Magnetoimpedance Sensor Research Articles

A Novel Experimental Approach to the Applicability of High-Sensitivity Giant Magneto-Impedance Sensors in Magnetic Field Communication

This article presents a new application field of a giant magneto-impedance (GMI) sensor. It shows valuable findings for the GMI sensor on the possibility of a new receiving element in magnetic field communication. The proposed GMI sensors serve as antennas and mixers in receiver systems. They have the advantage of being easily implemented and in terms of mass production and manufacturing processes due to the manufacture base on a printed circuit board (PCB). Their smaller size, lower cost, and higher sensitivity have more advantages than conventional magnetic sensors, such as the magneto-inductive, anisotropic magneto-resistive, and giant magneto-resistive sensors. Two types of PCB-based GMI sensors are proposed. The first type of GMI sensor is directly wound around the solenoid-shaped pickup coil onto an alumina insulation tube inserted with an amorphous microwire. The second type of GMI sensor has a patterned pickup coil that does not require the winding of the coil, similar to the patterned pickup coil of a micro electro-mechanical system-based GMI sensor. This GMI sensor provides a new geometry that can be easily manufactured with two PCB substrates. The proposed GMI sensors achieve the equivalent magnetic noise spectral density to the high-sensitivity characteristics of the pT/√Hz level. The equivalent magnetic noise spectral density of 1.5 pT/√Hz at 20.03 MHz is obtained for the first type of GMI sensor, and 3 pT/√Hz at 3.03 MHz is achieved the second type. The analyzed results of the bandwidth and the channel capacity for the two types of GMI sensors are acceptable. This first analysis confirms the possibility of the implementation of GMI sensors in magnetic field communication. The results of this experiment confirm the high performance of the proposed GMI sensors and their applicability in magnetic field communication. The detailed experimental results of the proposed GMI sensors are presented and discussed.

Accurate Measurements of the Rotational Velocities of Brushless Direct Current-Motors by Using an Ultrasensitive Magnetoimpedance Sensing System.

Reports on measurements of the rotational velocity by using giant magnetoimpedance (GMI) sensors are rarely seen. In this study, a rotational-velocity sensing system based on GMI effect was established to measure rotational velocities of brushless direct-current motors. Square waves and sawtooth waves were observed due to the rotation of the shaft. We also found that the square waves gradually became sawtooth waves with increasing the measurement distance and rotational velocity. The GMI-based rotational-velocity measurement results (1000–4300 r/min) were further confirmed using the Hall sensor. This GMI sensor is capable of measuring ultrahigh rotational velocity of 84,000 r/min with a large voltage response of 5 V, even when setting a large measurement distance of 9 cm. Accordingly, the GMI sensor is very useful for sensitive measurements of high rotational velocity.

Low-Frequency Noise Evaluation on a Commercial Magnetoimpedance Sensor at Submillihertz Frequencies for Space Magnetic Field Detection.

The purpose of this study was to measure the low-frequency noise and basic performance of a commercial magnetoimpedance (MI) sensor at sub-millihertz frequencies for use in space missions. Normally, space missions require measuring very weak magnetic fields with a long integration time, such as the space gravitational wave detection mission requiring sub-millihertz frequencies. We set up a platform for measuring the performance on this MI sensor, including low-frequency noise, measurement limit, linearity, and temperature stability. The results show that the low-frequency noise of the MI sensor is below 10 nT/√Hz at 1 mHz and below 100 nT/√Hz at 0.1 mHz; its measurement limit is 600 pT. The MI sensor is characterized by high precision, small size, and low noise, demonstrating considerable potential for application in magnetically sensitive experiments requiring long integration time. This is an effect way to solve the problem that there is on one suitable magnetic sensor at space magnetic field detection, but the sensor requires improvements in temperature stability.

Experimental Study of the Bias Direct Currents on the Transverse Giant Magnetoimpedance Effect in a Soft Ferromagnetic Microwire

This paper reports on an experimental study of influences of the bias direct currents on the transverse giant magnetoimpedance effect in a FeCoNiBSiMo microwire. Along with increasing the bias direct currents, the low field sensitivity of the impedance increases evidently at high frequency (10–120 MHz). The low field sensitivity (4 Oe) by presence of 30 mA of bias direct currents is about 3 times larger than that without using bias direct currents at 60 MHz. However, the high field sensitivity of the impedance decreases by use of bias direct currents at high frequency. In addition, the low field linearity is improved by use of bias direct currents at high frequency. The experimental results could be very useful for the design of multi-dimensional giant magnetoimpedance sensors with high low field sensitivity and linearity.

