Giant Magnetoimpedance Sensor Research Articles

High sensitivity giant magnetoimpedance (GMI) magnetic transducer: magnitude versus phase sensing

This paper presents the results of investigations recently done by our research group that lead to a new and much better approach to the design of GMI (giant magnetoimpedance) magnetic transducers, which considers the changes in the impedance phase characteristics of GMI sensors due to varying low-intensity magnetic fields, instead of the usual impedance magnitude characteristics considered in the GMI literature. The development process of this new class of magnetic field transducers is discussed, beginning with the definition of the ideal conditioning of the GMI sensor elements (the dc level and frequency of the excitation current and the sample length), proceeding to compare the differences observed between the impedance magnitude and phase of GMI sensors and closing with the electronic circuits that condition ribbon-shaped GMI sensors and read their phase or magnitude variation as a function of the longitudinal magnetic field. Simulation studies, including the full electronic circuit and based on the experimental data obtained from measured GMI curves, have shown that an improvement in the sensitivity of GMI magnetometers larger than ten times can be expected when phase-based transducers are used instead of magnitude-based transducers. Finally, it is also shown that phase-based transducers are highly adequate for miniaturization purposes.

Transverse, longitudinal and perpendicular giant magnetoimpedance effects in a compact multiturn meander NiFe/Cu/NiFe trilayer film sensor

A compact multiturn meander NiFe/Cu/NiFe trilayer film giant magnetoimpedance (GMI) sensor, with the width of 100 µm for NiFe film and 60 µm for Cu film, the space of 40 µm and a turn number of 10 is fabricated by the MEMS technique on a silicon substrate. The transverse, longitudinal and perpendicular GMI effects are respectively investigated in the magnetic field range of 0–120 Oe and the frequency range of 1–40 MHz. With the magnetic field it could be up to 86.6% for the transverse GMI effect at 15 MHz and 120 Oe, 166% for the longitudinal GMI effect at 15 MHz and 20 Oe and 165% for the perpendicular GMI effect at 10 MHz and 50 Oe. In addition, there are platform stages, which correspond to the magnetic field range of 0–20 Oe for the transverse GMI effect and 0–10 Oe for the perpendicular GMI effect. Furthermore, the peak of GMI effects covers a large frequency range, which could be up to about several tens of MHz. The GMI platform and the strong GMI effect could be attributed to the demagnetization effect and enhanced electromagnetic coupling from the compact meander sensor structure, respectively. The broad frequency peak originates from the different magnetization process in the straight segment in the meander structure.

Sensitivity improvement of GMI magnetic and pressure transducers for biomedical measurements

This work presents an experimental study aiming the sensitivity optimization of Giant Magnetoimpedance (GMI) sensors, by means of properly choosing the values of their conditioning parameters. The optimized GMI sensors, together with the development of improved transduction electronic circuits, can lead to the sensitivity enhancement of GMI biomedical, pressure and magnetic transducer prototypes, previously developed by the research group at LaBioMet, PUC-Rio. Those prototypes are, respectively, aimed at the measurement of arterial pulse waves and the localization of magnetic foreign bodies inserted in the human body. Thus, the experimental characterization of GMI ribbon-shaped samples (Co 70 Fe 5 Si 15 B 10 ) was performed, as a function of the external magnetic field, including the experimental evaluation of the asymmetric GMI effect (AGMI). The parameters that affect the behavior of the GMI samples were experimentally analyzed, such as the DC level (0 mA to 100 mA) and frequency (100 kHz to 10 MHz) of the excitation current, as well as the samples length (1 cm, 3 cm, 5 cm and 15 cm). The conditioning parameters, experimentally identified, that optimize the GMI samples sensitivity lead to a maximum specific sensitivity of 0.84 W·Oe -1 ·cm -1 (8400 Ω ·T -1 ·cm -1 ). A new electronic circuit was developed for conditioning and reading of the GMI samples, which directly contributed to the performance enhancement of both transducers. The electronic circuits developed were evaluated supposing the operation of the GMI samples in their most sensitive region. Comparing to previously developed prototypes, the optimum sensitivity achieved for the new configuration of the GMI magnetic transducer increased about 9 times (from 0.12 mV/nT to 1.08 mV/nT), and the sensitivity of the modified pressure transducer increased approximately 7 times (from 1 mV/Pa to 7 mV/Pa).

