| Popis: |
The electromagnetic method with pseudo-random sequence, which codes transmitting waveforms, has great significance for improving the depth and resolution of electromagnetic detection. The frequency distribution and energy distribution of 2n sequence pseudo-random signals are studied. The results show that the 2n sequence pseudo-random code contains a total of n principal components with equal amplitude and is evenly distributed on logarithmic coordinates. The energy of the transmitted signal is more concentrated on the main frequency component when we take n as an odd number. Therefore, the detection depth distribution of pseudo-random coded waveforms is more reasonable over the traditional electromagnetic method. Using a vertical magnetic coupler emission device and 27 pseudo-random sequence excitation signals, this paper calculated the electromagnetic fields distribution for homogeneous formation with low-resistance anomaly or high-resistance anomaly. The numerical simulations show that the pseudo-random electromagnetic response has good resolution for good conductor. It has the characteristics of low emission current, large depth of detection, and fast measurement speed. For the high-resistance body of the surrounding rock, the effective information can be achieved by extracting the abnormal response in the late stage. This provides a theoretical basis for the use of pseudo-random electromagnetic methods to find metal ore, water-bearing geological bodies, and oil and gas reservoirs. |
