Multi-Mode Love-Wave SAW Magnetic-Field Sensors

Abstract

A surface-acoustic-wave (SAW) magnetic-field sensor utilizing fundamental, first- and second-order Love-wave modes is investigated. A 4.5 μ m SiO2 guiding layer on an ST-cut quartz substrate is coated with a 200 n m (Fe90Co10)78Si12B10 magnetostrictive layer in a delay-line configuration. Love-waves are excited and detected by two interdigital transducers (IDT). The delta-E effect in the magnetostrictive layer causes a phase change with applied magnetic field. A sensitivity of 1250 ° / m T is measured for the fundamental Love mode at 263 M Hz . For the first-order Love mode a value of 45 ° / m T is obtained at 352 M Hz . This result is compared to finite-element-method (FEM) simulations using one-dimensional (1D) and two-and-a-half-dimensional (2.5 D) models. The FEM simulations confirm the large drop in sensitivity as the first-order mode is close to cut-off. For multi-mode operation, we identify as a suitable geometry a guiding layer to wavelength ratio of h GL / λ ≈ 1.5 for an IDT pitch of p = 12 μ m . For this layer configuration, the first three modes are sufficiently far away from cut-off and show good sensitivity.

A Model for the Magnetoimpedance Effect in Non-Symmetric Nanostructured Multilayered Films with Ferrogel Coverings

“…This fact is due to a decrease of the transverse permeability in the magnetic sub-layers under action of the stray fields. The dependences shown in Figure 4 describes qualitatively experimental results obtained previously [ 5 , 7 , 20 , 34 ]. The calculated frequency dependences of (Δ Z / Z ) max are similar for both the positions of the ferrogel layer, however, the maximum MI ratio is higher when the ferrogel is placed onto the surface of thin multilayer ( Figure 4 ).…”

“…The influence of the stray fields induced by MNPs on the frequency dependence of the maximum MI ratio is illustrated in Figure 4 . The presence of the stray fields results in a decrease of (Δ Z / Z ) max value with an increase of the concentration of MNPs in the ferrogel [ 7 , 34 ]. This fact is due to a decrease of the transverse permeability in the magnetic sub-layers under action of the stray fields.…”

“…In general, magnetic sensors can be divided into two groups: magnetic sensors for label-free detection processes [ 3 , 4 ] and magnetic devices for detection of magnetic labels [ 1 , 2 , 5 , 6 ]. Although label-free magnetic detector prototypes were of special interest recently [ 7 , 8 ], a major part of the studies is related to the possibility to detect magnetizable nanoparticle concentrations [ 9 , 10 ]. There are different solutions for the detection: in “in vitro” experimental models [ 1 , 10 , 11 , 12 ], nanoparticles inside living cells [ 13 , 14 ], in continuous flow in medical devices or in blood flow [ 15 , 16 ], as a part of the implants or embedded into a natural tissue or artificial composites mimicking a natural tissue [ 5 , 17 , 18 , 19 ].…”

Roadmap on Magnetoelectric Materials and Devices

“…Depending on the design, i.e., delay line length and wavelength, bandwidths of up to 1 MHz can be achieved making them particularly interesting for artificial current sensing [431]. Higher order Love modes can also be excited, but generally show lower sensitivities than the fundamental mode [432]. However, with a guiding layer to wavelength ratio of about 3/2, three different modes can be excited simultaneously, while providing sufficient sensitivities.…”

Magnetoelastic Coupling and Delta-E Effect in Magnetoelectric Torsion Mode Resonators

“…It has been used for a different kind of delta-E effect sensors where shear waves, traveling through the magnetoelastic material, are influenced by the delta-E effect. This concept was realized with bulk acoustic shear waves in amorphous ribbons [ 38 ] and recently with surface acoustic shear waves in magnetic thin film devices [ 10 , 39 , 40 , 41 , 42 ]. Only very few studies investigate torsion modes in beam structures [ 43 , 44 ], either with electrostatically actuated cantilevers [ 43 ] or double-clamped beams [ 44 ].…”