RFID Tags

What is a tag?

• Tag is a device which can be attached to an item with the purpose of identifying the item with the RFD reader

• Contains information about the item

• Has the capability to provide that information on request from the reader

Tag Placed on an Item

Some Facts About Tags

• All tags are composed of the same basic components because they offer same basic functionality, which helps to identify and track an item

• Tags come in different forms, shapes, and sizes: these factors depend on application

• Tags must be properly places on items so that they can be easily read by readers

Functional Components of a Tag

• Components for storing information about an item

• Components for processing the request for information coming in from a reader

• Components for preparing and sending the response to the reader

Chip

Antenna

Substrate

Chip

• Chip is used to generate and process a signal

• It is an integrated circuit (IC) made of silicon

Functional Components of a Chip

• Logical unit – implements the communication protocol used for tag-reader communication

• Memory – used to store data• Modulator – used for modulating the outgoing

signals and demodulating incoming signals• Power controller – responsible for supplying

power needed for operating the chip

Antenna

• A tag’s antenna receives the signal (a request for information or other command) from a reader and transmits a response signal (identification) back to the reader

• Made of metal-based materials• Note the following (true for readers as well):

– Antennas are used by tags operating at UHF and microwave frequencies

– Tags operating at LF and HF use inductive coils (as antennas to send and receive signal using the inductive coupling technique

• Why? Antenna size has to be substantial for LF

Substrate

• Substrate – layer that houses the chip and the antenna

• Support structure for the tag

• Can be made of different materials: plastic, PET, paper, glass epoxy, etc.

Substrate usage requirements

• Dissipating of static charge buildup

• Durability under specific operating conditions

• Mechanical protection for chip, antenna, and connections

• Smooth printing surface

Tag Size

• Tag size may depend on the item on which the tag is placed, environment, and application– Large tags can be used on large items, such

as cars– Small, rectangular-shaped tags

ISM Frequencies

• RFID systems are radio systems

• There are other radio services in RF spectrum

• Therefore, it is important that RFID does not disrupt other radio services

• Industrial, scientific, and medical frequencies (ISM) can be used for RFID systems

RF Frequency RangesName Frequency

RangeRead Range for Passive Tags

Low Frequency (LF)

30-300 kHz <50cm

High Frequency

(HF)

3-20 MHz <3m

Ultrahigh Frequency (UHF)

300 MHz-3GHz <9m

Microwave Frequency

3 GHz – 300 GHz

>10m

Global UHF Frequency Bands

Area Frequency Band Power

United States 902-928 MHz 4 W

Australia 918-926 MHz 1 W

Europe 865-868 MHz 2 W

Hong Kong 865-868 MHz

920-925 MHz

2 W

4 W

Japan 952-954 MHz 4 W

Tag Types: Active and Passive

• Tag types are determined by the following factors:– Can the tag initiate the communication?– Does the tag have its own power source?

• Active and passive tags

Passive Tags

• Passive tags do not have a power source (battery)

• Cannot initiate communication

• It responds to the signal sent by the reader by taking power from the reader’s signal

• Reader’s signal “wakes up” the tag

Passive Tags

1. The passive tag’s antenna (or coil) receives the signal from the reader

2. The antenna sends the signal to the IC

3. Part of the signal is used to power IC

4. The IC powers up, processes the incoming signal, and sends the response

Passive Tags

• Placement: because a passive draws energy from the reader, it must be placed within the interrogation zone

• Size and range: since there is no battery, passive tags tend to be smaller in size and have shorter range

• Lifespan: because there is no need to replace a battery, passive tags have a longer life

• Memory: the memory varies from 1 bit to several kilobytes

• Price: inexpensive (~$0.10)

1-bit Tags (EAS)

• EAS – Electronic Article Surveillance

Passive Tags

• Passive tags can operate at any frequency: LF, HF, UHF

• Depending on frequency, the range can be from 2 mm to 5 meters

• The passive tags are simpler and cheaper, and therefore are more popular

• LF passive tags are suitable for applications that require reading from a close range

Semipassive Tags

• Has its own power source (battery) but does not initiate communication

• It responds to the signal sent by a reader by using the power from the reader’s field

• Battery is used for powering IC

Semipassive Tags: Characteristics

• Operation:– Can send a response only when has adequate power from the reader – Similar to passive

• Size and range:– Larger than passive (because of battery)– Produces stronger signal– Larger read range

• Lifespan : shorter than passive• Memory:

– Varies– Typically has more memory

• Size (more room for components)• Battery (more energy to work with memory)

• Can perform internal operations (e.g. logging temperature) even in the absence of the reader

EPC Classification of Tags

• EPC – Electronic Product Code – on organization created by MIT Auto-ID Center, which is a consortium of 120 corporations and universities

• Each EPC tag contains EPC identification code

Class Type Memory Communication Other Properties

0 P Read-only Does not initiate communication EPC number is encoded during manufacture and can be read by a reader

0+ P Same as Class 0, but you can write once

Does not initiate communication

1 P Read and write-once

Does not initiate communication The EPC number is not encoded during manufacturing but can be encoded later

2 P Read and write-once

Does not initiate communication Encryption

3 SP Read and rewrite

Does not initiate communication Class 2 capabilities plus extras, such as integrated sensors

4 A Read and rewrite

Can initiate communication; power their own communication; tag-to-tag communication possible

Class 3 capabilities plus extras

5 A Read and rewrite

Can initiate communication; power their own communication; tag-to-tag communication possible

Class 4 capabilities plus extras

Labeling a Tag

• Inlay – bare-bones tag (antenna, chip, substrate)

• Insert – an inlay inserted between a label in the front and an adhesive layer in the back– Thick inserts for harsh environments– Paper-thin inserts for parcels– Postage stamp-sized inserts (DVDs)

Smart Labels

• Smart Label – a barcode label that has an embedded RFID tag inside

• You can print readable/scannable information on the label

• Components– Inlay– Label face stock – covers the top of inlay and

provides area for printing information– Adhesive– Release liner – at the bottom of inlay

Tag Housing

Placing Tags

• Materials

• Antenna polarization– Linear

• Horizontal – align • Vertical - align• Circular - OK

• Experimenting

Conclusion

• The basic functionality of any tag is to store information about the item to which it is attached and to provide this information when requested by a reader

• Tags have three basic components: chip, antenna, substrate

• Two types of tags: active (can initiate communication) and passive (cannot initiate communication)

• Tag should be placed in a way that makes it readable to the reader