Magnetoresistive Magnetometer Research Articles

Verification and calibration of a commercial anisotropic magnetoresistive magnetometer by multivariate non-linear regression

Abstract. Commercially available anisotropic magnetoresistive (AMR) magnetometers exhibit on the order of 1 nanotesla (nT) sensitivity in small size, weight, and power (SWaP) packages. However, AMR magnetometer accuracy is diminished by properties such as static offsets, gain uncertainty, off-axis coupling, and temperature effects. This work presents a measurement of the magnitude of these effects for a Honeywell HMC1053 magnetometer and evaluates a method for calibrating the observed effects by multivariate non-linear regression using a 24-parameter measurement equation. The presented calibration method has reduced the vector norm of the root mean square error from 4300 to 72 nT for the data acquired in this experiment. This calibration method has been developed for use on the AERO (Auroral Emissions Radio Observer) and VISTA (Vector Interferometry Space Technology using AERO) CubeSat missions, but the methods and results may be applicable to other resource-constrained magnetometers whose accuracies are limited by the offset, gain, off-axis, and thermal effects that are similar to the HMC1053 AMR magnetometer.

BIRDS-2: A Constellation of Joint Global Multi-Nation 1U CubeSats

BIRDS-2, the second generation of the Joint Global Multi-Nation Birds (JGMNB) project is a constellation of 1U CubeSats from Laboratory of Spacecraft Environment Interaction Engineering (LaSEINE), Kyushu Institute of Technology, Japan. The BIRDS-2 project consists of three identical 1U built by a group of students from four nations; Japan, Malaysia, Philippines, and Bhutan. It consists of 6 missions; Camera, Automatic Radio Packet Service-Digipeater (APRS-DP), Store and Forward (S&F), COTS GPS, Anisotropic Magneto Resistance Magnetometer (AMR-MM), and detection of single-event latch-up (SEL). The objective of BIRDS-2 is to provide an opportunity to learn the entire satellite system cycle, to lay down the foundation of the sustainable space program, and to create international networks of the ground station to assist the infant space program of the participating country. A total of 11 members learns the satellite development in a lean concept of 30m radius of the work area. The paper will describe the bus system of the BIRDS-2 CubeSats and the development process throughout the one year and three months of the project timeline. Completion of BIRDS-2 flight models remarks the successful design of the CubeSats bus system and waiting for the launch and deploy from International Space Station (ISS) around 3rd quarter of this year.

Aluminum Alloy Sensitization Evaluation by Using Eddy Current Techniques Based on IGMR-Magnetometer Head

To control the quality of conductive materials such as copper, aluminum, or steel, various non-destructive testing techniques based on eddy current monitoring are routinely employed. Some marine alloys such as the Al-5000 series are the subject of interest notably in shipbuilding because of their good mechanical properties. However, this type of material is often subjected to intergranular corrosion and stress corrosion cracking when sensitized (i.e., after a regular increase in temperature). This paper deals with the evaluation of sensitization on an aluminum alloy by using an eddy current technique utilizing an improved giant magnetoresistance magnetometer as the head sensor. The magnetic field responses of different samples, which have been subjected to different heat treatments, are presented. The results are compared to an analytical model, which takes account of the setup and sample, in order to evaluate the material property evolution due to the sensitization. We show, clearly, that the given heat treatment (>175 °C) has induced a material conductivity variation.

Magnetocardiography Using a Magnetoresistive Sensor Array.

In previous magnetocardiography studies, magnetocardiograms (MCGs) have been obtained using superconducting quantum interference device (SQUID) systems. SQUID is the most sensitive instrument for measuring low-frequency magnetic fields, but it requires liquid helium for cooling, so operating costs are high. In contrast, magnetoresistive (MR) magnetometers function by detecting the change in resistance, caused by an external magnetic field, and have much lower costs. This study was aimed to evaluate feasibility of the MR sensor array for acquiring MCGs.We used an MR sensor array, which was developed for measuring magnetic fields in the picotesla range, with a reduced noise level (TDK Corporation, Tokyo, Japan). A 30-channel MR sensor array was placed in a magnetically shielded room, and the cardiac magnetic field over the anterior chest walls of five healthy subjects was recorded.For all five subjects, MCGs were successfully recorded using the MR sensor array. The cardiac magnetic field corresponding to P, QRS, and T waves on an electrocardiogram (ECG) was detectable by signals averaging 272 ± 27.5 beats.An MR sensor array can be used to measure cardiac magnetic fields. Our results will contribute to the development of low-cost devices for recording MCGs, which will help develop non-invasive diagnostics in cardiovascular medicine.

