Generation of Ultrasound in the Megahertz region

Hi Joe, I'm not sure how far you can propogate sound (in air) in the megahertz region. The only graph I can find is here,

But, Figure 5 only goes to 240khz. The formula above it says you would have

21db of loss per foot in air. Mike

Medical ultrasound uses frequencies in the 1 to 20 MHz area, so there are transducers available, but they might be pricey. At those frequencies, it would have to be water or some liquid medium with a high enough speed of sound, not air.

If you try to use an ordinary quartz crystal in water, I think you'd have to insulate it electrically in something that would pass the sound waves, since the crystal is high impedance/voltage. It may also be that applying a high intensity drive would shatter the crystal.

There are ultrasonic cell disintegrators used in biology labs that put out very high intensity sound into water (hundreds of watts), but they work in the 20-25 kHz range. If the Bragg effect depends on high intensity, they might be more effective than rangefinders, and maybe you could borrow one from the biology department.

-- John

Hi:

I have a relevant question

What is the highest-frequency of ultrasound that can propagate through air on earth's atmosphere?

Thanks,

Radium

well, sound travels at aprox 770 mph, that would be the choking point. anything below that was be greatly suppressed until you start moving more more down away from the 770 factor. Also remember, temperature and movement plays a roll on it, look around for the data. I'm sure you can find it somewhere.

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

I think your timezone is wrong. Or else your clock is. :-) BTW, Radium is a troll. He will keep asking short little questions in order to keep people making long winded responses. And then say stupid things like "I dind't understand that, could you rephrase it" etc..... Play along if you like, but I thought I should let you know. :-)

This is a bit OT, but hey it's Friday

Many moons ago when I was a programmer, I worked in St Louis for a stock brokerage company. They had these bad-ass laser printers that printed on continuous forms paper at a rate of 30"/second. No matter what size fonts or lines/inch, the paper always moved at the same speed. Amazing machine (Siemens 0777 Laserdrucken (sp?)), especially the stacker. At any rate, there was some documentation laying around and it included a theory of operation. Well how could anyone resist looking at that. ;-)

Now to the point. The laser went thru a "lens" (might have been quartz, I don't recall). The lens was somehow vibrated/modulated by several audio range frequencys. This had the effect of splitting the beam into multiples that, IIRC, came out parallel. By turning a tone on or off, the beam would reciprocate at that position. This allowed the laser to scan the drum 6 times as fast since it was drawing with multiple beams. Pretty smart IMO. It's been 20 years so please forgive my rusty memory on the details. :-)

The fuser/stacker was a seperate module so the paper travelled several feet in the open with the print on the paper only being held in place by static electricity. People couldn't resist not touching it when the door was open, but don't touch the edge. Not many places can you get a paper cut that results in stitches. I wish I had video of it in operation. The stacker was just incredible. Paddle wheels, flappers and air puffing jets to coax the continuous form paper into fan-folding back up. The key to getting the stacker to work was to feed the first two pages thru the fuser pre-folded. That way you could tell how it had to fold back up. After the fuser "ironed" the perforations, you couldn't tell which way it originally went. But the paper knew. ;-) It had just enough memory that if you didn't start it correctly it would mess up every 100 pages or so.

site:

I've always wondered how much a regular quartz crystal would scatter a laser beam when driven hard. Some crystals have a quartz disc with plated electrodes in the center and a clear rim, so you could un-can one, shoot the laser through the clear part, and build a nasty oscillator that drives it insanely hard. These crystals mostly run shear mode.

John

Thank you all for the responses. This demonstration would not be carried out in air. For precisely the reasons you cited. Sound does travel about 5 times faster in water, about 1500 meters/sec. In fact, I was thinking of using water, just because it is so abundant, and behaves non linearly with light and sound together.

Yes, I know about Massa Corp. they are about 10 miles from where I live. They build sonar and sonar imaging arrays, mostly for the Navy.

About quartz crystal. It is also a non linear medium. When a laser hits it, depending on what angle it is to the crystal axis, it exhibits birefringence (ie, 2 different indices of refraction), so you will see 2 beams emerge. It's really cool to watch. 1 beam in , 2 come out. They are polarized oppositely also, if they enter the crystal unpolarized. Otherwise, they can become circularly polarized, or elliptically polarized. When you modulate it at audio frequencies, all kinds of cool stuff can happen. I never saw one get split into 6 beams tho, but it wouldn't surprise me.

Fish finders usually use 2 frequencies, around 50Khz and 160Khz, but that is not high enough. They would be waterproof at least.

The equation for the Bragg scattering has only the angle of diffraction, the speed of sound, and the frequency in it. I don't think amplitude makes much difference.

Maybe I will order some quartz crystals and take them apart. What's to lose? They are cheap enough.

I think I'll mosey on over to the alt.sci.lasers forum. Maybe Sam or someone over there has an idea.

Thanks again for the responses,

Joe

1 m/s = 2.2369 mph

344.226384728865841119406321248156 m/s = 770 mph

Wave velocity = frequency x wavelength

344.226384728865841119406321248156 m/s = 1 Hz X 344.226384728865841119406321248156 m

I still don't get it? What is the max frequency possible? Seems like their is no limit, yet there is. This is extremely confusing.

Just what is the highest-ultrasonic frequency in which acoustic wave can travel through air on earths atmosphere if the speed of sound in

770 mph????

site:

See if you can find one of the old FT-243 military type crystals. They were built for rugged service in tube equipment, and at higher drive than today's crystals.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Hmm, I wonder if the medical profession ever uses disposable ultrasound transducers? This may sound outrageous, but they use other disposable transducers, such as pressure transducers for blood, which are much cheaper in the disposable form than the research-grade form. It is cheaper to thow away a $50 disposable than to sterilize a $1000 unit.

You might think you could snag a disposable unit on its way out to the medical waste bin, but there would be liability issues if they let you do that. (What if it had AIDS-contaminated blood on it?)

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!

It sounds like you are looking for an acoustooptic modulator, or AOM. They are sold commercially; try a google search for more info.

On 30 Mar 2007 06:46:47 -0700, "Joe" Gave us:

No such thing, dingledorf.

Oh gawd, not again. Why don't you just check things out before going off like that? There is most certainly ultrasound in the MHz range. Just go to any OB/GYN clinic and ask to see the ultrasound machine. Have someone read to you what is clearly written on the wand/probe/transducer. 3MHz

Guess what, there are radio waves in the kHz range. Spooky huh?

Joe,

You might want to look up some of the surface acoustic waves work at Bell Labs done in the 70's. Some of the authors to check would be Gary Boyd, Larry Coldren and P.K.Tien.

Later...

Ron Capik

Ever hear of an optical phonon?

Later...

Ron Capik

Devices are commercially available. Googling acousto-optic, I eventually found:

RF drivers:

AOM modules for deflecting laser beams:

Also of possible interest:

Mark

On Sun, 01 Apr 2007 17:17:48 GMT, Ron Capik Gave us:

Crunchy WinterGreen LifeSavers.