An Adaptive Wide-Band Impedance Matching Network for Frequency-Domain Electromagnetic Method Transmitter Systems

The frequency-domain electromagnetic (FDEM) method leverages the skin depth effect to extract subsurface information at varying depths. However, inductive suppression in the transmitter system reduces transmission current at high frequencies, severely degrading the signal-to-noise ratio (SNR) and exploration performance. Traditional impedance matching methods are insufficient due to limited tunability or lack of continuous adjustment. To address these limitations, this article proposes a switch-controlled capacitor impedance matching network (SCCIMN) for adaptive, continuous impedance matching across 1–100 kHz. First, the circuit structure of the SCCIMN is introduced, along with the equivalent principle of SCC. Then, a detailed parameter design scheme is provided to ensure the SCCIMN meets the specified requirements. Next, an adaptive control strategy is proposed, enabling the SCCIMN to achieve continuous automatic adjustment within the designated frequency range. Finally, simulations and experiments validate the proposed approach, demonstrating that SCCIMN effectively enhances the transmission current, with a current enhancement rate exceeding 100% across the entire frequency band, more than doubling the transmission current. Furthermore, the SCCIMN exhibits excellent dynamic performance: Proportional-integral-derivative (PID)-based frequency switching is completed within 50 ms, while a look-up table (LUT) approach enables near-instantaneous switching and stabilization within a single cycle. Comparative experiments with switched-capacitor array impedance matching networks (SCAIMNs) also confirm that the SCCIMN significantly enhances the SNR. Therefore, the proposed SCCIMN holds considerable potential for practical applications of the FDEM method.