Research And Implementation Of Left-hand Material FDTD Algorithm Based On Lorentz Model

Finite-difference time-domain algorithm plays an important role in solving electromagnetic problems.It is widely used in many fields because of its advantages such as simple and intuitive,the capable of displaying rich time domain information and obtaining frequency domain information through simple calculation.However,the traditional FDTD algorithm is limited by the Courant-Friedrich-Levy stability condition which can cause lowly computational efficiency and even can't run when dealing with large size problems or fine structures.In order to overcome the shortcomings of the traditional FDTD algorithm,researchers have constantly improved the algorithms.Now,many unconditional stable algorithms which are not restricted by the CFL condition have been proposed,and the ADI-FDTD algorithm is one of them.This paper takes the finite difference time domain algorithm as the research object and compares and analyzes the traditional FDTD algorithm and ADI-FDTD algorithm in conventional media.Based on the traditional FDTD algorithm for left-handed Lorentz model and the relationship between traditional FDTD algorithm and ADI-FDTD algorithm in conventional media,the corresponding ADI-FDTD algorithm is proposed.At the end,the proposed Lorenz model left-hand material ADI-FDTD algorithm is applied to the calculation and simulation of MRI.And according to the relevant results,the feasibility of the proposed algorithm is analyzed and summarized.Firstly,the related theory and solving method of finite-difference time-domain difference algorithm in general are introduced and a simulation model is established.The characteristics of the traditional FDTD algorithm and ADI-FDTD algorithm of vacuum medium and their relationship are verified by using programming software and imaging software,which can provide a theoretical basis for the latter.Then the FDTD algorithm of left-handed material is introduced.Left-handed material is a new type of electromagnetic material.It has unique properties such as negative refraction effect,and its related research is of great importance.Because the FDTD algorithm in conventional media can't be directly applied to solve the electromagnetic problem of left-handed materials,and the Lorentz model in the left-handed materials has universal applicability,so the traditional FDTD algorithm which is matched with the left-handed material of Lorenz model is introduced and the ADI-FDTD algorithm for left-handed material is proposed based on the relationship of the FDTD algorithms in conventional media.After that,the two algorithms in left handed materials are compared and simulated.According to the data and image obtained,the proposed algorithm is discussed and analyzed.The results can prove that the Lorenz model ADI-FDTD algorithm is an efficient electromagnetic calculation method.Finally,the algorithms mentioned above are applied to the research and implementation of MRI.At present,MRI technology has been widely studied and applied in the fields such as medicine and life science.It is of great significance to carry out the related simulation and research of MRI and the finite-difference time-domain algorithm is one of the commonly used simulation algorithms.For the simulation of MRI,the local body of the mouse is mathematically modeled and the birdcage coil is used to provide radio frequency excitation.The simulation experiment can verify that the left-handed material will make the MRI image better,and the ADI-FDTD algorithm will make the overall simulation less expensive and more efficient.In addition,calculating the specific absorption rate from the data obtained from the simulation can verify that the proposed algorithm is safe for MRI simulation of organisms.According to the obtained results,the proposed Lorenz model ADI-FDTD algorithm of left-handed material is able to meet the design requirements.