Low-cost Magnetometer Research Articles

Citizen science: Development of a low-cost magnetometer system for a coordinated space weather monitoring

As part of Ham Radio Science Citizen Investigation (HamSCI) Personal Space Weather Station (PSWS) project, a low-cost, commercial off-the-shelf magnetometer has been developed to provide quantitative and qualitative measurements of the geospace environment from the ground for both scientific and operational purposes at a cost that will allow for crowd-sourced data contributions. The PSWS magnetometers employ a magneto-inductive sensor technology to record three-axis magnetic field variations with a field resolution of ∼3 nT at a 1 Hz sample rate. The measurement range of the sensor is ±1.1×106 nT) and is valid over a temperature range of −40 °C to +85 °C. Data from the PSWS network will combine these magnetometer measurements with high frequency (HF, 3–30 MHz) radio observations to monitor large-scale current systems and ionospheric disturbances due to drivers from both space and the atmosphere. A densely-spaced magnetometer array, once established, will demonstrate their space weather monitoring capability to an unprecedented spatial extent. Magnetic field data obtained by the magnetometers installed at various locations in the US are presented and compared with the existing magnetometers nearby, demonstrating that the performance is very adequate for scientific investigations.

A novel calibration algorithm and its effects on heading measurement accuracy of a low-cost magnetometer

The Earth's magnetic heading plays a critical role in numerous applications, including navigation and orientation. The digital compass, which is made with a three-axis magnetometer, has proven to be a very cost-effective tool for providing measurements of the Earth’s magnetic heading. To obtain accurate heading measurements for end users, magnetometer calibration is a vital step to mitigate magnetic measurement distortions caused by hard-iron and soft-iron effects. However, current calibration approaches are often complex and lack performance evaluation at different noise levels. In this paper, we present a novel and efficient calibration algorithm that is conceptually simpler than most existing calibration methods and can be easily implemented. We hypothesized that a low-cost magnetometer as used in a smartphone would achieve 1-degree heading measurement accuracy after calibration using our new algorithm. Before applying this new algorithm to real-world data, we verified its effectiveness through numerical simulations. Our study demonstrated that, as the signal-to-noise ratio (SNR) increased, the root-mean-squared errors (RMSEs) of the estimated calibration parameters approached the corresponding Cramer-Rao bounds (CRBs). Experimental results showed that a magnetic heading accuracy of 1.37 degrees was attained for a smartphone located in Texas, U.S.A., which was more accurate than the heading accuracy obtained using the smartphone’s internal calibrated data. This study suggests that our calibration approach can allow low-cost magnetometers to provide highly accurate heading measurements, offering a cost-effective solution for various applications, including precise navigation.

Calibration of 3-Axis Low-Cost Magnetometer Using the Least Square Ellipsoid Fitting Algorithm

Calibration of 3-Axis Low-Cost Magnetometer Using the Least Square Ellipsoid Fitting Algorithm

Robust capsule-robot positioning with limited magnetic observations: An inertial-enhanced approach

ABSTRACT The capsule robot has become an important tool in covering the entire spectrum of digestive tract disease diagnosis. To achieve magnetic capsule-robot localization, the Levenberg-Marquardt (LM) algorithm has become a mainstream approach that provides accurate solutions in the general case. In practice, however, to meet the requirements of wearability, fewer sensors and lower power consumption are required. When the number of sensor observations becomes smaller, local convergences and outliers may occur in positioning results. To mitigate this issue, this paper makes two contributions to enhance the robustness of capsule-endoscope positioning, especially when the quality of magnetic observations is low. First, it proposes a two-step approach that initializes the capsule attitude by using inertial measurements before estimating the position. Second, it presents an improved LM-based positioning algorithm based on vest-type magnetic sensor arrays. Furthermore, to verify the proposed approach, a vest-type wearable device with two low-cost magnetometer arrays is designed. Test results have shown the effectiveness of the proposed LM method in enhancing positioning when there is a lack of observations.

