High Magnetic Sensitivity Research Articles

Increasing the sensitivity of Love wave MSAW sensors by magnetoelastic layer thickness variation

Abstract Increasing the magnetic field sensitivity is one of the major challenges in the study of magnetic surface acoustic wave (MSAW) sensors. In this paper, Love wave MSAW sensors are investigated in a Transmissive Single Port Delay Line (TSP-DL) configuration, on ZnO (700 nm)/Y-X LiNbO3. CoFeB (100 nm) or CoFeB(100 nm)/SiO2(3 nm)/CoFeB(100 nm) sensitive magnetoelastic layers are placed in the acoustic path between two electrically connected interdigital transducers. The fundamental Love wave on ZnO(700 nm)/ Y-X LiNbO3 presents a high electromechanical coupling coefficient (K 2), resulting in a high signal amplitude, which is favorable for delay lines performances. Additionally, shear waves are highly sensitive to the magnetic field due to the large ΔG effect in the magnetoelastic layers. A maximum frequency shift of 0.36% was achieved using a CoFeB(100 nm)/SiO2(3 nm)/CoFeB(100 nm) stack as the sensitive layer, with a high maximum magnetic sensitivity of 3630 ppm mT−1 (1482 kHz mT−1 at 410 MHz). This sensitivity is among the highest reported in the literature on magnetic SAW sensors.

Passive temperature-compensated fiber Fabry-Perot magnetic field sensor.

A passive temperature-compensated magnetic field sensor based on the material thermal-optics effect has been proposed. The proposed structure is easy to fabricate, consisting of only two single-mode optical fibers adhered to a magnetostrictive rod and the Fabry-Perot (FP) cavity filled with polydimethylsiloxane (PDMS). Benefitting from the negative thermal-optics coefficient of PDMS, the temperature cross-sensitivity of the sensor decreased from 351.02pm/°C to 12.59pm/°C, while exhibiting a high magnetic field sensitivity of 160.66pm/mT@38.47-61.52mT. The proposed sensor avoids complex control systems, composite structures, and bulky packaging. This feature effectively compensates for temperature influences during magnetic field detection, making it an ideal candidate for stable magnetic field sensors in practical applications.

Oriented Alginate-Poly(vinyl alcohol) Electrospun Nanofibers for Multimodal Sensing and Gesture Language Recognition.

Flexible nanofiber sensors have gained substantial attention in extending application scenarios owing to their desirable lightweight, comfort, and breathability. Nevertheless, disorder and uneven dimension issues of nanofibers are the leading concerns in their multifunctional response, which often leads to erratic response signals as well as poor linearity. In this work, a high-performance oriented nanofiber film with a three-dimensional network consisting of alginate sodium, poly(vinyl alcohol), and poly(ethylene oxide) was successfully fabricated by a controllable directional electrospinning technique. The main properties of the nanofibers are capable of being regulated intentionally by varying the electrospinning temperature, collector rotation speed, and polymer concentrations. Based on the favorable structure orientation, the nanofiber film displays satisfied biodegradability and high mechanical strength (575.1 MPa). Being integrated with modified magnetic particles, the sensors not only display a fast response speed, high magnetic sensitivity, and exceptional recoverability in response to magnetic fields but also show favorable sensitivities and reliable long-term durability under mechanical excitations. As a wearable sensor, it can accurately perceive the physiological signals generated by the human body in real-time. Furthermore, with the assistance of a convolutional neural network model, a gesture language recognition system is developed by integrating multiple sensors to realize a high recognition accuracy (∼99.08%). This study provides a feasible strategy to manufacture high-performance multimodal sensors for wearable human-machine interaction applications.

Thermally Driven Spin Transport of Epitaxial FeRh Films with a Non-magnetic Pt Layer via the Longitudinal Spin Seebeck Effect.

