Terfenol-D is a magnetostrictive material made from a combination of terbium, iron, and dysprosium. It has the unique ability to change its shape or size in response to a magnetic field, making it useful in various applications, such as sensors and actuators. This material is known for its high magnetostrictive properties, which means it can produce significant mechanical strain when exposed to a magnetic field. As a result, Terfenol-D is often used in advanced technologies, including sonar systems and vibration control devices, enhancing performance in these fields.