Metal-to-glass ratio and the Magneto-Impedance of glass-covered CoFeBSi microwires at high frequencies

High frequency [1-500 MHz] measurements of the Magneto-Impedance (MI) of glass-covered Co$_{69.4}$Fe$_{3.7}$B$_{15.9}$Si$_{11}$ microwires are carried out with various metal-to-wire diameter ratios. A twin-peak, anhysteretic behaviour is observed as a function of magnetic field. A maximum in $\Delta Z/Z$ appears at different values of the frequency $f$, 125, 140 and 85 MHz with the corresponding diameter ratio $p$ = 0.80, 0.55 and 0.32. We describe the measurement technique and interpret our results with a thermodynamic model that leads to a clearer view of the effects of $p$ on the maximum value of MI and the anisotropy field.Comment: 5 pages and 6 figure

Direct and Non-Invasive Monitoring of Battery Internal State Via Novel GMI-IDT Magnetic Sensor

Efficient battery management systems (BMSs) in rechargeable battery-based systems require precise measurements of various battery parameters including state of charge (SOC), state of health (SOH) and charge capacity. Presently, SOC, charge capacity and SOH can only be indirectly inferred from long-term measurement of current, open circuit voltage (OCV), and temperature using multiple sensors. These techniques can only give an approximation of SOC and often require knowledge of the recent battery history to prevent excessive inaccuracy.To improve the performance of the BMS, an alternative method of monitoring the internal state of Li-ion batteries is presented here. Theoretical analysis of Li-ion batteries has indicated that the concentration of active lithium ions in the cathode is directly related to the magnetic susceptibility of the electrode materials. While charging/discharging, due to the change in the oxidation and/or spin state of metal atoms, the magnetic moment in the cathode varies. This indicates the potential for directly probing the internal state of the Li-ion batteries during charging/discharging by monitoring the changes in magnetic susceptibility via an appropriately designed magnetic sensor. In this research, a highly sensitive micromagnetic sensor design is investigated consisting of a single interdigital transducer (IDT) shunt-loaded with a magnetically sensitive Giant Magnetoimpedance (GMI) microwire. This design takes advantage of the coupling of the impedance characteristics of the GMI microwire to the IDT transduction process. The initial GMI-IDT sensor design is further developed and modified to maximize sensitivity and linearity. The sensor can detect magnetic field in the range of 900 nT and minute changes less than 1 μT when operated at or near its peak sensitivity. In addition, an appropriate procedure for preconditioning the GMI wire is developed to achieve sensor repeatability. Furthermore, using the identified optimum geometry of the experimental setup, the proposed sensor is implemented in monitoring the internal state of two types of Li-ion cells used in electric vehicles (EVs). The initial characterization results confirm that the GMI-IDT sensor can be used to directly monitor the charge capacity of the investigated Li-ion batteries. Other possible applications also include energy storage for renewable energy sources, and portable electronic devices

Nanostructured giant magneto-impedance multilayers deposited onto flexible substrates for low pressure sensing

Nanostructured FeNi-based multilayers are very suitable for use as magnetic sensors using the giant magneto-impedance effect. New fields of application can be opened with these materials deposited onto flexible substrates. In this work, we compare the performance of samples prepared onto a rigid glass substrate and onto a cyclo olefin copolymer flexible one. Although a significant reduction of the field sensitivity is found due to the increased effect of the stresses generated during preparation, the results are still satisfactory for use as magnetic field sensors in special applications. Moreover, we take advantage of the flexible nature of the substrate to evaluate the pressure dependence of the giant magneto-impedance effect. Sensitivities up to 1 Ω/Pa are found for pressures in the range of 0 to 1 Pa, demostrating the suitability of these nanostructured materials deposited onto flexible substrates to build sensitive pressure sensors

Sensor Applications of Soft Magnetic Materials Based on Magneto-Impedance, Magneto-Elastic Resonance and Magneto-Electricity

The outstanding properties of selected soft magnetic materials make them successful candidates for building high performance sensors. In this paper we present our recent work regarding different sensing technologies based on the coupling of the magnetic properties of soft magnetic materials with their electric or elastic properties. In first place we report the influence on the magneto-impedance response of the thickness of Permalloy films in multilayer-sandwiched structures. An impedance change of 270% was found in the best conditions upon the application of magnetic field, with a low field sensitivity of 140%/Oe. Second, the magneto-elastic resonance of amorphous ribbons is used to demonstrate the possibility of sensitively measuring the viscosity of fluids, aimed to develop an on-line and real-time sensor capable of assessing the state of degradation of lubricant oils in machinery. A novel analysis method is shown to sensitively reveal the changes of the damping parameter of the magnetoelastic oscillations at the resonance as a function of the oil viscosity. Finally, the properties and performance of magneto-electric laminated composites of amorphous magnetic ribbons and piezoelectric polymer films are investigated, demonstrating magnetic field detection capabilities below 2.7 nT.The authors would like to thank the financial support from the Basque Government under ACTIMAT (Etortek program), PE12UN025 (Saiotek program) and IT711-13 (Research Groups) projects; and from the Spanish Government under project MAT2011-27573-C04. Andoni Lasheras wants to thank the Basque Government for financial support under PhD Grant. Technical and human support provided by SGIker (UPV/EHU), especially by Inaki Orue, is gratefully acknowledged

Magnetic microwires with unique combination of magnetic properties suitable for various magnetic sensor applications

There is a pressing demand to improve the performance of cost-effective soft magnetic materials for use in high performance sensors and devices. Giant Magneto-impedance effect (GMI), or fast single domain wall (DW) propagation can be observed in properly processed magnetic microwires. In this paper we have identified the routes to obtain microwires with unique combination of magnetic properties allowing observation of fast and single DW propagation and GMI effect in the same microwire. By modifying the annealing conditions, we have found the appropriate regimes allowing achievement of the highest GMI ratio and the fastest DW dynamics. The observed experimental results are discussed considering the radial distribution of magnetic anisotropy and the correlation of GMI effect, and DW dynamics with bulk and surface magnetization processes. Studies of both Fe- and Co-rich microwires, using the magneto-optical Kerr effect, MOKE, provide information on the magnetic structure in the outer shell of microwires. We have demonstrated the existence of the spiral helical structure in both studied microwires. At the same time, torsion mechanical stresses induce helical bistability in the same microwires, which allow us to consider these microwires as materials suitable for sensors based on the large Barkhausen jump.This work was funded by Spanish MCIU under PGC2018-099530-B-C31 (MCIU/AEI/FEDER, UE) by the Government of the Basque Country under PIBA 2018-44 project and Elkartek (CEMAP and AVANSITE) projects and by the University of Basque Country under the scheme of “Ayuda a Grupos Consolidados” (Ref.: GIU18/192)