# Design of an Energy Harvester Based on a Rubber Bearing Floating Slab Track
## 5 Parameter Optimization Design
### Spherical Shell Thickness  
When studying the influence of the spherical shell thickness on the energy harvester, the horizontal axis radius of the inner cavity of the spherical shell was kept constant, at 11 mm. The axial ratio was controlled by changing the outer radius of spherical shell, i.e., the piezoelectric layer radius R. In the parameter value list, R = range (12, 1, 23) was defined, and the spherical shell thickness T = R-r\({}_{2}\) ranged from 1 mm to 12 mm. The peak stress, peak vertical displacement, peak voltage, and total electricity of the spherical energy harvester with different spherical shell thicknesses were obtained.  
As shown in Figure 27, the peak stress decreased with increasing spherical shell thickness. The spherical shell thickness T increased from 1 mm to 12 mm, and the peak stress of the energy harvester decreased from 4.28 MPa to 0.81 MPa, with a decrease in 81.1%. Figure 28 shows the variation of the peak vertical displacement, which decreased with increasing spherical shell thickness from 4.22 \(\times\) 10\({}^{-4}\) mm to 1.65 \(\times\) 10\({}^{-4}\) mm, with a decrease of 60.9%.  
As can be seen from Figure 29, the peak voltage first increased and then decreased when the spherical shell thickness was continuously increased, and the peak voltage was 6.7 V when the thickness T = 4 mm. As the thickness increased from 1 mm to 12 mm, the peak voltage of the energy harvester increased from 3.6 V to 5.9 V, with an increase in 63.8%. As shown in Figure 30, the change of total electricity increased with the increase in spherical shell thickness, showing a linear trend. With the increase in sphe  
Figure 28: Peak vertical displacement under different spherical shell thicknesses.  
Figure 27: Peak stress under different spherical shell thicknesses.  
total electricity of energy harvester increased from 3.91 \(\times\) 10\({}^{-8}\) J to 1.86 \(\times\) 10\({}^{-7}\) J, with an increase of 4.8 times.  
When the spherical shell thickness varied in the range of 1-12 mm, the peak stress and vertical displacement of the energy harvester were within the safety range, so the electrical properties were also given priority to determine the thickness of the spherical shell. When the thickness of the spherical shell was 4 mm, the peak voltage of the energy harvester can be taken to the maximum value of 6.7 V, which meets the minimum output voltage requirement (0.4-1.5 V). At this time, the total electricity was 1.05 \(\times\) 10\({}^{-7}\) J, and the optimal spherical shell thickness was 4 mm.  
Through numerical simulation of the dimension parameters H, R, I, and T of the spherical energy capture structure, it was found that the peak voltage and total electricity of the spherical energy structure increased with the increase in piezoelectric layer thickness H. The peak voltage first increased and then decreased when increasing the piezoelectric layer radius R, and the total electricity increased with the increase in piezoelectric layer radius R. The peak voltage and total electricity decreased with the increase in spherical shell axial ratio I. The peak voltage first increased and then decreased with the spherical shell thickness T getting larger, and the total electricity increased with the thickness T of the spherical shell. Considering obtaining better electrical performance and combining it with the actual situation, the optimal size of the spherical energy harvester was obtained as shown in Table 5, and the energy harvester cell under the optimal size is shown in Figure 31.  
Figure 30: Total electricity under different spherical shell thicknesses.  
Figure 29: Peak voltage under different spherical shell thicknesses.