This book explores the rapidly evolving field of acoustic metamaterials, focusing on their ability to manipulate sound waves through asymmetric transmission, acoustic focusing, and acoustic asymmetric focusing. It introduces innovative research methods and achievements, such as the use of underwater plate-like metamaterials, airborne metamaterials, and phase-controlled metamaterials to achieve precise control over sound propagation in 2D and 3D spaces. Readers will be particularly interested in the novel applications of these materials in medical ultrasound, underwater...