Dc Magnetic Flux Research Articles

An overview of commercially available Teslameters for applications in modern science and industry

<p>The Hall-effect based Teslameters (also called Gaussmeters) are the mostly applied instruments for measuring DC and AC magnetic flux densities in modern science and industry. This paper gives an overview of commercially available Teslameters at the high-end performance level. The Teslameters have been evaluated by following characteristics that are published by suppliers: probe dimensions, magnetic field sensitive volume, accuracy, magnetic resolution, measurement range, frequency bandwidth, temperature coefficient sensitivity, and price/performance ratio.</p><p>The Teslameter that best matches the measurement needs in various application fields incorporates a 3-axis integrated Hall probe, analog electronics based on the spinning-current technique, an analog-to-digital converter, an embedded computer, and a touch-screen display. The 3-axis Hall probe is a single silicon chip integrating both horizontal and vertical Hall magnetic sensors and a temperature sensor. The spinning-current eliminates most of the Hall probe offset, low-frequency noise, and the planar Hall voltage. The errors due to the Hall sensor non-linearity and the variations in the probe and electronics temperatures are eliminated by a calibration procedure. The errors due to the angular imperfections of the Hall probe are eliminated by a calibration of the sensitivity tensor of the probe. This Teslameter can measure magnetic field vectors from about 100 nT to 30 T, with the spatial resolution of 100 µm, magnetic resolution ±2 ppm of the range, the accuracy 0.002 % of the range, a temperature coefficient less than 5 ppm/°C, and angular errors less than 0.1°.</p>

交直流漏磁钢轨裂纹检测对比研究

我国铁路钢轨表面裂纹是钢轨损伤的主要缺陷形式。针对钢轨裂纹缺陷的特点，从电磁场基本理论出发，研究直流漏磁、交流漏磁检测原理，搭建检测系统平台。实验比较研究了两种技术分别在手推、电机驱动低速和电机驱动高速三种巡检情况下的漏磁信号。提出了通过计算检测系统对缺陷的分辨率，来精确比较两种方法检测信号的优劣。实验表明，手推式和速度低于2 m/s的电机驱动低速巡检条件下，两种方法都能全面检测出缺陷，但交流漏磁信号比直流漏磁信号分辨率更高，信号更稳定，检出效果更好。电机驱动速度大于2 m/s时以及高速条件下，直流漏磁比交流漏磁能更准确地检测出缺陷。结合两种方法的优势，可互补实现对钢轨不同巡检条件下的裂纹全面检测。 The surface cracks are the main defects of rail track. Based on the characteristic and electromagnetic theories, the DC magnetic flux leakage (MFL) and AC MFL are studied. And the measurement system is built up. Experiments are applied to study the MFL signals of DC MFL and AC MFL technology with hand-move, low-speed and high-speed motor drive. The defects detection solutions are calculated to compare DC MFL and AC MFL accurately. The experiment results propose that these two technologies can detect the surface cracks with hand-move and low-speed (<2 m/s) motor drive. AC MFL has higher solutions, more stable signals and better results than those of DC MFL. When the rotation speed is more than 2 m/s, DC MFL is more accurate. Combining each other these two technologies can detect the rail track in different measurement conditions.

Finite-Element Analysis and Experiment of Current Superimposition Variable Flux Machine Using Permanent Magnet

We have proposed a current superimposition variable flux reluctance machine that can control its torque constant. This machine can be operated by using a six-phase superimposition current composed of ac-armature and dc-field currents. In this paper, we propose a current superimposition variable flux machine using permanent magnets. The permanent magnets increase the dc magnetic flux. First, the structure and operational principle of this machine are described. Next, the torque characteristics are computed under vector control. Finally, the computed characteristics are verified by carrying out measurements on a prototype.

