Have you ever seen water pipes breaking and water flooding the street or your bathroom? Power plants and chemical plants have lots of pipes. What if they also burst frequently? Of course, it would be a disaster! Someone has to check that they are safe and repair any cracks and defects before serious damage can occur.
Ever been on a flight or on a train? Do you know that before you got on, the engine, the wings, wheels or railtracks would have been tested by one or two methods to check they are safe. There is a lot of work behind the scenes to make sure structures and components are not going to fail dramatically (or not dramatically, either way).
The area of research concerned with the health of things like airplanes, bridges and power plants is called non-destructive testing. It does what it says on the box - it is testing things without destroying them!
One of the commonly used methods of testing is to use ultrasound. You may have had a medical ultrasound scan before. This is very similar, only the patients are big pieces of metal or pipes or intricate engine blades.
In ultrasonic testing we usually send a pulse of ultrasound and "listen" for reflections, and locate any defects in the bulk of the tested component - this is similar to medical ultrasound. We can also look at waves propagating at the surface, they will behave differently if there is a surface crack.
I am developing a new way of sensing and visualising ultrasound using thin films of polymer with droplets of liquid crystal inside the film. Ultimately, I want to develop smart paint, that will visualise ultrasound and will make inspections significantly faster, cheaper, simpler and thus more widely available. I want to make sure we can check safety of our infrastructure with high reliability, and with minimal effort - so that our world is becoming a safer and better place to live!