Resonator-Based Bidirectional Lorentz Force Magnetic Sensor

We present a low power high sensitive in-plane resonant bidirectional Lorentz-force magnetic micro-sensor operating in air at ambient pressure. The concept is based on the detection of the resonance frequency shift of an electrothermally straight micro-beam resonator operated near the buckling point. Powered at 20 $\mu \text{W}$ , the micro-sensor shows a measured sensitivity (S) of 3.32/(mA.T), which is very high compared to the state of the art. The proposed method is simple in design making it promising for achieving practical low-cost magnetometer.

Human-interactive Mapping Method for Indoor Magnetic Based on Low-cost MARG Sensors

Indoor magnetic map (IMM) based on magnetic field fluctuations can be used in map assisted indoor positioning and navigation, etc. However, many IMM mapping solutions are time-consuming, labor-intensive, and high-cost, which limit the development and application of IMM. To solve the issues of accuracy, efficiency, and cost of IMM mapping collaboratively, we absorbed the idea of simultaneous localization and mapping (SLAM) method, and proposed a human-interactive mapping method of IMM based on the low-cost magnetometer, accelerometer, and rate gyro, i.e., MARG sensors. First, we defined IMM as the structured data set with a series of position stamps and magnetic field fluctuations. Then, we proposed the concept of general sensory calibration source (GSCS) and related metrics for human-interactive activities which provide virtual information to eliminate the time-accumulated error of position stamps and assist in obtaining stable magnetic field fluctuations. Finally, we conduct a series of experiments to verify the performance of the proposed method. The test results show that the proposed method can not only meet the requirements of mapping accuracy but also significantly improve mapping efficiency and reduce mapping cost, which is superior to other state-of-the-art algorithms. Specifically, the significant results are as follows: the mapping accuracy is about 0.31 m, and the mapping efficiency is 1800 m$^2$ per hour, and the cost of the main module of IMM mapping does not exceed U.S. $10.

Magnetic Field Variations in Alaska: Recording Space Weather Events on Seismic Stations in Alaska

ABSTRACTSeismometers are highly sensitive instruments to not only ground motion but also many other nonseismic noise sources (e.g., temperature, pressure, and magnetic field variations). We show that the Alaska component of the Transportable Array is particularly susceptible to recording magnetic storms and other space weather events because the sensors used in this network are unshielded and magnetic flux variations are stronger at higher latitudes. We also show that vertical-component seismic records across Alaska are directly recording magnetic field variations between 40 and 800 s period as opposed to actual ground motion during geomagnetic events with sensitivities ranging from 0.004 to 0.48 (m/s2)/T. These sensitivities were found on a day where the root mean square variation in the magnetic field was 225 nT. Using a method developed by Forbriger (2007, his section 3.1), we show that improving vertical seismic resolution of an unshielded sensor by as much as 10 dB in the 100–400 s period band using magnetic data from a collocated three-component magnetometer is possible. However, due to large spatial variations in Earth’s magnetic field, this methodology becomes increasingly ineffective as the distance between the seismometer and magnetometer increases (no more than 200 km separation). A potential solution to this issue may be to incorporate relatively low-cost magnetometers as an additional environmental data stream at high-latitude seismic stations. We demonstrate that the Bartington Mag-690 sensors currently deployed at Global Seismographic Network sites are not only acceptable for performing corrections to seismic data, but are also capable of recording many magnetic field signals with similar signal-to-noise ratios, in the 20–1000 s period band, as the observatory grade magnetometers operated by the U.S. Geological Survey Geomagnetism Program. This approach would densify magnetic field observations and could also contribute to space weather monitoring by supplementing highly calibrated magnetometers with additional sensors.

Globally Asymptotic Stable Attitude Estimation with Application to MEMS Sensors

Aiming at the requirement of attitude information module with high precision, small size and low power consumption for the control of miniature UAV, a practical attitude estimation algorithm based on the micro-electro-mechanical sensor is proposed in this paper, which realizes the accurate estimation of the attitude of the UAV under the condition of low acceleration. A low-cost MEMS gyroscope, accelerometer, and magnetometer are used in the system. The Euler angle is obtained by the state observer method based on Direction Cosine Matrix (DCM) which can be got by fusing the sensor data. Firstly, based on the basic idea of TRIAD algorithm, a method to determine the attitude rotation matrix by accelerometer and magnetometric measurement is proposed. Compared with the traditional method, this method does not have to calculate the inverse of the matrix. Secondly, a state observer is intended to estimate the attitude of the system. The state observer doesn't have to observe the bias of the gyroscope, but still ensures the convergence of the Euler angle. Finally, the simulation based on the actual sampling data of the MEMS sensor shows that the output of the state observer designed in this paper still has high accuracy and good dynamic characteristics under the condition of gyroscope noise and bias.

