Re: Generation of Ultrasound in the Megahertz region

On 30 Mar 2007 11:34:51 -0700, "John O'Flaherty" <quiasmox@xxxxxxxxx>
wrote:

On Mar 30, 7:46 am, "Joe" <nuisancewildl...@xxxxxxxxxxxxx> wrote:
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
about this or maybe has done it before. Any info, links, or references
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.


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



.

Relevant Pages

  • Re: Generation of Ultrasound in the Megahertz region
    ... Does anyone know how I could generate sound waves in the Megahertz ... I have also googled for:Bragg Effect, photoelastic effect, Bragg ... Medical ultrasound uses frequencies in the 1 to 20 MHz area, ... These crystals mostly run ...
    (sci.electronics.basics)
  • Re: Generation of Ultrasound in the Megahertz region
    ... Does anyone know how I could generate sound waves in the Megahertz ... I would like to do a demonstration for my class on the Bragg ... Medical ultrasound uses frequencies in the 1 to 20 MHz area, ...
    (sci.electronics.basics)
  • Re: Generation of Ultrasound in the Megahertz region
    ... Does anyone know how I could generate sound waves in the Megahertz ... 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 ...
    (sci.electronics.basics)
  • Re: Generation of Ultrasound in the Megahertz region
    ... Does anyone know how I could generate sound waves in the Megahertz ... I would like to do a demonstration for my class on the Bragg ... acousto optic effect an have come up empty as far as a ...
    (sci.electronics.basics)
  • Generation of Ultrasound in the Megahertz region
    ... Does anyone know how I could generate sound waves in the Megahertz ... 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 ...
    (sci.electronics.basics)