Sensitive Magnetic Sensor Research Articles

Drone-Borne Magnetic Gradiometry in Archaeological Applications.

The use of magnetometers arranged in a gradiometer configuration offers a practical and widely used solution, particularly in archaeological applications where the sources of interest are generally shallow. Since magnetic anomalies due to archaeological remains often have low amplitudes, highly sensitive magnetic sensors are kept very close to the ground to reveal buried structures. However, the deployment of Unmanned Aerial Vehicles (UAVs) is increasingly becoming a reliable and valuable tool for the acquisition of magnetic data, providing uniform coverage of large areas and access to even very steep terrain, saving time and reducing risks. However, the application of a vertical gradiometer for drone-borne measurements is still challenging due to the instability of the system drone magnetometer in flight and noise issues due to the magnetic interference of the mobile platform or related to the oscillation of the suspended sensors. We present the implementation of a magnetic vertical gradiometer UAV system and its use in an archaeological area of Southern Italy. To reduce the magnetic and electromagnetic noise caused by the aircraft, the magnetometer was suspended 3m below the drone using ropes. A Continuous Wavelet Transform analysis of data collected in controlled tests confirmed that several characteristic power spectrum peaks occur at frequencies compatible with the magnetometer oscillations. This noise was then eliminated with a properly designed low-pass filter. The resulting drone-borne vertical gradient data compare very well with ground-based magnetic measurements collected in the same area and taken as a control dataset.

High Sensitivity Magnetic Field Sensor Based on Magneto-Optical Surface Plasmon Resonance

High Sensitivity Magnetic Field Sensor Based on Magneto-Optical Surface Plasmon Resonance

Highly Sensitive Magnetic Field Sensor Based on Few-Mode Fiber Interferometry

Highly Sensitive Magnetic Field Sensor Based on Few-Mode Fiber Interferometry

Fabrication of half-metallic Co2FeAlxSi1–x thin film with small magneto-crystalline anisotropy constant K1

A tunnel magnetoresistance (TMR) sensor is a highly sensitive magnetic sensor workable at room temperature. To achieve smaller magnetic field detection, both a high TMR ratio and small magnetic anisotropy of the free layer are required. In this study, we developed single crystalline Co-based Heusler alloy Co2FeAlxSi1-x films as the free layer of TMR sensors and systematically investigated their crystalline and magnetic properties. The magnetic tunnel junction (MTJ) with these alloys is a promising device for highly sensitive TMR sensors due to their half-metallicity. We evaluated the B2 and L21 ordering parameters SB2 and SL21. SB2 was above 80 % for all the samples and SL21 was 48 % at a maximum, which indicates that all the samples exhibit half-metallicity. In addition, we evaluated their first magneto-crystalline anisotropy constant K1 from magnetization curves. K1 changed from positive to negative as Al component x increases and K1 was about 1200 erg/cc at x = 0.33. These results indicate that Co2FeAlxSi1-x films around x = 0.33 have a good candidate for the free layer of TMR sensors because of their half-metallicity and small magnetic anisotropy.

Magnetization switching by electric field in ZnFe2O4/ZnO heterostructure

We have fabricated the ZnFe2O4/ZnO (ZFO/ZnO) heterostructure on a silicon substrate by pulsed laser deposition technique and studied the magnetization switching by the electric field in the ZFO/ZnO heterostructure using an indigenously developed optical cantilever beam magnetometer setup. The magnetization (M) vs electric field (E) curve reveals that the magnetization of the ZFO film has been switched by an electric field applied along the thickness of the ZnO film. The saturation magnetization is found to be 28.77 MA/m from the M–E curve. The emergence of electric field-driven magnetization switching in the ZFO/ZnO heterostructure is attributed to the strain-mediated magnetoelectric coupling between the electric polarization of the ZnO film and the magnetization of the ZFO film as evidenced by the butterfly-type hysteresis behavior of magnetization with the applied electric field. However, the realization of electric field-controlled magnetization switching in the ZFO/ZnO heterostructure is regarded as a potential aspect for the fabrication of energy-efficient spintronic devices such as magnetoelectric random access memory cells, highly sensitive magnetic field sensors, magneto-logic devices, and neuromorphic devices.

