## 4 Experimental Evaluations
### Experimental Results of Actuator Performance
The hole in the top electrode has a clear effect on the dual-electrode ERA's performance. It can, therefore, be reasonably inferred that if the actuator was fabricated for optimal use and a hole was not made in the top electrode, the dual-electrode ERA's performance with both electrodes activated would exceed its current maximum of 14.32 g-forces. In summary, the proposed dual-electrode actuator's performance when only using the top electrode with a hole was worse than its performance when using the bottom electrode only. The dual-electrode actuator's performance when activating only the bottom electrode without a hole was similar to the single-electrode actuator, indicating that variances caused by manufacturing did not significantly impact the ERA's performance. To further evaluate the actuators' performance, a \"mock-up\" display panel test setup was employed. The purpose of this evaluation was to compare the performance of the single and dual-electrode actuators when they were mounted onto a small tablet-sized rectangular panel. Note that the scope of this study was not to evaluate the performance of the actuators on large displays, but rather to examine the effect of the electrode configurations in ERAs. Thus, more comprehensive, full-scale large display  
Figure 8: Experimental acceleration response of the dual-electrode actuator powering the bottom, top, and both electrodes. Figure 7: Experimental acceleration response of single-electrode actuator and dual-electrode actuator. testing will be conducted in a future study. Figure 9 shows the mock panel test setup. As shown in Figure 9, the single-electrode ERA was mounted onto the bottom of a fabricated mock-up panel, which is supported by ultra-soft silicone supports at its four corners. An accelerometer was mounted onto the top surface of the panel to measure the output vibration intensity at the display surface, created by the ERA. Figure 9 shows the equivalent dual-electrode ERA setup. For both tests, the input signals described earlier were used. Figure 10 shows the frequency response results of the panel testing. As seen in the figure, the resonance peak occurs at 158 Hz for both testing cases. The results show that the dual-electrode ERA produced a consistently higher vibration intensity throughout the entire frequency range considered in this study. Furthermore, the dual-electrode actuator produced a higher maximum acceleration (3.88 g-forces at 158 Hz) compared to the single-electrode actuator, which produced a maximum of 2.36 g-forces at 158 Hz. Similar to the actuator-only testing, the additional electrode increased the maximum intensity by 1.52 g, or nearly 65%, compared to the single-electrode actuator. In short, the dual-electrode ERA, with both electrodes activated, outperforms the single-electrode counterpart in producing the maximum peak vibration intensity even when mounted on an external mass. Note that Pacinian Corpuscles are most sensitive to sinusoidal vibrations around 150-160 Hz and that the detection threshold value for fingertip of vibration feedbacks is around 0.05 g [17; 18]. The mock-up panel testing results showed that the developed dual-electrode ERA is resonant at 158 Hz, which is the most sensitive area for humans, and it can generate a vibration output 77 times greater than the activation threshold. Thus, the results indicate that the proposed dual-electrode ERA can provide sufficiently strong haptic sensations. The proposed dual-electrode ERA can generate significantly improved vibration feedback than single-electrode ERA, making it more suitable for a large touch-sensitive display (TSD) requiring large vibration haptic feedback. The double electrode ERA is a thin plate structure, so multiple ERAs can be mounted on the back of the large TSD for conveying enhanced haptic feedback to users. Figure 11 illustrates this concept that multiple dual-electrode ERAs can be used to generate for the large TSD.