Min-Woo Han

Shape memory alloys (SMAs) are widely used as soft actuators due to their shape memory effect, variable stiffness, and simple actuation via Joule heating. To achieve larger and more diverse deformations, SMA wires can be integrated as fibers into textile structures, enabling the fabrication of textile actuators using conventional textile manufacturing methods. These actuators provide high compliance and ergonomic conformability, making them more human-friendly than other types of soft actuators. Nevertheless, few studies have examined their modal behavior, limiting the application of SMA-based textile actuators. This study focuses on knitted SMA-based textile actuators and investigates nine morphing patterns—six plane-based and three band-based—designed with knitting codes. The actuators exhibited deformations that matched the predicted shapes. In addition, the plane-based patterns were analyzed to examine the relationship between loop transition boundaries and deformation axes in controlling bending angles. Demonstrations of knitted morphing flowers highlighted the scalability of the designs. Furthermore, quantitative evaluation of actuation forces in horizontal and vertical directions confirmed that actuator performance can be tuned through structural design.

The surge in demand for patient-specific orthopedic implants necessitates the precise optimization of design and processing parameters for artificial trabecular bone. This research utilizes Voronoi-based porous structures to replicate the irregular geometry characteristic of natural trabecular bone. All specimens were fabricated through fused deposition modeling (FDM) with polylactic acid (PLA). The study systematically investigated the influence of four primary parameters, namely build orientation, extruder temperature, layer height, and pore count, on compressive strength. To ensure experimental efficiency, the research implemented a Taguchi L20 orthogonal array. Subsequent signal-to-noise (S/N) ratio analysis identified the optimal parameter set as a y-90° build orientation, an extruder temperature of 200 °C, a layer height of 0.2 mm, and a count of 150 pores. These findings underscore the necessity of integrated geometric and process parameter optimization to advance additive manufacturing for orthopedic applications.

As drone technology rapidly evolves, innovative designs that can change their shape or mimic natural flight mechanisms have emerged. This study systematically categorizes and analyzes these advanced strategies for drone design through a comprehensive review of literature from 2001 to 2025. Two main approaches are examined: deformable drones and nature‐inspired drones. Deformable drones are subcategorized into extendable, foldable, and tilting types based on their operational mechanisms. Extendable drones include sliding and scissor‐like mechanisms, while foldable drones are classified by folding direction and mechanism, with size variation ratios of 0.37–1.46. Tilting drones are categorized into body, rotor, and arm tilting based on degrees of freedom and weight classifications. Nature‐inspired flapping drones are analyzed by mass, wingspan, and flight duration across different actuator types. The findings reveal that deformable drones excel in maneuverability and confined space adaptability, while nature‐inspired designs offer advantages in miniaturization and energy efficiency. This study provides the first comprehensive overview of deformable drone technology, offering guidance for specialized applications in environmental monitoring, rescue operations, and urban mobility.

Soft robotics offers enhanced flexibility, adaptability, and safety compared with traditional rigid-body systems, making it particularly suitable for applications involving human interaction and unstructured environments. Among the various actuation mechanisms developed for soft robots, shape memory alloy (SMA)-textile actuators have emerged as a promising solution owing to their lightweight, silent operation, and high energy density. This study investigates the actuation performance and deflection behavior of a soft knitted gripper fabricated using SMA-based textile actuators configured in a P-loop pattern. To model and predict the deformation behavior of the gripper, an equivalent unit cell (EUC) model was implemented in ABAQUS. This model was employed to analyze and compare the deflection capabilities of the soft knitted gripper against the EUC model. Geometric nonlinearity was incorporated to simulate large deformations resulting from the shape memory effect under electrical excitation. The analysis focused on the bending behavior of the P-loop structure, which is critical for effective gripping and manipulation tasks. Experimental validation was performed by applying varying voltages to the gripper and measuring the resulting deflection angles. Results indicate that increasing the applied voltage significantly enhanced bending, with maximum deflection angles up to 180°, demonstrating the actuator's strong performance. Numerical simulations from the EUC model closely aligned with experimental results, with only a 5% deviation in maximum bending angle, thereby confirming the accuracy and reliability of the proposed modeling approach. This study demonstrates that the EUC model is exceptionally proficient in estimating the actuation behavior of SMA-textile-based soft grippers. The findings provide significant insights for the design and enhancement of next-generation soft actuators and underscore the potential of SMA-textile composites in modern soft robotic systems and biomedical applications requiring conformal, compliant actuation.

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.

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.