Radio frequency heating apparatus

[vaibhava]

Can anyone help me/suggest some links to make a radio frequency heating apparatus?
I need to carry out radio frequency heating (heating by radio waves) of some reactant samples.
Please help..

 

[davenn]

a microwave oven comes to mind :)

Dave

 

[vaibhava]

Yeah that is pretty convenient! But I don't want heating by microwaves. I need radio wave heating. Can you help me out on that?

 

[davenn]

Yeah that is pretty convenient! But I don't want heating by microwaves. I need radio wave heating. Can you help me out on that?

microwaves IS radio wave heating

maybe you had better explain what you are trying to achieve

cheers
Dave

 

[vaibhava]

microwaves IS radio wave heating

maybe you had better explain what you are trying to achieve

cheers
Dave

Oh ok. Microwaves have a little higher frequency than radio waves. I need to heat my reaction mixture using waves with a smaller wavelength. Its something like radio therapy to heat malignant tissues.

 

[vaibhava]

Oh ok. Microwaves have a little higher frequency than radio waves. I need to heat my reaction mixture using waves with a smaller wavelength. Its something like radio therapy to heat malignant tissues.

Sorry my bad. I meant a little smaller frequency.

 

[davenn]

Oh ok. Microwaves have a little higher frequency than radio waves. I need to heat my reaction mixture using waves with a smaller wavelength. Its something like radio therapy to heat malignant tissues

Microwaves are just one section of a very wide radio frequency spectrum.
You mean longer wavelength :) Smaller wavelength is even higher microwave radio.

ok medical radiotherapy is not a field of electronics I am familiar with. Have had various treatments in that area tho :(

what specifically are you trying to heat. does the heating speed up the reaction ?
is it a very confined area that need to be heated up so as not to heat up other surrounding material ?

Do you know of any specific commercial equip that uses the same principal ?

Dave

 

[vaibhava]

Microwaves are just one section of a very wide radio frequency spectrum.
You mean longer wavelength :) Smaller wavelength is even higher microwave radio.

ok medical radiotherapy is not a field of electronics I am familiar with. Have had various treatments in that area tho :(

what specifically are you trying to heat. does the heating speed up the reaction ?
is it a very confined area that need to be heated up so as not to heat up other surrounding material ?

Do you know of any specific commercial equip that uses the same principal ?

Dave

I hope your treatment went well :)
I am trying to carry out a reaction by irradiating reaction mixture with radio waves. It speeds up the reaction to a great extent as dipoles in the sample try to align with the alternating electric field, hence producing heat.
I know of commercial microwave reactors. Haven't come across longer wavelength radio wave reactors. One place I saw that RF heating was attained by keeping reaction mixture between two electrodes connected to a RF generator. I am not able to figure out what an RF generator is.

 

[davenn]

A RF generator is basically a transmitter, tho in this case for your use, its transmitted energy is probably kept relatively confined ..within a chamber of some sort. In the same way the a microwave oven operates. I guess your real problem is knowing what frequency is needed for your system... that I can't help you with. But once you know that, I and others on this forum will be able to offer suggestions on how to build the generator (transmitter).

The reason that 2.45GHz is used in microwave ovens is because water molecules resonate well at that freq. That resonance (vibration) is what causes the heating ... ie... the hi speed motion of the water molecules within the food.

cheers
Dave

 

[davenn]

ok I am off to bed, getting late here in my country and I have to work tomorro :)

maybe some others will chime in with added suggestions, whilst I sleep

good nite
Dave

 

[vaibhava]

ok I am off to bed, getting late here in my country and I have to work tomorro :)

maybe some others will chime in with added suggestions, whilst I sleep

good nite
Dave

oh ok. I will try to determine the frequency which will serve best for my purpose. And then get back to you.

Thanks a lot!
Good night :)

 

[skeptic2]

The reason that 2.45GHz is used in microwave ovens is because water molecules resonate well at that freq.

From Wikipedia: http://en.wikipedia.org/wiki/Microwave_oven
"Microwave heating is sometimes explained as a resonance of water molecules, but this is incorrect: such resonance only occurs in water vapor at much higher frequencies, at about 20 GHz."

While just about any frequency will work, the higher the frequency the more efficient it will probably be. The location where your sample is heated should be RF shielded and the door should be interlocked with the power to the unit to prevent RF exposure to workers. If you are not an expert in RF, you should find someone who is because if you are not careful, you could get RF burns.

 

[vaibhava]

I will have to determine the best frequency for my purpose by actually conducting the experiment. I think an optimum frequency between 10-100 MHz should work for me.
Can you help me make an RF generator for that?

I will take caution in shielding the waves by enclosing the reaction mixture and the electrodes in a cavity..

 

[vk6kro]

You can apparently still buy DIATHERMY machines, although they are expensive.

These used to be an oscillator on about 27 MHz using large transmitting vacuum tubes.

If the shielding was not good, the devices could radiate a very rough signal and cause interference. Since they had power supplies that were not even filtered, the signal was very rough.

You may be able to find circuits for these, although building one to meet current regulations would be a big challenge.

 

[vaibhava]

I tried to find about various diathermy apparatus and found them too costly for my work.
So I want to build an RF generator that could serve my purpose of RF heating.
Can you please help me on how to make it?
Or if you could give me some links where I can get the required help?

 

[skeptic2]

This is not a trivial project. How much experience do you have with building RF transmitters?

I once worked with an RF dryer that ran at 5000 volts at 1 amp on 27 MHz. The radio tube was the size of a soccer ball. The oscillator was tuned plate, tuned grid (TPTG) and as soon as the oscillator began oscillating the grid was detuned to prevent the tube from overheating. The oscillation was detected with a photocell against a small florescent tube that wasn't connected to anything. If the oscillation was lost for any reason, the power was immediately killed.

Why do you want to use RF heating instead of much simpler electric or radiant infrared heating?

 

[slbirla71]

Due to not much demand of low capacity RF heating system, is quite expensive to get RF system whereas 500 W of mcirowave oven with magntron one can buy readily in $30.

Designing comlete RF generator for small capacity is not worth of your effort. I would suggest you to buy 500 W RF generator (best place to start is ebay). If not avaialbe then new one will cost you $6000. Instead of going for automatic netowrk analyzer and connecting with 50 ohm coaxial cable to the parallel plate eletrodes, you can use a set of variable capiator and inductor. You can cotnact me for further help on design. I have assembled such unit for our reseach purpose.