# Experimental Verification of the CFD Model of the Squeeze Film Lifting Effect
## 3 Results
### Results of Spherical Deformation  
The series of CFD calculations that were carried out assumed the idealized shape of the oscillator (Figure 10). The surface was modeled as an ideally spherical dimple with a varying diameter of the sphere and a constant position of the edge fixed at \(\phi\)40. Frequencies of the bottom surface were \(f=5,\ 10,\ 15,\ 20\) kHz. The shape of the dimple was modeled as perpetually (concaved, with controlled amplitude \(A\) and the mean position of the center of oscillator \(x_{0}=0.5\ \upmu\mathrm{m}+A\). The samples used for the calculations were modeled with masses between 5 g and 20 g with 5 g increments and a diameter of \(\phi\)40. The example of lifting results is shown in Figure 11. The figure shows the relation between the movement of the sample and the oscillator. The motion of the sample is characterized by the same frequency as the motion of the oscillator, which was observed for all inspected cases. Additionally, the motion of the lifted object and the membrane are generally in counter-phase. Figure 9: CFD calculation results for the sample (\(\phi\)20 mm, m = 0.373 g, f = 2.76 kHz). Figure 12 shows the CFD results of minimal lifting heights of the masses over the spherically deformed dimple. In all cases, there is a clear decline in the levitation height while the frequency of kinematic excitation of the membrane is raised. The levitation height of the sample asymptotically decreases. In the results, the most beneficial heights are at the lowest frequencies (i.e., 5 kHz). The increase of the height is restricted by the lift-off conditions--frequency and amplitude of the vibrating plate--the phenomenon described by [PERSON] et al. [12]. The lifting height also decreases with the decreasing amplitude of the vibration of the membrane and the increase of the mass of the object lifted. The influence of the membrane motion magnitude can be attributed to the amount of energy added to the system with each motion cycle; the larger amplitude of motion of the membrane, the higher lifting heights can be achieved. The heights achieved in the calculations vary from 5 to 60 \(\upmu\)m. The heights achieved in this experiment are higher than those reported by other researchers. Figure 11: Example of motion of the sample in relation to the motion of the oscillator \(m=10\) g; \(f=5\) kHz; \(A=1.5\)\(\upmu\)m.  
Figure 10: Idea of the geometry of spherical deformation calculation. The behavior of the modelled sample during the levitation is commonly overlooked during the experimental and theoretical results. The analysis of the results of the motion of the lifted elements shows a radical decrease in the amplitude of lifted objects with the increase in the frequency of excitation (Figure 13). The major factor governing the dependency is the inertia of the objects. In systems characterized by a higher frequency, the motion energy emitted by the vibrating system is dampened by the fluid film and not transferred to the object itself. It is worth noting that in all cases, the amplitude of motion of the lifted object is always lower than that of the excited plate. Figure 12: The minimal levitation height based on the CFD model of spherically deflecting membrane for masses: (a) 5 g; (b) 10 g; (c) 15 g; (d) 20 g.  
Pressure profile changes in progressive time steps are presented in Figure 14 for two separate cases, which differ from the frequency of oscillations. Pressure profiles for low frequency (5 kHz) are more complex and irregular than those calculated at higher frequency (25 kHz). One can notice that a similar level of absolute pressure values was calculated irrespective of the analyzed frequency; however, cases with net positive pressures have slightly higher values than those with negative pressures. This allows to generate a small positive pressure that allows the lifting of the object.