Resolution limit of anisotropic magnetoresistance(AMR) based vector magnetometer

An AMR based vector magnetometer was developed for the Separated Payload program to explore the field-aligned currents in Earth polar region. It has the advantages of low volume and CubeSat platform compatible mass while still maintains adequate resolution. In order to determine the resolution limit of AMR based magnetometer, we measured the sensor’s intrinsic noise. This characteristic was in conflict with our prototype magnetoresistive magnetometer since phase sensitive detection(PSD) could only reject noise from interfacing circuit without affecting the signal to be measured. We believe that besides flipping the magnetization direction periodically, the set/reset technique also functions as a modulation to the magnetic field. The sensor operates at the modulation frequency and its noise level is much lower than that at low frequency. This technique is analyzed theoretically and a description from frequency perspective is given. By modulating the signal beyond corner frequency of the sensor and amplifier, both the sensor and interfacing circuit work in white noise region. Then we calculate the theoretical resolution limit of HMC1001 based magnetometer and the result shows that the noise floor is 24.9 pT/Hz0.5@1 Hz under 5 V bias with proper-matched amplifier.

Deconvolution of High-Resolution Magnetic Field Scans for Improved Current Density Imaging

Inverse problems are gaining more and more importance in the field of nondestructive testing (NDT). Magnetic imaging is an NDT method, which leads to an inverse problem if the underlying current density should be determined. With the current density, characteristics of an electrical conductor such as the geometry or the conductivity can be determined. In particular, for analyzing novel electrically conductive materials, the uniformity of the conductivity is a critical characteristic. A deconvolution-based method is presented to determine the current density distribution within an inhomogeneous electrical conductor from the resulting magnetic field measured with a state-of-the-art giant magnetoresistive magnetometer.

Eddy-current non-destructive testing system for the determination of crack orientation

Detecting the orientation of deep oriented cracks is a major challenge in the development of Eddy-Current (EC) Non-Destructive Testing (NDT). In fact, the detection sensitivity of EC-NDT depends on the interaction between the crack length direction and the EC flowing in the materials. In conventional EC-NDT systems, the induced currents are primarily generated along a single direction in the tested sample. This paper presents a new excitation method for generating a pseudo-rotating ac magnetic field and, consequently, pseudo-rotating eddy currents. This method significantly improves the detection of deep cracks of any orientation. The detected signal due to the crack is measured by an Improved Giant Magneto-Resistance Magnetometer (IGMRM). The magnetic flux density signature of the crack is studied using a 3D finite element model. Numerical and experimental results demonstrate the potential and the efficiency of this method.

Design and Simulation of Attitude Determination and Control Subsystem of CubeSat Using Extended Kalman Filtering and Linear Quadratic Gain Controller

This paper describes an integral scheme of the design and simulation of the Attitude Determination and Control Subsystem (ADCS) of CubeSat. CubeSat is an educational low-cost, cube-shaped Pico spacecraft. Attitude Determination (AD) is the problem of expressing the orientation of a spacecraft with respect to a given coordinate system. Three axis magneto-resistive digital magnetometer is selected as an attitude sensor. The International Geomagnetic Reference Field (IGRF) is used as reference for magnetometer to obtain attitude information. An enhanced orbit estimate/propagator is implemented to provide position information to IGRF model. Satellite environmental torque is modeled along with satellite kinematics and dynamics. Attitude estimation is done using Extended Kalman Filter (EKF) while the magnetic coils are used as actuators. Attitude Control is applied using Linear Quadratic Regulation (LQR) Controller. The designed ADCS is implemented in Matlab/Simulink.

Attitude Determination with Magnetometers and Accelerometers to Use in Satellite Simulator

Attitude control of artificial satellites is dependent on information provided by its attitude determination process. This paper presents the implementation and tests of a fully self-contained algorithm for the attitude determination using magnetometers and accelerometers, for application on a satellite simulator based on frictionless air bearing tables. However, it is known that magnetometers and accelerometers need to be calibrated so as to allow that measurements are used to their ultimate accuracy. A calibration method is implemented which proves to be essential for improving attitude determination accuracy. For the stepwise real-time attitude determination, it was used the well-known QUEST algorithm which yields quick response with reduced computer resources. The algorithms are tested and qualified with actual data collected on the streets under controlled situations. For such street runaways, the experiment employs a solid-state magnetoresistive magnetometer and an IMU navigation block consisting of triads of accelerometers and gyros, with MEMS technology. A GPS receiver is used to record positional information. The collected measurements are processed through the developed algorithms, and comparisons are made for attitude determination using calibrated and noncalibrated data. The results show that the attitude accuracy reaches the requirements for real-time operation for satellite simulator platforms.

