Patent ID: 7656154

Claim:
A magnetic field measuring system comprising: a biomagnetic measurement device including a detection coil and a superconducting quantum interference device (SQUID) magnetometer; an optical pumping magnetometer configured to measure environmental magnetic noise in the biomagnetic measurement device, the optical pumping magnetometer including: a light source; a vapor cell filled with an alkali metal gas; an optical system configured to convert beam from the light source into circularly polarized beam and to make the circularly polarized beam incident on the vapor cell; a photodetector configured to detect the beam passing through the vapor cell; Helmholtz coils configured to apply a static magnetic field to the vapor cell; means for applying an oscillating magnetic field in a direction orthogonal to the static magnetic field to the vapor cell, the means including a voltage controlled oscillator and radio-frequency (RF) coils; and a lock-in amplifier configured to perform lock-in detection of a phase between an output signal from the photodetector and a signal transmitted from the voltage controlled oscillator to the RF coils; magnetometers configured to measure environmental magnetic noise entering the vapor cell of the optical pumping magnetometer in directions except a direction of application of the static magnetic field; magnetometer drive circuits respectively connected to the magnetometers; current converters configured to respectively convert outputs from the magnetometer drive circuits into an amount of current; and output current from the current converter is inputted to magnetic field generating coils, the magnetic field generating coils being configured to apply a magnetic field to the vapor cell, the magnetic field being formed in an opposite phase to the environmental magnetic noise entering the vapor cell in the direction except the direction of application of the static magnetic field.