Ultrasonic testing is widely used by metalcasters to detect sub-surface defects, measure thickness, and determine certain material properties. UT by the conventional method involves generating ultrasound with a piezoelectric crystal that converts electrical energy into mechanical energy. Then, that mechanical energy is transmitted into the test subject by means of a liquid couplant.

Because the sound is transmitted into the part through a liquid from an outside transducer, this technique has limited usefulness when the test subject is hot, oily, or dirty — or when it has a rough or oxidized surface. Also, conventional UT can’t easily be applied to on-line testing.

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