Magnetic gradiometry with a low-cost magneto-inductive sensor: A case study on Baba-Ali iron ore deposit (Western Iran)

Recently, the magneto-inductive (MI) magnetometers are commercially available off-the-shelf (COTS). Thanks to their low price, size, weight, power consumption, and fairly good resolution, these low-cost magnetometers are of interest to scientists in various fields of study. Inspired by a magnetic gradiometry magnetometer, we set up two MI sensors with a spacing of around 70 cm and performed a magnetic survey along 8 profiles on Baba-Ali iron ore deposit in western Iran with a proton magnetometer as a standard magnetometry survey instrument. These measurements are performed simultaneously with the set-up magnetometer. The comparison of proton magnetometer and MI sensors measurements shows that even the slight changes in the Earth’s magnetic field appeared on the proton magnetometer measurements also are displayed in the set-up MI magnetometer. Also, we showed that in high gradients which the proton magnetometer has a problem to measure a magnetic field the MI sensors can measure the Earth’s magnetic field.

Attitude determination by unscented Kalman filter and solar panels as sun sensor

CubeSats have became a common platform for education and technology demonstration. To overcome restrictions on CubeSat design, the Attitude Determination and Control System can use the photovoltaic panels to replace sun sensor. This work presents an attitude estimation method based on an unscented Kalman filter, using low cost gyroscope and magnetometer sensors and solar panels as a sun sensor. Data are simulated considering the influence of the Earth albedo on solar panels, and results are compared to those obtained by an extended Kalman filter.

A New Quaternion Kalman Filter Based Foot-Mounted IMU and UWB Tightly-Coupled Method for Indoor Pedestrian Navigation

In the field of indoor pedestrian navigation (IPN), the orientation information of a pedestrian is often obtained by means of strap-down inertial navigation system (SINS). To deal with the problem of divergence in SINS based orientation estimates, additional orientation sensors, such as a camera, are needed to provide external orientation observations, resulting in increased cost and complexity of system. Although a low-cost magnetometer (or compass) can be used, it is significantly affected by geomagnetic disturbances indoors. Besides, the magnetometer can only give the heading observation which is insufficient to correct orientation errors in all three directions. In this paper, we propose a novel IPN method based on shoe-mounted micro-electro-mechanical systems inertial measurement unit and ultra-wideband. The biggest advantage of this method is able to obtain high-precision position and orientation estimates at low cost. In addition, in the proposed method, the data fusion is implemented by a quaternion Kalman filter which does not involve any complex linearization and hence the system complexity is reduced. Experimental results show that a decimeter level position accuracy is achieved and the orientation drifts can be limited to 0.066 radians in indoor environments.

Magnetometer Calibration for Small Unmanned Aerial Vehicles Using Cooperative Flight Data.

This paper presents a new method to improve the accuracy in the heading angle estimate provided by low-cost magnetometers on board of small Unmanned Aerial Vehicles (UAVs). This task can be achieved by estimating the systematic error produced by the magnetic fields generated by onboard electric equipment. To this aim, calibration data must be collected in flight when, for instance, the level of thrust provided by the electric engines (and, consequently, the associated magnetic disturbance) is the same as the one occurring during nominal flight operations. The UAV whose magnetometers need to be calibrated (chief) must be able to detect and track a cooperative vehicle (deputy) using a visual camera, while flying under nominal GNSS coverage to enable relative positioning. The magnetic biases’ determination problem can be formulated as a system of non-linear equations by exploiting the acquired visual and GNSS data. The calibration can be carried out either off-line, using the data collected in flight (as done in this paper), or directly on board, i.e., in real time. Clearly, in the latter case, the two UAVs should rely on a communication link to exchange navigation data. Performance assessment is carried out by conducting multiple experimental flight tests.