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.

Magnetic Flux Sensor Based on Spiking Neurons with Josephson Junctions.

Josephson junctions (JJs) are superconductor-based devices used to build highly sensitive magnetic flux sensors called superconducting quantum interference devices (SQUIDs). These sensors may vary in design, being the radio frequency (RF) SQUID, direct current (DC) SQUID, and hybrid, such as D-SQUID. In addition, recently many of JJ's applications were found in spiking models of neurons exhibiting nearly biological behavior. In this study, we propose and investigate a new circuit model of a sensory neuron based on DC SQUID as part of the circuit. The dependence of the dynamics of the designed model on the external magnetic flux is demonstrated. The design of the circuit and derivation of the corresponding differential equations that describe the dynamics of the system are given. Numerical simulation is used for experimental evaluation. The experimental results confirm the applicability and good performance of the proposed magnetic-flux-sensitive neuron concept: the considered device can encode the magnetic flux in the form of neuronal dynamics with the linear section. Furthermore, some complex behavior was discovered in the model, namely the intermittent chaotic spiking and plateau bursting. The proposed design can be efficiently applied to developing the interfaces between circuitry and spiking neural networks. However, it should be noted that the proposed neuron design shares the main limitation of all the superconductor-based technologies, i.e., the need for a cryogenic and shielding system.

Highly sensitive surface acoustic wave magnetic field sensor based on the loss mechanism

Currently, the surface acoustic wave (SAW) magnetic field sensing technique utilises the SAW velocity/frequency mechanism of magnetoacoustic interaction as an indicator of the magnetic sensitivity mechanism. However, this method has low sensitivity and poor stability. To address this problem, a dynamic magnetoelastic coupling theoretical model is constructed to theoretically simulate the influence of the ΔE effect of magnetically sensitive thin films on SAW propagation attenuation. This study describes a high-sensitivity SAW magnetic field sensing mechanism based on magnetoacoustic attenuation. The simulation results show a clear relationship between the acoustic propagation loss and external magnetic field, indicating a structure-property relationship. An amorphous soft magnetic material (Fe90Co10)78Si12B10 was used as a magnetically sensitive thin film due to its high permeability, low coercivity (Hc), low hysteresis, ease of magnetisation and demagnetisation. SAW magnetosensitive device operating on a frequency of 200 MHz has been experimentally developed using a standard semiconductor photolithography process. A SiO2 layer was deposited on a 36° YX-LiTaO3 substrate as a waveguide, and a (Fe90Co10)78Si12B10 layer was on the top of the propagation area as a magnetosensitive film. The experimental results showed that the acoustic loss change due to the magnetic field variation was 4.63 dB within a magnetic field range of 0 Oe to ±10 Oe, which agreed with the theoretical results. The sensor had a sensitivity of 0.7546 dB Oe−1 within the range of 0–4 Oe and the lower detection limit of magnetic fields was 0.272 Oe, low hysteresis error of 0.54%, multiple repeatability error of 0.13%, excellent repeatability and stability were achieved in the experiments from the developed sensing device.

Highly sensitive magnetic field sensor using magnetic fluid filled dual-core photonic crystal fiber

