A review of elastic plate wave metamaterials

Abstract

Elastic waves are widely used in our daily life, such as non-destructive testing, mineral exploration, analog signal processing and sensing systems, etc., benefiting from their important advantages such as low loss and small wavelength (relative to electromagnetic waves). However, the transmission mechanism of elastic waves in traditional materials is relatively simple, so the ability to manipulate elastic waves using traditional materials is very limited. Metamaterials are artificial materials with unique physical properties that natural materials do not possess. In the 21st century, with the prosperity of metamaterials, elastic metamaterials have also been developed, which greatly enriches people's manipulation methods for elastic waves. This paper focuses on the representative plate wave among elastic waves, and systematically reviews the development of metamaterials for plate waves, their main research progress and their potential in future information functional devices. First, we present the history of metamaterial development. After comparing elastic waves with electromagnetic waves and airborne acoustics, we discuss the challenges of controlling elastic waves. Next, we introduce the plate wave in elastic waves in detail. We then review several representative applications using plate-wave metamaterials, including subwavelength imaging, cloaking, vibration isolation, and waveguiding, and their research progress in microwave information processing and energy harvesting. Two dimensional elastic metalenses used for subwavelength imaging enable evanescent waves to have far-field transmission capabilities, which enriches the spatial range for people to effectively control and utilize plate waves. The research on 2D elastic cloaking has enabled people to have a deeper understanding of the governing equations of the plate wave, and to a large extent has enhanced people's ability to control the transmission path of the plate wave. Compared with traditional materials, elastic metamaterials can theoretically completely suppress vibration, which greatly enriches people's ability to adjust the spatial energy distribution of plate waves. Various 2D elastic waveguides have been proposed, which greatly enriches people's ability to control the plate wave transmission path, and provides a basis for people to realize acoustic-based analog circuits in the future. In terms of practical applications, we introduce the device attempts of plate wave metamaterials in recent years: Microwave acoustic devices (such as resonators) and energy harvesting. In these two aspects, since the existing electronic systems are highly mature and have near-limit process and technical capabilities, the plate wave metamaterial must find its own unique value before it can be expected to become a part of the mainstream design. Despite some impressive achievements, some core challenges remain in this field, e.g., low frequency and broadband (limited by principle), high frequency (limited by processing difficulty), the balance of material function and performance, and environmental adaptability. In the future, plate wave metamaterials should be developed towards solving these problems. It is worth noting that research breakthroughs in physical common problems will always improve people's ability to manipulate elastic waves; for example, the introduction of topological band theory into plate phononic crystals may be a promising direction. With the emergence and solution of novel physical problems, the understanding and manipulation of plate waves will rise to a higher level. We hope that this paper can provide some reference and inspiration for researchers in related fields.