propagation+by+layers
131Ultrasound — Not to be confused with Supersonic .Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Although this limit varies from person to person, it is approximately 20 kilohertz (20,000 hertz) in healthy,… …
132Quantum dot — Part of a series of articles on Nanomaterials Fullerenes …
