Sensitive Magnetic Sensor Research Articles

Highly sensitive handheld diamond magnetic field sensor allows for bio-diagnostics

A new compact device shows promise for field testing nanotesla scale magnetic fields in biological samples and mechanical systems.

Highly sensitive magnetic field sensor based on a metglas/bidomain lithium niobate composite shaped in form of a tuning fork

This study reports the creation of a highly sensitive, low-frequency magnetic field sensor based on a composite multiferroic consisting of a bidomain lithium niobate/metglas laminate shaped in form of a tuning fork. An efficient suppression of acoustic and thermal noises in the measurements of AC magnetic fields has been achieved. As a piezoelectric component we used a y + 128°-cut lithium niobate single crystal. A metglas foil (serving as a magnetostrictive component) was antisymmetrically bonded to each tine of the tuning fork. The sensor demonstrated a 6.7 times increase of the sensitivity to magnetic fields as compared to a single-plate magnetoelectric (ME) sensor: the magnetic field detection limit was enhanced from 20 pT to 3 pT at a frequency of ca. 318 Hz, without any additional shielding from external noises. The advantages of the ME sensors based on bidomain lithium niobate over those based on PZT or PMN-PT are a much higher thermal stability, anhysteretic piezoelectric effect, large resistance to creep, lead-free nature and simple and cheap fabrication process. Ultimately, the tuning-fork ME sensors based on bidomain lithium niobate single crystals might be used in low frequency, ultra-sensitive, cheap and high-temperature magnetic field sensors for biomedical or space applications.

Hybrid Magnetic Sensor Combined With a Tunnel Magnetoresistive Sensor and High-Temperature Superconducting Magnetic-Field-Focusing Plates

Magnetoresistive (MR) sensors are widely used, particularly in consumer products. However, in applications requiring extremely sensitive magnetic sensors, superconducting quantum interference devices (SQUIDs) are primarily used. In this study, we develop a hybrid magnetic sensor by combining an MR sensor with two high-temperature superconducting (HTS) plates to achieve sensitivity that lies between those of MR sensors and SQUIDs. In addition, we apply a modulation method for measuring the absolute magnetic field. A nanogranular in-gap tunnel MR sensor is installed inside the slit between the magnetic-field-focusing HTS plates, and the magnetic response is evaluated. Using the magnetic-field-focusing characteristics of the HTS plates (made from YBa2Cu3O7‐δ) and the MR sensor inside the slit between the two plates, the sensitivity and noise characteristics are improved. Adjustment of parameters, such as MR sensor height from the slit, slit width of the HTS plates, and plate size allow sensitivity control depending on the application. Moreover, the absolute magnetic response and low noise in low-frequency regions are obtained through ac modulation.

Demonstration of vector magnetic field sensing by simultaneous control of nitrogen-vacancy centers in diamond using multi-frequency microwave pulses

An ensemble of nitrogen-vacancy (NV) centers in diamond is a fascinating candidate for realizing a sensitive magnetic field sensor. In particular, since the axes of the NV centers are distributed along four directions, a collection of measurement data from NV centers with different axes provides information on the vector components of a magnetic field. However, in the conventional approach, the low measurement contrast of NV centers limits the sensitivity of vector magnetic field sensing. Recently, to overcome this problem, multi-frequency control of the NV centers has been proposed. The key idea is that four types of NV centers with different axes are simultaneously controlled by multi-frequency microwave pulses. Here, we demonstrate vector magnetic field sensing with an ensemble of NV centers in diamond via such multi-frequency control with pulsed-type measurements. We use Hahn echo pulses and extract information on the vector components of an applied AC magnetic field. We find that the sensitivity of the vector field sensing with multi-frequency control is better than that with single-frequency control for every vector component of a magnetic field.

Increasing the electrochemical system performance using a magnetic nanostructured sensor for simultaneous determination ofl-tyrosine and epinephrine

Designing a sensitive magnetic nanostructured sensor for simultaneous determination ofl-tyrosine and epinephrine.

