Science Buddies: "Ask an Expert"

I am currently working on a wireless electricity transfer project. I am at the point where I am able to light an LED at the range of about 2-3 feet. I am looking for a way to amplify the transmitting power so I can power larger things such as cell phones, LCDs, etc. I am thinking that an RF amplifier could be appropriate for the job, but anyone has any ideas?

milkyud - Congratulations! If you are now capable of lighting an LED from 2-3 feet, this means about 20-30 mA at 1.5-2.0 V, or about 40mW of power. How are you achieving this? What is your desired new power transfer goal. More power, more distance? How can you scale what you are doing now? To assist, it would be interesting to know what your current transmission/reception method is. Carrier frequency, antenna design, induction method etc. Obviously boosting the power from the transmit side is one variable. Is your transmit/receive setup optimized? Are the impedences optimized? Give us some more information on your current setup and perhaps we can suggest some performance improvements. This is an interesting experiment. You are well on your way.

Rick Marz

Hi,

Yes an RF amplifier might be good way to boost the distance you could couple. Here is a review of WiTricity company technology trying to commercialize the concept you are working on:

http://www.witricity.com/pdfs/4.0_home_ ... _03-04.pdf

http://news.bbc.co.uk/2/hi/8165928.stm

http://www.witricity.com/pdfs/Electrici ... aralis.pdf

Here is the WiTricity website:

http://www.witricity.com/pages/company.html

Note that these sites suggest the optimum frequency to use is about 100 Mhz, so you need an appropriate RF oscillator as well as Rf amplifier.

Good luck and best regards,

Barrett L. Tomlinson

CAUTION: You can't operate on arbitrary frequencies and radiate RF power at arbitrary power levels without causing electromagnetic interference. There are regulations on the use of the frequency spectrum. In particular, YOU DO NOT EVER want to end up operating in any of the aircraft navigation or communications bands. You really don't want to put lives at risk do you? You need to look up the spectrum allocation and figure out how to stay in an experimental use band. Note: These bands are small, few, and far between.

It is far more challenging to directionally control your radiation pattern and to focus the energy in a specific direction rather than radiating in all directions.

Well right now, I am using an HP agilent function generator. My transmitting coil is just 4 alligator clamps connected to each other in a closed circuit that is connected to the funtion generator, and my reciever is a 20 revolutions, 18 gauge, 3.3in in diameter copper coil with an LED connected. The optimum operating frequency is 2.93 mHz. The function generator is set to give out 16 or so volts and about .08 amps. In an Intel video, I see their set up is a function generator connected to an AR RF amplifier. From the RF amplifier, the cable is going out to the transmitting coil.
Also, Craig, is it possible if you can give me some insights on that?

bump.

Here is the FCC United States frequency allocation chart http://www.ntia.doc.gov/osmhome/allochrt.pdf 2.93 MHz is in the aeronautical mobile so I would strongly discourage using an RF amplifier in that frequency range. If you go to 3.75 MHz, you will be in the middle of the 80 meter (wavelength) amature radio frequency band where during daylight hours you aren't likely to interfere with anybody as long as you stay less than 2 watts of power. Your 16v * 80 mA is 1.28 w so you aren't very efficient at power transfer. 2 watts at night in the 80 meter band is enough to communicate very long distances so you really don't need an RF amplifier to do better in terms of distance.

You really need to do some reading on anteneas and E and M fields. Loop antennas are highly directional and you should be able to improve your transmitting antenna and do better.

Is this supposed to be a Science Fair project? If yes, what is your hypothesis? What is your experimental proceedure? What are you trying to keep constant and what is your independent variable and what are your measured (dependent) variable(s)?

Demonstration projects typically don't do very well at Science Fairs, particularly at this grade level.