A prototype of giant magnetoimpedance-based biosensing system for targeted detection of gastric cancer cells

A targeted detection of gastric cancer cells is achieved by combining the giant magnetoimpedance (GMI)-based biosensing system and RGD-4C peptide coupled, chitosan covered superparamagnetic iron oxide particles (RGD-Fe 3O 4@chitosan). The micro-patterned GMI sensor for targeted detection is made of Co-based ribbon and fabricated by micro electromechanical system (MEMS) technology. Functionalized nanoparticles were designed by coating Fe 3O 4 with chitosan and conjugating with RGD-4C peptides. The targeted cells were trickled down into the detection area of the system. The detection of each sample is carried out in ten-fold manner and average value is taken as the final result. This system can identify the differences between targeted cells and non-targeted cells. It is of considerable interest due to its potential application in the biomedical field of various specific detections.

Magnetic Sensor System Using Asymmetric Giant Magnetoimpedance Head

Recently sensitive micro-magnetic sensors are strongly required in various technologies such as BT and IT. This paper gives the comprehensive analysis of the Asymmetric Giant MagnetoImpedance (AGMI) sensor's performance with negative feedback. Asymmetrical behavior of the GMI is required for linear magnetic field sensors as the sensitivity and linearity for magnetic field are the most important parameters in the practical application of GMI to magnetic sensors, and this has been realized by magnetic field annealing in amorphous ribbon. A novel AGMI sensor was developed and the performance of the sensor was carefully studied with and without applying negative feedback. The sensor uses 10 mm times 1 mm times 20 mum Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">66</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> ribbon as a sensing element. On applying the negative feedback the sensor shows excellent linearity free from hysteresis, independent of temperature variations. The sensitivity AGMI sensor was found to be 0.27 V/Oe in dynamic range of -2 ~ 2 Oe.

Giant Magneto Impedance Sensors Based on Microwire and Sandwiched Structures for Non Destructive Testing Applications

Giant Magneto Impedance Sensors Based on Microwire and Sandwiched Structures for Non Destructive Testing Applications

Improved GMI Sensors Using Strongly-Coupled Thin Pick-Up Coils

The performance of Giant Magneto-Impedance (GMI)-based magnetometers is currently limited by electronics, particularly as regards the equivalent magnetic noise. Thus, it is crucial to increase the sensitivity before demodulation. With that objective, we analyze one solution, using a wire-wound device, consisting of a very thin pick-up coil wrapped around a GMI wire, as a sensing element. We present an electrical sensor model using classical two-port network impedance parameters. It allows us to predict the expected improvement in sensitivity, simulating the device implementation in an appropriate electronic design. Preliminary results suggest an improvement in sensitivity by a factor 2 for a 0 dBm sinusoidal excitation voltage source at 10 MHz. Noise measurements support this analysis and show an intrinsic output magnetic noise improvement in the same ratio.

Angle Sensors Based on Oblique Giant Magneto Impedance Devices

The measurement of external magnetic field orientation using Giant Magneto Impedance (GMI) sensors has been performed. A soft magnetic alloy of Co30Fe34Ni36 was electroplated on a Si wafer with a CoFeNi seed layer. V-shaped microwire patterns were formed using a conventional photolithography process. An external magnetic field was generated by a rectangular AlNiCo permanent magnet. The reference direction was defined as the external magnetic field direction oriented in the middle of 2 GMI devices. As the orientation of the magnetic field deviated from the reference direction, variation in the field component along each device introduced voltage changes. It was found that, by taking the voltage difference between the left and right arms of the Vshaped device, the nonlinearity of each device could be significantly reduced. The fabricated angle sensor had a linear range of approximately 70 o and an overall sensitivity of approximately 10 mV.

Operating Field Optimization of Giant Magneto Impedance (GMI) Devices in Micro Scale for Magnetic Bead Detection

Giant magneto impedance (GMI) effect devices for magnetic bead detections were examined. Since commercialized magnetic beads in biological applications are superparamagnetic in nature, not only for improvement of maximum sensitivity but also precise optimizations of operating fields are crucial for sensor applications. We have found that operating fields and maximum sensitivity can be enhanced by the tailoring aspect ratio in microscopic GMI sensors. With an aspect ratio of 3.3-3.8, the GMI sensors were found to exhibit an overall GMI ratio of more than 110% and a maximum sensitivity of 1.61 mV/Oe (15.4%/Oe) at the operating field of 43.1 Oe. Our results demonstrate that microscopic GMI sensors are highly sensitive to magnetic bead detections.

