Ultrasonic Thickness Measurements of Sub-millimetre Thickness Sheets

摘要

Pulse-echo ultrasonic thickness measurements typically perform poorly on samples with a thickness of less than one millimetre. Here, Lamb waves have been used to measure the thickness of sub-millimetre thick metal sheets by measuring the phase velocity of the first order symmetric and anti-symmetric waves. These waves have been generated and detected using electromagnetic acoustic transducers (EMATs). The technique under development allows thickness measurements to be made without exact knowledge of the material properties of the sample, giving calibrationless measurements. We describe the method of calculating the phase velocity from the unwrapped phase spectrum, and present preliminary experimental results.