FeRh has been demonstrated to be an important material for the observation of magnetic phase transitions, such as the first-order transition from an antiferromagnetic (AFM) to a ferromagnetic (FM) state, in response to changes in the temperature. This is because of the magnetic moment induced in Rh atoms above the magnetic phase transition temperature. In the present study, we focus on the longitudinal spin Seebeck effect (LSSE), which involves the generation of spin voltage as a result of a temperature gradient in FM materials or FM insulators, and experimentally assess the effect of the crystalline quality of FeRh films and the properties of the substrate on the LSSE thermopower during the FM-AFM phase transition. The measured LSSE thermopower of an epitaxial (110)-oriented FeRh film grown on an Al2O3 substrate is approximately 60 times higher than that of a polycrystalline FeRh film on a SiO2/Si substrate. This can be explained by the high magnetic sensitivity and superior FM properties of (110)-oriented epitaxial FeRh films. Furthermore, by comparing the transverse thermoelectric voltage for in-plane magnetized (IM) and perpendicularly magnetized (PM) configurations, we quantitively evaluate the contribution of the exclusive anomalous Nernst effect (ANE) to the LSSE signals in the FeRh/Al2O3 structure, finding it to be approximately 15-30% over a temperature range of 75-300 K. LSSE measurements in Pt/FeRh films are thus demonstrated to provide a versatile pathway for the development of thermoelectric power generation applications and other practical spintronics and neuromorphic computing devices.

Vector magnetic field characteristics of magneto-shape effect with high figure of merit based on fiber optic vernier effect

The vector magnetic field structures utilizing magnetic fluid (MF) mainly rely on the magneto-refractive index effect (MRI), which has the low spatial resolution due to the long sensitive length. In this article, the vector magnetic field characteristics of the magneto-shape effect (MSE) are simulated and experimentally studied based on the fiber optic vernier effect. The high vector magnetic field sensitivity can be achieved under the condition of Φ128*73 μm in the sensitive area by combine the MSE and vernier effect. The distribution of magnetic field on the concavity of MF varies with magnetic field direction, giving rising to MF concavity different deformations. The magnetic field observation structure based on fiber optic vernier effect are fabricated to verify the vector magnetic field characteristics of MSE. The observation structure is subjected to one-dimensional and two-dimensional magnetic field. The test results demonstrate that the magnetic field sensibility can reach 2.36 nm/Gs, 3.88 nm/Gs and 4.52 nm/Gs under 0–55.0 Gs, 55.0–91.7 Gs and 91.7–119.2 Gs in Y direction field. The magnetic field sensibility is 0.91 nm/Gs in Z direction field. The magnetic field direction sensitivity can reach 1.16 nm/° in XY dimensional field. The structure of the MSE is very compact and the size is very small, which is very helpful for detecting the narrow space and gradient magnetic field.

High-sensitivity vector magnetic field sensor based on a V-shaped multimode-no-core-multimode fiber structure.

This work proposes and investigates a bent multimode-no-core-multimode optical fiber structure for vector magnetic field sensing applications. The bent no-core fiber (NCF) serves as the sensing area, and the gold film is deposited on its surface to excite the surface plasmon resonance effect. Due to the strong evanescent field of the unclad and bent NCF, the as-fabricated sensor exhibits a high sensitivity of 5630 nm/RIU in the refractive index range of 1.36-1.39. Magnetic fluid is employed as the magneto-sensitive material for magnetic field sensing, exhibiting a high magnetic field intensity sensitivity of 5.74 nm/mT and a high magnetic field direction sensitivity of 0.22 nm/°. The proposed sensor features a simple structure, low cost, point sensing, and excellent mechanical performance.

All-solid highly sensitive fiber-tip magnetic field sensor based on a Fabry-Perot interferometer with a breakpoint structure.

