Noncontact flexural vibration modal testing of metallic cylinders using the electromagnetic acoustic coupling principle

This investigation develops an eddy-current method to excite flexural vibrations of metallic cylinders in a non-contact manner without any mechanical movement of actuating units. The eddy-current method has been used widely in many applications including damping generation and vibration reduction, but it was rarely used for the generation of mechanical vibrations of a structure for noncontact vibration test. The key in this method is to use a specially-configured figure-of-eight coil that supplies a dynamic magnetic field onto the cylinder and to install two permanent magnets inside the coil with specific polarities. Unlike existing eddy-current methods, the present method does not require any mechanical motion of actuating units due to the specially-configured actuating magnet circuit. Numerical simulations showed that the direction of the Lorentz force generated by the magnetic circuit is in the desired direction. The validity of the developed eddy-current excitation method was first checked in the flexural modal analysis of a slender aluminum pipe. The proposed non-contact excitation method was then applied to the drive shaft of a vehicle as a practical application.