A low-cost device for measuring local magnetic anomalies in volcanic terrain

Abstract. Reconstructions of the past behavior of the geomagnetic field critically depend on the magnetic signal stored in extrusive igneous rocks. These rocks record the Earth's magnetic field when they cool and retain this magnetization on geological timescales. In rugged volcanic terrain, however, the magnetic signal arising from the underlying flows may influence the ambient magnetic field as recorded by newly formed flows on top. To measure these local anomalies in the Earth's magnetic field directly we developed a low-cost field magnetometer based on a fluxgate sensor. To improve the accuracy of the obtained paleomagnetic vector and user-friendliness of the device, we combined this fluxgate sensor with tilt and GPS sensors to rotate the measured magnetic vector to true north, east, and down. The data acquisition is done using a ruggedized laptop, and data are immediately available for first-order interpretation. The first measurements done on Mt. Etna show local variations in the ambient magnetic field that are larger than expected and illustrate both the accuracy (certainly <0.5∘ in paleomagnetic direction) and potential of our new device.

Road Vehicle Detection and Classification Using Magnetic Field Measurement

This paper presents a road vehicle recognition and classification approach for intelligent transportation systems. This approach uses a roadside installed low-cost magnetometer and associated data collection system. The system measures the magnetic field changing, detects passing vehicles, and recognizes vehicle types. We introduce Mel Frequency Cepstral Coefficients (MFCC) to analyze vehicle magnetic signals and extract it as vehicle feature with the representation of cepstrum, frame energy, and gap cepstrum of magnetic signals. We design a 3-dimensional map algorithm using Vector Quantization (VQ) to classify vehicle magnetic features to 4 typical types of vehicles in Australian suburbs: sedan, van, truck, and bus. In order to train an accurate classifier, training samples are selected using the Dynamic Time Warping (DTW). The verification experiments show that our approach achieves a high level of accuracy for vehicle detection and classification.

UAV Sensor FDI in Duplex Attitude Estimation Architectures Using a Set-Based Approach

A fault detection and isolation algorithm for the attitude estimation of an unmanned aerial vehicle (UAV) using low-cost magnetometers, accelerometers, and gyroscopes, implemented in an inertial measurement unit (IMU) is proposed. Assuming the availability of double triaxial gyros, accelerometers, and magnetometers, the possibility that fault can occur both in input (gyros outputs) and in output (accelerometers and magnetometers outputs) to the kinematic nonlinear relations underlying attitude estimation must be taken into account. If an extended Kalman filter (EKF) can compensate for biases on gyroscopes, fault detection, for all sensors, is first obtained with a comparison between homogeneous sensor outputs. Then, the isolation of the faulted gyro is carried out through the analysis of the EKF bias estimates, whereas a set-based approach is used to isolate faulted accelerometers or magnetometers. For these sensors, isolation tests involve the solution of a linear programming problem on a moving time window in the discrete time domain. In order to show the practical applicability and robustness against measurement noise and different kind of faults, a set of simulations involving experimental data collected during flights of a tricopter UAV are discussed.

Calibration of Magnetometers with GNSS Receivers and Magnetometer-Aided GNSS Ambiguity Fixing.

Magnetometers provide compass information, and are widely used for navigation, orientation and alignment of objects. As magnetometers are affected by sensor biases and eventually by systematic distortions of the Earth magnetic field, a calibration is needed. In this paper, a method for calibration of magnetometers with three Global Navigation Satellite System (GNSS) receivers is presented. We perform a least-squares estimation of the magnetic flux and sensor biases using GNSS-based attitude information. The attitude is obtained from the relative positions between the GNSS receivers in the North-East-Down coordinate frame and prior knowledge of these relative positions in the platform’s coordinate frame. The relative positions and integer ambiguities of the periodic carrier phase measurements are determined with an integer least-squares estimation using an integer decorrelation and sequential tree search. Prior knowledge on the relative positions is used to increase the success rate of ambiguity fixing. We have validated the proposed method with low-cost magnetometers and GNSS receivers on a vehicle in a test drive. The calibration enabled a consistent heading determination with an accuracy of five degrees. This precise magnetometer-based attitude information allows an instantaneous GNSS integer ambiguity fixing.

