基于“磁滞复用”的超宽频（DC-10kHz）弱磁传感器技术研究

On the research of mineral resources in deep, oil and gas resources, scale and structure of the lithosphere and its features of dynamics, electromagnetic exploration is one of the important tools using broad frequency magnetic sensor. Broad frequency magnetic sensor is always developing towards the trends of more broad application frequency band,higher sensitivity, lower noise level and suitable for array electromagnetic exploration simultaneously. This project presents an approach to multiplexing the hysteresis loop features of magnetic material with the shape of long and straight, which break out the traditional thought on the magnetic sensor design for electromagnetic exploration. This project employs bidirectional saturation feature of hysteresis loop to measure super long period magnetic field. To measure magnetic field with middle or high frequency, relative magnetic permeability at the neighborhood of arbitrary point in linear working area of hysteresis loop is adopted as magnetic amplifier, combined with induction loop. The project will resolve the key problem of super broad frequency magnetic sensor and its miniaturization. The main researches are as following: Firstly, to optimization configuration of the hysteresis loop, the spatial distribution of the magnetic flux of long and straight magnetic material is studied as well as the relationship between the structure of magnetic material and itself; Secondly, the characteristics of the sensitivity and noise level of magnetic field versus frequency needs to be analyzed ,which are measured by hysteresis loop bidirectional saturation and magnetic amplifier effect respectively; The third is to analyze statistical regularity of the measurement precision of bidirectional saturation magnetic detecting based on stochastic resonance; The fourth is to remove the 1/f noise of induction magnetic based on multi-route and double chopper and further to suppress the entire noise; Finally, the sensor is precisely self-calibrated. The goal of the project is to develop a novel sensor for weak magnetic signal with super broad frequency band of DC-10kHz.

深部矿产资源、油气资源、岩石圈尺度结构、构造及动力学特征等研究中，应用宽频磁传感器的电磁法探测为其重要工具之一。宽频磁传感器始终在向更宽应用频带、更高灵敏度及更低噪声水平方向发展，同时适用于阵列式电磁探测。本项目突破国际上电磁探测用磁传感器设计的传统思维，复用长直磁性材料磁滞回线特性，利用其双向饱和时间差测量超长周期磁场，利用其线性区某点及该点临域的相对磁导率作为磁放大器结合感应线圈测量中高频磁场，研究超宽频磁传感技术及其小型化问题。主要研究长直磁性材料磁通的空间分布及其与尺寸结构的关系，以优化磁滞回线形态；双向饱和式磁场测量与磁放大效应的感应式磁场测量二者灵敏度与噪声水平随频率的变化规律；基于随机共振的双向饱和式磁场测量精度统计规律分析；基于多径双斩波的感应式磁场测量的1/f噪声抑制及总体噪声优化；传感器精密自标定方法。最终实现可测量DC-10kHz超宽频弱磁信号的新型传感器。

本项目基于磁芯“磁滞复用”原理，突破单一磁通门传感器或感应式磁传感器测量瓶颈，研制一种低噪声、超宽频（DC-10kHz）磁传感器。首先分析并推导感应式磁传感器基本参数数学公式，并进一步建立感应式磁传感器噪声、重量等指标模型，采用罚函数法求解此模型，最终得到传感器最佳参数配置。采用前置并联JFET结构搭建低噪声前置放大电路，实际测试等效输入电压噪声2.1nV√Hz。针对RTD磁通门传感器，主要研究了新型磁通门传感器——时间差（RTD）型磁通门传感器的原理及数学模型，通过对磁芯退磁效应和感应信号幅值的计算指导时间差型磁通门传感器敏感元件的设计，并且采用动态反正切模型和双稳态势能模型对磁芯动态磁滞回线进行拟合，预测RTD传感器的输出和分析工作中的RTD磁通门传感器的磁滞回线形态，最后进行磁通门传感器系统检测电路的设计，得到的RTD磁通门传感器的灵敏度指标为0.0268 us/nT，噪声指标小于100 pT/√Hz。在详细分析感应式磁传感器及RTD磁通门传感器工作机理及数学模型的基础上，提出一种新型感应式磁传感器与RTD磁通门复合宽频测磁方法，RTD磁通门与感应式磁传感器分别工作在低频/高频模式。感应式磁传感器磁芯采用两段空心结构，RTD磁通门敏感元件安装在空心磁芯之间，不仅使复合磁传感器结构更加紧凑，并进一步提高了磁通门灵敏度。利用有限元仿真软件Maxwell对比分析磁芯内部的磁通分布情况，从而得到最佳复合传感器结构。研制了精密磁场标定线圈装置，标定磁场最大误差为0.3%。项目研制一款复合磁传感器并进行实际指标测试，DC-1Hz频带（RTD磁通门低频工作模式）灵敏度0.38us/nT, 噪声70pT/√Hz；1Hz-10kHz频带（感应式磁传感器高频工作模式）灵敏度100mV/nT，噪声10pT/√Hz @ 1Hz，实现宽频（DC-10kHz）低噪声的磁场测量。项目执行期间发表SCI论文4篇，EI论文2篇，授权国家发明专利2项。