Magnetic SAW RFID Sensor Based on Love Wave for Detection of Magnetic Field and Temperature

TL;DR

This paper presents a Love wave-based magnetic and temperature sensor using a layered ZnO/LiNbO3 structure with differential measurement for accurate magnetic field detection and RFID capability.

Contribution

It introduces a novel reflective delay line configuration with dual paths for simultaneous magnetic and temperature sensing, enhancing accuracy and enabling RFID integration.

Findings

High sensitivity to temperature (-63 ppm/°C) and magnetic field (-781 ppm/mT).

Effective temperature compensation via differential measurement.

Good repeatability across temperature variations.

Abstract

Magnetic field measurement including a temperature compensation is essential for a magnetic field sensor. This study investigates a magnetic surface acoustic wave (MSAW) sensor in a reflective delay line configuration with two acoustic propagation paths with and without magnetic field sensitive layer. The delay in path with sensitive layer leads to magnetic field detection and the one without enable temperature measurement and thus compensation for the first path. The developed sensor is based on a ZnO/LiNbO$_3$ Ycut (X-direction) layered structure as Love wave platform. Love wave as a shear wave being more favorable for magnetic detection. Co-Fe-B is considered as sensitive layer to detect magnetic field changes and is deposited on the top of ZnO, but only on one of the two paths. We combined an original configuration of connected IDTs with a high electromechanical coupling coefficient (K$^2$) mode to improve the signal amplitude. The achieved sensor exhibits a high temperature and magnetic field sensitivity of -63 ppm/$^\circ$C and -781 ppm/mT, respectively. The temperature compensation method for magnetic field measurement is demonstrated using a differential measurement by subtracting the delay times obtained for the two paths with and without the sensitive layer. Finally, The sensor exhibited good repeatability at various temperatures. Moreover, the device developed allows in addition to the multisensor functionality, the radio frequency identification (RFID) which is necessary for the deployment of sensor networks.