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Abstract In recent years, there has been a significant increase in the prevalence of electronic wearables, among which flexible magnetoelectronic skin has emerged as a key component. This technology is part of the rapidly progressing field of flexible wearable electronics, which has facilitated a new human perceptual development known as the magnetic sense. However, the magnetoelectronic skin is limited due to its low sensitivity and substantial field limitations as a wearable electronic device for sensing minor magnetic fields. Additionally, achieving efficient and non-destructive delamination in flexible magnetic sensors remains a significant challenge, hindering their development. In this study, we demonstrate a novel magnetoelectronic touchless interactive device that utilizes a flexible giant magnetoresistive sensor array. The flexible magnetic sensor array was developed through an electrochemical delamination process, and the resultant ultra-thin flexible electronic system possessed both ultra-thin and non-destructive characteristics. The flexible magnetic sensor is capable of achieving a bending angle of up to 90 degrees, maintaining its performance integrity even after multiple repetitive bending cycles. Our study also provides demonstrations of non-contact interaction and pressure sensing. This research is anticipated to significantly contribute to the advancement of high-performance flexible magnetic sensors and catalyze the development of more sophisticated magnetic electronic skins.

Abstract In recent years, there is a meteoric rise in the prevalence of electronic wearables, and flexible wearables have attracted tremendous attention in human–machine interfaces due to their high biocompatibility, functionality, conformability, and low‐cost. Flexible magnetic smart skin is part of this rapidly progressing field of flexible wearable electronics, which has paved the way for a new path for human perceptual development, as they may form a new perception, also known as magnetic sense, that is, the capacity to detect and interact with magnetic fields. In this review, the concept of the magnetic smart skin is defined: magnetoelastomers and flexible magnetic sensors. In magnetoelastomers, different sources of magnetic field, structures, and applications are summarized by recent and renowned research. In flexible magnetic sensors, different flexible substrates, sensor types, and applications are also summarized. This review further concludes by discussing the outlook and current challenges of magnetic smart skin in human–machine interfaces.

Abstract Due to the high application value in intelligent robots, tactile sensors with large sensing area and multi‐dimensional sensing ability have attracted the attention of researchers in recent years. Inspired by bionics of hairs on human skin, a flexible tactile sensor based on magnetic cilia array is developed, showing extremely high sensitivity and stability. The upper layers of the sensor are multiple magnetic cilia containing magnetic particles, while the lower layer is a serpentine flexible circuit board with a magnetic sensor array. When magnetic cilia are bent under force, the magnetic sensor array can detect changes in the magnetic field, thereby the magnitude and direction of external force can be obtained. The proposed sensor has a resolution of 0.2 mN with a working range of 0–19.5 mN and can distinguish the direction of external force. The large sensing area and short response time make this sensor suitable for sliding tactile detection, and experiments show that the sensor can be also applied in object recognition with a success accuracy of 97%. In addition to the shape of objects, the sensor can identify whether there is magnetism inside objects, making it of significant value in intelligent robots and modern medicine.

Magnetoresistive (MR) sensors have great application prospects in the field of weak magnetic field detection due to their high sensitivity, small size, and low power consumption. However, 1/f noise greatly limits the low-frequency detectivity of MR sensors. In order to suppress 1/f noise, this paper proposes a two-dimensional synchronous motion modulation (TDSMM) structure based on microelectromechanical systems (MEMS). This structure can effectively reduce 1/f noise by modulating the frequency of the measured magnetic field in the high-frequency band. Theoretical analysis and finite element simulation were conducted on three different modulation models: TSDMM, magnetic flux concentrators motion modulation, and MR components longitudinal motion modulation. The results showed that the modulation efficiency of the TDSMM reached as high as 127%, which is currently the highest value in MR-MEMS sensors. The TDSMM MEMS structure has been successfully manufactured, and the resonant frequency of the transverse resonator is twice that of the longitudinal resonator, enabling extremely high modulation efficiency. The noise spectral density of giant-magnetoresistive components on a silicon-on-insulator substrate was tested, and the noise level in the high-frequency band was three orders of magnitude lower than that in the low-frequency band. These results position MR-MEMS sensors with TDSMM structures as highly competitive candidates in the field of ultra-weak magnetic field detection.