A giant magnetoimpedance-based separable-type method for supersensitive detection of 10 magnetic beads at high frequency

A sensitive separable-type detection method based on giant magnetoimpedance effect in NiFe/Cu/NiFe/Cu/Cr films for detecting traces of magnetic beads (4.5 μm) at high frequency (> 5 MHz) was presented in this paper. A microcavity with a basement thickness of 0.3 mm was fabricated by Micro-nano carving technology, and was immobilized on the meander-shaped sensing elements for loading Dynabeads. Large resistance variations were observed in the frequency range of 30 MHz∼120 MHz by the presence of Dynabeads. This method is able to detect Dynabeads as low as 10 particles using one single giant magnetoimpedance sensor without external magnetic fields and redundant washing steps, demonstrating high sensitivity, low complexity and nondestructive characteristic.

Alpha Rhythm and Visual Event-Related Fields Measurements at Room Temperature Using Magneto-Impedance Sensor System

In order to achieve the alpha rhythm and visual event-related fields (ERFs) measurements at room temperature, we have newly proposed a high-performance magneto-impedance (MI) sensor system with peak-to-peak voltage detector by synchronized switching, which utilizes the time-differential measurement in each MI element for suppressing the low-frequency noise components and increasing the stability of the sensor system. A high field detection sensitivity with good linearity is obtained via new MI sensor system, which is approximately $1.3\times $ higher than that of the previous MI gradiometer. The noise level we achieved here is lower than 2 pT/Hz $^{1/2}$ in an unshielded environment, for the frequency range of 1–100 Hz. Meanwhile, we have demonstrated the new MI sensor system for room temperature alpha rhythm and visual ERFs measurements. We have achieved a clear sensitivity for spontaneous brain activity with SNR of about 8. As expected, the alpha rhythm signals simultaneously measured by EEG and MI sensor are significantly attenuated when the subject opens eyes and intensified with closed eyes. The considerable enhancement of alpha rhythm measured by MI sensor when the subject had closed eyes further evidences the signals recorded are emanating from spontaneous brain activity. For visual ERFs measurements, we have achieved a clear sensitivity for P300 brain activity for all subjects and demonstrated the tendency of P300 latency to increase with the target/standard discrimination difficulty.

The Influence of Pulsating Tensile Stress on Residual Magnetic Field of P91 Steel Samples

ABSTRACT Measurements of Residual Magnetic Field RMF (the tangential component parallel to the load direction) were taken on the surface of P91 steel plate samples (X10CrMoVNb9-1) subjected to periodic pulsating tensile cyclic loads with the use of flux-gate and magneto impedance sensors, and preliminary measurement results are compiled and analyzed. The study investigates how the microstructure and load cycle parameters affect the RMF changes due to stress variations. Each combination of parameters: microstructure and load cycle corresponds to the characteristic variability pattern of magnetization and its maximum and minimum values.

Magneto-Impedance Sensor Driven by 400 MHz Logarithmic Amplifier.

A thin-film magnetic field sensor is useful for detecting foreign matters and nanoparticles included in industrial and medical products. It can detect a small piece of tool steel chipping or breakage inside the products nondestructively. An inspection of all items in the manufacturing process is desirable for the smart manufacturing system. This report provides an impressive candidate for realizing this target. A thin-film magneto-impedance sensor has an extremely high sensitivity, especially, it is driven by alternatiing current (AC) around 500 MHz. For driving the sensor in such high frequency, a special circuit is needed for detecting an impedance variation of the sensor. In this paper, a logarithmic amplifier for detecting a signal level of 400 MHz output of the sensor is proposed. The logarithmic amplifier is almost 5 mm × 5 mm size small IC-chip which is widely used in wireless devices such as cell phones for detecting high-frequency signal level. The merit of the amplifier is that it can translate hundreds of MHz signal to a direct current (DC) voltage signal which is proportional to the radio frequency (RF)signal by only one IC-chip, so that the combination of a chip Voltage Controlled Oscillator (VCO), a magneto-impedance (MI) sensor and the logarithmic amplifier can compose a simple sensor driving circuit.

