Theoretical and experimental study of layered SAW magnetic sensor

Abstract

In this paper we implement full model using Comsol Multiphysics software, leading to study both SAW structures, resonator and delay line. A general finite element method (FEM) of two-dimensional piezo-magnetic devices is used. In magnetostrictive thin film, a coupling between AC/DC module and structural mechanics module was implemented by adding appropriate terms to the subdomain variables for strain and magnetic field. The methodology was first validated using SAW resonator based on Quartz substrate and Nickel IDT. Variation of resonance frequency, quality factor and electromechanical coupling coefficient were investigated versus magnetic field intensity and direction and compared with published experimental results. The model was then considered to study original structures and predict their behaviors and sensitivities to magnetic fields. Thus both SAW structures Ni/ZnO/IDT/LN-Y128 and Ni/Al2O3/IDT/LN-Y128 were investigated. The first one simulated and realized experimentally shows a moderate sensitivity 0.65 ppm/mT when the fundamental SAW is considered (159 MHz) and 2.1 ppm/mT when considering the third pseudo-harmonic (460 MHz). For the second structure, the sensitivity was enhanced by a factor 9 using comparable operating frequency while a sensitivity of 31.5 ppm/mT is obtained when considering device operating at 815 MHz.