Research on the Transmitting Technology of a Portable Near-Surface Frequency-Domain Electromagnetic Detection System Based on a Multicoil Parallel Strategy

Portable near-surface frequency-domain electromagnetic (FDEM) can effectively recognize underground electrical anomalies. However, because the transmitting device of conventional portable near-surface FDEM systems is a transmitting coil and has a high operating frequency ( $>$ 1000 Hz), the inductive resistance of the coils results in a decrease of the transmitting current, which in turn results in a decrease in the transmitting magnetic field. It would result in low detection efficiency and poor signal-to-noise ratio of the system. Currently, several techniques can increase the transmitting current. However, these techniques have problems in that they are difficult to solve the design parameters, and the deviation of the component parameters has a large influence. Because of the above problems, a multicoil parallel strategy (MCPS) is proposed in this article. The MCPS proposes to optimize the conventional single transmitting coil to a multicoil co-axial parallel (MCAP) structure. MCPS can increase the transmitting current amplitude at any of the target frequencies without increasing the power of the power supply. First, this article analyzes the feasibility of the MCPS in practice. The analysis is mainly included in the following three aspects: 1) the feasibility of MCPS in an ideal state is analyzed; 2) the influence of mutual inductance and resonant capacitance deviations on MCPS is analyzed; and 3) the performance parameter requirements of resonant capacitors are analyzed. The results of the simulation show that the MCPS can simultaneously increase the amplitude of transmitting currents at multiple target frequencies. In practice, MCPS has strong stability and suitability. Further, this article verifies the MCPS with an actual circuit. The experimental results show that compared to the conventional single-coil transmitting system, the MCPS increases the current amplitude by 1.86 times, 1.87 times, and 2.04 times, respectively, at the three target frequencies, increases the transmitting magnetic field by 1.28 times, 1.5 times, and 1.75 times, respectively, and improves the signal-to-noise ratio by 3.94 dB. Finally, this article discusses the results of simulation and experiments. The methods to further improve the effectiveness of MCPS applications and future research directions are concluded.