應用於無線配戴式感測節點之軟板天線設計

A Flexible Antenna for Wearable Wireless Sensor Nodes

邱弘棋(Hung-Chi Chiu)

指導教授 ： 甘堯江

元智大學/電機通訊學院/通訊工程學系/碩士(2011年)

https://doi.org/10.6838/YZU.2011.00263

摘要

隨著無線通訊、半導體製程技術的蓬勃發展，無線通訊感測的技術在醫療應用領域引起廣泛地注意以及研究，與這些即時監測與醫療相關等研究則統稱為行動醫療照護(Mobile Healthcare)。前端生理感測裝置依照實際應用，通常以環型配帶或貼附的方式固定於預計感測的身體部位。

本論文針對手腕脈搏感測應用設計合適的軟板天線，所設計的感測裝置採用德儀的整合射頻晶片CC430或是Tmote Mini，此兩個晶片之工作頻率分別為866MHz (779 MHz ~ 928 MHz)與2.4GHz (2.4 GHz ~ 2.484 GHz)。所設計的天線以倒F型天線為基礎，採用軟性電路板架構以方便環型配帶，首先設計可同時於雙頻段工作的軟板天線，此雙頻天線的配戴方式於實際應用時，量測位置較難調整，因此修訂感測節點的形狀並考慮小型化，所以只針對2.4GHz頻段設計合適的軟板天線。

本天線應用於脈搏感測時，會貼近人體手腕進行心跳血壓之感測，由於人體對於天線參數或特性會造成某種程度的影響，進而導致無線傳送的問題。藉由探討與研究人體對天線的效應，觀察到進入手腕的電磁波除造成天線工作頻率偏移與效率過低外，也相對會增加SAR值，所以本論文使用電磁能帶間隙結構形成接近同相的電波反射，抑制人體對天線的影響，進而能夠讓配戴式脈搏感測節點的軟板天線發揮正常無線傳送之效能。

關鍵字

天線 ； 軟板天線 ； 配戴式天線 ； 人體效應 ； 無線感測 ； 電磁能帶間隙

並列摘要

Due to the rapid development of the semiconductor and MEMS technology, the sizes of the mote and sensors of the wireless sensor networks (WSN) are reduced tremendously. Hence, continuous wireless monitoring of the human activity and health status, so called mobile health care, become much more feasible. For mobile health care, abbreviated as M-health, the sensor node is usually attached on the human body and that forces the planar antenna the better choice for the node.

This thesis presents the antenna design based on the printed planar inverted-F antenna (PIFA) for a wearable wireless pulsation sensor node. The first antenna proposed is a dual-band modified PIFA for 866MHz (779MHz~928MHz) and 2.4GHz(2.4GHz~2.48GHz). This antenna is fabricated on a 29cm long strip with flexible FR-4 substrate and can be wore on the wrist. However, this antenna occupies an area with 13cm x 3.1cm and then an antenna with smaller size is proposed but only for 2.4GHz. The second antenna is implemented on a four-layer flexible PCB and the circuit effect on the antenna is measured.

During the pulsation measurement, the sensor node is worn on the wrist and the antenna is basically adjacent to the skin with the distance of the thickness of the flexible PCB, about 0.3mm. In this case, the human tissues affect the performance of the antenna significantly, especially on the frequency detuning and the efficiency. Those effects result from the absorption of electromagnetic wave by the tissues inside the wrist. To reduce the wave into the wrist and have quasi in-phase reflected wave, an electromagnetic bandgap structure (EBG) is proposed and inserted between the antenna and skin. Satisfactory results on improving the working frequency and efficiency are observed and presented in this thesis. The EBG-based solution is then shown to be a feasible mean to have the wireless transmission of the pulsation sensor node work properly.

並列關鍵字

body effect ； wireless sensor node ； EBG ； antenna ； flexible antenna ； wearable antenna

參考文獻

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