Sound and vision

A camera system that produces images using sound rather than light could create far more detailed pictures than conventional ultrasound equipment.

The acoustic device, developed by a team led by Dr Chris Stevens, a lecturer in engineering science at Oxford University, could be used in enhanced medical ultrasound and airport security scanning to provide images of hidden hard plastic and ceramic objects. The device can also produce clear pictures underwater and through smoke and fog.

Sound imaging is already used in medical ultrasound and underwater sonar systems. However, the resolution of images produced by current technology is limited by the amount of sound data that can be collected.

The Oxford device works like a digital camera, where data from an array of light-sensitive detectors is correlated on a CCD chip to build an image. But in the case of the Oxford device, data from a large array of microphones is used.

Existing sound imaging devices using microphone arrays require a separate analogue-to-digital converter for each microphone, as well as complex electronic systems involving several wiring connections for each microphone. The Oxford researchers have developed a small-scale system that can carry out this task very quickly, despite collecting data from a large microphone array.

The invention also takes a new approach to manufacturing large arrays of microphones and uses a method for collecting information on both the phase and the amplitude of the soundwaves picked up by the microphone array, which allows 3D images to be produced.

‘Unlike sonar, which goes backwards and forwards to build an image, this technology takes a 3D picture, like a camera using sound,’ said Terry Pollard, project manager for the device at ISIS Innovation, Oxford University’s technology transfer arm.

‘The project’s mentor is a keen scuba diver and wanted to use this device for locating shipwrecks in murky waters. However, it has been developed so that it can be used anywhere that is examined using ultrasound.’

The researchers are now building a demonstration model of the device featuring 225 microphones, along with the associated electronics and computer processing systems. This should be complete by this summer.

On a related audio note, researchers at Oxford have combined the benefits of speakers and headphones to produce a high-quality portable surroundsound system for use in the home. The invention can produce highquality surround sound that has accurate bass and treble effects. This will also be important in reproducing sound for the expanding market in portable DVD players and for directional effects in computer gaming. The technology also has the potential to improve headphone bass sounds. The system uses the natural effect of the listener’s head and ears on sound localisation, while cutting out room reflections and resonance. As less amplification is needed, the unit is less likely to distort the sound, while less power is required, saving energy.