The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Steve D Sharples - One of the best experts on this subject based on the ideXlab platform.
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Single Pixel Camera Methodologies for Spatially Resolved Acoustic Spectroscopy
Applied Physics Letters, 2021Co-Authors: Rikesh Patel, Steve D Sharples, Matt Clark, Michael G. SomekhAbstract:Spatially resolved Acoustic Spectroscopy (SRAS) is a laser ultrasound technique used to determine the crystallographic orientation (i.e. microstructure) of materials through the generation and measurement of surface Acoustic wave velocity on a sample. Previous implementations have used a grating pattern imaged onto the surface to control the frequency of the generated wave in a single direction-grain orientation can be computed by acquiring wave velocities in different directions on the surface (gathered by physically rotating the grating pattern). This paper reports an advance to this methodology, inspired by single pixel cameras, using a coded grating pattern, created using a spatial light modulator, to excite surface Acoustic waves in multiple directions simultaneously. This change to the optical arrangement can simplify the overall system alignment, remove mechanical complexities and is well suited for point-by-point full orientation imaging, potentially allowing for faster orientation imaging using SRAS microscopy. Improvements to the robustness of measurement may be expected to extend the applicability of SRAS in the material science field. To demonstrate this methodology, experiments were conducted on isotropic and anisotropic samples.
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Spatially resolved Acoustic Spectroscopy (SRAS) microstructural imaging
2019Co-Authors: Matt Clark, Rikesh Patel, Steve D Sharples, Adam T. Clare, Paul Dryburgh, Don Pieris, Richard J. SmithAbstract:Spatially resolved Acoustic Spectroscopy (SRAS) is an Acoustic microscopy technique that can image the microstructure and measure the crystallographic orientation of grains or crystals in the material.It works by measuring the velocity of surface Acoustic waves (SAWs) via the Acoustic spectrum. In the usual configuration, the SAWs are generated by laser using a pattern of lines and detected by laser at a point close to this grating-like source. The use of the Acoustic spectrum as a means of measuring the velocity has a number of practical advantages which makes the technique robust and fast and gives good spatial resolution. This makes the measurement suitable for imaging and gives it many advantages over traditional laser UT and microstructural measurement techniques.As SRAS is a laser ultrasound testing technique (LUT) which can be applied to a wide range of industrially relevant samples as a non-destructive evaluation technique. There are no size limitations on the samples that can be imaged and the surface preparation required is significantly more relaxed than many other techniques with the capability of operating on many as manufactured finishes. This permits the use of SRAS as an online inspection tool, for instance during additive or subtractive manufacturing, as a QA tool during manufacture or as an NDE/T tool in service.Spatially resolved Acoustic Spectroscopy (SRAS) is an Acoustic microscopy technique that can image the microstructure and measure the crystallographic orientation of grains or crystals in the material.It works by measuring the velocity of surface Acoustic waves (SAWs) via the Acoustic spectrum. In the usual configuration, the SAWs are generated by laser using a pattern of lines and detected by laser at a point close to this grating-like source. The use of the Acoustic spectrum as a means of measuring the velocity has a number of practical advantages which makes the technique robust and fast and gives good spatial resolution. This makes the measurement suitable for imaging and gives it many advantages over traditional laser UT and microstructural measurement techniques.As SRAS is a laser ultrasound testing technique (LUT) which can be applied to a wide range of industrially relevant samples as a non-destructive evaluation technique. There are no size limitations on the samples that can be imaged and the su...
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Orientation imaging of macro-sized polysilicon grains on wafers using spatially resolved Acoustic Spectroscopy
Scripta Materialia, 2017Co-Authors: Rikesh Patel, Steve D Sharples, Wenqi Li, Richard J. Smith, Matt ClarkAbstract:Due to its economical production process polysilicon, or multicrystalline silicon, is widely used to produce solar cell wafers. However, the conversion efficiencies are often lower than equivalent monocrystalline or thin film cells, with the structure and orientation of the silicon grains strongly linked to the efficiency. We present a non-destructive laser ultrasonic inspection technique, capable of characterising large (52 × 76 mm2) photocell's microstructure - measurement times, sample surface preparation and system upgrades for silicon scanning are discussed. This system, known as spatially resolved Acoustic Spectroscopy (SRAS) could be used to optimise the polysilicon wafer production process and potentially improve efficiency.
