Sensitive Magnetic Field Sensors Research Articles

Surface acoustic wave in yttrium iron garnet as tunable magnonic crystals for sensors and signal processing applications

Experimental results on investigation of magnonic crystals arising at surface acoustic wave (SAW) propagation in yttrium iron garnet as an artificial structure for surface magnetostatic waves propagation are presented. Tuning of magnonic gap frequency and gap depth were obtained by changing frequency and intensity of SAW that was explained in the frame of inelastic scattering of magnetostatic waves by SAW. Such tuning was shown can compensate drift of parameters due to possible change of temperature when using magnonic crystals as very sensitive magnetic field sensors. Suggested magnonic crystals are promising also for signal processing in GHz range.

Exchange biasing of magnetoelectric composites

Magnetoelectric composite materials are promising candidates for highly sensitive magnetic-field sensors. However, the composites showing the highest reported magnetoelectric coefficients require the presence of external d.c. magnetic bias fields, which is detrimental to their use as sensitive high-resolution magnetic-field sensors. Here, we report magnetoelectric composite materials that instead rely on intrinsic magnetic fields arising from exchange bias in the device. Thin-film magnetoelectric two-two composites were fabricated by magnetron sputtering on silicon-cantilever substrates. The composites consist of piezoelectric AlN and multilayers with the sequence Ta/Cu/Mn(70)Ir(30)/Fe(50)Co(50) or Ta/Cu/Mn(70)Ir(30)/Fe(70.2)Co(7.8)Si(12)B(10) serving as the magnetostrictive component. The thickness of the ferromagnetic layers and angle dependency of the exchange bias field are used to adjust the shift of the magnetostriction curve in such a way that the maximum piezomagnetic coefficient occurs at zero magnetic bias field. These self-biased composites show high sensitivity to a.c. magnetic fields with a maximum magnetoelectric coefficient of 96 V cm(-1) Oe(-1) at mechanical resonance.

Fabrication of magnetic tunnel junctions with a bottom synthetic antiferro-coupled free layers for high sensitive magnetic field sensor devices

Magnetic tunnel junctions with a Ni80Fe20/Ru/Co40Fe40B20 synthetic antiferro-coupled bottom free layer and an MgO barrier layer have been fabricated. Double annealing process was carried out in order to obtain linearity against magnetic field with hysteresis-free resistance response. The effect of the annealing temperature and NiFe thickness in the free layer on the magnetic field sensor performance was investigated. We have observed a very high sensitivity of 25.3%/Oe while keeping linearity.

Detecting Ferrite Nanobeads for Sentinel Lymph Node Mapping with a Highly Sensitive Hall Differential Magnetic Field Sensor

We fabricated a novel type of Hall differential magnetic field sensor for anti-cancer sentinel lymph node (SLN) mapping using ferrofluid as a marker. A pair of Hall devices are mounted on both end surfaces of a ferrite core (10 mm ϕ ×32 mm) of an electromagnetic coil which generates an AC exciting magnetic field at 2.5 kHz. The signals are retrieved by a digital phase sensitive detection circuit. Mapping a ferrofluid (ResovistR) sample of l00μg in Fe atomic amount (comparable to that accumulated in human SLNs) was attained when the sample was placed within 6 mm distance from the sensor head. The detectable distance is limited primarily due to the magnetic induction effect of the metal XYZ stage which held the sample.

Sensitive Magnetic Field Sensor Based on Compensated Double Pick Up Coil

Sensitive magnetic field sensor based on compensated double pick up coil has been developed. In order to confirm sensitifity of modified design, experiment carried out in two steps. Firstly, sensitify of conventional design is clarified. Here pick up coil as an active sensor and solenoid as an exitation coil is separately made. Secondly, modified sensor of integrated configuration is developed. Here for both active flux gate sensor and the exitation coil is made in same one core magnetic. Ferrite and standar foil soft magnetic is utilized in this experiment. In attention, frequency of 50 Hz is used for the whole experimens. A result showed that sensitvity of the integrated configuration sensor is much larger than conventional one. Then, power consume of the integrated flux gate sensor is much lower than conventional. Finally, a range measurement of the integrated configuration sensor can be realized less than 20 T which potential may perhaps sense a change of natural local magnetic field.

