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Bandwidth is an important parameter for accelerometers, in some cases, even surpassing sensitivity. However, there are few studies focused on the relationship between bandwidth and environmental conditions in practical application of accelerometers. In this paper, we systematically analyze the influence of environment on the bandwidth of accelerometers, obtaining the amplitude-frequency response curves versus damping ratio and properties of materials, wherein temperature and humidity were found as the two dominant factors that influence the bandwidth of accelerometers. Common temperature and humidity variations can result in bandwidth degradation of about 25% according to our theoretical analysis. The finite element method (FEM) is introduced to verify our theoretical analysis, and the accordance of the FEM simulation results and the theoretical results confirmed the validity of our analysis. Furthermore, a modification design is proposed to compensate for the influence of temperature and humidity on the bandwidth of accelerometers. By choosing materials with an appropriate Young's modulus and coefficient of thermal expansion, the degradation of the bandwidth was substantially diminished by more than one order of magnitude, which can serve as a strong guide for the future realization of accelerometers with a steady and large bandwidth. ispartof: MICROMACHINES vol:12 issue:8 ispartof: location:Switzerland status: published

This paper proposes a novel method for identifying the number and positions of cracks and reconstructing crack shapes. It assumes that two-dimensional scanned eddy-current testing (ECT) signals obtained from a steam generator tube are a picture image, then a template matching method with the help of genetic algorithms predicts the number and positions of cracks. The present method employs the superposition of crack signals and a nonlinear scaling technique of a signal profile on the crack length that are verified by numerical simulation. The number and positions of the cracks are satisfactorily predicted. The crack-shape reconstructions from the predicted positions with the help of inverse analysis are achieved with a satisfactory degree of accuracy.

Eddy current testing (ECT) is a nondestructive testing method for metal materials. Numerical methods are applied to predict the ECT signals, to aid in the design of ECT probes, and to reconstruct crack shapes from their ECT signals. For the testing of nonferromagnetic materials, the high accuracy of some numerical simulation techniques has been demonstrated and several fast computational methods have been presented. However, the numerical calculation of electromagnetic fields in ferromagnetic materials remains a difficult and time-consuming task. Representing cracks in ferromagnetic materials with secondary electric and magnetic sources leads to a fast method for predicting ECT signals as presented in this article. The method developed here, that can be used to treat ferromagnetics, is an extension of the precomputed database approach based on the magnetic vector potential method. With the aid of precomputed databases, ECT signals of different cracks can be computed from changes in the secondary sources in a small region, without considering the geometries of the whole conductor. This results in fewer degrees of freedom than those of typical finite element approaches, and the method provides a forward simulator that is about 80 times faster than the conventional one without loss of accuracy, even in the case of ferromagnetic materials.

This paper demonstrates the crack detection of thick-walled non-magnetic metal plates by eddy current testing, which is difficult because of Kelvin skin effect generally. The purpose of this research is the development of an new eddy current testing probe for cracks in thick-walled plates and crack shapes quantitative evaluation. The probe was designed, based on the numerical computation using 3D fast eddy current code. The advantages of this new probe are strong eddy current on the back of specimens and gentle decrement of eddy current in the thickness direction. Through experiments, we confirmed that this probe can detect the back artificial defect with 0.5 mm thickness on IN-CONEL 718 specimen with 7.0 mm thickness. Reconstruction of crack shapes was performed based on the experimental results with the inverse problem code developed by authors. The length and depth of reconstructed defects approximately agree with those of real crack.

This paper describes the inverse analysis in the frame works of a round-robin test for the testing of steam generator tubes by eddy-current testing (ECT). An ECT probe with high space resolution was newly proposed, for the purpose of better and easier crack shape evaluations. This new probe is applied to the round-robin test pieces including natural crack samples and a multicrack sample. Inverse problems of the crack shape reconstructions are solved by a fast forward simulator and the conjugated gradient method. Experimental ECT signals as well as results of reconstructions are shown. Treatments of a natural crack and multicracks are discussed.

