Proposal of Coil Structure for Air-Core Induction Magnetometer

Proposal of coil structure for air-core induction magnetometer is presented. The key point is the lamination factor which refers to the ratio of winding number compared with an ideal Brooks-coil. A decrease in lamination factor produces an increase in flux-to-voltage transfer ratio, and a decrease in noise floor level of the magnetometer. The size of coil defines the 20 dB/decade slope in frequency response of the magnetometer. While a magnetometer consisting of a coil with low lamination factor has high cutoff frequency, the sensitivity is better than of a coil with high lamination factor even if the frequency is lower than the cutoff frequency. Some magnetometers having few hundred ft/Hz^1/2 are fabricated, and demonstrate the validity of the idea. This design method may allow us to develop an ultra-sensitive, high-spatial-resolution induction magnetometer comparable to SQUID sensor.