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Spatially resolved Acoustic Spectroscopy for selective laser melting
Journal of Materials Processing Technology, 2016Co-Authors: Richard J. Smith, Matthias Hirsch, Rikesh Patel, Adam T. Clare, Wenqi Li, Steve D SharplesAbstract:Additive manufacturing (AM) is a manufacturing technique that typically builds parts layer by layer, for example, in the case of selective laser melted (SLM) material by fusing layers of metal powder. This allows the construction of complex geometry parts, which, in some cases cannot be made by traditional manufacturing routes. Complex parts can be difficult to inspect for material conformity and defects which are limiting widespread adoption especially in high performance arenas. Spatially resolved Acoustic Spectroscopy (SRAS) is a technique for material characterisation based on robustly measuring the surface Acoustic wave velocity. Here the SRAS technique is applied to prepare additively manufactured material to measure the material properties and identify defects. Results are presented tracking the increase in the measured velocity with the build power of the selective laser melting machine. Surface and subsurface defect measurements (to a depth of ∼24 μm) are compared to electron microscopy and X-ray computed tomography. It has been found that pore size remains the same for 140 W to 190 W melting power (mean: 115-119 μm optical and 134-137 μm velocity) but the number of pores increase significantly (70-126 optical, 95-182 velocity) with lower melting power, reducing overall material density.
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Spatially resolved Acoustic Spectroscopy for rapid imaging of material microstructure and grain orientation
Measurement Science and Technology, 2014Co-Authors: Richard J. Smith, Jethro Coulson, Matt Clark, Wenqi Li, Michael G. Somekh, Steve D SharplesAbstract:Measuring the grain structure of aerospace materials is very important to understand their mechanical properties and in-service performance. Spatially resolved Acoustic Spectroscopy is an Acoustic technique utilizing surface Acoustic waves to map the grain structure of a material. When combined with measurements in multiple Acoustic propagation directions, the grain orientation can be obtained by fitting the velocity surface to a model. The new instrument presented here can take thousands of Acoustic velocity measurements per second. The spatial and velocity resolution can be adjusted by simple modification to the system; this is discussed in detail by comparison of theoretical expectations with experimental data.
Milan Timko - One of the best experts on this subject based on the ideXlab platform.
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Acoustic Spectroscopy of functionalized carbon nanotubes in magnetic fluid
Journal of Magnetism and Magnetic Materials, 2020Co-Authors: Jozef Kúdelčík, Peter Bury, Peter Kopcansky, Milan Timko, Stefan Hardoň, Zuzana MitróováAbstract:Abstract Acoustic Spectroscopy is used to study the rearrangements of multi-walled carbon nanotubes (MWCNTs) functionalized by Fe3O4 magnetic nanoparticles dissolved in transformer oil under the influence of a magnetic field at various temperatures. Three methods for the application of the magnetic field are used: a jump change, a linear increase or decrease and a constant magnetic field with a change of its orientation to the Acoustic wave. The rearrangements of MWCNTs/Fe3O4 to new structures (chains) by the influence of a magnetic field is confirmed by changes in the Acoustic attenuation. From the measurement results, the lifetime of the chains after the switch-off of the magnetic field is less than 30 s. Such a rapid change is due to the fact that the nanotube chains are held by magnetic forces, resulting from the same direction of the magnetic moments of bound magnetic nanoparticles. A temperature-dependent hysteresis effect is observed with a linear change of the magnetic field. From our experiments, it follows that the reorientation of MWCNTs by magnetic nanoparticles with the magnetic field was gradual. The effect of the anisotropy of the Acoustic attenuation is observed at a magnetic flux density of 200 mT and at various temperatures. Three MWCNT/Fe3O4 concentrations diluted in the transformer oil are used for the measurements and their influences on the structural changes with various developments of the magnetic field are discussed.