Electro-optic modulation devices are essential components in the field of integrated optical chips. High-speed, low-loss electro-optic modulation devices represent a key focus for future developments in integrated optical chip technology, and they have seen significant advancements in both commercial and laboratory settings in recent years. Current electro-optic modulation devices typically employ architectures based on thin-film lithium niobate (TFLN), traveling-wave electrodes, and impedance-matching layers, which still suffer from transmission losses and overall design limitations. In this paper, we demonstrate a lithium niobate electro-optic modulation device based on bound states in the continuum, featuring a non-overlay structure. This device exhibits a transmission loss of approximately 1.3 dB/cm, a modulation bandwidth of up to 9.2 GHz, and a minimum half-wave voltage of only 3.3 V.

To mitigate the impact of low-frequency noise from the tunnel magnetoresistance (TMR) current sensor and ambient stray magnetic fields on weak current detection accuracy, we propose a high-resolution modulation-demodulation test method. This method modulates and demodulates the measurement signal, shifting low-frequency noise to the high-frequency band for effective filtering, thereby isolating the target signal from the noise. In this study, we developed a Simulink model for the TMR current sensor modulation-demodulation test method. Practical time-domain and frequency-domain tests of the developed high-resolution modulation-demodulation method revealed that the TMR current sensor exhibits a nonlinearity as low as 0.045%, an enhanced signal-to-noise ratio (SNR) of 77 dB, and a heightened resolution of 100 nA. The findings indicate that this modulation-demodulation test method effectively reduces the impact of low-frequency noise on TMR current sensors and can be extended to other types of resistive devices.

At present, traditional magnetic field sensors have shortcomings such as large size, complex structure, poor anti-interference ability, and low sensitivity, which are limited in large-scale applications. The magneto-optical sensor has the characteristics of small size, high-integration, stable and reliable in extreme working environment and high sensitivity, which can effectively overcome the above defects and easier to convert it into application products. In this paper, we summarize the magneto-optical sensor based on different used materials, include magnetostrictive materials and magneto-optical materials. We analyzed the sensing mechanisms of these two magneto-optical sensors in detail. The characteristics, structure and performance of magneto-optical sensors are analyzed, the current research progress is summarized, the future development direction of magneto-optical sensors is proposed, and the challenges and development prospects of magneto-optical sensors are analyzed.

Compared with electroplating, liquid casting enables the rapid formation of a three-dimensional solenoid coil with a narrower line width and greater thickness, which proves advantageous in enhancing the comprehensive performance of the micro-electromechanical system (MEMS) fluxgate sensor. For this reason, a MEMS fluxgate sensor based on liquid casting with a closed-loop Fe-based amorphous alloy core is proposed. Based on the process parameters of liquid casting, the structure of the MEMS fluxgate sensor was designed. Utilizing MagNet to build the simulation model, the optimal excitation conditions and sensitivity were obtained. According to the simulation model, a highly sensitive MEMS fluxgate sensor based on liquid casting was fabricated. The resulting sensor exhibits a sensitivity of 2847 V/T, a noise of 306 pT/√Hz@1 Hz, a bandwidth of DC-10.5 kHz, and a power consumption of 43.9 mW, which shows high sensitivity and low power consumption compared with other MEMS fluxgates in similar size.

(001)-oriented FeAlSi polycrystalline thin films with a flat surface and B2-ordered structure were grown on thermally oxidized SiO2 substrates using MgO buffer layers. The FeAlSi thin films composition-adjusted to the Sendust alloy exhibited a low coercivity (Hc) after the annealing process. We utilized these films as bottom electrodes of magnetic tunnel junctions (MTJs) and characterized their tunnel magnetoresistance (TMR) effect. The TMR effect was 35.9% at room temperature. In addition, the TMR ratio increased to 51.0% when a thin CoFeB layer was inserted into the FeAlSi/MgO interface, without degrading the small switching field of the FeAlSi electrode. These MTJs with a small switching field and relatively high TMR ratio using the FeAlSi electrode are promising for highly sensitive MTJ-based magnetic sensor devices.

