Abstract: A device for measuring a quantity of a superparamagnetic material includes four coils (1-4) and a unit for injecting, into the coils, a direct current and two alternating currents of different frequencies. The quantity of superparamagnetic material is derived from an amplitude of a component at a mixing frequency, which frequency is a linear combination of the frequencies of the two alternating currents. The device is designed to reduce the influence of stray electromagnetic fields and inadvertent signal offsets on the measurement results. The device may advantageously be used for immunoassays.

Abstract: A device for measuring a magnetic material includes four coils having cores made of a superparamagnetic material, and a unit for injecting, into the coils, a direct current and two alternating currents of different frequencies. The value of the magnetic field is derived from the value of the direct current required to cancel an amplitude of a component at a mixing frequency. A structure of the electrical connections to the coils reduces disturbances caused by the alternating currents used with respect to the detection of the component at the mixing frequency. Moreover, specific configurations of the coils reduce the influence of stray electromagnetic radiation on the measurement results. The device can also be used to measure direct currents.