stoddart NM-25
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Offline Token

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #5 on: July 19, 2010, 2310 UTC »
Actually, this concept is in widespread use already. RFID tags using "backscatter" tecehnology need no batteries.

True, but I was suggesting more at the consumer level, able to power things someone can use (not that you can't use RFID tags, I built a lock for my garage and a kill switch for one of my cars using one), and be able to turn it off and on.
T!
Mojave Desert, California USA

Offline L Cee

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #6 on: July 20, 2010, 0053 UTC »
Actually, this concept is in widespread use already. RFID tags using "backscatter" tecehnology need no batteries. They capture the energy from the broadcast antenna, and use it as power to return a signal with digital information. These tags are used throughout the toll industry, as well as in other applications, such as theft prevention. However, the tags don't retain power for any length of time; they are only active when in the antenna's field. The developments mentioned here would be a step beyond that.

Question:

Could this concept be used to power one of the "low power" or "flea power" beacons?
Do I understand this concept correctly? Could you capture the radio wave energy from a powerful broadcast station (like is received on the coil of a crystal radio) and use that energy to power another device?
L Cee
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Fansome

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #7 on: July 20, 2010, 0158 UTC »
Actually, this concept is in widespread use already. RFID tags using "backscatter" tecehnology need no batteries. They capture the energy from the broadcast antenna, and use it as power to return a signal with digital information. These tags are used throughout the toll industry, as well as in other applications, such as theft prevention. However, the tags don't retain power for any length of time; they are only active when in the antenna's field. The developments mentioned here would be a step beyond that.

Question:

Could this concept be used to power one of the "low power" or "flea power" beacons?
Do I understand this concept correctly? Could you capture the radio wave energy from a powerful broadcast station (like is received on the coil of a crystal radio) and use that energy to power another device?

Sure it could. The key issue, as mentioned above, is that the amount of power available is very low. I don't have any information on how much power a small device could hope to tap, but it's gotta be pretty small. However, an approach for a beacon might be to just sit quiet for an extended length of time, maybe days, maybe weeks, storing the energy somewhere like a battery. Once enough was saved to be useful, it could then go on the air for as much time as the stored energy would allow, and then go back to sleep. What the length of the active and inactive parts of this cycle might be, I don't know. You'd also have to have some pretty sophisticated, low-power electronics to capture the energy.

The advantage of this method would be that the beacon could be completely hidden, unlike one that relies on solar power.

If you think about it, this is a sort of "Maxwell's Demon" approach to broadcasting. That would be a good name for a station.

Offline L Cee

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #8 on: July 20, 2010, 0238 UTC »

If you think about it, this is a sort of "Maxwell's Demon" approach to broadcasting. That would be a good name for a station.
[/quote]

An interesting idea and there are some cool Maxwell's Demon images on the internet for QSL art.
;)
L Cee
East Coast - USA

Offline SW-J

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #9 on: July 20, 2010, 0330 UTC »

The advantage of this method would be that the beacon could be completely hidden, unlike one that relies on solar power.


Antenna ... what provisions are you going to make for an antenna - a 1/2 Lambda radiator of some sort; even loaded shorty can require 1/10 Lamda?

(Isotropic point-source radiators have not been perfected yet ...)
o Icom IC-756ProII, ProIII, Alinco DX-70, Kenwood TS-680s
o WinRadio G303e, Degen/Kaito 1103/DE1103, Stoddart NM-25
o 1/2 wave 80m Dipole used with several tuners
o Tuned loops from 2' thru 16' diam. capable of 160m thru 10m

Offline Seamus

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #10 on: July 20, 2010, 0331 UTC »
There are several variations of a "charge and dump" circuit collectively referred to as "solar engines", which are used to build simple autonomous mechanisms.  They sit and charge capacitors from tiny solar cells until a specified threshold voltage is met, at which point they activate, dumping the cap into the load portion of the circuit.  This is usually used to drive small motors that the cells wouldn't normally be able to drive on their own, though they are also used to power other loads.  The basic "Miller Solar Engine" circuit is quite simple, requiring only a handful of components.  The Canadian company Solarbotics sells epoxy-encapsulated cells with circuit traces pre-printed on the back for building them.

If you work out the RF scavenger portion, I imagine that replacing the solar cell in a solar engine circuit wouldn't be too difficult.

