Hall Effect Magnetometer Research Articles

Probing with Each Step: How a Walking Crab-like Robot Classifies Buried Cylinders in Sand with Hall-Effect Sensors.

Shallow underwater environments around the world are contaminated with unexploded ordnances (UXOs). Current state-of-the-art methods for UXO detection and localization use remote sensing systems. Furthermore, human divers are often tasked with confirming UXO existence and retrieval which poses health and safety hazards. In this paper, we describe the application of a crab robot with leg-embedded Hall effect-based sensors to detect and distinguish between UXOs and non-magnetic objects partially buried in sand. The sensors consist of Hall-effect magnetometers and permanent magnets embedded in load bearing compliant segments. The magnetometers are sensitive to magnetic objects in close proximity to the legs and their movement relative to embedded magnets, allowing for both proximity and force-related feedback in dynamically obtained measurements. A dataset of three-axis measurements is collected as the robot steps near and over different UXOs and UXO-like objects, and a convolutional neural network is trained on time domain inputs and evaluated by 5-fold cross validation. Additionally, we propose a novel method for interpreting the importance of measurements in the time domain for the trained classifier. The results demonstrate the potential for accurate and efficient UXO and non-UXO discrimination in the field.

Parallel array of planar Hall effect sensors for high resolution magnetometry

We introduce a planar Hall effect magnetometer in the form of a parallel array of permalloy-based elliptical sensors. The number of ellipses in the array and other fabrication parameters are optimized with the support of numerical simulations. We obtain equivalent magnetic noise (EMN) of 16 pT/Hz at 100 Hz, 25 pT/Hz at 10 Hz, 98 pT/Hz at 1 Hz, and 470 pT/Hz at 0.1 Hz. The exceptional EMN without the use of magnetic flux concentrators highlights the advantages of the design. The presented magnetometer, characterized by its simplicity, affordability, and ability to operate at room temperature, is anticipated to be useful for applications requiring pT resolution.

Precision Hall Effect magnetometer.

The article presents a Hall effect magnetometer for use in a desktop Electron Paramagnetic Resonance spectrometer with a permanent magnet system and scanning coils. High accuracy and long-term stability at a small size and low cost are achieved through the use of digital signal processing, sequential data filtering in the time and frequency domains, as well as digital correction of raw data based on calibration information. The exciting current of the Hall sensor has the form of an alternating-signsquare wave formed by a high-speed H-bridge powered by a stable direct current. Generation of control signals, time selection of data, and their accumulation are performed using Xilinx Field-Programmable Gate Array Artix-7. MicroBlaze embedded 32-bit processor is used to control the magnetometer and interface with adjacent levels of the control system. Taking into account the individual characteristics of the sensor, including the offset voltage, the nonlinearity of the magnetic sensitivity, and their temperature dependences, is carried out by correcting the data obtained by calculating a polynomial depending on the raw magnitude of the field induction and the temperature of the sensor. The polynomial coefficients are individual for each sensor, are determined once during the calibration process, and are stored in the dedicated Electrically Erasable Programmable Read-Only Memory. The magnetometer has a high resolution of 0.1 µT and an absolute measurement error of not exceeding 6 µT.

Continuous wave desktop coherent superheterodyne X-band EPR spectrometer

This article describes a desktop X-band superheterodyne spectrometer designed to measure EPR spectra in the vicinity of g = 2. The spectrometer operates in the vicinity of the 9.2 GHz frequency in the power range of about 40 mW–1 nW. The device uses Time Locking concept with digital quadrature detection of intermediate frequency (100 MHz) and the synthesis of all signals used in the device from a single driving oscillator. To register CW spectra, a TE102 rectangular cavity with the capability of matching and frequency tuning is used. The microwave part of the spectrometer is implemented in the form of two non-tunable modules based on microstrip technology and commercially available microwave MMICs. Two modes of operation are provided – both with PLL of microwave sources with a highly stable driving oscillator as a reference and an AFC system without frequency modulation. All signal processing after digitization of the intermediate frequency is performed digitally using FPGA resources. It is possible to record EPR spectra both with magnetic field modulation at various frequencies and without modulation. The bandwidth of the receiving path can be selected from the widest 46 MHz to about 1.5 kHz, which allows the spectrometer to be used both for recording weak signals and for recording fast-flowing processes. The spectrometer uses a magnetic system on permanent magnets Sm-Co with magnetic field uniformity of about 3 * 10−5. Changing the magnetic field in permanent magnets is done using scanning coils which provides a field change of >800 G (p-p). The control of the magnetic field induction in the magnet gap is performed by a specially designed precision Hall effect magnetometer, which provides a resolution of 1 mG with an absolute error of no more than 0.2 G. A personal computer for spectrometer control is connected via Ethernet. The spectrometer is stable and easy to use. The high performance of the spectrometer is confirmed by the recorded spectra.

