korea university ubiquitous lab. chapter 5. characteristics of tags ph.d chang-duk jung

Korea University Ubiquitous LAB.

Chapter 5. Characteristics of tags

Ph.D Chang-Duk Jung


Components of RFID tags

• The chip and the antenna reside on the substrate, which is made of either rigid or flexible material.

• The antenna is made up of a metal or a metal-based material.

• The chip, which is an integrated circuit (IC) made of silicon, has an electrical connection with the antenna.


Types of tags

• Active– Have an internal power source, such as a battery

• Battery powers the IC and transmits a signal to the reader

– Read range from 20 meters through 100 meters

• Passive– Have no internal power supply– Activated by the reader – Read distances ranging from 2 millimeters through 4.6

meters

• Semi-passive – Passive tags with batteries – Battery constantly powers the IC– Larger reading distance than passive tags


Active tags vs. passive tags

Functionality

Active tags Passive tags

Power Powered by a battery; have an active transmitter

Powered by the radio signal of an RFID reader, which activates them

Read range Designed for communicationsup to 100 feet from the RFID Reader

Can be read from a distance of about 15 feet. (Semi-passive RFID tags contain a small battery that boosts the range.)

Input / Output Can be read/write Can be read-only or read/write

Data storage Memory size varies according to application requirements; some system can use up to 1 MB of memory

Memory size varies from 32 bitsthrough 128 bits of data

Durability Large and heavy; dependent on battery life

Lighter and more durable

Cost Expensive Cheap


Inductive vs. backscatter coupling

• Inductive coupling– LF and HF passive tags use inductive coupling– A coil in the reader antenna and a coil in the tag antenna form

an electromagnetic field– Readers can read LF tags from within 1 foot and HF tags up to

3 feet

• Backscatter coupling– UHF passive tags use backscatter coupling – A reader antenna emits radio waves but does not form any

electromagnetic field – Readers can read UHF passive tags up to 10 feet or more


Antenna

• Polarization– The principle of changing the direction of the magnetic

field

• Radiation patterns– A radiation pattern is a three-dimensional plot of its

radiation from the source.


Radiation patterns

• Elevation pattern– A graph of the energy

radiated from the antenna as you view it from the side

• Azimuth pattern– A graph of the energy

radiated from the antenna as if you were looking at it directly from above the antenna


Radiation patterns

• 3D pattern


Antenna types

• Dipole antenna• Linear polarized antenna• Circular polarized antenna• Omnidirectional antenna• Monopole antenna• Crossed-dipole antenna• Helical antenna• Slotted antenna


Dipole antenna


Dipole antenna (cont’)

• Half-wavelength dipole – The total length of the antenna is half the wavelength of the used

frequency to optimize the energy transfer from the reader antenna signal to the tag

• Quarter-wavelength dipole– It relies on the reflective ground plane to provide an image of the

antenna to complete the dipole. The gain of the antenna varies considerably depending on its deployment.

• Dual dipole antenna– It consists of two dipoles that can greatly reduce the tag’s orientation

sensitivity , a reader can read this tag at different tag orientations

• Folded dipole – It consists of two or more straight electric conductors that are

connected in parallel, each electric conductor being half the wavelength of the used frequency


Linear polarized antenna

• The RF waves emanate in a linear pattern from the antenna

• These waves have only one energy field


Circular polarized antenna

• RF waves radiate from a circular polarized antenna in a circular pattern

• These waves have two component energy fields that are equal in amplitude and magnitude, but have a phase difference of 90 degrees

• Therefore, when a wave of one energy field is at its highest value, the wave of the other field is at its lowest


Omnidirectional antenna

• A non-directional antenna • Radiates maximum power uniformly in all directions • A perfectly omnidirectional antenna is an isotropic

antenna. The isotropic antenna is a theoretical construct derived from actual antenna radiation patterns


Antenna types (cont’)

• Monopole antenna– Single antenna with

• applied source feed• ground plane

– Uses reflection from the ground plane• The other end of its pole is an RF reflection from the ground

• Crossed-dipole antenna – Transmitting and receiving antennas oriented orthogonally

to each other

• Slotted antenna– Exhibits radiation characteristics that are similar to those of the

dipole– Provides little antenna gain– Doesn’t exhibit high directionality


Helical antenna

• Consists of a conducting wire wound in the form of a helix

• The direction of the coil determines its polarization• The space between the coils and the diameter of the

coils determine its wavelength


Integrated circuit

• The power control/rectifier converts AC power from the reader antenna signal to DC power. It also supplies power to other components of the microchip

• The clock extractor extracts the clock signal from the reader antenna signal• The modulator modulates the received reader signal. The tag’s response is

embedded in the modulated signal, which is then transmitted back to the reader

• The logic unit implements the communication protocol between the tag and the reader.

• The microchip memory stores data. You can generally segment this memory into several blocks or fields.


Substrate

• A plastic or Mylar layer that the metal of the transponder antenna adheres to.

• Some of the materials used for a substrate are polyethylene terephthalate (PET), paper, and polyvinyl chloride (PVC) or glass epoxy material.

• Substrate materials can be rigid or flexible. It is the support structure for the RFID tag


Smart labels


Smart labels (cont’)

• A semiconductor wafer processed into chips that have the ability to store data. These chips are small with enough data storage capacity

• An antenna made of a conductive material – permits the chip to receive and send data to and from an RFID reader

• A substrate on which the antenna – can be printed, and to which the chip can be adhered

• A label face stock – covers the inlay and provides a readable print area

• A release liner – serves as the bottom layer for the inlay. By using this layer, you can convert

the pressure-sensitive face and inlay into rolls for easy distribution, and remove the layer when you place the smart label on the carton or pallet

• An adhesive – attaches the inlay to the face stock and the release liner to the inlay and face

stock


Insert

• RFID inserts are available in different sizes for various applications:– Postage stamp-sized inserts are fixed into a case or package to

be applied to a video cassette– Paper-thin inserts are inserted into pressure-sensitive labels

that are applied to packages for parcel tracking– Rugged credit cards are thick inserts, which are used to create

intelligent labels intended for use in harsh environments


Packing items

Effects of material on RFID system

Material composition Effects on RF signals

Corrugated cardboard Absorption from moisture

Conductive liquid Absorption

Glass Attenuation (weakening)

Group of cans Multiple propagation effects; reflection

Human body/animal Absorption; detuning; reflection

Metal Reflection

Plastic Detuning (dielectric effect)


Unit summary

• RFID tags consist of three components: chip, antenna, and substrate

• The types of tags, such as passive, active, and semi-passive • The difference between inductive and backscatter coupling.• Different types of tag antennas, such as dipole, linear

polarized, circular polarized, omnidirectional, monopole, crossed-dipole, and helical

• Antenna properties, such as polarization and radiation patterns, which will help you to select an antenna

• Two components of the tag, integrated circuit and substrate.• Labels and inserts• The various considerations that you need to take care of

when packing tagged items


Review questions

• List the components of an RFID tag.

• What are the different types of tags and how are they categorized?

• How do passive, active, and semi-passive tags differ from each other?

• What are the various types of tag antennas and configurations that are widely deployed?

• What are the basic components of an IC attached to a tag antenna?

• What are the key components of a smart label?

korea university ubiquitous lab. chapter 5. characteristics of tags ph.d chang-duk jung

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