# Design of an Energy Harvester Based on a Rubber Bearing Floating Slab Track
## 4 Performance Comparison of Energy Harvesters
### Mechanical and Electrical Performance  
Since the electrical signal output from the energy harvester varies with excitation, an energy harvesting circuit is required to capture or store the electric energy generated by the structure [35; 36]. While the energy harvesting circuit also has certain requirements for the output signal of the energy harvester, it generally requires the minimum output voltage of the energy harvester to be around 0.5-1.4 V. If the output voltage of the energy harvester is less than the minimum turn-on voltage, the circuit will be in an open circuit and will not be able to transmit or store electric energy. Therefore, the output voltage of the energy harvester is one important electrical characteristic.  
As shown in Figure 5(a), the stress of the disk energy harvester was concentrated at the force transmission plate, and the peak stress was 0.45 MPa. As shown in Figure 5(b), the output voltage of the disk energy harvester had an obvious laminar distribution along the axial direction, and the maximum value was 0.62 V. The total electricity generated was calculated to be 1.09 \(\times\) 10\({}^{-9}\) J.  
As shown in Figure 6(a), the stresses in the symbol energy harvester were concentrated at the top and bottom edges of metal caps with a peak stress of 3.62 MPa. As shown in Figure 6(b), the output voltage of the symbol energy harvester was obviously distributed in layers along the axial direction, and the maximum value was 6.5 V. The total electricity generated by this energy harvester was calculated to be 9.37 \(\times\) 10\({}^{-8}\) J.  
Compared with the disk energy harvester, the output voltage and total output energy of the symbol energy harvester were greatly increased. The output voltage was about 10 times higher than that of the disk energy harvester, and the total output energy was an order of magnitude higher than that of the disk energy harvester. However, the symbol energy harvester showed a significant stress concentration at the change of geometric sizes, and the peak stress was about eight times higher than that of the disk energy harvester.  
Figure 5: Numerical model of energy harvesters.  
As shown in Figure 8a, the stress of the spherical energy harvester was concentrated at the bottom edge of the spherical shell, but there was an obvious uniform gradual change of stress along the surface of the spherical shell, thus effectively reducing the peak stress, which was 1.25 MPa. As shown in Figure 8b, the output voltage of the spherical energy harvester also showed obvious laminar distribution along the axial direction, and the maximum value was 6.7 V. The total electricity generated by the spherical energy harvester was calculated to be \(1.17\times 10^{-7}\) J.  
Compared with the disk energy harvester, the total output energy of the spherical energy harvester was greatly improved, being two orders of magnitude higher than that of the disk energy harvester. And compared with the cy  
Figure 8: Mechanical and electrical properties of the spherical energy harvester.  
Figure 6: Mechanical and electrical properties of disk energy harvester.  
Figure 7: Mechanical and electrical properties of the cymbal energy harvester.  
the spherical energy harvester also showed some stress concentration at the bottom of the spherical shell, the peak stress was reduced by 65% compared with the symbol one due to the good stress homogeneity of the spherical shell structure. The spherical energy harvester had both good mechanical properties as well as superior electrical properties. Its output voltage was 11 times more than that of the disk energy harvester, and the total output electric energy was 20% more than that of the symbol energy harvester.