Research On The Real-Time Data Processing Technology For Shallow Surface Electromagnetic Detection Based On FPGA

With the rapid development of urbanization and the increasing frequency of human activities in recent years,shallow surface exploration activities such as route laying,archaeological excavation and geological exploration have gradually become a research hotspot.Ground penetrating radar,frequency domain electromagnetic method and time domain electromagnetic method are often used in the exploration and detection of surface shallow layer.Compared with the other two methods,frequency domain electromagnetic method has the advantages of high signal-to-noise ratio,strong anti-interference ability and low cost.This paper summarizes the basic principle and workflow of electromagnetic detection of shallow surface.Based on the frequency domain electromagnetic detection system developed by Jilin University,in order to improve the overall real-time and efficiency of the system,a real-time data processing system based on FPGA has been designed.By using the parallel processing characteristic of FPGA,the original digital processing module DSP of the system has been replaced to deal with the algorithm of orthogonal lock-in amplification.Based on FPGA + STM32 architecture,a shallow surface electromagnetic detection system has been designed,which can process the data at the same time of data acquisition and detect the metal anomalies in the shallow surface.The main contents of this paper are as follows: 1.Data acquisition and front-end conditioning circuit design.Based on the theory of high circuit and analog-to-digital conversion,the front-end data acquisition system has beendesigned to ensure the signal accuracy and transmission speed.2.Digital signal processing technology.Based on the principle of weak signal detection,the phase amplitude analysis of weak electromagnetic signal is carried out by using the orthogonal lock-in amplification technology in digital phase-locked,and the shallow soil information is obtained to identify whether there is metal abnormal body in the surface.3.High efficiency control unit design.The architecture of FPGA + STM32 is adopted.STM32 and FPGA communicate through FSMC bus.A data buffer FIFO(first input first output)module has been built in FPGA.The cache module reads the reference signal from the reference signal table built in STM32.A double precision floating-point arithmetic module has been built in FPGA.The reference signal and the input signal transmitted by the A / D converter have been orthogonal locked and amplified to obtain the I and Q components that can reflect the nature of the shallow surface abnormal body.The interference of channel phase delay is eliminated by channel phase correction technology.The interference of mineralization reaction caused by mineralized substance in soil was eliminated by soil phase correction technology.The experimental results show that the signal processing system of this structure can achieve the purpose of rapid detection of metal objects with a certain depth,and the detection curve drawn is clear and obvious.Compared with the original system,the new system has faster data processing speed,and the processing time of the new system is reduced by 31.4%,which improves the overall real-time performance of the system.