Hybrid Seminumerical Simulation Scheme to Predict Transducer Outputs of Acoustic Microscopes
01 Feb 2016-IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control (IEEE)-Vol. 63, Iss: 2, pp 275-289
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.
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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
Cites methods from "Hybrid Seminumerical Simulation Sch..."
...present problem, volume discretization-based methods, such as finite element method (FEM) and finite difference time domain (FDTD), are thus deemed suboptimal [22]....
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01 Sep 2016
TL;DR: In this article, a synthetic aperture focusing technique based on a semi-numerical simulation approach (SIRFEM) is proposed to measure the physical dimensions of flaws in solid specimen by pulse-echo mode acoustic microscopy.
Abstract: This contribution is concerned with a technique to precisely measure the physical dimensions of flaws in solid specimen by pulse-echo mode acoustic microscopy. We have implemented a synthetic aperture focusing technique (SAFT), which is based on a semi-numerical simulation approach (SIRFEM). In acoustic microscopy, one normally applies single-element transducers with center frequencies above 10MHz. Due to the very short wavelengths, numerical simulations demand a very fine discretized measurement setup. This would lead to extensive calculation costs. Therefore, we model the sound propagation in the fluid coupling medium between transducer surface and specimen analytically by the spatial impulse response (SIR) method. Only the mechanical wave propagation in the solid specimen is then simulated by a higher-order finite element method (FEM). This coupled SIRFEM method can be used to calculate the RF signal output (i.e., echo data) of ultrasonic transducers. The presented model-based SAFT algorithm is based on an optimized filter-kernel, which is generated by an adapted SIRFEM simulation.
3 citations
Cites methods from "Hybrid Seminumerical Simulation Sch..."
...For this purpose, we used an exemplary Bmode scan generated by a SIRFEM simulation....
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...Therefore, a B-mode scan was simulated by SIRFEM to act as a sample dataset....
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...SIRFEM is exploited to calculate a matched filter kernel for an advanced SAFT algorithm in order to increase the spatial resolution in the B-mode image significantly....
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...The principles of model-based SAFT as well as the underlying SIRFEM simulation approach are presented in Sec....
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...For this purpose, a SIRFEM simulation of a specimen containing a flaw is computed....
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01 Jan 2019
TL;DR: In this article, the basic steps of the Galerkin's method were studied for simulation of piezoelectric sensors and actuators and the coupling of different physical fields was discussed.
Abstract: In this chapter, we will study the fundamentals of the FE method, which are important for simulating the behavior of piezoelectric sensors and actuators The focus lies on linear FE simulations Section 41 deals with the basic steps of the FE method, eg, Galerkin?s method Subsequently, the FE method will be applied to electrostatics (see Sect 42), the mechanical field (see Sect 43), and the acoustic field (see Sect 44) At the end, we will discuss the coupling of different physical fields because this represents a decisive step for reliable FE simulations of piezoelectric sensors and actuators For a better understanding, the chapter also contains several simulation examples
3 citations
TL;DR: In this article, an advanced synthetic aperture focusing technique for acoustic microscopy is presented, which enables an almost precise reconstruction of the reflectivity distribution of both fluid-like and solid specimens.
Abstract: This contribution deals with an advanced synthetic aperture focusing technique for acoustic microscopy, which enables an almost precise reconstruction of the reflectivity distribution of both fluid-like and solid specimen. The presented approach is designed for single-element ultrasonic immersion transducers as they are commonly used in scanning acoustic microscopes. In practice, the resulting images offer at least lateral and axial resolutions of a focused image, which was acquired by a transducer with double center frequency. Moreover, the results show very low side lobe levels and the approach reconstructs the shape of inner defects even in images with present multiple reflections. A comparison with the well-known delay-and-sum technique reveals that the introduced approach offers a significantly more precise reconstruction of the given reflectivity distribution, especially when a complex reflectivity distribution is investigated. The advanced synthetic aperture focusing technique is applied to a generic test samples and to a curved multi-layered compound specimen.
2 citations
01 Jan 2019
TL;DR: In this article, a semi-analytical approach was used to calculate sound fields and electrical transducer outputs for common transducers, e.g., piston-type transducers.
Abstract: This chapter addresses piezoelectric ultrasonic transducers that are specially designed to generate and receive sound waves in fluid media, ie, air or water Moreover, we will also discuss ultrasonic transducers for medical diagnostics Section 71 deals with a semi-analytical approach to calculate sound fields and electrical transducer outputs for common transducer shapes, eg, piston-type transducers In doing so, the complex structure of a piezoelectric ultrasonic transducer is reduced to an active surface, which can generate and receive sound pressure waves The semianalytical approach will be used in Sect 72 to determine sound fields as well as directional characteristics of common transducers Section 73 details the axial and lateral spatial resolution of spherically focused transducers operating in pulse-echo mode In Sect 74, we will study the general structure of piezoelectric ultrasonic transducers This includes single-element transducers, transducer arrays as well as piezoelectric composite transducers Afterward, a simple one-dimensional modeling approach is shown that allows analytical description of basic physical relationships for piezoelectric transducers under consideration of their internal structure Section 76 contains selected examples for piezoelectric ultrasonic transducers Finally, a brief introduction to the fundamental imaging modes of ultrasonic imaging will be given which is an important application of piezoelectric ultrasonic transducers
1 citations
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TL;DR: A cognitive journey towards the reliable simulation of scattering problems using finite element methods, with the pre-asymptotic analysis of Galerkin FEM for the Helmholtz equation with moderate and large wave number forming the core of this book, is described in this article.
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526 citations
TL;DR: This book surveys higher-order finite difference methods and develops various mass-lumped finite element methods for the transient wave equations, and presents the most efficient methods, respecting both accuracy and stability for each sort of problem.
Abstract: Solving efficiently the wave equations involved in modeling acoustic, elastic or electromagnetic wave propagation remains a challenge both for research and industry. To attack the problems coming from the propagative character of the solution, the author constructs higher-order numerical methods to reduce the size of the meshes, and consequently the time and space stepping, dramatically improving storage and computing times. This book surveys higher-order finite difference methods and develops various mass-lumped finite (also called spectral) element methods for the transient wave equations, and presents the most efficient methods, respecting both accuracy and stability for each sort of problem. A central role is played by the notion of the dispersion relation for analyzing the methods. The last chapter is devoted to unbounded domains which are modeled using perfectly matched layer (PML) techniques. Numerical examples are given.
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