An all-solid fiber-tip Fabry-Perot interferometer (FPI) coated with a nickel film is proposed and experimentally verified for magnetic field sensing with high sensitivity. It is fabricated by splicing a segment of a thin-wall capillary tube to a standard single-mode fiber (SMF), then inserting a tiny segment of fiber with a smaller diameter into the capillary tube, and creating an ultra-narrow air-gap at the SMF end to form an FPI. When the device is exposed to magnetic field, the capillary tube is strained due to the magnetostrictive effect of the nickel film coated on its outer surface. In addition, owing to the unique breakpoint sensitivity-enhancement structure of the air-gap FPI, the elongation of the capillary tube whose length is over 100 times longer than the air-gap width is entirely transferred to the cavity length change of the FPI, and the sensor is extremely sensitive to the magnetic field as proved by our experiments, achieving a high sensitivity of up to 2.236 nm/mT for a linear magnetic field range from 40 to 60 mT, as well as a low-temperature cross-sensitivity of 56µT/°C. The all-solid stable structure, compact size (total length of ∼3.0 mm), and reflective working mode with high magnetic field sensitivity indicate that this sensor has good application prospects.

Very High In‐Plane Magnetic Field Sensitivity in Ion‐Implanted 4H‐SiC PIN Diodes

AbstractIn this study ion‐implanted lateral 4H‐SiC pin diodes are reported, which show an unexpectedly high room temperature in‐plane magnetic field sensitivity approaching 100 % at 0.5 Tesla. Using dedicated TCAD simulations the underlying transduction mechanism is studied, and the effect of implantation‐induced carrier traps on the observed high sensitivity is unraveled. The study shows how such traps can greatly control the injection conditions at the highly doped implant regions providing a plausible explanation for an observed portion in the IV‐characteristics of the pin diodes exhibiting the aforementioned high magnetic field sensitivity.

Stretchable Magneto-Mechanical Configurations with High Magnetic Sensitivity Based on "Gel-Type" Soft Rubber for Intelligent Applications.

"Gel-type" soft and stretchable magneto-mechanical composites made of silicone rubber and iron particles are in focus because of their high magnetic sensitivity, and intelligence perspective. The "intelligence" mentioned here is related to the "smartness" of these magneto-rheological elastomers (MREs) to tune the "mechanical stiffness" and "output voltage" in energy-harvesting applications by switching magnetic fields. Hence, this work develops "gel-type" soft composites based on rubber reinforced with iron particles in a hybrid with piezoelectric fillers such as barium titanate. A further aspect of the work relies on studying the mechanical stability of intelligence and the stretchability of the composites. For example, the stretchability was 105% (control), and higher for 158% (60 per 100 parts of rubber (phr) of barium titanate, BaTiO3), 149% (60 phr of electrolyte iron particles, EIP), and 148% (60 phr of BaTiO3 + EIP hybrid). Then, the magneto-mechanical aspect will be investigated to explore the magnetic sensitivity of these "gel-type" soft composites with a change in mechanical stiffness under a magnetic field. For example, the anisotropic effect was 14.3% (60 phr of EIP), and 4.4% (60 phr of hybrid). Finally, energy harvesting was performed. For example, the isotropic samples exhibit ~20 mV (60 phr of BaTiO3), ~5.4 mV (60 phr of EIP), and ~3.7 mV (60 phr of hybrid). However, the anisotropic samples exhibit ~5.6 mV (60 phr of EIP), and ~8.8 mV (60 phr of hybrid). In the end, the composites prepared have three configurations, namely one with electro-mechanical aspects, another with magnetic sensitivity, and a third with both features. Overall, the experimental outcomes will make fabricated composites useful for different intelligent and stretchable applications.

