The high-frequency carrier-type (HFC-type) magnetic field sensor realizes very high sensitivity without any cooling apparatus for the sensor element. An important technique for obtaining high sensitivity is the use of a high-frequency current applied to the sensor element. The maximum sensitivity is obtained at frequencies up to the ferromagnetic resonance of the sensor magnetic thin film; for example, hundreds of megahertz for amorphous CoNbZr films. It is becoming important to study high-frequency circuits for driving HFC-type magnetic field sensors in order to achieve any practical applications such as nondestructive testing or biomedical applications. In this paper, a method of reflection signal measurement is studied in order to measure alternating magnetic fields with very small magnitude. A theoretical formula based on an equivalent circuit model was obtained for the relation between the sensor property and measurement sensitivity. An experimental confirmation was carried out by comparing this formula with experimental results. Finally, the measurement of a small alternating magnetic fields was effected by combining reflection signal measurement with the carrier-suppressing method.
