I need to design a wireless power transmitter and receiver, so that at least 3 W (at 5 V) power is received at receiver section. Transmitter and receiver can be at maximum distance of 2 to 4 m. The transmitting and receiving antenna cant be more than 1 m. My idea is to generate a high frequency wave, and amplify it using MOSFET connected in cascade. Then improve the power by darlington power transistors and transmit it using an antenna. Rectify it in receiver by using Schottky diodes.
Please help me to choose.
1. Appropriate operating frequency (please don’t suggest microwave)
2. Appropriate MOSFET and darlington transistors
3. Appropriate antenna design (may be directive or non directive)
4. Passive filter in receiver end
5. Can I increase the power strength of signal, simply by using high power amplifiers and coupling it to antenna by using transformer?
I know that radiated power is proportional to square of antenna current, which is again a function of radiation resistance. entire things goes more and more complicated in this way. Please help me to design such a transmitter (efficiency can be anything).
The 13.56 MHz band is where this type of work is being done. This is an ISM (Industrial, Scientific, Medical) band. I'd have to see what the maximum field strength allowed in this band is. And you will run into the FCC E-field and H-field strength limits for personnel close to the antenna.
But let's take a quick analysis of this. Note that I have not researched this and have only read casually about it. However, I just ran an antenna analysis using EZNEC and two tuned 1 meter diameter loops work. Modeled in free space with no losses, 1 amp in the driven antenna results in 0.8 amps in the second antenna. With practical antennas there will be detuning and losses that will reduce the power transfer efficiency. Placing the antennas 1/2 meter above lossy earth and using aluminum conductors the power transfer suffers and 1 amp in one antenna produces 1/4 amp in the other. The power transfer efficiency is 6%.
RF amplifiers for this frequency are easy to build and they are available off-the-shelf. An example of a tuned loop is the MFJ-1788. Going off-the-shelf would certainly work if you have a couple thousand dollars. The output of the receiving antenna can be applied to a Schottky diode bridge. The MFJ-1788 can handle 100 watts and 6 watts could be transferred. The output would be 6 watts into 50 ohms and the voltage is 17 V RMS. Anyway, this is an example of what is possible and not too difficult to implement.