Safe and ultrasound

Ultrasonic modelling techniques are being developed to assess the behaviour of complex materials

Researchers at Nottingham University are creating ultrasonic platforms that could examine the structure of complex materials and microscale objects, such as the component parts of cells.

Complex materials, such as metal matrix composites of reinforcing wires in titanium or aluminium used in aircraft manufacture, are effectively opaque to ultrasound, so there is no non-destructive way of telling if they are defective. While it is relatively simple to take an overall measurement, the complexity at the micro scale makes it difficult to understand what may be happening inside.

Project leader Dr Matt Clark said: ‘The difficulty you encounter is relating your measurement to the state of the material. We’re looking at using powerful modelling techniques to model these complex materials and understand how the state of the material affects their behaviour and, therefore, the ultrasonic measurement.’

These materials are typically made by assembling the components and pressing them together under high temperature and pressure to fuse all the parts together. If the manufacturing process is not perfect — if a wire crosses over, for example — you can end up with imperfect bending and voids within the material.

‘From a conventional ultrasonic point of view, the imperfect bending looks perfect and the voids look like another wire, so you can’t tell a defect from the normal state of the material,’ said Clark.

‘But if you observe some of the more subtle changes, especially from the lower frequencies, which are fully accessible to the measurement techniques, you can infer that there are some changes that have taken place. By drawing a relationship between the model and the measurement, you can work out what is going on,’ he added.

The nanoscale application aims to bring a set of basic ultrasound diagnostic tools to the fields of nanoscience and nanoengineering. ‘When you try to do this, you come up against some fundamental problems in terms of how you do ultrasonics at this scale,’ said Clark. ‘To look at something nano sized, you need a nano-sized transducer. As these can’t be wired, they will be powered by high-speed lasers to generate the ultrasound.’

The other arm of the project looking at nanoscale ultrasound will address making nanostructured materials and engineering micro-/ nano-electro mechanical systems (MEMs/NEMs). It could also deliver biological and medical ultrasonics on a scale not seen before. ‘Instead of trying to look through the body, we’ll be trying to measure the structural properties of individual cells by placing the sensors inside them,’ explained Clark.

By the end of the five-year project, the researchers hope to have made substantial inroads in both arms of the research. They aim to get some measurements out into industry for these complex materials and will have input from Rolls-Royce and Airbus, with whom they work closely.

The team has already built prototype nanoscale ultrasonic transducers operating at 10GHz and has measured signals from them. They are attached to a substrate and need to be liberated, packaged and inserted into the devices to be examined.

Berenice Baker