I was recently awarded a five year EPSRC early career fellowship to study the manipulation of microscopic particles using the forces generated by ultrasonic waves.
I am exploring a range of projects spanning from applications of ultrasound in tissue engineering and bio-detection, through advanced device design and fabrication, to fundamental modelling of acoustic radiation forces. I’m also actively involved in taking interactive exhibits to public engagement, including stands at the Royal Society Summer Exhibition, Cheltenham Science Festival, Glastonbury Science tent, and many other venues. I am also interested in the interface between Science and Engineering and the Arts, and am currently exploring sculptural exhibits.
I graduated in Electronics and Computer Science at the University of Southampton, and was an IET scholar. During my 2001 Ph.D., "Vibration powered generators for self-powered microsystems", I created the world’s first piezoelectric vibration energy harvester, and was a key part of the recent dramatic growth of interest in energy harvesting. My designs also led to the spin-off company Perpetuum. I sit on the management board of the pan-European research network, USWnet.
Ultrasonic particle manipulation
When small particles such as human cells or bacteria are placed in an ultrasonic sound field, they experience a force that can be used to move them around.
By carefully controlling that field it is possible to manipulate thousands of cells at once, creating an acoustic tweezers (or 'sonotweezers'). This ability to precisely position such tiny objects opens up many exciting applications that would be difficult using other technologies such as optical tweezers that can only manipulate a much smaller number of particles simultaneously.
In my research I focus on two main application areas: tissue engineering and bio-detection systems.
The ultrasonic forces can also be used to manipulate bacteria, typically pushing them against sensor surfaces or enhancing their concentration to make detection more reliable. We have recently demonstrated this as part of the European funded AQUALITY project, aimed at detecting bacteria in drinking water.
The principle is similar to the ultrasonic sorting device shown in the video and diagram below, which can distinguish between particles that reflect differing amounts of ultrasound. Here we show fluorescent polystyrene micro-beads sorted by size. A "sheath flow" is used to align all the particles at the bottom of the chamber, and as they flow through the active region the larger, green beads are pushed to the top of the channel to be collected at a separate outlet. This can be seen in the video which is taken through a microscope looking down outlet 1 through the transparent glass layer that forms the top of the device.
Investigating acoustic forces
Ultrasonic manipulation is a complex, non-linear phenomenon. We investigate the underlying mechanisms of both the radiation forces and the acoustic streaming that often accompany it. We also pioneer new types of device including creating more dextrous sonotweezers.
Previously I have developed vibration energy harvesting. Here, I investigated ways of extracting small amounts of energy from vibrations present around a device, with the aim of creating a wireless sensor node. This can be used, for example, to monitor the health of machinery in large industrial complexes where changing batteries, or installing large quantities of wiring is impractical. My designs were taken up by the spin-out company, Perpetuum, that has grown to be a world leader since it was founded in 2004. My tapered piezoelectric generator designs have also been taken up by a range of companies worldwide.