RFID (Radio Frequency Identification) is a technology in which information stored in the chip of RFID tag can be read remotely, without physical contact, using RF energy emitted by the RFID reader antenna. The RFID tag itself consists of a chip and an attached antenna, by means of which it receives the signal and responds back to the reader. RFID tags are very diverse and significantly affect the success of the entire RFID system. They appear in a different physical form, differ among others reading range, price, mounting method for the product, etc.
RFID tags are made of 2 elements:
- an integrated circuit (chip), which is the heart of an RFID tag, and it stores all information in it. Some chips can store more information than others. Most UHF markers are compatible with Class 1 Generation 2 standard (ISO 18000-6C) and use 96 bits of EPC (Electronic Product Code) storage, which is enough space to store 24 hexadecimal characters (0-9, A-F). However, some tags are more expensive because they have expanded user memory to store more information,
- a coil antenna whose size affects the range of the RFID tag’s operation. A small tag has a small coil antenna, which gives a shorter reading range, while larger tags with larger coil antennas will have a larger reading range. In addition, the environment that surrounds them has a large impact on the range of the antenna. Water and metal absorb and reflect the RF wave and significantly reduce the effectiveness of RFID systems. In this environment, special markers are used that are less susceptible to water and metal influence.
When speaking of the form of the RFID tag, we mean its physical form. Depending on the application, RFID tags have different shapes and sizes, can be labeled or placed in a protective enclosure.
Types of RFID tags:
Inlay is the most basic form of RFID tag. It is usually a transparent label on which an electronic chip and antenna are applied. These labels can be provided with an adhesive that is used to permanently apply the tag to the element.
Label is a RFID paper or synthetic label that incorporates a chip and an antenna, and also allows the label to be printed, e.g. with a barcode or any other character.
Housings – an RFID tag can be placed in a special housing. This is the most diverse way of delivering RFID tags. Such a housing can protect against impact, temperature, humidity, water, contact with the metal surface. It can also have special fasteners.
Depending on the way of RFID tags supply, we distinguish active and passive tags.
Active RFID tags are battery powered and actively transmit the signal. They have a longer read range and are more expensive due to the cost of the battery and the transmitter.
Passive RFID tags do not have a built-in power supply. The energy for activating the chip comes exclusively from the wave emitted by the RFID reader. They are much cheaper than active tags and generally have a smaller range.
RFID tags operating in the UHF frequency band complying with the EPC Global Class 1 Gen 2 standard have four types of memory:
- EPC (Electronic Product Code Memory) memory,
- user memory,
- TID (Tag Identification Memory) memory,
- Reserved Memory.
EPC and User memory banks are banks that “transfer” our information. The other two banks store control data. User memory, or User memory, is a bank that does not have to be present in the tag structure. This memory is optional and is used in tags in which the user requires additional space to record information, e.g. when the EPC is too small for it.
EPC Memory stores the EPC code or electronic product code. It has a minimum of 96 bits of writeable memory. There are tags that have the option of allocating more bits to the EPC memory. Many of them exist with 128 bit memory, there are also those that have up to 496 bit of EPC memory. The EPC code from this bank is most often used as the unique identifier of the tag. This is the first recordable bank in the RFID tag.
User Memory – used if the user needs more memory than the one available in the EPC bank. Usually it is 512 bit, but there are also RFID tags that have 4k or even 8kB. This is the second writable bank in the RFID tag.
TID Memory is used only to store a unique identification number assigned by the manufacturer who produced the tag. This part of the memory cannot be changed.
Reserved Memory – a memory bank storing an access password and a kill password. Each of the passwords has 32 bits. The destructive password permanently deactivates the tag (very rarely used), and the access password is set to block and unblock the tag’s recording capabilities. Most users do not use this storage area unless their applications contain sensitive data.
When selecting RFID tags, you should consider:
- geographic region, where the tags will be used – just like with readers and antennas, the RFID marker should be chosen in accordance with the frequency that is legally permitted in the given geographical area. Additionally, remember that both the reader and the RFID tag should be tuned in the same band. which will allow them to communicate,
- external factors – if the RFID tag has to be resistant to extreme temperatures, dust, water, dirt or an intensive washing process, then it is necessary to choose a type RFID Tag that is designed withstand such conditions,
- the mounting surface on which the RFID tag will be applied – in general, the markers work well on surfaces such as plastic, wood and cardboard. Only some RFID tags are able to work on metal, glass or liquid surfaces. Tags designed to work on a more demanding substrate cost more than typical tags,
- the amount of available space for physical RFID tag applications – tags are produced in various sizes and shapes for the best match for specific solutions. Depending on the design and the amount of space on the object to be marked size may play a key role in the selection of the ideal marker,
- RFID tag attachment – the shape and material of which the object is made are two important aspects when choosing the RFID tag attachment. Most tags are attached using special adhesives (e.g. on cardboard surfaces), and some of them require the use of rivets or screws to attach them to metal pallets,
- required reading range – to select the most suitable one, test different markers. It should also be remembered that there are many other factors affecting the scope of RFID readings, including amplification of the antenna, the power of transmitting the reader or orientation of the RFID tag itself,
- RFID tag programming – can be based on data that is already programmed in the RFID tag or you can program the tags with specific data yourself. The programming method can determine the choice of the RFID tag. Tags, like labels, can be programmed using RFID printers, and only some of them can be programmed using a hand-held RFID reader.
Metal surfaces will reflect the wave emitted by the RFID reader and cause interference that standard RFID tags cannot deal with. In order to overcome this obstacle, tag manufacturers have created special RFID tags that use an additional layer of material separating the RFID antenna from the metal object on which the tag is mounted.
The use of RFID tags for marking metal surgical instruments, industrial tools and IT resources such as laptops and servers is popular. RFID tags for metal are also used in industry and production, where metal semi-finished products are identified.
Due to the fact that many metal objects marked with RFID are exposed to demanding external conditions, the tags themselves must also be resistant to them. There are RFID tags available on the market that are able to cope with high temperatures, are resistant to impacts, etc.