Artificial piezoelectric metamaterials

Piezoelectric materials, due to their unique electromechanical coupling properties, play an indispensable role in electromechanical devices. Therefore, continuously enhancing the performance of piezoelectric materials and maximizing their intrinsic piezoelectric properties are key to the development of related devices. However, since the discovery of piezoelectric materials, these modulation methods have been limited to intrinsic property enhancements such as ion doping, defect introduction, domain engineering, polarization optimization, and grain texturing. Although significant progress has been made, these approaches appear to have reached a developmental bottleneck. As a result, the emergence of piezoelectric metamaterials, combining the intrinsic piezoelectric properties of piezoelectric materials with the unnatural structural characteristics of mechanical metamaterials, provides a new pathway for the further development of piezoelectric materials and devices. In this review, a detailed discussion on the design principles and characteristics of piezoelectric metamaterials is conducted, including the construction and control of artificial vibration modes and non-zero piezoelectric coefficients. Subsequently, an in-depth analysis of the design strategies for artificial structures, various advanced fabrication methods, and the latest applications in actuators, energy harvesters, sensors, acoustic transducers, and smart devices are provided. Finally, based on a comprehensive summary of the latest advancements in piezoelectric metamaterials, future research prospects are proposed to guide and assist in the study of piezoelectric metamaterials and the development of piezoelectric materials and devices. Through the detailed discussion in this review, it is believed that piezoelectric metamaterials with the integration of "material-structure-function", currently in a vigorous development stage, are poised to demonstrate significant developmental potential in the foreseeable future, making the tangible reality realization for disruptive innovation of self-adaptive smart devices.