• Title, Summary, Keyword: magnetometer

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Design and Fabrication of Improved Null-Type Torque Magnetometer (개선된 구조의 Null-Type 토크마그네토미터의 설계 및 제작)

  • Kim, Dong-Hyun;Shin, Sung-Chul;Hur, Jeen
    • Journal of the Korean Magnetics Society
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    • v.8 no.6
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    • pp.388-394
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    • 1998
  • We designed and fabricated an improved null-type torque magnetometer for measuring magnetic anisotropy of magnetic materials. This torque magnetometer has a measurement range of $~{\pm}15$ dyne.cm, and the range can be controlled. Resolution is ~0.0005 dyne.cm. Noise level is less than 0.01 dyne.cm with one measurement, and less than 0.004 dyne.cm with 10 averaged measuremets. The precision is less than 0.5 %. In contrast to typical null-type torque magnetometers, we placed a small ferrite magnet in the Helmholtz coil, instead of placing coil in the permanent magnet. From this novel sturucture, we can design a geometrically isotropic and relatively light-weight sample rod. Also, we can prevent the effect of input and output lines of coil exposed in the magnetic field in torque meter. Consequently, our novel null-type torque magnetometer can have a better sensitivity, faster response time, and smaller distortion of torque curve than commercially available torque magnetometers.

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Detecting Steel Pile Using Bore-hole 3-components Fluxgate Magnetometer (강관말뚝 탐지를 위한 시추공 3성분 자기탐사)

  • Lee, Heui-Soon;Rim, Hyoung-Rea;Jung, Ho-Joon;Jung, Hyen-Key;Yang, Jun-Mo
    • Journal of the Korean earth science society
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    • v.31 no.7
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    • pp.673-680
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    • 2010
  • A steel pile often utilized to bear heavy loads of the upper sub-structure, e. g., bridge constructions and tall buildings. As the steel piles are driven in the underground, it is not easy to detect the depth of the existing pile foundation when there is no detailed foundation information available. However, accurate informations of the depths of piles becomes critical required when reinforcing the existing structures or constructing new ones at the adjacent stage to assure the safety of existing structures. In this study, we tested the applicability of the three components borehole fluxgate magnetometer for detecting the depths and locations of steel piles which are commonly used in civil engineering. Results showed that the information of location as well as the depth of steel piles could be obtained by using data from the three components borehole fluxgate magnetometer.

Performance Enhancement and Countermeasure for GPS Failure of GPS/INS Navigation System of UAV Through Integration of 3D Magnetic Vector

  • No, Heekwon;Song, Junesol;Kim, Jungbeom;Bae, Yonghwan;Kee, Changdon
    • Journal of Positioning, Navigation, and Timing
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    • v.7 no.3
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    • pp.155-163
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    • 2018
  • This study examined methods to enhance navigation performance and reduce the divergence of navigation solutions that may occur in the event of global positioning system (GPS) failure by integrating the GPS/inertial navigation system (INS) with the three-dimensional (3D) magnetic vector measurements of a magnetometer. A magnetic heading aiding method that employs a magnetometer has been widely used to enhance the heading performance in low-cost GPS/INS navigation systems with insufficient observability. However, in the case of GPS failure, wrong heading information may further accelerate the divergence of the navigation solution. In this study, a method of integrating the 3D magnetic vector measurements of a magnetometer is proposed as a countermeasure for the case where the GPS fails. As the proposed method does not require attitude information for integration unlike the existing magnetic heading aiding method, it is applicable even in case of GPS failure. In addition, the existing magnetic heading aiding method utilizes only one-dimensional information in the heading direction, whereas the proposed method uses the two-dimensional attitude information of the magnetic vector, thus improving the observability of the system. To confirm the effect of the proposed method, simulation was performed for the normal operation and failure situation of GPS. The result confirmed that the proposed method improved the accuracy of the navigation solution and reduced the divergence speed of the navigation solution in the case of GPS failure, as compared with that of the existing method.

