Magnetic Flux Guides Research Articles

On the influence of magnetic flux guide location to the out-of-plane magnetic field sensing of chip-scale AMR sensor

The anisotropic magneto-resistive (AMR) sensors could detect external magnetic fields through the change of magnetization and resistance. Typically made of thin films, the AMR sensors are generally only sensitive to the in-plane magnetic field. The AMR sensors with Ni pillar array structures as magnetic flux guides have been presented to enhance the detection of out-of-plane magnetic fields. However, the magnetic flux lines transmitted from adjacent pillars may interact with each other, so that their directions will be changed accordingly. Thus, the locations of pillar guides may influence the distribution of magnetic flux lines, and further change the out-of-plane magnetic field sensing performance of the AMR sensor. To gain insight on this design consideration, this study introduces a serpentine routing AMR film with flux guides distributed along each wire gaps. By varying the gap of the serpentine AMR wire and the distance between the pillar and the AMR wire, the influence of flux guide location on the out-of-plane magnetic field sensing is investigated. Through microfabrication processes, the flux guide array can be batch fabricated and defined at appropriate locations, and further monolithically integrated with AMR sensor. Measurements show that for a serpentine AMR sensor with a gap of 70 μm, the sensitivity can be increased by 4.6-fold as the distance between flux guide and AMR film decreases from 20 μm to 0 μm. Moreover, when the flux guide fixed in the middle of gap of the serpentine AMR sensor, the sensitivity can be improved by 5.6-fold as the gap decreases from 70 μm to 50 μm.

Superconductor/magnetoresistance mixed sensor with magnetic flux guides for three-dimensional magnetic field measurement

The superconductor/magnetoresistance (SC/MR) mixed sensor has the advantage of ultra-high sensitivity, but it is only sensitive to unidirectional magnetic fields that are perpendicular to the superconducting flux-to-field transformation amplifier (SFTA). This inherent characteristic limits its applications in three-dimensional magnetic field detection. This paper presents a new architecture of the SC/MR mixed sensor with magnetic flux guides to realize three-dimensional magnetic field measurement. The finite element analysis method was used to confirm the performance of the mixed sensor, which theoretically proved the feasibility of three-dimensional magnetic field measurement and analyzed the influence of the magnetic field detection errors caused by the installation errors of MFGs. Finally, a mixed sensor composed of a whole-SFTA, four tunneling magnetoresistances, and two layers of MFGs was prepared, and experimental performances were obtained. Indeed, the mixed sensor can measure the three-dimensional magnetic field. This work is a meaningful contribution to the development of three-dimensional weak magnetic field detection.

Superconductor/magnetoresistance mixed sensor with magnetic flux guides for in-plane magnetic field measurement

A superconductor/magnetoresistance (SC/MR) mixed sensor often has very high-precision detection capability, but it is only sensitive to the out-of-plane magnetic field that is perpendicular to the superconducting flux-to-field transformation amplifier (SFTA). This inherent characteristic makes it impossible for a primary SC/MR mixed sensor to measure the in-plane magnetic field, which limits its application in many fields. This paper presents a new architecture of SC/MR mixed sensors with two magnetic flux guides (MFGs) to realize in-plane magnetic field measurement, which is attributed to the combined effects of MFGs and SFTA. The finite element method simulations are used to study the magnetic flux converting effect of MFGs and magnetic field amplification effect of SFTA, which theoretically proves the feasibility of in-plane magnetic field measurement and reveals the influences of the sizes and spacing of MFGs on magnetic field magnification. Experimental results show that the SC/MR mixed sensor with MFGs can simultaneously sense the in-plane and out-of-plane magnetic fields, and the performance of the mixed sensor with MFGs is comparable to the primary one. The magnification and resolution of the mixed sensors with MFGs to the in-plane magnetic fields are, respectively, improved by 2.91 times and 2.23 times compared to those without MFGs to the out-of-plane magnetic fields. The work described in this paper is of great significance for the development of three-component weak magnetic field detection.

