Detection of Extremely Weak and Wideband Bio-Magnetic Signals in Non-Shielded Environments Using Passive Coil Sensors

We report a coil-based passive sensing system and associated Digital Signal Processing (DSP) capable of detecting extremely weak and wideband bio-magnetic signals without the need for shielding. Our previous work showed potential in this direction but was limited to detecting magnetocardiography (MCG) signals that are the strongest emanated by the human body as well as narrowband. In a major step forward, we advance our DSP with notch and Empirical Mode Decomposition filters, in addition to bandpass filtering and averaging utilized in the past and refine our coil design. We characterize the system's noise performance, analyze effectiveness of the DSP methods, and validate performance
in vitro
. The proposed system considerably outperforms our previous design: noise levels at 10 Hz and 100 Hz are reduced by ∼46% and ∼92%, respectively, while detection sensitivity is improved by ∼94% across a ∼3333% wider signal bandwidth. That is, signals as low as magnetomyography (MMG) and evoked Compound Action Potentials (eCAP) and of frequency range comparable to magnetoneurography (MNG) can now be retrieved passively, in non-shielded environments. As a proof-of-concept, we utilize a single sensor and 24 minutes of recording; however, these parameters are scalable, as is the strength and frequency range of detectable bio-magnetic signals. To this end, we include discussions on how the hardware and DSP components can be parameterized and adjusted to fit diverse clinical needs. The proposed system can empower seamless detection of MCG, MMG, eCAP, and MNG, among others, opening unexplored opportunities for the future of medical diagnostics, monitoring, and treatment.