應用於金屬彎曲表面之RFID標籤天線

Abstract

本論文之研究為設計用於金屬表面且可彎曲的RFID標籤天線，使用頻段為902-928MHz，設計上的重點為因應天線從平面沿著不同半徑的圓柱彎曲產生共振頻率偏移使得阻抗匹配變差，提出一種補償機制降低因彎曲造成的變化。為了使天線可彎曲，天線製作使用2層基板與2層銅箔，上層基板為FR4，下層基板為泡棉，2層銅箔位於FR4板的上層以及泡棉的下層。下層銅箔為接地面可與金屬表面貼合，上層銅箔由饋入結構、輻射體結構及微晶片所構成，此天線結構沒有任何的貫孔與短路面。微晶片連接一環形共振腔形成饋入結構提供高電感阻抗，再耦合至輻射體，達到天線與微晶片間的阻抗匹配。輻射體上有一環狀方形槽孔，藉由耦合能量至槽孔所隔離的矩形寄生元件，使該結構提供的電感效果用來降低天線在金屬表面彎曲造成的共振頻率偏移影響，讓原先的頻率還有良好的阻抗匹配。透過量測，天線在平面以及貼附在不同半徑的金屬圓柱下，共振頻率幾乎沒有偏移也保持良好的阻抗匹配。本天線的設計細節及實驗結果在論文中有詳細討論。

This thesis proposes a conformal antenna for RFID metal tag. In many applications, RFID tags need to attach to different radius of the cylindrical metallic objects. However, the bending effect will cause severed frequency shifts and the impedance mismatch. Therefore, we propose a compensation mechanism to reduce bending effects. For smoothly attaching to bending objects, the substrate of the proposed antenna chose a 0.4mm-thickness FR4 substrate backed by a 1.1mm-thickness foam layer and a ground plane. The antenna does not have any shorting pins or walls. Chip, feeding network and the radiating body are placed on the top of FR4 substrate. The chip connected to a loop to provide a high inductance impedance, and it coupled to the radiator body to achieve impedance matching between the antenna and chip. The radiating body embedded an annular rectangular slot, and radiator coupling energy to the parasitic patch. This structure provides the inductive effect to reduce the impact of the antenna resonance frequency shift caused by bending from the metal surface . The structure can let the antenna maintain good impedance matching. The measured results show that the resonant frequency of the proposed antenna remain almost unchanged in different scenarios, such as placed on the plane or attached to different radius of cylindrical objects. The design details of antenna and experimental results are discussed in detail in the thesis.