Alternative Current Field Research Articles

The effect of current frequency and magnetic field direction in alternative current-field annealing on the GMI and magnetic properties of Co-based wires

The effects of applied current annealing frequency, amplitude and magnetic field direction during alternative current-field annealing on giant magnetoimpedance (GMI) and magnetic properties of Co68.15Fe4.35B12.5Si15 wire have been investigated. This annealing process leads to a complex domain structure because of the existence of the variable internal circumferential field and external static magnetic field. We have demonstrated that the applied current annealing with different frequencies, amplitudes and magnetic field directions can improve the magnetic properties and the GMI response. In the as-quenched wire, GMImax and saturation magnetization (Ms) are equal to 220% and 78.5 emu/g respectively. They grow up to 400% and 87.2 emu/g, respectively, while the amplitude of the 50 Hz annealing current is 400 mA and the applied magnetic field, perpendicular to the wire, cancels out the earth's magnetic field. In contrast, the samples annealed by 50 Hz (500 mA) and 100 kHz (400 mA) alternative currents show GMImax = 50% and 140%, and also Ms = 41.8 and 40.7 emu/g, respectively. Altogether, our results show that alternative current-field annealing at appropriate conditions improves the GMI response and makes the samples more suitable for magnetic sensing.

J053042 誘電泳動の数値解析

In this paper, control of particle trajectory based on dielectrophoresis(DEP) is studied numerically. First alternative electric current field is solved by using conservation equation of electric current in frequency domain. Secondly, particle which is forced by the above mentioned electric field, gravity and Stokes viscous drag, is tracked by using the kinematic equations from Newton's second law. It was found that particle trajectories can be controlled by setting a different phase to the electric potential applied on multi-electrodes.

A fuzzy alignment approach to sizing surface cracks by the AC field measurement technique

In real world applications, one major issue with most of non-phenomenological methods is the need for a large and complete databanks. In most practical cases, it is impossible to obtain a complete and representative database that includes sufficient number of representative examples. This fact renders most of available defects and cracks databases useless. In this paper, an aligning method is formalized by a fuzzy recursive least square algorithm as a learning methodology for electromagnetic alternative current field measurement (ACFM) probe signals of a crack (data). This method along with a set of fuzzy linguistic rules, including adequate adaptation of different crack shapes (knowledge) for combining knowledge and data whenever the superposition theory can be utilized, provide a means to compensate for the lack of sufficient samples in available crack databases. We have shown that the combination of this fuzzy inference method and the method of the adaptation for different crack shapes provides sufficient means as a priori empirical knowledge for the training system. This approach significantly reduces the need for a large and complete crack databases. The validity of the proposed methodology is demonstrated by examining the sizing errors in the case of several surface cracks with elliptical depth profile when inverting their respective ACFM signals.

Removal of Probe Liftoff Effects on Crack Detection and Sizing in Metals by the AC Field Measurement Technique

In the alternative current field measurement (ACFM) technique, the nonzero value of liftoff distance for the magnetic sensor acts as a low-pass filter on surface crack signals, causing errors in crack detection and sizing. We present a blind deconvolution algorithm for liftoff evaluation and surface crack signal restoration. The algorithm employs the available closed-form expressions for the distribution of electromagnetic fields at the metal surface in the vicinity of a crack. To examine the accuracy of the algorithm, we use the original and the restored signals for crack sizing by a wavelet network inversion method. We present simulated and experimental results to demonstrate the role of the proposed algorithm in improving the inversion process.

Using AC field measurement data at an arbitrary liftoff distance to size long surface-breaking cracks in ferrous metals

We propose a model-based inversion method to size long surface-breaking cracks in ferrous metals using alternative current field measurement (ACFM) data at an arbitrary liftoff distance. This method employs conjugate gradients optimization to invert measured surface ACFM signal to crack depth. To alleviate the adverse effect of sensor liftoff uncertainty on crack sizing, we propose a blind de-convolution algorithm for reconstructing respective surface ACFM crack signal. In this algorithm, the partially known filter function associated with the sensor liftoff is estimated from which the surface crack signal can be restored. The validity of the proposed inversion method is demonstrated by comparing the actual and predicted depths of several simulated and machine-made long cracks in mild steel test blocks.

The Quantitative Measurement Model of ACFM Based on Swept Frequency Method

The alternative current field measurement (ACFM) technique is a new non-destructive testing (NDT) method to evaluate the surface flaws, and in contract to other methods it has advantages of non-contacting and non-calibrating. Precise locating and crack length measurement can be easily achieved. But it is rather difficult to measure the crack depth with the complicated mathematic model. Its application is thus limited. On this ground, the swept frequency method is introduced to make up of this shortage. The penetration depth of eddy current that is theoretically different for different operational frequencies is the principle of crack depth measurement of the swept frequency method. By means of measuring the switching-frequency of the characteristic curve, the information of flaw depth is achieved by sweeping frequency. The paper introduced the physical model of ACFM and assayed the errors of measurement. Some methods were introduced to decrease the errors. The crack depth is proportional to the interval of the switching-frequency of flaw and of no-flaw, which is detected at the position of minimum value of Bz.

Effective nonlinear AC response to composite with spherical particles

An effective nonlinear alternative-current (AC) response to granular nonlinear-composite with spherical inclusions embedded in a host medium under the action of an external AC field is investigated by using a perturbation approach. The local potentials of composite at higher harmonics are derived both in a region of local inclusion particles and in a local host region under the action of a sinusoidal field E-1 sin o t + E-3 sin 3o t. An effective nonlinear-response to composite and the relationship between the effective nonlinear-responses at the fundamental frequency and the third harmonics are also studied for the spherical inclusions in a dilute limit.

Single large DNA molecule analysis using fluorescence microscopy

A large DNA analysis method which enable to obtain spatial information of positions of specific sequences along DNA molecule has been developed. Making use of the phenomenon that large DNA molecule is elongated stably under alternative current field in a concentrated linear polymer solution, direct observation of elongated individual lambda DNA molecules with fluorescence probes was carried out using fluorescence microscopy. Then, the spatial positions of the fluorescence spot of the probe on the DNA molecule were determined by image analysis.

The applicability of two computer techniques to separate the remanent magnetization (RM) components acquired in laboratory fields

Thermal remanent magnetization (TRM) and anhysteretic remanent magnetization (ARM) components were imposed on natural rock samples. The artificial laboratory components had different directions and the blocking temperature and/or coercivity spectra were overlapping. Two methods, principal component analysis (PCA) by Kirschvink and analytical modelling of demagnetization data (by Stupavsky and Symons, S&S) were used to resolve these components. The PCA technique calculated lines fitted to the demagnetization path with ASD = 10° (angular standard deviation), and the S&S method used four types of intensity decay curves for calculated components. Both methods (PCA and S&S) resolved perfectly the one-component case. The two- or three-component case results strongly depended on spectra overlapping, and on the angles between component directions and magnetic minerals in samples. Principal component analysis gave more reliable results for separated spectra of TRM and thermally cleaned samples, whereas the S&S technique was more efficient for the case of strong spectra overlapping of ARM components and the alternative current field (AF) demagnetization method. Remarkable anisotropy of RM was observed which influences the results for the haematite-bearing samples.