Table 2 Specification of the applied UPV equipment

Type of ultrasonic transducers

Undamped dry-point-contact transducers

Transducer configuration

Array of seven dry-point-contact transducers

Operating frequency

50 kHz

Maximum thickness of the inspection object

2.5 m

Indication resolution of the propagation time of ultrasonic waves

0.1 \(\mathrm{\mu s}\)

Indication resolution of the propagation velocity of ultrasonic waves

10 m/s