# Generation of Ultrasound in the Megahertz region

J

#### Joe

Jan 1, 1970
0
Hello to the group,

Does anyone know how I could generate sound waves in the Megahertz
region? I would like to do a demonstration for my class on the Bragg
Effect (a non linear optical effect where a high frequency sound wave
will couple with a laser beam and cause the optical beam to diffract
and even possibly deflect, in the right medium).

It is part of our study of non linear optical effects in different
media. The only acoustic transducers I have been able to find are the
standard 24khz and 40Khz transducers used for rangefinding, alarms,
etc. Those frequencies are not high enough to cause the coupling
effect I was hoping to demonstrate.

I visited this site:
http://www.americanpiezo.com/piezo_theory/applications.html

I have also googled for :Bragg Effect, photoelastic effect, Bragg
scattering, acousto optic effect an have come up empty as far as a
practical way to demonstrate the effect.

I am wondering about using an off the shelf crystal at, say, a few
megahertz, removing the metal casing around it, and trying that. I
know they are cheap enough, but not sure if it would work. I know that
the higher the frequency, the thinner the 'slice' of quartz inside. I
thought I would run it by the group first and see if anyone knows
are welcome.

TIA,
Joe

A

#### amdx

Jan 1, 1970
0
Joe said:
Hello to the group,

Does anyone know how I could generate sound waves in the Megahertz
region? I would like to do a demonstration for my class on the Bragg
Effect (a non linear optical effect where a high frequency sound wave
will couple with a laser beam and cause the optical beam to diffract
and even possibly deflect, in the right medium).

It is part of our study of non linear optical effects in different
media. The only acoustic transducers I have been able to find are the
standard 24khz and 40Khz transducers used for rangefinding, alarms,
etc. Those frequencies are not high enough to cause the coupling
effect I was hoping to demonstrate.

I visited this site:
http://www.americanpiezo.com/piezo_theory/applications.html

I have also googled for :Bragg Effect, photoelastic effect, Bragg
scattering, acousto optic effect an have come up empty as far as a
practical way to demonstrate the effect.

I am wondering about using an off the shelf crystal at, say, a few
megahertz, removing the metal casing around it, and trying that. I
know they are cheap enough, but not sure if it would work. I know that
the higher the frequency, the thinner the 'slice' of quartz inside. I
thought I would run it by the group first and see if anyone knows
are welcome.

TIA,
Joe
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,
http://www.massa.com/fundamentals.htm
But, Figure 5 only goes to 240khz. The formula above it says you would have
21db of loss per foot in air.
Mike

J

#### John O'Flaherty

Jan 1, 1970
0
Hello to the group,

Does anyone know how I could generate sound waves in the Megahertz
region? I would like to do a demonstration for my class on the Bragg
Effect (a non linear optical effect where a high frequency sound wave
will couple with a laser beam and cause the optical beam to diffract
and even possibly deflect, in the right medium).

It is part of our study of non linear optical effects in different
media. The only acoustic transducers I have been able to find are the
standard 24khz and 40Khz transducers used for rangefinding, alarms,
etc. Those frequencies are not high enough to cause the coupling
effect I was hoping to demonstrate.

I visited this site:http://www.americanpiezo.com/piezo_theory/applications.html

I have also googled for :Bragg Effect, photoelastic effect, Bragg
scattering, acousto optic effect an have come up empty as far as a
practical way to demonstrate the effect.

I am wondering about using an off the shelf crystal at, say, a few
megahertz, removing the metal casing around it, and trying that. I
know they are cheap enough, but not sure if it would work. I know that
the higher the frequency, the thinner the 'slice' of quartz inside. I
thought I would run it by the group first and see if anyone knows
are welcome.

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.

R

Jan 1, 1970
0
Hi:

I have a relevant question

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

Thanks,

A

#### Anthony Fremont

Jan 1, 1970
0
Jamie said:

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.

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.

J

#### Jamie

Jan 1, 1970
0
Hi:

I have a relevant question

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

Thanks,

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.

A

#### Anthony Fremont

Jan 1, 1970
0
John said:
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.

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
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.

J

#### John Larkin

Jan 1, 1970
0
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.

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

J

#### Joe

Jan 1, 1970
0
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
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.

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

R

Jan 1, 1970
0
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.

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????

M

#### Michael A. Terrell

Jan 1, 1970
0
John said:
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

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

B

#### Bob Masta

Jan 1, 1970
0
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.

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
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator

R

#### redbelly

Jan 1, 1970
0
Hello to the group,

Does anyone know how I could generate sound waves in the Megahertz
region? I would like to do a demonstration for my class on the Bragg
Effect (a non linear optical effect where a high frequency sound wave
will couple with a laser beam and cause the optical beam to diffract
and even possibly deflect, in the right medium).

It is part of our study of non linear optical effects in different
media. The only acoustic transducers I have been able to find are the
standard 24khz and 40Khz transducers used for rangefinding, alarms,
etc. Those frequencies are not high enough to cause the coupling
effect I was hoping to demonstrate.

I visited this site:http://www.americanpiezo.com/piezo_theory/applications.html

I have also googled for :Bragg Effect, photoelastic effect, Bragg
scattering, acousto optic effect an have come up empty as far as a
practical way to demonstrate the effect.

I am wondering about using an off the shelf crystal at, say, a few
megahertz, removing the metal casing around it, and trying that. I
know they are cheap enough, but not sure if it would work. I know that
the higher the frequency, the thinner the 'slice' of quartz inside. I
thought I would run it by the group first and see if anyone knows
are welcome.

TIA,
Joe

It sounds like you are looking for an acoustooptic modulator, or AOM.

M

#### MassiveProng

Jan 1, 1970
0
Does anyone know how I could generate sound waves in the Megahertz
region?

No such thing, dingledorf.

A

#### Anthony Fremont

Jan 1, 1970
0
MassiveProng said:
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?

R

#### Ron Capik

Jan 1, 1970
0
Joe said:
Hello to the group,

< ...snip... >

I have also googled for :Bragg Effect, photoelastic effect, Bragg
scattering, acousto optic effect an have come up empty as far as a
practical way to demonstrate the effect.

I am wondering about using an off the shelf crystal at, say, a few
megahertz, removing the metal casing around it, and trying that. I
know they are cheap enough, but not sure if it would work. I know that
the higher the frequency, the thinner the 'slice' of quartz inside. I
thought I would run it by the group first and see if anyone knows
are welcome.

TIA,
Joe

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
--

R

#### Ron Capik

Jan 1, 1970
0
MassiveProng said:
No such thing, dingledorf.

Ever hear of an optical phonon?

Later...

Ron Capik
--

R

#### redbelly

Jan 1, 1970
0
Hello to the group,

Does anyone know how I could generate sound waves in the Megahertz
region? I would like to do a demonstration for my class on the Bragg
Effect (a non linear optical effect where a high frequency sound wave
will couple with a laser beam and cause the optical beam to diffract
and even possibly deflect, in the right medium).

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

RF drivers:

AOM modules for deflecting laser beams:
http://www.quanta-tech.com/Acousto_optic_products/deflectors.php

Also of possible interest:
http://www.rocotech.co.uk/ao_deflectors.htm
http://www.rp-photonics.com/acousto_optic_modulators.html
http://www.acoustooptic.com/constitution-bragg-cell.html

Mark

M

Jan 1, 1970
0

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