PURPOSE: To tilt the flux-current characteristic of a SQUID fluxmeter and increase the flux-voltage conversion factor of the fluxmeter so as to reduce flux noise by making the injecting position of a bias current asymmetric with respect to inductances.

CONSTITUTION: Although the graph showing the flux-voltage characteristic of a SQUID fluxmeter usually becomes a symmetric sine wave, the graph becomes to rise steeply and the characteristic becomes to tilt as a whole, since the injecting position 2 of a bias current IB is asymmetric with respect to inductances 3 and 4. In the graph showing the flux-flux vs voltage conversion factor characteristic obtained from the graph showing the flux-voltage characteristic, the flux-voltage conversion factor is a measure representing dV/dΦ. The ratio of external magnetic fluxes Φ to the magnetic flux quantum Φ0 is shown as the abscissa and the voltage (microvolts) is shown as the ordinate. Since the graph showing the flux-voltage characteristic is inclined, the value of the flux-voltage conversion factor (dV/dΦ) in the graph showing the flux-flux vs voltage conversion factor characteristic also increases. Therefore, the amplitude of the output voltage of a SQUID(superconducting quantum interference device) becomes larger and the SQUID does not produce much noise.