microwave paint
microwave paint
(OP)
I am trying to coat a glass vessel with a microwave paint that will contain the microwaves within the glass vessel. Can anyone tell me what thickness of paint I should use, as I assume the paint will be silver. I looked at specs for copper paint and it appears only to go to 1GHZ, and I need 2.45GHZ reflection. The field strength is around 50 w/cm squared.
If you have any other suggestions for the paint, I am open. I have tried building a stainless steel enclosure around the vessel, and it still emits quite a bit of radiation, and I also tried an aluminum vessel. Would coating the inside of the aluminum with silver paint help? the vessel is shaped like a cylinder, and so is the containment vessel, but I cannot get the levels down to consumer safe levels yet. Would several redundant cylinders help? Maybe attenuating a little bit each cylinder? Also, do each cylinder need to be grounded. From what I understand, the reflective layer should also be grounded.
thanks for your answer, and if you have a proprietary answer, then maybe we might have a employment situation or consulting arrangement. We are in need of a top notch microwave engineer with thinking out of the box ideas.
If you have any other suggestions for the paint, I am open. I have tried building a stainless steel enclosure around the vessel, and it still emits quite a bit of radiation, and I also tried an aluminum vessel. Would coating the inside of the aluminum with silver paint help? the vessel is shaped like a cylinder, and so is the containment vessel, but I cannot get the levels down to consumer safe levels yet. Would several redundant cylinders help? Maybe attenuating a little bit each cylinder? Also, do each cylinder need to be grounded. From what I understand, the reflective layer should also be grounded.
thanks for your answer, and if you have a proprietary answer, then maybe we might have a employment situation or consulting arrangement. We are in need of a top notch microwave engineer with thinking out of the box ideas.





RE: microwave paint
If youwant to coat a glass vessel, take it to a vapor deposition house and have them deposit pure metal on the glass surfaces. You can use any good conductor, like gold, silver, copper, tin. It would have to be at least 5 skin depths thick, which might require electroplating after the metal is sputtered on first.
You can use a metal loaded paint. Silver is a good one. But that is not going to be as good as a pure metal coating, as a paint has metal bits AND some sort of non-conductive binder. Depending on the fill, it will stop being very conductive at some high frequency, possibly in the 15 GHz region.
But if you havea crack anywhere where the vessel metal does not contact the metal stopper, there will be a lot of RF leakage.
RE: microwave paint
RE: microwave paint
Multiple layers separated by say 1mm will give a dramatic improvement in shielding. The layers do not need to be earthed and are probably best left isolated. The biggest problem is joining the shield to make it continuous. This is made worse when you enter the shield. If you enter the shield with say one power wire and you fail to use a filtered feethru, the shielding will be defeated (will not work). This would be the prime reason why your shielding, whilst looking complete, will not work.
RE: microwave paint
My first vessel I just wrapped with a thin copper metal and it worked very well.
That was before I looked up the specs for copper, and could not find where it was good for 2.45 GHZ.
Sometimes this microwave stuff is just magic to me. I am a physicist and electronics engineer, but I really salute you microwave guys. Sometimes things work, and the next time they don't.
I have tried coating it (painting it) with silver, then copper, then silver, and it worked pretty good the first time. The next time I tried it, it did not work very well. Maybe my technique and not paying as much detail to it as the first time. The two cylinders around the vessels were a failure. Maybe I need to put filters on the power lines to the transformer, as I am using the old transformer, capacitor, diode circuit to feed the magnetron.
I did notice the inverter supplied more and better power to the magnetron than the transformer circuit did.
thanks for the great posts.
RE: microwave paint
If you use vacuum deposition of the metal then you will not have a problem. If you use foil the critical part is how well you join the sheets. Both faces needs to be really clean and you will want to overlap the sheets by say 2cm to get a low impedance joint.
>Maybe I need to put filters on the power lines to the transformer, as I am using the old transformer, capacitor, diode circuit to feed the magnetron.
Yes! You absolutely need filters on ANY wire going through the shield. Even if the wire is not connected to anything at all, say 1 inch outside the screen and 1 inch inside, the shielding will appear to be completely useless. What you have is a receive antenna on the inside and a transmit antenna on the outside. The shield might just as well not be there in this case.
