An AMR sensor-based measurement system for magnetoelectrical resistivity tomography

The magnetic object localization is widely utilized in sea mine detection, identification of vehicles and unexploded ordnance. And the Anisotropic Magneto-resistive (AMR) sensor is applied in compassing, navigation systems, and magnetometer. Thus, a novel magnetic object localization method based on AMR sensor is presented in this paper. Firstly magnetic object localization theoretical model is established, and magnetic field and magnetic gradient need to be measured for localization. And then detection and localization hardware construction is designed and realized. The weak magnetic field detection method and measurement modules are discussed. At last, the lab test based on AMR sensor is carried out. The results show that it is an effective method for magnetic object localization and when the magnet of surface magnetic field is 0.9T, the location error is not more than 10% from 50cm to 140cm. AMR sensor is a valuable choice for magnetic object localization measurement.

Ta/MgO/NiFe/MgO/Ta anisotropic magnetoresistive thin film sensors, which can be used for magnetic scales, were prepared. To improve the magnetoresistance ratio of the sensors, these sensors were vacuum-annealed with the magnetic field applied, and then, both the static and dynamic magnetoresistive responses of the sensors were obtained. The experimental results have shown that the instability of magnetic anisotropy occurs in the sensors after vacuum-annealing, leading to the significant hysteresis and abnormal output voltage peaks. To investigate the underlying physics, the distribution of the non-uniform demagnetizing field along the width of an anisotropic magnetoresistive (AMR) strip is considered, and both the static and dynamic responses of the AMR elements have been calculated on the basis of the Stoner–Wohlfarth model. The results have shown that the calculated results are in good agreement with the experimental data. The calculated results have revealed that the angles between the anisotropic field and the external magnetic field are different during the field cyclings of Hmax (maximum magnetic field) to −Hmax and −Hmax to Hmax. The angle difference is up to 6°, leading to different magnetoresistive responses. This paper is helpful for the understanding about the magnetization rotations in magnetic sensors and the manufacturing of sensors.

We report the detection of nuclear magnetic resonance (NMR) using an anisotropic magnetoresistive (AMR) sensor. A "remote-detection" arrangement was used in which protons in flowing water were prepolarized in the field of a superconducting NMR magnet, adiabatically inverted, and subsequently detected with an AMR sensor situated downstream from the magnet and the adiabatic inverter. AMR sensing is well suited for NMR detection in microfluidic "lab-on-a-chip" applications because the sensors are small, typically on the order of 10 mum. An estimate of the sensitivity for an optimized system indicates that approximately 6 x 10(13) protons in a volume of 1,000 mum(3), prepolarized in a 10-kG magnetic field, can be detected with a signal-to-noise ratio of 3 in a 1-Hz bandwidth. This level of sensitivity is competitive with that demonstrated by microcoils in superconducting magnets and with the projected sensitivity of microfabricated atomic magnetometers.

In this paper, we present a new technique to unify and intensify the magnetic fields that results in higher performance of Anisotropic Magneto-Resistive (AMR) current sensors and consequently develop a closed loop controller for 100W synchronous GaN buck converter at 1MHz. The closed loop operation of high switching frequency converters at high power has always been a big challenge due to lack of access to current information. The proposed method that also intensifies the magnetic fields through the sensor, significantly improves the bandwidth limits, and reduces electromagnetic interference (EMI) on AMR sensors, making them applicable for high switching frequency and high current power electronics converters. After verifying uniform distribution concept through simulation, we also implemented a prototype of AMR current sensors onto Printed Circuit Board (PCB) for verification of the concept at high frequency converter. We then present the design procedure and associated challenges of an integrated analogue peak current controller for creating the closed loop operation of a GaN buck converter at high switching frequency.

Magnetic field sensors are widely used in smart electronic systems for transportation, structural health monitoring, current sensing, geomagnetic navigation, and other applications. Among various sensor types, anisotropic magnetoresistance (AMR) sensors are often selected for their compact size, high sensitivity, and low cost. However, their performance is significantly affected by temperature-induced drift in magnetic field measurements. This study evaluates the temperature stability of three AMR sensors − LSM303AGR, LIS3MDL, QMC5883L − and a fluxgate sensor, DRV425. Results show that LSM303AGR demonstrates the best temperature stability in magnetic fields under 100 μT, with an average drift of 24.8 nT/K, and a sensitivity drift of −488 ppm/K, while LIS3MDL is suitable for measuring stronger fields due to its linear temperature characteristic despite a higher drift of 152.9 nT/K. Sensor measurement drift amounts to 12 % to 76 % of magnetic field threshold over a 50 °C range in practical reference application (10 μT), but algorithmic compensation using application-specific or diverse datasets can reduce drift to as low as 4.9–7.9 % of the reference threshold in fields under 100 μT. These findings highlight the importance of tailored compensation strategies when using AMR sensors for reliable long-term magnetic field monitoring.

