What I do for a living (Part Two)

In the last post, I wrote about the biological aspect of my work and now I'm going to get more physic(al?). I trained as a physicist, and see myself more as an engineer (which is really just applied physics). My salary comes from a large EPSRC (that's the government research council for engineering and physical sciences) grant  for a project known as Sonotweezers. The grant was worth roughly £2m and split between four universities (Dundee, Glasgow, Southampton and Bristol), but being a lowly post-doc, I don't see much of that £2m - so don't get the wrong idea!

The aim of the Sonotweezers project is to research and develop electronically controlled devices which use ultrasound waves to manipulate particles and objects. Before explaining what I do with them, I'll tell you a bit about how it works. All sound, from the stuff you can hear to the higher frequencies that bother dogs and above (say, for looking at your unborn baby), is just pressure. And, by definition, pressure is just force divided by an area of surface. So, if you have pressure, you have force.

Clear as mud? Ok, consider a deep sea diver. The pressure of the sea down below is much higher than at the surface, and can result in a crushing of the diver, hence James Cameron, while commercialising human tragedy, had a specially created submarine that could withstand large pressure. This pressure on the diver is uniform all around him, pushing him to his core.

Pressures on a deep-sea diver giving rise to forces.

Now, consider what would happen if on his right hand side the pressure was higher than the left. He'd still be getting crushed, but more so on his right hand side. Provided that he's floating down there, he'd find himself being pushed more on his right hand side. This is an unbalanced force,and by Newton's equation of Force being mass times acceleration, he'd accelerate away from the higher pressure on his right.

So, in our laboratory we create non-uniform pressure fields around objects to move them. We do this with ultrasound because the higher frequencies mean the objects we can move are much smaller than if we did it with audible sounds. People have used lower frequencies to levitate objects in the past, useful research like floating ants and fish.

Ultrasound standing waves giving rises to forces on cells

I use ultrasound quite like that picture there, to push cells around when they want to move somewhere else. This allows us to get a measurement of how much force the cell is able to produce, and that helps us better understand the motions that I spoke about last time. It's mainly an engineering job, since the physics are understood, but getting them to work with biology is the main problem.

Ok, this was a bit longer than I thought, so there's going to be a third (and possibly final) part of this where I'll tell you about the computing that I do. There will be some more pretty pictures (perhaps prettier as a computer will have drawn them...)

Hope you're enjoying reading these, and again, happy to answer questions.

\0/ SCIENCE.