分析水下目标的大比例变换总场散射场源FDTD方法

为解决探测水下目标的电磁散射问题，提出大比例变换的总场-散射场源时域有限差分（FDTD）方法.该方法包含两次FDTD计算：第一次计算采用细网格得到激励源周围的近场值；第二次计算采用粗网格得到远距离的电磁场值.两次FDTD计算通过总场-散射场边界建立联系.实现细粗网格的大比例变换，例如变换比例N=10，大大节省了计算时间，降低了计算内存的消耗，提高了计算效率.通过算例验证该方法的正确性和有效性.最后，计算水下岩层中存在异常体时的电磁响应，指出当岩层中异常体电导率不同时，接收点处电磁场的幅值和相位均不相同.

A Large-Scaled Total-Field Scattered-Field Source FDTD for Underwater Targets

For detecting underwater targets, a total-field scattered-field source FDTD is proposed. Two FDTD simulations are included. Tangential electromagnetic fields on exchange surface are recorded in first simulation with fine grids. In second simulation, equivalent source is added with coarse grids at total-field scattered-field surface. Ratio of coarse grid to fine grid can be extremely large, such as N=10 while run time and consumed memory are reduced. Precision and validity of the method in calculating radiated fields of line current source are verified. Finally, the method is utilized to analyze electromagnetic response of underwater space with obstacles. Flexibility of the method in simulating a realistic underwater electromagnetic problem is illustrated. It is pointed out that delay time and magnitude of timing waveforms at receive points are different with conductivity difference of abnormal bodies.