Research On Trenchless Dual-coil Magnetic Induction Deep Sounding System

In the past few decades,along with the rapid development of electronic communication,energy transmission as well as water conservancy and hydro power,trenchless technology has been applied widely.As the key technology of trenchless technology,measurement while drilling,positioning technology and sounding technology are receiving extensive attention and vigorous research.Therefore,this thesis conducts a systematic and in-depth study on the sounding technology of trenchless technology,building a high-precision sounding system.And the specific research content is as follows:At first,the thesis analyzes the underground electromagnetic environment,uses a solenoid coil with a very low frequency current as the underground transmitting antenna and uses the ground receiving coil to receive the magnetic field according to the distribution characteristics of the quasi-static field generated.On the above basis,this paper founds a dual-coil bathymetry model.In the experimental part,the double-coil sounding model is tested,and the results indicates that the double-coil sounding model can achieve through-the-earth sounding.However,the error is relatively large under noise interference.For the sake of solving the problem mentioned above,this paper analyzes the noise that affects the sounding accuracy and proposes two methods so as to reduce noise interference.First of all,the author carries on a research on adaptive noise elimination algorithm,and an adaptive noise elimination algorithm based on LMS is proposed,which can achieving eliminate noise without prior knowledge of noise.After that,based on the attenuation characteristics of very low frequency signals and the characteristics of 1/f noise,a frequency selection method is designed to reduce noise interference during signal transmission.In the simulation part,this thesis uses MATLAB to test the LMS-based adaptive noise elimination algorithm.The results suggest when the signal frequency is 20 KHz,the algorithm can effectively improve the signalto-noise ratio of noise signals.Finally,based on the dual-coil sounding model,this paper designs a complete throughearth sounding system,and divides the sounding system into four modules,signal transmitting module,signal receiving module,signal conditioning module and host computer.The signal transmitting module adopts the DDS module scheme of STM32F103 and AD9834,which realizes the generation of multi-frequency VLF signals;The signal conditioning module adopts program-controlled amplification and second-order Butterworth band-pass filter to realize the filtering and amplification of the received signal;The signal acquisition and processing module adopt the scheme of STM32F103 and AD7606 to fulfill three-channel data acquisition;The upper computer uses Lab VIEW and MATLAB script to complete the adaptive noise elimination algorithm based on LMS and displays the sounding data.In the final experimental part,this paper carries out tests on the system's very low frequency signal transmission and reception capabilities,noise reduction capabilities in different environments,and penetration sounding capabilities,the results showing that the penetration sounding system designed in this paper has better noise reduction capabilities and accuracy of through-the-earth sounding.