Investigation of Noise Reduction and SNR Enhancement in Search Coil   Magnetometers at Low Frequencies
  Here, a generalized induction coil sensor model, more generalized than other models, has been considered and the equivalent magnetic field of the coil thermal noise and the sensor signal to noise ratio are calculated theoretically based on the dimensions and geometry of the coil winding and its core. Our calculations indicate that the equivalent magnetic field of the thermal noise can be minimized by the coil to core weight ratio. Moreover, it is found that the sensor signal to noise ratio can be maximized with only a special value of core aspect ratio length to diameter of core ratio. The calculation results here exhibit good agreement with the experimentally measured noise data. 
Abolghasem Nourmohammadi, Seyed Mohammad Hassan Feiz, Mohammad Hassan   Asteraki
physics.ins-det quant-ph