Moment-free solenoids are composed of two groups of solenoids in a nested manner. Through a certain number of coil turns and a certain current direction of each group of coils, the magnetic field outside the solenoids rapidly attenuates, and the total magnetic moment of the solenoid coils is zero. Its main characteristics and advantages are: when working, it will not produce magnetic interference to the environment beyond a certain distance, and will not magnetize the magnetic substances nearby; Especially prominent is the use in the magnetic shielding barrel, which can reduce the mutual influence between the magnetic shielding layer and the coil magnetic field to a negligible degree.