A new construction of magnetometer with commercially available AMR (anisotropic magnetoresistive) sensors intended for vehicle detection experiments is presented. Initial experiments with simple AMR gradiometer indicated viability of the approach in a real- world setup. For further experiments and acquisition of representative data, a new design of precise multi-channel magnetometer was developed. The design supports two models of commercial AMR sensors: the proven and reliable, but obsolete Honeywell HMC1021-series sensors and newly available Sensitec AFF755B sensors. In the comparison the two types are similar in most achieved parameters, except offset stability in flipped operation regime. Unfortunately, the new AFF755B sensors seem to have perhaps inferior coupling of the flipping (set/reset) coil to the ferromagnetic core that causes insufficient saturation of the AMR material. The issue is being solved by Sensitec, current deliverables of the AFF755B have “product sample” status (September 2015).

Unlike conventional positioning systems that rely on multiple sensors, the positioning system proposed in this study uses a single anisotropic magnetoresistive (AMR) sensor to measure the magnetic field of a target permanent magnet. This approach significantly reduces the system hardware cost and complexity, facilitating the miniaturization of positioning systems. Leveraging a BP neural network model, which is shown to be fast and accurate, the positioning system obtains the real-time magnetic field of the target magnet using a single sensor, subsequently converting three-axis magnetic field data into coordinate information to achieve real-time tracking and localization. The results show that the root mean square errors (RMSEs) for the X and Z axes in the simulation are 0.27 mm and 0.26 mm, respectively, while the RMSEs for the X, Y, and Z axes in the actual test are 0.83 mm, 1.15 mm, and 0.85 mm, respectively. It is also observed that the positioning error correlates with variations in the magnetic field with respect to position, which originate from the strong distance-dependent nonlinearity of the magnetic field. This method not only reduces hardware costs but also maintains accuracy. It is particularly well-suited to applications requiring high-precision positioning and tracking, achieving millimeter-level accuracy within a volume of 50 × 40 × 40 mm3. It has potential applications in aerospace intelligent connectors, medical devices and automation systems, where space and signal lines are limited.

In the last decade, wireless sensor networks (WSN) have gained considerable importance and momentum. They are used with a growing diversity of sensors in a plethora of applications, e.g., from Ambient Intelligence (AmI), Assisted Living (AAL) to agriculture. WSN based measurement and instrumentation systems commonly have to operate under tight power consumption constraints. In particular, WSN benefiting from micro-electro-mechanical-system (MEMS) miniaturization have a very limited power budget due to poor energy density of storage elements. While highly optimized microcontrollers are available by now, today's sensors and sensor electronics are the predominant cause of power consumption in WSN. The standard approach tries to minimize standby currents by low-power sensor, bridge, and amplifier design. In contrast, this paper investigates an approach of duty-cycled, reconfigurable sensor electronics for resistive bridge sensors, that seamlessly integrates into microcontroller' sleep modes. The circuit is optimized for the particular case of anisotropic magneto-resistive (AMR) sensor based localization in autonomous WSN. In a systematic analysis amplifier currents, slew-rate, and read-out or on-time T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> are optimized for minimum power consumption of a tri-axial AMR sensor. At the required read-out rates, e.g., one measurement per minute, energy consumption can be reduced to a factor 1.5·10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> of the continuous operation. A reconfigurable chip in a standard 0.35 μm bulk CMOS technology is under preparation adding flexibility for different sensor types and calibration needs.

The specific features of numerical calculation of the magnetization-reversal process in thin-film components with large linear dimensions and a complex topology in relation to magnetoresistive transducers (sensors) are considered. The calculated value of the sensor sensitivity obtained within the framework of a uniform and micromagnetic magnetization-reversal model is compared with experimental data. Calculations of the magnetization-reversal process within the framework of the micromagnetic model show the positive effect of edge magnetization pinning which is manifested in the mutual compensation of current and magnetization- distribution nonuniformities; it can be used to enhance the sensitivity of anisotropic magnetoresistive (AMR) sensors.

A common practice used by the Germans and collaborators in World War II, as part of the Holocaust, was to use existing Jewish cemeteries as places for mass burial. Research was completed at the Old Jewish Cemetery in Riga, Latvia, the Livas Jewish Cemetery in Liepaja, Latvia, and the Zaliakalnis Jewish Cemetery in Kaunas, Lithuania. The Old Jewish Cemetery in Riga was adjacent to the Riga Ghetto and was used to bury individuals murdered in the ghetto. In Kaunas, an area of the Zaliakalnis Jewish Cemetery is devoid of grave stones, and literature sources and testimony indicate that this area was used for the mass burial of Jews from the Kaunas Ghetto and other mass killings. In Liepaja, the local Jewish Heritage Foundation believes that there are mass graves within the Livas Cemetery. Methodologies for this research include the use of a pulseEkko Pro 500-megahertz ground-penetrating radar (GPR) system. Electrical resistivity tomography (ERT) data were collected through a linear array of electrodes coupled to a direct current (DC) resistivity transmitter and receiver. Analysis of aerial photography and satellite images was also employed at each location. ERT and GPR data indicate three separate trench anomalies in the Old Jewish Cemetery in Riga. The presence of these anomalies corroborates Holocaust survivor testimony that bodies were buried in mass graves in that area. In the Zaliakalnis Jewish Cemetery in Kaunas, ERT and GPR data indicate an anomaly in the western part of the cemetery, and ERT data further indicate two other possible mass graves. In Liepaja, preliminary GPR analysis indicates an anomaly in a cleared section of the cemetery. Based on the presence of geophysical anomalies in all three cemeteries, which correlate with literature sources and Holocaust survivor testimony, there is a high probability that mass graves are present at each site. Future research directions include expanding the search areas in each cemetery, additional literature and testimony-based research, and the addition of other geophysical methodologies.

