A New Weak-Coupling Method with Eccentric Dual Bucking Coils Applied to the PRBS Helicopter TEM System

Area of Science:

• Geophysics
• Electromagnetism
• Signal Processing

Background:

• Helicopter transient electromagnetic (HTEM) systems utilize weak-coupling coils to enhance signal-to-noise ratio and protect data acquisition circuits.
• Pseudorandom Binary Sequence (PRBS) HTEM systems offer high-precision measurements for identifying geological model responses.
• Standard PRBS signals can cause saturation due to rapid on/off transitions, limiting system performance.

Purpose of the Study:

• To propose a novel weak-coupling coil structure, eccentric dual bucking coils, for multi-receiver EM systems.
• To address the signal saturation issue associated with standard PRBS signals in HTEM systems.
• To evaluate the performance improvement offered by the new coil structure and PRBS method compared to traditional techniques.

Main Methods:

• Analysis of PRBS current characteristics and transmitter-receiver magnetic field distribution.
• Design and simulation of eccentric dual bucking coils using Maxwell software.
• Theoretical analysis and data simulation comparing PRBS and traditional square wave methods for data preprocessing.
• Validation of the proposed method through ground experiments.

Main Results:

• The proposed eccentric dual bucking coils structure was simulated and found feasible for multi-receiver EM systems.
• The PRBS method, with the new coil structure, demonstrated the ability to acquire earlier-time response data compared to the traditional square wave method.
• Data preprocessing analysis indicated advantages of the PRBS method, considering factors like residual primary field.

Conclusions:

• The eccentric dual bucking coils offer a viable solution for improving weak-coupling in multi-receiver EM systems.
• The PRBS HTEM method, enhanced by the new coil design, provides superior data acquisition capabilities, particularly for early-time responses.
• The proposed approach is reliable and effective for geophysical exploration, as confirmed by experimental validation.