【摘要】 本文采用偏置电流反转的频率与磁通调制频率相等的方案,研制了带偏置电流反转的dcSQUID测试系统,明显降低了YBCO双晶结dcSQUID的1/f噪声.在3Hz处,磁通噪声由静态偏置时的3.2×10-40/Hz降低到5.9×10-50/Hz.1/f噪声的角频率从1kHz下降到3Hz.前放的设计,采用低噪声集成电路,整个磁通锁定环置于测试杆顶端,简化了电路,提高了测试系统的稳定性.在白噪声区,测得最低磁通噪声为1.6×10-50/Hz.前放的噪声系数为1.1dB.更多还原

【Abstract】 According to the bias current and flux modulation scheme, we have designed an integral dc SQUID measurement system. In this scheme, both the flux and bias current are modulated at the same frequency. We observed that the bias reversal technique obviously reduces the low frequency noise of YBCO bicrystal junction dc SQUID. The magnetic flux noise was reduced from 3.2×10\+\{-5\} \-0/H\-z at 3Hz with static bias to 5.9×10\+\{-5\} \-0/H\-z with bias reversing.\;About the design of preamplifier we used integrated circuit instead of former preamplifier composed by discrete components. Thus the whole flux locked loop can be placed at the end of the test rod, to reduce the shielding problems inherent in conventional SQUID electronics. In the white noise region the tested minimum flux noise is 1.6×10\+\{-5\} \-0/H\-z , among which the noise of the circuit of measurement system is far less than that of SQUID. The noise factor of preamplifier is 1.1dB.更多还原