Dielectric Heating

[Nick1911]

Does anyone know what radio frequencies cause dielectric heating?

Clearly the microwave range, (2.4-5 GHz) but what outside of that?

Thanks!

 

[Fly320s]

I'd guess that they all do, given enough transmit power.

[280plus]

With or without the magnetic pulse wave? 

No, just kidding, I don't know... 

[Brad Johnson]

Depends on the resonant frequency of the object to be heated.

Brad

[Gewehr98]

We used to run March Plasmods in our forensics lab, to ash organic samples for analysis without flames. They have Pyrex vacuum chambers inside, with an RF coil antenna around the chamber, and a nice, high-output RF amplifier with separate power supply.  When the petri dish w/sample was pumped down to a given vacuum level, the RF was turned on, and a small amount of oxygen bled into the chamber, not enough to overwhelm the Alcatel turbopump, but enough to combust the sample with a beautiful plasma glow. 

After a few hours in this environment, you'd have a petri dish with nothing but ash inside, ready for density separation and other chemical processing. 

This is an example of one:

[Nick1911]

Depends on the resonant frequency of the object to be heated.

Brad

Interesting.  For my purposes, organic materials and water.  (If that's not vague enough...)

[Brad Johnson]

Hmm...

Don't have any of my old texts around, but I seem to remember the true resonant frequency of water is actually in the thousands of GHz (a couple terahertz).  If memory serves, the reason that the 2.45 GHz frequency (microwave ovens in the U.S.) heat anything with water content is that it happens to be a harmonic of the full resonant wave. 

I'm sure, given enough energy, just about any frequency would create some kind of heating.  That much energy can't be absorbed by water or anything organic without something happening.

Again, it's been a couple of decades since I really delved into it and my soon-to-be 40 yr old memory may not be dredging up the proper information.  Others with better info, please chime in now...

Brad

[Headless Thompson Gunner]

Interesting.  For my purposes, organic materials and water.  (If that's not vague enough...)

Good God, man!  What on earth are you building now?!

[280plus]

 

He's kinda like Stewie, coming up with a new evil plan every couple days or so...

Harmonics, I'm getting off on a tangent but harmonics is why digital recording will NEVER sound as good as analog. The number of harmonics in any musical tone are infinite. The number of bits storing the info digitally is not. Plain and simple. The easiest place to hear this is the cymbals. Like the high hat. They lose so much in the lack of harmonics that they sound like a hiss instead of the ringing tone a cymbal produces live. An analog recording will pick up ALL the harmonics, not just the ones it chooses to. Ahhh, I feel better now. 

Now back to your regularly scheduled thread...

[Len Budney]

All radio energy causes some level of heating. What you're interested in is the specific absorption rate, which depends on frequency. Microwaves, in general, have the highest SAR.

--Len.

[Nick1911]

All radio energy causes some level of heating. What you're interested in is the specific absorption rate, which depends on frequency. Microwaves, in general, have the highest SAR.

--Len.

That's interesting, but I'm having trouble finding any solid data amongst the cell phone fear mongers.  What I'd really like to find is a whole body SAR vs. frequency chart spanning for the low megahertz into the hundreds of gigahertz.

[Len Budney]

... cell phone fear mongers... What I'd really like to find is a whole body SAR vs. frequency chart spanning for the low megahertz into the hundreds of gigahertz.

*cough* You're welcome.

Now that you know what SAR is, you have a good chance of finding the answer to your question. I did attempt to find you such a chart. I spent about a minute looking, which appears to be longer than you spent. It looks like you clicked a couple links at the bottom of the Wikipedia article and that's it.

--Len.

[Nick1911]

 

Thank you Len, I do appreciate you answering the question, that is exactly what I'm looking for.  I'll keep digging.