以平行化時域有限差分法研究數種奈米天線結構

Abstract

時域有限差分法已被廣泛地運用在諸多光電電磁學問題的計算與模擬上。我們利用C語言自行開發三維時域有限差分模擬器，並利用多台電腦透過訊息傳遞介面協定來加速模擬，減少運算時間。本論文中，我們利用平行化時域有限差分模擬器，來分析奈米十字對天線，以及奈米螺旋天線與奈米十字對天線的有限陣列。十字對天線又細分為十字對天線、變化型十字對天線、與三叉戟對型天線。首先我們以一個寬頻的電磁波作為波源，垂直照射在奈米天線，得到天線間隙之局部場增強、頻譜響應及共振波長。接著，我們將天線擺放成陣列來觀察其特性變化。模擬結果顯示，當我們在天線的間隙處，適度的加上平行的金屬尾翼，會使得共振波長紅移，藉由改變金屬尾翼長度，可以使得變化型十字對天線、三叉戟對天線、螺旋天線依序紅移60%、52%、與16%共振波長。此外螺旋天線與十字對天線相比，在相同的天線面積大小內，有更長的共振波長與更強的局部場增加。在相同的天線面積下，有著較強局部場和較長的共振波長的螺旋天線，當天線縮小時，其共振波長的減小和局部場的降低不致於太大，為其優點。

The Finite-difference time-domain (FDTD) method has been widely used in computational electromagnetics. In this research, a parallelized three-dimensional (3D) FDTD simulator in C language is constructed and several computers are combined to speed-up the simulations by using the message passing interface (MPI) protocol. Then, the simulator is employed to study nano-antennas including the cross-pair antenna, the modified cross-pair antenna, the trident-pair antenna, and the spiral antenna. The antennas are simulated with a broadband source. The local field enhancement in the antenna gap is calculated, including the broadband responses and the resonant wavelengths. Then, three different arrangements of two- and four- element arrays are simulated. The most important finding is that the wing length at the antenna gap will make the resonant wavelength red-shift. By varying the wing length, the resonant wavelengths of the modified cross-pair, the trident, and the spiral antenna can be increased by 60%, 52%, and 16%, respectively. The spiral antenna seems to possess larger gap enhancement and resonant wavelength than the cross-pair, the trident-pair, and the modified cross-pair with the same antenna size (450 X 450 nm2). Thus, the spiral antenna has the advantages of reducing the antenna footprint without decreasing too much in the gap enhancement and resonant wavelength.