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Aiming to enhance the performance of magnetic field sensors, this study focuses on depositing electrospun TiO 2 /PVA/CTAB composite nanofibers onto cobalt-based amorphous magnetic ribbons. The nanofibers have diameters of about 175–325 nm, where TiO 2 nanoparticles are uniformly dispersed in the fibers. The nanofiber-coated ribbons were analyzed using the giant magneto impedance (GMI) effect and we measured significant variation in the GMI ratio. The results demonstrate that the GMI response of the ribbon coated with nanofibers electrospun for 15 min exhibits a remarkable increase of 340% at a frequency of 10 MHz, compared to 290% for the uncoated ribbon. Nanofibers can be utilized for chemically or physically bonding additives to their surface, particularly for applications, where it is needed, for example, to detect biomaterials. Given their dielectric nature, these fibers hold potential for shielding against space charges and adhering to chemical components. They can be integrated with other materials to enhance the magnetoimpedance effect. Therefore, the application of non-magnetic electrospun nanofibers as coatings on magnetic sensors shows significant promise in augmenting their sensitivity and overall performance.

We report on a method for ultrasensitive detection and quantification of the pathogen Escherichia coli ( E. coli ), type O157:H7. It is using a tortuous-shaped giant magnetoimpedance (GMI) sensor in combination with an open-surface microfluidic system coated with a gold film for performing the sandwich immunobinding on its surface. Streptavidin-coated super magnetic Dynabeads were loaded with biotinylated polyclonal antibody to capture E. coli O157:H7. The E. coli -loaded Dynabeads are then injected into the microfluidics system where it comes into contact with the surface of gold nanofilm carrying the monoclonal antibody to form the immunocomplex. As a result, the GMI ratio is strongly reduced at high frequencies if E. coli O157:H7 is present. The sensor has a linear response in the 50 to 500 cfu·mL −1 concentration range, and the detection limit is 50 cfu·mL −1 at a working frequency of 2.2 MHz. In our perception, this method provides a valuable tool for developing GMI-based microfluidic sensors systems for ultrasensitive and quantitative analysis of pathogenic bacteria. The method may also be extended to other sensing applications by employing respective immunoreagents. Graphical Abstract Fig. (a) Graphical illustration of the test setup. (b) Relationship of GMI signal vs. E. coli O157:H7 concentration.

The giant magnetoimpedance effect of multilayered thin films under stress has great application prospects in magnetic sensing, but related studies are rarely reported. Therefore, the giant magnetoimpedance effects in multilayered thin film meanders under different stresses were thoroughly investigated. Firstly, multilayered FeNi/Cu/FeNi thin film meanders with the same thickness were manufactured on polyimide (PI) and polyester (PET) substrates by DC magnetron sputtering and MEMS technology. The characterization of meanders was analyzed by SEM, AFM, XRD, and VSM. The results show that multilayered thin film meanders on flexible substrates also have the advantages of good density, high crystallinity, and excellent soft magnetic properties. Then, we observed the giant magnetoimpedance effect under tensile and compressive stresses. The results show that the application of longitudinal compressive stress increases the transverse anisotropy and enhances the GMI effect of multilayered thin film meanders, while the application of longitudinal tensile stress yields the opposite result. The results provide novel solutions for the fabrication of more stable and flexible giant magnetoimpedance sensors, as well as for the development of stress sensors.

The performances of common magnetic sensors in the field of microcurrent detection are presented. The giant magneto-impedance (GMI) effect is summarized, and the possibility of picoampere microcurrent measurement using the GMI effect sensor is proved. The classical design scheme of the GMI effect current sensor is improved, and a GMI sensor chip model that can realize picoampere microcurrent measurement is preliminarily established, which lays a theoretical foundation for further development of GMI microcurrent sensor with high performance, small volume, and low cost.

