Deployable structures are essential for satellite systems, space habitats, and space exploration. These structures remain compact during launch and extend in space, effectively addressing the constraints of space transportation. This paper provides a comprehensive review of recent research developments in this field. It investigates fundamental design concepts that favor lightweight, high-strength, and high-efficiency structures, which are well-suited for space environments. The research explores innovative structures, such as deformable structures and rigid links, to enhance efficiency and durability in harsh space environments. Recent technical advances, including innovative deployment techniques and autonomous systems, are examined to emphasize their significance in increasing the overall efficiency of space operations. This review also highlights key challenges, such as ensuring dependability in severe conditions, while recommending high-potential research areas. Overall, this comprehensive review offers valuable insights for academics, engineers, and stakeholders aiming to enhance the performance and sustainability of space missions.

Acoustic metamaterials (AMs) are artificially structured materials composed of subwavelength units that enable acoustic phenomena not achievable with conventional materials and structures. This review defines and presents a distinct category referred to as soft acoustic metamaterials (SAMs), which use soft materials or reconfigurable structures to achieve enhanced acoustic functionality. These systems make use of the inherent flexibility of their materials or the deformability of their geometry to support passive, active, and adaptive functions. To capture this structural and functional diversity, we introduce a three-dimensional classification that considers geometry, acoustic control mechanisms, and functional responsiveness as interrelated aspects. The geometry is classified into two-dimensional metasurfaces and three-dimensional bulk structures. The control mechanisms include local resonance, phase modulation, attenuation, and structural reconfiguration. The response type refers to whether the system behaves passively, actively, or adaptively. Using this approach, we provide an overview of representative implementations and compare different design approaches to highlight their working principles and application areas. This review presents a structured classification for soft acoustic metamaterials and offers a foundation for future research, with broad potential in intelligent sound systems, wearable acoustics, and architectural applications.