Design and Verification of Wide-band Search Coil Magnetometer Based on Transimpedance Preamplifier

The search coil magnetometer is widely used in space exploration and geological prospecting due to its high sensitivity and low noise level. This study presents a search coil sensor based on a transimpedance preamplifier to achieve a wide frequency bandwidth. The sensor directly connects the output signal of the inductive coil to the transimpedance preamplifier, which converts the AC magnetic field signal into an electrical signal. A signal transfer model of a magnetic sensor based on a transimpedance preamplifier is established, and the theoretical formula for sensitivity and noise is deduced. The search coil sensor is designed and developed using this formula to achieve a bandwidth of 0.01～10 kHz and a noise level of 1 fT·Hz^–1/2 at 1～10 kHz. A signal modulation method evaluates the sensor’s performance for efficient amplitude and phase extraction at a specific frequency. The dual sensor differential method eliminates environmental interference during sensor noise assessment, and a phase difference analysis evaluates the homologous frequency bands of signals detected by two probes. As a result, the sensor achieves a 1 fT·Hz^–1/2 noise level in the 1 kHz to 10 kHz range.