Active materials convert one type of energy to another. For example, photovoltaics convert light to electrical voltage and piezoelectrics convert electrical energy to mechanical energy (such as sound), or vice versa. Piezoelectrics were very commonly known in the middle of the phonograph era—piezoelectric crystals in the arm of the turntable converted the vibrations from groves in records to electrical signals which were send through an amplifier and speakers to enjoy music. Now piezoelectrics are the active component of ultrasound used to image fetuses or other medical applications. They are also used for applications ranging from your wristwatch or seat belt buzzers to the fuel injector of your car. They have many defense applications as well, such as in sonar and hydrophones. New applications include generating energy from ambient noise or even raindrops.
The best piezoelectrics are ferroelectrics. Ferrroelectrics have a permanent electrical polarization. You can think of polarization as a positive charge on one side of the crystal and a negative charge on the other. The plus and minus signs can be switched by applying an electric field. Ferroelectrics are very interesting not only in their manifold useful applications, but also are very interesting in their fundamental physics. What makes these materials so extraordinarily sensitive to applied electrical and stress fields? How can their properties be optimized? Can we design new materials that have better properties?
We perform fundamental research into ferroelectrics at the Geophysical Laboratory, using theory and experiment to better understand how these materials work. We also work on designing new materials using the fundamental understanding we are developing.