Search

The emerging market of wearable devices for tracking and positioning requires the development of highly flexible magnetic sensors. Due to the stable magnetoresistance ratio and simple fabrication process, sensors based on the anisotropic magnetoresistance (AMR) effect have been proposed as promising candidates. However, the stability of AMR sensors under different bending situations has rarely been investigated. In this work, we proposed a flexible AMR magnetic sensor deposited on an ultra-thin Kapton substrate, which exhibits excellent anti-fatigue behavior at different bending curvatures ranging from 1/3 to 1/10 mm−1. Experimental results show that the sensitivity of our proposed flexible AMR sensor remains as high as 0.25 Oe−1 after being bent 500 times, showing promising potential for application in wearable electronic devices. [ABSTRACT FROM AUTHOR]

Measurement of 3D vector magnetic field is of vital importance for the development of magnetic navigation, biomedical diagnosis, and microimaging. Traditional 3D magnetic sensors require cooperation of multiple sensors on three orthogonal planes, resulting in disadvantages of bulky size and low spatial resolution. Recently proposed spin orbit torque sensor based on ferromagnetic/heavy‐metal heterostructures can detect three magnetic field components individually due to the different symmetries of current‐polarity‐dependent magnetization dynamic. However, the large driving current density and complex driving procedure hinder their practical application, especially in AC magnetic field detection. Herein, 3D magnetic sensors with dramatically reduced driving current density are reported, one fifth of the original value, by exquisite engineering of the magnetic anisotropy in Pt/Co/Ta heterostructures. With further reduced perpendicular magnetic anisotropy, the sensor in the easy‐cone state demonstrates a record‐high sensitivity of 31196 V A−1 T−1. More importantly, the easy‐cone state sensor can work with an ultralow driving current density of 3.8 kA cm−2, which is three orders lower than previous results. Although easy‐cone state sensor can only measure the z‐axis field, highly compact 3D magnetic sensor can be realized by adoption of two anisotropic magnetoresistance sensors, promising great potential application in space‐ and energy‐restricted scenarios. [ABSTRACT FROM AUTHOR]

Large working range is of vital importance for magnetic sensors when exposed to complicated magnetic field profile, especially in automation and power industry where large field variation is frequently encountered. The design for traditional magnetic sensors, e.g., magnetoresistive and fluxgate magnetometers, utilizes ferromagnetic materials with ultrahigh permeability to maximize the field sensitivity, resulting in strictly confined dynamic range due to limited saturation field. Here, an integratable ferromagnetic resonance (FMR) prototype magnetic sensor with high sensitivity and theoretically unlimited working range is reported. An ultrawide working range (>450 mT) which is more than two orders larger than that of commercial sensors with similar field resolution is experimentally verified. Moreover, the FMR magnetometer is a vector sensor in contrast to the traditional scalar sensors based on magnetic resonance. With a navigating magnetic field of 50 μT (ca. the Earth's magnetic field), the resolution for azimuth angle is 0.006°. Compared with traditional nuclear magnetic resonance and electron paramagnetic resonance sensors with large size and high power consumption, the compact FMR sensor with large dynamic range and high sensitivity has much broader application prospects, especially in magnetically harsh environments. [ABSTRACT FROM AUTHOR]

A magnetic field sensor consisting of a surface acoustic wave (SAW) generator and a cantilever beam with NdFeB permanent magnets are developed. The working principle of this magnetic sensor relies on the center frequency shift of the SAW device under the magnetic field as a consequence of the torque-effect-induced deformation of the cantilever, which changes the stress on the piezoelectric LiNbO3 and the spacing between the interdigital transducers (IDTs). Compared with other magnetic sensors based on acoustic resonance, the performance of our proposed sensor is greatly enhanced due to the structural design by incorporating the magnetic torque effect. High sensitivity of 1277.69 kHz/Oe and a large percentage change in frequency of 5.177% are achieved in this magnetic sensor near a resonant frequency of 848 MHz. The proposed magnetic sensor based on SAW and torque effect exhibits great potential for applications in magnetic field detection. [ABSTRACT FROM AUTHOR]