SQUID and Hall Effect Magnetometers for Detecting and Characterizing Nanoparticles Used in Biomedical Applications

SQUID and Hall Effect Magnetometers for Detecting and Characterizing Nanoparticles Used in Biomedical Applications

Terrain Classification Based on Sensed Leg Compliance for Amphibious Crab Robot

Characterization of terrain in real time allows autonomous legged robots to modify their gait to better suit their environment and recognize hazardous conditions. We present a novel approach for terrain classification for legged robots with passively compliant components, in which terrain information is gathered by measuring component deflection during operation by means of low cost Hall effect magnetometers and embedded magnets. The effectiveness of this approach is demonstrated on a hexapod robot designed to operate in the surf zones of beaches. Datasets of sensor measurements corresponding to three types of granular terrain are collected in both a laboratory and outdoor beach environment, and are used to train support vector machine (SVM) classifiers. Results show that, using time domain features of measurements from each leg, a mean accuracy of 99.3% and 92.4% through 10-fold cross-validation can be achieved for the laboratory and beach datasets, respectively. For the beach dataset, this accuracy is found to be slightly greater than for a classifier trained on measurements from an on-board inertial measurement unit (IMU) (91.6%), while an accuracy of 95.1% can be achieved by combining the information from both sensor modalities as inputs to a single classifier. The effect of the Earth’s magnetic field on the measurements and considerations for data collection are also discussed.

Method for Creating High-Sensitivity Two-Stage Hall Effect Magnetometers with High Linearity and Spatial Resolution

Method for Creating High-Sensitivity Two-Stage Hall Effect Magnetometers with High Linearity and Spatial Resolution

Determination of effective magnon mass of neodymium magnet by temperature dependence of spontaneous magnetization

The effective mass of a magnon in a neodymium magnet is evaluated using Bloch temperature dependence of spontaneous magnetization. We use the Hall effect magnetometer and thermo-couple thermometer for measurement of the temperature of the water in which the encapsulated commercial magnet is immersed. The experiment can be repeated in every school and methodological remarks for experimental data processing are given with great detail and attention. The purpose of the paper is to illustrate the simple relation between the quantum spectrum of magnons and the easily measured magnetic field of a permanent magnet.

Трехкомпонентный датчик силы на базе упругого силиконового элемента и магнитометра

The presence of force-moment sensing of robotic systems makes it possible to improve the quality of the interaction between the robot and the objects of the external environment. There are many ways to provide force-moment sensing, one of which is to use multicomponent force sensors. However, their cost is quite high, so it is important to search and develop more profitable technical solutions. In this regard, a three-component force measurement sensor was developed, built on the basis of an elastic silicone element, with a built-in permanent magnet, and a hall-effect magnetometer. This technical solution is low-cost. The paper describes the technological process for the production of a three-component force measurement sensor, based on 3D printing of the body with an FDM printer, which makes it cheap to manufacture, and molding of two-component silicone. The paper considers the process of soldering SMD components to boards using a soldering hair dryer, stencils and solder paste, and shows a stand for calibrating the manufactured sensors, consisting of micrometric screws and parts printed on an FDM 3D printer. The mathematical method for calibration is based on the least squares method. The result of calibration of a three-component force measurement sensor is given. The research results in the development of a working sensor with the following characteristics: resolution — 1 mN, sensor sensitivity — 0.005 T / N.

Thickness dependence of elliptical planar Hall effect magnetometers

We fabricate elliptical planar Hall effect magnetometers with Permalloy thickness ranging between 25 and 200 nm. We study the thickness dependence of their equivalent magnetic noise by examining the effect of the layer thickness on the signal and noise including Joule heating contributions. Sensors with a thickness of 50 nm achieve equivalent magnetic noise as low as ∼24 pT/√ Hz at 50 Hz and ∼36 pT/√ Hz at 10 Hz, which are the best reported values for any type of magnetic sensor of similar or smaller size. These results are achieved without the use of magnetic flux concentrators, which helps to reduce the sensor volume while improving its spatial resolution and reducing the complexity and time of its production and, hence, its potential cost. We discuss different routes for further resolution improvements.

