Fluxgate Based Detection of Magnetic Material in Soil Subsurface

We have developed a micro fluxgate magnetic sensor using new printed circuit board (PCB) technology. The fluxgate sensor consisted of five PCB stack layers including one layer of magnetic core and four layers of excitation and pick-up coils. The center layer as a magnetic core was made of micro patterned amorphous magnetic ribbon with an extremely high DC permeability of ~100,000, and the core had a rectangular ring shape. Four outer layers as an excitation and pickup coils had a planar solenoid structure. The amorphous magnetic core was easily saturated due to the high permeability, low coercive field, and closed magnetic path for the excitation field. The chip size of the fabricated sensing element was 7.3 × 5.7 mm2. Excellent linear response over the range of –100 μT to +100 μT was obtained with sensitivity of 780 V/T at excitation sine wave of 3 Vp-p and 360 kHz. A very low power consumption of ~8 mW was measured. This low power, small size, and high sensitive fluxgate sensor to measure a low magnetic field is very useful for various applications.

The fluxgate sensor uses the nonlinear characteristics of soft magnetic materials to measure the geostationary magnetic field, which has the characteristics of high sensitivity, wide magnetic measurement range and easy portability, and is widely used in geological exploration, navigation, space technology and other fields. In this paper, the research is based on the second harmonic method of the development of fluxgate sensor, since the second harmonic contains static magnetic field direction and amplitude information, so the second harmonic signal to noise ratio enhancement can effectively improve the resolution of the fluxgate sensor. In this paper, the induction signal is first resonated to the second harmonic frequency using a resonant circuit, and then filtered after an amplification circuit, the second harmonic signal-to-noise ratio is significantly enhanced by 13 times.

This paper presents a micro fluxgate sensor fabricated by Si-based Micro Electro Mechanical Systems (MEMS). To measure X- and Y-axis magnetic fields, two fluxgate sensing elements were perpendicularly aligned. The fluxgate sensor was composed of rectangular-ring shaped magnetic core, solenoid excitation and pick-up coils. The 2 /spl mu/m thick Ni/sub 0.8/Fe/sub 0.2/ (permalloy) magnetic core layer was electroplated with photoresist frame using sputtered Ni/sub 0.8/Fe/sub 0.2/ seed layer. The fabricated fluxgate chip size was 4.5/spl times/2.7 mm/sup 2/. Excellent linear response over the range of -100 /spl mu/T to +100 /spl mu/T was obtained with 210 V/T sensitivity at excitation square wave of 2.8 V/sub p-p/ and 1.2 MHz. When two-axis fluxgate sensing element was rotated in terrestrial field, induced second harmonic voltages from X-and Y-axis were sine and cosine wave without distortion, respectively. It is very useful to commercialize the portable navigation system including north-up and map matching, military research, medical research, and space research.

This chapter describes the design and scientific results from a new tri-axial magnetometer for atmospheric and space studies. The new instrumentation features multi-frequency (1 KHz -1.5 MHz), multi-bandwidth (1 Hz -10 KHz), multi magnetic field measurement range, low-power and re-configurable operation. This novel architecture is based on producing a programmable receiver independent of the fluxgate sensor used. Any ring-core, race-track or parallel type fluxgate sensor may be connected to the input and a working system is produced within hours. The current implementation is based on a novel shielded 3-dimensional sensor optimised for previously unseen low-power consumption compared to existing tri-axial macro-sensors. As a fully digital system the sensor's output is sampled after the amplification stage. The full extent of the complex solar wind -magnetospheric -ionospheric system is measured by the magnetometer, due to the receiver's programmable dynamic range (DR) and the programmable cross-correlator integration time. The field-programmable gate array (FPGA) hardware implementation yields to a programmable filtering scheme that selects different centre frequencies and desired signal bandwidths. The output is directly in nT to avoid any unnecessary software post-processing calibration procedures and to ensure compatibility of results amongst users. The user selects either the magnetic field's vector components or the total intensity to be present at either the universal asynchronous receiver and transmitter (UART) or the fast 10/100 Mbps Ethernet communications ports. The development of the magnetometer's sensor is based on the implementation of a novel design methodology for producing optimised fluxgate sensors for low-power consumption. The sensor is qualified for both ground-based and spaceborne observations. The results are of interest to the aerospace and defence industries, since fluxgate sensors exist in airborne and spaceborne systems for decades. Lowering power consumption is followed by simplification of the accompanying electronic circuits. The system is constantly being enriched by research results from an ongoing collaboration with NASA's Jet Propulsion Laboratory (JPL) on a different project for future missions (Dekoulis & Murphy, 2008). The presented system is complementing existing and under development state-of-the-art systems, such as, scalar/vector magnetometers. The system acts as a pathfinder for future high-resolution planetary exploration missions.

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.

This paper presents a new switch-type MI sensor using amorphous wire and a CMOS inverter IC with a positive feedback loop. The MI (Magneto-Impedance) chip is composed of a single amorphous wire (30 μm diameter and 2 mm length) and two coils (feedback coil and pickup coil). This sensor circuit has high sensitivity and low power consumption. A switching magnetic field is set up using the variable resistance of a positive feedback loop. A switching magnetic field is independent of the frequency and amplitude of the external magnetic field. This on/off MI sensor will be useful for application to automobile anti-lock braking systems (ABS) and to magnetic stripe card readers.

