We present first, encouraging results obtained with an experimental apparatus based on Coherent Population Trapping and aimed at detecting biological (cardiac) magnetic field in magnetically compensated, but unshielded volume. The work includes magnetic-field and magnetic-field-gradient compensation and uses differential detection for cancellation of (common mode) magnetic noise. Synchronous data acquisition with a reference (electro-cardiographic or pulse-oximetric) signal allows for improving the S/N in an off-line averaging. The set-up has the relevant advantages of working at room temperature with a small-size head, and of allowing for fast adjustments of the dc bias magnetic field, which results in making the sensor suitable for detecting the bio-magnetic signal at any orientation with respect to the heart axis and in any position around the patient chest, which is not the case with other kinds of magnetometers.
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