Small electromagnetic acoustic transducer with an enhanced unique magnet configuration

Hongjun Sun, Ryoichi Urayama, Tetsuya Uchimoto, Toshiyuki Takagi, Mitsuo Hashimoto

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


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.

Original languageEnglish
Article number102205
JournalNDT and E International
Publication statusPublished - 2020 Mar


  • Lift-off distance
  • Permanent magnet configuration
  • Small electromagnetic acoustic transducer
  • Vertical magnetic flux density


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