Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

Other Reading (Olympus): Dual element transducers utilize separate
transmitting and receiving elements, mounted on delay lines that are usually
cut at an angle (see diagram on page 8). This configuration improves near
surface resolution by eliminating main bang recovery problems. In addition, the
crossed beam design provides a pseudo focus that makes duals more
sensitive to echoes from irregular reflectors such as corrosion and pitting.
One consequence of the dual element design is a sharply defined distance/
amplitude curve. In general, a decrease in the roof angle or an increase in
the transducer element size will result in a longer pseudo-focal distance and
an increase in useful range, as shown in Figure (13).