Improving the sensitivity of a high-T_c SQUID at MH_z frequency using a normal metal transformer

摘要

Superconducting quantum interference devices (SQUIDs) can be used to detect the signals of nuclear quadrupole resonance (NQR). The NQR frequencies of some interesting materials are in the order of MHz. However, the sensitivity of a high-T_c SQUID is normally not enough to detect the weak NQR signals. To improve the sensitivity of a high-T_c SQUID at MHz frequency, we used a transformer made of normal copper wire. The transformer was composed of a pickup coil, an input coil and a capacitor. The pickup coil was used to detect the magnetic field; the input coil was used to couple the field to the SQUID; and the capacitor was used to create a resonant frequency. By using the normal metal transformer, the magnetic field resolution of the high-T_c dc SQUID was improved by about 38.8 times