Design of a double core linear magnetometer based on asymmetric magnetoimpedance effect in nanostructured Finemet ribbons

Abstract The techniques used to produce magnetic sensors encompass many aspects of physics and electronics and are going to develop with each passing year. In this paper, we introduce a double core giant magnetoimpedance sensor. The sensing elements are provided by heat treating the FeCuNbSiB (Finemet) ribbons at 560 °C for 1 h to achieve a high magnetic permeability associated with the nanostructured state. Sensor cores are exposed to a dc current bias in order to provide asymmetric giant magnetoimpedance (AGMI) behavior. The sensor detects both direction and amplitude of the magnetic field with a sensibility of 2 mV/Oe.

Large Magnetoimpedance Effects in Nanostructured Fe-Rich Composite Materials for GMI Sensor Applications

In this letter, a systematic study of the giant magnetoimpedance (GMI) effect in nanostructured Ferich composite materials reported. The nanostructure of Fe-rich composite materials consisting of ultra-fine nanoscale Fe(Si) grains embedded in a residual amorphous matrix was attained by annealing their amorphous precursors at a proper temperature (550 °C). The impedance measurements were conducted in the frequency range of 1-10 MHz for a dc magnetic field varying within ±300 Oe. We demonstrated that the nanocrystallization of the alloys led to an improved magnetic softness of the material and, hence, to the GMI effect. It was obvious that, at low frequencies (f ≤ 4 MHz), the maximum value of GMI was observed at near zero field (H dc 0) and the GMI profiles exhibited a typical single-peak feature. At high frequencies (f ≥ 5 MHz), however, a two-peak feature was observed. More interestingly, the GMI ratio and its field sensitivity reached the highest values of 170% and 64%/Oe at a frequency of 2 MHz, respectively. This result is very beneficial for developing highly sensitive GMI sensor applications. The observed GMI features in nanostructured Fe-rich composite materials can be interpreted by adapting the skin-effect model in conjunction with the magnetic-field dependence of the longitudinal permeability. Author

Study of hysteresis for steplike giant magnetoimpedance sensor based on magnetic energy

A giant magnetoimpedance sensor with a steplike impedance property was reported in the case of amorphous soft magnetic thin film in a rectangle shape with an in-plane uniaxial easy axis in a controlled direction. The steplike change of impedance happens simultaneously with a change of magnetic domain, and its physical basis was declared as the intersection of the level of magnetic energy in each case of these domain structures. An actual variation of steplike impedance as a function of external magnetic field typically has a hysteretic property. In this study, an explanation of the hysteretic property is discussed based on an introduction of asymmetrical threshold energy, and then an experimental confirmation is carried out for the proposed analytical model.

Equivalent Magnetic Noise Limit of Low-Cost GMI Magnetometer

We present a noise analysis of a giant magnetoimpedance (GMI) sensor using a peak detector at the optimal magnetic field working bias point of a sensor wire, by considering internal noise sources (intrinsic GMI device associated noise sources and conditioning electronic noise sources). An expression is obtained for the theoretical expected noise for known electronic design parameters and physical characteristics of the GMI wire. The most significant contributions to noise in a GMI measurement, using two basic oscillators (either a simple discrete RC oscillator or quartz oscillator) along with a peak detector, are presented. We discuss the expected extrinsic equivalent magnetic noise limit.

GMR- AND GMI-BASED SYSTEMS FOR NONDESTRUCTIVE EVALUATION OF PRINTED CIRCUIT BOARD

Advances in magnetoresistive type sensors provide a new technique for nondestructive evaluation of metal structures. Giant magnetoresistive and giant magnetoimpedance sensors provide high sensitivity and reduced size with GMI sensors also adding capabilities of high frequency range of measurements. Being produced with thin film processing techniques, the manufacturing cost of these sensors is low. An example is considered of detecting defects in printed circuit boards. System details and experimental results are provided. Computational modeling validation is introduced based on finite element as well as method of moments analysis.

