高频时域电磁场模拟

根据不同时域电磁场的频率特性,从频率域到时间域的转换一般有二种方法,即线性滤波算法(余弦变换)和快速傅氏变换(FFT)。利用高密度采样的线性滤波算法计算余弦变换,对层状介质的甚早期瞬变电磁进行模拟,并与均匀半空间的闭合解析式结果进行对比,证明了该方法的有效性。另外,从层状介质的高频电磁场响应出发,利用FFT算法,有效地模拟了不同频率和地电参数的GPR射线,以及层状介质的剖面图。甚早期瞬变电磁和低频GPR的频率,都跨越了传统电磁法中所忽略的中间频率。这里的主要目的就是通过对比选择有效的模拟方法,利用模拟结果来分析该频段时域电磁场的特征。

High frequency electromagnetic modeling in time domain

According to frequency characteristics of the time electromagnetic filed, two methods, linear filtering algorithm(cosine transform) and fast Fourier transform algorithm(FFT), are usually used to transform the electromagnetic fields from frequency to time domain. The very early transient electromagnetic responses in a layered earth is calculated and compared to the closed-form analytic expressions, the numerical algorithm is proved to be valid. Then, the fast Fourier transform algorithm is applied to forward modeling of the single ground penetrating radar trace and section in different frequencies. Both methods of very early transient electromagnetic and low-frequency ground penetrating radar operates over the intermedial frequencies between the traditional transient electromagnetic and ground penetrating radar.