Research And Design Of Transient Electromagnetic Signal Receiving And Acquisition System

The transient electromagnetic detection method is a time-domain electromagnetic technique that effectively overcomes the limitations of traditional detection methods in terms of terrain and efficiency.It enables rapid acquisition of geographic information over large areas.This method utilizes a large magnetic moment emission source for excitation,and the receiving end captures the secondary field signal excited by the geological medium.The characteristics of the secondary field signal can be used to extract formation information.The thesis focuses on the research and design of the transient electromagnetic signal receiving and acquisition system.The system receives broadband time-domain signals below 25 k Hz,and the changing characteristics of the signal reflect geological information of the corresponding formation.Transient signals exhibit significant variations in magnitude between the early and late signals,posing requirements on the dynamic range of the receiving system.The receiving system also needs to be synchronized with the transmitter’s off-time to achieve accurate collection of the secondary field.To address these challenges,the transient electromagnetic receiving and acquisition system should meet the following requirements: large dynamic range;high sampling rate and highresolution acquisition capability;synchronization capability with the transmitter.The design of the receiving and acquisition system is based on relevant theoretical considerations.It mainly includes the following four parts.Firstly,the analog circuit of the receiver is simulated and designed.The performance of the analog filters is verified and suitable operational amplifier components are selected.Based on the requirements of other system parameters,appropriate ADC is chosen.The design of the communication module and power module is completed along with chip selection.Secondly,FPGA completes functions such as ADC control,data acquisition,storage,and real-time uploading.Two operating modes are designed: manual gain setting and automatic gain switching,to ensure that the signal amplitude is within the optimal sampling range of the ADC.Thirdly,the thesis analyzes the 50 Hz filtering technique in the transient electromagnetic receiving system..Thesis choose the digital phase-sensitive detection algorithm(DPSD).Then analyzes the principle of digital phase-sensitive detection,sets the operational parameters,and successfully implements it on FPGA.Fourthly,a GPS-based transmission and reception synchronization function is added.It can cope with various scenarios such as long-distance detection in the wild or tunnel confined spaces.According to the design content,complete the physical realization of the system and the step-by-step test.Furthermore,verifying the effectiveness of PGA gain control,validating the application effect of DPSD in the transient electromagnetic signal receiving and acquisition system.The design completes the expected effect.