Search

Aiming at the shallow surface electromagnetic detection instrument system widely used in urban underground space exploration and underground target induction, a three-frequency resonance transmitting scheme is proposed to solve the problems of low efficiency in conventional single-frequency transmission method and high-voltage stress ( $d\text{v}/d\text{t}$ ) in multifrequency pseudorandom transmission method. According to the specific transmitting coil and the required transmitting frequency, a three-frequency resonant matching circuit is designed to transmit the current signal with three frequency components, the fundamental and two low-order harmonics. Compared with 2n sequence pseudorandom transmitting mode, the current of resonant method is continuous without step, which reduces the influence on the received signal. In this article, the principle of three-frequency resonance is analyzed. The simulation experiment and laboratory test are carried out to verify the feasibility of the proposed method.