Leander Claes

Leander Claes
Paderborn University | UPB · Department of Electrical Engineering and Information Technology

Dr.-Ing.

About

65
Publications
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239
Citations

Publications

Publications (65)
Article
Full-text available
In the non-destructive determination of material properties, the utilization of ultrasound has proven to be a viable tool. In the presented paper, a laser is used to create broadband acoustic waves in plate-shaped specimens by applying the photoacoustic effect. The waves are detected using a purpose-built ultrasonic transducer that is based on piez...
Article
Ultrasonic methods are widely established in the NDE/NDT community, where they are mostly used for the detection of flaws and structural damage in various components. A different goal, despite the similar technological approach, is non-destructive material characterization, i.e. the determination of parameters like Young’s modulus. Only few works o...
Article
Full-text available
A measurement procedure using a modified two-chamber pulse-echo experimental setup is presented, enabling acoustic absorption and bulk viscosity (volume viscosity) measurements in liquids up to high temperature and pressure. Acoustic absorption measurements are particularly challenging, since other dissipative effects, such as diffraction at the ac...
Article
Schlieren imaging allows visualising local density modulations in optically transparent media, which enables to analyse ultrasonic wave propagation. In typical measurement setups, spatial filtering is applied. Commonly, phase information of the ultrasonic wave is lost, which e.g. prevents accurate tomographic reconstruction. In this work two method...
Article
In this paper a measurement procedure to identify viscoelastic material parameters of plate-like samples using broadband ultrasonic waves is presented. Ultrasonic Lamb waves are excited via the thermoelastic effect using laser radiation and detected by a piezoelectric transducer. The resulting measurement data is transformed to yield information ab...
Article
The estimation of accurate piezoelectric material parameters is a fundamental prerequisite for simulation-driven design of piezoelectric actuators and sensors. Previous studies show that a full set of material parameters can be determined in an inverse procedure using a single disc-shaped specimen with an electrode structured for increased sensitiv...
Preprint
Full-text available
A model for the generation of heat due to mechanical losses during acoustic wave propagation in a solid is considered in a Kelvin-Voigt type framework. In contrast to previous studies on related thermoviscoelastic models, in line with recent experimental findings the present manuscript focuses on situations in which elastic parameters depend on tem...
Article
Zusammenfassung In diesem Beitrag wird ein Ansatz zur Identifikation eines vollständigen Satzes piezoelektrischer Materialparameter basierend auf der Messung der elektrischen Impedanz anhand eines einzelnen Probekörpers durch Lösung eines inversen Problems vorgestellt. Vorangegangene Arbeiten zeigen, dass die Regularisierung des zur Lösung eingeset...
Article
Guided acoustic waves can be used for a multitude of different testing and material characterisation purposes. The options for evaluation are especially plentiful if a method for broadband excitation, e.g. thermoelastic excitation using focused, pulsed laser radiation, is used, and if the distance between excitation and detection of the acoustic wa...
Article
Simulation-driven design processes of piezoelectric actuators and sensors necessitate precise material parameter knowledge. Historically, the IEEE standard on piezoelectricity is used for this purpose, which proposes an analytical method for material parameter identification based on resonance frequency evaluations. This method requires different i...
Article
Obwohl Ultraschall für den Menschen weder hör- noch sichtbar ist, sind die Einsatzgebiete sehr vielfältig. Daher ist es für die Untersuchung von akustischen Phänomenen und die Analyse von technischen (Ultraschall-)Komponenten von Interesse, die Schallausbreitung darstellen zu können. Eine Methode dazu ist die sogenannte Schlierentechnik, welche in...
Code
Modular field simulation tool using finite differences. Features: One-dimensional, linear acoustic field simulation; two-dimensional, linear acoustic field simulation; axial-symmetric, three-dimensional, linear acoustic field simulation; nonlinear acoustic field simulation in ideal gases; nonlinear acoustic field simulation for arbitrary fluids us...
Article
Schlieren imaging allows visualising local density variations in optically transparent media and is thus also suitable for displaying ultrasonic fields. By applying tomographic reconstruction to multiple two-dimensional schlieren images recorded at different rotation angles, a three-dimensional model of the ultrasonic field can be obtained. Typical...
Article
Full-text available
An inverse measurement procedure for the determination of a full set of piezoelectric material parameters using a single sample is presented. The basis for the measurement procedure is a measurement of the frequency-dependent impedance of the sample. To yield sufficient sensitivity of this measurement with respect to all material parameters (mechan...
Presentation
A requirement for the increasingly simulation-driven design process of piezoelectric actuators and sensors are accurate material parameters. Historically the parameters of piezoelectric materials are determined using the well-known IEEE standard on piezoelectricity. However, the method proposed in this standard, which is an analytical approach base...
Article
Full-text available
An explicit approach using symplectic time integration in conjunction with traditional finite difference spatial derivatives to solve the wave equation in moving media is presented. A simple operator split of this second order wave equation into two coupled first order equations is performed, allowing these split equations to be solved symplectical...
Conference Paper
Full-text available
