一种SLF/ULF频段基于磁通负反馈的钻孔电磁波接收天线
A Borehole Electromagnetic Wave Receiving Antenna Based on Flux Negative Feedback Technology in SLF/ULF Band

当前国内外钻孔电磁波CT有基于电偶极子模型的电天线系统和基于磁偶极子模型的磁天线系统。由于电天线需要满足天线准则(波长的1/4或者1/2)因而长度较长，当电天线模型传播距离与尺度可比时，由于近场的强非线性以及方向性会受到结构影响因而电偶极子模型等效性差。基于磁天线的CT仪器电磁波此时由于频率结构的特点，磁偶极子模型等效性好。在某国家重大专项中根据实际要求采用基于磁偶极子模型技术的钻孔电磁波CT系统，该系统要求天线接收交变磁场，频段为30 Hz~3000 Hz (SLF/ULF)，通带内灵敏度应是坦平状。本文采用磁通负反馈技术结合噪声匹配分析等方法，对接收天线进行了理论分析和设计，制作了相应的天线样机，经实验室刻度和现场测试天线各项指标满足项目要求。
At present, electromagnetic wave CT at home and abroad has electric antenna system based on electric dipole model and magnetic antenna system based on magnetic dipole model. Because the electric antenna needs to meet the antenna criterion (1/4 or 1/2 of the wavelength), the length is long. When the propagation distance of the electric antenna model is comparable to the scale, the strong nonlinearity and directivity of the near field will be affected by the structure, so the equiva-lence of the electric dipole model is poor. The electromagnetic wave of CT instrument based on magnetic antenna has good equivalence due to the characteristics of frequency structure. In a major national project, according to the actual requirements, the borehole electromagnetic wave CT sys-tem based on magnetic dipole model technology is adopted. The system requires the antenna to receive alternating magnetic field, the frequency band is 30 Hz~3000 Hz (SLF/ULF), and the sensi-tivity in the pass band should be flat. In this paper, the receiving antenna is theoretically analyzed and designed by using flux negative feedback technology combined with noise matching analysis, and the corresponding antenna prototype is made. After laboratory calibration and field test, each index of the antenna meets the project requirements.