Researchers develop “rectenna” to convert radio waves to electricity

Aug 04, 2011 by Bob Yirka weblog

Researchers from Nihon Dengyo Kosaku Co., Ltd, (DENGYO) a Japanese communications infrastructure company, have developed a device they call the “rectenna” that can convert radio waves moving around in the air, to electricity. The name comes from combining the word “rectifier” (a device that is normally used to convert AC power to DC, but can also be used to detect radio signals) with “antenna”.

In the demonstration video, the researchers say that the rectenna can convert both WiFi and digital terrestrial broadcast signals, though the amount it converts depends of course on the amount of radio waves in the vicinity. The rectenna comes in two sizes, one for converting WiFi signals, the other for terrestrial. The WiFi version is small, just 12 mm thick, while the terrestrial version is 30 mm thick. Each looks like a plain soft-white pad.

Engineers demoing the two devices say electricity produced by the WiFi version is in the microwatts at a distance of just 10cm from the source, not a lot of course, but enough to power a small sensor or tag, they say. As for the terrestrial version, they were able to generate about 1.2mV and 0.06µW of power inside the exhibition hall, where the video was made, at the Tokyo Big Sight. The signals received were from a digital terrestrial broadcast sent from the Tokyo Tower which was about 5.5km away.

While neither device converts very much power, the team is confident that uses could be found for such converters, or perhaps new devices created that could take advantage of small amounts of power. They also note that in some areas, such as very near the Tokyo Tower, the rectenna is able produce much more power; in one case it was able to produce 6mW of power, at a distance of 3 or 4 kilometers from the tower.

In practical terms it appears the devices might be useful for capturing in the home and using the produced to power LED monitor lights or as sensors that wake-up other gadgets when someone wants to use them. If enough rectenna’s were connected in a home, consumers might even see lower power bills at the end of the month.

Via DigInfo TV

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Shootist
3.3 / 5 (7) Aug 04, 2011
Researchers from Nihon Dengyo Kosaku Co., Ltd, (DENGYO) a Japanese communications infrastructure company, have developed a device they call the rectenna that can convert radio waves moving around in the air, to electricity. The name comes from combining the word rectifier (a device that is normally used to convert AC power to DC, but can also be used to detect radio signals) with antenna.


The term being, perhaps, 70 years old?

Science writers writing about science should at least know the lexicon.

daqman
5 / 5 (4) Aug 04, 2011
Did someone leave all of the content out of this article? There seems to me to be absolutely nothing new here. The power levels quoted in the article are consistent with those that you could get from a regular ferrite radio antenna in a resonant circuit with a diode to convert to DC and a capacitor to smooth. There has to be something new for it to be news worthy but all of that is missing from the article.
antonima
5 / 5 (2) Aug 04, 2011
People were arrested for using rectennas during WWII because it interfered with radio communication. They will get a lot of criticism if they want to go large scale, unless they make a good argument for its use.
Waterdog
5 / 5 (2) Aug 04, 2011
Anybody ever hear of Nikoli Tesla? Look him up. He invented our modern electrical system. He also proposed using similar devices (albeit much larger) to collect broadcast power a hundred years ago!
Nikola
5 / 5 (1) Aug 04, 2011
It's Nikola, and yes he did propose wireless power.
axemaster
not rated yet Aug 04, 2011
What on earth are they going to do with a few milliwatts? Not much!
TheGhostofOtto1923
3 / 5 (4) Aug 04, 2011
Did someone leave all of the content out of this article? There seems to me to be absolutely nothing new here. The power levels quoted in the article are consistent with those that you could get from a regular ferrite radio antenna in a resonant circuit with a diode to convert to DC and a capacitor to smooth. There has to be something new for it to be news worthy but all of that is missing from the article.
May I direct your attention to the LINK provided at the end of the article which takes you to the source. As you can see it was lifted verbatim. I do not know if physorg reprints all such newsreleases without editing but the ones that it does are obviously the work of the original authors, and not physorg.

