Halbach array magnet, electromagnetic ultrasonic sensor, defect measurement apparatus, defect measurement method, metal material manufacturing method, metal material quality control method, metal material manufacturing facility, solidification position measurement apparatus, solidification position measurement method, and casting facility

A Halbach array magnet comprising:

• a magnet unit in which a plurality of magnets is arranged in a Halbach array;
• a fixing jig that is one or a plurality of non-magnetic materials, the fixing jig being configured to at least fix each of the magnets of the magnet unit;
• and
• a yoke that is a magnetic material and is provided on a different side of biased magnetic field formed by the magnet unit.

An electromagnetic ultrasonic sensor comprising:

• a magnet unit in which a plurality of magnets is arranged in a Halbach array;
• a fixing jig that is one or a plurality of non-magnetic materials, the fixing jig being configured to at least fix each of the magnets of the magnet unit;
• and
• a yoke that is a magnetic material and is provided on a surface side different from a side where a magnetic field formed by the magnet unit is biased.