Design and fabrication of low-noise superconducting quantum interference device magnetometer

Superconducting quantum interference device (SQUID) is the most sensitive magnetic flux sensor known, which is widely used in biomagnetism, low-field nuclear magnetic resonance, geophysics, etc. In this paper, we introduce a high-sensitivity SQUID magnetometer, which consists of an SQUID and a flux transformer. The SQUID is first-order gradiometer configuration, which is insensitive to interference noise. The flux transformer includes a multi-turn spiral input coil and a large-sized pickup coil. And the input coil is inductively coupled to the SQUID through mutual inductance. We present an SQUID magnetometer fabricated with Nb/Al-AlO<i><sub>x</sub></i>/Nb Josephson junction technology on a 4-inch silicon wafer at our superconducting electronics facilities. We develop a fabrication process based on selective niobium etching process consisting of five mask levels. In the first two mask levels, the trilayer is patterned by a dry etch to define base electrode, contact pads, and interconnects. The shunt resistor and a dielectric insulating layer are then deposited and patterned by using lift-off and dry etchant, respectively. Finally, the niobium wiring layer is deposited and patterned by using reactive ion etching to define input, pickup and feedback coils. The measurement of the SQUID magnetometer is performed inside a magnetically shielded room. The operating temperature is realized by immersing the SQUID into the liquid helium (4.2 K). Moreover, a superconducting niobium tube is employed to protect the SQUID from being disturbed by external environments. A homemade readout electronics instrument with low input voltage noise is used to characterize the SQUID magnetometer. The results of low-temperature measurements indicate that the magnetometer has a magnetic field sensitivity of 0.36 nT/Φ<sub>0</sub> and a white flux noise of 8 μΦ<sub>0</sub>/√Hz,corresponding to a white field noise of 2.88 fT/√Hz. This kind of SQUID magnetometer is suitable for multi-channel systems, e.g., magnetocardiography, magnetoencephalography, etc. Although the SQUID process development benefits from the rapid advance of semiconductor process technology, the uniformity of the SQUID on one wafer is fluctuated due to the film deposition. Now, we have realized a best SQUID yield of 50% on a 4-inch wafer. In the future, the SQUID chip yield should be improved by well controlling the optimizing process. The device yield is expected to reach as high as 80%.

Impedance Change Ratio and Sensitivity of Micromachined Single-Layer Thin Film Magneto-Impedance Sensor

Thin-film techniques are important in the miniaturization of electronic devices. We studied a thin-film magneto-impedance element made with Co-based amorphous soft magnetic material and developed a highly sensitive magnetic field sensor with high spatial resolution. Thin films are several micrometers thick, and show significant impedance changes as frequencies change from the megahertz to the gigahertz region. Multilayer systems are often used to achieve a large impedance change, but they typically require a complex thin-film structure and a length of several millimeters. Our thin-film sensors have lengths between 30 µm and 1 mm in a simple monolayer configuration and successfully overcome the demagnetizing field. The impedance change ratio was 300% for a 1 mm long element at 1 GHz and between 20–30% at 1 GHz for a miniaturized element of 30 µm. The sensors had a maximum sensitivity of 33.4%/Oe.

First-principles prediction of ultralow resistance-area product and high magnetoresistance ratio in magnetic tunnel junction with a rock-salt type ZnO barrier

A magnetic tunnel junction (MTJ) is a highly sensitive magnetic sensor which is widely used as a read head of a hard disk drive (HDD). In order to increase the areal density of HDDs, it is necessary to reduce the resistance-area product of the MTJ with keeping the high magnetoresistance ratio. Using the first principles calculations, we show that the rock-salt type ZnO (RS-ZnO) based MTJ satisfies these requirements. The results show that the Fe/RS-ZnO/Fe MTJ is a promising candidate for a read head of an ultra-high density HDD with the recording density of 5 Tbit/in2.