A high sensitivity fiber optic magnetic field sensor that utilizes a dual-core photonic crystal fiber (DC-PCF) filled with magnetic fluid (MF) has been proposed and validated to simultaneously detect magnetic field intensity and temperature. DC-PCF is a multimode fiber that supports various modes of light transmission and induces intermodal interference within fiber core. The numerical analysis of the mode characteristics of DC-PCF is conducted. The sensing structure relies on the use of a DC-PCF with air holes filled with a suitable material, such as MF substance. The analysis of the working principle of the DC-PCF for sensing and measurement is conducted by considering its structural characteristics and mode characteristics. The effective refractive index (ERI) of MF is affected by external magnetic field intensity and temperature. To extract the effective frequency points, the fast Fourier transform (FFT) method can be employed. Additionally, the inverse fast Fourier transform (IFFT) method can be utilized to determine the magnetic field sensitivity, which can reach up to 1.562 nm/mT. Furthermore, the temperature sensitivity can be as high as −1.043 nm/°C. The sensor demonstrates excellent repeatability and showcases low detection limits of 0.0128 mT and 0.0192 °C, respectively. Additionally, the proposed sensor exhibits substantial potential for further development in the field of high sensitivity magnetic field detection applications.

A development of high sensitivity magnetic sensor based on giant magnetoresistance with simple implementation on smartphone

In this paper, the magnetic field-based sensor that can connect with smartphones through Bluetooth connectivity was developed. The design of this high sensitivity magnetic sensor system used Giant Magnetoresistance (GMR) sensors in the form of SOIC8 with AA002-02 series from NVE Corp. The results obtained from the measurements show that the sensor is able to work well when connected to an Android-based smartphone. Measurements were carried out by placing a magnet with a magnetic field strength of 0.4 T in the direction of the sensitivity plane of the GMR sensor. The result showed that the closer the magnet distance relative to the GMR sensor the more voltage signal output from the sensor. Since this developed method is simple but effective for detecting position of magnetic object, the further development of this method will be benefit for many applications.

High-sensitivity and directional-identification fiber magnetic field sensor via polarimetric fiber ring laser with a fiber Faraday rotator

A highly sensitive fiber magnetic field sensor with directional identification utilizing multi-longitudinal-mode fiber ring laser (FRL) based on polarization-mode beat frequency (PMBF) is experimentally demonstrated. A bismuth-doped iron garnet (BIG), as a kind of fiber Faraday rotator, is embedded in the FRL and serves as a fiber magnetic field probe, whose birefringence shows strong dependence on the external magnetic field due to magneto-optical Faraday effect, leading to the frequency drift of PMBF. Thus, the external magnetic field can be characterized by monitoring the change in a certain PMBF. Additionally, the drift direction of the tracked PMBF is closely related to the applied magnetic field direction, which is attributed to the non-reciprocity of Faraday magneto-optical rotation. Therefore, it shows the good ability to distinguish the applied forward (positive) and reverse (negative) magnetic field. The experimental results reveal that the tracked PMBF signal near 100 MHz has opposite frequency drift signs in the forward (positive) range of 0–20 mT and reverse (negative) range of 0 - −20 mT, which can be used to identify the axial orientation of the applied magnetic field. Additionally, it shows the maximum magnetic field sensitivities of −100.76 and −105.73 kHz/mT in the positive and negative magnetic field ranges, respectively. The designed device makes full use of the advantages of the fiber laser that rapidly demodulates the magnetic field with the help of high-speed digital processing technology, as well as fast response, high integration and low cost of fiber Faraday rotator, offering potentials in high-sensitivity magnetic field measurement in a confined space.

Highly Sensitive Magnetic Field Sensors Based on a D-Type Fiber With Bi₂O₂ Se Film

Highly Sensitive Magnetic Field Sensors Based on a D-Type Fiber With Bi₂O₂ Se Film

Nitrogen concentration control during diamond growth for NV- centre formation.

