Rapid and multiplexed measurement is vital in the detection of food-borne pathogens. While highly specific and sensitive, traditional immunochemical assays such as enzyme-linked immunosorbent assays ...(ELISAs) often require expensive read-out equipment (e.g. fluorescent labels) and lack the capability of multiplex detection. By combining the superior specificity of immunoassays with the sensitivity and simplicity of magnetic detection, we have developed a novel multiplex magnetic nanotag-based detection platform for mycotoxins that functions on a sub-picomolar concentration level. Unlike fluorescent labels, magnetic nanotags (MNTs) can be detected with inexpensive giant magnetoresistive (GMR) sensors such as spin-valve sensors. In the system presented here, each spin-valve sensor has an active area of 90μm×90μm, arranged in an 8×8 array. Sample is added to the antibody-immobilized sensor array prior to the addition of the biotinylated detection antibody. The sensor response is recorded in real time upon the addition of streptavidin-linked MNTs on the chip. Here we demonstrate the simultaneous detection of multiple mycotoxins (aflatoxins B1, zearalenone and HT-2) and show that a detection limit of 50pg/mL can be achieved.
Research in nondestructive evaluation is constantly increasing the sensitivity of detection of small cracks embedded deep in layered aircraft structures. Pulsed eddy-current (PEC) techniques using ...coil probes have shown considerable promise in detection and characterization of buried cracks in multilayered structures. In this paper, we describe the design and development of a nondestructive inspection system that uses pulse excitation of a planar multiline coil to generate a transient field that is detected via a giant magnetoresistive (GMR) field sensor. An analysis algorithm using features in time and frequency domain processes the experimentally measured signals for automatic detection of small cracks under fasteners in multilayered structures at a depth of up to 10 mm.
We compare alternative concepts of magnetic field sensors, which are capable of working under very high and even extreme temperature conditions, and outline their respective principal technological ...and physical limitations. We review basic work done in this field and draw a conclusion which approaches seem to be the most promising for the realization of such magnetic field sensors.
The hysteresis of magnetoresistive sensors remains a considerable cause of inaccuracy of positioning applications. The phenomena itself has been well studied and described by different physical and ...phenomenological models. Various biasing techniques have been proposed. However, the increased fabrication and computational price they require is undesirable. In this paper, a computational algorithm for the compensation of hysteresis of linear and rotary encoders is proposed. A lagging-domain model based on play operators is presented for prediction of hysteresis. The outlined procedure for the calibration of parameters allows the use of the algorithm for various types of encoders without knowing their exact material properties. The method was tested on different anisotropic magnetoresistive and tunneling magnetoresistive sensors. Results show that the impact of hysteresis was reduced by up to 90% without a significant increase of computational time or production costs.
This paper reports on the integration of magnetic tunnel junction (MTJ) sensing devices with magnetoresistance responses above 150% on flexible substrates. The sensors are integrated in a fabrication ...process based on polyimide materials, and demonstrate sensitivities up to 250 μV/Oe for bias currents in the 100-μA range. Assessment of the sensors performance is done under controlled mechanical load conditions, and the magnetoresistance is only slightly affected (1% variation) while sensitivity changes by 7.5% when the bending radii reduce down to 5 mm. The results demonstrate the high potential of the MTJ sensors to be used in applications requiring bending and conforming to non-planar geometries, bringing magnetoelectronic technologies to hard-to-reach regions of space.
Magnetic nanoparticles (MNPs) have been widely utilized in the biomedical field for numerous years, offering several advantages such as exceptional biocompatibility and diverse applications in ...biology. However, the existing methods for quantifying magnetic labeled sample assays are scarce. This research presents a novel approach by developing a microfluidic chip system embedded with a giant magnetoresistance (GMR) sensor. The system successfully detects low concentrations of MNPs with magnetic particle velocities of 20 mm/s. The stray field generated by the magnetic subject flowing through the microchannel above the GMR sensor causes variations in the signals. The sensor’s output signals are appropriately amplified, filtered, and processed to provide valuable indications. The integration of the GMR microfluidic chip system demonstrates notable attributes, including affordability, speed, and user-friendly operation. Moreover, it exhibits a high detection sensitivity of 10 μg/μL for MNPs, achieved through optimizing the vertical magnetic field to 100 Oe and the horizontal magnetic field to 2 Oe. Additionally, the study examines magnetic labeled RAW264.7 cells. This quantitative detection of magnetic nanoparticles can have applications in DNA concentration detection, protein concentration detection, and other promising areas of research.
