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Michael Nierla

Bio: Michael Nierla is an academic researcher from University of Erlangen-Nuremberg. The author has contributed to research in topics: Acoustic microscopy & Transducer. The author has an hindex of 3, co-authored 8 publications receiving 22 citations.

Papers
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Journal ArticleDOI
TL;DR: A seminumerical simulation method called SIRFEM is presented, which enables the efficient prediction of high-frequency transducer outputs and is able to predict reflections at inner structures as well as multiple reflections between those structures and the specimen's surface.
Abstract: We present a seminumerical simulation method called SIRFEM, which enables the efficient prediction of high-frequency transducer outputs. In particular, this is important for acoustic microscopy where the specimen under investigation is immersed in a coupling fluid. Conventional finite-element (FE) simulations for such applications would consume too much computational power due to the required spatial and temporal discretization, especially for the coupling fluid between ultrasonic transducer and specimen. However, FE simulations are in most cases essential to consider the mode conversion at and inside the solid specimen as well as the wave propagation in its interior. SIRFEM reduces the computational effort of pure FE simulations by treating only the solid specimen and a small part of the fluid layer with FE. The propagation in the coupling fluid from transducer to specimen and back is processed by the so-called spatial impulse response (SIR). Through this hybrid approach, the number of elements as well as the number of time steps for the FE simulation can be reduced significantly, as it is presented for an axis-symmetric setup. Three B-mode images of a plane 2-D setup—computed at a transducer center frequency of 20 MHz—show that SIRFEM is, furthermore, able to predict reflections at inner structures as well as multiple reflections between those structures and the specimen’s surface. For the purpose of a pure 2-D setup, the SIR of a curved-line transducer is derived and compared to the response function of a cylindrically focused aperture of negligible extend in the third spatial dimension.

5 citations

Proceedings ArticleDOI
01 Nov 2014
TL;DR: In this paper, a semi-numerical simulation approach, the so-called SIRFEM, is presented to efficiently predict transient output signals of ultrasonic imaging systems operating in pulse-echo mode.
Abstract: A semi-numerical simulation approach, the so-called SIRFEM is presented. This approach can be applied to efficiently predict transient output signals of ultrasonic imaging systems operating in pulse-echo mode. In particular, we concentrate on acoustic microscopes, which exploit ultrasound waves with center frequencies >10 MHz to visualize inner structures of solid specimens. While the ultrasound pulses between ultrasonic transducer and specimen surface are analytically modeled (spatial impulse response), we perform finite element simulations to describe wave propagation in the specimen. As the computed B-mode images for a plastic sample containing various inclusions (e.g., air) demonstrate, SIRFEM provides reliable transducer outputs. This implies that both, reflections at inner structures and multiple reflections between specimen surface and those structures are considered.

5 citations

Journal ArticleDOI
TL;DR: In this article, an iterative finite-element scheme that accounts for the inverse-magnetostrictive (Villari) effect is proposed to optimize the dimensions of inverse-MAGNETOSTrictive microelectromechanical pressure sensors with a view to maximum sensitivity.
Abstract: This paper proposes an iterative finite-element scheme that accounts for the inverse-magnetostrictive (Villari) effect. To do so, the permeability of magnetostrictive materials is updated according to the internal mechanical stress of the material at the end of each iteration step until convergence is reached. VSM measurements of prestressed thin-film samples are used to evaluate the stress-dependent permeability. Using the implemented scheme, it is possible to optimize the dimensions of inverse-magnetostrictive microelectromechanical pressure sensors with a view to maximum sensitivity. Such sensors feature a sandwichlike structure with a planar coil embedded between two magnetostrictive layers. To date, only insufficient simulation results regarding the optimization of such devices have been published. We present the results of simulations incorporating the inverse-magnetostrictive effect that show the influence of the dimensions of single layers on the overall sensitivity.

5 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compared three vector Preisach models with respect to computational efficiency and practical applicability in terms of magnetic polarization curves measured by a vibrating sample magnetometer.
Abstract: Purpose – The numerical computation of magnetization processes in moving and rotating assemblies requires the usage of vector hysteresis models. A commonly used model is the so-called Mayergoyz vector Preisach model, which applies the scalar Preisach model into multiple angles of the halfspace. The usage of several scalar models, which are optionally weighted differently, enables the description of isotropic as well as anisotropic materials. The flexibility is achieved, however, at the cost of multiple scalar model evaluations. For solely isotropic materials, two vector Preisach models, based on an extra rotational operator, might offer a lightweight alternative in terms of evaluation cost. The study aims at comparing the three mentioned models with respect to computational efficiency and practical applicability. Design/methodology/approach – The three mentioned vector Preisach models are compared with respect to their computational costs and their representation of magnetic polarization curves measured by a vector vibrating sample magnetometer. Findings – The results prove the applicability of all three models to practical scenarios and show the higher efficiency of the vector models based on rotational operators in terms of computational time. Originality/value – Although the two vector Preisach models, based on an extra rotational operator, have been proposed in 2012 and 2015, their practical application and inversion has not been tested yet. This paper not only shows the usability of these particular vector Preisach models but also proves the efficiency of a special stageless evaluation approach that was proposed in a former contribution.

