Abstract: In the joule balance experiment, the suspension system will swing when force vectors are loaded on, which will introduce a systematic error in the Planck constant h measurement. A precision passive electromagnetic damper for both suspension coil and test mass pan is proposed. The principle of the electromagnetic damper is eddy current effect and it is composed of metal damping piece and permanent magnet. To eliminate the inherent force in the magnetic field, the damping piece is made of diamagnetic material andparamagnetic material in a certain proportion by using “Cu-Al-Cu” three-layer sandwich structure, then the magnetic field forces of three-layer dampers can be cancel each other. In addition, to avoid the magnetization of the test mass by the strong magnetic field leaking from the damper, multi-layer magnetic shield is designed, which contains an internal single-layer electrician pure iron shield and an external double-layer permalloy shield. The results of finite element simulation analysis and experiments show that: the inherent force is about 0.92 μg when the damping piece is static in the magnetic field; the leakage magnetic field at the position of the test mass is about 5.04 μT, less than the earth’s magnetic field; the swing time of the suspension system is reduced about 88.3% by using the designed electromagnetic dampers; overall, the proposed electromagnetic dampers meet the requirements of joule balance experiment.

Key words: mass quantum metrology, electromagnetic damper, joule balance, low magnetic field leakage, no inherent force