The Near-surface Electromagnetic Detecting Transmission System Design

With the development of our social economy, city construction change rapidly, highbuildings, subway, underground pipelines, underground storage and landfill of maintenancefacilities increase rapidly during the passing days and engineering and relatedenvironmental geological problems become the focus of our research. The engineeringgeological and environmental geological problems mostly occur in the near surface, so thenear-surface detection and assessment is particularly important.Conventional excavation and drilling methods generally cost too much, have longconstruction period and are destructive. They are very difficult to carry out in cityconstruction. Electromagnetic method detects the structure and material formation bymeasuring the dielectric parameters and magnetic parameter, having the advantages of highefficiency and non destructive economic. Therefore, to design a set of near-surfaceelectromagnetic detection equipment to carry out the relevant aspects of the work is veryimportant. The frequency domain electromagnetic detection is a reasonable and efficientgeological method, and it has a wide application prospect in the exploration technology.In this paper, the research comes from the development project of Jilin provincescience and technology Portable near-surface electromagnetic imaging system. Accordingto this project, the transmitting system must be stable and high efficient and it’s portabilityshould be taken into consideration, so consider the system’s special needs in the design,therefore, on the basis of general ways to put more in line with the method is morereasonable and feasible project requirements.In the research of the method, firstly analyze near-surface electromagnetic detectioninstrument and its application background, at the same time, analyze and compare severalmethods of multi-frequency electromagnetic signal transmitting system in this paper on thecommonly used at home and abroad. To evaluate the advantages and disadvantages, according to the requirement of the project design more in line with the expected objectivesof the unipolar SPWM method of FPGA and embedded NiosII is generated based onMulti-frequency Electromagnetic signal. In this paper, the principle of this method isexplicitly introduced, and the important parameters were calculated and simulated,demonstrating the feasibility of this method.In order to realize this method, this paper analyzes the hardware platform, evaluates ofseveral commonly used hardware platform, then introduces FPGA and embedded NiosIIhardware platform. The core control platform of NiosII and other components areintroduced in this paper.The whole system consists three parts: the multi-frequency waveform generationmodule, driver module and full-bridge inverter module. First establish embedded soft coresystem by SOPC Builder, adding system components and other components that the systemdoes not provide. Using Verilog to produce each sub module, at the same time, the outputwaveform of each module is theoretical simulated and actual tested. The working principleis analyzed in detail in the driving circuit module, the key parameters of components aremathematical calculated and simulated. Full bridge inverter module introduces circuitmodel and mathematical model of the switching device of the inductive load. In order tocalculate the turn-on loss, turn-off loss and switching loss, switching loss of power drivingdevice are analyzed in detail, making out the specific mathematical expression. At the sametime of four kinds of commonly used absorption circuit analysis and evaluation, choose amore suitable RC absorption circuit for the design, and the parameters of key componentsfor the theoretical analysis and mathematical calculation, through the actual test to verifythe correctness of the theoretical analysis.This article finally gives specific inductive load test case of Multi-frequencyElectromagnetic emission signal waveform and the experiment results are analyzed. At theend of the finished surface electromagnetic transmitting system deficiencies and putforward suggestions for improvement.