Effects of modulation schemes on the performance of directly coupled high-T-c dc SQUID magnetometers

We have designed and fabricated the directly coupled YBa2Cu3O7-delta de SQU ID magnetometers with two different modulation schemes to study the crossta lk effect in the on-chip multi-channel magnetometers, In one of the modulat ion schemes, the modulation current was directly injected into the SQUID bo dy and the pick-up coil. The modulation efficiency was changed by the ratio of the modulation current flowing through the SQUID to the pick-up coil. I n the other schemes, the modulation flux is mutually coupled through an ext ernal coil, and the modulation efficiency was changed by the mutual inducta nce of the external coil and the magnetometer, The results show that the mo dulation efficiency was varied when the value of self-inductance or the mut ual inductance of SQUIDs change, Usually, lower modulation efficiency resul ts in a higher crosstalk. The performance of magnetometers was also influen ced by different modulation schemes. Their noise spectrum was compared as e vidence.