Animal magic

The technique used by bats to catch insects at night could be adapted to find tumours deep inside a person's body.

Engineers at Strathclyde University hope this will be one of the outcomes of their research on new ultrasonic acoustic systems that could be used in applications from imaging through to materials characterisation.

Currently, communication systems use sophisticated coding for transmission, detection and recognition of electronic data.

Despite this, the potential for ultrasonic systems appears relatively untouched in the human world but is used extensively and successfully in the wild.

'Bats, dolphins and whales use complex acoustic waveforms for object identification and navigation,' said Gordon Hayward, the principal investigator of Strathclyde's programme.These waveforms, he said, are specially coded to a specific object such as prey.

The researchers hope their systems — characterised by new transducer and array structures — will imitate the way animals use coded waveforms with matched filtering.

Matched filters, commonly used in radar, work when a known signal is transmitted, and the reflected signal is examined for common elements of the outgoing signal. In the wild, a bat may emit a signal which is specific to successfully finding prey rather than, say, a falling leaf.

The researchers will work with a team of mathematicians to identify new coding sequences for a wide variety of targets, such as cancer cells, and demonstrate the outcome with computer simulations and laboratory tests.

But it will be a challenge. For while bats had millions of years of evolution to optimise their codes, Hayward hopes to have results in the next three years.

Once the optimal codes are determined, Hayward said the next major step would be to develop transducers that can handle wider frequency ranges closer to those of a bat. 'Bats can emit signals over a wide frequency range, but their bandwidth is much higher than can be coped with by normal ultrasound transducers,' said Hayward.

One way to improve the transducer performance is to modify its configuration and materials, which are traditionally piezoelectric ceramics. This may alter how they respond to a signal's harmonics.

'Transducers in their most common mode have a peak in response at the fundamental and odd harmonics, meaning the first, third, fifth. but they have nulls in their response in the second, fourth and sixth,' said Hayward. 'We are going to look at new structures where we don't have these nulls.'

Without them, he said, the frequency range will dramatically increase. Other than increased range, the transducer will differ from conventional devices because it will not only send a signal into a material, but it will also tailor the acoustic response to get maximum information from a target.

Hayward said his research group's systems could have applications beyond the medical sector in areas such as defence. One example, he said, is the detection and removal of under-water mines.

'With improved image capability, you could envisage a mine hunter locating a mine, then classifying it and sending a small robotic vehicle to dispose of it,' he said. 'Some of that technology already exists, but this would make it better.'

He added that the technology could also assist communications when other options are not possible. One example of this, he said, is inside nuclear reactors. Here, Hayward envisages tiny robots testing the inside of the reactor and transmitting data to an acoustic station inside the wall. The information would be transmitted through the wall to another station and then to a mobile phone.

The technology also has applications with non-destructive testing. Hayward's team has recently received a grant to form a coded ultrasound research centre at Strathclyde to enable the UK to be at the forefront of the technology.

The team has also built partnerships with the universities of Virginia and Southern California, where researchers have already used ultrasound to create images at the cellular level.

The hope now is to achieve even smaller targets, better resolution and greater penetration.