A Study of Triaxial Fluxgate Magnetometer

A Study of Triaxial Fluxgate Magnetometer Yue Zhang1, a, Chenxiao Cao2,b 1Beijing Nano Tesla Technology Co. Ltd, Beijing 100074, China

2Beijing Nano Tesla Technology Co. Ltd, Beijing 100074, China

azhangyue@nano-tesla.com, bcaochenxiao@nano-tesla.com

Keywords: Fluxgate magnetometer, triaxial Fluxgate magnetometer, high temperature, high resolution

Abstract. This paper is devoted to study triaxial fluxgate magnetometer, and it begin with principle of fluxgate magnetometer, and then its structure, electric design and test result analysis are introduced. At present, its development tendency is to simplify and miniaturize, we carried out study of triaxial fluxgate magnetometer. Its technical specifications such as resolution, noise, response of step up, setting up time and sensitivity meet or even better than original design requirements. At first design of triaxial fluxgate magnetometer is determined and a transducer is developed. Secondly, a high temperature circuit is developed with SOI (Silicon on Insulator) electronics wafer and hybrid circuit technology. At last, 5 specifications test results are presented from aspects of high temperature and high accuracies, respectively.

Introduction Fluxgate magnetometer is a sensor, which measures weak magnetic field with non-linearity between magnetic induction and density of high-ductility magnetic core under satisfactory excitation condition[1-2]. Compared with other magnetic test equipments, fluxgate magnetometer has many advantages such as: high resolution and wide range of measurable weak magnetic field, and it is reliable, simple, economic and durable, also it is can be used in measuring components of magnetic field and in movement situation[3-4]. So from its beginning in 1930’s, it has been obtained continually development and improvement, and has been used in wide range of application, such as geomagnetic research, geo-exploration, weapon, intelligence, undestroyed flaw detection and space magnetic field measurement research[5]. Because of its comprehensive technical and economic advantages, fluxgate device is needed by wide application range, and it has many sorts. Its development tendency is resulted from its defects and insufficient, which make it difficult to meet real requirement [6-7]. There are four direction of its development: to raise test temperature, accuracy, resolution, and to develop triaxial in one fluxgate magnetometer of small size. There are few related literatures about triaxial fluxgate magnetometer; also there are no robot products of triaxial fluxgate magnetometer [8-9]. This paper introduced a triaxial fluxgate magnetometer, which possesses three orthogonal measurement coils. These three coils produce three measurements axial. There is one permeable core in the center of three coils, and this core is working with three coils to become the sensor of triaxial fluxgate magnetometer, and allows the three magnetic field components simultaneously measuring at the same point in space. With SOI (Silicon on Insulator) electronics wafer and hybrid circuit technology, the triaxial fluxgate magnetometer can work in wide temperature range from -50℃ to +210℃. So it is suitable for down deep hole drilling application and high temperature hole drilling application. Also it is suitable for ultra-reliable application such as defense, aeronautic and aerospace. Accuracy-guaranteed operation temperature range is from -50℃ to +185℃, its setting up time is 20mS, response of step up is 10mS, and resolution is 10nT. Its noise is about 10 nT. So it is able to be used in wide application range. 1 Structure of Triaxial Fluxgate Magnetometer 1.1 Structure Principle Triaxial fluxgate magnetometer (see Fig 1.1) is composed of excited circuit, fluxgate magnetometer and measurement circuit. Fluxgate magnetometer is its important component part. Triaxial fluxgate magnetometer presented in this paper, has three coils, which construct three measurements axial. There is a permeable core in the center of three coils for operation with three coils. Three coils and a core construct triaxial fluxgate magnetometer, which can be used for measuring magnetic field at a point in space, and measuring three components of magnetic field.

Fig 1.1 Triaxial fluxgate magnetometer 1.2 Design of Triaxial Fluxgate Magnetometer Triaxial fluxgate magnetometer (illustrated in Fig 1.2) is composed of magnetic core; measurement coil and measurement pedestal, and later is a hexahedron. There are three axial: X axis, Y axis and Z axis, and the measurement coils are around these axial. Inner cavity of hexahedron is used for installing magnetic core. This cavity is constructed from two orthogonal rings. Magnetic core, measurement pedestal make three measurement axial (X, Y, Z) spaces symmetrically. Magnetic core is made of permeable material, and excitation coil is around magnetic core. Excitation coil and measurement coil are connected with patch board. Magnetic core and pedestal should have the matched heat expansion coefficient [10]; coils should be durable under high temperature, and excellent insulators.