The MMM Expert System: From a Reference Signal to The Method Validation

This paper presents the first step in the methodological approach to the validation of the metal magnetic memory (MMM) method in the non-destructive testing (NDT) applications and in the systems used for diagnosis of early stages of material fatigue in mechanical constructions (structural health monitoring, SHM, and prognosis health management, PHM). The study is focused on the properties of the external natural source of magnetisation of the object under MMM examination and the impact of the magnetisation components. The precise data obtained from measurements of the Earth's geomagnetism (from ground stations and satellites) and the revised model of the Earth's magnetism can be applied in order to calibrate high sensitivity magnetic field sensors, validate the measurement results and extend the functional capacity of the MMM method.

Magnetic Anisotropy and Magneto-Transport Properties of Co–Ni–N Granular Alloys Thin Films

The effect of nitrogen addition on the morphology, magnetic anisotropy, and magnetoresistance properties of Co–Ni–N granular thin films were investigated. The films were grown by electrodeposition onto aluminum substrates at room temperature. By a complex process of cationic catalysis occurring at the cathode/electrolyte interface, nitrogen is adsorbed in the Co–Ni film. Finally, a granular film grows by a tridimensional progressive nucleation mechanism. The nature of the grains and of the interface between them influences exchange interactions between grains, which play an important role in determining the magnetic anisotropy. From the magnetic measurements, we found that the magnetic anisotropy constant varied in the range Keff=(−21.5÷36.6)×104 J⋅m−3 and the coercivity varied between Hc=(13÷67) kA⋅m−1 depending on the sodium nitrate content in the plating bath. The Co–Ni–N granular thin films display large values (∼160%) of magnetoresistance. These large values of magnetoresistance make such structures attractive for applications as sensitive magnetic field sensors.

Investigating the use of magnonic crystals as extremely sensitive magnetic field sensors at room temperature

We have experimentally demonstrated that a magnonic crystal—an artificial magnetic structure for controlling propagation of magnetostatic waves—can be used as an extremely sensitive sensor for detecting magnetic fields. Functional characteristics of the sensor were studied at room temperature and in a normal noisy space without considering any magnetic shielding.

A Sensitive Magnetic Field Sensor Utilizing the Giant Magneto-Impedance Effect in Field-Annealed Co-Based Amorphous Ribbons

A Sensitive Magnetic Field Sensor Utilizing the Giant Magneto-Impedance Effect in Field-Annealed Co-Based Amorphous Ribbons

Every slow-wave impulse is associated with motor activity of the human stomach

Using a newly developed high-resolution three-dimensional magnetic detector system (3D-MAGMA), we observed periodical movements of a small magnetic marker in the human stomach at the typical gastric slow-wave frequency, that is 3 min(-1). Thus we hypothesized that each gastric slow wave induces a motor response that is not strong enough to be detected by conventional methods. Electrogastrographies (EGG, Medtronic, Minneapolis, MN) for measurement of gastric slow waves and 3D-MAGMA (Innovent, Jena, Germany) measurements were simultaneously performed in 21 healthy volunteers (10 men, 40.4+/-13.6 yr; 11 women, 35.8+/-11.6 yr). The 3D-MAGMA system contains 27 highly sensitive magnetic field sensors that are able to locate a magnetic pill inside a human body with an accuracy of +/-5 mm or less in position and +/-2 degrees in orientation at a frequency of 50 Hz. Gastric transit time of the magnetic marker ranged from 19 to 154 min. The mean dominant EGG frequency while the marker was in the stomach was 2.87+/-0.15 cpm. The mean dominant 3D-MAGMA frequency during this interval was nearly identical; that is, 2.85+/-0.15 movements per minute. We observed a strong linear correlation between individual dominant EGG and 3D-MAGMA frequency (R=0.66, P=0.0011). Our findings suggest that each gastric slow wave induces a minute contraction that is too small to be detected by conventional motility investigations but can be recorded by the 3D-MAGMA system. The present slow-wave theory that assumes that the slow wave is a pure electrical signal should be reconsidered.

