# Experimental Study of See-Saw Mode Nano-Vibration on Orifice-Type Restrictors
## 2 Materials and Methods
### Simulation on One-Orifice-Type Restrictor Based on FEM FSI
The greater the inlet air velocity, the greater the restrictor vibration, as shown in Figure 4. Interestingly, the peak-valley values of the time-averaged amplitudes on the circumference are identical (0.003 nm) under different air-supply pressures, meaning that even if the speed of the inlet air changes (representing the air-supply pressure and the gas film distribution change), the restrictor maintains the same rotational amplitude. If the vibration signal is expressed with direct-current (DC) and alternating-current (AC) components, the inlet air velocity only changes the DC component. Although our simulation did not completely adhere to the actual structural parameters (e.g., air-supply pressure and film thickness of the restrictor), which were limited by the simulation conditions, the results obtained still provide useful qualitative results. Then, we examine the true vibrational state of the restrictor via experimentation. vibration isolation platform, etc. The restrictors were placed on an ultra-precise plate with a restricting block, which limits the restrictor's movement when gas is supplied. When the restrictor is in its steady state, there is little-to-no friction between it and the restricting block. For its nanometric measurement, a high-performance laser vibrometer POLYTEC OFV505/5000 was employed, equipped with a DD-900 displacement decoding card that measures a range of 0.5-100 m with 0-2.5 MHz measurement bandwidth and 0.5 pm displacement resolution. Two orifice restrictors (double-ring- and double-U-grooved) were investigated using the experimental device. In our previous work [25], we studied the double-ring-grooved restrictor style. Both restrictors were 75 mm \(\times\) 50 mm \(\times\) 14 mm, as shown in Figure 6. From the bottom surface, orifices having diameters of 0.2 mm and square-cross-section grooves with depths and widths of 0.2 mm are present. From the upper surface, reflection stickers were dispersed along P1-P7, as required for the laser vibrometer. P1, P2, P3 and P4 are in the corners 5 mm from the edges. P7 is near the center. P5 and P6 are near the midpoints of P1 and P7 and P2 and P7, respectively. Because it is very difficult to adjust the position of the laser vibrometer, shifting is inevitable. The measurement process is shown in Figure 7. First, after the reflection stickers are pasted, the laser vibrometer (on a tripod) is placed so that the beam falls on the P1 sticker. Second, the pressure regulator is adjusted to an air-source pressure of 0.5 MPa. Third, the amplitude-frequency curve of the vibration data is measured by the laser vibrometer. When the prominent frequency point in the amplitude-frequency curve stops changing  
Figure 5: Experimental device with a vibrometer. Figure 6: The examined restrictors: (**a**) double-ring-grooved; (**b**) double-U-grooved; and (**c**) upper surface. with time (5 s), vibrational data are recorded at a time interval of 5.12 s with a sampling frequency of 102.4 kHz. Fourth, the pressure-regulating valve is adjusted to 0.4, 0.3, 0.2 and 0.1 MPa, and the above steps are repeated for each. Finally, the gas source is turned off, and the laser vibrometer is used to measure the normal vibration of the restrictor in a no-gas state. Then, the vibration measurement of P1 is complete. The tripod is then moved so that the laser beam of the vibrometer falls on the next reflection sticker. Everything is repeated until all positions are measured. These steps apply to both restrictor types. The entire experiment is then repeated for all restrictors in accordance with the above steps. Note that P5 and P6 are not included in the double-U-grooved-style restrictor tests.