Soft magnetostrictive materials: Enhanced magnetostriction of Fe‐based nanocrystalline alloys via Ga doping

Soft magnetostrictive materials, having a combination of high soft magnetic properties and substantial magnetostriction, are highly sought for a wide range of applications. Nonetheless, a trade‐off relationship exists between soft magnetic properties and magnetostriction in single‐phase crystalline alloys due to their inherent magnetocrystalline anisotropy. In this study, we introduce the soft magnetostrictive material based on conventional Fe‐based nanocrystalline soft magnetic alloys whose structure quenches magnetocrystalline anisotropy, infused with Ga. All the samples exhibited nanocrystallization behavior and solid‐solution α‐Fe(Ga) was precipitated as a nanocrystalline phase. The net magnetostriction increased with increasing Ga content, concurrently maintaining high magnetic sensitivity with or without Ga addition. As a consequence of this compatibility of properties, the Ga‐doped sample exhibited a magnetostriction susceptibility 1.77 times higher than that of the base alloy. The soft magnetostrictive materials proposed in this study are poised for potential deployment in vibration energy harvesters and strain sensors.

Functional magnetic alginate/gelatin sponge-based flexible sensor with multi-mode response and discrimination detection properties for human motion monitoring

The functional flexible sensors that can simultaneously detect multiple external excitations have exhibited great potential in the human-machine interaction and wearable electronics. However, it is still a primary challenge to develop a multi-mode sensor that can achieve sensitivity equilibrium towards different stimuli, and effectively recognize external stimulus while in a facile and cost-effective material and methodology. This study presented a functional flexible sensor based on natural polymer sodium alginate and gelatin sponge electrode which could detect both external mechanical and magnetic stimuli with superiorities of outstanding sensing capability and stability. With the optimal multilayered structure, it possessed high magnetic responsive sensitivity of 0.45 T−1, excellent stability and recoverability. Its electrical property variations also displayed high sensitivity and durability under cyclic stretching, bending and compressing stimuli for 1000 cycles. More importantly, the sensor could not only respond to magnetic field and compression stimuli with contrary electrical responses, but also recognize the respective input signals to decouple different stimuli in real time. Furthermore, it was developed as electronic skins and smart sensor arrays for human physiological signals and mechanical-magnetic detection. Based on excellent multifunctional response characteristics, the sensor showed significant potential in next-generation intelligent multifunctional electronic system and artificial intelligence.

Design of a highly sensitive cascaded rectangular ring resonator embedded with gold nanorods and gratings for multipurpose application

This study introduces a sensor consisting of a metal-insulator-metal (MIM) structure, having an integration of gold nanorods and gratings, to perform various functions including sensing refractive index, detecting blood components, monitoring temperature, and measuring magnetic fields. The sensor's spectral properties are studied analytically in the MIR region implementing finite element method. Furthermore, the potential in the RI sensing is extensively examined by modulating the geometrical parameters, ultimately establishing a direct relationship with the transmittance profile. Following computational experiments, the best possible configuration exhibits the maximum sensitivity of 6118.685 nm/RIU. This research shows the biosensing applications by the detection of near-infrared and visible blood components such RBC, Hb, WBC, plasma, and water with a high sensitivity of 3185.05 nm/RIU. Moreover, ethanol is employed to evaluate the proffered sensor's temperature sensing feature and a maximum sensitivity 1.18 nm/°C was attained. Furthermore, this sensor can be used for magnetic field detection as it shows a high magnetic field sensitivity of 354.66 pm/Oe. The structural model is simple. Besides, this design has the potential to serve as a substitute for sensors that rely on silver. It is chemically stable and performs well in refractive index measurement, biosensing, temperature sensing and magnetic field detection.

High sensitivity of diamond nitrogen-vacancy magnetometer with magnetic flux concentrators via enhanced fluorescence collection

Diamond nitrogen-vacancy (NV) centers magnetometer is attracting more and more attention due to their room-temperature solid-state property. High sensitivity is crucial for practical applications of diamond NV magnetometers. However, the sensitivity of the diamond magnetometer needs to be improved for weak magnetic measurement. Recent studies have shown that diamond with magnetic flux concentrators (MFC) makes it feasible to achieve low-frequency sensitivity at fT/Hz level. Here, we demonstrate an enhanced fluorescence collection method to improve the sensitivity of diamond NV magnetometer with MFC. A high magnetic field sensitivity of 0.47 pT/Hz (>100Hz) is achieved under resonance conditions, which is about two times higher than that without improved fluorescence collection. We then integrate the diamond magnetometer (probe size ∼8×9×13 cm3) with a shielded sensitivity of 1 pT/Hz (>30Hz). Our method offers a solution for the high-sensitivity diamond NV magnetometer. Thus, this work enables an ultra-compact and scalable platform for quantum sensing based on the diamond NV center technique. Future, diamond NV magnetometers could be proposed used in shipwreck detection, cardiac magnetic field measurement, explosives detection, etc.

