Magnetic materials are also widely used in the military field. For example, ordinary mines or mines can only explode when they touch a target, so the effect is limited. If magnetic sensors are installed on mines or mines, because tanks or warships are made of steel, the sensors can detect changes in the magnetic field to explode mines or mines when they are close (without touching the target), increasing the lethality. The traditional artillery guns use the thrust generated by the instantaneous expansion of the ammunition to accelerate the projectile quickly and launch the cannon. The electromagnetic gun puts the projectile in the solenoid and energizes the solenoid. Then the magnetic field generated by the solenoid will generate a huge driving force for the projectile, and the projectile will be fired. This is the so-called electromagnetic gun. Similar to electromagnetic missiles.