Study On Magnetic Sensor With Quartz Tuning Fork

In modern measurement, sensors are efficient approaches to get information and magnetic sensor is a class of sensors especially suitable for various applications such as aerospace, industrial automation, transportation and environmental monitoring etc. Utilizing the property of high transduction efficiency from magnetic energy to mechanical energy and quick response, Terfenol-D(TbxDy1-xFe2-y), which is a kind of giant magnetostrictive materials, is widely used in magnetic sensors. However, magnetostrictive/piezoelectric magnetic sensors have lower quality factor and higher energy dissipation. We will study the composite sensor with new structure in order to improve the mechanical quality factor.Considering that a U-shaped quartz tuning fork has the properties of being compact in volume with rather simple shape, possessing high mechanical quality factor and low cost, our research group developed a new high-Q composite magnetic sensor with Terfenol-D and a quartz tuning fork. This kind of magnetic sensor consists of a tuning fork covered with a magnetic-film, a Terfenol-D bar and a device of bias magnetic field. The Terfenol-D bar stresses in magnetic field, which brings on the change of magnetic field around the composite tuning fork and correspondingly the resonant frequency of the tuning fork is altered. Thus the magnetic field is sensed by measuring the change of the resonant frequency.The work presented in the thesis includes:①The piezoelectric effect and oscillation mode of quartz crystal, the species and performance parameters of magnetic materials are introduced. And moreover, the operating characteristics of magnetostrictive materials are described.②A composite magnetic sensor with mangtic-film and a quartz tuning fork is studied, and the principle of the magnetic sensor is analyzed.③A composite magnetic sensor using magnetostrictive material and a quartz tuning fork is studied, and the principle of the magnetic sensor is analyzed.④Another new high-Q composite magnetic sensor is studied. It consists of a tuning fork covered with a magnetic-film, a Terfenol-D bar, and a device of bias magnetic field. According to the operating characteristics of each part, the elementary operating principle of the composite magnetic sensor measuring external environment static magnetic field is analyzed. ⑤According to the theory of equivalent magnetic charge, the influences of the needle tip and the Terfenol-D bar on the magnetic field distribution are analyzed. Magnetic field distribution with the needle tip is also analyzed based on the simulation model of a bias magnetic field by using Ansoft finite element software.⑥Experimental setup is built in order to test the frequency variation or the mechanical quality factor alternation in the composite magnetic sensor. The resonant frequency change vs. magnetic field is acquired. The testing results indicate that the sensitivity of the composite magnetic sensor can reach 24.1Hz/mT, and the mechanical quality factor of the magnetic sensor can reach 8000.