Rectenna

Wireless & IoT
1

Hi,

I am new to Antennas etc… But I am trying to make a simple rectenna, which seems easy. Antenna some scotchky diodes to a capacitor, but I would like to know what kind of voltage would I get from the antenna that the capacitor would charge to? I assume small, so I though I can put a resistor to increase the voltage even though I might kill the current since I just want to charge up the capacitor then use it later.

I was worried a resistor with an antenna might be too much resistance to stop any signal.

I pretty much want to charge a capacitor to 3-5 volts with a goal of eventually charging a battery I guess. Anyone have any experience tips, links etc…?

Its an old technology, but most googling yields completed projects with no explanation or nano sized rectennas, which is beyond me. Thanks for any help.

2

Check out Dave Jone’s commentary on the “Airnergy” device that is claimed to charge batteries at wifi hotspots.

http://www.youtube.com/watch?v=P8s3Xjeg0sk

There is also a nice collection of stories at the Daily Telegraph:

http://www.telegraph.co.uk/technology/3 … icity.html

And no discussion is complete without mention of Richard Box’s amazing “Light Field” art project:

http://www.stopgeek.com/richard-boxs-light-field.html

3

Well I will go as far as saying that the articles are interesting, I have yet to watch the youtube clip, but I guess I was hoping for more technical information on the subject rather than affirmation of the concept. I do appreciate the links though, and I intend to check out the youtube clip when I have a chance. If there is more technical instructions or tips I would also appreciate that.

4

The youtube clip is the most important, because the author goes through how to estimate the power that you can expect to obtain from

an antenna in a typical situation. Usually, it is on the order of microwatts and hardly enough to charge a battery. If you happen to live

directly under high voltage power lines, or next to a commercial TV or radio transmitter, you might get milliwatts.

5

To be honest if I could get only milliwatts that would probably still be successful for me. All I need is to possibly use a device once a day for a moment, and that is best case, worst case even once a month would be great, or even once a year. It is seriously low power.

I just cannot find a simple way to get a specific level of charge from a capacitor when using an antenna.

Meaning, yes I can take scotchky diodes to a capacitor, but what if that voltage is too low or too high (granted I am more concerned about it being too low). And of course how to hook this up reliably to something that can charge a battery even if it takes a year.

6

It is trivial to regulate a voltage that is too high. However, until you’ve established that there is sufficient RF energy (and at what frequencies) available at the location of interest, you are wasting your time worrying about the circuitry details.

7

Need a house adjacent to a clear-channel AM broadcast station (50,000 W).

8

No I wanted to regulate voltage up not down, meaning over the period of a year to have a super capacitor or a battery charged to 5 Volts means I need to step up the voltage, but I believe I will either use a step up transformer worst case or I might try to use a joule thief, similar principle.

And yes, I watched the youtube clip, but its not an issue because, I am not charging a phone.