Experimental set up of a magnetoelectric measuring system operating at different temperatures

The magnetoelectric effect is the phenomenon whereby through a magnetic stimulation can be produced an electrical response or vice versa. We implement a magnetoelectric voltage measuring device through the dynamic method for a different range of temperatures. The system was split into an electric set and an instrumentation and control set. Design and element selection criteria that the experimenter must take into account are presented, with special emphasis in the design of the sample holder, which is the fundamental component that differentiates the system operating at high temperature and the one operating at room temperature. The experimental equipment consists of an electromagnet with DC magnetic flux density (B) in a range of (0.0 to 1.6) KOe, a Helmholtz coil which operates with a sinusoidal B between (0.0 and 0.016) KOe and a PT100 temperature sensor. A tubular heating resistance, a Checkman temperature control and an SSR 40A were used for controlling the temperature. As an application of the system, the transverse and longitudinal magnetoelectric coefficient was measured for a thin film of BiFeO3 at room temperature and 307K. It was observed that the behaviour of the longitudinal and transverse magnetoelectric coefficient matches the reported value and decreased with increasing temperature.

Novel Principle for Flux Sensing in the Application of a DC + AC Current Sensor

This paper presents a new concept for measuring DC and AC magnetic flux densities within a ferromagnetic material. It is based on a measurement of the material's magnetostriction, which is its relative change in length due to the magnetic flux density inside the material. This dimensional change is converted to an electrical signal using a piezoelectric strain sensor. An additional sinusoidal AC excitation of the core material provides higher sensitivity of the length measurement and overcomes the inherent high-pass characteristic of the piezoelectric sensor. Therefore, flux density signals from DC to the kilohertz range can be measured. The concept's feasibility is demonstrated with the design and implementation of an isolated DC + AC current sensor with a measurement range of $\pm \mbox{A}$ and a bandwidth from DC to 20 MHz.

A Novel Dual-Input Boost-Buck Converter with Coupled Inductors for Distributed Thermoelectric Generation Systems

A dual-input boost-buck converter with coupled inductors (DIBBC-CI) is proposed as a thermoelectric generator (TEG) power conditioner with a wide input voltage range. The DIBBC-CI is built by cascading two boost cells and a buck cell with shared inverse coupled filter inductors. Low current ripple on both sides of the TEG and the battery are achieved. Reduced size and power losses of the filter inductors are benefited from the DC magnetic flux cancellation in the inductor core, leading to high efficiency and high power density. The operational principle, impact of coupled inductors, and design considerations for the proposed converter are analyzed in detail. Distributed maximum power point tracking, battery charging, and output control are implemented using a competitive logic to ensure seamless switching among operational modes. Both the simulation and experimental results verify the feasibility of the proposed topology and control.

Flux Dynamics, ac Losses, and Activation Energies in (Ba $$_{0.6}$$ 0.6 K $$_{0.4})$$ 0.4 ) Fe $$_{2}$$ 2 As $$_{2}$$ 2 Bulk Superconductor

Flux pinning and thermally assisted flux flow are studied in a (Ba $$_{0.6}$$ K $$_{0.4})$$ Fe $$_{2}$$ As $$_{2}(T_\mathrm{c}$$ =38.3 K) bulk samples in magnetic fields up to 18 T via ac susceptibility measurements. Ac susceptibility curves shift to higher temperatures as the frequency is increased from 75 to 1,997 Hz in all fields. The frequency ( $$f)$$ shift of the susceptibility curves is modeled by the Anderson-Kim Arrhenius law $$f = f_{0}\mathrm{exp}(-E_\mathrm{a}{ /kT})$$ to determine flux activation energy $$E_\mathrm{a}/k$$ as a function of ac field $$H_\mathrm{ac}$$ and dc magnetic flux density $$\mu $$ $$_\mathrm{0} H_\mathrm{dc}$$ . $$E_\mathrm{a}/k$$ ranges from 8,822 K (761 meV) at $$\mu $$ $$_{0} H_{dc}$$ = 0 T to 1,100 K (95 meV) at 18 T for $$H_\mathrm{ac}=$$ 80 A/m (1 Oe). The energies drop very quickly in a non-linear manner as $$\mu $$ $$_{0} H_\mathrm{dc}$$ increases from 0 to 1 T, and more gradually, in a linear-like manner, as $$\mu $$ $$_{0} H_\mathrm{dc}$$ increases further to 18 T, suggesting some kind of vortex transition. For ac fields of 400 A/m (5 Oe) and higher, the Arrhenius model starts breaking down, at around $$\mu $$ $$_{0} H_{ \mathrm dc}$$ = 2 T. As the dc magnetic flux density increases further, this breakdown becomes significant for $$\mu _{0} H_\mathrm{dc}$$ = 15 and 18 T at ac fields of 400 A/m and higher. Extensive mapping of the de-pinning, or irreversibility, lines shows broad dependence on the magnitude of the ac field, frequency, in addition to the dc magnetic flux density.

