Precise Sound Velocity Measurements

The laser ultrasonic method allows to determine the ultrasonic wave velocity in investigated material. The short duration and high quality of laser excited ultrasonic pulses make it possible to measure the velocity of ultrasonic waves with precision accuracy on a small base (the statistical spread of measurements exceeds 5x10 -4 with a path length more than 2 mm. The relative accuracy of the velocity measuring of a longitudinal ultrasonic wave in the range 4-10 mm/μs is no worse than 0.1% at a base of 30 mm.

The speed of sound is determined by the echo method. The laser ultrasound echo-method has a significant advantage over the shadow method since can be used for one-sided access to the investigated object. The velocity of longitudinal ultrasonic waves in the investigated object is determined from the difference in the arrival times of the ultrasonic pulse reflected from the inhomogeneity and the pulse reflected from the generator-sample boundary to the transducer.
The thickness of the sample and the time delay of the longitudinal ultrasound wave reflected from the rear surface make it possible to measure the sound velocity with high accuracy using a PLU-6P-02 transducer and UDL-2M defectoscope.
 


 

When there is no data on the thickness of the sample, for example, one-sided access to the object, a PLU-6N-02 transducer is used to measure the ultrasound velocity using the UDL-2M defectoscope. Calculations are made based on the measured time delay of the head wave.
 


The small dimensions of the laser-ultrasonic beam (2 mm) allow the local measurement of the velocity of the longitudinal and shear waves simultaneously.