Stress and field contactless sensor based on the scattering of electromagnetic waves by a single ferromagnetic microwire

Abstract

In this paper, we report an experimental study on the microwave modulated scattering intensity for a single Fe2.25Co72.75Si10B15 amorphous metallic microwire. The modulation is driven by applying a bias magnetic field that tunes the magnetic permeability of the ferromagnetic microwire. Furthermore, by using a magnetostrictive microwire, we also demonstrate that the microwave scattering is sensitive to mechanical stresses. In fact, we present a wireless microwave controlled stress sensor, suitable for biological applications, as a possible use of this effect. In addition, a first order theoretical approximation accounts for the observed influence of the magnetic permeability on the scattering coefficients. That model leads to predictions in good agreement with the experimental results.

Liquid pressure wireless sensor based on magnetostrictive microwires for applications in cardiovascular localized diagnostic

“…As shown in Ref. 30, the application of the stress induces a magnetoelastic anisotropy, with strength given by the product of the stress and the magnetization constant, that decreases the relative permeability, µ r of the microwire. Figure 2b shows the Fast Fourier Transform of curves in Figure 2a to quantify the frequency and amplitude of the signals.…”

“…The scattering coefficient is directly related to the electrical current induced along the microwire by the incident wave that can be modified by the magnetic permeability of the microwire. 30 The a.c. bias field gives rise to a modulation of the microwire permeability that, through its effect on the induced current, is reflected as a modulation of the scattering coefficient S 21 . …”

“…The modulation of the S 21 parameter shown in Figure 2a is produced by the application of a bias field with frequency f bias = 100 mHz although the modulated signal shows a frequency of f mod = 200 mHz, which is exactly twice the value of the bias frequency due to the tuning of the scattering by sample magnetization. 30 Moreover, the use of even a weak magnetostrictive microwire, as the one chosen, allows us to modify its magnetic permeability by application of mechanical stresses. It can be noticed how the modulated pattern of S 21 is modified under the application of the different mechanical stresses and correlated with the silicon test tube strain.…”

“…29 In the frequency range of GHz some experimental and theoretical studies of the effect of the magnetization on the scattering properties of a single microwire have been recently developed. 30 This kind of work gives experimental evidence showing that the microwave scattering by a single microwire depends on the magnetic permeability with sufficient strength to be experimentally detected as an effect of the GMI.…”

“…The coercive field measured under a 10 Hz applied field is 3 Oe. The relative permeability of the microwire changes between 800 and 2 when the applied field varies between 0 and 20 Oe, 30 respectively. We selected this composition because, as stated above, Co rich microwires are well known to exhibit a noticeable high GMI effect.…”