Subsurface stratigraphy interpretation often relies on sparse borehole data. Due to the inherent spatial variability and limited borehole data, uncertainty inevitably exists in the interpreted subsurface stratigraphy. Geophysical approaches such as electrical resistivity tomography (ERT) provide continuous subsurface data in the concerned cross-section. Though the reliability of the geophysical data derived is much lower than that of the solid borehole data, the continuous subsurface data obtained from geophysical investigations might be taken as a complement to the sparse borehole data in the subsurface stratigraphy interpretation. This paper proposes an innovative subsurface stratigraphy interpretation approach, which takes advantage of the high reliability of sparse borehole data and the abundance of ERT data. This approach is partially developed based on the random field approach recently advanced by the authors, and the relationship between ERT data and borehole stratigraphies is mapped with the algorithm of the support vector machine. The uncertainty of the interpreted subsurface stratigraphy arising from the random selection of the training and testing datasets (for training the mapping relationship between ERT data and stratigraphies) is analyzed by a “ bootstrapping” method. Furthermore, field tests of site investigation at four benchmark stratigraphic cross-sections are conducted, and high-quality ERT and borehole data are collected. Based on the high-quality site investigation data obtained, illustrative applications of the proposed approach are presented.

We report our recent work on thick-film permalloy (NiFe) and NiCo-alloy anisotropic magnetoresistive (AMR) sensors made by thermal spray. Various sensor layouts have been fabricated and characterized. The AMR effect of 2.45% and 2.68% is obtained in as-sprayed permalloy and NiCo-alloy sensors. Resistivity of thermal-sprayed thick film is 40-60 /spl mu//spl Omega/ cm, which is higher than bulk material. A maximum /spl Delta/R/R value of 5.2% is achieved after thermal annealing. A high-/spl Delta/R/R value and low-saturation fields are the important features of thermal spray sensors. The very promising results demonstrate the potential applications of thermal spray sensors.

The article discusses a field geophysical complex that includes the Earth's gravity and magnetic fields parameters meters — an digital zenith camera (DZC), a relative gravimeter, onboard quantum magnetometer and ground magnetovariation station. This complex allows determining such parameters of the Earth's gravity field as acceleration and anomalies of gravity, plumb line deviations, horizontal components of the acceleration of gravity and gravitational gradients, and parameters of the Earth's magnetic field — absolute and anomalous values of induction. Maps of the Earth's gravity and magnetic fields can be used in various fields, in particular, in the creation and testing of integrated autonomous navigation systems using the parameters of these fields. The paper presents examples of parameter maps created using this complex. The measurement error of acceleration and gravity anomaly is 10 µGal, plumb line deviation is ≈ 0.2″, horizontal components of gravity acceleration are ≈ 1 mGal, gravitational gradients are 10 Eötvös at a distanc

Location and corrosion detection of tower grounding conductors based on electromagnetic measurement

Durusu Lake is the biggest and most important freshwater source supplying drinking water to the European side of Istanbul. In this study, electrical resistivity tomography (ERT) and transient electromagnetic (TEM) measurements were applied to detect a possible salt water intrusion into the lake and to delineate the subsurface structure in the north of Durusu Lake. The ERT and TEM measurements were carried out along six parallel profiles extending from the sea coast to the lake shore on the dune barrier. TEM data were interpreted using different 1-D inversion methods such as Occam, Marquardt, and laterally constrained inversion (LCI). ERT data were interpreted using 2-D inversion techniques. The inversion results of ERT and TEM data were shown as resistivity depth sections including topography. The sand layer spreading over the basin has a resistivity of 150–400 Ωm with a thickness of 5–10 m. The sandy layer with clay, silt, and gravel has a resistivity of 15–100 Ωm and a thickness of 10–40 m followed by a clay layer of a resistivity below 10 Ωm. When the inversion of these data is interpreted along with the hydrogeology of the area, it is concluded that the salt water intrusion along the dune barrier is not common and occurs at a particular area where the distance between lake and sea is very close. Using information from boreholes around the lake, it was verified that the common conductive region at depths of 30 m or more consists of clay layers and clay lenses.