Magnetoimpedance Effect in the Ribbon-Based Patterned Soft Ferromagnetic Meander-Shaped Elements for Sensor Application.

Amorphous and nanocrystalline soft magnetic materials have attracted much attention in the area of sensor applications. In this work, the magnetoimpedance (MI) effect of patterned soft ferromagnetic meander-shaped sensor elements has been investigated. They were fabricated starting from the cobalt-based amorphous ribbon using the lithography technique and chemical etching. Three-turn (S1: spacing s = 50 μm, width w = 300 μm, length l = 5 mm; S2: spacing s = 50 μm, width w = 400 μm, length l = 5 mm) and six-turn (S3: s = 40 μm, w = 250 μm, length l = 5 mm; S4: s = 40 μm, w = 250 μm and l = 8 mm) meanders were designed. The ‘n’ shaped meander part was denominated as “one turn”. The S4 meander possesses a maximum MI ratio calculated for the total impedance ΔZ/Z ≈ 250% with a sensitivity of about 36%/Oe (for the frequency of about 45 MHz), and an MI ratio calculated for the real part of the total impedance ΔR/R ≈ 250% with the sensitivity of about 32%/Oe (for the frequency of 50 MHz). Chemical etching and the length of the samples had a strong impact on the surface magnetic properties and the magnetoimpedance. A comparative analysis of the surface magnetic properties obtained by the magneto-optical Kerr technique and MI data shows that the designed ferromagnetic meander-shaped sensor elements can be recommended for high frequency sensor applications focused on the large drop analysis. Here we understand a single large drop as the water-based sample to analyze, placed onto the surface of the MI sensor element either by microsyringe (volue range 0.5–500 μL) or automatic dispenser (volume range 0.1–50 mL).

Effect of YIG nanoparticle size and clustering in proximity-induced magnetism in graphene/YIG composite probed with magnetoimpedance sensors: Towards improved functionality, sensitivity and proximity detection

Proximity-induced magnetism (PIM) in graphene (Gr) adjacent to a magnetic specimen has raised great fundamental interests. The subject is under debate, and yet no application is proposed and granted. In this paper, toward accomplishment of fundamental facts, we first explore the effect of particle size and clustering in the PIM in Gr nanoplates (GNPs)/yttrium iron garnet (YIG) magnetic nanoparticle (MNP) composite. Microscopic analyzes suggest that fine MNPs distributed uniformly on the GNPs have higher saturation magnetization due to the PIM in the GNPs. We propose that such magnetic plates can thus be used to shield the stray field generated on the surface of magnetic sensors and play a role as a magnetic lens to prevent the field emanating outside the body of a magnetic specimen. The GNPs/YIG composites are coated on a magnetic ribbon and proposed for application in magneto-impedance (MI) sensors. We show that such planar magnetic flakes enhance the MI response against the external applied magnetic field significantly. The suggested application can be furthermore developed toward bio-sensing and magnetic shielding in different magnetic sensors and devices.

Detection of AFP with an ultra-sensitive giant magnetoimpedance biosensor

Detecting cancer biomarkers is important for early cancer diagnosis and ensuring timely medical checkups. A magnetic biosensor is one effective tool for sensitive detection of these biomarkers. Herein, we propose an ultra-sensitive magnetic biosensor system composed of an off-diagonal giant magnetoimpedance (GMI) sensor, a simple microfluidic chip and a Helmholtz coil. The GMI sensor was found to provide highly sensitive detection in an external magnetic field (Hext) ranging from −1.2 Oe to 1.2 Oe with maximum sensitivity of 35 V/Oe. We investigated the sensitivity of the sensor system to detect magnetic beads (MBs) at different Hext. Biodetection with the sensor system was conducted with immunoassays between MB-labeled antibody and AFP antigen immobilized on the glass substrate of the open chamber on the chip. The output signal of the sensor system exhibited a linear correlation with the concentration of AFP antigens from 100 fg/mL to 1 μg/mL and a lower limit of detection (LOD) of 100 fg/mL. This ultra-sensitive GMI biosensor provides a useful approach for detecting cancer biomarkers.

