What is RFID Tag? What are UHF RFID Tag Types?

Contents

1. What are RFID Tags?
2. How Do UHF RFID Tags Work?
3. What's Inside the UHF RFID Tag?
4. Label Form Factors
5. Label Positioning
6. Label Addition Methods
7. Application Surface Materials
8. Label Special Features
9. Relationship between Label Reading Interval and Size

What are RFID Tags?

RFID tags are placed on items to identify or track items over time or throughout their lifecycle. RFID tags can be used to track all types of objects, track assets or inventory in industries such as healthcare, retail and manufacturing. This guide covers the main considerations to take into account before deciding on or purchasing an RFID tag. Each tag can differ significantly from the next, making it imperative to select a tag designed to work in environments and applications similar to your application for best results.

How RFID Tags Work?

RFID tags communicate with RFID readers and antennas via electromagnetic waves. The reader/antenna combination directs electromagnetic radio waves to nearby RFID tags. The energy from the waves used by the RFID tag's antenna creates a current that moves towards the centre of the tag energising the integrated circuit (IC). The IC switches on, modulates the energy with data from memory banks and routes a signal back through the tag's antenna. The remaining, modulated energy that responds to the reader/antenna is known as "backscatter".

Brief Information About UHF RFID Tags:

• Most of them have no batteries and are powered solely by electromagnetic waves.
• Those with batteries (Battery Assisted Passive RFID Tags and Active RFID Tags) can achieve much longer reading intervals.
• Unlike barcodes, they do not require line of sight.
• The way the tags match or communicate with the RFID reader is called "backscatter".
• An algorithm called "Collision Avoidance" on each tag defines the order in which to respond if there is more than one tag in the reading area.
• The reading range can vary from inches to 120 feet, depending on the tag.
• The integrated circuit (IC) has four memory banks - EPC, TID, User, Reserved.
• Each tag type has a uniquely shaped antenna to provide the best reactance.

What's Inside the UHF RFID Tag?

A basic UHF RFID tag consists of an antenna and IC.

Antenna - The antenna of a tag is specific to the tag type. Its job is to receive RF waves, energise the IC and then scatter the modulated energy back to the RFID antenna.

Integrated Circuit (IC) - The integrated circuit, also called a chip, consists of four memory banks. It includes information processing, sending and receiving information, and collision avoidance protocols. Each type of IC is unique. The main difference between ICs is the number of bits in the respective memory banks.

The four memory banks are as follows:

 

• EPC Memory Bank - Contains the Electronic Product Code, which can vary in length from 96 to 496 bits. Some manufacturers use a random, unique number, while others use random repeating numbers.
• User Memory Bank - The user memory bank can range from 32 bits to 64k bits and is not present in every IC. If the tag has a user memory bank, it can be used for user-defined data about the item. This can be information such as item type, last service date or serial number.
• Reserved Memory Bank - The reserved memory bank contains access, lock passwords that allow tag memory to be locked by the user and require a password to view or edit.
• TID Memory Bank - The TID memory bank contains the Tag Identifier, a random, unique number set by the manufacturer that cannot be changed. In order for the reader to read this number instead of the EPC, the reader settings must be changed to match.

As there is a possibility that a label's EPC number may not be unique, it is imperative that it is checked before purchase. The specifications may mean "unique, random EPC number" or "Not guaranteed to be unique". If you purchase a tag that does not have a unique random EPC number, it may need to be re-encoded with a new specific number. RFID readers cannot distinguish between two tags that share the same EPC value.

The EPC number of each tag is read to identify the tag as well as the item being labelled. If no software is used, the tag will only read the EPC number; however, by including software, it is possible to associate this number with a name, serial number or even an image in a database.

Label Form Factors

Tags

Labels are RFID tags characterised by being paper thin and flexible. The main difference between tags and inlays is that inlays are typically transparent and can be produced with or without adhesive. Tags have a paper or plastic face so that graphics or text can be printed on them and read clearly.

Often grouped together due to form factor and cost, labels are cost effective. When purchased in higher quantities, they can be purchased for as little as US$0.10 per tag. These tags are produced in rolls of several thousand pieces and can be passed through an RFID printer to be printed and encoded.

Labels and fillings usually weigh less than one gram. They vary in length and width from less than about ½ inch to several inches.

Hard Tags

UHF RFID hard tags are classified as such because they are thicker than hard and paper-thin tags. Hard tags are made of many materials such as polycarbonate, ceramic, ABS, steel, polystyrene and polypropylene.

Because of their greater rigidity and larger size, they are more expensive than labels. Depending on the specifications, hard tags can range from just under $1 per tag to over $15 per tag. Just like regular labels, these labels can be cheaper when purchased in higher quantities.

Rigid labels vary greatly in size and weight. The smallest labels are about 0.2 grams and the largest, robust hard labels can weigh over 250 grams. The shapes and sizes of hard tags vary greatly and can range from the size of a small pencil eraser to the size of a licence plate.

Label Positioning

Label positioning may seem like something to consider after a label purchase, but it is important both at the decision-making stage and at the post-purchase stage.

