Study On Collecting The Transient Electromagnetic Signal

Transient electromagnetic method is a method of geophysical exploration, Now TEM has been widely used in mineral exploration, drilling, aviation and marine areas. With the development of socio-economic and urban construction, The trend that people take attention on the engineering and geological environment is gradually increasing, Therefore, High-resolution near-surface detection and evaluation is necessary. As the causes of transient electromagnetic detection system, such as low receiver sampling rate, receiver coil transient effects ,and so on. Blind spots exist when TEM detects the shallow geological survey.Based on the National Natural Science Foundation project " Transient Electromagnetic Method 'frontier' issues and key technologies of drag systems". Analysis of the homogeneous half-space transient electromagnetic field propagation, Study on the induced current and corresponding changes of the secondary magnetic field in ore body. On this basis, the paper conducted the following study.â‘ Based on circuit theory, The theoretical model and transfer function of the receiving coil is established, Analysis of transient causes of receiving coil. On this basis, Proposed a "The dynamic test method of changing damping resistance receiving coil parameters" for measuring the coil parameters, In the case of the same excitation, Change the damping resistance will produce different distortion signal. Derived the receiver coil parameter estimation method. Complete the simulation and experimental tests with MATLAB, Analysis of the problems and solutions for the method.â‘¡Based on VHS-ADC high-speed digital signal processing platform and WTEM-1D high-power transmitter, Construct the TEM prototype system. First of all, proposed the "double ADC analogue to digital converter technique based on linear fitting " to improve the resolution of the system built-in ADC, for meeting the requirements of high resolution signal acquisition. Secondly, Study the characteristics of transient electromagnetic signals, Proposed a "sub-frequency sampling" method, High-speed sampling for early signals, and low-speed sampling On the middle and late. Solve the data storage problems of real-time and high-speed system. At last, Design prototype system architecture of TEM, Complete the VHS-ADC system model, interface design, simulation, FPGA code generation, and carried out on-line debugging with the transmitter. â‘¢To test the prototype receiver, an air-raid shelter on the school field was detected. To compare with the performance of the prototype system receiver, The GDP32 multi-function receiver have take the same test.Transient electromagnetic receiver prototype system has been worked all normal, with the basic functions of transient electromagnetic exploration. The high-density sampling for the early signals, Provided the basic data for Shallow high-resolution inversion. By experimental results, Prototype system can accurately detect air-raid shelter, and achieve the purpose of detecting shallow exploration.