A High Resolution and Full Information Magnetic Field Measurement System

According to the development and need of the underwater magnetic field measurement, this paper offers a development method and realizing a process of a full information magnetic field measurement system based on high sensitive magnetoresistive magnetometers of HMC1001&HMC1002. The system includes the magnetic and degree sensors system , data storage module ,the control and data acquisition system. The system’s main features include its high resolution, full information, mass storage , low power and synchronously multichannel A/D. The noise of the system is measured in a magnetic shield canister and the result is 5nT. Performances of the system have been tested in practical and results prove the system meets the need of the actual underwater magnetic field measurement in application.

The Magneto-Resistive Magnetometer of BCU on the Tatiana-2 Satellite

The magneto-resistive magnetometer (MRM) of the Block of Central University (BCU) payload onboard the Tatiana-2 satellite is made of anisotropic magneto-resistive (AMR) sensor chips, which have appealing features of small size (10 × 15 × 7 mm^3), light weight (2 grams) and low power consumption (100 mW). The small MRM is packaged together with other instrument/subsystems of the BCU into a 1.6 kg payload box for convenient installation. In this report, we present the design, calibration, and flight data analysis of the MRM. In particular, the detailed methods of pre-flight calibrations are described. The calibrated data revealed typical patterns of the global geo-magnetic field structure and of field-aligned current (FAC) distribution in the high latitude ionosphere, though the MRM of BCU only has a resolution of 24 nT and a sampling rate of 2.22 Hz. Moreover, the current density derived from our magnetic field measurements are about 2 and 3 μA m^(-2), respectively, for downward and upward FAC, which are comparable to those typically observed at auroral latitudes during a quiet geomagnetic condition.

Error Compensation of 3-Axis Magnetoresistive Magnetometer

To eliminate errors of 3-axis magnetoresistive magnetometer, according to its offset errors, sensitivity errors and non-orthogonal errors which specialty was considered, an error compensation model of magnetoresistive magnetometer was established. And the calculation method of the error compensation model, which did not need accelerometers, was proposed to correct the magnetometer errors. The results show the algorithm of error compensation model decrease the root mean square error of the magnetometer from 413nT to 82nT. Thus the 3-axis magnetoresistive magnetometer could fast and accurately measure the geomagnetic field.

Characteristics of the dual-bridge giant magnetoresistance magnetometer

The responsivity and the field noise characteristics of the giant magnetoresistance (GMR) magnetometer driven by an alternating magnetic field are investigated. The harmonic spectrum of the sensor voltage shows that only the odd harmonics of excitation frequency are sensitive to the external dc field. To cancel out the even harmonics, the dual-bridge GMR magnetometer with the balanced output is proposed. With the dual-bridge configuration, the field-to-voltage transfer coefficient is doubled and the field noise is reduced by a factor of 1.4. The minimum field noise is 7 nT∕√Hz at 1 Hz with the ac excitation power of 5.5 mW. The proposed sensor is suitable for the electronic compass application.

Radiation tolerance of a spin-dependent tunnelling magnetometer for space applications

To meet the increasing demand for miniaturized space instruments, efforts have been made to miniaturize traditional magnetometers, e.g. fluxgate and spin-exchange relaxation-free magnetometers. These have, for different reasons, turned out to be difficult. New technologies are needed, and promising in this respect are tunnelling magnetoresistive (TMR) magnetometers, which are based on thin film technology. However, all new space devices first have to be qualified, particularly in terms of radiation resistance. A study on TMR magnetometers' vulnerability to radiation is crucial, considering the fact that they employ a dielectric barrier, which can be susceptible to charge trapping from ionizing radiation. Here, a TMR-based magnetometer, called the spin-dependent tunnelling magnetometer (SDTM), is presented. A magnetometer chip consisting of three Wheatstone bridges, with an angular pitch of 120°, was fabricated using microstructure technology. Each branch of the Wheatstone bridges consists of eight pairs of magnetic tunnel junctions (MTJs) connected in series. Two such chips are used to measure the three-dimensional magnetic field vector. To investigate the SDTM's resistance to radiation, one branch of a Wheatstone bridge was irradiated with gamma rays from a Co60 source with a dose rate of 10.9 rad min−1 to a total dose of 100 krad. The TMR of the branch was monitored in situ, and the easy axis TMR loop and low-frequency noise characteristics of a single MTJ were acquired before and after irradiation with the total dose. It was concluded that radiation did not influence the MTJs in any noticeable way in terms of the TMR ratio, coercivity, magnetostatic coupling or low-frequency noise.