Tremendous progress has been made in boosting the realization of magnetoelectric (ME) magnetometers based on the direct ME effect (DME) for bulk ME laminates. In this work, we studied the potential of an electrically driven bulk magnetic field sensor based on the converse ME effect (CME). Starting from a discussion about the dependence of the induced voltage from the pickup coil on coil parameters and the CME coupling process, we then experimentally measured the optimized bias field in the off resonance region and observed the double-peak phenomenon that occurred within the resonance window. More importantly, the optimization with respect to the sample's dimension, excitation voltage, and frequency was conducted to improve the sensing capability for low-frequency magnetic fields. It was experimentally found that a limit of detection (LoD) of ∼115 pT for a magnetic field of 10 Hz and ∼300 pT for a magnetic field of 1 Hz was achieved when exciting the ME laminate at 1 V without any bias field. In this case, the power consumption for the ME laminate is only 0.56 mW, which is much lower compared to tens of milliwatts (10–100 mW) for optically pumped or flux gate sensors (excluding the power consumption from the electronics) and also shows advantages over conventional ME magnetic field sensors based on DME with a current pump.

Parametric models for 3D topographic amplification of ground motions considering subsurface soils

A contactless induced-current bio-impedance system for monitoring brain cryosurgery procedure was modeled and numerically simulated, where the excitation coil was also performing as the measuring, or pick-up coil. A segmented three-dimensional (3D) MRI database was used for building the volume conductor geometry, and the numerical finite-volume method was employed for solving the forward problem for calculating the scalar potential distribution and the second-order voltage change on the pick-up coil. Several coil configurations were considered, varying in their relative positioning to the 3D head model. For each case, the sensitivity of the measured voltage change on the excitation coil to the volume of a frozen lesion was calculated. The highest sensitivity (1.1 x 10(-5) relative voltage change per mm3 of frozen tissue) was obtained for a coil arrangement where its closest segment to the volume conductor is at the maximum distance away from the frozen region position. The simulated system signal-to-carrier ratio was O(10(-8)).

The casing inspection tool was introduced to the oil industry in 1960, and since that time a number of logs have been recorded in various areas of operation. The purpose of this paper is to report results thus far obtained with this corrosion-detecting tool. To properly evaluate results of interpretation procedures as developed through field use, interpretation principles as a result of laboratory and field experience, actual field results in various areas and recommended operating procedures. Examples of various casing inspection logs are presented along with follow-up well information necessary to properly evaluate results of interpretation techniques. Principle of Operation The casing inspection log uses a method of measuring the effect of eddy currents on a magnetic field. The instrument consists of two radial coils, an exciter coil and a pick-up coil. Fig. 1 is a block diagram of the instrument. The exciter coil is fed from an AC source at the surface, and the resulting magnetic field sets up eddy currents in the casing wails. These eddy currents cause the magnetic field to be attenuated and shifted in phase, and the resulting magnetic field is detected by the pick-up coil. The pickup signal is amplified and transmitted to the surface by modulating a 3 kc carrier. In the surface instrument the carrier is separated from the exciter voltage, amplified and demodulated. At this point the signal is a true reproduction of the bottom-hole signal from the pick-up coil. The phase of this signal is compared with the phase of the exciter voltage, and the resulting phase shift is recorded on a strip-chart recorder. The theory of eddy currents indicates that phase shift is determined by four factors: casing wall thickness, frequency, magnetic permeability and resistivity of the metal. The basic phase-shift equation which follows shows that the phase shift is directly proportional to casing wall thickness. (1) where phi = phase shift, D = depth, mu = magnetic permeability, p = resistivity in micro-ohmcm, andF = frequency in cycles/sec. The factors of magnetic permeability and resistivity of the metal are practically always unknown for any joint of casing, and logs run thus far indicate that these factors vary considerably among types of casing and manufacturers. There are also indications that stresses placed upon casing as set in wells seem to affect magnetic permeability of the metal. This problem is minimized by using a reference joint to arrive at a metal thickness scale, and using that reference joint for all subsequent logs recorded in the same well. To detect small corroded areas, a differential pick-up coil is used. The log obtained is linear with respect to wall thickness, with an exaggerated indication of small non-conformities. Equipment The down-hole tool is illustrated in Fig. 2. Centralizing springs are used at the top and bottom of the tool to minimize wear on the two coil housings. The tool has been designed to withstand normal well temperatures of 350F and pressures of 20,000 psi. It has been operated in wells to 13,500 ft. The construction and operation of the tool are such that satisfactory results can be obtained with any type of well fluid. In the surface control panel the phase angle is measured by a transistorized phase detector. A linear output voltage which is proportional to the phase angle is produced to drive a strip-chart recorder pen in the surface equipment. P. 377ˆ

Micro fluxgate sensor with cascaded planar ring cores

The magnetic field sensing performance of FeCo-based soft magnetic alloys with varying Fe/Co ratio

CMOS magnetic sensors with integrated ferromagnetic parts

Fluxgate sensors with straight wire or rod cores are used in nondestructive testing (NDT), portable gradiometers, and sensor arrays and for the detection of small objects. We show that their sensitivity at the voltage output mode depends on the excitation parameters, properties of the core material and geometry, pick-up coil length, but only slightly on the pick-up coil diameter. This finding allows one to design multiwire cores with large wire pitch, which decreases their magnetic interactions and thus reduces demagnetization and correlation of their noise. As a result, using <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> wires theoretically increases sensitivity <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula>-times, which is not achievable with dense cores. We have demonstrated this tendency for <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> up to 8 and one type of permalloy wire.

Abstract. The paper discusses the possibility of improving temperature and noise characteristics of fluxgate variometers. The new fluxgate sensor with a Co-based amorphous ring core is described. This sensor is capable of improving the signal-to-noise ratio at the recording short-period geomagnetic variations. Besides the sensor performance, it is very important to create the high-stability compensation field that cancels the main Earth magnetic field inside the magnetic cores. For this purpose the new digitally controlled current source with low noise level and high temperature stability is developed.