Analysis of the electrical, magnetic and structural properties of A3B6 type layered semiconductor crystals intercalated with metals with reference to their military applications

Magnetic sensors are key elements in many security and military systems. Magnetic sensors are often used for military applications such as navigation, position tracking and antitheft systems. Nowadays sensitive magnetic sensors are used in many technical systems, including modern anti-tank missiles to identify the center of the target area and a minimal armor region.The applications of magnetoresistive structures based on semiconductor crystals of InSe for high precision measurement of the magnetic field are outlined in this article. Possibilities of using magnetic field sensors based on InSe structures for revealing the armour military vehicles are discussed. The impact of metal impurities on the layered structure of the semiconductor material as referred to the strong covalent bond within the layers as well as the weak van-der-Waals bond in the interlayer space is studied. Nyquist diagrams for InSe crystal with the impurities of nickel at different temperatures ranging from liquid nitrogen to room temperature are analyzed. Temperature is shown to be a significant factor for affecting the Nyquist diagrams. The curvature of the Nyquist diagrams for intercalated InSe varies with the temperature as opposed to the pure InSe. Topological images of crystal surface obtained by using atomic force microscopy confirmed the layer structure of nickel-intercalated InSe. Structures with alternating layers of semiconductor and metal provide the fundamental control of magnetic properties. These structures have a sharp anisotropy of magnetic susceptibility. The investigated semiconductor crystals with impurities of 3d-elements can extend the functionality of modern magnetic sensors designed to detect heavy armor.

Defect-induced, temperature-independent, tunable magnetoresistance of partially fluorinated graphene foam

The magnetoresistance (MR) of graphene is fixed under a particular magnetic field and temperature but can be further improved or controlled by introducing artificial defect states. These artificial defects can be introduced via fluorination, which is a conventional method to control the magnitude of the MR required for magnetoelectronic applications. One of the main benefits of fluorination is the defluorination, which occurs within a few days. Herein, tunable and temperature-independent magnetotransport of graphene foam (GF) is achieved using a controlled fluorination process. The magnitude of the MR decreases with the increasing fluorination time (i.e., 30, 60 and 90 min), indicating that defect-induced scattering plays a major role in the magnetotransport properties of fluorinated GF (FGF). The magnitude of the MR in the FGF specimens at room temperature (under a magnetic field strength of 5 T) was observed for three months; a particular value of the MR (FGF-30–59%, FGF-60–58%, FGF-90–37%) is observed that is higher in magnitude than that on the first day of fluorination. In this way, fluorination of GF can provide a pathway to tune the magnetotransport properties, which is very useful for magnetoelectronics devices, especially highly sensitive magnetic sensors.

Magnetoelectric magnetic field sensors

Abstract

Microstructure, magnetic properties and the giant magnetoimpedance effect of amorphous CoSiB thin films deposited by different preparation methods

Controlling the film thickness and soft magnetic properties are the two key factors for giant magnetoimpedance effect (GMI). In this paper, we reported that the ion beam assisted deposition (IBAD) is useful for preparing the GMI materials thin films. The CoSiB thin films with a thickness of a few micron prepared by IBAD shows a very superior ability to combine with the substrate compared with DC and RF sputtering method. Meanwhile, the thick CoSiB thin film by IBAD method also exhibits a good soft magnetic property, but the grown CoSiB films by RF sputtering showed thickness-driven spin orientation behavior in thick CoSiB films leading to the deterioration of its soft magnetic properties. Thus, a Ti layer was introduced to eliminate thickness-driven magnetic behavior in thick FeNi films and thereby preserve their magnetic softness. Furthermore, we found that the GMI effect of CoSiB films prepared by IBAD is stronger than that of magnetron sputtering. Especially, an excellent GMI phase effect in a low frequency range was observed in the CoSiB film prepared by IBAD, which was beneficial for high sensitive magnetic sensor design. In the end, x-ray diffraction and x-ray photoelectron spectroscopy analyses suggest that all the thin films prepared by the sputtering or IBAD method show the metallic glasses structure, thus the origin of the difference in magnetism is may be due to their different short-order structure.

A Highly Sensitive Magnetic Field Sensor Based on a Tapered Microfiber

A compact all-fiber magnetic field sensor based on the combination of a magnetic fluid and a nonadiabatic microfiber is experimentally demonstrated. By using a fusion splicer combined with an additional flame brushing, the nonadiabatic microfiber, with an abrupt taper, a small waist diameter and a long region, provides a strong evanescent field and a long sensitive distance. The result indicates that a sensitivity as high as 309.3 pm/Oe can be achieved in the range from 0 to 200 Oe. The designed nonadiabatic microfiber sensing structure suggests potential application as a tunable all-in-fiber photonic and other newly fashioned magneto-optical photonic devices.