Purpose This paper aims to investigate the influence of structure parameters on giant-magnetoimpedance (GMI) effect measured by non-contact method. Design/methodology/approach The GMI sensor contains a Co-based internal magnetic core fabricated by laser cutting and an external solenoid. The influences of magnetic permeability of magnetic core and structure parameters on GMI effect were calculated in theoretical model. The output impedance, resistance, reactance and GMI ratio were measured by non-contact method using impedance analyzer. Findings Enhancing external magnetic field intensity can decrease the magnetic permeability of core, which has vital influences on the magnetic property and the output response of GMI sensor. In addition, increasing the width of magnetic core and the number of solenoid turns can increase the maximum GMI ratio. The maximum GMI ratio is 3,230% with core width of 6 mm and solenoid turns of 200. Originality/value Comparing with traditional contact-measured GMI sensor, the maximum GMI ratio and the magnetic field sensitivity are improved and the power consumption is decreased in non-contact measured GMI sensor. GMI sensor measured by non-contact method has a wide range of potential applications in ultra-sensitive magnetic field detection.

The dependence of a longitudinal giant magnetoimpedance (GMI) effect of a [Fe 21 Ni 79 /Cu] 5 /Cu/[Fe 21 Ni 79 /Cu] 5 film element on the position of a magnetic insert is investigated in a model experiment on detecting a clot in a blood vessel. The magnetic insert is an epoxy composite containing 30 wt.% of the iron oxide microparticles. An investigation of the magnetic properties of the film element and the magnetic composite cylinder-shaped sample is performed. The magnetic insert is placed at a distance of 1.1 mm above the film surface and can be displaced perpendicular to its longer side with a step of 1 mm. As soon as the magnetic insert approaches the element, the maximum value of magnetoimpedance (MI) ratio for resistance is observed to decrease, and there is a shift of the curves of the MI ratio for resistance along the external magnetic field lines. The magnetic stray fields influencing the film in each position of the magnetic insert are simulated with the Comsol software and compared with the GMI response.

We studied the giant magnetoimpedance (GMI) effect and magnetic properties of Finemet-type FeCuNbSiB microwires. We observed that the GMI effect and magnetic softness of glass-coated microwires produced by the Taylor–Ulitovski technique can be tailored by controlling the magnetoelastic anisotropy of as-prepared FeCuNbSiB microwires, and can also be considerably improved either by heat treatment and/or choosing the suitable fabrication conditions. We observed a considerable magnetic softening of the microwires after the appropriate annealing. This magnetic softening correlates with the devitrification of amorphous samples. Amorphous Fe-rich microwires exhibited a low GMI effect (GMI ratio below 5%). A considerable enhancement of the GMI effect (GMI ratio up to 100%) has been observed in heat-treated microwires with nanocrystalline structure.

We studied the effect of annealing on the giant magnetoimpedance (GMI) effect, magnetic domain wall dynamics, and magnetic properties of amorphous iron (Fe) and cobalt (Co)-based microwires prepared by the Taylor–Ulitovsky technique. We observed that the properties can be tailored by controlling the magnetoelastic anisotropy of CoFeBSiC microwires during wire formation and also controlling the magnetic anisotropy by further heat treatment. A high GMI effect has been observed in the as-prepared Co-based microwires. High domain wall velocity and rectangular hysteresis loops have been observed in additionally heat-treated microwires. We observed increasing of the wall velocity under stress in some annealed samples. We demonstrated that, for certain annealing conditions, we can observe coexistence of the GMI effect and magnetic domain wall propagation in the same sample.

We report on a biosensing system for ultrasensitive detection of Dynabeads protein A (DPA) that employs the magnetoimpedance (GMI) effect. The system is capable of detecting DPA via magnetic signals in the form of a magnetoimpedance change. The GMI ratio shows distinctive changes because of the induced fringe field produced by the superparamagnetic Dynabeads. The GMI ratio undergoes an overall downturn at high frequencies, but the drop becomes smaller with increasing DPA concentration. This phenomenon has not been observed so far. At a concentration of 0.1 μg mL −1 , the GMI ratio drops by 8.53 % at a frequency of 1.4 MHz. In other word: almost 90 Dynabeads can be detected. We believe that this novel scheme has a large potential in high-sensitivity and miniaturized immunoassays. Figure The GMI biosensing system is established for ultrasensitive detection of Dynabeads protein A. The rectangle nano-Au film is used for immobilization of the Dynabeads protein A. The longitudinal external field ( He ) is generated by a DC field source (0–125 Oe). The GMI biosensor is driven by AC with an amplitude of 10 mA (0.1–5 MHz).

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.