## 5 Conclusions  
By combining GMM magnetostriction and the FBG grating sensing approach, a GMM-FBG current sensor is designed with a soft ferrite as the magnetic conduction material for detecting a large electric current in a high-voltage power system. Conforming to the complete nonlinear constitutive model for the GMM material, the temperature drift characteristics and mechanism of ferrite-GMM current detection assembly are analyzed through finite-element multi-physics simulations of correlating solid mechanics, magnetostatics and thermal expansion. The Bragg wavelength response of the GMM-FBG optical modulator at various temperatures is evaluated by elasto-optics and multi-physics simulations of coupling magnetostriction and thermal strain to elucidate the temperature drift characteristics and mechanism. In addition to the full-coupling model of the GMM rods, the physical field of thermal expansion is also comparatively correlated to the magnetostatic field in the ferrite magnetizer to analyze the thermal strain effect on the magnetic-strain response of the ferrite-GMM assemblage.  
It is indicated by the temperature-drifted magnetostrictive stress-strain relations that the slope of the stress-strain curve decreases to inhibit GMM magnetization as the temperature increases, while the GMM rod tends to saturate in magnetization as the temperature inhibition fades away in the high-stress region of large current excitation. In addition, the magnetic flux abatement caused by thermal expansion in the GMM rod accounts for the dominant degradation of magnetostrictive performance. The significant difference in the expansion coefficients of FBG and GMM being cemented to each other on the side surface leads to thermal stress as temperature varying in the GMM-FBG modulator, which reduces the sensitivity and range of this current sensor. Finally, the sensing characteristics of the GMM-FBG current sensor at various temperatures achieved by multi-physics finite-element simulations are numerically fitted to a temperature-drift function, which provides a valuable insight into the scale calibration required for highly accurate current measurements in the elevated temperature environment.  
Conceptualization, investigation, W.-F.S.; methodology, formal analysis, data curation, Y.L.; resources, project administration, funding acquisition, W.Z.; writing--original draft preparation, writing--review and editing, W.-F.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Science and Technology Project of Shenzhen Power Supply Bureau Co., Ltd. (Grant No. 09000020220301030900517) and the National Research Foundation, SP Group, Energy Market Authority of Singapore and Nanyang Technological University under Energy Programme (Grant No. EMA-EP010-SNJL-002). Grand No. KFKT202210 from Key Laboratory of Special Machine and High Voltage Apparatus (Shenyang University of Technology), Ministry of Education.  
Not applicable.  
Not additional data are available.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.