3 citations

Journal ArticleDOI
TL;DR: A novel stageless evaluation scheme for a vector Preisach model that exploits rotational operators for the description of vector hysteresis to resolve the discretizational errors that arise during the application of the standard matrix-based implementation ofpreisach-based models.
Abstract: Purpose This paper aims to present a novel stageless evaluation scheme for a vector Preisach model that exploits rotational operators for the description of vector hysteresis. It is meant to resolve the discretizational errors that arise during the application of the standard matrix-based implementation of Preisach-based models. Design/methodology/approach The newly developed evaluation uses a nested-list data structure. Together with an adapted form of the Everett function, it allows to represent both the additional rotational operator and the switching operator of the standard scalar Preisach model in a stageless fashion, i.e. without introducing discretization errors. Additionally, presented updating and simplification rules ensure the computational efficiency of the scheme. Findings A comparison between the stageless evaluation scheme and the commonly used matrix approach reveals not only an improvement in accuracy up to machine precision but, furthermore, a reduction of computational resources. Research limitations/implications The presented evaluation scheme is especially designed for a vector Preisach model, which is based on an additional rotational operator. A direct application to other vector Preisach models that do not rely on rotational operators is not intended. Nevertheless, the presented methodology allows an easy adaption to similar vector Preisach schemes that use modified setting rules for the rotational operator and/or the switching operator. Originality/value Prior to this contribution, the vector Preisach model based on rotational operators could only be evaluated using a matrix-based approach that works with discretized forms of rotational and switching operator. The presented evaluation scheme offers reduced computational cost at much higher accuracy. Therefore, it is of great interest for all users of the mentioned or similar vector Preisach models.

3 citations


Cited by
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Journal ArticleDOI
TL;DR: The fatigue phenomenon in magnetostrictive coating was underlined by characterizing the prepared FeCo thin-film coated magnetic device cyclically and a design of dotted-pattern with Cr transition layer was employed to build the SAW based magnetic-device.
Abstract: Magnetostrictive thin-film coated Surface Acoustic Wave (SAW) devices were promising for sensing magnetic field owing to their superior features as micro-size, fast response, and high sensitivity originated from the magnetostrictive effect. However, the magnetostriction nature in magnetostrictive thin-film causes significantly mechanical fatigue in service, deteriorating the sensor performances. In this work, the fatigue phenomenon in magnetostrictive coating was underlined by characterizing the prepared FeCo thin-film coated magnetic device cyclically. Obvious shedding was observed in FeCo coating after cyclic testing and the magnetic-sensitivity decreases significantly. One of the reasons is the weak adhesion of FeCo thin-film towards the substrate. As an available way allowing enhancement of adhesion, a Cr thin-film was employed as the transition-layer to weaken the mechanical fatigue. However, it accompanied by the issue of the reduced magnetostrictive coefficient and the obstruction in magnetostrain-tranfer to piezoelectric substrate. As a result, the slump in sensitivity was observed. To address such issues, a design of dotted-pattern with Cr transition layer was employed to build the SAW based magnetic-device. High magnetic-sensitivity and excellent long-term stability were achieved because of the release of coercive force in FeCo dots and enhancement of the FeCo adhesion to the substrate.

12 citations

Journal ArticleDOI
TL;DR: The approach presented in this contribution combines the synthetic aperture focusing technique (SAFT) with an iterative inversion scheme to locate and quantify small flaws in a more reliable way to show suitability for large forging inspection.
Abstract: Ultrasonic nondestructive testing of steel forgings aims at the detection and classification of material inhomogeneities to ensure the components fitness for use. Due to the high price and safety critical nature of large forgings for turbomachinery, there is great interest in the application of imaging algorithms to inspection data. However, small flaw indications that cannot be sufficiently resolved have to be characterized using amplitude-based quantification. One such method is the distance gain size method, which converts the maximum echo amplitudes into the diameters of penny-shaped equivalent size reflectors. The approach presented in this contribution combines the synthetic aperture focusing technique (SAFT) with an iterative inversion scheme to locate and quantify small flaws in a more reliable way. Ultrasonic inspection data obtained in a pulse–echo configuration are reconstructed by means of an Synthetic Focusing Technique (SAFT). From the reconstructed data, the amount and approximate location of small flaws are extracted. These predetermined positions, along with the constrained defect model of a penny-shaped crack, provide the initial parametrization for an elastodynamic simulation based on the Kirchhoff approximation. The identification of the optimal parameter set is achieved through an iteratively regularized Gauss–Newton method. By testing the characterization method on a series of flat-bottom holes under laboratory conditions, we demonstrate that the procedure is applicable over a wide range of defect sizes. To show suitability for large forging inspection, we additionally evaluate the inspection data of a large generator shaft forging of 0.6-m diameter.

