News & Views

How to Make a Hammer out of a Coffee Cup

By Sean Gleeson on Friday, September 10th, 2010

As described in earlier blogs, in order to capitalize on the ability to put energy into something solid and then be able to measure certain geometric properties of the the test object, we have to initiate the energy wave within the object.  To put it in terms that I like to think in, ” we need a hammer”.  Unfortunately a  hammer is more known for the amount of damage it does when transferring energy than the sweet finesse required to test   ” non-destructively”………. Obviously…… a better hammer is going to be required.

The hammer of choice in ultrasonic testing is a device called a transducer.  To understand how a transducer works, it is necessary to get a feel for the phenomenon called ” The Piezoelectric Effect”.  A piezoelectric substance is one that produces an electric charge when a mechanical stress is applied (the substance is squeezed or stretched). Examples of this substance would be crystals and some ceramics.  As the animation to the left is attempting to describe, if a piezoelectric substance is mechanically stressed. as in hitting it with a hammer, an electric charge will be produced.

Conveniently, this process is reversible (below). If a charge is introduced into a piezoelectric material, a mechanical stress will be produced.  This stress will manifest itself as a vibration.  We can couple this energy to an item we want to inspect, ( steel block, pregnant women’s belly…. whatever) and then used in conjunction with the rest of our system to look inside of object. 

So, how do you make a hammer out of a coffee cup? 

The coffee cup I am referring to would be ceramic and so, in theory, if your coffee cup was made from the right type of ceramic material, you could take a small piece of it, put some electricity to it and cause it to vibrate. You could then use it as the hammer we need to perform Ultrasonic testing. 

The next Blog? On your mark, get set, go!!!

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