Electronic/Computer Engineering

Question

Sir, I am working on microwave power transmission mini model for my semester project. How to make a Rectenna for wireless power transmission? Can bulk power be transmitted through RF waves? Can a two way Rectenna be made?

Answer

A rectenna is basically a dipole with a bridge rectifier at the feedpoint. Most practical rectennas are actually arrays of these dipole/rectifier combinations with all the positive and negative outputs tied together. Since the power received by each dipole is quite small, you want to use diodes with low foward voltage drop and low forward resistance.

You didn't mention what frequency you are using, which would be important. The dipole would nominally be about a half wavelength long.  If you were working at 2.4 GHz, for example, the wavelength is about 12.5 cm, so the dipole would be about 6cm long (that is, two 3 cm elements). 

How much power do you want to transmit? If your goal is only to show that "some power" can be transmitted, then microwatts will do. If you want to light up a hundred watt light bulb, that's another story.

 And, any time you're transmitting significant microwave power, you need to be concerned about safety.  The usual limit for power density is on the order of a milliwatt/square centimeter. So, if you had an array that was a meter on a side(10⁴ square cm), you could have an incident power of  10 Watts, which would need to come from somewhere. 

As for bidirectional/two-way rectennas, since the rectenna has the rectifiers, it's hard to make it work for transmitting power. One could design a system that would send/receive power (not at the same time) if you worked out the details of switching back and forth. These would generically be a phased array. The Proceedings of the IEEE has papers on wireless power transmission periodically, as does IEEE Spectrum. A bit of time with a suitable search engine should find them.