Receiving resonant phase-modulated signals using atomic magnetometer for magnetic communications

Telecommunication in harsh environments, such as an electrically conductive medium, requires the use of carrier bands with very-low and ultralow frequencies for radiofrequency links. Recent advancements in atomic magnetometers operating at very-low frequencies have facilitated the reception of digitally modulated signals. We demonstrate the ability to transmit and receive quadrature phase-shift keying (QPSK) signals using a multi-resonant loop antenna and atomic magnetometer. The introduced multi-resonant loop antenna noticeably enhances the bandwidth, with an expansion exceeding 70% compared with a single-loop antenna. Additionally, utilizing an atomic magnetometer, we successfully demodulated a QPSK signal with a carrier frequency of 20 kHz and a symbol rate of 150 symbols per second. The acquired measurements reveal an error vector magnitude of 7.29% and a signal-to-noise ratio of 30.9 dB. These findings highlight the potential of the proposed system for efficient and reliable very-low frequency telecommunication in challenging environmental conditions.

I. Introduction

In recent years, innovative communication technologies that employ magnetic fields in the radiofrequency (RF) band have emerged, offering a novel approach to extending communication space [1, 2]. AC electromagnetic fields experience high attenuation in an electrically conductive medium, such as metals, solid materials, and water, making low frequency signals advantageous when dealing with strong medium absorption in terms of skin effect. However, the nature of low frequency magnetic field limits the signal range and requires a large characteristic size of the antenna for the RF link between transmitters and receivers. Consequently, it becomes crucial to employ a compact antenna that is insensitive to wavelength, such as a resonant loop coil. This type of antenna generates a magnetic field at a specific frequency based on its matching capacitance, rather than relying on its physical diameter. Furthermore, the RF atomic magnetometer (RFAM) stands out among atomic magnetometers due to its frequency band and inherent noise characteristics, which contribute to improved communication range and data rate [4].