Magnatron rectenna project

I have a project where I would like to power an electric motor wirelessly using RF energy at close distance using the 2.45Ghz spectrum (Microwave Magnatron) Yes I know there are better ways to do this and It may seem a little mad but I am keen to use this method for reasons that I shall not discuss to keep things short.

Although I know little about this field I am perfectly aware of the dangers of Magnatrons, the entire experiment will be conducted in a safe fully shielded environment.

Now please assume that I know nothing about electronics, because its really not my field.

Now, I understand that this should technically be possible (In my mind) but may be difficult due to that fact that the motor and electronics will be exposed to large amounts of RF energy at close distance which is generally a big no no. I would assume with my basic understanding of electronics that they could shielded somewhat by encasing them in a Faraday cage.

My setup would look something like so.

Input 2.45Ghz 1000W > 1/4 wave Dipole Antenna > Bridge rectifier > Low pass filter > Regulator > Load

Now my questions are.

  1. Can this actually in practice be achieved or am totally mad?
  2. Could a small 1W brushed motor be powered with a 1000W Magnatron at 50-100cm, and if so, could it effectively be shielded? The motor will be driving a small plastic prop.
  3. Could the antenna be designed so poorly that it only captured 1-2watts of power?
  4. If not, then could the excess of power be dumped into a resistive element?
  5. What diodes would I need to perform rectification at this kind of frequency?

1) Tempted to say 'yes' and 'yes'!

2) Probably, the free-space path loss isn't completely ludicrous for even an isotropic radiator and you can have a directional antenna (reflector behind dipole, horn, whatever).

3) Absolutely! Anything can be designed as poorly as you like!!

4) Most of the power will go around the load realistically, so you'd need RF absorbing material behind to remove reflections from the shield. Though you could use a dish to concentrate the received power. Containers of water are very good at absorbing microwaves (heat up your soup while you work!)

5) Schottky diodes designed for high power microwave mixers might be one possibility. Danger of overload of course..

Go to your library and check out the September 1984 edition of the Microwave Theory and Techniques journal. There is an article on page 1230 called “The history of power transmission by Radio waves”

It will answer a lot of your questions.

Oh, and the answer to almost any RF diode question is 1N34A.

1N34A - According to datasheet it can replace point-contact devices... Not sure a germanium device would last long thermally stuck onto a motor!

Except for a rectenna you have dozens or hundreds pretty far removed from the motor.

Look at Hertz's early experiments...

Allan

I appreciate all the reply's. I was hoping to find an online copy of "The history of power transmission by Radio waves" but was unsuccessful. I've looked into several related patents ranging from the 60's to the 90's and have been surprised at the level of detail covered in the diagrams and explanations, even covering theory and manufacturing techniques.

Anyway, what I would like to find now is the cheapest and most available diode that could be used for the purpose? The 1N34A Diodes seem pretty expensive to experiment with at $2-3 each considering that I may blow quite a few times in the process. Hopefully someone can give me a recommendation.

Tesla thought he could transmit power efficiently using e-m radiation over long distances.

He was wrong.

Allan

allanhurst: Tesla thought he could transmit power efficiently using e-m radiation over long distances.

He was wrong.

Allan

In the general case that is true. But in specific applications (RFID tags) it works pretty well.

You can purchase a ready made lab in the form of a microwave oven. Then all you have to do is design the device and place it inside and push the button…

If you are truly a beginner, there is no other really safe way to play with this stuff. Knowing about the dangers, and knowing exactly how to avoid them, are two different things.