Figure 1 shows the principle of the pulse-echo method
. A pulser/receiver supplies a high voltage electrical pulse to the transducer and amplifies the received ultrasonic wave signal.
Ultrasonic pigs use the pulse-echo method, in which a transducer generates an ultrasonic pulse that travels through a coupling medium (e.g.
The scanning probes for the pulse-echo method had a diameter of 10 mm.
In the contact method (also known as the pulse-echo method
), an ultrasonic probe (transducer) is pressed against the casting surface with a couplant to maintain a good contact between the casting and the transducer, which sends and receives sound signals.
The pulse-echo method has the advantage of being single contact method requiring access from one side only, but has the disadvantage of requiring samples of lower thickness compared with the through-transmission technique.
The ultrasonic measurements during cure were performed with the pulse-echo method in isothermal conclitions (25 [pm] 1[degrees]C and 30 [pm] 1[degrees]C) by placing the resin sample, in form of a thin sheet (about 2 mm thickness), between the transducer and a heated plate (Fig.
For example, the ultrasonic pulse-echo method
was utilized to characterize polymers in both the solid and molten states (11-13), to measure the polymer melt temperature during injection molding (14) and to study the mold cavity conditions in a simple plate mold (15, 16).
The system performs phase-sensitive detection of acoustic echoes produced with either pulse-echo methods
or through transmission techniques.