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Study of structural arrangement in ferrofluid by dielectric and Acoustic Spectroscopy
2018 ELEKTRO, 2018Co-Authors: Stefan Hardon, Peter Bury, Milan Timko, Jozef Kúdelčík, Michal Rajnak, Peter KopcanskyAbstract:In the paper two methods of investigation of ferrofluid in magnetic and electric fields were used, namely the Acoustic and the dielectric Spectroscopy. The measurements were done at temperature 15 °C. The effect of structural changes in ferrofluid upon the effect of a magnetic field by the Acoustic Spectroscopy was studied. At jump change of the magnetic field to 100, 200 and 300 mT a continuous change of the Acoustic attenuation caused by an aggregation of magnetic nanoparticles to new structures was observed. The changes in dielectric parameters and structural arrangement of magnetic nanoparticles in ferrofluid upon the effect of magnetic and electric fields have been studied by the dielectric Spectroscopy, too. The frequency dependence of dissipation factor was measured by a capacitance method within the frequency range from 1 mHz to 10 kHz at the application of a magnetic and an electric fields. The magneto-dielectric effect was also observed.
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Acoustic Spectroscopy of magnetic fluids based on transformer oil
Journal of Intelligent Material Systems and Structures, 2016Co-Authors: Jozef Kúdelčík, Peter Bury, Peter Kopcansky, Stefan Hardoň, Milan TimkoAbstract:The structural changes in a magnetic fluid (formation of clusters) upon the effect of an external magnetic field were studied by Acoustic Spectroscopy. The properties of magnetic fluid dispersed in inhibited transformer oil ITO 100 have been studied by the analysis of changes in the Acoustic wave absorption coefficient. The absorption coefficient of Acoustic waves was measured as a function of an external magnetic field in the range of 0-400 mT, parallel to the direction of Acoustic wave propagation. The magnetic fluids change their structure under the influence of an external magnetic field and do not return immediately to the initial state after the magnetic field switching off. It is supposed that the cluster of magnetic nanoparticles formed in the fluid subjected to a magnetic field remains after the field has been removed for the some time.
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Structure of transformer oil-based magnetic fluids studied using Acoustic Spectroscopy
Journal of Magnetism and Magnetic Materials, 2013Co-Authors: Jozef Kúdelčík, Jozef Drga, Vlasta Závišová, Peter Bury, Peter Kopcansky, Milan TimkoAbstract:The structural changes in transformer oil-based magnetic fluids upon the effect of an external magnetic field and temperature were studied by Acoustic Spectroscopy. The attenuation of Acoustic wave was measured as a function of the magnetic field in the range of 0-300 mT and in the temperature range of 15-35 °C for various magnetic nanoparticles concentrations. The effect of anisotropy of the Acoustic attenuation was determined, too. The both strong influence of the magnetic field on the Acoustic attenuation and its hysteresis were observed. When a magnetic field is increased, the interaction between the external magnetic field and the magnetic moments of the nanoparticles occurs, leading to the aggregation of magnetic nanoparticles and following clusters formation. However, the temperature of magnetic fluids also has very important influence on the structural changes because of the mechanism of thermal motion that acts against the cluster creation. The observed influences of both magnetic field and temperature on the investigated magnetic fluid structure are discussed.