Negatively charged nitrogen-vacancy (NV-) centres formed in diamond crystals are point defects that have potential applications in various quantum devices such as highly sensitive magnetic sensors. To improve the sensitivity of magnetic sensors using NV- centres, it is essential to precisely control the nitrogen concentration in the crystals. In this paper, we demonstrated that nitrogen concentration in diamond can be controlled with high precision for the following two representative growth methods. One is the high-pressure/high-temperature (HPHT) synthesis method and the other isthe chemical vapour deposition (CVD) method. The nitrogen concentration of HPHT-grown diamond decreased semi-logarithmically with increasing contents of titanium or aluminium as nitrogen getter materials. The nitrogen concentration of CVD-grown diamond increased linearly with increasing the flow rate ratio of nitrogen to carbon. NV- centres were formed by controlling the total fluence of electron beams so that approximately 20% of the nitrogen became NV- centres. The coherence time of electron spin of NV- centres obtained by the Hahn-echo pulse sequence T2 of these diamond crystals was inversely proportional to the nitrogen concentration. A comparison of T2 of the NV- centres for HPHT-synthesized and CVD-grown diamonds showed no significant difference between them. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'.

Highly sensitive magnetic field sensors based on Fe2O3 nanorods grown on the surface of a tapered few mode fiber.

A magnetic field (MF) sensor with a stable structure and high sensitivity has been proposed and experimentally verified. We used the water bath method to produce a layer of Fe2O3 nanorods on a tapered few mode fiber (FMF) surface to form a Mach-Zehnder interferometer (MZI). The experiment found that the nanostructure produced on the surface of FMF were particularly stable and firm. Under the action of an external MF, the magnetic permeability of a Fe2O3 nanorod will change, leading to a change in its refractive index, resulting in a linear shift in the resonance wavelength of MZI. The experimental results showed that the MF sensitivity of MZI reached -0.5348 nm/mT in 10 mT∼80 mT. In addition, MZI has a certain sensitivity to environmental humidity and temperature. A long-period fiber grating and a fiber Bragg grating are cascaded with MZI to achieve a simultaneous measurement of three quantities and eliminate their cross-sensitivity.

Magnetic field tunable piezoelectric resonator for MEMS applications

In this report, the Ni0.50Mn0.35In0.15/Pb0.96La0.04Zr0.52Ti0.48O3 (Ni-Mn-In/PLZT) bulk acoustic wave (BAW) resonator has been fabricated using the sputtering deposition technique. The magnetoelectric effect in the Ni-Mn-In/PLZT resonator has been investigated. The increase in magnetoelectric coupling coefficient (MECC) with the increment in the frequency of applied HAC is observed. The potential of the Ni-Mn-In/PLZT BAW resonator as a magnetic sensor is tested by measuring the shift in the resonant frequency of the reflective (S11 parameter) response in the presence of the externally applied magnetic field. The Ni-Mn-In/PLZT resonator exhibits a frequency shift of 730 MHz in the 1200 Oe magnetic field, among the largest magnetic field-induced frequency shifts in literature. The rarely reported complete dependence of acoustic velocity, coupling coefficients, magnetic sensitivity, and frequency peak shift on the strength of the external magnetic field is investigated. The acoustic velocity increases from 1237 m/s to 1394 m/s, and the electromechanical coupling coefficient increases from 0.0199 % to 0.0206 % after applying the 1200 Oe magnetic field. The reflective responses have been fitted using the Modified-Butterworth Van Dyke (MBVD) model in terms of hardly reported RLC equivalent circuits. The experimental results and extracted parameters from MBVD modeling exhibit high accuracy. This interaction between multiferroic orders and elastic resonance peaks opens a new window for highly sensitive future magnetic field sensors, wireless communication devices, and magnetic field tunable filters.

A convenient and robust design for diamond-based scanning probe microscopes.

Nitrogen-vacancy centers in diamond have been developed as a sensitive magnetic sensor and broadly applied on condensed matter physics. We present a design of a scanning probe microscope based on a nitrogen-vacancy center that can operate under various experimental conditions, including a broad temperature range (20-500K) and a high-vacuum condition (1 × 10-7 mbar). The design of a compact and robust scanning head and vacuum chamber system is presented, which ensures system stability while enabling the convenience of equipment operations. By showcasing the temperature control performance and presenting confocal images of a single-layer graphene and a diamond probe, along with images of a ferromagnetic strip and an epitaxial BiFeO3 film on the SrTiO3 substrate, we demonstrate the reliability of the instrument. Our study proposes a method and a corresponding design for this microscope that extends its potential applications in nanomagnetism and spintronics.

