Dual-frequency transmitter configuration for shallow surface electromagnetic detection

In shallow surface electromagnetic detection, the square wave scheme is generally used in conventional transmission systems. Based on frequency-domain electromagnetic (FDEM) sounding theory, high-frequency measurement helps to improve vertical resolution. However, long grounded cable inductance produces severe reactive power suppression at high frequency transmission frequencies, which will reduce detection. To further improve detection accuracy and efficiency, a dual-frequency transmitter configuration is proposed in this article for shallow surface detection. The transmitter simultaneously powers two LC series resonant circuits for the detection of shallow and deep area. Dual-frequency control strategy is adopted, with both bridge arms being provided with constant switching frequency operation. According to the equivalent model of the transmission system, the control of the load branches is independent of each other. The LC series resonant circuit guarantees a wide passband to match long cable inductance that cannot be accurately estimated in advance. Simulations and experimental tests were carried out using this transmitter configuration and control technique. The simulation and experimental results are in general agreement, verifying the feasibility and effectiveness of the proposed dual-band transmitter configuration.