Re: How Ultrasonic transducers are constructed

Great question!

The basic physical phenomenon behind ultrasonic transducers is something 
called "piezoelectricity" or "the piezoelectric effect".  What happens is 
that certain crystals or ceramics generate a voltage when pressure is 
applied to them and they are compressed.  Similarly, if you apply an 
electric voltage to the piezoelectric crystal, it will deform.  A typical 
order-of-magnitude number (in english units) for this effect is 1 volt 
per 0.001 inch of compression.  In other words, if you compress the right 
crystal by .001 inch, about 1 volt of electricity is generated.

So now we have a handle on how ultrasonic transducers work;  they work a 
lot like RADAR.  In the first step, transmission, a high frequency 
electric voltage is applied to a piezoelectric crystal which causes it to 
deform rapidly and send out a pressure wave.  Then the high frequency 
voltage is turned off, and you wait a few microseconds.  The pressure 
waves that you've just sent out bounce off whatever is in their path and 
return back to the crystal.  Here, the reflected pressure waves hit the 
crystal and generate an electric voltage.  This voltage is sensed, 
processed by computer, and an image is generated.  The key thing to 
making all this work is the piezoelectric effect.

Hope this answers your question!