Butta Mattia, Janošek Michal, Pařez Jakub, Inchausti Alexander Valeriano, Chiriac Horia
Faculty of Electrical Engineering, Czech Technical University in Prague, 166 27 Prague, Czech Republic.
Institute of Material Science of Madrid-CSIC, 28049 Madrid, Spain.
Sensors (Basel). 2022 Mar 10;22(6):2162. doi: 10.3390/s22062162.
Orthogonal fluxgates in fundamental mode based on (Co0.94Fe0.06)72.5Si12.5B15 cores have recorded very low noise in literature, especially if Joule annealing is performed on the core for a short period of time. However, for annealing time longer than 20-30 min, the noise of the sensor has a tendency to increase. In this work, we investigated this phenomenon, and we have found its origin in a monotonic increase of magnetostriction during the annealing process. We show that the wires with vanishing magnetostriction in their as-cast form exhibit positive magnetostriction after long-time annealing (more than 30 min), which increases the noise of the sensor. After researching the effect of the magnetostriction after annealing on the noise, we propose an alloy with a reduced amount of iron. Less iron leads to a larger as-cast negative magnetostriction, which becomes almost zero after long-time annealing (60 min), bringing further reduction of noise. We prove this effect on two wires from two different manufacturers, although with the same composition. The noise decrease with prolonged annealing is mainly observable in the low-frequency region: at 100 mHz, the noise of a single-wire sensor decreased from 20pT/Hz to 6pT/Hz when the annealing time was prolonged from 10 to 60 min.
基于(Co0.94Fe0.06)72.5Si12.5B15磁芯的基模正交磁通门在文献中记录到了非常低的噪声，特别是当对磁芯进行短时间的焦耳退火时。然而，当退火时间超过20 - 30分钟时，传感器的噪声有增加的趋势。在这项工作中，我们研究了这种现象，并发现其根源在于退火过程中磁致伸缩的单调增加。我们表明，铸态时磁致伸缩消失的导线在长时间退火（超过30分钟）后会出现正磁致伸缩，这增加了传感器的噪声。在研究了退火后磁致伸缩对噪声的影响后，我们提出了一种铁含量降低的合金。较少的铁会导致更大的铸态负磁致伸缩，在长时间退火（60分钟）后几乎变为零，从而进一步降低噪声。我们在来自两个不同制造商但成分相同的两根导线上证明了这种效果。随着退火时间延长，噪声降低主要在低频区域可见：在100毫赫兹时，当退火时间从10分钟延长到60分钟时，单线传感器的噪声从20皮特斯拉/赫兹降至6皮特斯拉/赫兹。
