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What is LEctenna and how does it work? 
 

LEctenna, short for light emitting diode (LED) rectifying antenna, features a fast-switching Schottky diode paired with a standard LED together in parallel, placed in a test tube to isolate the wires. In electrical engineering, putting components in parallel means connecting both of their pairs leads together. Isolation means they are separated from other nearby objects so other electrical effects don’t interfere with your circuit.

While simple in its construction, LEctenna acts to rectify incoming radio signals into DC electricity that lights up the LED. This happens because as electromagnetic waves pass through the LEctenna device, they cause the charge distribution to flip between opposite sides of the diodes. Typically this would create a net zero voltage across the LED, preventing it from lighting up. But because of the Schottky diode’s fast-switching at 2.4 GHz (the same frequency as wi-fi) and low capacitance, this results in clipping that allows for a net positive voltage across the LED, allowing it to light up.

One of the most interesting applications of the power beaming LEctenna demonstrates is in space-based solar power. Using this wireless power technology, we may someday be able to harvest solar energy in space and beam it down for use on Earth. This would allow us to collect solar power day or night, and in any kind of weather. Sunlight is also brighter in space than anywhere on Earth. This technology could be an incredible option in the future for providing clean energy to power the world. 


 

Why is power beaming important?
 

Power beaming is an energy transmission idea with roots tracing back to the aspirations of Nikola Tesla. He lived a long time ago, but power beaming could be used for a lot of modern applications like space solar power, powering drones, and charging mobile devices or medical implants.

LEctenna is our name for a light emitting diode (LED) rectifying antenna. It converts microwave energy into direct current (DC) electricity which is used to power a light-emitting diode. When LEctenna’s LED turns on, it’s showing you the energy from radio waves!
 

Next we are going to show you how you can build your own LEctenna, but first let’s show you a LEctenna demo we put together with NASA on the International Space Station:

 

 


 

Now let's build one!

First you need the parts. Here’s the list, which you can typically order online: 

  • NTE112 Schottky diode* (preferred) or 1N5711 Schottky Diode (NOTE: Chanzon 1N5711 diodes do not appear to behave the same as the ST Microelectronics 1N5711 and won’t work. Other good alternatives are the Hitachi 1SS106 and NTE583.)
  • An LED
  • Test tube or ruler
  • Optional tools: solder, soldering iron, and pliers
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*Special thanks to Dante Yang, at University of New Mexico's COSMIAC research center, for identifying the NTE112 diode.


Once you have the parts, here’s a brief video of how you put it together:

 

 

 

Here are some pro tips: 

  • Make sure the two diodes are pointing in opposite directions.
  • Make sure there’s plenty of electrical contact between the diode leads. This is where solder can help bind them, if you have it available.
  • Twist the wires so that electrical contact starts as close to the diodes as possible.
  • If your LEctenna isn’t lighting, try rotating your LEctenna to different angles. Sometimes signal sources are polarized.
  • Adjust where you hold the LEctenna to make sure your hand isn’t interfering with the signal.
 

If those don’t work and you need more help, you can contact us at: lectenna@nrl.navy.mil


 

Now let's take the Challenge!

Make your LEctenna better and get a prize!  Here's how:
 


 


How did you do?

Send us a photo or short video on social media (#lectenna, social media icon links) or to: lectenna@nrl.navy.mil  and we’ll send you LEctenna swag!
Quantities are limited.  

LEctenna Patch

 

* PLEASE NOTE: Children under 13, please ask a parent first. The U.S. Naval Research Laboratory will not use your submissions without your permission. However, we may re-share your social media posts if you choose to send your LEctenna info that way.


 

 

Additional LEctenna Facts: 
 

The maximum light-up distance for the LEctenna is dependent on the power of the signal’s source and its antenna pattern. For omnidirectional antennas, the energy will drop off at a rate inverse to the square of the distance from the source. This can be lessened by either using a directional antenna or by building or procuring a waveguide.

Additionally, we’ve found a significant amount of variation in the distance at which the LEctenna will light up, depending on the particular Schottky diode. We wanted to make sure that we kept the device suitable for 2.4 GHz since consumer wi-fi provides a versatile and easily accessible source of radio energy. Unfortunately, most Schottky diodes suitable for the GHz range are teeny-tiny surface-mounted devices. We tested to see if these could work with LEctenna, but they proved to be difficult to work with and very fragile. We eventually settled on the 1N5711 through-hole Schottky diode in order to help maintain a simple and durable build.

Part of the intention for making LEctenna as simple as we did was to help ensure accessibility to younger students in roughly the middle to high school age range. By using through-hole components, we sacrificed making a potentially more optimized device in favor of making a device that could be built by almost anyone. Even soldering, while helpful in extending the range, isn’t crucial for making an effective LEctenna.

While searching for suitable components for the LEctenna devices, we had key minimum requirements that we wanted them to meet to consider them successful for our purposes. While there were other Schottky diodes that we observed to work with the LEctenna when placed in front of a microwave amplifier, we wanted to ensure that the devices would work with easily accessible sources that we could expect our audiences to have in their home. Sources such as microwave ovens, wi-fi routers, and in particular, smart phones with wi-fi.

Modern wi-fi enabled cellphones have antennas that are able to operate as a receiver as well as a source of 2.4 GHz microwaves. By switching on and off the phone’s airplane mode, we were able to cause the phone to send out a signal in an attempt to connect to any nearby routers. This signal could then be intercepted by the LEctenna devices acting as a source receiver causing the LED to light up.

Since creating the device, our goal has been to reach out to students interested in STEM in order to help make them aware of power beaming technology via LEctenna. We hope you have found this inspring!

 

Feel free to reach out to us with any questions at: lectenna@nrl.navy.mil

 

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