Off‐diagonal magneto‐impedance in amorphous microwires with diameter 6–10 μm and application to linear magnetic sensors

AbstractOff‐diagonal component of magneto‐impedance tensor with pulse excitation is very promising for high sensitivity magnetic field sensor applications. We report novel results on studies of off‐diagonal MI effect and magnetic properties in amorphous glass‐coated microwires with nearly‐zero and negative magnetostriction constant and metallic nucleus diameter ranging between 6 μm and 10 μm. Off‐diagonal impedance tensor ζφz (Hex) has been investigated in ultra‐thin amorphous glass‐coated microwires in as‐cast state and after Joule heating treatment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

CPT Magnetometer with Atomic Energy Level Modulation

We propose and experimentally investigate a coherent population trapping state based magnetometer prototype with 87Rb atoms. Through modulating Zeeman sublevels with an ac magnetic field, not only a phase sensitive detection scheme suitable for miniature magnetometer is realized, but also the detection resolution of magnetic field intensity could be improved by a factor of two. Our study result indicates that it is a promising low power consumption miniature sensitive low magnetic field sensor offering spatially resolved measurement at the sub-millimetre level.

Piezoelectric transformer based ultrahigh sensitivity magnetic field sensor

Magnetoelectric particulate composites with varying ferrite content (3–20mol%) were synthesized in the system Pb(Zr0.52Ti0.48)O3 (PZT)–Ni0.8Zn0.2Fe2O4 (NZF) and it was found that 0.8PZT-0.2NZF composite material exhibited high response of the order of 450mV∕cmOe at the low frequency of 1kHz with 600Oe dc bias. This is one of the highest magnitudes reported for the sintered particulate composite materials. This material was used to fabricate a magnetic field sensor which utilizes the piezoelectric transformer structure with ring/dot electrode pattern. The size of the magnetic field sensor was ϕ20×1.5mm2. The sensor was characterized for the changes in the output voltage and resonance frequency shift under constant current condition. A dramatic change in the magnitude of the output voltage and frequency shift was observed on application of the magnetic field. The sensor design presented in this letter clearly shows the possibility of fabricating an extremely cost-effective magnetometer.

Magneto-sensitive nickel nanowires fabricated by electrodeposition into multi- and single-ion track templates

Polycarbonate templates of (30±1) μm thickness containing cylindrical etched-track nanochannels of (500±50) nm diameter were used for electrodeposition of Ni nanowires. Using 104 channels per cm2, the most favourable deposition potential of − 1.0 V was determined in a potentiostatic mode by varying the deposition potential with respect to an Ag/AgCl reference electrode over a range between − 0.1 V and − 1.5 V. The deposition efficiency at − 1.0 V was estimated around 10%. The resulting single wires had a resistance around 200 Ω and showed an anisotropic magnetoresistance (AMR) effect of 1%, applicable to directionally sensitive magnetic field sensors.

Shape Flow Casting and In-rotating-liquid-spinning Processes for the Continuous Production of Wires and of High-strength and Soft Magnetic Metallic Fibres

Computer-controlled facilities for continuous casting of metallic fibres and wires performing in-rotating-liquid-spinning (INROLISP) and shape flow casting (SFC) were designed and installed to determine and control the near-net-shape casting processes over an extended production period. In particular, the flow behaviour of the melt jet was experimentally investigated and theoretically described using fluid dynamic equations. The controlling process parameters, such as the velocity of the melt jet, the stable free flight length, the nozzle geometry and cooling rate, were examined and optimised. Several pure metals as well as microcrystalline and amorphous alloys were cast into continuous fibres and wires of high quality. Microstructural features and mechanical properties of rapidly quenched fibres and thin wires were also evaluated. Of great potential application is the production of amorphous softmagnetic Fe base and Co base thin wires with diameters of about 30 to 50 μm. These microwires are used as sensor cores in highly sensitive novel magnetic field sensors based on a magneto-electric effect.Direct casting of wires with diameters up to 3 mm is carried out using the shape flow casting technique. The SFC facility is an highly instrumented modified meltspin facility, performing rapid substrate quenching. The process principles of the SFC technology, which enable a flexible production of steel, nickel base alloy wires and other novel materials are presented. The microstructural features are correlated with the process parameters.

