Sensor applications of soft magnetic materials based on magneto-impedance, magneto-elastic resonance and magneto-electricity

Abstract

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.

Figure 1.

Schematic description of the Magneto-Impedance multilayer sandwiched (MS) structure used in this work. Each sample has different Py thickness (Δ) and different number of repetitions of the [Py/Ti] structure (3, 6 and 12 for samples MSPy100, MSPy50, and MSPy25, respectively), being the Cu central conductor of 500 nm in all cases.

Figure 2.

Vibrating sample magnetometer (VSM) hysteresis loops measurements, with the applied magnetic field perpendicular to the easy axis.

Figure 3.

Distribution of perpendicular anisotropies from the second harmonic response.

Figure 4.

Schematic view of the closing magnetic flux at the lateral edges of the [Py(100 nm)/Ti] ₃ and [Py(50 nm)/Ti] ₆ multilayers.

Figure 5.

Relative magneto-impedance and sensitivity as a function of the applied magnetic field at 40 MHz.

Figure 6.

Frequency dependence of the maximum value of the ΔZ/Z ratio, maximum value of the ΔR/R ratio, maximum value of the sensitivity s [(ΔZ/Z)/ΔH] and maximum value of the sensitivity of the real part of the impedance s [(ΔR/R)/ΔH] for the three multilayer sandwiched structures.

Figure 7.

Magnetoelastic resonance of an amorphous ribbon. The inset shows the dependence of the resonant frequency on the applied magnetic field.

Figure 8.

(a) The magnetoelastic sample is glued to a glass rod, fixed to the cap of the vial; (b) When the cap is fitted to the vial, the sample is immersed in the oil.

Figure 9.

Fitting of a measured resonance curve to Equation (3). Best fit parameters are: f_r = 56.73 kHz; δ_r = 0.0022; f_a = 60.82 kHz; δ_a = 0.0121; A = 38.07 mV; 2πa = 8.57 × 10⁻⁶ mV/Hz; b = −55.97 mV.

Figure 10.

Magnetoelastic resonance curves measured for oils with different viscosities. The dashed lines correspond to the fitting of the experimental curves to Equation (2).

Figure 11.

Dependence of best-fit parameters on oil viscosity η. (a) Amplitude of the resonance; (b) Resonance frequency; (c) The resonance frequency shift (from the resonance frequency in air) scales with the square root of the product of the viscosity times the density of the oil; (d) Damping parameter.

Figure 12.

Measured remnant polarization as a function of temperature for commercial PVDF piezoelectric polymer and the new piezolelectric 2,6(β-CN)APB/ODPA (poly-2,6) polyimide.

Figure 13.

Geometry of the three-layer L-T sandwich configuration: magnetostrictive ribbons are longitudinally magnetized while the piezoelectric polymers were transversely poled.

Figure 14.

Measured α_ME magnetoelectric coupling coefficient for our L-T type laminated composite with VITROVAC 4040^® as magnetostrictive constituent and ceramic PZT or PVDF polymer as piezoelectric constituent. Sizes of the devices are almost the same, as hinted by their close resonant frequencies.

Figure 15.

Room temperature measured α_ME magnetoelectric coupling coefficient for our L-T type laminated composite with METGLAS 2826 MB as magnetostrictive constituent and a 40/60 copolyimide as piezoelectric constituent. Reprinted with permission from [56]. Copyright 2013 IEEE Xplore.

Figure 16.

Magnetoelastic resonance curves measured for different ribbon pieces with length ranging from 4 cm to 1 cm. The inset shows also the measured resonance frequency and the induced signal at the resonance, as a function of the length of the resonant magnetostrictive ribbon.