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We present encouraging results obtained with an experimental apparatus based on coherent population trapping\ud and aimed at detecting a biological (cardiac) magnetic field in a magnetically compensated but unshielded\ud volume. The work includes magnetic-field and magnetic-field-gradient compensation and uses differential detection\ud to cancel common mode magnetic noise. Synchronous data acquisition with a reference (electrocardiographic\ud or pulse-oximetric) signal makes possible improvement of the signal-to-noise ratio in off-line averaging.\ud The setup has the significant advantages of working at room temperature with a small-size head, and the\ud possibility of fast adjustments of the dc bias magnetic field, which makes the sensor suitable for detecting a\ud biomagnetic signal at any orientation with respect to the axis of the head and in any position on the patient’s\ud chest, which is not the case with other kinds of magnetometers

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