Bilateral comparison of DC magnetic flux density between NML-SIRIM and KRISS (P1-APMP.EM-S13)

A bilateral comparison of magnetic flux density has been performed between Korea Research Institute of Standards and Science (KRISS) and National Metrology Laboratory, SIRIM (NML-SIRIM), and registered as APMP.EM-S13 in the BIPM key comparison database. This comparison was piloted by KRISS and the results of the NML-SIRIM were linked to those of the CCEM.M-K1 key comparison through KRISS. The mean value of the coil constant and the uncertainty of the mean reported by both laboratories were used in the calculation of the degree of equivalence (DOE).Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

International comparisons to establish the traceability in the global network of geomagnetic observatories to SI units

The international comparisons in the field of earth-level dc magnetic flux density measurements with the participation of six National Metrology Institutes (NMIs) and four geomagnetic observatories (GMOs) have been carried out in 2013 and 2014 under the auspices of the Regional Metrology Organization Asia Pacific Metrology Programme (APMP). The obtained expanded uncertainty (k = 2) of the weighted mean value of correction values does not exceed 0.1 nT in the range of 20 μT to 100 μT, which was one of the main aims of this comparison.VNIIM (D I Mendeleyev Institute for Metrology) was the pilot laboratory for this comparison registered in the Key Comparison Data Base (KCDB) under index APMP.EM-S14. Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Final report on P1-APMP.EM-S9: VNIIM/KRISS bilateral comparison of DC magnetic flux densityby means of a transfer standard coil

The purpose of this bilateral comparison is to check the conformance of the base quantities of magnetic measurements, DC magnetic flux density and its ratio to a current, as reproduced at VNIIM and KRISS. In these institutes adequate conditions for precise measurements in low magnetic fields are provided and the appropriate equipment for attaining a high level of accuracy is available.The results in this report cover the comparisons of two units, T/A and T, reproduced by the two institutes. The experimental comparison data show good agreement within the estimated uncertainty components of the standards. The coordinated values of the unit of DC magnetic flux density and its ratios to DC current show a standard uncertainty at the level of 1 × 10−6 to 1.2 × 10−6 (k = 1) using the value of the gyromagnetic ratio of the shielded protons γp that was recommended by CODATA in 2010, the experimental determination of the ratio (γ4He/γp) of 4He atoms to protons, and the standards of the two institutes.The results give a basis for carrying out multilateral comparisons of standard quantum magnetometers of metrological institutes in the framework of APMP with participation of geomagnetic observatories, which require the establishment of a unified standard of the unit of DC magnetic flux density. They also show the possibility of decreasing the uncertainty of the determination of the unit of DC magnetic flux density from direct comparisons of standard quantum magnetometers.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by APMP, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Theoretical and Experimental Results of DC and AC Magnetic Flux Transformation Using HTS Superconducting Closed Loop

This paper presents the results of my experiments that may open a new path for advanced applications by using continuous closed superconducting YBCO loops. I examined a novel arrangement of a perfectly closed superconducting loop made of HTS wire in DC and AC flux transformer. I designed a self-limiting transformer with this solution. At the same time I also tested the operation of the continuous YBCO loop developed with my own technology. In the first experiment I used YBCO superconducting rings made from a bulk. Later I used superconducting wire. I could carry out these experiments because earlier I had elaborated the machining of the YBCO bulk and wire.

