A new technique for making dynamic focus annular probe, for use on underclad defects

The use of focussed sensors for ultrasonic checking is becoming more and more frequent. This type of sensor enables energy to be concentrated better in a confined zone. While the technique of dynamic focussing is widely used in medical applications, with linear arrays, the use in non-destructive inspection of sensors with arrays of transducers of more complex form was for long limited by difficulties of application and manufacture. These sensors have parasitic modes that seriously affect their optimum use. The authors present here a new technique for manufacturing arrays of any shape. Then they give the results obtained with such sensors on reference reflectors and on underclad cracks