'Single-sided' autofocusing of sound in layered materials

Anew technique-'single-sided' autofocusing-is proposed and its possible use for inspecting layered materials is surveyed. Based on linear acoustics and the recently developed mathematical theory of focusing, single-sided autofocusing answers the question, 'Given single-sided access, how does one focus sound to a point inside a one-dimensional layered medium at a specified time-given that the velocity profile is unknown?'