An On-Site Harmonic Noise Cancellation Antenna With a Multinode Loop for Magnetic Resonance Sounding Measurement

Abstract

Magnetic resonance sounding (MRS) is a geophysical method to detect aquifers directly in the earth’s magnetic field, which offers the benefit to evaluate groundwater qualitatively and quantitatively. Due to the influence of powerline harmonic noise, the reliability of obtaining the weak MRS signal (10–9 V) is severely limited with a square antenna or a conventional <xref ref-type="fig" rid="fig8" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">figure-8</xref> antenna. To realize the high signal-to-noise ratio (SNR) measurement of groundwater, we first propose a multinode antenna consisting of four <xref ref-type="fig" rid="fig8" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">figure-8</xref> antennas connected around nodes, which has better geometric symmetry and antiphase magnetic dipoles to cancel the magnetic fluxes caused by noise. The simulation results show that the noise suppression effect of the new antenna is better than that of the square antenna and <xref ref-type="fig" rid="fig8" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">figure-8</xref> antenna and is independent of the layout angle. We successfully applied the multinode antenna to test the noise-canceling ability in the urban environment and the detection of field underground aquifers, which verified the superiority of the new antenna in improving the efficiency and the SNR. To be specific, the adoption of this antenna can increase the detection efficiency by 4–8 times and improve the SNR by 10 dB with the same sensitivity compared with the conventional antennas. The utilization of on-site noise suppression characteristic in multinode antennas provides a novel idea for MRS with high SNR, especially in areas with severe noise interference.