RE: microwave paint
the link to the paint is: http://www.lessemf.com/paint.html
The silver paint that I used: http:/
Best Regards
RE: microwave paint
Copper has a resistivity of 1.7E-8 ohm.metres
The copper paint is 0.3 ohm/sq for 1 mil (=0.001") thickness. This is 0.00762 ohm.mm or 7.62E-6 ohm.metres.
The resistivity of the paint is therefore 448x higher than the pure metal. This means that the skin depth is sqrt(448) times higher, ie 21x higher. Hence the skin depth at 2.45GHz is actually 27µm rather than 1.3µm. So the minimum material thickness needs to be at least 100µm.
It looks like you should try at least four coats to build up the thickness to a suitable level.
RE: microwave paint
RE: microwave paint
RE: microwave paint
No, no arcing has occurred. I have coated vessels this way before and used them, and the last one lasted nearly three years. However, I let this one run dry without any water in the vessel and the magnetron and the vessel did not turn out so good. This phenomenon that I am describing is something that I have seen with a new vessel design. Before the design was irregular, and now I am using a vessel that is a rather perfect cylinder. I was wondering if I haven't made a wave guide that might be resonating somehow. My prior vessels were irregular cyclinder types made by hand blown glass and joining pieces together, where the later ones are made on a glass machine and are rather uniform.
My question relates to whether a microwave oven, because of its square shape, is a non resonating wave guide that tends to attenuate the rf, where a cylinder becomes a resonating wave guide that acts like an antenna.
What is throwing me is this slow build up in rf energy from the shielding layer that cycles. Is this from the coating not be right, the coating being too small, or from the shape of the vessel?
RE: microwave paint
Curious what the purpose is, is it a fun with plasma generation experiment?
If you only trying to shield the outside world from the rf internal to the vessel, then your experiment of building a stainless steel cabinet around the vessel was a 99% answer and you didn't realize it. You needed a little help connecting that metal enclosure to your rf source to prevent leakage at the interface.
If you look at a microwave oven, open one up and remove the little cardboard plate inside, you'll see a rounded proble in a small 2"x4" cavity. This probe/cavity which provides the rf source energy is perfectly contacting the metal box of the oven. I really believe that you didn't have a good contact between your rf source and your stainless steel cabinet hence you saw high leakage levels. RF leaks easily through any small crack opening. Example, if in your microwave oven, the rf source and the oven cabinet had a 0.001" gap for even one inch length, you'd have arcing and high rf leakage. The door on a microwave oven does have a small gap with a magic length of 1/4 wave which helps, seemingly by magic (though not really) to keep rf in. The door gap is far away from the rf source which helps prevents arcing (unless you get some food in it and it bulges a bit).
kch (antenna engineer)
www.toyon.com
RE: microwave paint
The loss in a rectangular cavity should be similar to the loss in a cylindrical cavity, ie low compared to the load. An irregular cavity will make simple modes more difficult to excite. In a rectangular cavity you should have a good idea where the peak electric field will occur. In an irregular cavity it would be difficult to guess where the field maxima would occur. Try moving the load.
RE: microwave paint
However, I cannot move the load due to the design. I can increase the load quite a bit. I saw in another forum you talked about HFSS and modeling a waveguide. Do you think that HFSS is capable of modeling a magnetron antenna output, surrounded by water in a vessel, then coated on the exterior. Would it give me the loading of the water, the VSWR, the attenuation, etc? I know nothing about this package, and was wondering if it was worth buying it, or if there are consultants out there who could model the invention with the software to optimize the output wattage strength and the shielding? It does behave like I am using too much wattage in the magnetron and that the magnetron is squegging. Also, the shielding might be building up a charge on it, then dissapating it, and building up again.
RE: microwave paint
Here's a link to his website.
ht
Jim doesn't give me income for referrals, but tell him one beer would be nice (one beer keg).
kevinchiggins
www.toyon.com
RE: microwave paint
Getting a contractor with their own licence and the skill to use the package is much more cost-effective.
RE: microwave paint
RE: microwave paint