7 citations

Journal ArticleDOI
TL;DR: This novel concept of wirelessly powered signal regeneration will improve the remote detectability and operation flexibility of various physiological sensors.
Abstract: Chronic pressure monitoring by wireless and batteryless sensors are desirable for maintaining proper function of biomedical implants. Compared to capacitive, piezoelectric, and piezoresistive sensors, inductive sensors are less susceptible to capacitance fluctuation in the environment, and they can convert loading pressure into inductance changes for wireless detection as resonance frequency shifts. However, inductive sensors normally require the use of ferromagnetic materials for frequency tuning; their frequency responses are harder to detect over larger distance separations. Without using ferromagnetic materials, we will utilize two coaxially coupled resonators whose mutual inductance (and thus resonance frequency) is modulated by the thickness of an elastic substrate that can deform under pressure loading. By modifying one of the coupled resonators into a parametric resonator that contains nonlinear capacitors and an extra conductor across its virtual grounds, the sensor can utilize wireless pumping power to enlarge backscattered signals whose peak response frequency is linearly correlated with the loading pressure. This linear relation is observable beyond the near-field region, even though the distance separation between the sensor and the measurement loop is ten-fold the sensor's circuit dimension. This novel concept of wirelessly powered signal regeneration will improve the remote detectability and operation flexibility of various physiological sensors.

7 citations

Journal ArticleDOI
TL;DR: A seminumerical simulation method called SIRFEM is presented, which enables the efficient prediction of high-frequency transducer outputs and is able to predict reflections at inner structures as well as multiple reflections between those structures and the specimen's surface.
Abstract: We present a seminumerical simulation method called SIRFEM, which enables the efficient prediction of high-frequency transducer outputs. In particular, this is important for acoustic microscopy where the specimen under investigation is immersed in a coupling fluid. Conventional finite-element (FE) simulations for such applications would consume too much computational power due to the required spatial and temporal discretization, especially for the coupling fluid between ultrasonic transducer and specimen. However, FE simulations are in most cases essential to consider the mode conversion at and inside the solid specimen as well as the wave propagation in its interior. SIRFEM reduces the computational effort of pure FE simulations by treating only the solid specimen and a small part of the fluid layer with FE. The propagation in the coupling fluid from transducer to specimen and back is processed by the so-called spatial impulse response (SIR). Through this hybrid approach, the number of elements as well as the number of time steps for the FE simulation can be reduced significantly, as it is presented for an axis-symmetric setup. Three B-mode images of a plane 2-D setup—computed at a transducer center frequency of 20 MHz—show that SIRFEM is, furthermore, able to predict reflections at inner structures as well as multiple reflections between those structures and the specimen’s surface. For the purpose of a pure 2-D setup, the SIR of a curved-line transducer is derived and compared to the response function of a cylindrically focused aperture of negligible extend in the third spatial dimension.

5 citations

Journal ArticleDOI
TL;DR: In SSCB-SAFT, the entire imaging procedure is converted to multiple scan-conversion operations of spherical surfaces to speed up the imaging procedure by avoiding the time-consuming computations of root-mean-square distances.
Abstract: Drawing-arc-based synthetic aperture focusing technique (DAB-SAFT) is capable of greatly improving the imaging speed by reinterpreting the focusing process in the forward direction, but it is only suitable for a two-dimensional (2-D) ultrasonic testing. By extending DAB-SAFT to fast 3-D ultrasonic imaging, this paper proposes both spherical scan-conversion-based SAFT and a spherical-surface-conversion-based SAFT (SSCB-SAFT) for a 3-D nondestructive testing. In SSCB-SAFT, the entire imaging procedure is converted to multiple scan-conversion operations of spherical surfaces. To obtain the coordinates of pixels on a given spherical surface, the spherical scan-conversion algorithm is presented based on circular scan conversions to speed up the imaging procedure by avoiding the time-consuming computations of root-mean-square distances. Besides, the performance of DAB-SAFT is further improved based on the relative positions between different scanning positions, which largely reduce the number of circular arc scan-conversion operations. This acceleration strategy is also applicable to SSCB-SAFT. The simulation experiments show that the improved SSCB-SAFT speeds up the imaging procedure four times while maintaining the same results.

5 citations