| The dipolar interaction in soft magnetic materials will affect the magnetic properties and the practical application as sensing elements.Hence,it is crucial to investigate the mechanism and key factors of the dipolar interaction for the design of sensing element and its application.In this thesis,heat treatment was employed to ameliorate the magnetic properties of acousto-magnetic ribbons.The variation of acousto-magnetic properties and bias field matching of the multiple ribbons with the ribbon number was studied.The dipolar interaction between ribbons was revealed by measuring the hysteresis loops of the ribbon(OverR)N and the heterostructure acousto-magnetic marker(OverR)N/Bias R.The symbols of OverR,Bias R represent the overlapped ribbon and the bias magnet ribbon,respectively.A dipolar magnetization model was employed to reveal the dependence of dipolar interaction on the reverse magnetization process and the acoustic-magnetic properties of multiple ribbons.Furthermore,the influence of geometric structure of multiple ribbons on the dipolar interaction and magnetic properties of the materials were also studied.In addition,we have designed two kinds of FINEMET ribbons,i.e.(OverR)N,(OverR/I)N/Probe R.The symbols of OverR,I and Probe R represent the overlapped ribbon,the insulator and the Probe ribbon.The influence of dipolar interaction on anisotropy between ribbons was investigated by transversal magneto-impedance effect(TDGMI)and longitudinally driven magneto-impedance effect(LDGMI).The results showed that the TDGMI effect of Probe R ribbon and the LDGMI effect of OverR ribbon were highly correlated with the dipolar interaction between FINEMET ribbons.The main contents and results are as follows:1.The influence of dipolar interaction on the properties of acousto-magnetic marker:(1)In composite structural acousto-magnetic marker(OverR)N,the anisotropy field increases with the number of ribbons because of the additional dipolar field between OverR ribbons,so the external magnetic field corresponding to the maximal resonance amplitude gradually moves to higher field.(2)The magnetic dipolar interaction is barely affected by the distance between OverR ribbons in 0-1.0 mm range.(3)By adding the bias magnet ribbon Bias R,the magnetization reversal fields of both materials all move to high magnetic field,as dipolar field between ribbons and the dipolar field of ribbons over the bias magnet increased.(4)The magnetic dipolar field linearly superimposes on on the anisotropic field.This relation is verified by a dipolar magnetization model.The dipolar field of 1.60 Oe between two OverR ribbons with the length of 38.5 mm,the width of 6 mm and the thickness of 0.03 mm and the geometric factor of 2.00*10-4 can be estimated.2.The influence of dipolar interaction in Fe-based nanocrystalline ribbon on the TDGMI:(1)In composite structural FINEMET ribbon(OverR/I)N/Probe R,the transversal GMI Probe R ribbon effectively detected a platform caused by the dipolar field from neighboring ribbon(OverR/I)N and the width of platform was in accordance with the shift of peak of GMI curves before 10 MHz.The analysis of the dipolar magnetization model shows that it is attributed to the linear superposition of the dipolar field on the peak field and the platform terminal field.The dipolar field generated by one OverR ribbon with the length of 26 mm,the width of 0.6 mm and the thickness of 0.033 mm and its geometric factor are calculated about 0.30 Oe and 2.42*10-5,respectively.The magnetic dipolar interaction decreases the effective permeability of the probe strip,and then raises the characteristic frequency and maximum MI.(2)The distance between two OverR ribbons changing in 0-0.7 mm range barely affected the dipolar interaction while the interaction decreases with increasing the length of OverR ribbon because of a decreasing in its geometric factor.When the driving current varies in the range of 2 ~ 20 m A,it does not affect the Probe R ribbon to measure the dipolar field produced by the OverR ribbon.In 10 k Hz-10 MHz range,the terminal field shifting is never affected by frequency.Nevertheless,the peak field shifting seriously affected by eddy current loss and rotation damping after 10 MHz,thus it cannot reflect the dipolar interaction in high frequency.3.The influence of dipolar interaction in Fe-based nanocrystalline ribbon on the LDGMI:(1)In composite structural FINEMET ribbon(OverR)N,the "bell-shaped" curve of LDGMI broadens as a whole affected by the dipolar interaction among the OverR ribbons.The analysis of the dipolar magnetization model shows that this is due to the linear superposition of the dipolar field on the nucleation field and the platform terminal field.The dipolar field generated by one OverR ribbon with the length of 26 mm,the width of 0.6 mm and the thickness of 0.033 mm and its geometric factor are calculated about 0.49 Oe and 3.95*10-5,respectively.The magnetic dipolar interaction decreases the effective permeability of the Probe R ribbon,and then raises the characteristic frequency and maximum MI.(2)The geometric factor increases with the length decreasing of the OverR ribbon,thus it brings higher dipolar field.The driving current varying in the range of 0.3~3 m A,the driving field does not affect the dipolar field produced by the OverR ribbon.In 10 k Hz-10 MHz range,there are greater eddy-current losses under the nucleation field than under the terminal field,then the former changes more than the latter with the frequency.But the dipolar field decreases slightly.3.The influence of dipolar interaction in Fe-based nanocrystalline ribbon on the GMI sensor:(1)A micro MI sensor based on planar spiral coils is developed.The multi-core is adopted to ensure the performance of the sensor after miniaturization,which meets the practical requirements.(2)The multi-core and the dipolar interaction among them simultaneously modulates the sensitivity and bias field of the sensor.The sensor with five cores for detecting iron gear can be operated to detect the distance up to 3 mm,which is favorable for wheel speed sensor. |
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