Microscale Structures are becoming increasingly important in applications ranging from biological implants to display technologies. An essential characteristic of microstructures is their mechanical properties. Performing repeatable and accurate measurements of these properties on operational structures has to date proved to be extremely difficult. Such monitoring would enable the effects of fabrication steps during manufacture on mechanical properties to be reliably characterised. Additionally it would enable ready assessment of the impact of packaging, environmental conditions and continuous usage on mechanical integrity. This project focuses upon monitoring these mechanical properties (density, stiffness etc.) using a non contact optical technique. This approach uses an optical signal to produce an ultrasonic response in the material and this response is monitored optically. The complexity of this response enables the determination of mechanical material properties through curve fitting involving carefully structured numerical mathematical inversion techniques. For simple structures the response can be modelled analytically and this analytical model inverted numerically. For more complex structures reliable computer modelling is essential for both forward and inverse analysis. The project therefore has parallel strands examining both simple and more complex microstructures and making extensive use of finite element modelling techniques where appropriate to augment the experimental techniques. Additionally for very simple structures the measurement method will be referenced against contact based systems developed through our partners at the National Physical Laboratory. We have demonstrated the basic principle on larger scale geometrically simple structures and are confident that repeatability in the order of 1% is achievable. Extending the technique to microstructures does however present significant research challenges in realising gigahertz bandwidth ultrasonic excitation (where the wavelength is comparable to structural dimension) and detection and in accommodating more complex structural artefacts, in addition to producing microscale detection and excitation optics.
|Effective start/end date||1/10/07 → 28/08/11|
- EPSRC (Engineering and Physical Sciences Research Council): £677,610.00