This paper describes a newly developed arrayed multi-coil probe for the testing of steam generator tubes by eddy current testing. Owing to the multi-coil arrangement, it is possible to detect cracks in the whole round of the tube without rotation. Geometry of the probe was decided with the help of numerical simulation, which leads to high detectability of the probe. The signals of this probe were predicted by the edge based finite element method, and comparison between experimental and numerical results showed good agreement. Furthermore, this probe is expected to be convenient to reconstruct the crack shape from its C-scan image.

This paper describes a new method for the simulations of signals noised by the presence of other materials except for test articles in eddy current testing (ECT). In the inspection of steam generator tubes in nuclear power plants, the sensor detects structures, for example support plates to fix the tubes, and deposits adhering to their outside, as well as tube defects. The signals from the structures are thought to be noises when finding the defects. The method developed here is based on a set of governing equations constructed with magnetic vector potentials, introducing a precondition that a small part of the inverse matrix of the coefficient matrix in an algebraic equation from finite elements and the potentials for the unflawed conductor model are stored. Following the reciprocity theorem, an impedance change due to a flaw, as an eddy current signal, can be computed through integration in the flaw region, and unknowns corresponding to the flaw region only are considered. It results in much smaller degrees of freedom than typical finite element approaches require, and the method provides a fast forward simulator. The fast forward simulator is tested with experimental measurements of ECT benchmark problems with noise factors mentioned above, and is compared with a conventional approach from the point of view of computational costs.

This paper demonstrates crack reconstruction from the relative signals, which overlap with noises in eddy current testing. A method for the reconstruction from the signals, a kind of inverse problem, has been developed with fast signal predictions and the steepest descent algorithm. The signal predictions use a pre-computed unflawed database approach based on edge-based finite elements and the reciprocity theorem.This approach makes it possible that the problem domain of an electromagnetic field is reduced to a small region where a crack/cracks possibly exist.In the inspection of steam generator tubes in nuclear power plants, this test detects deposits on the surfaces of thetubes and structures to fix the tubes such as support sheets or plates, and rigs, as well as defects.The signals from the structures are thought to be noises when finding out the defects.Crack profile identification is given from the crack signals with residual noises, which remain after multi-frequency processing of the signals disturbed by the presence of copper/magnetic deposits and support plantes.

This paper demonstrates the identification of crack depths using signals obtained from eddy current testing (ECT). The identification method is based on finite elements with the pre-computed unflawed database approach and a meshless crack representation technique, and parameter estimation in nonlinear problems. Four different cracks are estimated by using laboratory data.

An ECT probe was newly proposed in order to improve space resolution, for the purpose of better and easier crack shape evaluations. This new probe is applied to a round-robin testpieces including natural cracks and multi-crack samples. Experimental results of these samples as well as inversion crack shapes from experimental results are shown in this paper. Treatments of natural cracks and multi-crack are discussed.

In eddy current testing of steam generator tubes, the signals obtained are always noised by many factors because of the complex environment. Some of these noise factors are caused by the support plates, the expansion part of the tube and the tube sheets outside. Previous works show that the noises of support plates can be reduced by a multi-frequency method. However, the elimination of noises from the expansion part of the tube is proved impossible using the multi-frequency method only. A new signal processing method is introduced in this paper by applying a differential filter using the two dimensions scan data. Signal noise ratio (SNR) is increased significantly, even a small signal from outer defects can be recognized. Furthermore, a new method for the crack reconstruction from these noised signals has been developed with a fast signal prediction and the conjugate gradient algorithm considering the outside ferromagnetic structures such as support plates and tube sheets. The electromotive force signals used here for the crack reconstruction are laboratory data obtained by a newly developed four-sensor probe with mutual induction and differential outputs. Shapes of artificial cracks are reconstructed satisfactorily in short CPU time.