matchstick dielectric heater experiment

[Heaviside]

I am learning about electronics and would like to do an experiment on how a high frequency electric field can heat and dry out very tiny things at lower energy usage than nickel chromium wire, for example.

I would like to make an experimental capacitor with 4mm x 50mm plates with a gap of 3mm powered by a DC transformer. The dielectric material will be a matchstick (and air). I then would like to include a (Colpitts?) variable frequency oscillator and amplifier to test the heating/drying of frequencies between say 20MHz and 50MHz. I would like to also test a variety of different shaped 3d printed capacitors coated with conductive paint.

Is this a feasible project? Any advice would be most gratefully received.

 

[BradtheRad]

Is this anything like making your own microwave oven? On a small scale?

The frequency has something to do with its effectiveness. How fast the molecules vibrate. Hence you use less power at higher frequencies.

You'll want to be careful how close you get to it. There's a lot of talk about how risky it is for us to be exposed to strong rf fields. Manufacturers must devise effective seals in their microwave ovens.

You'll probably need to produce more power than a mobile device puts out. Your rf may cause interference with other rf communications. You'll need to take precautions to prevent this. You'll need to enclose your project in a metal box. Etc.

 

[Heaviside]

Is this anything like making your own microwave oven? On a small scale?

The frequency has something to do with its effectiveness. How fast the molecules vibrate. Hence you use less power at higher frequencies.

You'll want to be careful how close you get to it. There's a lot of talk about how risky it is for us to be exposed to strong rf fields. Manufacturers must devise effective seals in their microwave ovens.

You'll probably need to produce more power than a mobile device puts out. Your rf may cause interference with other rf communications. You'll need to take precautions to prevent this. You'll need to enclose your project in a metal box. Etc.

Yes, the dipole molecules in the dielectric will spin 180 degrees back and forth ("vibrate" as you say) as the polarity of the field changes at the rate of the MHz frequency. Microwave is a GHz frequency which is outside the range of any VFO I've heard of, but I'm not sure. And yes, a Farraday cage is certainly a good idea. Thanks.

But I'm not sure if this is a feasible project or not for a hobbyist.

 

[FvM]

This wikipedia article gives a brief overview of dielectric heating applications https://en.wikipedia.org/wiki/Dielectric_heating

Heating in the low MHz range (e.g. at ISM frequencies 13.56, 27.12 and 40.68 MHz) is used in industry since a long time.

But I'm not sure if this is a feasible project or not for a hobbyist.

Even the smallest "matchstick" setup is involving RF power in a several 100 mW up to W range and rather high RF voltage. It's requiring profound RF emgineering knowledge.

The efficiency advantage compaired to resistance heating is in concentrating the dissipated heat to the object. But you still need a certain energy amount to heat up matter and possibly evaporate water. It can be calculated by elementary thermodynamic relations.

 

[Heaviside]

Even the smallest "matchstick" setup is involving RF power in a several 100 mW up to W range and rather high RF voltage. It's requiring profound RF emgineering knowledge.

Maybe 5W? Maybe 500v? That sounds feasible to me provided it is safely shielded. Industry talks about dielectric heaters being much more energy efficient. And isn't it true that such a narrow capacitor gap makes it a lot easier to achieve the energy you need? Profound knowledge is also needed to make a 100,000V van der Graff generator but they are feasible for hobbyists.

 

[jiripolivka]

There is no such thing like "DC transformer". From your questions I can see your knowledge of electrical engineering is .limited. I would rather start to study, also material properties of those you want to heat.
RF power engineering is covered in many books, also IEEE branch has a Transactions magazine. You can google some basics.

 

[Heaviside]

There is no such thing like "DC transformer". From your questions I can see your knowledge of electrical engineering is .limited.

Correct. I appreciate your suggestion about in depth power engineering study and IEEE. Could you possibly give me and other thread readers a glimpse into the main one or two stumbling blocks a more knowledgeable engineer would encounter in trying to attempt this experiment at home?

 

[chuckey]

If you look at "Wikipedia", you can find the formula for the capacitance between two plates. Work this out, I would guess its say 20 PF at the most. this means that you need a very high voltage to drive any current through it. there are two ways of getting this , one is to use a high power radio frequency source, say 1 KW. The other way is to use "resonance" or tuning the capacitance with a coil. This way you would only need a few watts, most of which would be lost in the coil, but hopefully leaving enough to produce some heating in your test materials.
So go to a radio amateurs site and look to see what is involved in building a 5W transmitter. This will only give about 15V so its safe enough. The step up circuitry and the sample should all take place behind a earthed metal mesh as high voltage should be present.
Frank

 

[Heaviside]

Very constructive ideas. Thank you very much.