霍爾感應器用於近場磁感應通訊之探討

Abstract

隨著電信的發展與進步，現今的無線通訊有向物聯網發展的趨勢。但物聯網的多種應用同時也帶來了許多挑戰，舉例來說，低能量消耗，高資料傳輸量，和較小的體積設計。對物聯網來說，如何選擇一個近距離的物理層傳輸技術如射頻識別技術(Radio-Frequency identification)RFID，跟近場磁通訊(Near Field Magnetic Induction Communication )NFMIC是很重要的。 在一些要考慮溼度，土壤，人體組織…等的通道環境下，NFMIC的獨特性質使其有比RFID更好的表現。在NFMIC系統中，使用線圈來產生磁場以傳輸資訊。但由於線圈的特性，如果想要得到較大的傳輸磁場，就需要更多圈數，如此一來線圈的體積就會變大，這並不適合用於產品上。因此我們使用霍爾感應器(Hall sensor)替換接收端的線圈使體積縮小，由於霍爾感應器的輸出電壓是由磁場的變化跟偏壓的電流所影響，所以它有比線圈更小的體積，但同時也要付出一些效能上的代價，本篇論文會分析為了更小的體積會付出哪些代價。 論文的結構如下所示：第一章介紹物聯網，近場磁通訊與霍爾感應器。第二章提出使用線圈和霍爾感應器的兩種近場磁通訊系統模型。第三章規劃系統的需求及規格，並且說明如何處理記錄的資料。第四章比較量測到的資料與理論上推導的資料，並近一步比較訊雜比，通道容量。最後總結這個方法並且討論未來發展的方向和可行的運用。

There is a recent trend of Internet of Things (IOT) in modern wireless communications. Due to the various applications in IOT, there are many challenges, too. (e.g., low power consumption, high data rates, and the small volume). Because many applications of IOT are used in short-distance wireless communication. Thus, choosing a suitable wireless communication method in short distance is very important. For instance, Radio-Frequency identification (RFID) is suitable for air medium, and Near Field Magnetic Induction Communication (NFMIC) is suitable for non-air media. In Comparison with RFID, unique characteristics of NFMIC particularly make it more suitable than RFID in some circumstance, where the communication environment consists of humidity, soil or body organs. In NFMIC system, coils are usually needed to generate the magnetic field to transmit signals. According to the property of coil, if we want to produce a bigger magnetic field, the coil needs more turns. In this way, the volume of coil will increase, and it is not desirable. Hall sensors have smaller volume than coils, and it can replace coils in the receiver to reduce the volume of receiver. The working principle of Hall sensors is generating voltage by Hall Effect to sense the changes of magnetic fields. However, there is a tradeoff between performance and volume. In this study, the costs of small volume consist of low capacity, short available transmission distance and bad signal to noise ratio…etc. . This paper is organized as follows. Chapter 1 introduces the Internet of things (IOT), near field magnetic induction communication (NFMIC) and Hall sensors. Chapter 2 proposes two system models; the near field magnetic induction communication system and Hall sensor based system. Chapter 3 lays out system requirements and specifications, and presents how the experiment is conducted. Then Chapter 4 compares experimental and theoretical results. Furthermore, we also compare the signal to noise ratio, and channel capacities. In the end, we summarize this thesis and propose future work directions and possible applications in Chapter 5.