磁场对铁磁结构动态特性的影响

研究了两种铁磁材料结构(板梁和圆柱壳)在不同的磁场下固有频率的变化。频谱分析仪产生的扫频正弦信号通过压电陶瓷片对试件进行激励;压电薄膜作为感知元件再把感知信号送回频谱分析仪。根据共振原理,从频谱分析仪的频率响应曲线可以得到试件的各阶固有频率。通过改变外加磁场的大小,用同样的方法可以得到不同磁场下的固有频率。实验结果表明,铁磁板梁固有频率的变化很大程度上依赖于所施加磁场的方向:当磁场顺着板梁的长度方向时,板梁的固有频率会随着外加磁场的增大而增大;然而当磁场施加在板梁的厚度方向时,固有频率是先降低然后再升高。对铁磁材料圆柱壳,当磁场顺着圆柱壳的轴线方向增大时固有频率是逐渐增大然后达到一个饱和值。

Effect of Magnetic Field on the Dynamic Behavior of Ferromagnetic Structures

In this paper,variation of the natural frequency of two types of ferromagnetic structures(i.e.,beam-plate and circular cylindrical shell) due to the applied magnetic field was investigated.The sweeping sine singles from Frequency Spectrum Analyzer actuated the specimen by piezoelectric ceramic.PVDF working as sensors sent the responding singles back to Frequency Spectrum Analyzer.According to the theory of resonance,the natural frequencies of the specimen can be obtained from the frequency responding curve.The same processing can be conducted to obtain the natural frequencies of each mode by changing the magnitude of the external applied magnetic field.The obtained results show that shift of the natural frequencies of beam-plate depends strongly on the direction of the applied field.When the magnetic field is along the length direction of the beam-plate the natural frequencies increase with increasing the magnitude of magnetic field,confirming available model predictions.However,when the magnetic field is in the thickness direction and increases gradually the natural frequency decreases first before it increases again.For the ferromagnetic cylindrical shell,the natural frequencies of the shell increase and finally reach a saturating state with increasing the magnitude of the magnetic field applied in the axial direction.