微振動結構與稀薄氣體的流固交互作用對實際工業有很大範圍之應用,包括高頻的共振器、硬碟的讀寫頭及高敏感度的力量感測器等。因此藉由探討微振動結構與稀薄氣體薄膜間的流固交互作用,了解微結構之動力行為,將對於產業界與學術界有所幫助。本文旨以直接蒙地卡羅模擬法(DSMC)建立二維數值模型,探討稀薄氣體薄膜對微型振動平板的影響,了解氣體在不同壓力以及不同振動頻率下,所產生之黏滯阻尼力對品質因數(quality factor)的影響。經模擬結果顯示,品質因數將受到兩參數影響,一為氣體稀薄程度,品質因數會隨氣體壓力遞減而遞增;另一則為結構自然頻率,在相同氣壓下,較高頻之振動結構,其結構強度較強,較不易受到氣體阻尼力影響,更可得到理想的品質因數。其中,以平板振動頻率為43 KHz為例,當壓力高於1 torr以上時,由氣體阻尼控制結構運動行為,將不產生週期性的振動;反之,隨壓力降低結構振動行為持續越久,氣體壓力降至1 mtorr時,品質因數可達約2000。以此數值模擬動態結構的運動情形,證明DSMC方法對微結構能提出合理的預測,以利將來對於更複雜之幾何外型的結構進行性能預測。

The study of fluid-structure interaction between a vibrating microstructure and a thin rarefied gas film is applied broadly in industry, for example, high frequency micromachine sensors, read/write heads of modern hard disk drives, highly sensitive strength detecting devices, and etc. In order to figure out the dynamic behavior of the rarefied gas film, a 2-D numerical model using Direct Simulation Monte Carlo (DSMC) method is established to investigate the relationship of a quality factor with the high frequency and low pressure limit. The numerical results show that the quality factor is inversely proportional to gas pressure, but proportional to the vibrating frequency. For example, for the case of the vibrating plate with the characteristic frequency 43 KHz, gas damping suppresses the vibration of the plate, when the pressure is higher than 1 torr. However, as the pressure is decreased to 1 mtorr, the quality factor becomes 2000. In terms of the obtained results, it is believed that the in-house DSMC method can predict the behavior of a vibrating microstructure reasonably.

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