Pulsed-electromagnet EMAT for high temperature applications

This thesis is concerned with the design and implementation of an Electromagnetic Acoustic Transducer (EMAT) intended for high temperature ultrasonic applications; which benefits from a novel approach using a pulsed current electromagnet (PE) and a ceramic encapsulated spaced spiral coil, both designed to operate at elevated temperatures without any active cooling. In detail all the steps taken towards the development of the PE-EMAT and its supporting electronics are presented here, together with the finite element simulations performed for the electromagnetic and ultrasonic analysis; which includes: the computation of the flux density produced by the electromagnet and its variation with lift-off (gap between core and metallic sample), the calculation and visualisation of the magnitude of the current density induced by an alternating current flowing in two different EMAT coil designs in non-magnetic and magnetic samples; as well as the validation of the propagation of the ultrasonic wave generated/detected by the PE-EMAT. The experimental results regarding the performance of the PE-EMAT are also presented. Firstly, the performance at room temperature to show the shear wave generation in paramagnatic and ferromagnetic samples, the effect of the presence of an oxide layer adhered to the sample, and the lift-off performance. Secondly, the performance at a range of different temperatures to demonstrate that the PE-EMAT has been employed successfully at temperatures up to 600 oC, without using any active cooling system, and that is capable of performing ultrasonic measurements of sample thickness and material properties, without the use of any sort of couplant, nor the necessity of sample preparation.