 Etiket konumlandırmanın dört ana yönünü vardır. Boyut, Yön, Açı ve Yerleşim. Bunları ifade eden SOAP kısaltmasıdır. Aşağıda ideal etiketi seçmek için nasıl kullanılacağı ve ne zaman dikkate alınacağı hakkında bilgiler bulunmaktadır.

Size

Satın alırken etiketin boyutu önemli bir husustur. Etiket boyutu, yalnızca etiketlenen nesnenin boyutuna uyması gerektiği için değil, aynı zamanda etiket boyutu ile okuma aralığı arasındaki korelasyon nedeniyle de önemlidir. Kısacası, etiket ne kadar büyük olursa, okuma aralığı o kadar uzun olur.

Oryantasyon

RFID sisteminin antenine göre etiketin yönü dikey, yatay veya başka şekilde, ideal okuma hızlarının elde edilmesinde kritik bir faktördür. En iyi okuma hızlarını üreten etiketin yönünü bulmak için etiketi düz bir yüzey üzerinde döndürün ve farklı yönlerde test edin. Not olarak, dairesel polarize antenler kullanmak, etiket yönlendirmesinden kaynaklanan sorunları azaltmaya yardımcı olur.

Açı

Etiketin açısı ne kadar dik olursa, okuma aralığı o kadar kısa olur. Mümkünse etiketin ön tarafının doğrudan antene baktığından emin olun. Küçük bir açı bile etiketin okuma aralığında bir azalmaya neden olabilir. Bu sorunu azaltmak için, etiketleri birden çok açıdan kaplamak için bir dizi anten kullanmak en iyisidir.

Atama

En iyi okumaları oluşturan noktayı bulmak için öğenin çeşitli noktalarında okunabilirliği test edin. Örneğin bir karton kutuda, antene/okuyucuya bakacak tarafı bulun ve ardından en iyi sonuçları veren tarafı bulmak için bu yüzün çeşitli yerlerinde test edin.

Etiket Ekleme Yöntemleri

Tam etikete bağlı olarak, tutturma yöntemleri, yapıştırıcı gibi yaygın biçimlerden, streç film gibi benzersiz yöntemlere kadar değişebilir.  etiketler, çoğu uygulamada kalıcı bir yapıştırıcı türü kullanırken sert etiketler, etiket türüne, ağırlığına, uygulamaya ve uygulama ortamına bağlı olarak değişiklik gösterir. Aşağıda, RFID etiketleri için yaygın olarak kullanılan ekleme yöntemlerinin bir listesi bulunmaktadır.

Hangi ek yönteminin kullanılacağına karar vermek etikete, öğeye ve uygulamaya bağlı olacaktır. Tüm uygulamalarda, bir ek yöntem seçmek, bir etiket seçmek kadar önemli olabilir. Bir ekleme yöntemi başarısız olursa, etiket öğeden düşerek öğeyi artık izlenemez hale getirir ve uygulama artık doğru olmaz.

Aşağıda, uygulamanız için doğru bağlantı yöntemini seçmeden önce düşünmeniz gereken birkaç husus bulunmaktadır.

Yüzey Alanı - Tıpkı bir arabayı pencere veya tampon çıkartması için hazırlamak gibi, öğenin yüzey alanı da etiketin yapıştırılması için hazırlanmalıdır. Yönteme bağlı olarak yüzeyin pürüzsüz, tozsuz ve susuz ve temiz olduğundan emin olun.

Maruz Kalma – Etiket uzun süreli UV ışığına, neme, titreşime, basınca veya kimyasallara maruz kalacaksa, tutturma yöntemi de maruz kalacaktır. Yukarıda sıralananlar gibi belirli çevresel koşullar, benzer koşullarda güvenilir olduğu kanıtlanmış özel tutturma yöntemlerine ihtiyaç duyacaktır.

Sıcaklık – Yukarıda maruz kalma bölümünde belirtildiği gibi, seçilen ekleme yönteminin etiketleme ortamınızla benzer koşullarda test edildiğinden emin olun. Aşırı sıcaklıkların, tutturma için kullanılan bileşik veya nesne üzerinde erime ve kırılgan hale gelme gibi etiketten farklı etkileri olacaktır.

Uygulama Ömrü – Öğenin etiketlenmesi gereken süreyi tutacak bir etiket ve ek yöntemi seçin. Bazı tutturma yöntemleri, kimyasal yapıya bağlı olarak zamanla yavaş yavaş bozulur. Etiketin öğede kalması için gereken süreyi sürdürebildiğinden emin olmak için seçilen ekleme yöntemini değerlendirin.

Uygulama Yüzey Malzemeleri

The surface of the item to be tagged will greatly influence tag selection, and if there is more than one type of item surface, a different tag should be selected for each. For example, if an application is taking inventory of assets and one asset is metal and another is plastic, these two items will most likely need to be tagged with two different RFID tags.

The surface material of an object is important because most tags are tuned by the manufacturer to perform better when used on certain materials. The tag's antenna is very sensitive to the type of material it is placed on because of the way it sends and receives signals. Adding a tag to an incompatible type of surface material can result in a lower read range, lower read speed, or no read at all.