Laser Additively Manufactured Magnetic Core Design and Process for Electrical Machine Applications

Additive manufacturing (AM) is considered the enabling technology for topology optimized components, with its unparalleled, almost free-form design freedom. Over the past decade, AM of electromagnetic materials has evolved into a promising new area of research. Considerable efforts have also been invested by the electrical machine (EM) research community to develop and integrate novel additive components. Several challenges remain, however, in printing soft magnetic flux guides—most prominently, reducing the induced eddy currents to achieve competitive AM core efficiency. This paper demonstrates the workflow of laser additive manufacturing magnetic cores with superior magnetic properties to soft magnetic composites (at 50 Hz excitation): describing the workflow, parameter tuning for both printing and annealing, and shape optimization. Process optimization yielded the optimal energy density of 77 J/mm3 and annealing temperature of 1200 °C, applied to prepare the samples with the highest relative density (99.86%), lowest surface roughness Rz (0.041 mm), minimal hysteresis losses (0.8 W/kg at 1.0 T, 50 Hz), and ultimate yield strength of 420 MPa. For Eddy current suppression, the sample (5 × 5 × 60 mm toroid) with bi-directional grading reached specific core losses as low as 1.8 W/kg (W10,50). Based on the findings, the advantages and disadvantages of AM graded cores are discussed in detail.

Hybrid Integration of Magnetoresistive Sensors with MEMS as a Strategy to Detect Ultra-Low Magnetic Fields.

In this paper, we describe how magnetoresistive sensors can be integrated with microelectromechanical systems (MEMS) devices enabling the mechanical modulation of DC or low frequency external magnetic fields to high frequencies using MEMS structures incorporating magnetic flux guides. In such a hybrid architecture, lower detectivities are expected when compared with those obtained for individual sensors. This particularity results from the change of sensor’s operating point to frequencies above the 1/f noise knee.

Designs of Novel Magnetic Flux Guides for Three-Axis Magnetic Sensor

In general, giant magnetoresistance (GMR) sensors are only sensitive to the magnetic field in the plane of the substrate due to fabrication restraints. Then, a three-axis magnetic sensor based on GMR sensors has to be assembled to obtain three magnetic field components. Novel magnetic flux guides for three-axis magnetic sensor are described in this paper. These novel flux guides are designed with flux conversion structure and are able to bring magnetic flux out-of-plane to in-plane. With these flux guides, the magnetic field perpendicular to the chip surface can be detected with the GMR sensors in-plane. Then, numerical simulations are performed to validate the designs, and optimizations are made to improve the flux guides’ performance. Based on these works, a three-axis magnetic sensor based on the in-plane GMR sensors is proposed. Without assembling the $z$ -axis sensor, the integrated three-axis magnetic sensor is expected to have better angular position. According to the designs, the flux guides can be deposited with good symmetry. Therefore, Wheatstone bridges are configured to deduce a differential voltage, only relative to a certain component of the magnetic field. In addition, the magnetic field at the active region of the GMR sensor would be intensified. In addition, the sensitivity of the sensor can be improved due to the amplification ability of the flux guides.

Strategies for pTesla Field Detection Using Magnetoresistive Sensors With a Soft Pinned Sensing Layer

The detection of low-intensity and low-frequency signals requires magnetic sensors with enhanced sensitivity, low noise levels, and improved field detection at low operating frequencies. Two strategies to improve the detectivity levels of devices based on tunnel magnetoresistive sensors are demonstrated: 1) a large number of sensors connected in series or 2) an individual sensor with a large sensing area and integrated magnetic flux guides. State-of-the-art MgO-based magnetic tunnel junctions with a soft pinned sensing layer were used in this paper. For 952 sensors in series a sensitivity of 29.3%/mT and a detection level of 455 pT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> were obtained at 100 Hz, whereas the integration of magnetic flux guides in a single sensor yielded a sensitivity of 138.3%/mT and a detection level of 576 pT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at the same frequency. These two strategies imply a large device footprint, being suitable when a high spatial resolution is not an application requirement.

