Thickness measurement is an important primary measurement parameter. It itself and from the various derived para-meters, provides valuable information in testing and process industries. Although numerous techniques are avail-able for thickness measurement which provide very good results for transparent material and when both sides are accessible, but these methods have limitations in case of opaque material and when only one side is accessible. A new EMAT based non contact technique is reported in this paper which is capable of measuring thickness variation even in opaque material and if only one side is accessible.
Using EMAT it was possible to measure the thickness of a material in the order of a few nanometers. This was achi-evable by the facility developed at NPL, India to measure ultrasonic Time of Flight (TOF) to an accuracy of nano-seconds with deviation of 300 picoseconds. An experiment was done using EMAT to measure the variation in thickness due to stamped notch in an aluminium block having thick-ness of 25mm. EMAT system was able to measure considerable variation in the thickness due to notch. An experiment was also done on circular metallic pipe to determine the variation in inner diameter by measuring wall thickness. Excellent result was obtained with greater precision. This better precision is achieved because of Beam Width to Reflector ratio being close to unity. In case of flat plates this ratio is much greater than unity. To reduce this ratio to unity even in case of flat plates several samples were used in conjunction with EMAT and experiments were again performed on the above mentioned aluminium block to determine the variation in thickness due to notch
