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Propagation Experiment of VLF Electromagnetic Pulses in the Deep Underground

甚低频电磁脉冲在地下深处的传播实验

基本信息

批准号：
07650421
负责人：
NAGANO Isamu
金额：
$ 1.41万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07650421/
关键词：
Deep Underground Radar High-Power VLF Electromagnetic Pulse Wide Band Wave Form Capture FDTD method 3D Computer Simulation Underground Propagation 低周波大電流電磁パルスコンピュータシミュレーション

项目摘要

This research has been carried out over two years on the basis of following two categories :(1) Development of a wave form capture with a wide (100 dB) dynamic range to observe weak electromagnetic echoes from the deep underground(2) Computer simulation on the propagation of a VLF electromagnetic pulse in the deep undergroundAs for item (1), we have developed a wave form capture with a wide dynamic range to measure weak VLF echoes reflected from the deep underground which would be received simultaneously with a much stronger electromagnetic pulse directly coming from the transmitter. By using an automatic gain controlling circuit to select the gain (from 0 to 36 dB) of an signal amplifier, a total 100-dB dynamic range has been realized with a single 12-bit (66 dB) A/D converter. The developed wave form capture has been confirmed to work well for several test signals.As for item (2), a three-dimensional computer simulation code using a finite-difference timedomain (FDTD) method, has been developed to compute underground propagation of an electromagnetic wave radiated from a loop antenna on the ground. Using this simulation code, we have evaluated VLF scattering cross sections of metal plates of various sizes buried in the deep (-800m) underground. The results have been applied to estimate the loop current necessary to radiate a VLF radar pulse which produces its echo from the deep underground strong enough to be received by a search coil magnetometer on the ground.

（1）开发了用于观测地下深处微弱电磁回波的宽动态范围（100 dB）波形捕捉器（2）对甚低频电磁脉冲在地下深处的传播进行计算机模拟（3）关于第（1）项，我们开发了用于测量从地下深处反射的微弱甚低频回波的宽动态范围波形捕捉器，它将与直接来自发射机的强得多的电磁脉冲同时接收。通过使用自动增益控制电路来选择信号放大器的增益（从0到36 dB），用单个12位（66 dB）A/D转换器实现了100 dB的动态范围。对于第（2）项，开发了一个三维计算机模拟程序，使用时域有限差分法（FDTD）计算从地面环形天线辐射的电磁波在地下的传播。利用该程序计算了埋在地下800米深处不同尺寸金属板的VLF散射截面。结果已被施加到估计所需的回路电流辐射的甚低频雷达脉冲产生其回波从地下深处强到足以被接收到的地面上的搜索线圈磁强计。