| At present,many countries and regions around the world are still in the flames of war,which inevitably leads to a large number of unexploded ordnance(UXO),including landmines,shells and missiles.UXO usually scattered in near-surface areas,posing a severe threat to the safety of people’s lives and property.Moreover,even in peaceful areas,the leftover UXO from past wars still has a negative impact on people’s daily lives.Therefore,achieving precise detection of UXO is of crucial practical significance in safeguarding people’s lives and property.Electromagnetic detection,as one of the main methods for detecting UXO,has several advantages such as its high sensitivity,fast response speed and strong portability.With the rapid development of science and technology in recent years,the accuracy of magnetic field sensors has been further improved.Applying them to electromagnetic detection enables more accurate and rapid detection of UXO.Additionally,unlike other detection methods,electromagnetic detection is not affected by acoustic and optical noise in the environment,and provides more information about UXO including its spatial position,burial orientation,and composition material.Currently,electromagnetic detection methods can be divided into time-domain electromagnetic and frequency-domain electromagnetic methods based on different principles.Despite their successful employment in UXO detection,there are still some issues,such as limited detection range for small UXO,susceptibility of electromagnetic induction signals to environmental noise interference,and the inability to perform realtime imaging of UXO targets.To address these issues,this study aims to investigate an active imaging detection method for near-surface UXO based on electromagnetic induction/magnetic anomaly.This research analyzes and studies the time-frequency response characteristics of UXO,optimization design methods for active excitation coils and bipolar delayed staggered excitation methods.The main contributions of this thesis are as follows:Firstly,a magnetization theory model based on UXO targets is proposed.It is established by combining the magnetic dipole physical model and magnetic induction technique with the Jiles-Atherton magnetization modeling theory.Finite element physical simulation is conducted to verify the correctness of the magnetization theory model for UXO.Numerical simulation analysis is then performed on the time-domain and frequency-domain response characteristics of UXO targets.Secondly,a multi-parameter optimization design method for the active excitation coil based on particle swarm algorithm is proposed.The effects of various parameters of the excitation coil on the excitation magnetic field are studied and analyzed.Particle swarm algorithm is used to optimize the various parameters of the excitation coil.Subsequently,an active excitation coil capable of producing a highly uniform magnetic field is designed.Physical simulation is then conducted using finite element method on the designed active excitation coil,and the uniformity of the excitation magnetic field is analyzed and verified.Thirdly,a UXO imaging detection method based on bipolar delayed staggered excitation is proposed.Based on the electromagnetic induction theory,a bipolar magnetic field is generated by a bipolar square wave current to magnetize UXO targets.Electromagnetic imaging of UXO targets is achieved by using a coplanar magnetic sensor array.Furthermore,the effects of different interpolation algorithms,such as bilinear interpolation and cubic convolution interpolation,on UXO target imaging results are analyzed.Simulation experiments are conducted to verify the effectiveness of both the bipolar delayed staggered excitation method and the magnetic imaging method for UXO targets.Finally,an experimental platform for active imaging detection system is developed based on the aforementioned research findings.The optimal parameters obtained from the optimized design method for the active excitation coil are utilized to design an active excitation coil that is capable of generating a highly uniform magnetic field.The active excitation coil and H-bridge coil driver module are then combined to form the active excitation system.An induction-type magnetic sensor detection array is used in combination with a multi-channel data acquisition method to construct a magnetic anomaly data acquisition system.Additionally,a real-time magnetic anomaly data transmission system is developed based on the Kalman filtering algorithm and a highly stable network transmission protocol.Furthermore,an upper computer software system for real-time imaging detection of UXO targets is established by using the cubic convolution interpolation imaging algorithm in conjunction with graphical programming language and LabVIEW.Numerous comparative experiments are conducted by using the active imaging detection system on UXO targets,including Type 72 anti-personnel landmines,N4 mortar shells,and a large number of small-scale UXO targets.The experimental results demonstrate that the active imaging detection system is capable of imaging detection and posture identification of Type 72 anti-personnel landmines and N4 mortar shells at depths of up to 25 centimeters.Moreover,this system enhances the detection distances for these targets by approximately 60% and 150%,respectively,compared with Compared with traditional electromagnetic induction methods and magnetic anomaly detection methods.In addition,the system can effectively suppress external environmental magnetic interference and enables imaging detection of small-scale UXO targets such as 30 mm×50mm metal pipes and 16 mm×40 mm double-headed screws. |
