Magnetic Sensor Array Research Articles

Sensor array characteristics of MOS Hall-plates and the comparison with split-drain MAGFETs

This paper describes magnetic sensor array characteristics of MOS Hall-plates and the comparison with split-drain MAGFETs. A problem of the magnetic sensor array is the offset deviation which is caused by process imperfection. To investigate the magnetic sensor array characteristics suitable for an array structure, a test chip integrating magnetic sensor arrays with different structures of MOS Hall-plates and split-drain MAGFETs are fabricated using 0.25µm standard CMOS process. The ratio of the sensor signal to offset deviation of the MOS Hall-plates is three times higher than that of the split-drain MAGFET. From the measurement results of MOS Hall-plates with different shapes, it is found that a Hall-plate with longer channel and probes located closer to the center of the channel has small offset deviation.

Studies on the response of resistive-wall modes to applied magnetic perturbations in the EXTRAP T2R reversed field pinch

Arrays of magnetic coils and sensors in the EXTRAP T2R [P. R. Brunsell et al., Plasma Phys. Controlled Fusion 43 1457 (2001)] reversed-field pinch have been used to investigate the plasma response to an applied resonant magnetic perturbation in the range of the resistive-wall modes (RWMs). Measured RWM growth rates agree with predictions of a cylindrical ideal-plasma model. The linear growth of low-n marginally stable RWMs is related to the so-called resonant-field amplification due to a dominant ∣n∣=2 machine error field of about 2 G. The dynamics of the m=1 RWMs interacting with the applied field produced by the coils can be accurately described by a two-pole system. Estimated poles and residues are given with sufficient accuracy by the cylindrical model with a thin continuous wall.

Hexagons become the secondary pattern if symmetry is broken

Pattern formation on the free surface of a magnetic fluid subjected to a magnetic field is investigated experimentally. By tilting the magnetic field, the symmetry can be broken in a controllable manner. When increasing the amplitude of the tilted field, the flat surface gives way to liquid ridges. A further increase results in a hysteretic transition to a pattern of stretched hexagons. The instabilities are detected by means of a linear array of magnetic Hall sensors and compared with theoretical predictions.

EFFICIENT MAGNETIC LOCALIZATION AND ORIENTATION TECHNIQUE FOR CAPSULE ENDOSCOPY

To build a new wireless robotic capsule endoscope with external guidance for controllable and interactive GI tract examination, a sensing system is needed for tracking 3D location and 2D orientation of the capsule endoscope movement. An appropriate sensing method is to enclose a small permanent magnet in the capsule. The intensities of the magnetic field produced by the magnet in different spatial points can be measured by the magnetic sensors outside the patient's body. With the sensing data of magnetic sensor array, the 3D location and 2D orientation of the capsule can be calculated. Higher calculation accuracy can be obtained if more sensors and optimal algorithm are applied. In this paper, different nonlinear optimization algorithms were evaluated to solve the magnet's 5D parameters, e.g. Powell's, Downhill Simplex, DIRECT, Multilevel Coordinate Search, and Levenberg Marquardt method. We have found that Levenberg-Marquardt method provides satisfactory calculation accuracy and faster speed. Simulations were done for investigating the de-noise ability of this algorithm based on different sensor arrays. Also the real experiment shows that the results are satisfactory with high accuracy (average localization error is 5.6 mm).

Multipole Characterization of a Magnetic Source Using a Truncated SVD

This paper presents a new technique for characterizing a magnetic source using truncated singular value decomposition (TSVD). It shows how the smallest singular value of the matrix of signature magnetic fields relates to the sensitivity of the restored multipoles to noises. The crosstalk and altercation due to the truncation of singular values are introduced as the parameters to determine an acceptable truncation limit. Numerical simulations with standard sources are tested using a rectangular array of magnetic field sensors. The results show that TSVD can greatly improve the accuracy of the field restoration.

