Anisotropic Magnetoresistive Research Articles

Reference-Free Automated Magnetic Sensor Calibration for Angle Estimation in Smart Knee Prostheses

In this paper, we present a method for automated calibration of an implanted anisotropic magnetoresistive (AMR) sensor for measuring the internal-external rotation in a prosthetic knee without using any reference measurement. The measurement system consists of a permanent magnet and a 2-D AMR sensor configured and embedded into the prosthesis. Using the physical relation between the measurements of channels of sensor, we proposed a reference-free calibration method through the optimization. The parameters of the measurement model of the sensor obtained via the calibration were directly used in an angle estimator. Two different optimization approaches were tested, and the resultant estimates were compared with the reference angle with the expected ± standard deviation of error of -1.69° ± 0.65° and -1.17° ± 1.13°. The reference-free calibrated estimators were also compared with the reference-dependent least-square estimators. This latter comparison showed an offset error difference among the estimators while the coefficients of determination for the both reference-free and reference-dependent estimators were high, i.e., larger than 0.91. The good performances were maintained even when using a small portion of data for the optimization. The sensor-magnet misalignment effect was also investigated. The misalignment slightly worsened the mean error of the estimates, but neither dramatically affected the variance of error nor the coefficient of determination.

Direct experimental determination of the anisotropic magnetoresistive effects

We present an experimental study devoted to determine the magnetoresistive signals as imposed by the system magnetic anisotropy and applied current direction in a model ferromagnetic system. By having direct experimental access to the magnetization vector during the reversal (measured through angular- and field-dependent vectorial-resolved magnetization loops), we can predict both longitudinal and transverse magnetoresistive signals, i.e., anisotropic magnetoresistance and planar Hall effect. This has been done by experimentally disclosing the resistance changes occurring during (and simultaneously to) the magnetization reversal processes.

Vehicle Detection and Monitoring Setup Based on Anisotropic Magnetoresistance Sensors

The evolution in microelectronics and microarchitecture lead to the creation of cheap and reliable embedded magnetic sensors. Anisotropic Magnetoresistors (AMR), being able to measure one axis magnetic fields, have been employed in many applications so far. In this paper AMR sensor (HMC2003) manufactured by Honeywell Inc. was tested for its ability to detect the magnetic field of a vehicle. Two different sensor topologies were examined regarding their performance in vehicle detection and monitoring.

Experimental Study Noise of HMR2003 Sensor with or without the Use of Amplifier AMP04

Magnetic sensors offer many essential benefits: they enable contactless and thus without wear measurement of mechanical amounts of such as the rotation angle and angular velocity. And are a powerful and economical solution. In this work became a successful attempt to detect and record the noise of a Anisotropic Magnetoresistors (AMR) sensor, hte HMC2003, which manufactured by Honeywell Inc. was tested for its ability to detect the magnetic field and as well as how the corruption, which are involved due to the noise.

SPICE compatible behavioural modelling of resistive sensors

In this paper, a modelling technique for anisotropic magneto-resistors (AMRs) and piezo-resistors has been developed. These models are then used to model sensors using such elements. The motivation is to develop a platform which will help in the analysis of different performance parameters of such sensors and optimally design electronic systems for such sensor applications. Non-idealistic behaviour such as temperature and nonlinearity, hysteresis, mismatch, noise, etc have been considered while developing the model. The proposed technique helps us to study each of these non-idealities individually as well as understand the holistic sensor response. Root-cause analysis can, thus, be performed. Model parameters are derived from different product specifications and various characterization reports. The sensor's response predicted from the model is compared with the performance of these products. Response of the model is seen to closely follow the response of the actual product.

