Abstract
We have developed a magnetometer system using high-Tc SQUIDs, aiming to use in a basic physiological study of cardiac functions of small experimental animals. A cryostat was prepared to have a spacing of 3mm between the air & nitrogen at the bottom, where the capacity of liquid nitrogen was about 4L. Two direct-coupled SQUIDs were located within the cryostat in such a manner that a reference SQUID that detected environmental field noise was placed 8.5cm above a sensing SQUID. The feedback current of the reference SQUID was also supplied to the same type of coil at the sensing SQUID, to form a gradiometer at the level of signal detection. The whole system was operated within a magnetically shielded room having an attenuation of 50dB at low frequencies. The effect of the direct-feedback gradiometer to reduce external field noises was confirmed, where more than 20dB attenuation was obtained for the largest 50Hz noise in the shielded room. MCG signals of anesthetized rats were measured in a wide bandwidth of 0.5-200Hz.