Synchronous High-Speed Reluctance Machine With Novel Rotor Construction

A new mechanically robust construction for an ultrahigh-speed synchronous reluctance rotor is presented. The two-pole rotor design incorporates soft magnetic flux guides inside nonmagnetic matrix material. Two prototypes based on the concept were constructed and tested. This paper describes the electromagnetic and mechanical design principles of the novel rotor concept.

Designs of Slope Magnetic Flux Guides for 3-Axis Magnetic Sensor

Generally, giant magnetoresistive (GMR) sensors are only sensitive to the magnetic field in the plane of the substrate due to fabrication restraints. This paper designs and models slope magnetic flux guides that are deposited on the slope surface of a silicon substrate. Finite element method (FEM) simulations are used to optimize the flux guide designs. The flux guides can be deposited with good symmetry and are able to convert the out-of-plane magnetic flux to the GMR sensor plane. Meanwhile, a Wheatstone bridge is configured to deduce a differential voltage only relative to the z-component of the magnetic field. Additionally, the magnetic field in the active region of the GMR sensor would be intensified. With these flux guides, the magnetic field perpendicular to the chip surface can be detected with the GMR sensors in-plane. Also, the sensitivity of the sensor can be improved due to the amplification ability of the flux guides. An integrated 3-axis magnetic sensor with better angular position can be realized with the slope flux guides.

Embossing of Soft-Magnetic Structures and Influence on Magnetic Properties

Magnetic flux guides are often a part of MEMS. These flux guides are usually made by electroplating of soft magnetic materials like NiFe. The geometry of the flux guides influences the magnetic anisotropy. A new method for the fabrication of the flux guides is the embossing of the surface to influence the magnetic anisotropy. For this purpose the Institute for micro production technology (IMPT) at the Leibniz Universitaet Hannover designed and fabricated two tools for a molding press. The embossing tool for a molding press (silicon carbide) and a bond tool are applied. This contribution describes the fabrication of the embossing tools for the molding press and the embossing process of NiFe45/55 surfaces applying the fabricated tools and the wire bond tool. The embossed surfaces are characterized via a Kerr microscope.

Fabrication and Characterization of an Improved Micro Inductosyn

The standard linear Inductosyn® system consists of two measurement elements, a scale and a slider. The stationary scale contains a single meander winding, while the moving slider has two meander windings for sensing. Unlike the standard Inductosyn®, a second generation micro Inductosyn® system has four sensing windings, which enables to correct a wedge shaped air gap between scale and slide due to a misalignment occurring during the final assembly process. As its first generation micro Inductosyn® predecessor, it features magnetic flux guides not found in the standard Inductosyn® system to improve coupling. The micro displacement sensor was fabricated using Micro Electro-mechanical System (MEMS) technology. The sensor components, such as meander windings and flux guides, were fabricated by electrodeposition. Moreover, PECVD was used to create an insulating layer between these components. In order to evaluate the system, a mechanical test fixture and an electronic measurement system were created.

Integration of Electroplated CoFe in Trench Type Flux Guides for Magnetic MEMS Applications

For a magnetic MEMS application, the integration of soft magnetic flux guides with high saturation flux density is often needed. A complex form including a trench in substrate was designed to achieve its flux guide function. Electroplating CoFe with followed Chemical-mechanical Polishing (CMP) process was chosen as fabrication technology. Pulse current was selected as power supply for electrodeposition process. Experimental results show, that fine tuned pulse current parameters are necessary for electroplating high magnetic performance, low residual stress CoFe films into a trench form without any formation of cracks and voids. For the further system integration a planarization step is required. Since the CoFe layers show a strong response to the chemical attack causing etching, the mere mechanical polishing process is adequate for the planarization of CoFe. Furthermore, the application of alumina abrasives shows very good results regarding surface quality.