Modern CAD technique to design Gyrocompass for UAVs and robot, ships, Aircrafts navigation systems

This paper concerns the practical design and implementation of gyrocompass required for operation of all installed navigation equipments on robot, aircrafts, ships, also for UAVs. Most navigation systems today use some type of compass to determine heading direction. Using the Earth Os magnetic field, electronic compasses based on magneto-resistive (MR) sensors can electrically resolve better than 0.1 degree rotation and accuracy from 1 to 2 degree. Most of installed equipment on aircrafts, ships, and spaceship are form of computer-based navigation information system that complies with International regulations. These equipments can be Global position System (GPS), Radar, speed, direction, electronic chart display, height finder for aircrafts and spaceship, echo sounder for ships etc. In our design, Compass Module was utilized with Honeywell's HMC5883L 3-Axis Magnetometer, I2C, 2.7-6.5V, TTL-USB and microcontroller 16F877. For programming of the microcontroller, software PIC Basic pro was used, a window based Software. We are trying to use a cheap and good resolution within a small size Using Anisotropic Magneto resistive (AMR) technology that provides advantages over other magnetic sensor technologies. These anisotropic, directional sensors feature precision in-axis sensitivity and linearity. These sensors’ solid-state construction with very low cross-axis sensitivity is designed to measure both the direction and the magnitude of Earth’s magnetic fields, from milli-gauss to 8 gauss. The complete designed system has three outputs, the first one is USB port friendly user interface, the other two outputs are control logic state outputs. We used the designed gyro output to interface with Radar display so the targets direction can be measured in true mode instead of relative mode; as well, our designed module was employed in car protection in driver safety.

Low frequency noise of anisotropic magnetoresistors in DC and AC-excited metal detectors

Magnetoresistors can replace induction sensors in applications like non-destructive testing and metal detection, where high spatial resolution or low frequency response is required. Using an AC excitation field the magnetic response of eddy currents is detected. Although giant magnetoresistive (GMR) sensors have higher measuring range and sensitivity compared to anisotropic magnetoresistors (AMR), they show also higher hysteresis and noise especially at low frequencies. Therefore AMR sensors are chosen to be evaluated in low noise measurements with combined processing of DC and AC excitation field with respect to the arrangement of processing electronics. Circuit with a commercial AMR sensor HMC1001 and AD8429 preamplifier using flipping technique exhibited 1-Hz noise as low as 125 pT/. Without flipping, the 1-Hz noise increased to 246 pT/.

(Invited) Linear Magnetic Tape Heads and Contact Recording

Linear tape recording heads, introduced in 1984, originally were cylindrical ferrite structures having shunt-biased magnetoresistive sensors. In 2000, heads transitioned to flat-lapped, ceramic wafers and anisotropic magnetoresistive (AMR) sensors fabricated in hard disk drive (HDD) facilities. In 2008, heads transitioned to giant magnetoresistive (GMR) sensors. Engineering tape heads has meant dealing with problems related to the head-media interface. Examples include sub-nanosecond pulses in sensors having metal shields (ca. 1994), signal losses and telegraph noise caused by parasitic electrical connections and spacing due to deposits that form at low relative humidity. Wear management, especially with 'green' media, and stick-slip effects are on-going challenges. A strategy was created for protecting GMR tape heads, leading to the discovery of polycrystalline Al2O3 films.

Anisotropic Magnetoresistive Study in Bilayer NiFe-NiO for Sensor Applications

Related with the detection of weak magnetic fields, the anisotropic magnetoresistive (AMR) effect is widely utilized in sensor applications. Exchange coupling between an antiferromagnet (AF) and the ferromagnet (FM) has been known as a significant parameter in the field sensitivity of magnetoresistance because of pinning effects on magnetic domain in FM layer by the bias field in AF. In this work we have studied the thermal evolution of the magnetization reversal processes in nanocrystalline exchange biased Ni80Fe20/Ni-O bilayers with large training effects and we report the anisotropic magnetoresistance ratio arising from field orientation in the bilayer.

Autocalibration Method for Anisotropic Magnetoresistive Sensors Using Offset Coils

In this paper, we present a zero-cost indoor calibration method for anisotropic magnetoresistive (AMR) sensors. The implemented circuit is designed to calibrate AMR sensors using integrated coils. A microcontroller is used to generate an artificial three-dimensional magnetic field by injecting three separate currents into three offset coils. We show the similarity of the results for residual calibration norm by using this method compared with the calibration of the sensor in free Earth's magnetic field. Furthermore, this method does not need any other instruments such as Helmholtz coils or a platform for rotating the sensor. Here the sensor is placed inside a mu-metal box during calibration, and the calibration process is completely autonomous.

