As a core component of the bucking coil helicopter TEM system, the current pulse inverter should agree two crucial aspects, high power and fast turn-off. In this paper, based on the design and modeling of transmitting coil and bucking coil, a novel current inverter topology based on the double constant voltage clamping technology, which differs from the traditional single clamping technology is firstly proposed and analyzed. By using double clamping technology, both the current pulse's rising edge and falling edge are improved effectively. What's more, the turn-off time of the current inverter is adjustable, which is of great difference from the conventional clamping technology with nonadjustable turn-off time. The ground and field experiments are implemented to test the performance of the current inverter. The results of the ground test of the performance comparison with worldwide VTEM transmitter verify that it successfully converts the standard 28V DC source from helicopter power to bipolar approximately trapezoid pulses with a peak current of 300A and a much faster turn-off time than the VTEM transmitter. The results of field surveying further demonstrate that it achieves a high quality of primary field compensation and effectively improve the detection capability of the helicopter TEM surveying system.

For compensating the primary field coupling from the transmitting coil and the sensing coil, the bucking coil is often used to achieve pure secondary field for the helicopter transient electromagnetic (HTEM) system. Traditionally, the distributed capacitance of the bucking coil and the transmitting coil is ignored and pay few attentions to study it. In fact, it has very important influence on the turn-off current of the transmitter and the transient electromagnetic (TEM) field of the system. In this paper, a novel distributed capacitance model of the HTEM coils is theoretically established at the first time, its effects on the turn-off current and the TEM field are analyzed in detail. It finds that the turn-off current in the transmitting coil and the bucking coil are not equal caused by the distributed capacitance although they are connected in series. The field experiments are completed and proved that the measured TEM fields agree very well with the simulated results based on the distributed capacitance model. This is very helpful to optimize the early-time TEM field and promote the shallow TEM data interpretation capability for the HTEM surveying.

With the advancement of deep Earth exploration and urban underground space detection, addressing the challenges posed by environmental complexity and increasing data acquisition accuracy are increasingly critical. Conventional geophysical exploration techniques and their associated networking approaches cannot fulfill contemporary exploration requirements. Herein, the fundamental principles and inherent connections between seismic exploration and electromagnetic exploration are analyzed by comparing the circuit design for seismic and electromagnetic data-acquisition systems. Consequently, a technical solution for a seismo-electromagnetic joint acquisition system with high accuracies in both seismic and electromagnetic explorations is developed. A real-time host monitoring system is developed for both personal computers and mobile terminals. Moreover, a distributed hybrid networking scheme for this distributed seismo-electromagnetic high-accuracy acquisition system that incorporates wired, wireless, and self-storage intelligent arbitrary clipping is innovatively implemented, achieving a synchronization accuracy of <100 ns among various acquisition systems. The developed system is used for networking deployment in Zhangjiakou (Hebei, China), verification of key indicators in a coal mine with a depth of 848 m in Huainan (Anhui, China), and practical onsite explorations in Changzhi (Shanxi, China). The experimental and application results verify the reliability, stability, and practicality of the system. The proposed joint exploration technique fully leverages the advantages of distributed data-acquisition systems and can potentially shed light on the development of other joint research methodologies. The findings can increase the efficiency and accuracy of joint geophysical explorations, providing a solid foundation with regard to both machinery and technical aspects.

In the transient electromagnetic method (TEM), the early primary field signals can interfere with the secondary field signals due to the turn-off time and mutual inductance between the transmitting and receiving coils, resulting in a shallow blind area. This primary field coupling interference (PFCI) is particularly pronounced when using a multi-turn, small-loop coil structure, which significantly limits TEM’s effectiveness in near-surface detection. To address this issue, several decoupling techniques have been proposed. Among them, the off-center self-compensation technology is considered effective and has been applied in systems such as airborne TEM. However, this approach has drawbacks because it is susceptible to primary field remanence caused by structural errors, and its eccentric design results in inadequate detection capabilities and lateral resolution. To overcome these limitations, we proposed a new non-coplanar positive compensation decoupling technology. This device enhances structural stability by positioning a positive compensation coil co-axially with the transmitting coil and coplanar with the receiving coil. Additionally, the positive compensation coil effectively enhances the device’s shallow detection capability by both reducing the relative horizontal distance between the transmitting and receiving coils and providing stronger shallow excitation signals. Simulation and field experiment results demonstrate the effectiveness of the new device.