The Effect of Ultrasonic Resonance on Impedance in Magnetic Rods

When an ultrasonic wave is applied to the end of a magnetic rod and a standing wave is generated, high frequency stress will be generated at the standing wave nodes according to the frequency of the ultrasonic wave. The change in magnetic moment generated by this high frequency stress can be easily observed with a detector coil. On the other hand, since stress is not generated at the positions of the antinodes, an induced electromotive force is not produced in the detector coil. Therefore, observation of the stress distribution in the sample rod with the detector coil is possible. Since this phenomenon is reversible, a standing wave may also be generated by applying high frequency voltage, using a detector coil as an excitation coil. In that case, the impedance of the excitation coil changes from the node to the antinode positions. Therefore, it is possible to measure the stress distribution in a sample using only an excitation coil. This paper is a report of research into the effect that the standing wave in a magnetic rod exerts on the impedance of an excitation coil.