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Steve Sharples

Lecturer, Faculty of Engineering

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Expertise Summary

I have eight years of postdoctoral experience in the fields of laser ultrasonics, acoustic imaging and nondestructive evaluation (NDE) within the Applied Optics Group of the Electrical Systems & Optics Research Division. My research is focused on developing new themes in laser ultrasonic science and technology; in particular, the development of novel instrumentation and sensors applicable to the aerospace sector and advanced manufacturing. I have a unique - and broad - range of knowledge and experience, covering optics, ultrasonics, laser ultrasound techniques, instrumentation, ultrasonic sensors, RF electronic design, circuit layout, basic analogue VLSI design, hardware/software integration and programming. I am the primary laser safety contact within the research division, and I am jointly responsible for class 4 laser safety training.

Research Summary

There are four concurrent themes within my research portfolio:

  1. Nonlinear acoustic measurement techniques for detection of damage precursors: This core project within the RCNDE aims to use ultrasonics to study the relationship between material nonlinearity - essentially the deviation from Hooke's Law, which describes a simple linear relationship between stress and strain - and the level of fatigue experienced by a component through its lifetime. One implementation of this "nonlinear ultrasonic" technique, in which the acoustoelastic coefficient is determined, involves measuring the perturbation of velocity of high frequency laser-generated surface acoustic waves (SAWs) in the presence of a co-propagating low frequency SAW that induces stress in the material. This has involved developing incredibly sensitive instrumentation, that is not only capable of measuring changes in velocity to around one part in 10 6, but also is (a) sufficiently insensitive to temperature fluctuations that would otherwise swamp the measurement, and (b) sufficiently fast enough to permit imaging of material nonlinearity.
  2. SRAS technology demonstrator: I am the principal investigator on an East Midlands Development Agency technology demonstrator project, "SRAS for materials characterisation," continuing development of an instrument capable of rapid, high resolution, non-destructive imaging of the velocity of surface acoustic waves without any measurement perturbation, damage or contamination. I jointly hold a patent for the spatially resolved acoustic spectroscopy (SRAS) technique used, which can image material microstructure and provide other useful characterisation information, such as changes in coating thickness (30nm has been demonstrated). The optics of the SRAS instrument developed as part of this project has a footprint of 30x45cm, as opposed to the previous lab-bound generation (2.5x1.25m) - it is small enough to be transportable, and was recently exhibited (working) at the Let Nano Fly! / Flights of Fancy event at the Nottingham Contemporary, to members of the public. As well as improvements to the instrumentation, fundamental research relating the determination of crystallographic orientation to SAW velocity measurements in multiple propagation directions (via the elastic constants and density) for different crystal structures is ongoing. An exciting possibility is that the elastic moduli and crystallographic orientation could be determined using SRAS, given a number of grains with different orientations and the same moduli. Further development, on both the instrument and fundamentals of relationship between the SAWs and mechanical properties, will be carried out by the EngD student that I will supervise beginning in September 2011.
  3. Nano ultrasonics: I am the researcher on a challenging 2.5 month "nanoSRAS" micro project, funded through the "Let Nano Fly!" CDFA grant. This work investigates methods to overcome the optical diffraction limit which currently limits the spatial resolution of SRAS, and other laser ultrasonic methods of exciting and detecting SAWs. The starting point will be to see whether scanning near-field optical microscopy (SNOM) probes can be used to deliver optics to the sample surface and perform a proof of concept picosecond ultrasonic version of the SRAS measurement using these near-field optics. It should also be possible to photolithographically write features on the nanoscale which, when activated optically using conventional far field optics, will perform localised high frequency ultrasonic generation and detection at acoustic wavelengths shorter than that of light.
  4. Ultrasonic imaging sensor: I invented an adaptive imaging chip capable of remotely detecting ultrasonic waves

Selected Publications

  • SHARPLES, S. D., CLARK, M., SMITH, R. J., ELLWOOD, R. J., LI, W. and SOMEKH, M. G., 2011. Laser ultrasonic microscopy NONDESTRUCTIVE TESTING AND EVALUATION. VOL 26(NUMBER 3-4), 367-384
  • STRATOUDAKI, T, ELLWOOD, R, SHARPLES, S, CLARK, M, SOMEKH, MG and COLLISON, IJ, 2011. Measurement of material nonlinearity using surface acoustic wave parametric interaction and laser ultrasonics Journal of the Acoustical Society of America. 129(4), 1721-1728
  • SMITH, RJ, LIGHT, RA, SHARPLES, SD, JOHNSTON, NS, PITTER, MC and SOMEKH, MG, 2010. Multichannel, time-resolved picosecond laser ultrasound imaging and spectroscopy with custom complementary metal-oxide-semiconductor detector REVIEW OF SCIENTIFIC INSTRUMENTS. 81(2), 024901
  • ARCA, A., AYLOTT, J., MARQUES, L., CLARK, M., SOMEKH, M., SMITH, R., SHARPLES, S., STRATOUDAKI, T. and CHEN, X., 2011. CHOTs optical transducers NONDESTRUCTIVE TESTING AND EVALUATION. VOL 26(NUMBER 3-4), 353-366

Past Research

My previous research has involved developing new techniques, new instrumentation, and new insights into the interaction of acoustic waves with materials. My PhD, titled "All-Optical Scanning Acoustic Microscope" centred around using novel laser ultrasonic techniques for materials characterisation and nondestructive evaluation. During the course of my PhD I improved the instrumentation to such a degree that for the first time we were able to take images - rather than single point measurements - of surface acoustic waves (SAWs) which were generated and detected using lasers. This improvement in the instrumentation led to an area of research on "Adaptive laser ultrasound with programmable optical field distributions" (2000-2003), which had profound implications for ultrasonic testing integrity. This was the study of the deleterious effects of anisotropy and microstructure on the propagation of ultrasound, and improving the methods and mechanisms to model, measure, analyse and predict this behaviour. Demonstrations of these effects led to revelations amongst many industrial (and some academic) collaborators, as it explained beautifully some of the phenomena (including unreliable data) that they had been seeing.

Success in this initial work led directly to a Core Project in the new Research Centre for NDE, formed in April 2003, titled "NDE of Difficult Materials." (2003-2007). My work here used the understanding of acoustic aberration to develop techniques in three key areas. (1) Using the information gained from the effects of acoustic aberration to infer statistical properties (mean grain size, degree of anisotropy) of the material under investigation. (2) Acoustic aberration correction, whereby the aberration is detected using a novel multi-channel acoustic sensor which I developed, and applying correction to the generation pattern. This cancels out the effects of the microstructure, giving greater confidence and clarity for the detection of defects. (3) Development of a spatially resolved acoustic spectroscopy which is capable of imaging microstructure, crucial for estimating likelihood of structure-sensitive failure mechanisms.

From 2007-2008 I worked on a project entitled "Advanced ultrasonic techniques for highly scattering ordered and semi-ordered materials," which involved developing techniques for rationalising the amount of information necessary to determine key properties of these complex materials (such as degree of randomness, or porosity).

In a project extending the usefulness of 'ultra-fast' (>GHz) laser ultrasound systems, "Exotic ultrasonics for the real world" (2005-2009), I provided expertise in commercial optical detector arrays for parallelisation of optical sensors to detect high frequency ultrasonic waves, feeding from consultancy work (2005-2006) for Optical Metrology Innovations Ltd, to massively improve the speed of their photoreflectance spectrometer product using novel optical and electronic design.

Faculty of Engineering

The University of Nottingham
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Nottingham, NG7 2RD


telephone: +44 (0) 115 951 5533
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