| 摘要 |
PURPOSE:To suppress the current leaking from a drill pipe as low as possible even if the excavation depth becomes deep, and to obtain a receiving signal of sufficient magnitude on the ground by placing an insulator so as to surround the periphery of a transmitting antenna. CONSTITUTION:Underground information obtained from a sensor, etc., is modulated as an electric signal by a modulation transmitter 2, and this electric signal is applied to the upper and the lower electrodes 11, 12 of a transmitting antenna 1. In this case, a current corresponding to the modulated electric signal flows to the ground of the periphery of the transmitting antenna 1. However, by a peripheral insulator provided on the surface of a casing pipe 103, a current leaking to the ground from the transmitting antenna 1 comes to be scarcely generated in the upper part of a cross section A-A' in the figure. Accordingly, as for magnitude of a signal received in a receiving antenna buried in the vicinity on the ground, the potential on a drip pipe increases. |
