兆赫波的應用於醫學、生技以及顯像等方面具有相當的潛力，而我們的目標為設計一個結構簡單、效率較高的裝置。在此論文中，我們提出特殊結構的Smith-Purcell光柵式返波振盪器以產生強力的兆赫波。
　　我們先以Matlab計算單面光柵結構的邊界條件以解出其色散關係，並確定其與不同能量之電子束的操作頻率。接著，我們利用MAGIC 2D模擬軟體以觀察該結構和電子的作用情形，並發現兩者所解出的操作頻率甚為接近，進而從中確定先前計算之正確性。在此，我們亦模擬不同的光柵－電子束距離和電子密度對於表面波的飽和時間以及強度的影響，從這些結果觀察出單面光柵當操作於兆赫波範圍嚴苛的起振條件。
　　為了製造一個有更高能量耦合效率且容易被加工的結構，「半開放式光柵結構」在此提出。我們利用MAGIC 2D模擬，並發現其產生的表面磁場B_z可達一般Smith-Purcell光柵結構的四倍。於大尺徑電子束的模擬中，我們採用同步輻射中心電子槍的參數，並藉由ASTRA的模擬，確定三個聚焦線圈之磁場為130高斯、120高斯和170高斯分別置於陰極後方21.5公分、33.5公分和50公分。而產生之1A電子束的最小方均束徑可達0.41毫米於陰極後方80.5公分處。然而，於該模擬中，電子束並未完全地受到調制，其原因為不對稱的激發場未能完全涵蓋整個電子束。
　　我們亦提出一個包含金屬鍍介電質板和光柵的複合結構，利用光柵結構群聚電子，以額外的介電質激發切忍可夫輻射，而此一結構所激發的表面磁場可達一般光柵結構的六倍。該複合結構亦是對能量耦合有相當的增益。

THz waves have potential in medicine, biophysics, and imaging. In order to fabricate a simple device with high efficiency, here we propose a special kind of Smith-Purcell grating backward-wave oscillator (BWO) for THz generation.
First, the boundary conditions of the Smith-Purcell grating are solved by the Matlab code, and the operating frequency is determined by the dispersion relation and the beam line on the Brillouin diagram. Then we simulate the grating-structure by MAGIC 2D to observe the interaction between the structure and the electrons, and the results of the operating frequency in MAGIC 2D agree with the results in Matlab. Also, we simulate the grating with different current densities and beam-grating distances, and find that the restricted beam condition while operating at THz region.
In order to enhance the coupling efficiency, also to make the structure easy to manufacture, “semi-open” grating is proposed. From the result of MAGIC 2D simulation, we find the magnitude of the B_z field is 4 times as large as the conventional Smith-Purcell grating BWO on the surface of the grating. In thick beam simulation, the parameters of the E-gun in NSRRC are applied to the ASTRA simulation to determine the magnetic field for beam focusing. The calculated magnetic field of the solenoids are 130gauss, 120 gauss and 170 gauss at 21.5cm, 33.5cm and 50cm respectively and the rms beam size equals to 0.41mm at 80.5cm. Yet in MAGIC 2D simulation, the upper portion of the electrons is not well modulated due to the asymmetric excited mode profile.
We also propose another structure that contains both an optical grating and a dielectric coating metal plate. The dielectric layer provides the condition for stimulated Cherenkov radiation, and the excited magnetic field is 6 times of the field of single-side structure on the surface of the grating. We suppose it is a promising structure for enhancing the energy coupling between the beam and waves.

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