Designs and Characterizations of Soft Magnetic Flux Guides in a 3-D Magnetic Field Sensor

A 3-D magnetic field sensor based on the giant magnetoresistive (GMR) spin valve (SV) was designed for improving the energy efficiency in intelligent automating devices. Generally GMR SV sensors are selective only in the plane of the substrate due to fabrication restraints. For this application, a sensor with ultra-thin dimensions is required for the system integration. The approach using micro-assembly for the accomplishment of 3-D field detection is not possible. Therefore, the integration of soft magnetic materials is essential to deflect the magnetic flux for the detection of a magnetic field in the direction perpendicular to the substrate. In this paper the design of 3-D flux guides was presented. Finite element method (FEM) simulations were used to optimize the flux guide design. NiFe, with its high permeability μ, low coercivity H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and relatively high saturation flux density B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , was regarded as the suitable material for this application. Electroplating and patterning by means of photolithography promises to be the appropriate process to integrate this material after the deposition of the GMR multilayer. To characterize the magnetic properties measurements with a Vibrating Sample Magnetometer (VSM) as well as a hysteresisgraph were carried out.

Magnetic Field Enhancement with Soft Magnetic Flux Guides

In this work, a study of the sensitivity enhancement of spin valve sensors, when located in close proximity to magnetic flux guides, is presented. The magnetoresistance (MR) of spin-valve sensors, lithographically patterned into stripes with lateral dimensions, (length) l = 500 µm, (width) wsensor = 1, 2, 6 µm and placed near one/two Co93.5Zr2.8Nb3.7 (CZN) magnetic flux guide, is characterized at room temperature. CZN has a high permeability that together with a defined microstructured shape, is able to concentrate the magnetic flux in a small area, leading to an increase in sensor's sensitivity. The magnetic field amplification is estimated by comparison of sensor sensitivity with/without magnetic flux guides, in the linear operation range, and studied as a function of different parameters. Besides an enhancement in sensitivity, sensors also exhibit an important increase in the hard axis coercivity and a shift from MR(H=0) = 0.5, both attributed to the magnetic flux guides. Amplification factors of the order of 20 are observed..

HTS SQUID microscope head with permalloy flux guide

In order to improve the spatial resolution of an HTS SQUID microscope, permalloy rods with sharpened tip angles of 50/spl deg/ to 170/spl deg/ were placed in front of a SQUID as magnetic flux guides. A current carrying meander line on a printed circuit board with lines and spaces of two widths, 0.3 mm and 0.5 mm, was used as a magnetic field source. The magnetic field distribution was better resolved with the smaller tip angle. Also, a rod with a smaller tip diameter of curvature of 30 /spl mu/m could resolve the magnetic field distribution better than one with a 100 /spl mu/m diameter. It was further found that using a magnetic shield around the magnetic flux guide to suppress the inefficient magnetic field allowed the magnetic field image to be better resolved. The limits of the system's spatial resolution were examined with a 100 /spl mu/m wide meander line. Magnetized laser-printed characters of font size from 2 points to 5 points were also imaged. It was found that this method has a higher magnetic sensitivity and spatial resolution than a large SQUID system, and allows the position and distance from the sample to be adjusted.

Highly sensitive uncooled magnetometers: State of the art. Superconducting magnetic hybrid magnetometers, an alternative to SQUIDs?

We discuss the performances of highly sensitive magnetometers using flux gates, as well as magnetotransport effects (magnetoresistance - AMR/GMR and magnetoimpedance - GMI). Soft magnetic materials operating at room temperature or cryogenic temperatures are involved in these effects. We report on their performances (sensitivity, bandwidth, etc.) with emphasis on their noise properties. The latter often fall to 1-10 pT//spl radic/Hz even for active areas as low as 1-2 mm/sup 2/. Amorphous magnetic flux guides are often used to enhance the field sensitivity of micro-devices. Their replacement by superconducting concentrators, which could lead to much larger gain factors, is discussed. This review, together with new results, confirms a new research field which could lead to highly sensitive, low noise, superconducting-magnetic hybrid magnetometers.