# Design of an Energy Harvester Based on a Rubber Bearing Floating Slab Track
## 1 Introduction
The common energy harvesters are cantilever beam type [11; 12; 13; 14; 15], symbol type [16; 17; 18], multilayer stack type [19; 20], bridge type [21; 22], arch type [23; 24; 25], etc., and there are new energy harvesters [26; 27; 28; 29],2,201,242 made of composite materials, such as piezoelectric fiberboard (MFC), polyvinylidene fluoride (PVDF), and piezoelectric film. The symbol energy harvester is the earliest energy harvester designed and studied, and it is also recognized as energy harvester with comprehensive performance. It consists of metal caps at the upper and lower ends and piezoelectric layers in the middle, so it can capture radial and axial vibration energy at the same time and have high conversion efficiency. [PERSON] et al. [30] tested the ability of a symbol energy harvester to obtain electrical energy in a dynamic vibration environment, finding that metal end caps can increase ceramic endurance so that the whole structure can bear a higher load. [PERSON] et at. [31] used finite element software to analyze the geometrical parameters of cymbal energy harvesters applied to asphalt pavements, and the results showed that the energy harvesting efficiency was related to many factors, such as cymbal spacing, end cap thickness, and cavity height. The improvement and application of the cymbal energy harvester structure has also been concerned by many researchers. Based on the traditional cymbal energy harvester, [PERSON] et al. [32] designed a bridge structure energy harvester with metal end caps and a new type of electrode. Compared with the traditional cymbal piezoelectric energy harvester, the energy obtained was increased, and the failure period was obtained by cyclic loading of the prepared structure. It was found that the inconsistent thickness of the bonding layer was the cause of the structure failure. [PERSON] et al. [33] designed another radial layered cymbal piezoelectric energy harvester. To match the vibration frequency under traffic load, the metal end cap was calibrated by theoretical calculation and experimental test. The output power of the structure was not high, but a scheme to optimize the cymbal energy harvester structure was provided. The disadvantage of a cymbal piezoelectric energy harvester is that the metal end caps will cause stress concentration at the inner edge of ceramic plate, resulting in damage or fracture of the ceramic plate. In addition, the manufacturing process of a cymbal energy harvester is complex, and there are limitations in practical application. The sensors mentioned in the current article are limited to disk or cymbal structure and not used in the track bed; different from existing structures, this paper designed a spherical energy harvester based on a rubber bearing floating slab track, and the size range of the spherical energy harvesting structure was approximately determined based on the geometric spatial relationships of the actual track bed internal structure. Compared to the traditional disk and cymbal energy harvester, the mechanical and electrical properties of the spherical energy harvesting structure were studied by the numerical simulation method. Meanwhile, in order to improve the energy harvesting efficiency of the spherical energy harvester, the geometric parameters such as piezoelectric layer thickness, piezoelectric layer radius, spherical shell axial ratio, and spherical shell thickness were analyzed to obtain the optimal geometric size. The architecture of the paper is organized as follows: Section 2 introduces the spatial location where spherical sensors are suitable for harvesting energy in the track bed. Section 3 proposes the dimensions and parameters of spherical energy harvesting structure. Section 4 introduces the performance differences between the disk, cymbal, and spherical energy harvesting structure. Section 5 introduces the optimization process of geometric parameters of the spherical energy harvesting structure.