Hell, for that matter, just driving a straight CW transmitter with the basic "charge and dump" solar engine circuit should probably produce a series of beeps where the repetition rate varied with solar input.

Fansome

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #11 on: July 20, 2010, 0408 UTC »
I think that the antenna would not be as much of a problem as solar panels. Stealth wire is readily available that blends in very well with the background.


The advantage of this method would be that the beacon could be completely hidden, unlike one that relies on solar power.


Antenna ... what provisions are you going to make for an antenna - a 1/2 Lambda radiator of some sort; even loaded shorty can require 1/10 Lamda?

(Isotropic point-source radiators have not been perfected yet ...)


Offline SW-J

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #12 on: July 20, 2010, 0416 UTC »
I think that the antenna would not be as much of a problem as solar panels. Stealth wire is readily available that blends in very well with the background.


The advantage of this method would be that the beacon could be completely hidden, unlike one that relies on solar power.


Antenna ... what provisions are you going to make for an antenna - a 1/2 Lambda radiator of some sort; even loaded shorty can require 1/10 Lamda?

(Isotropic point-source radiators have not been perfected yet ...)


How big are your SPs? Little 2" x 3" panels for recharging those outdoor nitelights can supply 50 mW (2.5v x 20 mA) easily ...
 
o Icom IC-756ProII, ProIII, Alinco DX-70, Kenwood TS-680s
o WinRadio G303e, Degen/Kaito 1103/DE1103, Stoddart NM-25
o 1/2 wave 80m Dipole used with several tuners
o Tuned loops from 2' thru 16' diam. capable of 160m thru 10m

Offline Token

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Re: Bye-Bye Batteries: Radio Waves as a Low-Power Source
« Reply #13 on: July 20, 2010, 1445 UTC »

Sure it could. The key issue, as mentioned above, is that the amount of power available is very low. I don't have any information on how much power a small device could hope to tap, but it's gotta be pretty small.

Yeah, power is going to be pretty small.  The amount captured is going to depend on a lot of factors.  How wide is the power capture bandwidth?  How many stations are transmitting within that bandwidth?  More importantly what is the average received power level across that bandwidth?  Naturally the larger the antenna the larger the capture area and the higher the potential captured energy would be, a potential problem if you are trying to be stealthy with the antenna.  What is your conversion efficiency?  Are you going to put the item in a location near a high power transmitter or near several high power transmitters?  Or is it going to be more remote as many beacons are?

Pure guess work below, having not really ever investigated the pitfalls of this before.  I possibly have not considered a deal killer someplace.

As an example I just did a sweep of the AM broadcast band at my location in the desert, far from any transmitter.  About 15 stations could be seen at the signal level of about S9 +20 on a calibrated meter (eyeball average among those stations).  Calibrated in this case meaning S9 = 50 microVolts or -73 dBm on a 50 Ohm impedance.  So 15 stations being delivered to my receiver with on average -53 dBm each.  Or about -40 dBm of energy among those stations total, probably another 10 dB or so if you add in the other stations in the band, so call it -30 dBm for this exercise.  Or about 0.000001 Watts, 1 microWatt.  Before conversion loss.

At night I have often seen signal levels of S9 +40 dB from the same stations.  In the case above this would yield -10 dBm across the band, or 0.0001 Watts, 100 microWatts.  Possibly a bit more if things are good.

But what if you were 2 kM from the Mt Wilson Electronics Reservation?  Having done a power survey near there at one time I can say the power levels are very high, at a guess I would bet you could pull over 10 mW (+10 dBm, 100 times the above nighttime guestimate) at 2 kM 24 hours a day if you combined the FM and TV BC bands.  If you could get 50% efficiency in conversion, storage, and transmission that would allow a 500 mW transmitter to broadcast just over one minute per hour.

Yeah, while a cool idea I have to say solar cells are a bit more applicable for things like beacons.  True they only gather during daylight but a cheap ($20 US) 1.5 Watt cell can be had that measures 12" x 5".  If it gathers 1.5 W of power 8 hours a day that still means you can afford to spend 500 mW each hour around the clock, easily driving a 200 mW transmitter 24 hours a day, or a 1 Watt transmitter for maybe 15 minutes of every hour.
T!
Mojave Desert, California USA

 

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