★RFID的早期應用

★主動式 VS. 被動式 ★低頻/中頻/高頻/微波
★ RFID 的優點 ★ RFID的缺點 ★ RFID防碰撞問題 Anti-Collision

 


★ RFID的早期應用-感應卡 TOP
 感應卡分為接觸式(contact)及非接觸式(contactless)兩種;接觸式卡和讀卡機實體接觸才能完全感應,因與讀卡機直接接觸,所以使得晶片中的資料安全性提高,且儲存容量比非接觸晶片要高;然而經常使用會降低其使用壽命;目前健保卡就是屬於接觸式感應卡。
而非接觸式則因為內含感應天線,使讀卡機以感應的方式讀取資料,讀卡所需的時間比接觸式的短,使用上較為方便,且由於不須接觸,使用壽命較高,然而安全性卻不如接觸式;目前捷運悠遊卡即為此系統。
  

★主動式 VS. 被動式 TOP
RFID系統架構可分為電子標籤(Tag)、掃讀器(Reader)、天線(Antenna)三種。而電子標籤又分為被動式與主動式;主動傳輸RF信號的RFID單元稱為主動式標籤,它可讀寫並可重複使用;其記憶體大小可應需求而變化,有些甚至可達1MB,價格較昂貴,使用週期較短。其應用市場主要是國防醫療,如需要快速定位與讀取資料的軍事醫療;及些許工業市場,如交通道路自動收票、付費/保險紀錄的車輛管理運用。

而將僅進行RF信號反射或反向散射傳輸的RFID單元稱為被動式標籤,它唯讀,不可重複使用,主要負責儲存被識別物的相關資訊,如品名、編號、規格等;此外價格較便宜、無限使用週期、讀取區域較近。主要應用於快速紀錄追蹤,如動物管理;防盜防遺失,如門禁與貨運管理;還有消費市場應用,如超級市場產品管理。


★低頻/中頻/高頻/微波 TOP
此外依頻率來分,RFID分為低、中、高頻及微波四種。

低頻(LF)指頻率於125KHz、讀取距離小於0.5m、讀取方式以感應線圈的方式,其多應用於動物、門禁與POS。

中頻(HF)頻率則為13.56MHz,讀取距離介於0.5m,也是以讀取感應線圈為主,其多應用於智慧卡與圖書館管理系統。

高頻(UHF)頻率介於868-915MHz,其讀取距離介於3m、以電容式電場效應方式讀取,運用於淺板/紙箱與電子收費。

而微波的頻率則指2.45與5.8GHz,最大讀取距離在1m左右,同樣也是以電容式電場效應方式讀取,其主要應用在於供應鍊與電子收費系統。

在處理資料的速度以微波最快,高頻次之,再來是中頻與低頻;在惡劣環境(例如接近金屬或潮濕面)的讀取能力,則相反,以低頻效果最佳,中頻後是高頻,微波效果則最差;而被動式標籤的尺寸大小是以低頻最大,中高頻次之,微波最小。


★ RFID 的優點 TOP
體積小 - 傳統的磁性條碼受限於體積,不易嵌在較小的物品上,RFID則不然。日立(Hitachi)甚至已經發展出厚度僅有0.1mm、面積為0.4mm X 0.4mm的微型RFID晶片,薄到可以嵌入紙幣中;因此RFID的迷你體積可以隱藏在各種物品裡面。

主動式提供資訊 - 仗著無線通訊的優勢,RFID具有主動提供產品資訊的功能,因此運用於消費市場中,客戶不需要抵達櫃台即能結帳;甚至,當客戶推著推車在賣場移動時,賣場中的感應器便會自動統計推車中商品的售價,當商品即將售完,還可以自動通知商家補貨。

容量、速度與安全性 - RFID除了儲存的資料量遠比傳統條碼多、不容易被偽造外,辨識讀取速度每秒可達250個標籤,這種多工成效遠比傳統條碼一次掃瞄一個(單點連線流程,line-of-site)高得多,自然可以免除前述的困擾。

耐久性 - 一般傳統紙製或塑膠材質的條碼有時會因下雨、或潮濕的環境,及搬運的過程中遭致毀損而難以辨識。RFID具有可重複使用數十萬甚至數百萬次以上的特性,其材質也能夠被放置於較為惡劣的環境中,因此比條碼更具有耐久性,自然成本也較為節省。


