Abstracts Submitted: 464
Number of Users: 528
View Abstracts Submitted
Back to home Page
Electromagnetic acoustic transducers(EMATs) is widely used for couplant free ultrasonic inspection of electrically conducting materials. EMAT typically uses a permanent magnet and radio frequency(RF) coil for generation and detection of ultrasound. Rare earth magnets(NdFeB) are preferred to generate strong magnetic field (4-5 k Gauss) bias. Permanent magnet EMAT has the limitation of inspecting only non-ferrous materials. Its application is also limited to testing at elevated temperature due to relatively lower Curie temperature. For inspection of ferrous materials and inspection at elevated temperature pulsed electromagnet EMATs are used. Strong pulse electromagnet design that may replace the permanent magnet is challenging. To achieve strong field high current through the electromagnet coil need to be passed. This is achieved with the help of capacitor bank. The capacitor bank is charged to a particular voltage and discharged through the coil. IGBT is used to turn on current through the electromagnet. The pulsed electromagnet is enabled for a particular time duration during which ultrasound is transmitted and received. The pulse current of the electromagnet is synchronized with the excitation of RF coil. The duty cycle of the electromagnet current is kept relatively low. Generally, on time for the electromagnet is in the order of few milliseconds. The on time is crucial because it decides the maximum depth of the material that can be tested. In this article, the effect of RF coil excitation delay and electromagnet coil inductance have been demonstrated. The study reveals that the on time of the magnet is limited by the power dissipation across the magnet coil due to its finite resistance. The minimum RF coil excitation delay required is defined by the inductance value of the electromagnet because it takes some time for the current to reach the peak value. Due to this the field also takes the same time to reach the maximum value. The experimental study indicates that the optimization of the delay between the activation of the electromagnet and RF burst is important. It has also been observed that in order to ensure maximum received echo amplitude, RF coil must be excited at a time when the field strength of the magnet is maximum.
© Copyright 2017 All Rights Reserved