Microstructure and magnetic properties of SiO2/FeCoNiSi0.25 core-shell high-entropy alloys with nanotwinned structures

SiO2/FeCoNiSi0.25 core-shell high-entropy alloys (HEAs) containing nanotwinned structures combine good magnetic properties and bending ductility. This study successfully produced them by the combined mechanical alloying and spark plasma sintering method. The crystallization phase of the HEAs was a solid solution phase with a deformed twin face-centered cubic structure instead of a brittle intermetallic phase. In addition, the HEAs exhibited high yield strength (approximately 1365 MPa) and high plastic strain (about 22.5%). The magnetic intensity characteristics of the FeCoNiSi0.25 core-shell HEA significantly outperformed those of SiO2-shell-free HEAs. The improvement in mechanical properties and magnetic sensitivity can be attributed to the materials' strengthening and toughening by nanotwinned structures, while the excellent magnetic properties were due to the regulation of magnetic structure by grain boundaries and nanotwinned structures. These findings are instrumental in preparing HEAs with high magnetic sensitivity and an excellent combination of mechanical properties.

Angular magnetic field dependence of a doubly clamped magnetoelectric resonator

Angular dependence of magnetic field response of fully suspended resonant microelectromechanical double-clamped magnetoelectric beams was investigated as the basis for a vector magnetometer utilizing the magnetically induced change in fundamental resonance frequency. Strain-coupled magnetostrictive iron cobalt (FeCo) and piezoelectric aluminum nitride layers together constitute a magnetoelectric heterostructure with a high magnetic field sensitivity of 70 Hz/mT along the beam axis and a transfer function of 47 V/T at 10 Hz. The fundamental frequency shift to an external magnetic field is found to be strongly anisotropic with a relative variation of more than 3% between perpendicular and parallel field orientations with respect to the long axis of the beam at a field of 100 mT. This design can form the basis for an on-chip high sensitivity vector magnetometer operating with ultra-low power when multiplexed with two or more resonators.

Numerical Study of SQUID Array Responses Due to Asymmetric Junction Parameters

Superconducting quantum interference device arrays have been extensively studied for their high magnetic field sensitivity. The performance of these devices strongly depends on the characteristic parameters of their Josephson junctions, i.e. their critical currents and shunt resistances. Using a resistively shunted junction model and including thermal noise, we perform a numerical investigation of the effects of asymmetric Josephson junctions by independently studying variations in the critical currents and junction resistances. We compare the voltage response of a dc-SQUID with a 1D parallel SQUID array and study the maximum transfer function dependence on the number of junctions in parallel, the screening parameter and thermal noise strength. Our results show that the maximum transfer function and linearity increase with the number of junctions in parallel for arrays with different junction resistances, in contrast to SQUID arrays with identical junctions or with spreads in the critical currents.

A high magnetic field sensitivity PCF‐SPR sensor working in the near‐infrared wavelength band

AbstractA novel form of photonic crystal fiber (PCF) magnetic field sensor, utilizing surface plasmon resonance, has been developed and investigated. By depositing a layer of gold onto the interior surface of the left‐sided air hole and introducing magnetic fluid into the aperture to detect magnetic field changes, the plasma resonance effect was ingeniously combined with a dual‐core PCF to achieve magnetic field measurement. The displacement of the loss peak in the output spectrum was observed to gain insights into the magnetic field changes. By means of modulations in the thickness of the gold film, and the spacing and size of the air holes, the optimal parameters for the sensor were obtained. The optimized sensor exhibited a maximum magnetic field sensitivity of up to 6.23 nm/Oe, and the magnetic field detection resolution was approximately 10 μT, enabling precise detection of weak magnetic fields. This fiber sensor boasts a simple structure, ease of production, high sensitivity, and robust environmental adaptability, making it an attractive option for implementation.

