Measurement of Wall-Thickness at Extreme Temperatures Using EMATs

Electromagnetic Acoustic Transducers (EMAT) can be applied for temperatures ranging from very low minus numbers up to 1000 deg C. Reasons are the couplant free excitation of the ultrasound in the materials itself and a possible assembly of the probe without adhesives. Moreover using EMATs temperature changes of the specimens in the range below Curie-point do not affect significantly the calibration setting; they can also be used for technical surfaces with paint scalings of other thin coatings. But the practical use of EMAT is limited because of equipment costs and minor accuracy of measurement results are due to poor signal characteristics compared with established techniques based on piezo-electric transducers. A new EMAT instrument for wall-thickness measurement is presented. Special emphasis was put on the design of the transducer and the preamplifier to get precise data of high resolution.