Schlieren imaging is widely used to visualise local density modulations in optically transparent media, for example to make fluid flow or ultrasonic waves visible. In common schlieren setups, spatial filtering is applied. This is accomplished by a 2 f -arrangement consisting of two lenses, where f is the focal length of the used lenses. Between the...
Article
An approach for the non-destructive characterisation of adhesive bonds using guided ultrasonic waves is presented. Pulsed laser radiation is used to thermoacoustically excite broadband ultrasonic waves in a multi-layered sample, consisting of a metal plate adhesively joined to a polymeric layer using synthetic resin. The resulting signals are recei...
Article
In this paper a measurement procedure is presented to identify both elastic and viscoelastic material parameters of plate-like samples using broadband ultrasonic waves. These Lamb waves are excited via the thermoelastic effect using laser radiation and detected by a piezoelectric transducer. The resulting measurement data is transformed to yield in...
Thesis
Full-text available
The prerequisite for a complete description of fluid dynamic and acoustic processes is that all properties of the fluid are known. While fluid parameters such as the speed of sound or the shear viscosity are known for many liquids over a wide range of thermodynamic states, only limited measurement data exist for the bulk viscosity. In this thesis,...
Article
The progress in numerical methods and simulation tools promotes the use of inverse problems in material characterisation problems. A newly developed procedure can be used to identify the behaviour of piezoce-ramic discs over a wide frequency range using a single specimen via fitting simulated and measured impedances by optimising the underlying mat...
Article
Acoustic waves in plates have proven a viable tool for testing and material characterisation purposes. There are a multitude of options for excitation and detection of theses waves, such as optical and piezoelectric systems. While optical systems, with thermoelastic excitation and interferometric detection, have the benefit of being contactless, th...
Article
The increasingly simulation-driven design process of ultrasonic transducers requires several reliable parameters for the description of the material behaviour. Exact results can only be achieved when a single specimen is used in the identification process, which typically is prone to the problem of low sensitivities to certain material parameters a...
Conference Paper
Electrical engineering, as well as other technical and scientific study programs, typically include laboratory courses in which students work on practical exercises with electronic circuits. Usually, self-contained hardware for each topic being covered is applied. These pre-build electronic circuits are often complex and not easily understandable a...
Preprint
Full-text available
Most measurement methods based on ultrasound, such as sound velocity, absorption or flow measurement systems, require that the acoustic wave propagation is linear. In many cases, linear wave propagation is assumed due to small signal amplitudes or verified, for example, by analysing the received signal spectra for the generation of harmonic frequen...
Conference Paper
The increased number of simulation-driven design processes of ultrasonic transducers requires precise and consistent material parameters in order to obtain reasonable simulation results. An optimised triple-ring electrode set-up for a piezoelectric disc, which often are the active elements in ultrasonic transducers, ensures a sufficient sensitivity...
Conference Paper
Of all fluid and solid properties, quantities that describe losses are among the most challenging to quantify. In part, this is due to superimposed dissipative mechanisms, such as diffraction effects from spatially limited sources. Inherent to all these phenomena, however, is a specific frequency dependence. The nature of the frequency dependence v...
Article
Full-text available
A realistic description of fluid mechanical and acoustic processes requires the volume viscosity of the medium to be known. This work describes how the volume viscosity of pure fluids can be determined by measuring acoustic absorption with the pulse-echo method. The challenge in realizing such a measurement method lies in the separation of the diff...
Conference Paper
Although ultrasonic measurement techniques are widely used in non-destructive detection of material defects, the material parameters are still mostly determined destructively using tensile tests. One non-destructive method is the evaluation of guided ultrasonic waves, whose application on fiber-reinforced composites is also challenging due to their...
Conference Paper
Ultrasonic transducers are used in various industrial and research applications. Their electric impedance is frequency dependent, especially for mechanically undamped transducers. Moreover, the external conditions, such as varying temperature and different target media, affect the behaviour of the transducer. Therefore, an impedance mismatch occurs...
Article
For its usage in simulation-based design processes a precise knowledge of the employed material properties is inevitable. In the case of piezoelectric ceramics, the provided material parameters often suffer from large uncertainties and even inconsistencies since the standardised measurement procedure needs several specimens to determine a single se...
Conference Paper
Full-text available
For a realistic FEM-Simulation of mechanical systems, an accurate knowledge of the material parameters is necessary. Depending on the simulated component, high stresses might need to be considered. They can change the effective material parameters because of the nonlinear strain-stress relation which is normally assumed to be linear by Hook’s law....
Presentation
Full-text available
Um Störungen in Ultraschall-Messsystemen (z. B. für Schallgeschwindigkeitsmessungen) zu vermeiden, müssen Streusignale absorbiert oder gestreut werden. Kommerziell verfügbare Absorber sind typischerweise auf ein spezifisches Fluid, beispielsweise Wasser, und nur auf einen kleinen Temperaturbereich beschränkt. Es gibt jedoch einige Anwendungen, bei...
Conference Paper
Full-text available
