HIGH TEMPERATURE AND/OR HIGH SPEED THICKNESS GAUGING OF METALS

TWO DIFFERENT APPROACHES TO HIGH TEMPERATURE ELECTROMAGNETICACOUSTIC-WAVE TRANSDUCER (EMAT) DESIGN AND CONSTRUCTION WILLBE EVALUATED. THE RESULTING EMAT'S WILL BE USED TO PERFORM INSERTION LOSS, ULTRASONIC ATTENUATION AND ULTRASONIC VELOCITY MEASUREMENTS ON DIFFERENT STEEL SPECIMENS UP TO AT LEAST 1200 DEGREES F (MAXIMUM OPERATING TEMPERATURE MAY BE AS HIGH AS 2000 DEGREES F). THIS INFORMATION SHOULD PERMIT THE DESIGN OF BETTER EMAT'S (LOWER INSERTION LOSS) AS WELL AS CONTRIBUTE TO A BETTER UNDERSTANDING OF EMAT'S WHEN USED WITH MAGNETIC METALS. THE FIRST APPROACH USES A COOLED HEATSHIELD TO PROTECT THE ELECTROMAGNET CORE AND WINDINGS FROM THE HOT METAL IN WHICH THE ULTRASONIC WAVE IS BEING GENERATED. THE EMAT COIL IS PLACED ON OR NEAR THE HOT SURFACE AND IS NOT COOLED. A SECOND APPROACH USES HIGH TEMPERATURE INSULATION ON THE MAGNET CONDUCTOR SO THAT THE MAGNET WINDING CAN OPERATE AT AN ELEVATED TEMPERATURE, PROBABLY UP TO 2000 DEGREES F. IN THIS DESIGN, THE USEFUL LIMIT AS AN EFFICIENT CONTINUOUS DUTY ELECTROMAGNET EMAT IS DETERMINED BY THE MAGNETIC PROPERTIES OF THE CORE MATERIAL. THESE EMAT'S CAN BE USED FOR HIGH TEMPERATURE THICKNESS AND INTERNAL DEFECT DETECTION.