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The anisotropy of transformer oil-based magnetic fluids studied by Acoustic Spectroscopy
2012 ELEKTRO, 2012Co-Authors: Jozef Kúdelčík, Jozef Drga, Vlasta Závišová, Peter Bury, Peter Kopcansky, Milan TimkoAbstract:The anisotropy in transformer oil-based magnetic fluids upon the effect of an external magnetic field and temperature were studied by Acoustic Spectroscopy. When a magnetic field is increased, the interaction between the external magnetic field and the magnetic moments of the nanoparticles occurs, leads to the aggregation of magnetic nanoparticles and following clusters formation. However, the temperature of magnetic fluids has also very important influence on the structural changes because of the mechanism of thermal motion that acts against the cluster creation. In present the anisotropy of the transformer oil-based magnetic fluids can be described by two theories. Taketomi theory assumes existence of spherical clusters. These cluster form long chains, aligned in magnetic field direction. Later Shliomis proposed similar theory, in which these chains are formed by nanoparticles. A comparison of the experimental results with the predictions of the Taketomi theory allowed a determination of the cluster radius and the number density of the colloidal particles. These data allowed us to draw conclusions about the changes in the parameters describing the structure of the ferrofluid at different temperatures. On the basis of the measurements performed, it was possible to establish the proportion of the Acoustic wave used for excitation of the translational and rotational degrees of freedom.
Jozef Kúdelčík - One of the best experts on this subject based on the ideXlab platform.
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Acoustic Spectroscopy of functionalized carbon nanotubes in magnetic fluid
Journal of Magnetism and Magnetic Materials, 2020Co-Authors: Jozef Kúdelčík, Peter Bury, Peter Kopcansky, Milan Timko, Stefan Hardoň, Zuzana MitróováAbstract:Abstract Acoustic Spectroscopy is used to study the rearrangements of multi-walled carbon nanotubes (MWCNTs) functionalized by Fe3O4 magnetic nanoparticles dissolved in transformer oil under the influence of a magnetic field at various temperatures. Three methods for the application of the magnetic field are used: a jump change, a linear increase or decrease and a constant magnetic field with a change of its orientation to the Acoustic wave. The rearrangements of MWCNTs/Fe3O4 to new structures (chains) by the influence of a magnetic field is confirmed by changes in the Acoustic attenuation. From the measurement results, the lifetime of the chains after the switch-off of the magnetic field is less than 30 s. Such a rapid change is due to the fact that the nanotube chains are held by magnetic forces, resulting from the same direction of the magnetic moments of bound magnetic nanoparticles. A temperature-dependent hysteresis effect is observed with a linear change of the magnetic field. From our experiments, it follows that the reorientation of MWCNTs by magnetic nanoparticles with the magnetic field was gradual. The effect of the anisotropy of the Acoustic attenuation is observed at a magnetic flux density of 200 mT and at various temperatures. Three MWCNT/Fe3O4 concentrations diluted in the transformer oil are used for the measurements and their influences on the structural changes with various developments of the magnetic field are discussed.
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Study of structural arrangement in ferrofluid by dielectric and Acoustic Spectroscopy
2018 ELEKTRO, 2018Co-Authors: Stefan Hardon, Peter Bury, Milan Timko, Jozef Kúdelčík, Michal Rajnak, Peter KopcanskyAbstract:In the paper two methods of investigation of ferrofluid in magnetic and electric fields were used, namely the Acoustic and the dielectric Spectroscopy. The measurements were done at temperature 15 °C. The effect of structural changes in ferrofluid upon the effect of a magnetic field by the Acoustic Spectroscopy was studied. At jump change of the magnetic field to 100, 200 and 300 mT a continuous change of the Acoustic attenuation caused by an aggregation of magnetic nanoparticles to new structures was observed. The changes in dielectric parameters and structural arrangement of magnetic nanoparticles in ferrofluid upon the effect of magnetic and electric fields have been studied by the dielectric Spectroscopy, too. The frequency dependence of dissipation factor was measured by a capacitance method within the frequency range from 1 mHz to 10 kHz at the application of a magnetic and an electric fields. The magneto-dielectric effect was also observed.
