Small electromagnetic acoustic transducer with an enhanced unique magnet configuration

We describe a small electromagnetic acoustic transducer (EMAT) that is different from traditional large EMATs. The maximum vertical magnetic flux density decreases quickly, and its distribution becomes very uneven with increasing lift-off distance of the permanent magnet. To increase the magnetic fi...

Full description

Saved in:
Bibliographic Details
Published in:NDT & E international : independent nondestructive testing and evaluation 2020-03, Vol.110, p.102205, Article 102205
Main Authors: Sun, Hongjun, Urayama, Ryoichi, Uchimoto, Tetsuya, Takagi, Toshiyuki, Hashimoto, Mitsuo
Format: Article
Language:English
Subjects:
Electromagnetism
Engineering Sciences
Lift-off distance
Permanent magnet configuration
Small electromagnetic acoustic transducer
Vertical magnetic flux density
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:We describe a small electromagnetic acoustic transducer (EMAT) that is different from traditional large EMATs. The maximum vertical magnetic flux density decreases quickly, and its distribution becomes very uneven with increasing lift-off distance of the permanent magnet. To increase the magnetic field strength of a small magnet without increasing the thickness of the magnet configuration, we propose a different permanent magnet configuration. With the same lift-off distance of the magnet, the increase in the maximum vertical magnetic flux density is about 20% when using this configuration. When this lift-off distance is 1.5 mm, the configuration increases the amplitude of the received signal by 71.4% for an aluminium specimen; in contrast, only a 29.0% increase is achieved with a low-carbon steel specimen. This is because, in the latter, the vertical magnetic flux density is less than 0.66 T. The interplay between the Lorentz force and magnetostrictive force leads to a decrease in the efficiency of both forces in generating ultrasonic waves.
ISSN:0963-8695
1879-1174
DOI:10.1016/j.ndteint.2019.102205