Existing magnetoresistive angular position sensors possess an outstanding angle accuracy as well as a high robustness against challenging environmental conditions. Thus, this class of sensors plays ...an important role in automotive and industrial applications. However, due to upcoming international standards future angular measurement systems must be insensitive against magnetic stray fields. Unfortunately, state of the art magnetoresistive angle sensors provide only a limited stray field suppression. In the following a novel methodology is presented, which is able to eliminate the impact of stray fields with nearly arbitrary magnitude. Furthermore, our concept is based on well-established magnetoresistive angular sensing setups. From this follows, that the presented technique can be implemented easily. In this paper, the measurement principle as well as measurement results are presented.
Nanomagnetism deals with magnetic phenomena in nanoscale structures, involving processes at the atomic level. Magnetic sensors, which exhibit the surprising giant magnetoresistance (GMR) effect, are ...some of the first real applications of nanotechnology, and have become very important in the last two decades. In addition, high-performance magnetoresistance (MR) measurement is a critical technique in modern electrical applications, including electronic compasses, aviation navigation, motion tracking, noncontact current sensing, rotation sensing, and vehicle detection. Both GMR and tunneling magnetoresistance (TMR) sensors have been used in the state-of-art electronic compasses. A new planar design layout of a vector magnetometer is proposed in this report. It can sense variations in three-dimensional (3-D) magnetic fields. The planarization of a vector magnetometer is carried out with consideration of materials, magnetic schematics, as well as transducer circuit designs. The optimization of an advanced magnetic material for use in GMR and TMR sensors and its planarization in a 3-D design are crucial practical issues. This paper presents an overview of the planarization of vector magnetometers and the development of its applications. It focuses on recent works, covers an analytic model of magnetoresistive sensors, and methods of thin film fabrication. It also addresses the planar vector magnetometer with a flux-guide, the chopping technique, and techniques for microfabrication of substrates. Planarization in magnetic sensors will become increasingly exploited as nanomagnetism grows in importance.
Large area MTJs with linear response and very larger sensitivities are needed to fulfill the requirements for the detection of pT/Hz 0.5 magnetic fields at low frequency and room temperature. MTJ ...stacks with soft-pinned sensing layers have been developed and the stack was optimized, providing a tunable soft-pinning field over a large range of values. Sensitivities corresponding to resistance changes of up to 7%/Oe are obtained in patterned MTJs with areas of 20 × 20 μm 2 starting from films with high sensitivity soft-pinned layers made from 3.0Co 40 Fe 40 B 20 /0.21Ta/8.0Ni 81 Fe 19 /8.0Ir 20 Mn 80 .
The detection of corrosion on insulated and/or coated pipes remains a challenge. A non-destructive evaluation method has been proposed where a low-frequency AC current is directly injected into the ...pipe at distant locations, and perturbations in the magnetic field induced by current deflection around defects are measured. Structural health monitoring is made possible by detecting changes in the magnetic field due to defect growth using a permanently installed array of sensitive and inexpensive magnetic sensors. The performance of current deflection structural health monitoring is evaluated using a flexible and efficient framework. Individual sensor performance was first predicted using receiver operating characteristics obtained by evaluating the stability of the magnetic field signal measured outside of a section of coated undamaged riser pipe in an environmental chamber over repeated temperature cycles. A finite element model was then used to predict the magnetic perturbation due to defect growth which allowed the potential array configurations for structural health monitoring to be explored. Results suggest that 90% probability of detection and 0.1% probability of false alarm for
3
×
T
(wall thickness) diameter, 30% of T depth defects are possible outside of 25- to 50-mm-thick pipe coatings/insulation using 10–50 sensors per metre of pipe and 5–10 A of injected current. The structural health monitoring procedure was then demonstrated experimentally, an electrochemically grown defect being successfully monitored; this experiment also served to validate the three-dimensional finite element model. A very good agreement between the predicted and measured changes in the magnetic field due to the current deflection around the growing defect was obtained.
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