# Seismic Isolation via I-Shaped and T-Shaped Large-Scale Phononic Metamaterials
## 1 Introduction  
The control of mechanical waves is timelessly among the most fundamental problems in nature, as it is well known that manipulating elastic or acoustic waves could open new perspectives and create new potential applications in plenty of technological fields [1]. Phononic crystals (PCs) are artificial composite structures that consist of a periodic arrangement of inclusions in a host material, often called the matrix material [2]. One of their fundamental properties is that their dispersion relation could be modified in several ways, according to the choice of the matrix material, the topology, and the dimensions of the inclusions, together with the shape and the material chosen for them [3]. They were introduced three decades ago as a solution to the problem of controlling elastic and acoustic waves [4]. The presence of areas in their band structure where no mechanical wave propagation is allowed, also known as phononic band gaps (PBGs) [2], gave rise to even more capabilities of those composites and expanded their possible applications. The study of PCs has attracted a lot of academic interest the last decades, and numerous technological applications have been proposed and implemented, such as acoustic waveguides, cavities, and filters [5; 6; 7]. In addition, the concept of PCs was also applied to acoustic isolation, acoustic cloaking, and for hypersound and heat control [8]. Acoustic metamaterials came up, providing new functionalities not found in PCs and influencing, apart from acoustic waves, the study of elastic waves. Their unique properties arise due to their locally resonant constituent units [9]. Especially in the last decade, due to the significant progress madein both computational science and manufacturing technology, mechanical metamaterials have faced widespread development and have been considered as potential candidates for a large number of technological solutions [10]. One of the most intriguing ideas that came up in the community is the transfer of the concept of PCs and acoustic metamaterials (AMs) to manipulate the propagation of seismic waves, and thus seismic metamaterials were raised as a new branch of elastic metamaterials [11; 12]. Seismic waves are elastic waves that occur due to an earthquake event in the lithosphere of the Earth. They travel through the Earth, and when they reach its surface, they travel as surface waves, known as Rayleigh and Love waves [13]. Their dominant frequency ranges from a few tenths of Hz to the area of some tens of Hz. Thus, seismic waves belong to the lower edge of the phononic spectrum [8], and the challenge of controlling them to isolate a structure or even an urban area from an earthquake event is indeed noteworthy. In the literature, there have been proposed several ways of reclaiming structures inspired by PCs or AMs to manipulate seismic waves resulting in isolation of the base of a building or the area surrounding it [14]. [PERSON] described implementations of base isolation and an approximate linear theory of isolation that can be used for the design of base isolation systems that use multilayer elastomeric isolators [15]. [PERSON] et al. proposed a new configuration of seismic isolation foundation containing several concrete layers and some rubber blocks, which are placed periodically to form a periodic foundation [16]. [PERSON] and [PERSON] numerically examined structures that could be characterized as large-scale phononic metamaterials and have band gaps in the frequency spectrum of seismic waves when their dimensions are chosen appropriately [17]. [PERSON] and [PERSON] studied a new device that could be considered an attenuator of a seismic wave that reduces the amplitude of the wave exponentially. The structure is designed to support conventional seismic systems using AMs [18]. A simple and practical method of an earthquake-resistant design to support conventional aseismic designs using AMs to reduce the amplitude of a seismic wave exponentially was also studied by [PERSON] and [PERSON] [19]. [PERSON] et al.