Research On Key Techniques Of Shallow Surface Electromagnetic Detection System

The pace of human society modernization is graduallyaccelerating, theurbanization of the city is moving forward rapidly, and Infrastructure has beenconstantly expanded to underground space. All kinds of supply and dischargepipelines, communication cableand power cable have been reasonably buried inshallow surface of the city even between cities and countries by the city builders. Theignorance of the infrastructure burial situation will cause great economic lossesatthesame time the urban city is deeply constructed and developed.The unexplodedbomb in the aspect of military and Leakage of harmful solution, geological structuralabnormalities in the aspect of environment and geology constitute a serious securityrisk. Therefore, understanding and evaluation ofshallow surface structure isparticularly important.Electromagnetic detection methodhas become an importantmeans of shallow surface survey especially for its convenient, efficient, safe workingcharacteristics.This paper based on the foreign instrument case,re-analysis of the problemdemands. Designed and implemented a kind of frequency domain electromagneticdetection instrument specifically for shallow surface detection, Meet the higherrequirements of real-time, anti-interference, detection accuracy, efficiency and otheraspects in shallow surface detection,provides a hardware platform and theexperimental basis for the shallow surface detection and related work. The work ofthis paper is as follows:(1) Research and a brief analysis of the shallow ground electromagneticdetection principle, combining with foreign case gives the general design frameworkof instrument system. The main part consists of transmit power, analog conditioningparts, digital processing section and PC analysis and control software. Thecontrol,data transmission and further explanation units of the digital processingsection are respectively realized by FPGA, USB interface and the host computer.Power and analog part is controlled by the host computer instructiontranslated by FPGA. Users can finish real-time measuring conveniently andefficiently by facing to the host computer.(2) According to the s Periodic testing, find out the key problems affecting theemission accuracy, proposed a method of adding LC filter on the output terminal ofthe transmitting bridge to inhibit the random spike due to resonance generated byParasitic capacitance of the emission circuit and inductance of the coil. Analysis ofthe effect of temperature on the system,inhibit the temperature drift of the system bychoosing the appropriate device and installing cooling fan, improve the stability of thesystem emission signal.(3) Especially designed analog signal conditioning circuit and digital controlcircuit for received electromagnetic wave signal: low noise preamplifier and filter arerealized; build a digital circuit with FPGA and CY7C68013,the stepwise referencedorthogonal PSD calculation of the digital signal acquire by ADC is finished withinFPGA, Improved operational efficiency;calculated the amount of collected data,Ensure the system is a real-time system and build a synchronous tuning module inFPGA to ensure the synchronous acquisition of the system.(4) Host computer software is designed and programed by using MFC. Thesoftware can control drive circuit by API and receive data by communicating withUSB interface, what’smore, the display interface shows real-time curve of the result.The result and raw data can be saved at the same time and the result can also be sentto serial port.According to the coordinate rotation principle,digital phase correctionmethod and mineralization reaction inhibition method are proposed. The digital phasecorrection of the detection result has been realized in the host computer,makes thedetection resultcurve can truly reflect the frequency characteristic of the abnormalbody and learn the frequency characteristic of the soil to inhibit the interferenceproduced by mineralization reaction.(5) Conducted a number of simulation experiments in the test site, the detectiontest of various metal anomaly targeted has been done;experiments show that theinstrument system can quickly and accurately depict the I, Q component curve of the anomaly bodies; can eliminate soil disturbance after inhibit mineralization reaction.The difference of the frequency curve between different anomaly bodies isobvious,can be used to distinguish different abnormal bodies. For minor anomalybody (metal content0.1~1g) at a certain distance (10cm),the detecting curve can showthe obvious consistency,verifies the high sensitivity of the instrument with highsensitivity.