Highly sensitive magnetic field sensor based on uniform core fiber using Mn doped ZnO nanorods as cladding

Highly sensitive magnetic field sensor based on uniform core fiber using Mn doped ZnO nanorods as cladding

Realization of Different Anisotropy Direction for Each Thin-Film Magnetoimpedance Element on the Same Substrate

In this study, we have attempted to realize different magnetic anisotropy locally on the same substrate, i.e., different directions of the easy axis in each area by combining simple Joule heating and the application of a magnetic field with permanent magnets. Orthogonal arranged thin-film magnetoimpedance elements were fabricated on the same substrate, and the easy axis was successfully induced parallel to the width direction of each element, respectively. Each element shows the double-peak impedance profiles after Joule heating which is important to obtain higher sensitive magnetic field sensor. The results enable local anisotropy control, which has been difficult to realize previously, and contribute to the integration of multifunctional thin-film magnetic devices on a substrate.

Electrical conductivity of (Ni,Mn,Fe,Cu)3O4 ceramic semiconductors designed for temperature and magnetic field sensing

This research is focused on designing new ceramic oxides with the spinel structure for a potential application as sensitive temperature and magnetic field sensors. In this respect, the mixtures of ferrimagnetic NiFe2O4 with low-resistive Ni0.66Cu0.41Mn1.93O4 semiconductor (molar coefficient α=1/5 and 1/2) were prepared using the chemical co-precipitation technique followed by a low-temperature sintering of the cold-pressed powders. For the prepared materials, a variation of the electrical conductivity σdc with temperature T (in the range 50 K–400 K) is quantitatively analyzed using different theoretical concepts of the charge carrier hopping transport occurring in disordered materials with strong electron-phonon interaction. It has been shown that an increase in α from 0 to 1/2 causes a step-like change of the dc electrical conductivity and, simultaneously, a gradual change in the magnetization M determined in the saturation state. The temperature coefficient of resistance TCR of the prepared ceramics takes the values from −0.6%/K (at 400 K) to −19.6%/K (below 100 K). The highest absolute value of the magneto-resistance coefficient MR determined at 150 K (and at magnetic field 7 T) registered for ceramic oxide with α=1/2 was found to be 3.4%.

Highly sensitive refractive index and magnetic field sensor based on long-period fiber grating inscribed in tapered optical fiber

A refractive index (RI) and magnetic field sensor based on tapered long period fiber grating (LPFG) is proposed. We prepared two different periods of LPFGs (LPFG1 and LPFG2) using high-frequency CO2 laser point by point method on tapered single-mode fiber. Firstly, LPFG1 is used to measure the RI of sodium chloride solution. LPFG1 is immersed in sodium chloride solutions with different RI to measure the sensitivity of LPFG to RI. The experimental results indicate that LPFG1 is particularly sensitive to changes in environmental RI, with a sensitivity of 381.820 nm/RIU. Due to the special sensitivity of tapered LPFG to environmental RI, in order to eliminate the influence of residual sodium chloride on the surface of LPFG1 on magnetic field measurement, we use LPFG2 with similar parameters to measure the environmental magnetic field. LPFG2 was encapsulated in a glass capillary tube filled with the magnetic fluid (MF). After the environmental magnetic field changed, the RI of MF changed, causing the resonance peak wavelength of LPFG2 to drift. We measured the magnetic field using LPFG2 within the magnetic field range of 0.66 mT to 20 mT. Only in the magnetic field range of 1.95 mT to 4.6 mT, good linear fitting was achieved, with a magnetic field sensitivity of 1.242 nm/mT and a fitting coefficient of 0.9852. The experimental results indicate that LPFG inscribed in tapered optical fiber has high sensitivity to environmental RI and magnetic field. The sensor has a simple structure, small volume, easy production, and high sensitivity, which has certain practical application prospects.