One-dimensional AGMI sensor with Co66Fe4Si15B15 ribbon as sensing element

A novel asymmetric giant magneto impedance (AGMI) sensor was developed and the performance of the sensor was carefully studied. This one dimensional sensor can be further developed as a two-dimensional compass that can be used for navigational purposes. We used commercial Metglas 2714A ribbon. The sensor uses Co66Fe4Si15B15 ribbon as a sensing element.

Trilayer GMI sensors based on fast stress-annealing of FeSiBCuNb ribbons

Magneto-elastic properties and creep-induced anisotropy dependence of giant magneto-impedance (GMI) behaviour in nanocrystalline Fe 75Si 15B 6Cu 1Nb 3/Cu/Fe 75Si 15B 6Cu 1Nb 3 sandwich structures are reported. Magnetic ribbons are submitted to stress (5–175 MPa) and rapid annealing (a few tens of a second) at temperatures between 500 and 800 °C. In contrast with amorphous systems, transfer curves of nanocrystalline GMI sensors can be easily controlled by creep-induced anisotropy. High values of GMI ratio (a few hundreds of percent) are obtained in the radio frequency range. Nanotesla range is detectable with a sensitivity of 4500 V/A/T up to 1 kHz. These performances are interesting for magnetic sensors in non-destructive testing of embedded cracks, ac/dc space magnetometers, molecular recognition systems and selective detection applications.

Formalism to Optimize Magnetic Noise in Giant Magnetoimpedance-Based Devices

This paper describes a theoretical study of the sensitivity and intrinsic noise response in a longitudinal giant magnetoimpedance sensor of a magnetically soft microwire. We show that the ratio of the intrinsic magnetic noise voltage spectral density to the sensitivity is proportional to epsiv/sinthetas, where epsiv depends upon the internal field and frequency and thetas is the angle between the equilibrium magnetization and the axial applied static field. The model allows us to calculate the influence of the easy axis angle and the applied fields on sensor response and to obtain a working point. We show the conditions necessary to reduce the intrinsic noise level to the fT/radicHz level

Large enhancement of GMI effect in polymer composites containing Co-based ferromagnetic microwires

A new kind of composite material consisting of parallel Co-based ferromagnetic microwires embedded in a polymer matrix was designed and produced for high-performance sensor applications. A great enhancement of the giant magnetoimpedance (GMI) effect and its field sensitivity was achieved in these composite materials. It was found that the GMI effect strongly increased with increasing number of ferromagnetic microwires. At a given frequency of 10 MHz, the GMI ratio and its field sensitivity reached the highest values of 450% and 45%/Oe for the composite containing four microwires when compared with those of 14% and 1%/Oe for that containing one microwire. This indicates that the newly developed composite material is very promising for high-performance GMI sensor applications. It was revealed that the increase of the GMI effect in the composite sample was attributed to the decrease of electrical resistance and the increase of effective permeability. An increase of GMI effect with reducing microwire length was also observed and attributed to decrease of the electrical resistance.

Optimized GMI effect in electrodeposited CoP/Cu composite wires

Influences of deposition time and electrolytic current density on the giant magnetoimpedance (GMI) effect of electrodeposited CoP/Cu composite wires were systematically investigated. The CoP magnetic layer was electrodeposited onto the Cu wire of 50 μm diameter. The thickness of CoP magnetic layer was controllably varied either by changing deposition time between t=2 and 10 min with a fixed electrolytic current density or by changing electrolytic current density between j=130 and 900 mA/cm 2 at a given deposition time. Accordingly, the largest GMI effect was achieved in the wire sample with t=6 min and j=639 mA/cm 2. At the measured frequency of 10.7 MHz, the GMI ratio and its field sensitivity reached the highest values of 534% and 21%/Oe, which is promising for high-performance GMI sensor applications. It was proposed that the changes of deposition time and electrolytic current density caused variations in the domain structure of the CoP magnetic layer and hence the GMI behavior.

Eddy current nondestructive testing with giant magneto-impedance sensor

Technologies based on magnetic sensors with high sensitivity such as magneto-resistance (AMR, GMR), fluxgate or squid sensors have demonstrated their capability to improve the performances of the classical eddy current (EC) probes. In this paper, a new kind of magnetic sensor based on giant magneto-impedance (GMI) effect has been evaluated. This sensor combines good sensitivity performances at low frequencies and small size. The design of a probe using this new technology has been optimized with fast semi-analytical models. The performances of this GMI based probe have then been successfully evaluated on a 304 L stainless steel mock up for the detection of embedded flaws.