Magnetic domain structures of focused ion beam-patterned cobalt films using scanning ion microscopy with polarization analysis

Studies of magnetic domain distributions in patterned magnetic materials are of pivotal importance in the areas of ultrahigh density magnetic recording, MRAM design, and miniaturized magnetic sensor arrays. Scanning ion microscopy with polarization analysis (SIMPA) is used to perform in situ topographic and magnetic domain imaging and focused ion beam (FIB) patterning. For FIB-patterned 30 nm thick Co films, it is found that rectangular Co bars of sizes between 10–30 μm exhibit S type, whereas circular shaped magnetic elements show C type micromagnetic magnetization patterns. It is shown that SIMPA provides a simple way to directly identify different micromagnetic domain patterns.

Masticatory motion after surgical or nonsurgical treatment for unilateral fractures of the mandibular condylar process

Purpose We sought to compare mandibular motion during mastication in patients treated in either an open or a closed fashion for unilateral fractures of the mandibular condylar process. Patients and Methods Eighty-one male patients with unilateral condylar process fractures were treated either with (n = 37) or without (n = 44) surgical reduction and rigid fixation of their condylar process fractures. At 6 weeks, 6 months, 1 year, and 2 years after treatment, the subjects’ chewing cycles were recorded using a magnetic sensor array (Sirognathograph; Siemens Corp, Bensheim, Germany) while chewing Gummi-Bears (HARIBO, Bonn, Germany) unilaterally on the same side as the fracture and on the opposite side. The chewing cycles were analyzed using a custom computer program, and the duration, excursive ranges, and 3-dimensional cycle shape were compared between the 2 treatment groups at each time interval using multilevel linear modeling statistics. Results The 2 treatment groups did not differ significantly for any measure of cycle duration or any excursive range (except lateral excursions at 1 year post-treatment) at any of the time intervals. However, the 3-dimensional cycle shapes of the 2 groups did differ significantly at all time intervals. Conclusion Surgical correction of unilateral condylar process fractures has relatively little effect on the more standard measures (duration and excursive ranges) of masticatory function. However, surgical correction better normalizes opening incisor pathways during mastication on the side opposite the fracture.

A 2-D ferrous object imaging technique based on magnetic field sensor arrays

A set of new signal-processing algorithms is being presented in this work that allow for the construction of images of the physical view of ferrous objects. This imaging technique, called MAD-Camera, is based on the discrete-time, spatial sampling of two components of the magnetic anomaly field-vector. The MAD-Camera prevails over other conventional Magnetic-Anomaly-Detection (MAD) techniques for the following two reasons. Firstly, it may provide with a good estimation of all three components of the anomaly field-vector near the penetrating ferrous objects. This is equivalent with capturing a more detailed magnetic signature; similar penetrating objects can be discriminated. Secondly, the technique provides directly with the physical view of the penetrating objects. As a result, no magnetic-signature databases and pattern-matching algorithms are required for a MAD application to function.

Noninvasive antepartum recording of fetal S-T segment with a newly developed 151-channel magnetic sensor system

Objective: The objective of this study was to evaluate the efficiency of the detection of the S-T segment in the fetal PQRST complex that is recorded in the antepartum period with the use of a newly developed noninvasive 151-channel magnetic sensor array. Study Design: One hundred two fetal magnetocardiographic recordings were performed on normal fetuses with gestational ages that ranged from 27.5 to 39.5 weeks. After the removal of the interfering maternal heart signals, the fetal heart data were inspected to detect the presence of P, QRS, and T segments. Results: The QRS complex was detectable in 100%, the P wave was detectable in 95.1%, and the T wave was detectable in 87.3% of the recordings. Conclusion: Fetal magnetocardiography was recorded successfully, the QRS complex was observed in all subjects, and the T detection rate increased, with the gestational age reaching a peak of 97%. Further study of the S-T segment through the antepartum period could lead to advances in the detection of fetal jeopardy before labor. (Am J Obstet Gynecol 2003;188:1491-7.)

