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This study mainly investigates the impact of high speed digital modules' radiated EMI noise on receiving performance of wireless mobile device via built-in antenna coupling. We began with designing dipole and loop antenna to represent the routing and trace pattern for common-and differential-mode current flowing inside digital modules installed in mobile devices(such as Tablet, Notebook computers, and smart phones), and then observed the coupling effect of their EMI noise on receiving antenna ports. Utilization of EMI measuring equipment described in this paper not only can obtain the interference power corresponding to the frequencies and levels of noise from device under test (DUT), we can also derive the radiation patterns related to common-and differential-mode radiation from surface scanning results. We would then further establish the relationship between the DUT characteristics and noise locations to find the optimal placement for noisy DUT and antennas. The result of this study can help to establish the preliminary noise budget for those components built in the wireless communication platforms.

In recent years, the permanent magnet blushless motors w i t h slotted laminations and high energy magnets, such as neodymium-iron-boron (NdFeB) have been widely used as a spindle motor for CD-ROM drive [l-3]. However, in the slotted motor, cogging torque is generated due to the interaction between the rotor magnets and the slotting on stator. It is well known that cogging torque produces vibration and noise which may be detrimental to the performance of position and speed control systems. Hence, techniques to reduce cogging torque play an important role in motor design.n e cogging torque can be reduced hy skewing of either the stator slots, or the rotor magnets. However, due to the end effects, both techniques do not completely eliminate the torque variation. Furthermore, they increase the complexity of the motor construction and also increase leakage inductance, stray losses and reduces the average output torque.In this paper, an alternative approach to design a low cogging torque of spindle motor without skewed stator slots or rotor magnets is proposed. Optimal design of magnet arc width for minimizing cogging torque are investigated. Annlvtical TechniaueThe prototype motor is a ?.-phase, Ysonnected, permanent magnet brushless DC motor as shown in Fig. 1. It was designed as an outer-rotor motor with ring-shaped and radically oricnted rntor. There are 12 magnet poles (12p) made of bonded NdFeB material. The stator core consists of 9 slots (9s) and is made of laminations of silicon steel of 0.5 mm thick. The dimension of the motor is given in Table I [Z].In this paper, results are obtained from a two-dimensional finite element analysis based on a combination of the electromagnetic field and external circuit equations. The electromagnetic torque of the motor can be calculated from the rate of change of the total coenergy I+' with respect to a small perturbation ofthe rotor position, that is It is our p u r p o~ to investigate the effects of reducing the width of magnet pole arc with keeping the stator teeth width constant on average torque and cogging torque. Fig. 2(a) shows that the average torque is proportional to the width of magnet pole arc, as expected. The larger the width of magnet pole arc is, the larger the average torque. However, it can be seen in Fig. 2(h) that the cogging torque increases from 2.153 mNm at O=Onto 2.962 mNm at O = 3'. then decreases to 1.361mNm at B = 8". Based on the method proposed in this paper, an optimal design of configurations where the cogging torque is reduced and the average torque is high cnough can be daerniined. REFERENCES[I] C.