Multi-Mode Love-Wave SAW Magnetic-Field Sensors

A surface-acoustic-wave (SAW) magnetic-field sensor utilizing fundamental, first- and second-order Love-wave modes is investigated. A [Formula: see text] SiO(2) guiding layer on an ST-cut quartz substrate is coated with a 200 [Formula: see text] [Formula: see text] (Fe(90)Co(10))(78)Si(12)B(10) 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 [Formula: see text] / [Formula: see text] [Formula: see text] is measured for the fundamental Love mode at 263 [Formula: see text] [Formula: see text]. For the first-order Love mode a value of 45 [Formula: see text] / [Formula: see text] [Formula: see text] is obtained at 352 [Formula: see text] [Formula: see text]. 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 [Formula: see text] for an IDT pitch of [Formula: see text]. For this layer configuration, the first three modes are sufficiently far away from cut-off and show good sensitivity.