Giant magnetoresistance (GMR) sensors have been widely used in current detection, compass, automobile, and Internet of Things. The linearity of GMR sensors relies on a magnetic annealing process above the blocking temperature of the antiferromagnetic layer, which causes the same magnetization directions in the free and pinned ferromagnetic layers. Here we construct an orthogonal magnetic anisotropic structure by using a relatively low annealing temperature of 145 °C, where the magnetization direction of the free layer is perpendicular to that of the pinned layer so that a linear output can be realized. Quantitative magneto-optical kerr microscope (MOKE) is used to investigate the vector distribution of the magnetic domains, showing that an orthogonal anisotropy is established by the low temperature annealing process. GMR magnetic field sensor with a sensitivity of 0.78 mV/V/Oe and a measurement range of −20 to 20 Oe is demonstrated, which provides an effective method to enhance the linearity of the magnetic sensors with spin valve structures. [ABSTRACT FROM AUTHOR]

Magnetic sensors have various applications in navigation, power distribution, robotics, factory automation, and medical diagnosis. The development of highly sensitive magnetic sensors usually requires complicated and costly fabrication process. Herein, we report giant magneto-impedance of 41036% in the commercially available ferrite core inductors. A magnetic field detection limit of 10 nT at 1 Hz has been obtained by directly measuring the impedance of the as-obtained inductor without any optimization. With a 100 pF capacitor in series connection with the inductor where lower impedance facilitates the measurement process, a limit of detection of 625 pT at 1 Hz has been obtained in the series RLC resonator. These results can be understood in terms of the magnetic field-dependent self-resonance in the inductors which act as lumped RLC resonators. Compared with the traditional electromagnetic induction sensing mode, the magneto-impedance sensing mode shows 5000 folds improvement in the magnetic field detection capability. [ABSTRACT FROM AUTHOR]

Wireless strain sensors have received extensive attention owing to their wide application prospects in structural health monitoring, industrial automation, human activity monitoring, and intelligent robotic systems. Here, a wireless strain sensor prototype based on the magnetoelectric heterostructure of ferromagnetic thin films on a piezoelectric substrate has been developed. The ferromagnetic resonance (FMR) frequency of the sensor is strongly dependent on external strain due to the large magnetostriction of the film. The piezoelectric substrate with a programmable voltage has been used as a strain source for the characterization of the wireless strain sensor. The limit of detection of the wireless strain sensor is 0.54 με, which is comparable with that of commercial metal-foil sensors that need connection wires. More importantly, the FMR strain sensor shows a sensitivity of 65.46 ppm/με, indicating more than a 60 fold improvement than that of traditional wireless strain sensors based on patch antenna and RLC resonators whose frequency shift is mainly due to the strain induced dimension change. [ABSTRACT FROM AUTHOR]

Measurement of magnetic signal from an arbitrary direction is of vital importance for applications in magnetic navigation, space science, indoor positioning, and magnetic gesture recognition. However, magnetoresistive sensors, as vector magnetometers, are only suitable for detection of magnetic signals along the magnetic hard axis. Magnetoelectric coupling is introduced to control the magnetic anisotropy of a magnetoresistive pattern, realizing a 90° rotation of the magnetic hard axis and thus the sensing direction of the tunable sensor. The sensitivity along the initial magnetic easy axis can be enhanced 12.7‐fold while that along the initial hard axis can be depressed to be only 4.7% of the original value through magnetic anisotropy engineering. The tailorable directional sensitivity of the electric‐field reconfigurable sensor speaks to the strong potential of this system for practical applications requiring testing of localized magnetic fields, for example, magnetic diagnosis or biomagnetic characterization. [ABSTRACT FROM AUTHOR]

The magnetic field sensors based on anisotropic magnetoresistance (AMR) effect have been widely used in data storage, navigation, and medical diagnosis. However, the AMR effect of metal materials is relatively weak with an AMR ratio below 2%, which results in low voltage output. In order to improve the sensitivity of weak magnetic fields, we optimize the structure of the AMR sensor with a specific photolithographic process. We use two different designs of Hall bar and Wheatstone bridge with similar barber pole structures, and investigate the angular dependence as well as magnetic field dependence of AMR ratio and voltage output. With Wheatstone bridge, the magnetoresistance leads to a voltage output without dc components. The NiFe magnetic layer and the Au electrode are patterned into a highly conductive barber poles structure, and a high voltage output ratio of about 80% is obtained. At the same time, we achieve a high sensitivity of about 4.3 Oe−1, which implies potential applications in AMR effect-based magnetic field sensors. [ABSTRACT FROM AUTHOR]