A remarkably strong dependence of magnetoimpedance (MI) on tensile stress has been observed in the microwave frequency range for thin CoMnSiB glass-coated microwires exposed to a special thermal treatment. The MI ratio runs into more than 100% at 0.5-1.5 GHz when the tensile stress of 600 MPa is applied to the wire. It was demonstrated that a large MI change at such high frequencies is related predominantly with the dc magnetization orientation. A host of such microwires incorporated into a dielectric matrix may constitute a new sensing medium that is characterized by the stress-dependent effective permittivity. Such medium can be used for the microwave visualization of the stress distribution inside of a composite structure or on its surface.
Effect of the metal-to-wire ratio on the high-frequency magnetoimpedance of glass-coated CoFeBSi amorphous microwires
用高频[1-500 MHz]测量了玻璃包覆的Co $_{69.4}$ Fe $_{3.7}$ B $_{15.9}$ Si $_{11}$微丝的磁阻抗（MI）。观察到的双峰，无滞后行为作为磁场的函数。归一化阻抗的最大值$ΔZ$ / $Z$出现在频率$f$的不同值125、140和85 MHz处，相应的直径比$p$ = 0.80、0.55和0.32。我们描述的测量技术和解释我们的结果与一个热力学模型，导致更清楚地了解$p$对MI和各向异性场的最大值的影响。阻抗的实部和虚部的行为也进行了研究，它们显示的谐振，成为一个功能的DC字段$H_{DC}$的值大于或等于$H_{K}$的圆周各向异性场为每个$p $值。这些结果被解释的外壳磁化的旋转模型。
Current-modulation annealing to control microwave permittivity in composites with melt-extracted microwires
研究了采用电流调制退火（CCMA）技术制备的CoFeBSiNb微丝/环氧树脂复合材料的微波性能。当外加磁场增加时，我们观察到含有退火25 mm Nb掺杂微丝的复合材料样品的有效介电常数谱中的共振峰的位移。这一观察结果与厚微丝的吸收主导阻抗和铁磁共振现象是一致的。结果表明，CCMA是一种合适的技术，以释放内部残余应力。因此，对于含有少量Nb的样品，我们观察到CCMA允许我们抑制在含有铸态线材的样品中观察到的高频共振峰。然而，对于含有大量Nb的样品，尽管进行了CCMA处理，高频峰仍然存在。在这种情况下，在介电常数谱中的双峰特征的观察归因于共存的非晶相和少量的纳米微晶分布在导线表面。然而，由于长（35 mm）和短（15 mm）的铸态导线和不完美的导线-环氧树脂键合的大的静磁能，可以检测到的谐振峰和特征双峰的介电常数谱没有移动。总体而言，CCMA出现作为一个有前途的策略，以控制微波介电常数的复合材料与熔融提取的微丝。
