A close look at transducers.
In part one we touched lightly on what ultrasound is and what it is used for in non-destructive testing.
If you are still here then you obviously didn’t fall asleep and your interest has been piqued. Great!
The sound wave thingmabobs are actually called transducers. Which in my opinion (other opinions are available) is a fancy way of saying sound wave generator.
So how do these transducers create sound?
Cast your imagination back to France in the 1880’s. There is the smell of discovery and fresh baguettes in the air.
Two brothers, lets call them Jacques and Pierre. For those indeed were their names. are messing around with wire, magnets, glue and tinfoil and also some crystals.
Zut Alors!! We have discovered the piezo electric effect!
We will be ze toast of Paris, we will dine with Napoleon, we will dance La Marseillaise in the streets with ze peasants.
Ok well it didn’t quite go like that but that’s where it started.
Piezoelectric effect? Oh yeah right ok.
According to Wikipedia it’s the following:
The piezoelectric effect is a reversible process in that materials exhibiting the direct piezoelectric effect (the internal generation of electrical charge resulting from an applied mechanical force) also exhibit the reverse piezoelectric effect (the internal generation of a mechanical strain resulting from an applied ……………………….
Zzzzzzzzz, WAKE UP!
If you squeeze certain crystals and change their shape they produce an electric charge.
Conversely with the same crystal if you pass an electric charge over them they will change shape.
Changing shape causes a vibration and as we saw in Part 1
Sound caused by VIBRATIONS!!? AMAZING!
Back to the transducers!
A transducer contains a crystal. Electrical charge applied to a piezoelectric crystal thousands of time a second will cause the crystal to vibrate thousands of times a second.
Hey presto: Ultrasound!!!!
How does THIS work then?
Sound produced by the transducer passes from the transducer into the test material.
This will bounce off anything in its way and the returning sound will hit the transducer.
When the returning sound wave hits the crystal it transforms back into electricity.
In Part 3 we will discuss how the electrical signal can be used in an ultrasonic inspection system.