Mechanical Metamaterials for Sensor and Actuator Applications

Mechanical metamaterials (MMs) have emerged as a promising class of engineered materials, distinguished by their unique mechanical behaviors derived from architectural design rather than inherent composition. Recent advancements in the design, structural analysis, and manufacturing technology of architectured MMs have resulted in the development of high-performance sensors and actuators with new functionalities. In this review, important advances in MM-based sensors and actuators over recent years are summarized, from structural designs to fabrication and applications. We briefly outline the fundamental mechanical characteristics of key MMs, such as auxetic-, chiral-, pentamode-, origami-, and kirigami-based MMs, with an emphasis on the principles that drive their unique mechanical behaviors. We also discuss various fabrication methods employed to realize theoretical MM designs. These methods encompass additive manufacturing, subtractive manufacturing, micro-molding/casting, and other fabrication techniques that enable the production of complex MM structures. Moreover, we comprehensively explore the applications of MMs in sensors by categorizing their implementations as strain, pressure, and multimodal sensors, highlighting their superior performances compared to conventional devices. Additionally, we examine MM-based mechanical, pneumatic, thermal, and other types of actuators, showcasing their enhanced capabilities and functionalities. Finally, we provide perspectives on current issues that must be addressed to fully leverage the potential of MM in this field. By summarizing recent advances in MM-based sensors and actuators, this review paper aims to provide a comprehensive understanding of the design, fabrication, and applications of MMs in the context of mechanical engineering.