Eddy-Current Nondestructive Testing Using an Improved GMR Magnetometer and a Single Wire as Inducer: A FEM Performance Analysis

This paper describes an efficient nondestructive evaluation (NDE) eddy-current (EC) system using an improved giant magnetoresistance magnetometer (IGMRM) and a simple single wire as inducer. A three-dimensional finite-element method (3-D FEM) was implemented to evaluate the theoretical expected response of the system. The model was based on a modified magnetic vector potential and a reduced magnetic scalar potential, in conducting and nonconducting regions, respectively. The model robustness is established by comparing numerical and experimental results on a given benchmark aluminum plate sample. This efficient 3-D FEM model helps to understand the system performances. Moreover, the excitation frequency effect on the sensed signal is analyzed versus the benchmark sample thickness and the crack sizes. Results are also given and discussed in terms of signal-to-noise ratio.

Magnetorelaxometry using Improved Giant MagnetoResistance Magnetometer

Magnetorelaxometry measurements on immobilized superparamagnetic magnetite (Fe 3O 4) nanoparticles in freeze-dried samples using a low-cost Improved Giant MagnetoResistance Magnetometer (IGMRM) are presented. Fits to relaxation phenomenological model based on Moment Superposition Model (MSM) are used to extract the characteristic values. Concentrations of iron down to 3.85 μmol are identified in a 150 μl volume from experimental measurements. Also, the extracted amplitude characteristic value confidence intervals associated to measurements and detection performances are given.

Improvement in the detection of subsurface fatigue cracks under airframe fasteners using improved rotating giant magneto-resistance magnetometer head

Improved Giant Magneto-Resistance Magnetometers (IGMRM) offer many advantages for the detection of subsurface cracks. This paper presents new opportunities for the detection of fatigue cracks close to fasteners or rivets with an improved rotating head. The latter was developed around an IGMRM and a well designed electromagnetic flux focuser. The capabilities of the system for the first to the third aluminium layers (3 to 4 mm-thick each) flaw detection will be highlighted. Experimental Electro Discharge Machined (EDM) crack sizes under fasteners are several millimetres long and about 100 μm wide. Currently, results show the ability of the system to detect very easily a 7 mm-long machined crack near a rivet under 6 mm of aluminium. The use of IGMRMas afield detector, for improved low-frequency response and sensitivity of the device, is discussed. A 2D finite element modelling result of electromagnetic field distribution for this newly designed rotating probe is presented. Also, the complete system configuration is described.

Performance of Magnetic Pulsed-Eddy-Current System Using High Dynamic and High Linearity Improved Giant MagnetoResistance Magnetometer

Eddy-current nondestructive testing is commonly carried out using single-frequency time-harmonic excitations. Pulsed excitation offers a simple and effective alternative to classical eddy-current techniques and is classically implemented with coil(s) (transmitter and/or receiver). We present a pulsed-eddy-current-system alternative using a high-performance giant magnetoresistance magnetometer is presented. An analytical solution of the magnetic flux density created by the transient eddy current is given. Comparison with experimental results shows that the approximations are accurate (1% or better). System performances are presented and discussed versus sensor characteristics and compared to classical ones (transmitter/receiver coil systems)

Depth-resolved eddy-current detection with GMR magnetometer

The readout electronics of the giant magnetoresistive (GMR) magnetometer for detecting the low-frequency eddy-current signal is investigated. In feedback mode, the GMR magnetometer can sense the bipolar magnetic field up to ±16 gauss with a constant field-to-voltage transfer function at frequencies up to 10 kHz. The capability of the GMR magnetometer in depth-resolved eddy-current detection is demonstrated.

Low cost navigation system for UAV's

This paper describes the development of a navigation system for SIVA family of UAVs that incorporates measurements from low cost solid state IMU and magneto-resistive magnetometer, single receiver inexpensive GPS, and absolute and differential pressure transducers. The navigator is composed of three modules: an attitude estimator, a position and velocity estimator and a mission management module. All the UAV navigation, guidance, control and communication algorithms and processes run on a PC-104 Pentium I processor. The attitude estimator algorithm is a computationally-inexpensive nonlinear observer developed using Lyapunov theory that computes angular velocity corrections from two vector measurements: Earth's magnetic field and gravity, guaranteeing global Input to State Stability. The position and velocity estimator consists of a set of three static linear Kalman filters that correct the integration of local level components of acceleration with GPS, pressure derived altitude and airspeed measurements. The autonomous navigation is performed by means of pre-programmed mission data, composed by a set of mission elements which define the trajectory to guide the UAV through a safe path. Mission data, mission phases and ground control modes are managed by the mission management module.