Thanks to high sensitivity, excellent scalability, and low power consumption, magnetic tunnel junction (MTJ)-based tunnel magnetoresistance (TMR) sensors have been widely implemented in various industrial fields. In nondestructive magnetic flux leakage testing, the magnetic sensor plays a significant role in the detection results. As highly sensitive sensors, integrated MTJs can suppress frequency-dependent noise and thereby decrease detectivity; therefore, serial MTJ-based sensors allow for the design of high-performance sensors to measure variations in magnetic fields. In the present work, we fabricated serial MTJ-based TMR sensors and connected them to a full Wheatstone bridge circuit. Because noise power can be suppressed by using bridge configuration, the TMR sensor with Wheatstone bridge configuration showed low noise spectral density (0.19 μV/Hz0.5) and excellent detectivity (5.29 × 10−8 Oe/Hz0.5) at a frequency of 1 Hz. Furthermore, in magnetic flux leakage testing, compared with one TMR sensor, the Wheatstone bridge TMR sensors provided a higher signal-to-noise ratio for inspection of a steel bar. The one TMR sensor system could provide a high defect signal due to its high sensitivity at low lift-off (4 cm). However, as a result of its excellent detectivity, the full Wheatstone bridge-based TMR sensor detected the defect even at high lift-off (20 cm). This suggests that the developed TMR sensor provides excellent detectivity, detecting weak field changes in magnetic flux leakage testing.

Thanks to their high magnetoresistance and integration capability, magnetic tunnel junction-based magnetoresistive sensors are widely utilized to detect weak, low-frequency magnetic fields in a variety of applications. The low detectivity of MTJs is necessary to obtain a high signal-to-noise ratio when detecting small variations in magnetic fields. We fabricated serial MTJ-based sensors with various junction area and free-layer electrode aspect ratios. Our investigation showed that their sensitivity and noise power are affected by the MTJ geometry due to the variation in the magnetic shape anisotropy. Their MR curves demonstrated a decrease in sensitivity with an increase in the aspect ratio of the free-layer electrode, and their noise properties showed that MTJs with larger junction areas exhibit lower noise spectral density in the low-frequency region. All of the sensors were able detect a small AC magnetic field (Hrms = 0.3 Oe at 23 Hz). Among the MTJ sensors we examined, the sensor with a square-free layer and large junction area exhibited a high signal-to-noise ratio (4792 ± 646). These results suggest that MTJ geometrical characteristics play a critical role in enhancing the detectivity of MTJ-based sensors.

Magnetic flux leakage (MFL) testing is a method of non-destructive testing (NDT), whereby the material is magnetized, and when a defect is present, the magnetic flux lines break out of the material. The magnitude of the leaked magnetic flux decreases as the lift-off (distance from the material) increases. Therefore, for detection at high lift-off, a sensitive magnetic sensor is required. To increase the output sensitivity, this paper proposes the application of magnetic tunnel junction (MTJ) sensors in a bridge circuit for the NDT of reinforced concrete at high lift-off. MTJ sensors were connected to a full-bridge circuit, where one side of the arm has two MTJ sensors connected in series, and the other contains a resistor and a variable resistor. Their responses towards a bias magnetic field were measured, and, based on the results, the sensor circuit sensitivity was 0.135 mV/mT. Finally, a reinforced concrete specimen with a 1 cm gap in the center was detected. The sensor module (with an amplifier and low pass filter circuits) could determine the gap even at 50 cm, suggesting that MTJ sensors have the potential to detect defects at high lift-off values and have a promising future in the field of NDT.

Magnetic tunnel junctions (MTJs) that consist of two ferromagnets separated by a thin insulator are among the core devices used in spintronic applications such as magnetic sensors. Since magnetic sensors require high sensitivity for nondestructive eddy current testing, we developed and demonstrated magnetic sensors based on various configurations of serial MTJs. We fabricated sensors with 4, 16, 28, 40, and 52 serial MTJs in various numbers of rows (1, 4, 7, 10, and 13) to detect surface cracks via eddy current testing. All of the sensors could detect and discriminate between surface cracks 0.1mm in width and 0.1 to 1.0mm in depth on an aluminum specimen. Systematic studies on the effect of the number of MTJs showed a signal to noise ratio as high as 115 dB when detecting 0.1mm deep cracks with 28 serial MTJs in 7 rows. This suggests that suitably configured serial MTJ sensors can offer an excellent performance in the detection of tiny surface defects via eddy current testing. [ABSTRACT FROM AUTHOR]