An integrated magnetic microfluidic chip for rapid immunodetection of the prostate specific antigen using immunomagnetic beads.

The authors describe an integrated microfluidic chip for immunodetection of the prostate specific antigen (PSA) by using giant magnetoimpedance (GMI) sensor. This chip contains an immunoreaction platform and a biomarker detection system. The immunoreaction platform contains anincubation chamber anda reactive chamber to implement immunological reaction in microfluidics. The system can detect PSA rapidly with ultra-high sensitivity. Both are fabricated by MEMS technology. Immunomagnetic beads (If PSA binds to its antibody (that islabeled with immunomagnetic beads; IMBs)it will be trapped on the surface of self-assembled film. Trapped IMBs generatea stray magnetic field under the magnetization of the external applied magnetic field and can be detected by theGMI sensor. The chip can detect PSA with a detection limit as low as 0.1ng ∙ mL-1 and works in the 0.1ng ∙ mL-1 to 20ng ∙ mL-1concentration range. Compared to established GMI biosensors, the magnetic microfluidic chip reduces assay time, and lends itself to fast detection. It also avoids complex handling steps, enhances reaction efficiency and decreases experimental errors. Graphical abstract An integrated magnetic microfluidic chip which contains immunoreaction platform and biomarker detection system was designed and microfabricated by micro-electromechanical systems (MEMS) technology to detect prostate specific antigen (PSA) rapidly, and has promise in Point-of-care (PoC) diagnostic applications.

Effect of the temperature on the off-diagonal Giant Magneto-Impedance (GMI) sensors

Effect of the temperature on the off-diagonal Giant Magneto-Impedance (GMI) sensors

Magnetic domain transition controlled by distributed normal magnetic field for stepped magneto-impedance sensor

Magnetic domain transition controlled by distributed normal magnetic field for stepped magneto-impedance sensor

Temperature effect on GMI sensor: Comparison between diagonal and off-diagonal response

In this paper, the effect of temperature on Giant Magneto-Impedance (GMI) sensors is studied in amorphous wire Co-Fe-Si-B from Unitika. Both diagonal, Z11, and the off-diagonal, Z21, components of the impedance tensor are considered, with a primary focus on the changes of intrinsic sensitivity and offset, which are the most crucial relevant quantities for practical sensor implementation. Experiments are conducted in the almost industrial temperature range of [−20 °C, 120 °C]. For the component Z11, the results show a maximum change of the offset of −0.13 (A/m)/°C (170 nT/°C), at a 33 A/m bias field. The sensitivity at this field increases for temperatures between −20 °C and + 40 °C, and then it decreases (a maximum change of −0.5%/°C). For the off-diagonal component, Z21, the change of the offset near the zero-field is smaller (−0.015 (A/m)/°C or −19 nT/°C), whereas the sensitivity increases with temperature by about +0.4%/°C.

De-embedding zero-field signal in high-frequency magneto-impedance measurements of soft ferromagnetic materials

Abstract Devices based on soft ferromagnetic materials are promising for high-frequency flexible electronics. Especially, wide-range tunable ferromagnetic resonance response of ferromagnetic microwires and ribbons can be functionalized in the form of magneto-impedance sensors in stretchable, bendable and twistable environments. A vector network analyzer calibrated by standard techniques is required to characterize the high-frequency properties of such devices. However, most of the calibration techniques necessitate calculations, computer simulations, and/or fabricating calibration kits in the shape of various test fixtures. Here, we employ a fixture calibration method for high-frequency (up to 4 GHz) impedance measurements of CoFeSiB microwires and melt-spun ribbons taking zero applied magnetic field as the reference. This method is based on a virtual de-embedding procedure, in which a reference signal is subtracted from all the subsequent measurements, which reduces the time for the total calibration procedure down to few minutes. Applications of the method are not limited to the cases where applied magnetic field varies. Any external parameter (strain, temperature, pressure etc.) that can change the impedance is allowed by this method.

