Broadband Air-Core Brooks-Coil Induction Magnetometer

Frequency compensation technique to be implemented in an optimal design method of air-core Brooks-coil induction magnetometer is presented. It is confirmed that the capacitance of a cable between coil and electronics defines the limitation of upper frequency. The limitation of lower frequency is expanded by use of I/V converter with frequency compensation. The fabricated magnetometer demonstrates the noise floor level of 300 fT/Hz^1/2 at 100 Hz, and the flat frequency response from 0.2 Hz to 20 kHz. It is found that the capacitance to be use in the I/V converter is also key parameter to define the noise floor level, and the parameter could be neglected if the value is small. This result may allow us to explain why the induction magnetometer based on definition of inductance is more sensitive in low-frequency region than that based on Faraday´s law. A design of induction magnetometer having comparable diameter to SQUID sensor for biomagnetic measurements is also discussed