High-order pseudo random binary signals for frequency domain electromagnetic explorations

In the field of frequency-domain electromagnetic (EM) exploration with artificial sources, various signals have been employed. However, these signals often fail to encompass all relevant frequencies of interest (or effective frequencies), necessitating signal replacements during operations, which significantly affects fieldwork efficiency. To address this issue, a novel method for generating pseudo-random binary signals has been proposed, which can include a wide range of frequency components. With this method, the frequency requirements for most frequency-domain EM exploration projects can be met using only one waveform which is specially designed for the project. Therefore, the need for signal replacement during operations can be eliminated, leading to a great improvement in the efficiency of field work. The generation method is based on waveform superposition and hard clipping, combined with unit integration. To improve the efficiency of signal generation, a targeted improved multi-objective particle swarm optimization algorithm is used. In order to ensure the practicality of the generated signal, optimization targets the energy concentration and uniformity of effective frequencies, allowing for rapid generation of signals that satisfy engineering application requirements in just a few minutes. This type of signal has been successfully applied in numerous practical exploration projects, yielding excellent results and confirming its effectiveness in enhancing work efficiency and resistance to interference.