A New DC-Voltage-Balancing Circuit Including a Single Coupled Inductor for a Five-Level Diode-Clamped PWM Inverter

This paper proposes a new dc-voltage-balancing circuit for a five-level diode-clamped inverter intended for a medium-voltage motor drive with a three-phase diode rectifier used as the front end. This circuit consists of two unidirectional choppers and a single coupled inductor with two galvanically isolated windings. The inductor produces no net dc magnetic flux because the individual dc magnetic fluxes generated by the two windings are canceled out with each other. This makes the inductor compact by a factor of six, compared with the balancing circuit including two noncoupled inductors. Moreover, introducing phase-shift control to the new balancing circuit makes it possible to adjust the midpoint voltage. As a result, the dc mean voltages of all the four split dc capacitors can be balanced, independent of inverter control. Experimental results obtained from a 200-V 5.5-kW downscaled model verify the effectiveness of the new balancing circuit.

Analysis of the Dynamic Behavior of a Self-Commutated BTB System During Line Faults

This paper deals with a 50-MW self-commutated back-to-back (BTB) system intended for power-flow control between two ac transmission networks. It focuses on the dynamic behavior of the BTB system during single-line-to-ground and double-line-to-ground faults. Attention is particularly paid to the dc magnetic flux deviation in the grid and converter transformers, and the circulating current inside the grid transformers, which would produce undesirable effects on the system. Theoretical equations related to the amount of circulating current and the dc magnetic flux deviation are derived. The theoretical results developed in this paper are confirmed by computer simulation.

A DC-Voltage-Balancing Circuit for a Five-Level Diode-Clamped PWM Inverter Intended for Motor Drives

This paper proposes a new dc-voltage-balancing circuit for a five-level diode-clamped inverter intended for a medium-voltage motor drive. This circuit consists of two unidirectional choppers and a single coupled inductor with two galvanically-isolated windings. The dc magnetic fluxes in the magnetic core, which are generated by the two windings, cancel out each other. Therefore, the inductor does not generate any dc-magnetic flux in the magnetic core. This makes the inductor compact by a factor of six compared to previously used balancing circuits containing two non-coupled inductors. Experimental results obtained from a 200-V 5.5-kW downscaled model verify that the dc mean voltages of the four split dc capacitors are balanced well under all operating conditions.

Study of Signal Mechanism Based on Combining Magnetic Flux Leakage and Eddy Current Testing

In order to improve sensitivity through information fusion technology, a combined DC magnetic flux leakage and eddy current testing method is proposed. Experimental results indicate that the inner wall cracks in the steel pipe are detected by eddy current system. In fact, the dilemma between the experimental signal and skin effect principle is obviously. Two factors including permeability and magnetic flux leakage that have influence on eddy current signal are analyzed with finite element method and verification experiments of magnetic source. So the viewpoint, that the signal of the internal crack is caused by eddy current effect may be erroneous. Perturbed magnetic field is analyzed by using equivalent source method. Theoretical analysis shows that magnetic flux leakage produced by the crack is far stronger than perturbed magnetic field induced by eddy current effect. The induced electromotive force is created by the variation of the magnetic flux within the cross section of the pick-up coil when the probe moves along the steel pipe with a crack. The signal produced by eddy current effect is submerged. Therefore, the signal of eddy current probe is induced by magnetic flux leakage produced by the crack. Eddy current testing results of ferromagnetic materials under saturation magnetization should be reinterpreted.

An integrated superconductive magnetic nanosensor for high-sensitivity nanoscaleapplications

