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This paper presents a new method by sticking a copper ring on the permanent magnet pole of the permanent magnet brush dc (PMBDC) motor to reduce the electromagnetic vibration. First, the air-gap flux density distribution and radial force density distribution are derived and the principle of the electromagnetic vibration reducing technique by the copper ring is analyzed in detail. Then, finite-element method is used to calculate the Maxwell force and the vibration spectrum of a 2-pole 24-slot PMBDC motor and a modified motor. Finally, experimental results are given to validate the proposed technique, by testing the vibration spectrum of the two prototype PMBDC motors. It is shown that the acceleration of the motor with copper ring can reduce the vibration effectively compared with the origin motor, and the reduced ratio can be up to 40%. [ABSTRACT FROM AUTHOR]