The best known surface material that interferes with read range when tagged with the wrong type of RFID tag is metal. Metal causes problems with RFID for two reasons. First, metal reflects RFID waves. Second, RFID tags are manufactured to work on low dielectric surfaces (plastic, wood, cardboard), not high dielectric surfaces like metal. There are two easy ways to solve this problem. Either buy a metal-mount tag with a built-in, low-dielectric support, or buy a tag and place a low-dielectric material such as foam between them.

 

Labels Special Features

Almost all UHF RFID tags have special features that make them attractive for certain applications or environments. Often, these special features help narrow the search for the ideal tag.

While labels have only a few feature options, hard labels have several features. This explains their generally higher cost. Below is information on the special features that can be found on labels or hard labels and how they are used.

• Extreme temperature resistance - Labels with this capability can be used to label items in freezers or cold environments (down to -50°C) or high temperature environments (up to 250°C).
• Metal mountable - There are a few tags that can be metal mounted, but most metal mount RFID tags are hard tags. These tags are tuned to work well on metal. They should be used when labelling metal items unless a spacer is used to separate the metal object from the non-metal mountable tag. Tags made specifically for on-metal applications tend to achieve better read range than spacers added post-production.
• Printability - The ability to print directly on the face of a tag is a unique feature of tags that allows them to be visually identified or support marketing purposes. Most RFID tags can be operated from an RFID printer, which is well suited for large-scale operations. As a note, while it is not possible to print directly on rigid RFID tags, most can still support a manually applied label or sticker.

• Embeddability - The ability to be embedded into an item is very useful in some demanding applications where the label could potentially break or prevent the item from being used. Most embeddable applications involve wood or metal. The key to embedding tags in metal is to ensure that only three sides of the tag are covered with metal and one side is left open to allow reader/tag communication.
• Impact resistance - Some harsh application environments, such as construction sites, require labels that can withstand impact from other objects. Hard labels that are not impact resistant cannot withstand much impact before breaking and the label stops working.
• Vibration resistance - Vibration in vehicles, trains and certain types of machinery can be problematic for tags, not just RFID readers. Intense, constant vibrations need to be mitigated by using a tag that can withstand this type of repetitive, high-intensity motion.
• Customisable - Most labels can be customised with graphics, text or colours, but other labels can be customised to a specific shape and form factor, material type. A special adhesive can be supplied depending on the item being labelled. Some rigid labels can also be given a special adhesive. Labels can be applied by hand or produced in specific colours. Minimum order quantity is usually available, but truly customisable labels can be designed and shaped to the needs of the application.
• Autoclavable - An autoclave is a piece of machinery often used in the healthcare field to sterilise instruments after use. Normal RFID tags cannot withstand the heat of the sterilisation process, so it is necessary to choose an autoclavable tag for these applications.
• UV resistance - In applications where the item being labelled will spend a significant amount of time exposed to UV waves, if there is printed information on the face of the label, the label selected must be UV resistant. This includes printed labels that are not protected from sunlight for long periods of time.
• ATEX certified - ATEX certification means that RFID tags are approved for use in environments with explosive atmospheres. These tags are used for applications in environments such as mines or workplaces with activities that release flammable gases or vapours.
• Chemical Resistance - Chemical resistance is a property used in the presence of airborne and water-based chemicals so that the label will not deteriorate.
• Ingress Protection - For dust/dirt or water related applications, it is extremely important to check the ingress protection ratings before selecting a label. The first digit of the IP rating will be 0 - 6 and indicates protection against solids such as dirt/dust. The second digit of the IP rating will be 0 - 9 and is the level of protection against liquids such as water. The highest IP rating for labels will be 67, 68 or 69 degrees depending on direct or indirect contact with liquids.
• High Memory - Tags that are available with a higher User or EPC memory can be used to store increased data on the tag such as service dates and complete item identification. While higher memory is good for some applications, most RFID systems associate the tag ID via software in a database containing the same information. This frees up memory on the tag and allows the tag to be read faster.

Relationship between Label Reading Interval and Size

One of the biggest misconceptions about UHF RFID tags is that all tags have approximately the same read range, regardless of size, material or tagged items. In reality, all of these factors combine to determine the overall read range of a tag, but the size of the tag is the most influential component.

Due to the fact that small antennas need to be small to fit on small tags, they can only transmit and receive data over a very small fraction of the distance of typical large tags. Some of the smallest UHF tags can be read from only a few inches away. Generally speaking, the read range increases as the size of the tag increases, and some of the largest passive tags can read over 35 metres (115 feet).

The correlation between read range and size indicates that there must be a compromise between each application to find the ideal tag. In some applications, such as tool tracking, the objects to be tagged may be so small that the size is non-negotiable. Therefore, the labels for that application will only have a short reading distance. When tracking items that are more favourable in terms of surface area, a medium to long range tag can be selected, providing a better balance between size and read range. Whether RFID is right for your application or if you have additional questions about RFID tags, feel free to contact us.