２個の永久磁石を用いた顎運動計測システムの測定誤差解析

We developed a new system to capture jaw movement. It consists of two magnets and biaxial fluxgate sensors. A magnet is fixed to a tooth in the bottom jaw of the subject and another is fixed to the subject's forehead. The system can naturally detect movement of the jaw as a rigid body, because it does not require such attachments as a clutch inside the mouth or a magnetic field sensor array in contact with the head. In this paper, we investigate five error sources of the jaw-tracking system, using a jaw model, and report the achievement of a positional accuracy of 1.5 mm and an axial accuracy of 2 degrees. Positional accuracy within 2 mm is achieved as a rigid body.

Source separation based processing for integrated Hall sensor arrays

Integrated arrays of Hall-type magnetic sensors are generally subject to significant crosstalk due to poor spatial selectivity of very closely spaced sensors. In this paper, we explore blind source separation as a signal processing technique to unmix a number of magnetic sources that impinge on the array. The processing consists of two stages: the first one estimates the source number and projects the observations on the signal subspace; the second stage is a source separation algorithm. Experimental results from a silicon array of Hall sensors, interfaced with a DSP, demonstrate real-time separation of two magnetic sources even under ill-conditioning of the mixing matrix.

２個の永久磁石を用いた顎運動計測システムの試作

We developed a new motion-capture system for jaw movement using two magnets and two-axial fluxgate sensors. Two magnets are fixed to a tooth in the lower jaw and to the forehead. The system can naturally detect the jaw movement as a rigid body because the system has no need for attachments such as a clutch inside the mouth or a magnetic field sensor array in contact with the head.

Processing magnetic sensor array data for AC current measurement in multiconductor systems

The continuous progress in magnetic sensor research provides increasing accuracy in measurement systems based on magnetic sensor arrays. Many industrial applications in the field of protection for low-voltage electrical systems require novel technologies of AC current sensors characterized by lower costs and wider measuring range in amplitude and frequency. For this purpose, a promising solution is the utilization of sensor arrays provided with signal processing techniques. In the paper, we propose a new principle for simultaneous measurement of polyphase currents flowing in parallel conductors of arbitrary cross-sections based on processing magnetic sensor signals. After describing the analytical solution of the measurement problem, theoretical uncertainty analysis is carried out. Preliminary experimental results confirm the validity of the new approach.

Circular arrays of magnetic sensors for current measurement

A single solid-state magnetic sensor can measure a current flowing in a conductor in a noncontact way. In order to improve the accuracy of the measuring system and to reduce the crosstalk effects of other magnetic fields, circular arrays of magnetic sensors can be fabricated, still preserving low costs. In those kind of arrays, the sensing elements are assembled on a circle around the conductor. The sum of the sensor output signals is an approximation of Ampere's circulation. A quite satisfactory crosstalk effects reduction can be thus achieved. More sophisticated algorithms that combine sensor output signals are necessary in order to further reduce crosstalk effects. This paper presents an algorithm that is able to calculate the intensity of a dc current flowing in a rectangular bus-bar, in the presence of crosstalk fields.

Interference rejection algorithm for current measurement using magnetic sensor arrays

Solid state magnetic sensors can measure a current by sensing the field near the conductor. Means are required to distinguish between useful and interference fields and that are those of conductors near the current under measurement and environmental fields. Starting from analytical expressions of the magnetic field, spatial harmonic analysis is performed. It is then possible to separate the effects of the field generated by the current under measurement from those of interference fields. A new algorithm based on spatial Discrete Fourier Transform (DFT) capable of calculating the current to be measured is presented. The algorithm can be implemented by a DSP that processes output signals of solid state magnetic sensors forming a circular array centred in the current conductor.

