Abstract: A vibration generating mechanism includes first and second permanent magnets spaced from each other with the same magnetic poles opposed to each other, and an electromotive actuator for driving the first permanent magnet. The electromotive actuator moves the first permanent magnet periodically and reciprocatingly relative to the second permanent magnet to change the opposing area of the first and second permanent magnets thereby causing the second permanent magnet to vibrate relative to the first permanent magnet.

Abstract: A magnet field generating apparatus for MRI, comprising:a plurality of permanent magnet assemblies disposed continuously around the angular inner circumference of a hexagonal tubular yoke to provide a uniform magnetic field at the center portion of the hollow space inside said permanent magnet assemblies; the permanent magnet assemblies forming a main magnetic field by a pair of oppositely disposed permanent magnet assemblies which are trapezoidal or square in cross-section; other pairs of permanent magnet assemblies having a triangular or square cross-section; each of the pairs of oppositely disposed permanent magnet assemblies has a side surface in contact with a part of the inner peripheral surface of the yoke and forms a plurality of permanent magnet blocks which are magnetized perpendicularly to the side surface in contact with the yoke so that the permanent magnet assemblies are magnetized perpendicularly to the side surface thereof in contact with the yoke; magnetic pole pieces disposed on each surface