摘要：A new type of electromagnetic (EM) receiver has been developed by integrating four capacitive electrodes and a triaxial induction coil with an advanced data logger for tunnel exploration.The new EM receiver can conduct EM observations in tunnels, which is one of the principal goals of surface-tunnel-borehole EM detection for deep ore deposit mapping.The use of capacitive electrodes enables us to record the electrical field (E-field) signals from hard rock surfaces, which are high-resistance terrains.A compact triaxial induction coil integrates three independent induction coils for narrow-tunnel exploration applications.A low-time-drift-error clock source is developed for tunnel applications where GPS signals are unavailable.The three main components of our tunnel EM receiver are: (1) four capacitive electrodes for measuring the E-field signal without digging in hard rock regions; (2) a triaxial induction coil sensor for audio-frequency magnetotelluric and controlled-source audio-frequency magnetotelluric signal measurements; and (3) a data logger that allows us to record five-component MT signals with low noise levels, low time-drift-error for the clock source, and high dynamic range.The proposed tunnel EM receiver was successfully deployed in a mine that exhibited with typical noise characteristics. The new EM receiver can conduct EM observations in tunnels, which is one of the principal goals of the surface-tunnel-borehole EM (STBEM) detection for deep ore deposit mapping.The use of a capacitive electrode enables us to record the electrical field (E-field) signals from hard rock surfaces.A compact triaxial induction coil integrated three induction coils, for narrow-tunnel applications.
关键词：Tunnel EM prospecting; Capacitive electrode; Triaxial induction coil; Low time-drift-error clock source; EM data logger