Magnetometric resistivity: a new approach and its application to the detection of preferential flow paths in mine waste rock dumps

The injection of a low frequency electrical current in the ground between two electrodes A and B generates a magnetic field that can be measured at the ground surface with sensitive magnetic sensors. The map of the magnetic field, measured at the frequency of the injected current, can be used to determine the paths of the current through the ground. When the current is channelled along preferential conductive paths, the MagnetoMetric Resistivity (MMR) method can be used to detect these paths. Conductive current paths can be associated with preferential flow paths of groundwater when the two electrodes A and B are in the direction of the flow and when the flow path is highly electrically conductive with respect to the background. We first review the background equations for the magnetic field in MMR. Then, we provide the kernel of the problem using Biot and Savart law to connect the components of the observed magnetic field to the current density distribution. We also develop a simple approach to invert the magnetic field in terms of electrical current paths. To illustrate how the method works, we develop five synthetic models to test the sensitivity of the method to the properties of the conductive targets channelling the electrical current. The targets are characterized by different shapes, sizes, depths, and conductivity contrasts with the background. Then, we proceed with a case study for which the MMR method is used to identify and map preferential groundwater flow paths bypassing a mine waste rock dump drainage collection trench into the tailings pond. In this case, the conductivity of the flow paths is much stronger than the background conductivity due to the high mineralization of the ground water along these paths. The method underlines the 3-D architecture of these flow paths.

CMOS Magnetic Sensors for Wearable Magnetomyography.

Magnetomyography utilizes magnetic sensors to record small magnetic fields produced by the electrical activity of muscles, which also gives rise to the electromyogram (EMG) signal typically recorded with surface electrodes. Detection and recording of these small fields requires sensitive magnetic sensors possibly equipped with a CMOS readout system. This paper presents a highly sensitive Hall sensor fabricated in a standard $0.18~\mu \mathrm {m}$ CMOS technology for future low-field MMG applications. Compared with previous works, our experimental results show that the proposed Hall sensor achieves a higher current mode sensitivity of approximately 2400 V/A/mT. Further refinement is required to enable measurement of MMG signals from muscles.

Highly sensitive magnetic field sensor with normal-incidence geometry using Ni-based bilayer subwavelength periodic structure operating in visible-wavelength region

We successfully demonstrate a highly sensitive optical sensor for detecting magnetic fields with normal-incidence geometry that uses a Ni-based bilayer subwavelength periodic structure (SWS) operating in the visible-wavelength region. The electromagnetic field distribution within the SWS as calculated by the finite-difference time-domain method indicates that the bilayer SWS has the potential to detect minuscule magnetic fields without the need for a complex incidence system. Our bilayer Ni-SWS system with its very simple normal incidence geometry is experimentally able to detect magnetic field changes of the order of a few millitesla.

Highly Sensitive Planar Hall Magnetoresistive Sensor for Magnetic Flux Leakage Pipeline Inspection

Magnetic flux leakage (MFL) detection is frequently used for oil and gas pipeline inspection, especially for evaluation of the integrity of pipelines. The success of the MFL technique depends on many parameters. However, a sensitive magnetic sensor is an important requirement. Therefore, magnetic field sensors based on different mechanisms have been developed and applied to the MFL technique. In this paper, we evidence for the first time the capability of an innovative device based on a planar Hall magnetoresistance sensor devoted to MFL detection. This promising prototype combines all the required qualifications such as high sensitivity, low thermal drift, and bipolar and linear responses to the magnetic field. New achievements are carried out on embedded sensors in a testing platform reflecting pipeline environments. The ultrasensitive magnetic mapping concludes to a convincing technical approach with a high potential application toward MFL inspection, especially for the detection of shallow defects appearing at near side, far side, and sub-surface of a pipe wall.