Der stetig zunehmende Einsatz faserverstärkter Kunststoffe (FVK) in der Industrie ist eine wesentliche Voraussetzung für moderne Leichtbausysteme. Damit einher geht der Bedarf, diese Materialien messtechnisch zu charakterisieren, damit Bauteile einerseits anwendungsspezifisch optimal ausgelegt und andererseits im Betrieb überwacht werden können. Im...
Article
Data of material properties given by manufacturers of piezoelectric ceramics is often flawed due to, for example, slightly different manufacturing conditions for each production batch. Hence, the need for more reliable data arises. Recently published material parameter estimation methods are based on the solution of an inverse problem fitting imped...
Article
In this paper, a method for the characterisation of orthotropic, plate-shaped material samples is presented. Ultrasonic plate waves are excited at different angles and then detected. Then, a two-dimensional simulation model can be used to inversely estimate a set of material parameters for each angle of propagation. After merging these individual r...
Conference Paper
Full-text available
A complete characterisation of piezo ceramic materials typically requires several differently processed specimen. Since the results of all these measurements are combined to form one single set of material parameters, inconsistencies occur naturally. The problem when considering only one specimen is the lack of sensitivity for several material para...
Conference Paper
Full-text available
We present a non-destructive measurement procedure to obtain material properties on parts manufactured using the Fused-Deposition-Modeling (FDM) method. This manufacturing method leads to an anisotropic structure within the part and possible degradation of the material itself due to high temperatures. Utilizing our measurement setup, we obtain the...
Presentation
Full-text available
Neben der Schallgeschwindigkeit ist der Absorptionskoeffizient ein wichtiger Parameter zur Beschreibung akustischer und thermodynamischer Vorgänge in Fluiden. Obwohl Verfahren zur Messungen der akustischen Absorption bereits in der Vergangenheit beschriebenwurden, vernachlässigen die meisten von ihnen den Einfluss von parasitären dissipativen Wirku...
Conference Paper
Full-text available
Additively manufactured or 3d printed components are commonly used for rapid prototyping or small series production purposes. Their mechanical properties, especially in the acoustic regime, are sparsely researched as of now. Therefore, we present a non-destructive measurement procedure to characterize the properties of additively manufactured compo...
Conference Paper
Full-text available
Next to the sound velocity, the absorption coefficient of acoustic waves in fluids is an important thermodynamic property. Although measurements of acoustic absorption have been conducted in the past, most of them negate the influence of parasitic dissipative effects or rely on either analytical or empirical compensation. A typical method for measu...
Conference Paper
Full-text available
Zur zerstörungsfreien Materialcharakterisierung kann auf ultraschallbasierte Verfahren zurückgegriffen werden. Diese gewinnen zunehmend an Bedeutung im Bereich der Komponentenüberwachung zur Detektion der Alterung oder lokalen Schädigungen z.B. bei Flugzeugen oder Kraftfahrzeugen, aber auch allgemein im Bereich der Materialparameterbestimmung, da d...
Article
Zusammenfassung In diesem Beitrag werden verschiedene Aspekte der ultraschallbasierten Messtechnik hinsichtlich der Materialparameterbestimmung an viskoelastischen Materialien behandelt. Zunächst wird ein viskoelastisches Materialmodell unter Berücksichtigung von Anisotropie und Kausalität erarbeitet. Nachfolgend werden zwei verschiedene Verfahren...
Conference Paper
Full-text available
To prevent errors in ultrasonic measurement systems (e.g. for sound velocity measurements), stray signals have to be absorbed or dispersed. While absorbers are commercially available, they are typically limited to a specific fluid, for example water, and to only a small temperature range. There are, however, some applications where more flexibility...
Conference Paper
Ultrasonic measurement techniques are widely used for non-destructive detection of material defects. However, material properties, such as Young’s modulus, are still mostly determined destructively, especially for materials with high damping or strong anisotropy. One method for non-destructive material characterization creates and detects ultrasoni...
Conference Paper
The membrane-free optical microphone, an alternative concept to measure sound pressure, will be presented. A laser beam, locked to a millimeter-sized Fabry-Pérot interferometer experiences a change in wavelength, if the pressure of the medium and hence the refractive index inside the interferometer is altered by a sound wave. The resulting change i...
Article
Full-text available
For the numerical simulation of acoustic wave propagation in (measurement) systems and their design, the use of reliable material models and material parameters is a central issue. Especially in polymers, acoustic material parameters cannot be evaluated based on quasistatically measured parameters, as are specified in data sheets by the manufacture...
Conference Paper
Full-text available
By examining the propagation characteristics of acoustic waves through a specimen its material properties can be determined. One method to realize such a measurement is the excitation and detection of ultrasonic waves in plate-like waveguide structures. Therefore, a transducer with a small active area is required to detect guided waves with a small...

Questions

Questions (2)
Question
The equation in question is of the form u_xx + a * u_tt + b * u_xxt = 0 and was first published by Stokes in the 19th century but does not seem to haven an established name.
Conversely, the differential equation of the form u_xx + a * u_tt + b * u_xxt + c * u_ttt = 0 has an additional term and is commonly called the Moore–Gibson–Thompson (MGT) equation. It seem kind of strange that this one has been named while the equation with one fewer term has not.
Question
I know it's in Hamilton's Nonlinear Acoustics, but what's the original source?

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