Ultrasonic metal sheet thickness measurement without prior wave speed calibration

摘要

Conventional ultrasonic mensuration of sample thickness from one side only requires the bulk\udwave reverberation time and a calibration speed. This speed changes with temperature, stress,\udand microstructure, limiting thickness measurement accuracy. Often, only one side of a\udsample is accessible, making in situ calibration impossible. Non-contact ultrasound can\udgenerate multiple shear horizontal guided wave modes on one side of a metal plate. Measuring\udpropagation times of each mode at different transducer separations, allows sheet thickness to\udbe calculated to better than 1% accuracy for sheets of at least 1.5 mm thickness, without any\udcalibration.