A Resonant Magnetic Field Sensor With High Quality Factor Based on Quartz Crystal Resonator and Magnetostrictive Stress Coupling

A resonant magnetic field sensor is developed by using a piezoelectric quartz crystal double-ended tuning fork (DETF), two FeGa thin plates, and four quartz spacers. The double ends of the DETF are bonded to the ends of the magnetostrictive thin plates through four spacers with adhesive, allowing the magnetostrictive force to be converted into the longitudinal force in the DETF which leads to an increase of the resonant frequency of the DETF. This design brings the advantage of field-independent damping, i.e., the quality factor (Q-factor) of the sensor is found to be independent on the dc field, with an average value of about 3318 in the air due to the low internal loss in quartz. After an initially slow increase before the field reaching ~50 Oe, the resonant frequency of the sensor increases linearly with the increase of the applied dc field before reaching 280 Oe. The total frequency shift, sensitivity of the frequency shift per magnetic field, and field resolution in the linear region are 2.12% (~808.3 Hz), 3.5 Hz/Oe and 8 mOe, respectively. The results demonstrate a possibility and promising to realize a highly sensitive magnetic sensor with high-Q-factor quartz crystal as well as direct digital frequency output.

Insights into Magneto-Optics of Helical Conjugated Polymers.

Materials with magneto-optic (MO) properties have enabled critical fiber-optic applications and highly sensitive magnetic field sensors. While traditional MO materials are inorganic in nature, new generations of MO materials based on organic semiconducting polymers could allow increased versatility for device architectures, manufacturing options, and flexible mechanics. However, the origin of MO activity in semiconducting polymers is far from understood. In this paper, we report high MO activity observed in a chiral helical poly-3-(alkylsulfone)thiophene (P3AST), which confirms a new design for the creation of a giant Faraday effect with Verdet constants up to (7.63 ± 0.78) × 104 deg T-1 m-1 at 532 nm. We have determined that the sign of the Verdet constant and its magnitude are related to the helicity of the polymer at the measured wavelength. The Faraday rotation and the helical conformation of P3AST are modulated by thermal annealing, which is further supported by DFT calculations and MD simulations. Our results demonstrate that helical polymers exhibit enhanced Verdet constants and expand the previous design space for polythiophene MO materials that was thought to be limited to highly regular lamellar structures. The structure-property studies herein provide insights for the design of next-generation MO materials based upon semiconducting organic polymers.

Low-frequency magnetic sensing by magnetoelectric metglas/bidomain LiNbO3 long bars

We present an investigation into the magnetic sensing performance of magnetoelectric bilayered metglas/bidomain LiNbO3 long thin bars operating in a cantilever or free vibrating regime and under quasi-static and low-frequency resonant conditions. Bidomain single crystals of Y + 128°-cut LiNbO3 were engineered by an improved diffusion annealing technique with a polarization macrodomain structure of the ‘head-to-head’ and ‘tail-to-tail’ type. Long composite bars with lengths of 30, 40 and 45 mm, as well as with and without attached small tip proof masses, were studied. ME coefficients as large as 550 V (cm · Oe)−1, corresponding to a conversion ratio of 27.5 V Oe−1, were obtained under resonance conditions at frequencies of the order of 100 Hz in magnetic bias fields as low as 2 Oe. Equivalent magnetic noise spectral densities down to 120 pT Hz−1/2 at 10 Hz and to 68 pT Hz−1/2 at a resonance frequency as low as 81 Hz were obtained for the 45 mm long cantilever bar with a tip proof mass of 1.2 g. In the same composite without any added mass the magnetic noise was shown to be as low as 37 pT Hz−1/2 at a resonance frequency of 244 Hz and 1.2 pT Hz−1/2 at 1335 Hz in a fixed cantilever and free vibrating regimes, respectively. A simple unidimensional dynamic model predicted the possibility to drop the low-frequency magnetic noise by more than one order of magnitude in case all the extrinsic noise sources are suppressed, especially those related to external vibrations, and the thickness ratio of the magnetic-to-piezoelectric phases is optimized. Thus, we have shown that such systems might find use in simple and sensitive room-temperature low-frequency magnetic sensors, e.g. for biomedical applications.