Development of eddy current testing system for inspection of combustion chambers of liquid rocket engines

An eddy current testing (ECT) system using a high sensitive anisotropic magnetoresistive (AMR) sensor was developed. In this system, a 20 turn circular coil with a diameter of 3 mm was used to produce the excitation field. A high sensitivity AMR sensor was used to measure the magnetic field produced by the induced eddy currents. A specimen made of copper alloy was prepared to simulate the combustion chamber of liquid rocket. Scanning was realized by rotating the chamber with a motor. To reduce the influence of liftoff variance during scanning, a dual frequency excitation method was used. The experimental results proved that ECT system with an AMR sensor could be used to check liquid rocket combustion chamber.

The Development of Vehicle Position Estimation Algorithms Based on the Use of AMR Sensors

This paper focuses on the use of anisotropic magnetoresistive (AMR) sensors for imminent crash detection in cars. The AMR sensors are used to measure the magnetic field from another vehicle in close proximity to estimate relative position and velocity from the measurement. An analytical formulation for the relationship between magnetic field and vehicle position is developed. The challenges in the use of the AMR sensors include their nonlinear behavior, limited range, and magnetic signature levels that vary with each type of car. An adaptive filter based on the iterated extended Kalman filter (IEKF) is developed to automatically tune filter parameters for each encountered car and to reliably estimate relative car position. The utilization of an additional sonar sensor during the initial detection of the encountered vehicle is shown to highly speed up the parameter convergence of the filter. Experimental results are presented from a number of tests with various vehicles to show that the proposed sensor system is viable.

Design of Rotate Speed Sensor Based on MR Elements

In order to meet the needs of speed measurement for rotation system, a rotation sensor which based on the principle of Anisotropic Magnetoresistive Effect was designed in this paper. This paper presents the principle, detailed hardware circuit, frequency characteristics of the sensor, as well as the valid detection distance. The sensor used MR elements as the sensing element. It turned the change of the magnetic gear’s rotation speed into the change of the circuit’s output signal and ultimately achieved contactless rotation measurement of the magnetic gear. The hardware circuit of the sensor includes five parts: signal collection, impedance matching, signal amplification, digitalization processing and signal output. The tests show that its operating frequency ranges from 2 Hz to 6 KHz.

Development of an AMR-ACB Array for Gastrointestinal Motility Studies

The association between anisotropic magnetoresistive (AMR) sensor and AC biosusceptometry (ACB) to evaluate gastrointestinal motility is presented. The AMR-ACB system was successfully characterized in a bench-top study, and in vivo results were compared with those obtained by means of simultaneous manometry. Both AMR-ACB and manometry techniques presented high temporal cross correlation between the two periodicals signals . The contraction frequencies using AMR-ACB were 73.9 ± 7.6 mHz and using manometry were 73.8 ± 7.9 mHz during the baseline . The amplitude of contraction using AMR-ACB was 396 ± 108 μT·s and using manometry were 540 ± 198 mmHg·s during the baseline. The amplitudes of signals for AMR-ACB and manometric recordings were similarly increased to 86.4% and 89.3% by neostigmine, and also decreased to 27.2% and 21.4% by hyoscine butylbromide in all animals, respectively. The AMR-ACB array is nonexpensive, portable, and has high-spatiotemporal resolution to provide helpful information about gastrointestinal tract.

Reducing shoulder injuries among construction workers

Purpose The U.S. Bureau of Labor1 2008 report stated that the number of workers aged 65 or older is expected to rise by 36.6% from 2006 to 2016. This rise is expected to accompany a 6.9% decrease in the number of workers between ages 16 to 24 and a slight increase by 2.4% for workers ages 25 to 54. This indicates that the industry will face an aging workforce problem that can affect capacity and productivity if workers’ health is not properly monitored. An essential problem for the aging workforce is musculoskeletal disorders (MSDs), specifically work-related musculoskeletal disorders (WMSDs). In 2008, shoulder WMSDs constituted 6.9% of all WMSDs in construction, and this percentage was substantially higher for crafts such as electricians, carpenters, and painters. The main risk factor for shoulder WMSDs is prolonged forceful overhead work. This paper is presents a method to monitor shoulder WMSDs risk factor development and to act as an alarm to prevent the disorder from happening. Method An exoskeleton is being developed that will be worn by a worker to wirelessly track upper-arm motion in 3 dimensions using an array of anisotropic magnetoresistive (AMR) sensors, deployed over workers’ upper-arms. The sensory system will be controlled using a microcontroller with the ability to save data on an SD card for post-processing. Results & Discussion Alwasel et al. measured the angle of the upper-arm to trunk using AMR-sensors in an unpublished thesis. The problem with the use of AMR was the assembly itself since the sensor was not held at the center of joint rotation. However the device presented here will place AMRsensors at the center of joint rotation by extending the joint axis of rotation outside the body. This will provide enough data to help assess whether a worker is at risk of developing shoulder injury. This technique will help reduce the number workers that leave the workforce because of injury, and help maintain a good working environment. This technique will also assist in developing and applying health and safety guidelines to overhead work. Thus, it may ultimately help extend the productive age of the construction workforce.