Unscented Filtering Approach to Magnetometer-Only Orbit Determination

  • Cheon, Yee-Jin
    • 제어로봇시스템학회:학술대회논문집
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    • pp.2331-2334
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    • 2003
  • The basic difference between the EKF(Extended Kalman Filter) and UKF(Unscented Kalman Filter) stems from the manner in which Gaussian random variables(GRV) are represented for propagating through system dynamics. In the EKF, the state distribution is approximated by a GRV, which is then propagated analytically through the first-order linearization of the nonlinear system. This can possibly introduce large errors in the true posterior mean and covariance of the transformed GRV, which may lead to sub-optimal performance and sometimes divergence of the filter. However, the UKF addresses this problem by using a deterministic sampling approach. The state distribution is also approximated by a GRV, but is now represented using a minimal set of carefully chosen sample points. These sample points completely capture the true mean and covariance of the GRV, and UKF captures the posterior mean and covariance accurately up to the 2nd order(Taylor series expansion) for any nonlinearity. This paper utilizes the UKF to determine spacecraft orbit when only magnetometer is available. Several catastrophic failures of spacecraft in orbit have been attributed to failures of the spacecraft mission. Recently studies on contingency-major sensor failure cases- have been performed. For mission success, contingency design or plan should be implemented in case of a major sensor failure. Therefore the algorithm presented in this paper can be used for a spacecraft without GPS or contingency design in case of GPS failure.

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Observation of the Earth's Magnetic field from KOMPSAT-1

  • Hwang, Jong-Sun;Kim, Sung-Yong;Lee, Seon-Ho;Min, Kyung-Duck;Kim, Jeong-Woo;Lee, Su-Jin
    • Proceedings of the KSRS Conference
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    • pp.1236-1238
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    • 2003
  • The Earth's total magnetic field was extracted from on board TAM (Three Axis Magnetometer) observations of KOMPSAT-1 satellite between June 19th and 21st, 2000. In the pre-processing, the TAM's telemetry data were transformed from ECI (Earth Centered Inertial frame) to ECEF (Earth Centered Earth Fixed frame) and then to spherical coordination, and self-induced magnetic field by satellite bus itself were removed by using an on-orbit magnetometer data correction method. The 2-D wavenumber correlation filtering and quadrant-swapping method were applied to the pre-processed data in order to eliminate dynamic components and track-line noise, respectively. Then, the spherical harmonic coefficients are calculated from KOMPSAT-1 data. To test the validity of the TAM's geomagnetic field, Danish/NASA/French ${\phi}$rsted satellite's magnetic model and IGRF2000 model were used for statistical comparison. The correlation coefficient between ${\phi}$rsted and TAM is 0.97 and IGRF and TAM is 0.96. It was found that the data from on board magnetometer observations for attitude control of Earth-observing satellites can be used to determinate the Earth's total magnetic field and that they can be efficiently used to upgrade the global geomagnetic field coefficients, such as IGRF by providing new information at various altitudes with better temporal and spatial coverage.

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A semispherical SQUID magnetometer system using high sensitivity double relaxation oscillation SQUIDs for magnetoencephalographic measurements

  • Lee, Yong-Ho;Hyukchan Kwon;Kim, Jin-Mok;Kim, Kwoong;Park, Yong-Ki
    • Progress in Superconductivity and Cryogenics
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    • v.5 no.1
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    • pp.21-26
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    • 2003
  • We designed and constructed a multichannel superconducting quantum interference device (SQUID) magnetometer system to measure magnetic fields from the human brain. We used a new type of SQUID, the double relaxation oscillation SQUID (DROS). With high flux-to-voltage transfers of the DROS, about 10 times larger than the dc SQUIDs, simple flux-locked loop circuits could be used for SQUID operation. Also the large modulation voltage of the DROS, typically being 100 $mutextrm{V}$, enabled stable flux-locked loop operation against the thermal offset voltage drift of the preamplifier. The magnetometers were fabricated using the Nb/AlOx/Nb junction technology. The SQUID system consists of 37 signal magnetometers, distributed on a semispherical surface, and 11 reference channels were installed to pickup background noises. External feedback was used to eliminate the magnetic coupling with the adjacent channels. The liquid helium dewar has a capacity of 29 L and boil-off rate of about 4 L/d with the total 48 channel insert. The magnetometer system has an average noise level of 3 fT/√Hz at 100 Hz, inside a shielded loon, and was applied to measure auditory-evoked fields.

