A non-invasive single-channel SQUID magnetometer for fetal magnetocardiography has been developed. The signal is picked-up with a wire wound third order gradiometer. The optimal configuration of the flux transformer is a trade-off between sufficient sensitivity for the magnetic field originated in fetal heart and effective immunity against the ambient magnetic noise. The over all system performance together with the measuring probe and SQUID electronics is described. The balancing of the third order flux transformer is discussed as well as the signal processing of fetal magnetocardiogram recordings.
The application of SQUIDS and superconducting radiometers in clinical biomagnetic instrumentation for fetal magnetocardiography is presented. The paper focuses on the characteristics and performance of the third order flux transformer for fetal magnetocardiography with a good signal to noise ratio. An optimum figure of merit of the third order flux transformer was determined. The optimal signal-to-noise ratio (SNR) was used as the optimization criterion.