Nanoscale Trilayer Ni/Cu/Fe Investigation for MI Sensor Application

In this study, the effect of magneto-impedance (MI) in three-layer structures was studied. Ni/Cu/Fe sandwiched films were prepared by thermal evaporation on glass substrates. MI sensor impedance as a function of external magnetic field and the driving frequency was measured. MI ratios were obtained as large as 68% and 95% at 5 MHz and 15 MHz, respectively. The results showed that the three-layer structures had a dramatic increase in performance with respect to the single-layer magneto-impedance films.

A short review of magneto-impedance effect for biosensor

This short review paper is organized the following: a material with high magnetoimpedance effect, a various of the patterned in magneto-impedance sensor and bio-magneto impedance application. Various of the magnetic material is presented such as a wire magnetic, ribbon, a magnetic thin films as well as multilayers structure. A pattern of the magneto impedance sensor is also presented in this paper. Finally, recently progress of the bio-magneto-impedance sensing biomagnetic fields of human are reviewed.

Magneto-impedance properties of thin-film type sensors using CoNbZr/SiO2 multilayer films

Abstract Thin-film magneto-impedance (MI) sensors have attracted much attention because of their advantages such as high sensitivity at room temperature and ease of miniaturization. However, further improvement in their sensitivity is required for detecting weak biomagnetic signals such as the magnetic fields of the brain. Since the high-frequency permeability of magnetic multilayer films with insulator layers improves due to the reduction in eddy current loss in the films, sensors using such multilayer films are expected to show a larger impedance change. In this paper, we fabricated sensors using Co85Nb12Zr3/SiO2 multilayer films and investigated their properties to evaluate the effect of their use on the sensor properties. The high-frequency permeability of the multilayer films improved as compared with that of CoNbZr single-layer films due to the reduction in eddy current loss. Because of the improvement in the permeability, the maximum impedance change ratio (ΔZ/Z) of the sensors using the multilayer films increased from 140% to 280% as compared with that of the sensor using the single-layer films. Thus, the use of magnetic multilayer films is effective for increasing the ΔZ/Z value of MI sensors.

Design and Demonstration of Novel Magnetoencephalogram Detectors

Brain activities have attracted considerable attention in medical and healthcare areas and engineering applications. Magnetoencephalogram (MEG) is a non-invasive technique for mapping and evaluating the functional activity of the brain. It is commonly measured by superconducting quantum interference devices (SQUIDs) which is the most reliable sensitive magnetometer for MEG measurement. However, the SQUIDs are still threatened by the need of cryogenic cooling liquids and a shielding room. For recording non-invasive cranial nerve activity, the technology with no liquid helium and high spatial resolution has been required for about 30 years. Sensitive micro-magnetic sensors referred to as magnetoimpedance (MI) sensors based on MI effect in thin amorphous magnetic wires are utilized as an electronics compass in a cellar phone. We have developed a gradiometer based on MI sensor for the purpose of biomagnetic field measurement. The gradiometer is composed of a pair of MI elements with 1 cm length each: a sensing element and a reference element with a baseline of 3 cm. The developed MI gradiometer has good linearity and a high sensitivity of $1.2 \times 105$ V/T with no amplification by semiconductor device. The noise level of the gradiometer is approximately 2 pT/Hz1/2. The MI sensor has system noise higher than SQUIDs, but it has considerable advantages that can measure closely to the scalp. Because of proximity measurement, the magnetic field from brain measured by MI sensor is larger than the case of SQUIDs. The precise MI gradiometer was tested as MEG detectors. The spontaneous brain activity (alpha rhythm) measurements were carried out on a female subject. As expected, the alpha rhythm signals simultaneously measured by electroencephalogram and MI gradiometer were significantly attenuated when the subject opens eyes and intensified with eyes closed. The subject’s $\alpha $ wave MEG signal has a main frequency component of 10–11 Hz and the maximum amplitude is about 25 pT (effective value). Significant susceptibility of MI sensor to spontaneous brain activity was confirmed by signal-to-noise ratio of 8/1. In addition, the measurement of evoked magnetic field N100 was carried out in the unshielded environment. The measurement results about N100 in this paper are almost consistent with the previous study by SQUIDs.