Dongguan Magnetic Core Electromagnetic Technology develops and produces keep solenoids using permanent magnets. The working principle is similar to that of all linear motion electromagnets. Once the coil is energized, the slider moves towards the core and stops at the end position. After the power is disconnected, the slider remains in place. To return the slider, a reverse voltage (or current) must be applied. These electromagnets can be designed for both pull-in and push-out actions.

Retentive electromagnetic coils are available in two types: unidirectional and bidirectional. Unidirectional retentive coils only hold the core (self-lock) at one position at the end of travel. In contrast, bidirectional retentive electromagnetic coils feature a dual-coil structure, allowing the core to be held (self-locked) at two different positions at the start and end of formation, with both positions providing equal output torque (exhibiting bistable characteristics).