Planar Hall Effect Magnetometer With 5 pT Resolution

We integrate elliptical planar Hall effect (PHE) magnetometers with optimized high permeability magnetic flux concentrators. The integrated magnetometers exhibit at room temperature an equivalent magnetic noise of ~5 pT/√Hz at 10 Hz, 7.4 pT/√Hz at 1 Hz, and better than 100 pT/√Hz at 10 mHz. The results constitute more than an order of magnitude improvement over previously reported state-of-the-art PHE magnetometers, and demonstrate, for the first time, the ability of a magnetoresistive sensor to match the performance of state-of-the-art, high-end flux-gate, and miniature atomic magnetometers.

Parameter Identification in a Magnetic Suspension Force Transduction System

Abstract In force transduction systems, magnetic suspension can be used to facilitate the measurement of a force acting between two objects in different environments, namely, between the force transducer in one environment and the test object in another environment. In the past, it has been employed in densimetry and equations-of-state measurements of fluids and gases. An instrument being constructed at the National Institute of Standards and Technology (NIST), referred to as the magnetic suspension mass comparator (MSMC), also employs force transduction between two environments to provide a direct means of vacuum-to-air mass dissemination. Within this work, we discuss the identification, through a combination of finite element analysis and experimental measurements, of the system parameters used for feedback control of the suspension. A Hall effect magnetometer is used to determine the position of the suspended object. Emphasis is placed on experimentally and numerically characterizing the magnetic field and its appropriate gradients to determine the set point of operation. The information presented here is useful for a variety of applications that utilize magnetic suspension for force transduction.

Toward "plug and play" prospective motion correction for MRI by combining observations of the time varying gradient and static vector fields.

The efficacy of a Wireless Radio frequency triggered Acquisition Device (WRAD) is evaluated for high frequency (50 Hz) prospective motion correction in a 3-dimensional spoiled gradient echo pulse sequence. The device measures the rate of change in the gradient vector fields (slew) using a 3-dimensional assembly of Printed Circuit Board (PCB) inductors and the direction of the static magnetic field using a 3-axis Hall effect magnetometer. The slew vector encoding is highly efficient, because the Maxwell-term position encoding is observable, allowing overconstrained pose measurement using 3 sinusoidal gradient pulses lasting 880 μs. Since small offsets in the magnetometer can introduce bias into the pose estimates, sensor/system biases are tracked using a lightweight Kalman filter. The only calibration required is determining a geometric scaling factor for the pickup coils, which is specific to the device and will therefore be valid in any scanner. The device was used to perform prospective motion correction in 3 subjects, resulting in an increase in Average Edge Strength (AES) for involuntary and deliberate motion. The WRAD is simple to set up and use, with well-defined measurement variance. This could enable "plug and play" prospective motion correction if pulse sequence independence is achieved.

A Wireless Radio Frequency Triggered Acquisition Device (WRAD) for Self-Synchronised Measurements of the Rate of Change of the MRI Gradient Vector Field for Motion Tracking.

In this paper, we present a device that is capable of wireless synchronization to the MRI pulse sequence time frame with sub-microsecond precision. This is achieved by detecting radio frequency pulses in the parent pulse sequence using a small resonant circuit. The device incorporates a 3-axis pickup coil, constructed using conventional printed circuit board (PCB) manufacturing techniques, to measure the rate of change of the gradient waveforms with respect to time. Using Maxwell's equations, assuming negligible rates of change of curl and divergence, a model of the expected gradient derivative (slew) vector field is presented. A 3-axis Hall effect magnetometer allows for the measurement of the direction of the static magnetic field in the device co-ordinate frame. By combining the magnetometer measurement with the pickup coil voltages and slew vector field model, the orientation and position can be determined to within a precision of 0.1 degrees and 0.1 mm, respectively, using a pulse series lasting 880 μs . The gradient pulses are designed to be sinusoidal, enabling the detection of a phase shift between the time frame of the pickup coil digitization circuit and the gradient amplifiers. The signal processing is performed by a low power micro-controller on the device and the results are transmitted out of the scanner bore using a low latency 2.4 GHz radio link. The device identified an unexpected 40 kHz oscillation relating to the pulse width modulation frequency of the gradient amplifiers that is predominantly in the direction of the static magnetic field. The proposed wireless radio frequency triggered acquisition device enables users to probe the scanner gradient slew vector field with minimal hardware set-up and shows promise for the future developments in the prospective motion correction.

