周期性钻柱内孔波导微波传播衰减规律研究

Research on the attenuation law of microwave propagation within the periodic drill string bore waveguide

为掌握钻柱內孔微波传输的最佳频点,获取微波信道的衰减规律及有效传输距离,将钻柱内孔视为超长不规则有耗圆波导,采用电磁波耦合理论计算了微波最佳传输频点,分析了波导中的微波模式。采用微波传输等效电路法建立了信道模型,以及信号衰减规律模型。同时针对周期性超长钻柱,提出单位长度平均功率损耗系数对有效传输距离进行简化分析。研究结果表明,钻柱内孔沿轴向存在多个内径渐变段和突变点,微波传输存在大量反射过程,信道的阻抗变化是影响传输性能的主要因素,单位长度衰减系数小于0.3 d B/m。衰减模型比仅考虑表面电阻涡流损耗的模型更准确,对微波传输随钻监测系统的设计具有指导意义。

This study aims to obtain the best frequency point of microwave transmission in thedrill string bore,the attenuation law and the effective transmission distance of the microwave channel. The drill string bore is regarded as the irregular lossy cylindrical waveguide. The best frequency point and the microwave mode in the channel arecalculated by the electromagnetic wave coupling theory. The channel model and the signal attenuation rule areestablished by microwave transmission equivalent circuit method. Meanwhile,a simplified analysis method forcalculating the effective transmission distance is proposed for the ultra-long drill string channel by using average loss coefficient of unit length. The testing results show that the drill string bore has several inner diameter gradual change sections and sudden change points along the axial direction. There are a lot of reflection processes in the microwave transmission and the channel impedance change is the main factor affecting the transmission quality. The attenuation coefficient of unit length is less than 0. 3 d B/m. The attenuation model proposedin this paper is more accurate than the model only considering the eddy current loss of surface resistance,which is more helpful for guiding the design of microwave transmission measurement while drilling system.