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Wang Y.,Key Laboratory of Geo exploration Instruments | Wang Y.,Jilin University | Zhang X.,Key Laboratory of Geo exploration Instruments | Zhang X.,Jilin University | And 4 more authors.
Proceedings of IEEE Sensors | Year: 2017

Spin-exchange-relaxation-free (SERF) atomic magnetometer is the most sensitive magnetic detector in the world at present due to the fact that the broadening of spin-exchange collision is eliminated by operating at high alkali-mental density and low magnetic field. On that condition, the precession frequency of high-density alkali vapor becomes a constant fractional value of Larmor frequency, and the width of magnetic-resonance line gets narrower. This paper analyzes the principle of SERF regime and proposes an innovation based on measuring the slowing-down Larmor frequency directly instead of the complicated conventional method based on the width of magnetic resonance line. We calculated and simulated the slowing-down precession frequency and linewidth of magnetic resonance on certain conditions. The experimental results have verified that the method is valid to identify the regime of SERF of atomic magnetometer via detecting the slowing-down precession frequency. © 2016 IEEE.


Shi H.,Jilin University | Shi H.,Key Laboratory of Geo Exploration Instruments | Wang Y.,Jilin University | Wang Y.,Key Laboratory of Geo Exploration Instruments | And 2 more authors.
Journal of Sensors | Year: 2016

An optimized triaxis induction magnetometer has been designed and calibrated to minimize the influences from the nonorthogonality and the magnetic flux crosstalk. Utilizing the nonlinear least square method, contributions due to the nonorthogonal assembly of three transducers are cancelled. The magnetic flux crosstalk is a frequency-dependent error component in the calibration of the triaxis induction magnetometer. Influences from the assembly density, the frequency, and the feedback amount are analyzed theoretically, and an optimized sensor configuration which has a smaller crosstalk is achieved. Moreover, a mathematical compensation algorithm has also been utilized to suppress the residues crosstalk ulteriorly. To validate the theoretical analysis, a triaxis induction magnetometer was manufactured and the experiment setup has also been built. The experiment results show that the cross-outputs of the transverse induction magnetometers have been significantly decreased about two orders, indicating that the proposed method is applicable for the triaxis induction magnetometer. © 2016 Hongyu Shi et al.


Chen C.,Jilin University | Chen C.,Key Laboratory of Geo exploration Instruments | Liu F.,Jilin University | Liu F.,Key Laboratory of Geo exploration Instruments | And 4 more authors.
Sensors (Switzerland) | Year: 2015

An air-coil sensor (ACS) is a type of induction magnetometer used as a transducer to measure the variations of a magnetic field. This device is widely applied in helicopter transient electromagnetic method (TEM) exploration. Most helicopter TEM explorations generate common-mode noise and require extreme ACS specifications, both of which inevitably challenge geophysical explorations. This study proposes a differential air-core coil combined with a differential pre-amplifier to reduce the common-mode noise induced in exploration surveys. To satisfy the stringent performance requirements, including the geometric parameters and electrical specifications, the physical calculations in theory and the equivalent schematic of an ACS with noise location are investigated, respectively. The theory calculation and experimental result for the optimized ACS are then compared on the basis of a differential structure. Correspondingly, an ACS is constructed with a mass, resultant effective area, 3 dB bandwidth, signal-to-noise ratio, and normalized equivalent input noise of 2.5 kg, 5.5 m2 (diameter is 0.5 m), 71 kHz, 20 (the varying magnetic field strength is 1 nT/s), and 5.43 nV/m2, respectively. These data are superior to those of the traditional induction sensor 3D-3. Finally, a field experiment is performed with a fabricated sensor to show a valid measurement of the time-varying magnetic field of a helicopter TEM system based on the designed ACS. © 2015 by the authors; licensee MDPI, Basel, Switzerland.


Chen C.,Key Laboratory of Geo exploration Instruments | Chen C.,Jilin University | Liu F.,Key Laboratory of Geo exploration Instruments | Liu F.,Jilin University | And 6 more authors.
Sensors (Switzerland) | Year: 2016

The air-core coil sensor (ACS) is widely used as a transducer to measure the variation in magnetic fields of a helicopter transient electromagnetic (TEM) system. A high periodic emitting current induces the magnetic field signal of the underground medium. However, such current also generates a high primary field signal that can affect the received signal of the ACS and even damage the receiver. To increase the dynamic range of the received signal and to protect the receiver when emitting current rises/falls, the combination of ACS with magnetic flux compensation structure (bucking coil) is necessary. Moreover, the optimized ACS, which is composed of an air-core coil and a differential pre-amplifier circuit, must be investigated to meet the requirements of the helicopter TEM system suited to rapid surveying for shallow buried metal mine in rough topography. Accordingly, two ACSs are fabricated in this study, and their performance is verified and compared inside a magnetic shielding room. Using the designed ACSs, field experiments are conducted in Baoqing County. The field experimental data show that the primary field response can be compensated when the bucking coil is placed at an appropriate point in the range of allowed shift distance beyond the center of the transmitting coil and that the damage to the receiver induced by the over-statured signal can be solved. In conclusion, a more suitable ACS is adopted and is shown to have better performance, with a mass of 2.5 kg, resultant effective area of 11.6 m2 (i.e., diameter of 0.496 m), 3 dB bandwidth of 66 kHz, signal-to-noise ratio of 4 (i.e., varying magnetic field strength of 0.2 nT/s), and normalized equivalent input noise of 3.62 nV/m2. © 2016 by the authors; licensee MDPI, Basel, Switzerland.


PubMed | Key Laboratory of Geo exploration Instruments
Type: Journal Article | Journal: Sensors (Basel, Switzerland) | Year: 2016

The air-core coil sensor (ACS) is widely used as a transducer to measure the variation in magnetic fields of a helicopter transient electromagnetic (TEM) system. A high periodic emitting current induces the magnetic field signal of the underground medium. However, such current also generates a high primary field signal that can affect the received signal of the ACS and even damage the receiver. To increase the dynamic range of the received signal and to protect the receiver when emitting current rises/falls, the combination of ACS with magnetic flux compensation structure (bucking coil) is necessary. Moreover, the optimized ACS, which is composed of an air-core coil and a differential pre-amplifier circuit, must be investigated to meet the requirements of the helicopter TEM system suited to rapid surveying for shallow buried metal mine in rough topography. Accordingly, two ACSs are fabricated in this study, and their performance is verified and compared inside a magnetic shielding room. Using the designed ACSs, field experiments are conducted in Baoqing County. The field experimental data show that the primary field response can be compensated when the bucking coil is placed at an appropriate point in the range of allowed shift distance beyond the center of the transmitting coil and that the damage to the receiver induced by the over-statured signal can be solved. In conclusion, a more suitable ACS is adopted and is shown to have better performance, with a mass of 2.5 kg, resultant effective area of 11.6 m (i.e., diameter of 0.496 m), 3 dB bandwidth of 66 kHz, signal-to-noise ratio of 4 (i.e., varying magnetic field strength of 0.2 nT/s), and normalized equivalent input noise of 3.62 nV/m.

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