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How to Use Electromagnetic Waves for Charging

Electromagnetic waves carry energy. Radio stations, cellphones, Wi-Fi routers ̵2; all are sources of electromagnetic radiation, which means they all carry energy. Before you get too excited about the possibility of harvesting all that energy coursing through the air around you, remember that every device you have that uses these electromagnetic waves amplifies them after they̵7;re detected. The power level is generally fairly small. However, it is possible to build a system specifically to transmit energy and use it to charge portable devices.

Things You'll Need

Oscillator
Copper magnet wire
Cardboard tube
Capacitors
4 diodes

Instructions

- 1
  Wind the copper wire around the cardboard tube, coiling one loop flush with the next. Calculate the inductance of the coil using an online calculator. For example, if you have a 5-inch diameter cardboard tube and you wind it with 100 turns of wire, the inductance will be 1.4 millihenry.
- 2
  Connect one lead of a capacitor to the one of the wires leading to the coil. Calculate the resonant frequency of the combination using the equation
  frequency = 1 / sqrt(inductance x capacitance).
  For example, if you choose a 700 microfarad capacitor, the frequency would be:
  frequency = 1 / sqrt (1.4 x 10^-3 x 700 x 10^-6) = 1010 Hz, or about 1 kHz.
- 3
  Repeat Steps 1 and 2 and construct a duplicate of the assembly you̵7;ve already built. One will be the electromagnetic wave transmitting antenna and the other will be the receiving antenna.
- 4
  Connect one output of the oscillator to the unused lead of the capacitor of the transmitting antenna and the other output to the unused lead for the coil. Tune the oscillator to the frequency calculated in Step 2. For the example system, this would be 1 kHz.
- 5
  Build a full-wave bridge with the four diodes. Connect the four diodes such that two neighboring diodes both point away from their junction and the other two point towards their junction. Make one the left-hand side, and the other the right, and connect the two pairs together at top and bottom.
- 6
  Connect the receiving antenna to the full-wave bridge: the lead from the coil to the ̶0;top̶1; junction of the diodes and the lead from the capacitor to the ̶0;bottom̶1; junction of the diodes. The current will be generated between the ̶0;left̶1; and ̶0;right̶1; sides of the full-wave bridge.
- 7
  Line the two antennas up so the cardboard circles are lined up with each other.

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