Abstract
It analyses the composition and principle of high-sensitive wide-band magnetic-feedback inductive magnetic sensor to fulfil the demand of high-sensitive wide-band magnetic sensor in geological exploration. It studies main factors to the performance of wide-band magnetic sensor, such as turns of coils, core material features, and amplifier noise, specifies section-wise coil winding, the type and dimension of core material, and designs low-noise high-impedance LF chopping amplifier channel and composite amplifier with HF amplifier channel. The noise of magnetic sensor at 1 Hz is better than 10-4nT/Hz1/2, at 100Hz-1kHz band the noise floor is close to SQUID which can reach 10-6nT/Hz1/2. The magnetic sensor works at wide frequency band (0.0001Hz-10kHz) and ultra-low noise, which can meet the requirements of both AMT and CSAMT.
Highlights
High-sensitive wide-band inductive magnetic sensor is the most widely-applied magnetic receiver in electromagnetic prospecting, mainly used in the exploration of metal mineral, petroleum resources, and indepth geophysics[1,2,3].Electromagnetic prospecting is divided into audio frequency magnetelluric (AMT) and Controlled source audio frequency magnetelluric (CSAMT), with the former requiring high-sensitive magnetic sensor, and the latter wide frequency-band, the sensor shall fulfil field requirements like small size, light weight, and low power consumption[2]
Based on actual field environment, the paper studies how to realize wide frequency-band and low-noise of inductive magnetic sensor from theoretical and field design perspective, which can fulfil the requirements of both AMT and CSAMT exploration
The basic principle of magnetic sensor is Faraday’s law of electromagnetic induction, and inducted electromotive force Ui will be generated in case that cylinder coil, with N being the number of turns and S being sectional area, is placed in the magnetic field B(t) varied with time, which is shown as follows: UUii dddd(tt) dd(tt)
Summary
High-sensitive wide-band inductive magnetic sensor is the most widely-applied magnetic receiver in electromagnetic prospecting, mainly used in the exploration of metal mineral, petroleum resources, and indepth geophysics[1,2,3].Electromagnetic prospecting is divided into audio frequency magnetelluric (AMT) and Controlled source audio frequency magnetelluric (CSAMT), with the former requiring high-sensitive magnetic sensor, and the latter wide frequency-band, the sensor shall fulfil field requirements like small size, light weight, and low power consumption[2]. The basic principle of magnetic sensor is Faraday’s law of electromagnetic induction, and inducted electromotive force Ui will be generated in case that cylinder coil, with N being the number of turns and S being sectional area, is placed in the magnetic field B(t) varied with time, which is shown as follows: UUii. In the formula N is the number of turns, S sectional area, μr relative permeability of core, and B0 being magnetic field component in the direction of core. A layer of feedback coil is winded on inducted coil, with its inductance being Lf , resistance being Rf , and mutual inductance being M via formula MM = QQ√LL ∗ LLff; close coupling between inducted coil and feedback coil is in place with its factor Q=1, MM = √LL ∗ LLff. And transfer function H(ω) is shown as follows suppose gain of amplifying circuit being A, and output being V0: HH(ωω). Under the situation that feedback resistance is certain, i.e. feedback depth being constant, and that amplifying product A of amplifying circuit is increased, the more feedback factor is, LF stop frequency will be decreased, and HF stop frequency will be increased, which is conducive for spreading the width of frequency band
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