Design of High Gain and High Sensitivity Extremely-Low Frequency Magnetic Signal Receiving System

The low attenuation rate of extremely low frequency (ELF) (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$30\sim 300$ </tex-math></inline-formula>Hz) makes it of wide interest in submarine communication and long-distance cross-domain communication. In this paper, a high gain and high sensitivity magnetic signal receiving system is developed based on a new ELF mechanical antenna with a typical frequency point of 75 Hz. The system includes a magnetic sensing receiving antenna, an impedance conversion transformer, an amplifier, and a filter. Each module describes in detail the design and associated tradeoffs that allow this receiving system to be applied to any magnetically inductive antenna of the same impedance. In this paper, a receiving system is developed using a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.85\Omega $ </tex-math></inline-formula>-48.2mH impedance antenna as an example. The receiver system has a gain of 58.6 dB at an operating frequency of 75 Hz, a receiver sensitivity of 1.5pT/Hz<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{1/2}$ </tex-math></inline-formula>, an operating bandwidth of 10 Hz, and a rejection of 16.7 dB at an operating frequency of 50 Hz.