本論文主要探討結合Helmholtz共振腔之保護罩來改善小型四旋翼無人機之噪音，並針對特定噪音頻率以及某範圍的噪音頻域設計噪音抑制裝置，進行特定頻率範圍的噪音抑制工作。首先進行無人機噪音取樣，進行傅立葉轉換以及小波轉換，然後研究噪音來源及對應的消音方法，設計出結合Helmholtz共振腔之螺旋槳保護罩。分析部分，首先利用有限元素軟體 ANSYS 來模擬Helmholtz共振腔外部壓力震幅變化，以及聲壓變化，以預測在有加裝消音保護罩之情況下，噪音抑制的效果。設計部份則因要應用在小型無人機上，小型無人機負重有限，所以重量為第一考量。加工部分Helmholtz共振腔是使用3D列印的方式加工，多孔性、發泡性材料則是使用雷射切削過後與共振腔膠合。最後透過實驗為使用單螺旋槳加上保護罩進行實驗，實驗結果顯示本研究提出的三種不同的保護罩消音效果於10Hz-4000Hz分別可以消音3.72dB、4.14dB、4.98dB。

This research discusses the propeller shield with the Helmholtz resonator inside the combined foaming materials and porous material for noise reduction in UAVs. First, we analyze the noise sampling of the drone with both Fourier transform and wavelet transform, then study the source of noise and the corresponding noise reduction methods, and propose the design of three different propeller shield prototypes.
The most important design consideration is the weight of the prototypes. After all, they are to be applied to small drones, so weight is the first consideration. The Helmholtz resonator is made by 3D printing. Laser-cut porous and foaming materials are combined with the shield. They are glued to the Helmholtz resonator.
This research uses ANSYS to simulate the absolute pressure and acoustic pressure of the Helmholtz resonators to predict noise reduction effect by observing the amplitude and value changes.
The experimental results show that the noise reduction effect of three different propeller shields reduced 3.72dB、4.14dB、4.98dB in the 10Hz to 4000Hz frequency range in a single propeller experiment.

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