by measuring frequency or resonance of acoustic waves

Full Title

Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object (G01N3/00 - G01N27/00 take precedence) > Analysing fluids (using acoustic emission techniques G01N29/14 ) > by measuring frequency or resonance of acoustic waves