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 detection, acoustic communication, and noise reduction, as well as the development of advanced devices like broadband AF lenses and thermoacoustic phase-controlled metamaterials. The book is enriched with detailed illustrations, tables, and clear theoretical explanations, making complex concepts accessible. It provides valuable insights into the design and modulation of high-performance acoustic devices, offering both foundational knowledge and advanced techniques for practical applications. This work is particularly beneficial for researchers, engineers, and graduate students in acoustics, materials science, and related fields, as it bridges the gap between theoretical research and real-world applications.