SQUID Gradiometer Module for Fetal Magnetocardiography Measurements Inside a Thin Magnetically Shielded Room

Gradiometer module plays a significant role in fetal magnetocardiography (fMCG) system and its performance determines the signal qualities directly. In order to obtain the best signal-to-noise ratio (SNR) of the fMCG signals in a thin magnetically shielded room (tMSR), the baseline of the axial gradiometers need to be optimized. In this paper, direct current superconducting quantum interference devices which is composed of weakly damped Josephson Junctions with β
_c
> 3 and has a flux-to-voltage transfer coefficient of 500 μV/Φ
₀
is employed for our gradiometers. Superconducting connectivity technique is utilized to connect input coil and pickup coil. First-order gradiometers with different baselines are thus developed. After the evaluation of the magnetic flux density and gradient flux density inside the tMSR, measurement of fMCG signals are taken with the gradiometers mentioned earlier. The simulated fetal QRS peak signals about 2.5 pT could easily be identified in the realtime gradiometer module outputs with an SNR larger than 11 dB.