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Automatic Microwave Plasma Waveguide Tuner

Does anyone here have any experience with an automatic microwave tuner circuit?

I was considering using a 3-3/4" stroke push / pull solenoid coupled to an LVDT. Where I would put a microwave detector diode in the waveguide near the dummy load, and when reflected radiation is detected, move the tuner via the solenoid and LVDT to scan for the position that minimizes reflected power.

The planned application is regarding a microwave plasma jet that will inject glassy ceramic material into the flame to be melted and deposited. I suspect that varying rates of material deposition will change the load impedance and require continuous tunning. Thus the requirement for an automatic tunning circuit seems plausible.

--
Christopher R. Thompson
Student of Mechanical Engineering
California State Polytechnic University, Pomona
CSUHome: http://www.csupomona.edu/~cthompson1/
MyHome: http://christoffur.hopto.org/
Email: mailto:Christoffur-No-SpamIt-050@Verizon.Net
Reply to
O5O
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It might work. A 3.75" push-pull solenoid is not a good way of generating this sort of travel - the usual solution is a rotating stepper motor with a lead screw threaded through the axis. Go to

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and check out "linear actuators" for some examples. You can buy some of their stuff ex-stock from Farnell and RS Components.

Proper linear stepping motors - no lead screw - are more fun, but harder to get hold of. I've got one on my desk at the moment, but it cost $US2000 and it took four months from enquiry to delivery.

The LVDT is a nice position sensor, but bulky and a lot longer than the travel you are measuring. Heidenhain used to be the major supplier of linear messuring systems - and may still be for all I know.

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A lot depends on the precision and resolution that you need.

Reply to
bill.sloman

Ok Bill. Thanks a lot.

I don't think that I really know what is going to happen when I start feeding various materials into the plasma. I am guessing that a certain amount tunning will be necessary, and would like to make that process as automatic as possible.

What we are really after is minimum reflected power, and the position of the tunning element is only for reference. The circuit is either tunned or not, and there are only two directions of travel. If the circuit is tunned then movement in either direction will increase the reflected power, and if the circuit is un-tunned then one direction will increase the reflected power and the other will decrease it. I would think that your linear actuator with a stepper motor will work out quite nicely.

I will keep your advice in mind as I trudge on, and I have added your links to mine own.

Thanks again from, Chris.

Reply to
O5O

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