Study On Composite Magnetic Sensor Consisting Of Giant Magnetostrictive Material And SAW Resonator

Magnetic sensors are widely used: from magnetic detection to indirect measurement or control of many kinds of physical quantities which are related to magnetic filed. The magnetic sensing technology is progressing relatively with the emerge of new magnetic material. Terfenol-D, a giant magnetostrictive material, is increasingly employed in sensor and transducer due to its good performance such as quick responding and high magnetomechanical efficiency. SAW resonators which have many advantages such as stable frequency and small size, have been developed to detect various mechanical quantities such as pressure and accelerated velocity. A composite magnetic sensor consisting of Terfenol-D and a SAW resonator is researched. The resonant frequency of the SAW resonator varies with the stress induced magnetically. Resultantly, the magnetic intensity can be measured by the variation of the resonant frequency. Compared with traditional magnetic sensors, the composite magnetic sensor has the advantages of simple structure and low cost. Besides, it can work passively for wireless sensing.The main work is as follows:1. The stress sensing principle of one-port SAW resonator and the relationship between SAW resonant frequency and substrate strain are analyzed. Combined the principle and working modes of Terfenol-D, structure of the composite magnetic sensor is researched; the sensing structure of the composite magnetic sensor is constituted using two pieces of Terfenol-D gripping on the both sizes of SAW resonator.2. The static model of the composite magnetic sensor is established, and the stress of elastic sensing element is analyzed; the stress distribution on SAW substrate is simulated using finite element software ANSYS. According to the piezomagnetic equations and equilibrium of force, the output response of the magnetic sensor is analyzed, and the relationship between SAW resonant frequency and magnetic intensity is obtained. It is indicated that the sensitivity of the magnetic sensor is related to the piezomagnetic coefficient of Terfenol-D, length ratio and cross-sectional area ratio of Terfenol-D and SAW resonator.3. The experimental setup of the composite magnetic sensor is designed. The relationship between increment of SAW resonant frequency and magnetic intensity and the hysteresis characteristics curve are obtained separately in the static characteristic and the hysteresis characteristics experiment of the sensor. The experimental result indicates that the relationship between the output of the sensor and magnetic field is nonlinear due to nonconstant piezomagnetic coefficient of Terfenol-D. Besides, the sensitivity of the magnetic sensor is 40.6~341.6Hz/Oe, and the resolution of the magnetic field is 10-6~10-5 Tesla when the resolution of frequency detection is 1Hz and the frequency stability of SAW resonator is 0.1ppm.