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Influence of High-Frequency Near-Field Coupling between Magnetic Components on EMI Filter Design

Fig.1 (a) High frequency near-field stray flux explanation: Five turns model.
This work presents a detailed analysis of magnetic component coupling and its influence on EMI filter design. In contrast with other literature, the novelty of this paper reveals that magnetic coupling should be divided into two categories: low-frequency coupling and high-frequency coupling. It is proven that coupling is frequency related and high-frequency near-field stray flux distribution can differ dramatically from low frequency condition. The change of the near-field stray flux distribution is caused by displacement current from stray capacitors. By using the Biot-Savart equation, high frequency near-field distribution can be well predicted and matched with experimental results. In addition, single stage DM LC filters are utilized to demonstrate the influence of high-frequency coupling.

Fig. 1 (b) Equivalent model with stray cap.
Fig. 2. (a) Winding current distribution measurement: Measurement setup.

Fig. 2 (b) Measurement results.
Fig. 3 Predicted near-field stray flux for high frequency (20MHz).

Fig. 4. LC filter transfer gain affect by the near field coupling.
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