Before Pierre Curie met the chemist Marie Sklodowska; before they married and she took his name; before he abandoned his physics work and moved into her laboratory on Rue Lhomond where they would discover the radioactive elements polonium and radium, Curie discovered something called piezoelectricity. Some materials, he found—like quartz and certain kinds of salts and ceramics—build up an electric charge when you squeeze them. Sure, it's no nuclear power. But thanks to piezoelectricity, US troops could locate enemy submarines during World War I. Thousands of expectant parents could see their baby's face for the first time. And one day soon, it may be how doctors cure disease.

Ultrasound, as you may have figured out by now, runs on piezoelectricity. Applying voltage to a piezoelectric crystal makes it vibrate, sending out a sound wave. When the echo that bounces back is converted into electrical signals, you get an image of, say, a fetus, or a submarine. But in the last few years, the lo-fi tech has reinvented itself in some weird new ways.

Researchers are fitting people's heads with ultrasound-emitting helmets to treat tremors and Alzheimer's. They're using it to remotely activate cancer-fighting immune cells. Startups are designing swallowable capsules and ultrasonically vibrating enemas to shoot drugs into the bloodstream. One company is even using the shockwaves to heal wounds—stuff Curie never could have even imagined.

So how did this 100-year-old technology learn some new tricks? With the help of modern-day medical imaging, and lots and lots of bubbles.

Bubbles are what brought Tao Sun from Nanjing, China to California as an exchange student in 2011, and eventually to the Focused Ultrasound Lab at Brigham and Women's Hospital and Harvard Medical School. The 27-year-old electrical engineering grad student studies a particular kind of bubble—the gas-filled microbubbles that technicians use to bump up contrast in grainy ultrasound images. Passing ultrasonic waves compress the bubbles' gas cores, resulting in a stronger echo that pops out against tissue. "We're starting to realize they can be much more versatile," says Sun. "We can chemically design their shells to alter their physical properties, load them with tissue-seeking markers, even attach drugs to them."