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From: gene@cooper.cooper.EDU (Gene from EK Enterprises)
Newsgroups: misc.consumers,sci.electronics
Subject: Re: Ultrasonic Cleaners
Message-ID: <1124@cooper.cooper.EDU>
Date: Wed, 18-Nov-87 15:59:52 EST
Article-I.D.: cooper.1124
Posted: Wed Nov 18 15:59:52 1987
Date-Received: Sat, 21-Nov-87 11:50:16 EST
References: <4125@watdcsu.waterloo.edu>
Organization: The Cooper Union (NY, NY)
Lines: 89
Xref: mnetor misc.consumers:3506 sci.electronics:1765

in article <4125@watdcsu.waterloo.edu>, ttims@watdcsu.waterloo.edu (Tracy Tims) says:
> A cleaner with a reasonable tank size (3 to 5 litres) is quite expensive.
> 
> Does anyone have any experience or knowledge about them?  I would
> be willing to build one from scratch if it was easy enough.  Anyone
> knw how to build one?

Well, if you can get a relatively high powered ultrasonic transducer, it
might be worthwhile to actually build one.

As for the case/tank, you might even try your bathtub in a pinch! Personally,
I'd try a dedicated tank approach.

As for *how* they work, it's what's called cavitation of water. Under
ultrasonic stimulus, water molecules "bubble" in sync with ultrasonic waves.
It's not the sound that lifts off dirt and grime, but the bubbles' action.
(Talk about "scrubbing bubbles", literally!) Anyway, all that's needed is a
source of ultrasonic energy.

A common audio tweeter (piezoelectric) is available from Radio Shack. It
costs $5, handles 75W of power, and is (more or less) easy to waterproof.
Although I've never tried this, it *MIGHT* be possible just to enclose the
bugger in a Baggie and tie the open end tightly. If you're more adventurous,
you might try to just leave the beastie open, and dangle it underwater.
(Pure water is a great insulator (k=78.0), but enough impurity turns it into
a great conductor, too.)

As for the ultrasonic driver, a 555 timer works well directly. From a 9V
battery, you'll get exactly 9V across the piezo's terminals. HOWEVER, (!)
you can boost that to over 75V terminal voltage by "tuning out" the inherent
capacitance of the piezo.

First, approximate the frequency you'll be working with. (15kHz to 30kHz works
well in driving people, bugs, mice, etc., absolutely crazy. ;^) ) A good
starting value might be in that range. For now, assume 30kHz.

Next, measure the capacitance of the tweeter. The tweeter mentioned above has
a series capacitance of 1.2uF. Either a cap meter or a 'scope would work. The
way I did it is by using the tweeter itself as a capacitor and substituting
different "real" capacitors to get a frequency match on a 'scope. Later testing
on a genuine cap meter verified my earlier results, so don't be afraid to
experiment.

Next, connect up a 555 circuit (or any good oscillator with decent output drive
capability). Using the tweeter as the output, and a good 'scope across the
tweeter's terminals, check for an output at the selected frequency. You should
get the full battery voltage across the terminals.

Next, (aha!), calculate the required inductance, using the formula:

	f = 1 / ( 2 * pi * sqr( L * C ) )		(I think)

(For 1.2uF @ 15kHz, I got about 0.5mH. I don't have a calculator handy, so
you might want to verify the equation above. If it checks out within an order
of magnitude, it's ok.)

Get your hands on such an inductor. As a helpful hint, try your best to get
one with the largest possible wire size to minimize lead resistance. Inductors
from speaker crossovers are usually best.

Put that inductor in series with the tweeter and fire the circuit up. Now, you
should be able to read close to 75V across the tweeter's terminals... all from
a 9V battery! If you want to play around, you can vary the frequency and watch
the amplitude peak and fall off in either direction. The only drawback of this
inductor approach is that it is now frequency-selective. Still, a 2:1 frequency
variation shouldn't cause appreciable falloff.

Next, test the circuit in actual use. Try it in a small tank with a dirty part.
Then vary the frequency (or look it up, if possible) to get optimal results.
When it works on a smaller scale, try it in a bigger tank. If you actually
get around to building the bloody thing, you'll have a great sense of
accomplishment, believe me! At the very least, you'll have an ultrasonic
source which will keep mosquitoes away during the summer, mice in the winter
and possibly people all year round, if you lower the frequency to 15kHz ;^) .

At any rate...
					Enjoy!
					Gene

					...!ihnp4!philabs!phri!cooper!gene


	"If you think I'll sit around as the world goes by,
	 You're thinkin' like a fool 'cause it's case of do or die.
	 Out there is a fortune waitin' to be had.
	 You think I'll let it go? You're mad!
	 You got another thing comin'!"

			- Robert John Aurthur Halford