基於多鐵性材料之GHz頻段電氣小天線之設計與實驗驗證及其操作機制之探究

Abstract

多鐵性材料因其獨特的磁電耦合特性，在GHz頻段微型化天線設計深具應用潛力。本論文探討多鐵性天線的設計、開發與性能表現，最後得到的實驗結果與既有的理解與理論預測迥異。本研究的主要貢獻在於提供一個全新的實驗觀點，挑戰既有的假設與研究結論，進一步開啟對多鐵性天線輻射機制深入探討之可能性。論文中，我們首先回顧了電氣小天線(ESA)的基本理論，包括其理論限制、頻寬與效率之間的權衡，及其在生醫遙測與軍事通訊等領域之應用。ESA設計的主要挑戰在於如何克服尺寸縮小、頻寬及輻射效率之間的折衷，為了解決此問題，近年來學界提出一種新型機械驅動天線，稱為「機械天線」。這類天線透過機械運動來產生電磁輻射，而非依賴傳統的電流驅動機制，提供了一種可接近天線效能理論極限的新方法。然而，在GHz頻段實現機械激發仍面臨挑戰，因此需要尋求替代策略多鐵性天線。本論文進一步介紹以體聲波為驅動機制的多鐵性天線，這類天線利用壓電-磁致伸縮複合結構，在GHz頻率範圍內實現機械共振，若結合鐵磁性共振，這種設計能有效降低歐姆損耗並進而提升電磁輻射效率。最後，我們的實驗結果表明，相較於以往的研究成果，多鐵性天線在GHz頻段展現出根本性的差異，顯示出磁電輻射機制仍有待進一步深入探討，以利推動未來的研究發展。

Multiferroic materials have emerged as a promising solution for antenna miniaturization in GHz-band applications, leveraging their unique magnetoelectric coupling properties. This dissertation explores the design, development, and performance of multiferroic antennas. Our experimental results presented herein are among the few existing experimental verifications in the open literature, and they represent entirely new findings that differ significantly from existing theoretical predictions and understanding. The key contribution of this work lies in presenting a new experimental perspective that challenges prevailing assumptions and established conclusions, thereby paving the way for deeper inquiry into the underlying mechanisms of radiation from multiferroic antennas. The thesis begins with a review of electrically small antenna (ESA) fundamentals, including their theoretical limitations, bandwidth-efficiency constraints, and various practical applications in biomedical telemetry and military communications. A key challenge in ESA design is overcoming the inherent trade-off between size, bandwidth, and radiation efficiency. To address this, a new class of mechanically actuated antennas, known as “mechtennas,” was proposed. These antennas generate electromagnetic radiation through mechanical motion rather than conventional current-based mechanisms, offering a novel approach to approaching the Chu’s limit. Yet, GHz-frequency actuation remains a challenge, necessitating alternative strategies, such as strain-mediated antennas. The dissertation introduces bulk acoustic wave (BAW)-driven multiferroic antennas, which utilize a piezoelectric-magnetostrictive composite structure to achieve resonances at GHz frequencies. The design allows for efficient electromagnetic radiation with reduced ohmic losses. Finally, our experimental validation reveals that multiferroic antennas demonstrate fundamental differences in the GHz band compared to the previous findings. These findings call for further investigation into the underlying mechanism of magnetoelectric radiation in the future.