★ RFID的缺點 TOP
RFID目前的成本除了標籤部分外,配套的周邊與服務對一般企業來說仍然偏高,通常只有大企業負擔得起。因此,雖然市場普遍看好RFID,但需要各個領域的多數廠商加入,才可讓RFID如同條碼與POS系統一樣普及。

此外,引人爭議的是因消磁不完全而引發「個人隱私權」的問題;例如傳統磁性條碼常會因消磁不完全造成感應器誤判,進而影響消費者購物心情與店家商譽,甚或引發法律糾紛;RFID也可能會有類似的情況。再者,購物內容皆是個人隱私,若每一樣物品都內建RFID,不肖份子便可能輕易地在一定的範圍內窺視與收集到每個人的購物商品內容。

對於個人的消費情形隱私權,已讓大眾產生疑慮,隨著RFID技術普及到各層面,未來更可能使用在證照或身份證件等方面,資料曝光的危險性顯得更高;同時,隨之而來如駭客或是政府的監視,也都影響到民眾的權益。因此,我們可說RFID未來的市場有多大,安全與隱私權維護的憂慮就有多大。


★?RFID防碰撞問題 Anti-Collision TOP
請注意RTF or TTF主要針對UHF Passive Tag,其他不盡相同,如主動式,以下一些定義及相關資料提供參考

Most of the RFID systems available today are RTF (EPC, Matrics, Alien, ISO 18000-6 A and B, Philips). One exception is the iP-X series (EM4222 and related chips). Reading range depends probably more on the technology used in the chip manufacture and the sensitivity etc. of the reader, rather than on whether the protocol is TTF or RTF. RTF tags tend to be more complex and could therefore be more expensive, but this would also depend on the technology used.

However, Both TTF and RTF passive tags must be powered from the reader beam, and both contains digital circuitry, amongst other things for the anti-collision protocol. The only difference lies in who initiates the communication between tags and reader. In RTF the reader starts the conversation, and needs to be alerted to the presence of tags by some external means or has to poll for tags. In TTF, the tag announces its presence to the reader, so no external presence detection or polling is required.

RTF-Reader talks first:
A means by which a passive UHF reader communicates with tags in its read field. The reader sends energy to the tags but the tags sit idle until the reader requests them to respond. The reader is able to find tags with specific serial numbers by asking all tags with a serial
number that starts with either 1 or 0 to respond. If more than one responds, the reader might ask for all tags with a serial number that
starts with 01 to respond, and then 010. This is called "walking" a binary tree, or "tree walking." (See singulation.)

TTF-Tag talks first:
A means by which a reader in a passive UHF system identifies tags in the field. When tags enter the reader's field, they immediately
communicate their presence by reflecting back a signal. This is useful when you want to know everything that is passing a reader, such as when items are moving quickly on a conveyor. In other cases, the reader wants to simply find specific tags in a field, in which case it
wants to broadcast a signal and have only certain tags respond.

Singulation:
A means by which an RFID reader identifies a tag with a specific serial number from a number of tags in its field. There are different
methods of singulation, but the most common is "tree walking", which involves asking all tags with a serial number that starts with either a 1 or 0 to respond. If more than one responds, the reader might ask for all tags with a serial number that starts with 01 to respond, and then 010. It keeps doing this until it finds the tag it is looking for.

Active Tag - A U.S. patent for the anti-collision features of its eLink wireless communication protocol.
When several RFID tags are in the field of a single reader, their signals interfere with one another, confusing the reader. Most anti-collision protocols require active, or battery-powered, tags to remain "awake" while they communicate with the reader until all their serial numbers are read.

To conserve battery life, this came up with a protocol that doesn't require all tags to remain awake. The reader sends out a signal that
wakes up the tags and asks them to transmit the first bit of their serial number. The reader signals all the tags that don't send back a
one to go back to sleep until later. The reader keeps eliminating tags until it finds the one with the highest serial number. Then, it
wakes up the other tags and goes through the process again. This happens so quickly that it appears as though the tags are being read
simultaneously. The protocol works on up to 16 million tags.