This paper investigates how the Indian equity market is interconnected with other stock markets. A VAR (Vector Autoregressive Model) is developed in order to understand this phenomenon. We also seek to understand to what extent shocks in the Indian stock market transmit innovations to the stock markets of India's top trading partners. Furthermore, we seek to examine the variance decomposition that is explained by a unit-standard deviation- shock to the stock markets Hong Kong, Malaysia, Singapore, Switzerland, and the United States. We find that the stock markets of Hong Kong, Malaysia, Singapore, Switzerland, and the United States respond in time varying stages to innovations in the Indian stock market. [ABSTRACT FROM AUTHOR]

Hall devices using anomalous Hall effect of ferromagnetic Fe–Sn nanocrystalline thin films exhibit high sensitivity for detection of magnetic field comparable to that of semiconductor devices. For applying this material to magnetometry, superior detectivity owing to low electrical noise is a critical requirement. We investigate the magnetic-field sensitivity and the low-frequency noise spectrum as a detectivity for Fe–Sn Hall-cross devices. We detected typical noise behavior of 1/f and thermal noise. The noise-equivalent magnetic field reaches 0.3 μT/Hz1/2, which is comparable to that of semiconductor-based Hall sensors. A sufficiently low-noise spectrum evidences the potential applicability of Fe–Sn to Hall magnetometry. [ABSTRACT FROM AUTHOR]

The high sensitivity of magnetic tunnel junctions (MTJs) is independent of the field frequency, and sensors based on them have shown considerable potential in measuring secondary fields during eddy current nondestructive testing (ECT). In this study, sensors with 4, 16, 28, 40, and 52 serial MTJs were fabricated and characterized for detecting variations in magnetic fields. These micrometer-sized TMR sensors with serial MTJs exhibited low detectivities (2.0 ∼ 5.1 nT/Hz0.5 at 100 Hz). Furthermore, in ECT measurements, the sensors were used to detect far-side pits in a copper specimen, and the sensor with 28 serial MTJs offered the highest signal-to-noise ratios when detecting far-side pits with various diameters (2.5, 5.0, and 7.5 mm). In addition, the TMR sensors could detect millimeter-sized far-side pits having various depths and diameters, suggesting that they could detect buried defects in ECT. [ABSTRACT FROM AUTHOR]

Eddy current testing plays a significant role in detecting surface defects in a nondestructive testing field. The magnetoresistive sensors based on magnetic tunnel junction devices attracted considerable attention for their use in eddy current testing owing to their high sensitivity and capability of being miniaturized. We investigated the detection of surface cracks in eddy current testing using a single magnetic tunnel junction. A perpendicular component with a secondary magnetic field from an eddy current was measured by using an optimized rectangular magnetic tunnel junction device with an aspect ratio of 4 (20 × 80 µm2). Furthermore, according to the extracted ΔX and ΔV from the sensor output signal, surface cracks with various widths (0.1, 0.3, and 0.5 mm) and depths (0.5, 1.0, 1.5, and 3.0 mm) in aluminum specimens were successfully estimated using the magnetic tunnel junction device in eddy current testing when an excitation frequency of 1000 Hz was used. [ABSTRACT FROM AUTHOR]

We experimentally investigated the asymmetric transmission probabilities of spin-up and spin-down electrons at a (001)-Fe/Ag interface, which result in a highly spin-dependent interface resistance () that improves the magnetoresistive outputs of giant magnetoresistive devices whose ferromagnetic layers comprise only 3d transitional materials such as FeCo-based alloys. We quantitatively determined the spin-dependent interfacial parameters at FexCo100-x/Ag interfaces that were tuned by varying the Fe concentration x. Among the interfaces, the highest interface resistance of 0.65 mΩ·µm2 was obtained with an of 1.89 mΩ·µm2, which corresponds to ARF/N↑ ∼ 1.08 mΩ·µm2 and ARF/N↓ ∼ 7.98 mΩ·µm2 at a (001)-Fe/Ag interface. [ABSTRACT FROM AUTHOR]