>Hi All,
>I'd like how to know how to make a cheap, efficent, but
>powerful (high pressure, capable of compressing gases) Ultrasonic waves?
>I saw the standard quartz crystal oscillators but they seem
>VERY weak.  The ultrasonic cleaners don't seem very powerful
>either.  I need this for a school project so I'd prefer to
>build it myself (make modifications, etc.).  Does anyone know where I
>can get information on building one of these or, if that is
>not possible, where I can buy a unit that isn't too expensive.
>Please e-mail all responses to me because my Usenet server is
>down (sending this through a mail to news service).  Thanks in
>advance.
>Henry
>
The standard way to make high power ultrasonic waves without using piezo
devices is to drive ferrite core into saturation.  The magnetostriction
causes the core to change dimensions as it saturates.  If the winding on the
core is driven with a square wave of high enough amplitude (voltage) the
core can be made to vibrate violently.  The best efficiency is achieved by
driving the core at its mechanical resonant frequency.  To ensure good
coupling to the air I would attach a disk with a large surface area to the
ferrite core.
Mechanical impedance matching should be used.

Because the core saturates, the current in the winding can change very
quickly and needs to be limited.  This technique can produce very high power
but is definite not for the faint of heart because the electronics is
difficult.  WARNING: DO NOT TOUCH THE FERRITE WITH YOUR HANDS TO 'FEEL IF
ITS WORKIN'.  The ultrasonic energy can and will detatch the cartilidge from
the bones in your fingers!

We used this technique to generate enough power to crush mineral pellets.

Regards

Cobus de Beer