Formation of high-pressure difference using nonlinear deformation of spherical cap

We present a parametric study on formation of pressure difference through the simple deformation process of a spherical cap and subsequently fabricate a simple pneumatic device based on our findings. Nonlinear responses are observed in this deformation of the spherical cap, which allows the formation of a large pressure difference. The elastic hemispherical cap is attached to a cylindrical cup with the same inner radius and height as the inner radius of the cap, forming a shared cavity. Additionally, the cup is equipped with a pressure sensor and a check valve for controlling fluid flow between the inside and outside. "Open indentation" refers to indenting the cap toward the cavity while keeping the check valve open, whereas "closed restoration" refers to restoring the indented cap with the check valve closed. During open indentation, the cap is deformed, reducing the cavity's volume without changing the inner pressure. In closed restoration, as the indented cap is restored, the reduced cavity expands and the formed pressure difference hinders the restoration. The energy stored during the indentation varies based on the cap's geometry and material, influencing the extent of restoration. We first investigate the open indentation - closed restoration behavior and the formed pressure difference by fixing the inner diameter of the cap and adjusting the thickness to control thickness-to-radius ratio. Then, we also measure them by tuning material of the cap. Finally, we fabricate a simple pneumatic device by finding the optimal combination of geometric conditions and material to form high pressure difference.