O+UII abstracts
Morning session
Cheap Optical Transducers (CHOTs) for in-situ application and ultrasonic testing
Victoriya Ageeva
Applied Optics, Faculty of Engineering, University of Nottingham
Cheap optical transducers (CHOTs) are patterns on the surface of a component activated by lasers to generate and detect ultrasound. Excited optically, with minimal surface impact, and fully customisable, CHOTs provide a simple alternative to conventional piezoelectric transducers, offering wireless, remote operation. Of particular interest is application of CHOTs for in-situ ultrasonic inspection of hard-to reach and complex-geometry components such as those of aero-engines. Endoscopic CHOT pulser uses optical fibres to provide flexible instrumentation for testing of components with complex access paths. It is complemented by the development of the alternative CHOT fabrication methods to allow application of sensors in-situ, onto large and curved parts, as well as those already in service, challenging for laboratory-limited methods. The g-CHOTs (used for generation of surface acoustic wave) produced on film carriers to allow transfer of the transducer and application onto components in-situ are presented, including fabrication and functionality test results.
Analysis of the fundamental torsional guided wave field within a hollow cylinder using a 3D-FFT
Keith Thornicroft[1,2], Alex Haig[2], Cristinel Mares[1] and Peter Mudge[2]
[1] School of Engineering and Design, Brunel University. [2] TWI Ltd, Granta Park, Great Abington, Cambridge, CB21 6AL.
The field of guided wave testing (GWT) is a relatively new development within the non-destructive evaluation sector. The market for this technology has been driven by pipeline operators who have a need to screen for corrosion and degradation of their pipeline. In order to improve the detection capability of the guided wave tooling is it important to be able to optimise the output of the transducer array. This paper describes an experimental procedure which was implemented to quantify the output of a circumferentially distributed transducer array. Using a scanning laser vibrometer it was possible to sample an area of the pipe away from the transducer array and measure the displacement behaviour at each discrete point. With vibrometry information gained from both circumferential and axial positions over a range of frequencies, a 3D-FFT technique was developed that reveals circumferential mode order and axial wavenumber both of which are dependent upon frequency. The resultant plot shows the contribution of wave modes generated by the circumferentially distributed transducer array as received by the vibrometer.
Spatially resolved acoustic spectroscopy: a laser ultrasonic technique for materials characterisation
Wenqi Li, Richard Smith, Jethro Coulson, Matt Clark, Mike Somekh and Steve Sharples
Applied Optics, Faculty of Engineering, University of Nottingham
Material characteristics such as strength, stiffness and fracture resistance are strongly related to the underlying microstructure. In order to predict the mechanical behaviour of industrial materials such as titanium, nickel and their alloys, detailed knowledge about their texture is required. A robust measurement tool is introduced which can be used to determine the crystallographic orientation of a material.
Recent progress in laser ultrasonic multi-dectectors receivers for non destructing evaluation
M Messaoudi, B Pouet, S Breugnot
Bossa Nova Technologies, 11922 Jefferson Boulevard, Culver City, CA 90230
New laser interferometric schemes were recently introduced and improved in order to fully take advantage of possibilities offered by laser-based ultrasonic (LBU) inspection and to broaden their integration into industrial inspection systems and into laboratories setups. We will present the recent advances on a first LBU receiver based on multi-channel random-quadrature (MCRQ) detection. The MCRQ receiver is fiberized and well suited for industrial application such as thickness control on moving sample using zero group velocity Lamb wave resonance. The second receiver is based on two-wave mixing in photorefractive crystal and it has been improved to be able to measure simultaneously in-plane and outof-plane displacements. Thermoelastic generation on aluminium sample experiment enhances difference between both components, which opens up new prospects for ultrasound studies in the lab. Keyword Speckle, ultrasound, quadrature, two-wave mixing, interferometer, laser.
SKED: Speckle Knife Edge Detector
Samuel O Achamfuo-Yeboah, R A Light and S D Sharples
Applied Optics, Faculty of Engineering, University of Nottingham
The optical detection of ultrasound from optically rough surfaces is severely limited using a conventional setup because the detected light is speckled. We present a CMOS integrated circuit that can detect ultrasound in the presence of speckle. The detector circuit is based on the simple knife edge detector. It is self-adapting and is fast, inexpensive, compact and robust. The detector is implemented as a widefield camera with 32x32 smart pixels. We present the theory of its operation and discuss results validating the concept and operation of the device. We will also present results that show that it can work with optically rough surface finishes that have roughness (Ra) up to 2<math>\mu</math>m.
Quantified visualisation of elastic wave phenomena using refracto-vibrometry.
Rob Malkin
University of Bristol
This presentation will discuss time resolved quantitative evaluation of elastic stress waves in solid media by utilising an adaptation of the well-established laser Doppler vibrometry method. We show that the introduction of elastic stress waves in a transparent medium gives rise to detectable and quantifiable changes in the refractive index, which is proportional to stress. The method is tested for mechanical excitation at a range of frequencies in an acrylic bar. This refractometric quantification can measure internal strains as low as 1x10<math>^{-11}</math>. Additionally, finite element analysis is used to gauge the validity of the results. We also discuss the effect of signal integration along the laser path length. In the presented work an acrylic bar is used, this method however should be applicable to any transparent solid.
Laser-based ultrasonic characterisation of Ge membranes
Oksana Trushkevych, Vishal A Shah, Maksym Myronov, John E Halpin, Stephen D Rhead, Martin J Prest, David R Leadley, and Rachel S Edwards
Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
Piezoelectric transducers and laser interferometry are used to study vibrations of a 700 nm thick and 965<math>\times</math>965 µm square single crystal Ge membrane, in air and in vacuum. Ge on Si substrate is a basis for many optoelectronic devices, including sensors, photonic modulators, solar cells,and heterojunction bipolar transistors. Mechanically decoupling the Ge film from the Si substrate, producing a Ge membrane, can lead to a more rapid and higher sensitivity response in sensors, and allows adding new functionality to integrated systems. It is important to study the robustness to shock and the elastic behaviour of the membrane before building devices, and laser interferometry is an ideal method for these measurements. Resonance modes up to 3:2 of the membrane are studied in detail both in the frequency and the spatial domain, and residual stress of the membrane, as well as the quality factors of modes at various pressures, are extracted.
