There isn't one specific scientist who "discovered" ultrasonic waves. It's more accurate to say that the phenomenon of ultrasonic waves was gradually understood and explored through the work of several scientists over time.

Here's a breakdown of key contributions:

* 18th Century: Lazzaro Spallanzani (1729-1799) observed that bats could navigate in darkness and hypothesized that they used sound waves beyond human hearing.

* 19th Century: August Kundt (1839-1894) demonstrated the existence of sound waves with frequencies beyond human hearing using a method known as "Kundt's Tube."

* Early 20th Century: Pierre Curie (1859-1906) and Jacques Curie (1855-1941) studied the piezoelectric effect, which forms the basis for generating and detecting ultrasonic waves.

* Mid-20th Century: George Washington Pierce (1872-1956) developed the first practical ultrasonic generator using the piezoelectric effect.

So, while no single person "discovered" ultrasonic waves, the work of these and other scientists paved the way for the development and understanding of this important area of acoustics.