Eddy-current testing by flexible microloop magnetic sensor array

A flexible microloop magnetic sensor array has been developed for nondestructive evaluation in nuclear power plants and its fundamental characteristics have been investigated. A flexible micro-eddy current testing (micro-ECT) probe consists of a pancake-type exciting coil of the diameter of 3.2 /spl mu/m and a flexible microloop magnetic sensor array with an area of 14/spl times/14 mm/sup 2/ and a thickness of 125 /spl mu/m. The array has 16 microloop sensors made of copper formed on a flexible polyimide film by sophisticated photolithography. Each coil has 40 turns (8 /spl mu/m line and 8 /spl mu/m space) within an area of 2/spl times/2 mm/sup 2/. The flexible sensor array enables the micro-ECT probe to be applied to an arbitrary geometric configuration. The purpose of this work is to detect and reconstruct flaws in conductive tubing of a steam generator in a pressurized nuclear power reactor by using the flexible micro-ECT probe with higher spatial resolution than that of a conventional ECT probe. The spatial resolution of flaw detection was 3 mm and the detectability of an outer 20% flaw made by electric discharge machining was confirmed. The reconstruction of circumferential and axial flaws using the electromotive force and phase measured with the sensor array is described. Three-dimensional eddy current and magnetic field analysis was also performed for comparison with measured data. Finally, a design study of a practical and robust micro-ECT for a realistic tube configuration with respect to detectability was carried out.

New kind of highly sensitive magnetic sensors with wide bandwidth

In physical, technical and biological systems measurements of weak magnetic fields are of great importance. A highly sensitive magnetic sensor with a frequency output signal for robust information transmission is presented. It consists of a tuned r.f. oscillator the frequency of which is determined by a weak external magnetic field in the magnetic range of picotesla to microtesla (a magnetically controlled oscillator, MCO). This low-noise magnetic-field-to-frequency converter with a large bandwidth ( > 200 kHz at −3 dB) is very simple in construction, relatively cheap in production and shows a sensitivity of more than 200 GHz T −1. It is suitable for a magnetic readout system or an integrated magnetic sensor array, especially for high-frequency magnetic heads, navigation applications and for geomagnetic measurements.

Two Dimensional Micro Magnetic Sensor Array

This paper proposes two new kinds of two dimensional micro magnetic sensor arrays, which are designed for a position sensor in a micro superconducting magnetic conveyance system with feedback control. One is a magnetic switch array with a nickel cantilever structure fabricated by electro-plating. Another one is a Hall sensor array consisted of so-called a MOS-Hall element, which is a MOS device in fact, but works as a Hall element. We have fabricated these two different types of sensor arrays by micromachining process, and tested their performances. The sensing principle, fabrication process and experimental results are reported.

Yield improvement of a large area magnetic field sensor array using redundancy schemes

The circuit design of a large area magnetic field sensor array (LAMSA) is described. This prototype is developed for applications in magnetic field mapping and tactile sensor arrays. To enable the production of such a large sensor system, redundancy schemes are implemented and a laser interconnection post fabrication technique is used for fault repairs. The design restructurable capabilities rely on local redundancy schemes for the sensor grid and global redundancy schemes for the surrounding control circuits. Experimental results obtained on a laser restructurable subarray of magnetic field sensor cells are shown. A study of the robustness of the local sensor grid redundancy schemes is presented.

Effects of scanning and biasing circuit restructuring on the response of a large area magnetic field sensor array

A large area magnetic field sensor array (LAMSA) has been designed and fabricated with built-in redundancy to achieve higher yield. The laser-link technology is used as the restructuring tool. The sensor system response is measured and calibrated with a general regression analysis method. Using the same method, an algorithm to evaluate the effects of the restructuring schemes of the biasing and scanning circuits on the response is developed. From measurements taken before and after restructuring, the influence of the row and the column scanning circuits restructuring are found to be weak, provided the resistance values of the formed laser-links are low, especially in the case of the column scanning circuit. Restructuring of the cascode current mirror acting as active load has shown the close dependence of the sensor cell responses on the transistor parameters. Helped by these restructuring schemes, the initial yield of 23 tested chips of size 6/spl times/3 mm was raised from 39 to 61%.