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Acoustic Spectroscopy of magnetic fluids based on transformer oil
Journal of Intelligent Material Systems and Structures, 2016Co-Authors: Jozef Kúdelčík, Peter Bury, Peter Kopcansky, Stefan Hardoň, Milan TimkoAbstract:The structural changes in a magnetic fluid (formation of clusters) upon the effect of an external magnetic field were studied by Acoustic Spectroscopy. The properties of magnetic fluid dispersed in inhibited transformer oil ITO 100 have been studied by the analysis of changes in the Acoustic wave absorption coefficient. The absorption coefficient of Acoustic waves was measured as a function of an external magnetic field in the range of 0-400 mT, parallel to the direction of Acoustic wave propagation. The magnetic fluids change their structure under the influence of an external magnetic field and do not return immediately to the initial state after the magnetic field switching off. It is supposed that the cluster of magnetic nanoparticles formed in the fluid subjected to a magnetic field remains after the field has been removed for the some time.
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Study of structural changes in magneto-rheological fluids by Acoustic Spectroscopy
ELEKTRO 2016 - 11th International Conference Proceedings, 2016Co-Authors: Jozef Kúdelčík, Peter Bury, Stefan Hardoň, Michal Sedlačík, Miroslav MrlíkAbstract:© 2016 IEEE.The changes in structural arrangement in silicon oil based magneto-rheological fluids with carbonyl iron particles upon the effect of an external magnetic were studied by Acoustic Spectroscopy. The attenuation of Acoustic waves was measured for a jump change of the magnetic field at temperature 20 °C for various magnetic particles concentrations. The relaxation effects for the Acoustic attenuation after switching off the magnetic field and its decrease to the same value as for clean synthetic oil were observed. The change in attenuation coefficients of Acoustic waves in magneto-rheological fluid versus angle between the wave vector and direction of the applied magnetic field has been measured, too. From the measured anisotropy of attenuation coefficient structural change of magneto-rheological fluid in the magnetic field is evident. The observed influences of the magnetic field and concentration on the investigated liquids structure are discussed.
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Structure of transformer oil-based magnetic fluids studied using Acoustic Spectroscopy
Journal of Magnetism and Magnetic Materials, 2013Co-Authors: Jozef Kúdelčík, Jozef Drga, Vlasta Závišová, Peter Bury, Peter Kopcansky, Milan TimkoAbstract:The structural changes in transformer oil-based magnetic fluids upon the effect of an external magnetic field and temperature were studied by Acoustic Spectroscopy. The attenuation of Acoustic wave was measured as a function of the magnetic field in the range of 0-300 mT and in the temperature range of 15-35 °C for various magnetic nanoparticles concentrations. The effect of anisotropy of the Acoustic attenuation was determined, too. The both strong influence of the magnetic field on the Acoustic attenuation and its hysteresis were observed. When a magnetic field is increased, the interaction between the external magnetic field and the magnetic moments of the nanoparticles occurs, leading to the aggregation of magnetic nanoparticles and following clusters formation. However, the temperature of magnetic fluids also has very important influence on the structural changes because of the mechanism of thermal motion that acts against the cluster creation. The observed influences of both magnetic field and temperature on the investigated magnetic fluid structure are discussed.
Matt Clark - One of the best experts on this subject based on the ideXlab platform.
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Single Pixel Camera Methodologies for Spatially Resolved Acoustic Spectroscopy
Applied Physics Letters, 2021Co-Authors: Rikesh Patel, Steve D Sharples, Matt Clark, Michael G. SomekhAbstract:Spatially resolved Acoustic Spectroscopy (SRAS) is a laser ultrasound technique used to determine the crystallographic orientation (i.e. microstructure) of materials through the generation and measurement of surface Acoustic wave velocity on a sample. Previous implementations have used a grating pattern imaged onto the surface to control the frequency of the generated wave in a single direction-grain orientation can be computed by acquiring wave velocities in different directions on the surface (gathered by physically rotating the grating pattern). This paper reports an advance to this methodology, inspired by single pixel cameras, using a coded grating pattern, created using a spatial light modulator, to excite surface Acoustic waves in multiple directions simultaneously. This change to the optical arrangement can simplify the overall system alignment, remove mechanical complexities and is well suited for point-by-point full orientation imaging, potentially allowing for faster orientation imaging using SRAS microscopy. Improvements to the robustness of measurement may be expected to extend the applicability of SRAS in the material science field. To demonstrate this methodology, experiments were conducted on isotropic and anisotropic samples.
