| The shortage of natural resources is one of the main reasons that seriously affects economic development.Therefore,it is necessary to prospect and increase reserves,focused on the domestic.Time domain electromagnetic method based on Faraday’s law of electromagnetic induction,is one of the popular geophysical methods for mineral resources prospecting.However,when time domain electromagnetic detection is performed in an intricate noise circumstances,the short of prior knowledge of electromagnetic noise in the detection environment,make it necessary to process the data by increasing the emission current,filtering algorithm and other methods.The extraction error of electromagnetic response characteristic parameters still does not meet the requirements,and the inversion accuracy still lacks credibility,which is resulted in invalid experiments.As a result,the various efforts are in vain.To address the problem,this paper designs and realizes an environmental electromagnetic noise acquisition device.The noise which is of great significance for time domain electromagnetic detection is analyzed as well.By analyzing the components and characteristics of transient electromagnetic detection noise sources,an environmental electromagnetic noise acquisition device based on parallel amplifier circuits is designed.The coil sensor and matching resistance design is completed.The low-noise instrumentation amplifier AD8429 is selected as the pre-amplifier core component.The operational amplifier parallel circuit structure reduces the output voltage noise of the pre-amplifier and the voltage noise of the system is 800 n V.By analyzing the effect of the Q and n of the filter,this paper use a 2-order low-pass filter to suppress the spatial electromagnetic noise outside the band.The AD7764 with(35)(50)-modulation and oversampling technology is employed to complete the analog-to-digital conversion of data and achieves 24-bit high-precision collection.The data storage programme is designed by FPGA.The programme opens up an internal FIFO buffer area and adopting a ping-pong buffer structure.High speed and continuous storage of data is realized.By A/D isolation and independent electric source,the high-frequency electromagnetic interference of the circuit is suppressed.Theoretical calculations,simulations and tests have been carried out.In time domain electromagnetic detection,the signal always appears anti sign phenomenon,so that this paper mainly studies the influence of electromagnetic noise on the electromagnetic response considering induced polarization effect.PSO is used to extract all the polarization parameters of the theoretical response and the noise-containing response.The influence of electromagnetic noise on the polarization parameters extraction of time domain electromagnetic response of different parameter models is analyzed.The adaptive scalar Kalman and exponential fitting filter algorithms are applied to data processing for the complex component electromagnetic noise.The effectiveness of the algorithm is verified by the results of polarization parameters extraction before and after the filtering of the electromagnetic response with noise.Finally,the analysis method of environmental electromagnetic noise based on the polarization parameters of electromagnetic response is proposed.The performance of the environmental electromagnetic noise collection device is tested in practice.The noise collection and analysis of the laboratory,the Shaoguozhen and Jianshe Square subway stations are accomplished.showing that the collection system and the noise analysis method are effective.The final part summarizes the work of the full thesis and provides improvement plans and future prospects for the system deficiencies. |
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