(a) The negative refraction of sound wave based on topological surface state. (b) The acoustic interferometer based on topological hinge states.

Ultrasound close ultrasoundSound with a frequency greater than 20,000 Hz (20 kHz). is sound with a frequency greater than 20,000 Hz. Humans cannot hear ultrasound but many other animals can ...

Save guides, add subjects and pick up where you left off with your BBC account. Refraction close refractionProcess by which a wave changes speed and sometimes direction upon entering a denser or ...