The Construction of a Graphene Hall Effect Magnetometer

This paper deals with design and fabrication of graphene micro-Hall devices along with driving and processing electronics to construct a highly sensitive graphene magnetometer system. Graphene micro-Hall elements were fabricated by implementing microfabrication techniques. Custom driving and processing circuitry was designed and built on a printed circuit board and integrated with fabricated graphene Hall devices; reducing the offset equivalent magnetic field and greatly improving the sensitivity. The performance parameters were quantitatively analyzed for characterizing the sensitivity in terms of linearity, current-related sensitivity, and magnetic field resolution. The potential of graphene magnetometers for detection capability of low fields has been demonstrated with a current related sensitivity of 2540 V/AT and magnetic field resolution of 162 nT/ $\surd $ Hz.

Implementation of 16-Channel AMR Sensor Array for Quantitative Mapping of Two-Dimension Current Distribution

Implementation of 16-Channel AMR Sensor Array for Quantitative Mapping of Two-Dimension Current Distribution

An analog method of cross-talk compensation for a RGB wavelength division multiplexed optical link

Pulse-width modulation (PWM) over optical fiber can be a very advantageous data transmission approach when an electrically isolated data link is required. The use of wavelength division multiplexing allows multiple data streams to be sent through a single fiber independently. The present investigation aims to demonstrate a novel approach to reduce cross-talk in a three-channel RGB optical link without the need for complex optical componentry. An op-amp circuit is developed to reduce the cross-talk so that the resolution of the PWM data is preserved. An iterative Monte-Carlo simulation approach is used to optimize the op-amp circuit. The approach is developed for a set of three PWM Hall effect magnetometers with 12-bit resolution and 128 Hz sampling rate. We show that, in these conditions, the loss of resolution due to cross-talk is prevented. We also show that the cross-talk compensation allows the RGB PWM link to outperform other transmission schemes.

Two-axis silicon Hall effect magnetometer

A novel single-chip sensing device for measurement of two orthogonal magnetic-field components using a common transducer zone and, for the first time, containing four contacts, is presented. On a rectangular n-type silicon substrate, n+-ohmic planar contacts are implemented − two of them are elongated and serve as power supply, and the other two terminals, positioned in the middle of the region between the elongated ones, function as outputs. A proper coupling arrangement is used for obtaining the information about vector components Bx (parallel to the supply contacts) and Bz (perpendicular to the substrate). Actually, the 2D magnetometer integrates an in-plane sensitivе Hall element and a device with vertical magnetic-field activation. The sensor operation is determined by the direction of the individual parts of the curvilinear current trajectory and the Lorentz force deflection action on them. The 2D vector sensor interface circuitry in hybrid realization comprises three instrumentation amplifiers and a differential amplifier. Simple fabrication technology is applied, containing four masks. The effective spatial resolution volume is high, constituting about 90×60×40μm3. The respective channel-magnetosensitivities without amplification reached: the lateral sensitivity Sx≈17V/AT and the vertical sensitivity Sz≈23.3V/AT. The channel cross-talk at induction B≤1.0T is no more than 3% and the lowest detected induction Bmin for the two-axis device at supply 3mA over frequency range f≤100Hz is about 11μT.

Study of Magnetic Field Measurement System for g-2/EDM Experiment at J-PARC

Two magnetic field monitoring systems for g-2/EDM experiment at J-PARC are developed. One is a continuous-wave NMR magnetometer, which is used to measure the field homogeneity in a muon storage region. The other is a Hall effect magnetometer, which is used to measure the magnetic field around the muon injection region and that for focusing the muon beam. In order to improve the accuracy of the commercial NMR magnetometer, a digital signal processing system was implemented instead of an analog one. As for the Hall probe system, a three-axis Helmholtz coil system was fabricated to measure tilt angles of Hall sensors in a three-axis Hall probe. The field homogeneity of each Helmholtz coil was measured, and the result agreed well with the design values.

A High-Resolution Planar Hall Effect Magnetometer for Ultra-Low Frequencies

Recent reports have demonstrated field resolutions of planar Hall effect magnetometers in the picotesla range. Here, we report a significant improvement in the field resolution of these sensors by decreasing their preamplifier white noise and the sensing element 1/ $f$ noise. We design, build, and test a miniature transformer-matched amplifier with a record noise level of 200 pV/ $\surd $ Hz and improve the fabrication process of the sensing element to increase its volume and reduce its associated 1/ $f$ noise. The magnetometer exhibits a magnetic resolution of $\sim 200$ pT/ $\surd $ Hz at 1 Hz and $\sim 600$ pT/ $\surd $ Hz at 0.1 Hz. These values are threefold better than previously reported results. The obtained resolution may enable applications for which high-end magnetometers, such as fluxgates, are currently used. We discuss routes for the further improvement of the magnetic field resolution.