1996 Fiscal Year Final Research Report Summary
Propagation Experiment of VLF Electromagnetic Pulses in the Deep Underground
| Project/Area Number |
07650421
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
情報通信工学
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| Research Institution | Kanazawa University |
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Principal Investigator |
NAGANO Isamu Kanazawa University, Faculty of Engineering, Professor, 工学部, 教授 (50019775)
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| Co-Investigator(Kenkyū-buntansha) |
WU Xiang-Yang Kanazawa University, Faculty of Engineering, Research Associate, 工学部, 助手 (80272946)
YAGITANI Satoshi Kanazawa University, Faculty of Engineering, Lecturer, 工学部, 講師 (30251937)
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| Project Period (FY) |
1995 – 1996
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| Keywords | Deep Underground Radar / High-Power VLF Electromagnetic Pulse / Wide Band Wave Form Capture / FDTD method / 3D Computer Simulation / Underground Propagation |
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| Research Abstract |
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 underground
As 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.
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