Novel broadband measurement technique on PCB cells for the field- and stress-dependent impedance in ferromagnetic wires

Abstract

The lack of broadband impedance measurements has restricted the potential capabilities of ferromagnetic wire composites, which have been mainly evaluated through theoretical impedance calculated from existing models without considering wire domain microstructure. Here, we have developed an accurate method for measuring the impedance of ferromagnetic wires in a wide frequency range, from 100 kHz up to 15 GHz, under magnetic and stress stimuli. The broadband measurements were ensured by a more accurate microwave calibration on the PCB cell, extending the reference planes up to the wire sample ends and by compensating the sample waveguide properties using the phase unwrapping technique proposed in this work. In addition, a specially designed dogbone PCB measurement cell allows both field-and stress-dependent impedance measurements, efficiently transferring the tensile stress from the cell to the wire sample fixed onto it. The measured wire impedance can be then recalculated into the surface impedance, which constitutes the boundary condition in the antenna equation, describing the microwave scattering properties of a wire. The developed approach will make it possible to build a practically predictive scattering theory in composite materials with embedded wire inclusions and thus their implementation in real-world applications, such as remote stress monitoring.

High-Frequency Magnetoimpedance (MI) and Stress-MI in Amorphous Microwires with Different Anisotropies

“…In this field range, the sensitivity of the impedance change was low, of about a few percent per Oe. Similar high-frequency impedance behaviors in these types of wires were demonstrated in a number of publications [14][15][16].…”

“…In this field range, the sensitivity of the impedance change was low, of about a few percent per . Similar high-frequency impedance behaviors in these types of wires were demonstrated in a number of publications [14][15][16]. To enhance the MI sensitivity, researchers have proposed various annealing regimes in order to establish a required transverse anisotropy of small amplitude and small easyaxes deviations [17][18][19][20][21].…”

“…When the static magnetization was along the wire ( and did not change by the field, only the permeability parameter determined the field behavior of the impedance: it increased with much lower slope, and an inflexion point was seen in the plot of . In this field range, the sensitivity of the impedance change was low, of about a few percent per Similar high-frequency impedance behaviors in these types of wires were demonstrated in a number of publications [ 14 , 15 , 16 ].…”

Soft Magnetic Amorphous Microwires for Stress and Temperature Sensory Applications

“…The wire length for impedance measurements was 11 mm. The impedance spectra were deduced from the S 21 parameter (two-port measuring scheme) after making the calibration procedure with specially designed PCB-microstrip cells [47]. The sample was placed inside a Helmholtz coil that produced a slowly varying magnetic field up to 3000 A/m.…”

“…If the parameter λs is small in the range of 10−8−10−7, it is important to consider its stress dependence. A linear dependence between λs and a tensile stress σa was experimentally established [27,43,47,48,50]:λs(σa)=λs0−βσa.…”