An integrated magnetic nanosensor based on a niobium dc SQUID (superconductingquantum interference device) for nanoscale applications is presented. The sensor, having awasher shape with a hole of 200 nm and two Josephson–Dayem nanobridges of80 nm × 100 nm, consists of a Nb(30 nm)/Al(30 nm) bilayer patterned by electron beam lithography (EBL)and shaped by lift-off and reactive ion etch (RIE) processes. The presence of the niobium coils,integrated on-chip and tightly coupled to the SQUID, allows us to easily excite the sensorin order to get the voltage–flux characteristics and to flux bias the SQUID at its optimalpoint. The measurements were performed at liquid helium temperature. A voltage swing of75 µV and a maximum voltage–flux transfer coefficient (responsivity) as high as1 mV/Φ0 were directly measured from the voltage–flux characteristic. The noise measurementswere performed in open loop mode, biasing the SQUID with a dc magneticflux at its maximum responsivity point and using direct-coupled low-noisereadout electronics. A white magnetic flux noise spectral density as low as2.5 μΦ0 Hz−1/2 was achieved, corresponding to a magnetization or spin sensitivity in units of the Bohr magneton of100 spin Hz−1/2. Possible applications of this nanosensor can be envisaged in magnetic detection ofnanoparticles and small clusters of atoms and molecules, in the measurement of nanoobjectmagnetization, and in quantum computing.

Calculation of DC Magnetic Flux Deviation in the Converter-Transformer of a Self-Commutated BTB System During Single-Line-to-Ground Faults

This paper deals with a 50-MW self-commutated Back-To-Back (BTB) system intended for power-flow control between transmission networks. It focuses on the dynamic behavior of the BTB system during single-line-to-ground (SLG) faults that often result in voltage sags. A non-negligible amount of dc magnetic flux deviation appears in the converter-transformers of the BTB system just after the occurrence and restoration of an SLG fault. The dc deviation may bring magnetic flux saturation and an excessive magnetizing current to the transformers. This paper derives theoretical equations related to the dc deviation with reasonable approximation. The theoretical results are confirmed by computer simulation.

An Approach to Eliminating DC Magnetic Flux From the Series Transformer of a Dynamic Voltage Restorer

This paper proposes a control method for eliminating dc magnetic flux from the series transformer of a dynamic voltage restorer. The method is characterized by intentionally injecting no compensating voltage during a one-sixth line cycle (=3.3 ms at 50 Hz). The control method is independent of an initial phase angle of a voltage sag, thus requiring no flux detection. The period, during which no compensating voltage is injected, is one-third as short as that of an existing method. This paper confirms the effectiveness and viability of the proposed method. A 200-V 5-kW laboratory system verifies experimentally that the proposed method brings no dc magnetic flux to the series transformer. Moreover, the proposed method brings a smaller dc voltage drop to the dc load of a three-phase diode rectifier than the existing method does in the same conditions.

PMN-PT single crystal and Terfenol-D alloy magnetoelectric laminated composites for electromagnetic device applications

Magnetoelectric laminated composites of a length-magnetized magnetostrictive Tb0.3Dy0.7Fe1.92 (Terfenol-D) alloy plate sandwiched between two thickness-polarized, electro-parallel-connected piezoelectric 0.7Pb (Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) single crystal plates were fabricated and their converse magnetoelectric properties were evaluated. An electromagnetic control device using a laminated composite as the control element and an Alnico biasing magnet, two Mn-Zn F-yokes and a Mu-metal movable plate as the magnetic circuit was developed and characterized. The distribution of the dc magnetic flux lines and magnetic inductions of the device were analyzed using a finite element method. The quasistatic and dynamic magnetic inductions of the device were measured, together with the generative forces. The results revealed that the device has linear voltage-controlled magnetic inductions in excess of 0.6 G/V with flat responses in the measured frequency range of 0.1-40 kHz and large generative forces over 0.7 N at 160 V at the designated gaps of 1.0-1.2 mm. This coil-free device could be useful in broadband and precision magnetic flux/force control applications with negligible Joule heating losses.

Frequency-Tunable Josephson Junction Resonator for Quantum Computing

We have fabricated and measured a high-Q Josephson junction resonator with a tunable resonance frequency. A dc magnetic flux allows the resonance frequency to be changed by over 10%. Weak coupling to the environment allows a quality factor of ~7000 when on average less than one photon is stored in the resonator. At large photon numbers, the nonlinearity of the Josephson junction creates two stable oscillation states. This resonator can be used as a tool for investigating the quality of Josephson junctions in qubits below the single photon limit, and can be used as a microwave qubit readout at high photon numbers.