A New Type of Instrument with Its Special Excited Input-Signal in Inspecting Residual Stress

The issue of nondestructive testing in aeronautical structures is of considerable importance in the aviation industry today. And a high sensitivity magnetic field sensor, which has recently been developed is designed for non-destructive stress testing. It is based on idea of the magnetic field produced by pulsed currents and perturbed by the presence of stress. The sensor can be effectively utilized for the detection of defects and stress concentration in conducting materials using eddy current testing measurements. The principle of the measuring technique is based on the unbalance of the magnetic field where the stress or cracks exist. Also, the excited input-signal is special designed. A pulsed current was inputted and changed into a self-attenuation signal which does the effect in the probe.

Influence of local field inhomogeneity on the accuracy of precise total magnetic field monitoring

Long-term precise magnetic observations are being carried out at Eilat test site as a part of a multi-sensor geophysical monitoring program for active tectonic faults. Three highly sensitive potassium total magnetic field sensors with intrinsic noise of 0.05 pT Hz −1/2 constitute a horizontal gradiometer. The distance between the sensors was varied in the range 3–50 m to test the system operation in real field conditions. Our results show gradiometer time series, apparently containing residuals of external diurnal variations and micropulsations, which are essentially homogeneous over such short distances. The residual amplitude makes up less than 0.6% of the change in intensity of the external magnetic field but can be distinctly revealed thanks to extremely high gradiometer sensitivity. It turned out that such gradiometer performance could be explained by inhomogeneous remanent magnetization of surrounding rocks leading to slight mutual non-parallelism of Earth's magnetic field vectors at the places where the sensors were located. A cleaning procedure based on joint correlation analysis of total field gradiometer time series and Earth's magnetic field component data proved to be an effective method of correcting gradiometer data.

Sensitive In 0.53 Ga 0.47 As/InP (SI) magnetic field sensors

The usefulness of InGaAs/InP heterostructures for magnetic field sensor applications has been studied. Basic parameters of the Hall and magnetoresistive devices have been determined. Magnetic field sensitivities in a wide temperature range from 3.5 K to 300 K for layers with different carrier concentration from 2 � 1020 m−3 to 8 � 1023 m–3 have been measured. It is concluded that optimized lattice-matched InGaAs/InP heterostructures can be used as very sensitive magnetic field sensors. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Kish graphite as a magnetic field sensor

Magnetoresistance effect (MRE) and Hall effect have been applied to magnetic field sensors. As materials for the field sensor due to MRE, semiconductor compounds and ferromagnetic metals have been used, but graphite materials have not, though graphite exhibits positive magnetoresistance. A purified high quality Kish graphite (KG) exhibits a large transverse magnetoresistance ∆ρ/ρ even at room temperature. KG is a graphite flake precipitated from molten iron at high temperatures [1]. When the flakes are made at a very high temperature above boiling point of iron and purified carefully, they have higher crystallinity than that of HOPG and exhibit a nature very similar to single crystal graphite. In the present study, therefore, a sensitive magnetic field sensor was tried to prepare using such KG flakes. On the MRE sensors, a magnetic field is measured as a voltage change ∆V induced by the magnetic field under a constant electric current: ∆ρ/ρ = ∆V/V. ∆V increases with the increase of the sample voltage V under zero magnetic field, if the defect concentration in the sample does not increase with increasing V. V increases with the increase of current, sample length and sample thickness. However, the power W increases with increasing current I as W = IR, where R is the sample resistance, i.e. Joule heat generates and temperature of the sample should rise under a large current flow. In the case of KG, sample sizes are limited because of flakes. Therefore, reducing the sample thickness is important factor to increase V and ∆V in the present study, but a careful treatment for reducing the thickness is needed to increase ∆ρ/ρ, i.e. not to increase the defect concentration.

Planar Hall effect and magnetoresistance in Ni 81Fe 19 and Co square shaped thin films

Ni 81Fe 19 and Co thin films have been fabricated and their transport properties have been investigated for potential applications in ultra sensitive magnetic field sensors. The Ni 81Fe 19 films exhibit an anisotropic magnetoresistance (AMR) of 2.5% with a coercivity 2.5 Oe and the Co films exhibit an AMR of 0.7% with coercivity 11 Oe. Large planar Hall effect magnetoresistance values at room temperature are reported for both cases. An unbalanced Wheatstone bridge model is proposed to describe quantitatively the observed experimental Planar Hall Effect data.