VP1-10 EMI Shielding Effectiveness of Ferrofluid Layer in the Presence of Oscillating Magnetic Field
Creators: Hsin-Chieh Hsieh
Yan-Hom Li
Huan-Kuang Kuan
Publisher: name: IEEE
Year: 2025

This work investigates the impact of dynamic magnetic fields on ferrofluid instability and electromagnetic interference (EMI) shielding effectiveness (SE) of a flexible ferromagnetic material. The ferrofluid crests varies with magnetic field strengths and oscillating frequencies. Fig. 1 shows the periodical instability of a ferrofluid layer subjected to an oscillating magnetic field with a frequency of 1 Hz within one period. The ferrofluid exhibits pulsating instability, with crests periodically appearing and disappearing. At a frequency of 5 Hz, due to the phase lag between the ferrofluid oscillation and the magnetic field, the number of crests decreases and their height varies, resulting in oscillatory instability. However, excessively high frequencies cause static instability, preventing the ferrofluid crests from synchronizing with the magnetic field oscillations, and eventually returning to a stable state. Fig. 2 shows the comparison of EMI SEs of a ferrofluid layer with pulsating, oscillatory, and statistic instability, respectively. Experimental results indicate that when the crests exhibit pulsating (magnetic field frequency at 1 Hz) or oscillatory states (magnetic field frequency at 5 Hz), the SE also changes correspondingly with the pulsating or oscillatory state of the crests. Without the influence of a magnetic field, the ferrofluid remains in a horizontal state with no crest formation, providing SE of nearly 19 dB at EMW frequencies of 13 GHz and 16 GHz. When a magnetic field strength of 40.5 mT without oscillation (f=0 Hz) is applied to the ferrofluid, the SE is slightly declined due to the reduction of the layer thickness. As an oscillation field with a frequency of 1 Hz is applied, the pulsating instability of the ferrofluid crests enhances the highest of the SE to nearly 40 dB at EMW frequency of 15 GHz. When the oscillating frequency increases to 5 Hz, the oscillatory instability of the ferrofluid crests causes the highest SE of 37.7 dB at EMW frequency of 17.5 GHz. The results indicate dynamic crests significantly improve the SE of the EMI for the flexible ferrofluid layer.
This work investigates the impact of dynamic magnetic fields on ferrofluid instability and electromagnetic interference (EMI) shielding effectiveness (SE) of a flexible ferromagnetic material. The ferrofluid crests varies with magnetic field strengths and oscillating frequencies. Fig. 1 shows the periodical instability of a ferrofluid layer subjected to an oscillating magnetic field with a frequency of 1 Hz within one period. The ferrofluid exhibits pulsating instability, with crests periodically appearing and disappearing. At a frequency of 5 Hz, due to the phase lag between the ferrofluid oscillation and the magnetic field, the number of crests decreases and their height varies, resulting in oscillatory instability. However, excessively high frequencies cause static instability, preventing the ferrofluid crests from synchronizing with the magnetic field oscillations, and eventually returning to a stable state. Fig. 2 shows the comparison of EMI SEs of a ferrofluid layer with pulsating, oscillatory, and statistic instability, respectively. Experimental results indicate that when the crests exhibit pulsating (magnetic field frequency at 1 Hz) or oscillatory states (magnetic field frequency at 5 Hz), the SE also changes correspondingly with the pulsating or oscillatory state of the crests. Without the influence of a magnetic field, the ferrofluid remains in a horizontal state with no crest formation, providing SE of nearly 19 dB at EMW frequencies of 13 GHz and 16 GHz. When a magnetic field strength of 40.5 mT without oscillation (f=0 Hz) is applied to the ferrofluid, the SE is slightly declined due to the reduction of the layer thickness. As an oscillation field with a frequency of 1 Hz is applied, the pulsating instability of the ferrofluid crests enhances the highest of the SE to nearly 40 dB at EMW frequency of 15 GHz. When the oscillating frequency increases to 5 Hz, the oscillatory instability of the ferrofluid crests causes the highest SE of 37.7 dB at EMW frequency of 17.5 GHz. The results indicate dynamic crests significantly improve the SE of the EMI for the flexible ferrofluid layer.