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Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843
I always thought that pulses were used so as to deposit energy into a gas in a time interval faster than the time it would take for an arc to occur. And I've seen variations of the idea where the electric field is rotated (e.g., using a three phase AC voltage with three electrodes); changing direction fast enough that an arc breakdown doesn't occur.
In the case of this plasma pencil thing, the patent says the power supply can supply "AC", "RF" or "regulated voltage pulses of varying frequency"...from which I infer that the drive voltage isn't all that critical and that the critical thing here is the geometry of the ring electrodes and dielectric disks or whatever it is.
Moreover, the way I read the patent, the "carrier gas" can be just air, for example, which is good news, because I think every other similar low temperature "plasme jet" device I've seen (most of which were driven with RF at 13.56 Mhz) required helium or argon e.g., this one:
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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wrote ...
I always thought that pulses were used so as to deposit energy into a gas in a time interval faster than the time it would take for an arc to occur.
The intention is to get energy mostly into the electrons ... arcs aren't very good at that, but with dielectric barrier discharge you can't get arcs to begin with (ignoring dielectric failure).
PS. I think that patent should be invalidated for making a mockery of the definition of "Preferred Embodiment" as understood by any engineer, that part of the patent should be the useful part ... not the part to hem and hedge to try to expand scope to the point of complete uselessness. I'm pretty sure the actual preferred embodiment has one or both of the electrodes embedded in the dielectric, forming a dielectric barrier discharge setup.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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I should've worded it differently; "arc" was the wrong word. Put it this way: AC driven DBDs can be non-uniform, which is not desirable. Fast pulses are much better. Apparently, the faster you deposit the energy, the more uniform the plasma.
And yes I agree about the ridiculous way that patent is worded.
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Edit:
I found a paper that gives a little better idea of the construction of the "plasma pencil" (figure 3). It's a double dielectric barrier discharge being driven with pulses of 5 to 7 kv, 400 to 800 ns duration, @ 4 kHz.
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Plasma Pencil
