# Flexible Vibrotactile Actuator Based on Dielectric Elastomer for Smart Handheld Devices
## 4 Conclusions  
In this paper, we have proposed a thin, highly flexible, and lightweight vibrotactile actuator based on PDMS and Ecoflex, and experimentally optimized it to provide a variety of haptic sensations in real time. The proposed vibrotactile actuator is composed of an upper layer, an adhesive tape layer, a bumpy-shaped dielectric layer, and a lower layer. In this structure, because the electrostatic and elastic forces contribute to the operation of the proposed actuator, the haptic performance of the proposed actuator is improved. To experimentally optimize the proposed actuator, we prepared several dielectric layer samples having different weight ratios of PDMS and Ecoflex, and investigated the mechanical and dielectric properties of the prepared several dielectric layer samples. Furthermore, we fabricated several vibrotactile actuators based on the prepared dielectric layer samples and measured the haptic performance of each actuator. The results show that haptic performance of the proposed actuator keeps getting better as the amount of Ecoflex in the dielectric layer increases. However, as the weight ratio of PDMS to Ecoflex exceeded 1:5, the haptic performance decreased. Therefore, we selected the vibrotactile actuator based on dielect\({}_{1.5}\). To show the reproducibility of the proposed actuator, we fabricated five haptic actuators based on the dielect\({}_{1.5}\) and evaluated their haptic performance. The result shows that the difference in haptic performance of the samples was less than the JND of human tactile perception [21]. Therefore, humans can hardly distinguish the difference in vibration amplitude among actuators. Furthermore, we confirmed that the proposed haptic actuator possesses a fast response time (approximately 18 ms). Due to these reasons, we expect that the proposed haptic actuator will be used as a future tactile feedback module for various smart devices such as a foldable smartphone, a flexible visual display, a rollable infotainment system, etc.  
Conceptualization, Y.H.H.; validation, D.-S.C.; investigation and analysis, D.E.K.; supervision, S.-Y.K.; writing and editing, all authors. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Technology Innovation Program (10077367, Development of a film-type transparent/stretchable 3D touch sensor/haptic actuator combined module and advanced UI/UX) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea). This work was supported by Institute of Information & communications Technology Planning & Evaluation (IITP) grant funded by the Korea government (MSIT) (No. 2020-0-00594, Morphable Haptic Controller for Manipulating VR-AR Contents). This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2021R1C1C1005677).  
Not applicable.  
Data Availability StatementData are contained within this manuscript.  
We thank the Cooperative Equipment Center at Koreatech for assistance with the universal testing machine (UTM) experiments.  
The authors declare no conflict of interest.