High-frequency torsional modal testing of a long cylinder by magnetostriction

The torsional modal testing of cylindrical bodies still remains formidable. This is because pure torsional eigenfrequencies typically lying in the kilohertz frequency range are nearly impossible to excite by popular excitation methods. In this study, a torsional modal testing method using a set of magnetostrictive patches, specially arranged permanent magnets, and solenoids is investigated to cover a frequency range of a few kilohertz. The use of magnetostrictive patches for the testing was motivated by torsional wave experiments using the patches, but the use of special magnet configurations was a key to successful modal testing. The developed method was validated with experiments.