Low Cost microwave focusing
Low Cost microwave focusing
(OP)
Hello All:
Is there any commercial off the shelf microwave focusing apparatus from 5 to 1000W @ 2.45GHz? I may be dreaming here but I would like some sort of rod whereby I can focus the radiation onto materials. Any ideas would be appreciated.
Is there any commercial off the shelf microwave focusing apparatus from 5 to 1000W @ 2.45GHz? I may be dreaming here but I would like some sort of rod whereby I can focus the radiation onto materials. Any ideas would be appreciated.





RE: Low Cost microwave focusing
(see the ps below).
I've done what you are looking for in medical research a decade ago.
I used a cable to a notch antenna radiating into an elliptical reflector to focus on a spot of chicken breast. We had approximately a 1" diameter area that was cooked on the boneless chicken breast. Power was from a microwave oven with rf power coupled off into a coax. using a coax. to waveguide transition. The coaxial cable went through a new door we made out of aluminum and added a type n f-f adapter through the door to a cable outside which connected to the notch antenna (which we also designed and built). Worked pretty well and we could change the transmit average power on the microwave duty cycle control and set the maximum power by moving the waveguide to coax adapter closer or further from the microwave source aperture.
to focus it into a smaller spot, you need to change air to dielectric. You could probably get down to a 1/3 inch diameter spot with dielectric = 10, but 0.1" diameter would cost an added $30K in ceramic high dielectric. The part would be probably 6" long, 6" diameter and triangular in shape, or look like a large spinning top a child would play with, except the bottom would be somewhat flat. There's a bit more complication too on the sides.
You can't just change the elliptical reflector larger or smaller to change spot size. Laws of physics says your medium must change from air to something denser.
What size spot do you need to make?
kch
PS: GTRI (part of Georgia Tech) has a lense system to focus a spot as you discuss, but it's really expensive and you get a 5-10" diameter spot at 5-10 feet away. It's for dielectric testing, etc.
RE: Low Cost microwave focusing
Another option is a simple dish reflector.
Either way - with 1kw - take precautions.
RE: Low Cost microwave focusing
But if anybody else can suggest another off the shelf solution, that would be great.
If not, I'll have to roll up my sleeves and do what Higgler did with his project.
Merry XMAS
RE: Low Cost microwave focusing
Our ellipse was cheap. Purchased a 12" diameter Globe of Earth, cut it in half right through Equador, cut 4 slits in it and changed the hemiphere into an ellipse. Added metal tape on the inside.
Here's an antenna option. http://www.pasternack.com/Pdf/PE9824.pdf Not sure about the power rating, not specified. Maybe look around and compare prices. WG Cutoff is 2.078 GHz, so it'll work at 2.45 GHz.
The next size larger adapter (1.7-2.6 GHz band) might be too large and increase your spot size.
Good luck,
Kevin
RE: Low Cost microwave focusing
Merry Xmas.
RE: Low Cost microwave focusing
He could maybe start with satellite dishes and modify them with added shapes though to get an elliptical shape. Although some dishes like DirecTV have offest reflectors, you only have the upper part of a parabola, hence making it an ellipse might not be doable.
Kevin
RE: Low Cost microwave focusing
RE: Low Cost microwave focusing
RE: Low Cost microwave focusing
If you have small objects you want to just heat alot. Maybe the "focusing" requirement isn't necessary, and you can just concetrate your energy on your material simply.
i.e. Open your microwave oven and place you materials at the center of the RF power source for one. It will heat more from one side than another.
You could try to form an ellipse or hemisphere around the microwave power source so that all the energy stays confined and heats your material. Or attach a waveguide to your microwave oven and place your mateial in the center of the waveguide. That'll concentrate it. For higher concentrations, your normal waveguide could transition to ridged waveguide and all the power would be inside one small area.
This would be cheaper and faster than a semi-optical reflector type system. When I was working on our, we needed to head one spot inside an MRI medical imaging machine, so we needed minimum metal and couldn't use these heating options.
kch