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Spatially resolved Acoustic Spectroscopy (SRAS) microstructural imaging
2019Co-Authors: Matt Clark, Rikesh Patel, Steve D Sharples, Adam T. Clare, Paul Dryburgh, Don Pieris, Richard J. SmithAbstract:Spatially resolved Acoustic Spectroscopy (SRAS) is an Acoustic microscopy technique that can image the microstructure and measure the crystallographic orientation of grains or crystals in the material.It works by measuring the velocity of surface Acoustic waves (SAWs) via the Acoustic spectrum. In the usual configuration, the SAWs are generated by laser using a pattern of lines and detected by laser at a point close to this grating-like source. The use of the Acoustic spectrum as a means of measuring the velocity has a number of practical advantages which makes the technique robust and fast and gives good spatial resolution. This makes the measurement suitable for imaging and gives it many advantages over traditional laser UT and microstructural measurement techniques.As SRAS is a laser ultrasound testing technique (LUT) which can be applied to a wide range of industrially relevant samples as a non-destructive evaluation technique. There are no size limitations on the samples that can be imaged and the surface preparation required is significantly more relaxed than many other techniques with the capability of operating on many as manufactured finishes. This permits the use of SRAS as an online inspection tool, for instance during additive or subtractive manufacturing, as a QA tool during manufacture or as an NDE/T tool in service.Spatially resolved Acoustic Spectroscopy (SRAS) is an Acoustic microscopy technique that can image the microstructure and measure the crystallographic orientation of grains or crystals in the material.It works by measuring the velocity of surface Acoustic waves (SAWs) via the Acoustic spectrum. In the usual configuration, the SAWs are generated by laser using a pattern of lines and detected by laser at a point close to this grating-like source. The use of the Acoustic spectrum as a means of measuring the velocity has a number of practical advantages which makes the technique robust and fast and gives good spatial resolution. This makes the measurement suitable for imaging and gives it many advantages over traditional laser UT and microstructural measurement techniques.As SRAS is a laser ultrasound testing technique (LUT) which can be applied to a wide range of industrially relevant samples as a non-destructive evaluation technique. There are no size limitations on the samples that can be imaged and the su...
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Orientation imaging of macro-sized polysilicon grains on wafers using spatially resolved Acoustic Spectroscopy
Scripta Materialia, 2017Co-Authors: Rikesh Patel, Steve D Sharples, Wenqi Li, Richard J. Smith, Matt ClarkAbstract:Due to its economical production process polysilicon, or multicrystalline silicon, is widely used to produce solar cell wafers. However, the conversion efficiencies are often lower than equivalent monocrystalline or thin film cells, with the structure and orientation of the silicon grains strongly linked to the efficiency. We present a non-destructive laser ultrasonic inspection technique, capable of characterising large (52 × 76 mm2) photocell's microstructure - measurement times, sample surface preparation and system upgrades for silicon scanning are discussed. This system, known as spatially resolved Acoustic Spectroscopy (SRAS) could be used to optimise the polysilicon wafer production process and potentially improve efficiency.
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Spatially resolved Acoustic Spectroscopy for rapid imaging of material microstructure and grain orientation
Measurement Science and Technology, 2014Co-Authors: Richard J. Smith, Jethro Coulson, Matt Clark, Wenqi Li, Michael G. Somekh, Steve D SharplesAbstract:Measuring the grain structure of aerospace materials is very important to understand their mechanical properties and in-service performance. Spatially resolved Acoustic Spectroscopy is an Acoustic technique utilizing surface Acoustic waves to map the grain structure of a material. When combined with measurements in multiple Acoustic propagation directions, the grain orientation can be obtained by fitting the velocity surface to a model. The new instrument presented here can take thousands of Acoustic velocity measurements per second. The spatial and velocity resolution can be adjusted by simple modification to the system; this is discussed in detail by comparison of theoretical expectations with experimental data.
