| With the rapid developing of the economy,the demand for the resources is increasing year by year.As the stored resources is declining steadily,the deep exploration has become the potential solution to overcome the contradiction between the resources supply and demand.The frequency-domain electromagnetic method is an important technique for deep explorating in which the detection depth is inversely proportional to the frequency.In order to enhance the deep detection capability,a broadband exploration system must be developed,especially the broadband and low-noise magnetic sensing technology.In this thesis,to achieve the goal of broadband and low-noise magnetic detection,we combined the induction magnetometer and the Residence Times Difference(RTD)fluxgate magnetometer,and proposed a new integrated induction-fluxgate magnetometer based on the similarity of their sensing principles and the complementarity of the advantages.Firstly,we established the parameter models of the induction magnetometer and designed a low-noise pre-amplifier.The mathematic expressions of the core permeability,the coil resistance,inductance,capacitance,the volume and the weight have been derived mathematically.A high input impendence,low noise pre-amplifier was designed based on the Junction Field Effect Transistor(JFET),so as to match the high impendence of the induction magnetometer.The contributions of different noise sources in the pre-amplifier were analyzed,and then the total noise model was established and verified by experiments.Secondly,we have proposed the methods for widening the frequency band and optimizing the performances of the induction magnetometer.A closed-loop negative magnetic flux feedback structure is utilized to suppress the resonance of the induction coil,so as to widen the high frequency band.The chopping technology is utilized in the pre-amplifier to suppress the influence reasoned from the 1/f noise.Then the low frequency noise of the induction magnetometer was declined and the frequency band was widened.A tube core was proposed to decrease its weight without any performance loss for the induction magnetometer.The parametric model of the induction magnetometer was established and solved by the penalty function algorithm.And the relationship between the optimized parameters and the optimization goal was also discussed.Thirdly,the finite element method was used to optimize the structure and parameters of the integrated induction-fluxgate magnetometer.We proposed a dumbbell-shaped integration structure,in which the magnetic flux was concentrated into the core of the RTD fluxgate magnetometer,hence,its sensitivity was improved significantly.Furthermore,the relationships between the material,the length,the out diameter,the gap of the tube-core and the sensitivity enhancement of the RTD fluxate magnetometer have been analyzed and discussed.Finally,the optimal configuration of the integrated induction-fluxgate magnetometer was achieved.Fourthly,the performances of the proposed broadband and low noise integrated induction-fluxgate magnetometer are shown as follows.The frequency band is DC-10 kHz,which includs two operation modes and switches at 0.2Hz.The sensitivity in low frequency model is 0.38?s/nT,which is improved by 3.45 times compared with a single RTD fluxgate magnetometer,and the noise level is about 30pT/?Hz.The sensitivity in high frequency model is 2mV/nT@1Hz,and the noise performance is 3pT/?Hz@ 1Hz.Finally,the measurement errors due to the non-orthogonality and the magnetic crosstalk of the tri-axis magnetometer were analyzed and compensated.The transformation between the ideal and real coordinates has been derived,and the nonlinear algorithm was used to seek the non-ortogonal angles.The mechanism of the magnetic crosstalk was firstly analyzed based on the FEM simulation,and then was corrected theoretically.The measurement results show that the crosstalk error has been suppressed by 100 times significantly. |
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