An MFHPWM-Based Broadband Transmitting System for Frequency-Domain Electromagnetic Prospecting

In frequency-domain electromagnetic (FDEM) detection, the spectral energy transmission schemes with high-frequency point density help to improve detection efficiency and imaging accuracy. However, limited by the severe reactive power suppression of the transmitting coil or grounded cable, the strength of the primary field is suppressed, thus reducing the signal-to-noise ratio (SNR) and measurement accuracy. To solve this problem, a broadband transmitting system based on multifrequency hybrid pulsewidth modulation (MFHPWM) strategy is proposed in this article. The scheme allows flexible configuration of main frequency points. Then, the coverage of the required frequency points can be realized in a frequency band scan manner. In addition, a tunable resonance compensator is designed based on the modulation capacitor strategy to realize the resonance match with different MFHPWM signals, thus improving the signal strength. In this article, the principle of MFHPWM strategy is analyzed in detail. The circuit configuration and parameter design of the broadband compensator are then discussed. Finally, the feasibility of the proposed scheme is verified by simulation and laboratory experiments. Compared with the conventional spectral energy focusing transmitting schemes, the proposed scheme allows higher SNR in broadband operation.