Were physorg to take the time to rewrite and verify the content of said newsreleases they would need additional resources which I assume they do not possess, as well as legal consultation.

Perhaps your criticism might be better served directed toward the source? Shootist?
antialias_physorg
4.3 / 5 (6) Aug 04, 2011
What on earth are they going to do with a few milliwatts? Not much!

Read the article. It says quite plainly that such energy could be used to run a sensor.

Scenario: You have a building/bridge/... and you wish to embed thousands of microsensors in the walls to check for fatigue. Do you connect all the sensors to a power source? Much too expensive - since you don't need the data all the time.

So include a rectenna for each one. Once every month you drive by, send a pulse of energy (or simply have internal timers run off the EM in the environment wake the sensor up in predetermined intervals) and then have them send out their data.

Could be used for all kinds of things.
Sancho
not rated yet Aug 05, 2011
Thanks, Dagman, for clearing up a mystery. As a child I was given a Japanese transistor radio that worked without batteries -- I always wondered how. It was shaped like a rocket, had an "antenna" that pulled out from the nosecone, and had an alligator clip which was fastened to ground (my bed frame). The sound came through an ear bud.

As for the device outlined in this article, it would seem to be an ideal way to power a micro-surveillance device (like so much of the whiz-bang technology bruited on this site, another tool for Big Brother).
antialias_physorg
not rated yet Aug 05, 2011
As for the device outlined in this article, it would seem to be an ideal way to power a micro-surveillance device

This has been done already. The problem here is that when you use an antenna to tap into the ambient EM field you can measure the drop (this is one way how bug detectors work. Another way is by sending out a slew of frequencies and just checking which ones don't come back because the rectenna got them).

On a larger scale: People have already tried to power their homes sitting next to large radio/analog TV antennas. It works, but you get the feds on your case in no time (since it's quite noticeable that anyone 'downwind' of your house will have no radio reception anymore)
antialias_physorg
not rated yet Aug 05, 2011
Another neat application is that you can actually track stealth fighters/bombers with fair accuracy over countries with good mobile phone netwerks by tracking the local drop in EM field (since the stealth aircraft attempt to avoid reflecting EM radiation by short circuiting it through microscopic pieces of metal - in effect small antenna - embedded in their outr layer)
physyD
2 / 5 (4) Aug 05, 2011
Funny thing. First thing that popped in my head when I saw the title "Rectenna" was rectal antenna. Hmm. I must have issues...
bluehigh
1 / 5 (2) Aug 05, 2011
It says quite plainly that such energy could be used to run a sensor.


.. and power for the support circuits and interface to the sensor too?

A 50 or 60 Hz (depends where you live) resonant LC captures considerably more power just from domestic AC emitted by house wiring.

If you want to power sensor systems on a bridge then ensure theres a WiFi hotspot nearby - like 10cm near according to the article.

antialias_physorg
not rated yet Aug 05, 2011
If you want to power sensor systems on a bridge then ensure theres a WiFi hotspot nearby


As noted: you could drive over with a van specially fitted to emit the needed EM spectrum and have he sensors collect and transmit the adta then and there. For many applications you don't need continuous operation of the sensor.

Another article that was posted not too long ago on physorg had an idea for sensors that capture vibrational energy (embedded in roads) which would collect the nergy over time and allow the sensor to 'wake up' and perform a measurement every 15 minutes or so.

Such a scheme would apply even to rectenna-sensors that are in a very low EM environment.
bluehigh
1 / 5 (2) Aug 06, 2011
A much more powerful transmitter than just a tiddly WiFi device can fit easily in the back of a van thus eliminating the need for exotic rx antennas. Just a simple loop antenna under the van with a tiny resonant rx loop and heaps more power can be transferred.

Its not a matter of non-continuous operation of the sensor (and associated support circuit)- its that the sensor is fully non-functional until powered for a few moments when receiving power. At the power level transferred using the rectenna the data could not be saved or re-transmitted. Or is this van going to park over the sensor for some time (a long time!).