Gamma Irradiation of Magnetoresistive Sensors for Planetary Exploration

A limited number of Anisotropic Magnetoresistive (AMR) commercial-off-the-shelf (COTS) magnetic sensors of the HMC series by Honeywell, with and without integrated front-end electronics, were irradiated with gamma rays up to a total irradiation dose of 200 krad (Si), following the ESCC Basic Specification No. 22900. Due to the magnetic cleanliness required for these tests a special set-up was designed and successfully employed. Several parameters of the sensors were monitored during testing and the results are reported in this paper. The authors conclude that AMR sensors without front-end electronics seem to be robust against radiation doses of up to 200 krad (Si) with a dose rate of 5 krad (Si)/hour and up to a resolution of tens of nT, but sensors with an integrated front-end seem to be more vulnerable to radiation.

AMR gradiometer for mine detection

Anisotropic magnetoresistors (AMRs) are used to build an advanced mine detector. The sensing head involves a gradiometric pair of AMR sensors and a continuous-wave driven excitation coil, so the gradiometer is capable of detection of ferromagnetic materials as well as diamagnetic metals. The sensors are specially arranged to suppress the large AC-excitation field, so the mine detector senses both DC and AC field gradient responses of the object of interest. Being limited by the sensor and electronics noise of 268pT/√Hz at 1kHz, we were able to detect a 50mm×50mm×1.5mm aluminum test object in a 20cm depth using a 150μT, 1-kHz excitation field.

High Accuracy AMR Magnetometer and its Application to Vehicle Detection

The anisotropic magnetoresistive (AMR) sensors provide an excellent means of measuring the earth’s magnetic field. Low cost, high sensitivity, small size, noise immunity, and reliability are advantages of AMR sensor over other electrical alternatives. But the sensitivity of constant voltage biased AMR sensor changes greatly with the temperature of surrounding and cross-axis field. In this paper, constant current bias is used in order to reduce the sensitivity temperature coefficient of AMR sensor. At the same time, cross-axis field compensation is taken based on iteration. The results of experiment show that the sensitivity of HMC100x without cross-axis field compensation varies greatly with the variation of cross-axis field, the sensitivity of HMC100x with cross-axis field compensation is stable. It can be seen that proposed sensitivity compensation method is effective. Developed magnetometer is used for vehicle detection. Experimental results show that developed magnetometer is capable of detecting vehicle and its output variation curve shape is different for the ferrous cart moves over sensor along different direction.

INACCURACIES OF ANISOTROPIC MAGNETO-RESISTANCE ANGLE SENSORS DUE TO ASSEMBLY TOLERANCES

A large class of angle sensors uses a small permanent magnet attached to the rotor. The magnet is polarized perpendicularly to the axis of rotation, and a magnetic fleld sensor is placed ahead on the axis. The sensor circuit consists of two full bridges at 45 - , each having four anisotropic magneto-resistive (AMR) elements. Even though the electronic system may be calibrated to have nearly no errors like ofiset, nonlinearity, and mismatch, still signiflcant angle errors may result from assembly tolerances of the magnet and the sensor. This work gives an analytical description of the angle error caused by tilts and eccentricities of magnet and sensor elements against the axis of rotation. Particular emphasis is given to worst case combinations of all tolerances. One part of the angle error can be cancelled by an optimized layout of the AMR-resistors. The remaining part is identical to the case of giant magneto-resistive (GMR) angle sensors. Errors of both AMR and GMR angle sensors are efiectively reduced by identical optimization of the shape of magnets. One such optimized shape is disclosed.

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.