Wireless Power via RFID

2016-08-22 | By Shea McCombs

License: None

Green energy is one of the great pursuits of modern technology. Harvesting power from the air might seem like a pretty far-fetched idea.  However, not only is it possible, you can make your own light source with very minimal parts.

This project is great in exploring how radio frequencies interact with physical objects.

For this project you only need a few materials. A wire, a capacitor, two BAT54S dual diodes, an inductor and a 0805 LED. The value of the capacitor will be determined later as it will depend on the next few steps.

The first step is to make a spiral as shown above. This will serves to catch the radio frequencies which are used to power the LED. For this to work, we will need to attach a specific capacitance for the spiral to resonate at a desired frequency.

There are three ways to calculate the right value for the capacitor. The first is to use an inductance meter.  The second is to use a variable capacitor and adjusting it accordingly until you get the LED to work. The third way is to use the mathematical approach of calculating the values based on spiral diameter, length, number of turns and other factors. Whichever is most suitable for you will work.  For this particular product, the inductance meter read 1.16uH, so we’ll just round that down to 1uH.

Using the formula for calculating resonant frequency, we can determine that we would need a 138 pF capacitor in parallel with the coil to resonate at 13.56MHz, which is a fairly common world standard center frequency in the ISM band. However, since the two diodes listed above already have an input capacitance of 20pF each, you will need to adjust your capacitance requirement to only 98 pF.

Connect everything as shown above. The connections are pretty direct and the parts will be ok even if you aren’t the best solderer around. Double check the polarity, and secure your solders. You might want to enclose your finished product in a case as the parts can break easily.

Now that you’re set, pick up any device with a 13.56MHz field (RFID readers, NFC phones,etc.) and let there be light!

Source: http://shea241.blogspot.com/2015/01/building-rfid-powered-light.html

Formula for resonant frequency - http://www.1728.org/resfreq.htm

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