Integrated microHall magnetometer to measure the magnetic properties of nanoparticles.

Magnetic nanoparticles (MNPs) are widely used in biomedical and clinical applications, including medical imaging, therapeutics, and biological sample processing. Rapid characterization of MNPs, notably their magnetic moments, should facilitate optimization of particle synthesis and accelerate assay development. Here, we report a compact and low-cost magnetometer for fast, on-site MNP characterization. Termed integrated microHall magnetometer (iHM), our device was fabricated using standard semiconductor processes: an array of Hall sensors, transistor switches, and amplifiers were integrated into a single chip, thus improving the detection sensitivity and facilitating chip operation. By applying the iHM, we demonstrate versatile magnetic assays. We measured the magnetic susceptibility and moments of MNPs using small sample amounts (∼10 pL), identified different MNP compositions in mixtures, and detected MNP-labeled single cells.

An efficient and robust maneuvering mode to calibrate low cost magnetometer for improved heading estimation for pedestrian navigation

Personal navigation systems intend to provide the navigation information in any environment, indoors and outdoors, and at any time. In outdoor environments, the positioning solution is typically provided by using Global Positioning System (GPS). However, GPS is inaccurate or unavailable in most of indoor environments and therefore other externally-referenced sensing techniques are required. Inertial sensing techniques are used for pedestrian navigation in association with dead reckoning approach. Magnetometers can be used to derive the user’s heading by sensing the Earth’s magnetic field. In this paper, an efficient and robust maneuvering mode to calibrate low cost magnetometer is recommended for pedestrian navigation applications. Additionally, other maneuvering modes and errors associated with each mode to achieve best estimation for the calibration parameters in the 3D Space are also provided. Also, the effect of using different maneuvering modes (DMM) on the heading estimation for the pedestrian navigation is studied. The results show that the coordinated mode is suitable to perform the calibration process as the unit is rotated in a way to cover the whole 3D space.

Swarm Optimization-Based Magnetometer Calibration for Personal Handheld Devices

Inertial Navigation Systems (INS) consist of accelerometers, gyroscopes and a processor that generates position and orientation solutions by integrating the specific forces and rotation rates. In addition to the accelerometers and gyroscopes, magnetometers can be used to derive the user heading based on Earth's magnetic field. Unfortunately, the measurements of the magnetic field obtained with low cost sensors are usually corrupted by several errors, including manufacturing defects and external electro-magnetic fields. Consequently, proper calibration of the magnetometer is required to achieve high accuracy heading measurements. In this paper, a Particle Swarm Optimization (PSO)-based calibration algorithm is presented to estimate the values of the bias and scale factor of low cost magnetometers. The main advantage of this technique is the use of the artificial intelligence which does not need any error modeling or awareness of the nonlinearity. Furthermore, the proposed algorithm can help in the development of Pedestrian Navigation Devices (PNDs) when combined with inertial sensors and GPS/Wi-Fi for indoor navigation and Location Based Services (LBS) applications.

NetPICOmag: A low-cost networked magnetometer and its applications

NetPICOmag (NPM) is the culmination of a design effort to build a compact, low-cost, laboratory-grade, networked magnetometer designed for remote autonomous operation, suited for research and education. NPM allows wide placement of magnetometers sensitive enough to detect auroral activity and the daily variation, and is suitable for education projects and a range of geophysical applications. The use of networked microcontrollers and GPS timing is applicable to other small instruments for field or local deployment, and an onboard data logging capability has also been demonstrated. We illustrate the value of the placement of low-cost magnetometers to increase coverage in an area through the study of a Pc 5 pulsation event which took place on September 4, 2010. By combining results with those from auroral zone magnetometers supporting the THEMIS project, we find that the phase velocity of these morning sector pulsations was northward on the ground. The event took place under very quiet solar wind conditions, and credible mapping associates it with the inner magnetosphere. Another aspect beyond increasing areal coverage is increasing density of coverage, which becomes feasible with instruments of very low cost. We examine aspects of the April 5, 2010 space weather event which are possible to deduce from closely spaced magnetometers.