Fabrication and Soft Magnetic Properties of Fe–Si–Cr Composites with Double-Insulating Layers Suitable for High-Frequency Power Applications

Soft magnetic composites (SMCs) are composed of alloy materials with the core and insulating layers as the shell. These composites exhibit high saturation magnetic sensitivity and low hysteresis loss, making them a promising material for various applications. The investigation of double layers is considered valuable as it can effectively address the issues of low resistivity and high dynamic loss that arise from non-uniform insulating layers in SMCs. In this study, Fe-Si-Cr/SiO2 particles with a core–shell heterostructure were produced via chemical vapor deposition (CVD). The Fe-Si-Cr/SiO2 materials were coated with different weight percentages (1–6%) of sodium silicate (SS). Subsequently, Fe-Si-Cr-based SMCs were synthesized through high-pressure molding and heat treatment. The effect of the SS weight percentage on microscopic changes and magnetic characteristics was investigated. These findings indicated that a concentration of 4 wt% of SS was the most effective at enhancing magnetic characteristics. The resultant SMCs exhibited high resistivity (21.07 mΩ·cm), the lowest total loss (P10 mt/300 kHz of 44.23 W/kg), a relatively high saturation magnetization (181.8 emu/g), and permeability (35.9). Furthermore, it was observed that the permeability exhibited stabilization at lower frequencies. According to these findings, the combination of CVD and double layers could lead to the further development of SMCs in a variety of applications.

Four-Dimensional Printing of a Fiber-Tip Multimaterial Microcantilever as a Magnetic Field Sensor

“Lab on Fiber” technology integrates different micro- and nanoscale structures or materials onto optical fibers to create additional functionality. With the advanced femtosecond (Fs) laser-induced two-photon polymerization (TPP) technology, polymer microstructures printed on a fiber tip have great potential as micro-optical sensors. However, additional functionalization is usually required, which is costly and complex. Based on the advanced four-dimensional (4D) printing theory, for the first time, a successive multimaterial on-fiber TPP strategy is proposed here, and a fiber-tip polymer microcantilever-based magnetic sensor is prepared in one step. First, the cantilever and the supporting base on the fiber tip are printed by TPP, and then the magnetically responsive cube on the cantilever tip is printed with a self-made magnetic fluid photoresist. The whole process is completed in one step without additional treatment. The prepared sensor shows a minuscule size and a high magnetic sensitivity of 119 pm mT–1 in the range of 0–90 mT, suitable for weak or microspace magnetic field measurement at high spatial resolution. Especially, the proposed 4D successive on-fiber TPP strategy can be extended to other stimulus-responsive materials, providing new guidance for manufacturing various stimulus-responsive microsensors and microactuators on the fiber tip.

Fiber Optic All-Polarization Weak Magnetic Field Sensor Based on Sagnac Interferometer

A novel fiber-optic magnetic field sensor, based on a Sagnac structure, is proposed with the approach of polarization interference detection. The sensor takes advantage of common path interference, combining with a high magnetic field sensitivity sensing unit, composed of magneto-optical crystal, and magnetic field concentrators, to achieve high resolution, high stability, and large dynamic measurement of DC magnetic field signals. In this paper, the theoretical model is established and the related theory is derived in detail. The key technologies in the system are thoroughly investigated and verified. Experimental research on the proposed system is demonstrated and the results show that a DC magnetic field resolution of 5.6 nT and a dynamic range of larger than 70 dB is achieved. Furthermore, the linearity of the system is greater than 99.8% and the instability is less than 0.5%.