Vehicle Orientation Estimation by Using Magnetometer and Inertial Sensors (3축 자기장 센서 및 관성센서를 이용한 차량 방위각 추정 방법)

  • Hwang, Yoonjin;Choi, Seibum
    • Transactions of the Korean Society of Automotive Engineers
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    • v.24 no.4
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    • pp.408-415
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    • 2016
  • The vehicle attitude and sideslip is critical information to control the vehicle to prevent from unintended motion. Many of estimation strategy use bicycle model or IMU integration, but both of them have limits on application. The main purpose of this paper is development of vehicle orientation estimator which is robust to various vehicle state and road shape. The suggested estimator use 3-axis magnetometer, yaw rate sensor and lateral acceleration sensor to estimate three Euler angles of vehicle. The estimator is composed of two individual observers: First, comparing the known magnetic field and gravity with measured value, the TRIAD algorithm calculates optimal rotational matrix when vehicle is in static or quasi-static condition. Next, merging 3-axis magnetometer with inertial sensors, the extended Kalman filter is used to estimate vehicle orientation under dynamic condition. A validation through simulation tools, Carsim and Simulink, is performed and the results show the feasibility of the suggested estimation method.

Development of a New Vehicle Detector Combining CW Radar and Magnetometer Techniques (CW 레이다와 자계기술을 복합한 새로운 차량검지기 개발)

  • 정재영;김인석
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.10 no.4
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    • pp.564-581
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    • 1999
  • This paper introduces a new, small, low cost, robust and quick replaceable pavement-based vehicle detector using CW radar, magnetometer, and UHF small antennal techniques. The detector has been developed for a replacement of loop detectors having wide surface areas, for a more accurate operation under all weather conditions, and for no algorithmic change of the existing traffic information system. The detected vehicle information is sent by a small helical antenna embedded in a plastic material and received by a 5/8 $\lambda$ long GP antenna for signal processing. In a relatively good weather condition, the detector operates at 24 GHz. But in a heavy rain condition, magnetometer is activated by automatic switching.

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Magnetic Field Standards Using Magnetic Resonance

  • Park, Po Gyu;Kim, Wan-Seop;Joo, Sung Jung;Lee, Hyung Kew
    • Journal of the Korean Magnetic Resonance Society
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    • v.21 no.1
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    • pp.7-12
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    • 2017
  • The nuclear magnetic resonance (NMR) and atomic magnetic resonance (AMR) plays a fundamental role in achieving a high accuracy of magnetic field measurements. Magnetic field unit (T) was realized based on the shielded proton gyromagnetic ratio (${\gamma}^{\prime}_P$), helium-4 gyromagnetic ratio (${\gamma}_{4He}$) and related techniques. The magnetic field standard system has been disseminated by the NMR magnetometer and electromagnet, a Helmholtz coil system, and AMR magnetometer in the nonmagnetic laboratory. A magnetic field standard below 1 mT has been developed by using Cs and Cs- $^4He$ AMR with automatic compensation of an external magnetic field noise. The standards serve for the calibration of magnetometers and support the test of sensors and materials in the range from $5{\mu}T$ to 2.0 T with (1 to 50) ${\mu}T/T$ uncertainty (k=2).

Background Noise Reduction by Software Methods in the 37-channel SQUID Magnetometer System (뇌자도 측정용 37채널 스퀴드 자력계에서의 합성 미분계 및 적응필터, 주파수영역 적응필터에 의한 배경잡음 제거)

  • 김기웅;이용호;권혁찬;김진목;강찬석
    • Journal of Biomedical Engineering Research
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    • v.24 no.3
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    • pp.167-173
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    • 2003
  • Measuring subtle neuromagnetic signals requires eliminating background noises. Especially, a SQUID magnetometer is very sensitive to the magnetic noise even from a distant source. As typical software methods, we use the synthetic gradiometer of the adaptive filtering to reduce the noises. In this article, we present noise reduction effects in our 37-channel SQUID magnetometer system by applying each method including the frequency-domain adaptive filtering and discuss a selective application of the methods to the detection of clinical magnetoencephalogram signals.