High accuracy non-contact ultrasonic thickness gauging of aluminium sheet using electromagnetic acoustic transducers
✍ Scribed by S. Dixon; C. Edwards; S.B. Palmer
- Publisher
- Elsevier Science
- Year
- 2001
- Tongue
- English
- Weight
- 627 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0041-624X
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✦ Synopsis
Aluminium sheet thickness has been calculated from ultrasonic data obtained using a send±receive, radially polarised electromagnetic acoustic transducer (EMAT). Sheets in the thickness range between 0.1 and 0.5 mm have been measured using this noncontact approach at a stand-o of up to 1.5 mm. Normal incidence shear waves generated and detected in the sheet and the resultant waveforms have been processed using transit time measurements and Fourier analysis. Two broad band EMAT systems have been used to perform the measurements with centre frequencies of approximately 5 MHz and frequency content up to 10 and 20 MHz respectively. The most accurate measurements of thickness on thin sheets have been made using Fourier analysis and have yielded measurements accurate to within 0.2% (or 0.4 lm) for 280 lm thick aluminium sheets. Discrete shear wave echoes can be observed for sheets down to a thickness of 250 lm using the higher frequency EMAT system. However temporal measurements of these signals yield lower accuracy results when compared to the Fourier analysis method which is capable of sub-micron accuracy.