請用此 Handle URI 來引用此文件:
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/708
標題: | 基於剪切模態體聲波激發之多鐵電性天線之寬頻極化控制 Broadband Polarization Control of Bulk Acoustic Wave-Mediated Multiferroic Antenna Based on Thickness Shear Modes |
作者: | Rui-Fu Xu 許瑞福 |
指導教授: | 陳士元(Shih-Yuan Chen) |
關鍵字: | 微機電系統,微型化天線,射頻微機電系統, MEMS,Antenna miniaturization,RF MEMS, |
出版年 : | 2019 |
學位: | 碩士 |
摘要: | 近年來在5G、物聯網、生醫電子、穿戴式裝置等應用的發展之下,天線微小化已逐漸成為越來越重要的題材。天線微小化在過往有許多的嘗試,例如:使用高磁導率或是介電係數的基材、不同的天線設計等等。但不論在低頻或高頻頻段,只要天線相對於共振波長尺寸遠小於一時,輻射效率就會變得很差而不堪使用。2015年首次提出了利用機械聲波,採用多鐵電性材料來實現天線微小化的可能性,基本原理是機械聲波在相同的共振頻率下,波長相較電磁波小了千倍到萬倍左右,因此若能在合適的共振頻段減少耗損,將有可能實現天線微小化並逼近理論極限。然而在過往提出的設計概念中,主要是使用縱向波的共振來實現,在本研究中主要針對了這類型新的天線,首次提出了藉由平面電極來激發剪切模態的概念。因為剪切模態可以有對稱且相互垂直的兩個模態,因此若施加特定相位差將可進行極化控制。除了極化控制之外,剪切模態可激發橫向的磁流,因此若放置於金屬平面上,可期待得到更強而非相消的輻射。此類極化控制的設計概念,使用了COMSOL數值模擬及MATLAB的後處理計算來驗證。根據模擬結果在理想的九十度相位差饋入之下,此類圓極化模態擁有極寬頻的特性。相關設計由UCLA的Rob Candler教授之研究團隊製作晶片並在台大完成了量測,本論文亦將針對量測結果進行初步的探討與分析。 Antenna miniaturization has been more and more important these days. Many applications like IOT, biomedical devices, wearable devices, and 5G demand higher performance with smaller feature size. Many works on antenna miniaturization have been done before, such as using substrate with high permittivity or permeability, diverse structure antenna design, etc. However, no matter in UHF or VLF band, as long as the electrical size of an antenna is much smaller than one, the radiation efficiency will be extremely low, making the antenna infeasible. In 2015, theoretical groundwork of using multiferroic material to achieve antenna miniaturization was firstly propose, named “bulk acoustic wave-mediated multiferroic antenna”. The core concept is that the wavelength of mechanical wave is five orders of magnitude smaller than electromagnetic wave under the same resonant frequency. As long as the loss can be further reduced, it owns great potential to approach Chu’s limit for electrically small antennas. In the above mentioned works, the radiation is mainly generated based on longitudinal acoustic wave. In this thesis, thickness shear mode is used instead of longitudinal one. By using the shear mode, two sets of symmetrical but orthogonal resonant modes can be manipulate by applying 90° phase difference to generate circularly polarized (CP) wave. In addition, the shear wave can excite in-plane magnetic current, which will double the radiation instead of cancelling out each other when the device is placed above a metallic ground plane according to the image theory. Such concept can also be used for tunable polarization control. The design concept is preliminarily investigated through FEM-based multi-physics solver, COMSOL, and post processing by an in-house MATLAB code. It is shown that under the ideal input RF signal pair of equal magnitude and with 90° phase difference, the proposed design can achieve very broadband CP with satisfactorily low in-band axial ratio. The design is fabricated by Dr. Sidhant Tiwari from UCLA. The test pieces were tested, and the results thus obtained are presented and discussed through a couple of comparisons. This work envisions the possibility of broadband polarization control and/or tunability of electrically small antennas. |
URI: | http://tdr.lib.ntu.edu.tw/handle/123456789/708 |
DOI: | 10.6342/NTU201901864 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 電信工程學研究所 |
文件中的檔案:
檔案 | 大小 | 格式 | |
---|---|---|---|
ntu-108-1.pdf | 7.84 MB | Adobe PDF | 檢視/開啟 |
系統中的文件,除了特別指名其著作權條款之外,均受到著作權保護,並且保留所有的權利。