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Frequency spectrum spatially resolved Acoustic Spectroscopy for microstructure imaging
Journal of Physics: Conference Series, 2011Co-Authors: Steve D Sharples, Matt Clark, Michael G. SomekhAbstract:The microstructure of a material influences the characteristics of a component such as its strength and stiffness. A previously described laser ultrasonic technique known as spatially resolved Acoustic Spectroscopy (SRAS) can image surface microstructure, using the local surface Acoustic wave (SAW) velocity as a contrast mechanism. The technique is robust and tolerant of Acoustic aberrations. Compared to other existing methods such as electron backscattered diffraction, SRAS is completely non-contact, non-destructive (as samples do not need to be polished and sectioned), fast, and is capable of inspecting very large components. The SAW velocity, propagating in multiple directions, can in theory be used to determine the crystallographic orientation of grains. SRAS can be implemented by using a fixed grating period with a broadband laser excitation source; the velocity is determined by analysing the measured frequency spectrum. Experimental results acquired using this "frequency spectrum SRAS" (f-SRAS) method are presented. The instrumentation has been improved such that velocity data can be acquired at 1000 points per second. The results are illustrated as velocity maps of material microstructure in two orthogonal directions. We compare velocities measured in multiple propagation direction with those predicted by the numerical model, for several cubic crystals of known orientations.
Michael G. Somekh - One of the best experts on this subject based on the ideXlab platform.
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Single Pixel Camera Methodologies for Spatially Resolved Acoustic Spectroscopy
Applied Physics Letters, 2021Co-Authors: Rikesh Patel, Steve D Sharples, Matt Clark, Michael G. SomekhAbstract:Spatially resolved Acoustic Spectroscopy (SRAS) is a laser ultrasound technique used to determine the crystallographic orientation (i.e. microstructure) of materials through the generation and measurement of surface Acoustic wave velocity on a sample. Previous implementations have used a grating pattern imaged onto the surface to control the frequency of the generated wave in a single direction-grain orientation can be computed by acquiring wave velocities in different directions on the surface (gathered by physically rotating the grating pattern). This paper reports an advance to this methodology, inspired by single pixel cameras, using a coded grating pattern, created using a spatial light modulator, to excite surface Acoustic waves in multiple directions simultaneously. This change to the optical arrangement can simplify the overall system alignment, remove mechanical complexities and is well suited for point-by-point full orientation imaging, potentially allowing for faster orientation imaging using SRAS microscopy. Improvements to the robustness of measurement may be expected to extend the applicability of SRAS in the material science field. To demonstrate this methodology, experiments were conducted on isotropic and anisotropic samples.
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Spatially resolved Acoustic Spectroscopy for rapid imaging of material microstructure and grain orientation
Measurement Science and Technology, 2014Co-Authors: Richard J. Smith, Jethro Coulson, Matt Clark, Wenqi Li, Michael G. Somekh, Steve D SharplesAbstract:Measuring the grain structure of aerospace materials is very important to understand their mechanical properties and in-service performance. Spatially resolved Acoustic Spectroscopy is an Acoustic technique utilizing surface Acoustic waves to map the grain structure of a material. When combined with measurements in multiple Acoustic propagation directions, the grain orientation can be obtained by fitting the velocity surface to a model. The new instrument presented here can take thousands of Acoustic velocity measurements per second. The spatial and velocity resolution can be adjusted by simple modification to the system; this is discussed in detail by comparison of theoretical expectations with experimental data.
