**6. Conclusions**

Our simulation model successfully couples the piezoelectric physics with the laminar flow and heat transfer physics modules. Both prove that the adaptive lens was simulated at different voltages and temperatures to determine the actuator deflection, the fluid pressure, and the refractive power. The simulated results are in close agreemen<sup>t</sup> with the experimental results. The adaptive lens can vary the refractive power from −16 m<sup>−</sup><sup>1</sup> to 17 m<sup>−</sup><sup>1</sup> at 25 ◦C and from −15 m<sup>−</sup><sup>1</sup> to 28 m<sup>−</sup><sup>1</sup> at 75 ◦C. With this validation, we can now use our model reliably for further geometric optimization of our adaptive lens. Furthermore, the simulation model could be extended to also model the piezoelectric hysteresis and change in piezoelectric coefficients with the temperature.

**Author Contributions:** Conceptualization, U.W. and H.G.B.G.; methodology, U.W. and H.G.B.G.; software, H.G.B.G.; validation, U.W. and H.G.B.G.; formal analysis, U.W. and H.G.B.G.; investigation, U.W. and H.G.B.G.; resources, U.W. and H.G.B.G.; data curation, H.G.B.G.; writing–original draft preparation, H.G.B.G.; writing–review and editing, U.W.; visualization, H.G.B.G.; supervision, U.W.; project administration, U.W.; funding acquisition, U.W.

**Funding:** This work was financed by the Baden-Württemberg Stiftung gGmbH under the project VISIR<sup>2</sup> (Variable Intelligent Sensors, Integrated and Robust for Visible and IR light). The article processing charge was funded by the German Research Foundation (DFG) and the University of Freiburg in the funding program Open Access Publishing.

**Conflicts of Interest:** The authors declare no conflict of interest.