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Frequency spectrum spatially resolved Acoustic Spectroscopy for microstructure imaging
Journal of Physics: Conference Series, 2011Co-Authors: Steve D Sharples, Matt Clark, Michael G. SomekhAbstract:The microstructure of a material influences the characteristics of a component such as its strength and stiffness. A previously described laser ultrasonic technique known as spatially resolved Acoustic Spectroscopy (SRAS) can image surface microstructure, using the local surface Acoustic wave (SAW) velocity as a contrast mechanism. The technique is robust and tolerant of Acoustic aberrations. Compared to other existing methods such as electron backscattered diffraction, SRAS is completely non-contact, non-destructive (as samples do not need to be polished and sectioned), fast, and is capable of inspecting very large components. The SAW velocity, propagating in multiple directions, can in theory be used to determine the crystallographic orientation of grains. SRAS can be implemented by using a fixed grating period with a broadband laser excitation source; the velocity is determined by analysing the measured frequency spectrum. Experimental results acquired using this "frequency spectrum SRAS" (f-SRAS) method are presented. The instrumentation has been improved such that velocity data can be acquired at 1000 points per second. The results are illustrated as velocity maps of material microstructure in two orthogonal directions. We compare velocities measured in multiple propagation direction with those predicted by the numerical model, for several cubic crystals of known orientations.
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MICROSTRUCTURE IMAGING USING FREQUENCY SPECTRUM SPATIALLY RESOLVED Acoustic Spectroscopy (F‐SRAS)
2010Co-Authors: Steve D Sharples, Matt Clark, Michael G. SomekhAbstract:Material microstructure can have a profound effect on the mechanical properties of a component, such as strength and resistance to creep and fatigue. SRAS—spatially resolved Acoustic Spectroscopy—is a laser ultrasonic technique which can image microstructure using highly localized surface Acoustic wave (SAW) velocity as a contrast mechanism, as this is sensitive to crystallographic orientation. The technique is noncontact, nondestructive, rapid, can be used on large components, and is highly tolerant of Acoustic aberrations. Previously, the SRAS technique has been demonstrated using a fixed frequency excitation laser and a variable grating period (к‐vector) to determine the most efficiently generated SAWs, and hence the velocity. Here, we demonstrate an implementation which uses a fixed grating period with a broadband laser excitation source. The velocity is determined by analyzing the measured frequency spectrum. Experimental results using this “frequency spectrum SRAS” (f‐SRAS) method are presented. Ima...
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Frequency spectrum spatially resolved Acoustic Spectroscopy for microstructure imaging
2009 IEEE International Ultrasonics Symposium, 2009Co-Authors: Wenqi Li, Steve D Sharples, Matt Clark, Michael G. SomekhAbstract:The microstructure of a material influences the characteristics of a component such as its strength and stiffness. A previously described laser ultrasonic technique known as spatially resolved Acoustic Spectroscopy (SRAS) can image surface microstructure, using the local surface Acoustic wave (SAW) velocity as a contrast mechanism. The technique is robust and tolerant of Acoustic aberrations. Compared to other existing methods such as electron backscatter diffraction, SRAS is completely noncontact, nondestructive (as samples do not need to be polished and sectioned), fast, and is capable of inspecting very large components. The SAW velocity, propagating in multiple directions, can be used to determine the crystallographic orientation of grains. Previously, the method used a fixed frequency laser and variable grating period (k-vector) to determine the most efficiently generated surface waves, and hence the velocity. However, SRAS can also be implemented by using a fixed grating period with a broadband laser excitation source; the velocity is determined by analyzing the measured frequency spectrum. In this paper, experimental results acquired using this ¿frequency spectrum SRAS¿ (f-SRAS) method are presented for the first time. The results are illustrated as velocity maps of material microstructure in two orthogonal directions. The two different ways of performing SRAS measurements - f-SRAS and k-SRAS - are compared, and excellent agreement is observed. Furthermore, f-SRAS is much simpler, and is potentially much more rapid than k-SRAS because it can determine the velocity at each sample point in one single shot from the laser rather than scanning the grating period.
