Active Tag1
Active Tag2
UHF R
Module
Modern Transponders,
in addition to a unique identification code, have a re-writable memory and
sometimes an interface to peripheral devices. They are capable of working at
different frequency bands utilizing magnetic or electro-magnetic waves’
specific propagation and penetration properties. You can choose among Field
Activated (aka Passive) transponders, which get power from an Interrogator “Transceiver
(aka Reader) & Antenna, or Active transponders that have a battery on board
and generate a responding RF signals by converting DC power to electro-magnetic
wave. An Interrogator performs the simplified functions of Radar. It can find
transponders at certain distance, read a memory contents and encode the memory
with new data. This capability enables organization of decentralized Data Base
one of the powerful usage to substantially reduce a data stream and unload
usually busy IT infrastructure.
RFID Tags (Transponders)
Strictly speaking, Transponders (aka Tags) unambiguously classify a type of RFID technology. Available tag types made to work in wide frequency spectrum. Each type has unique properties and is dedicated to work under certain conditions and for specific applications.
There are two classes of transponder: Chip and Chipless.
Three key features of chip transponders: unique ID,
re-writable memory and ability to communicate through most opaque objects
define RFID applications. If you are not utilizing all tags’ capabilities, your
solution will be most likely inefficient.
Low Frequency (LF) and High Frequency (HF) Passive Chip Tags function
as magnetically coupled devices. In order to make tags operational they must
receive power that exceeds a power threshold – an activation power level that
needed to make tag working. The exact activation power level is variable value,
depending on chip type, transponder’s dimensions, surrounding environment and,
most importantly, on electrical properties of objects carrying tags. IC
modulates a load of tag’s antenna that in turn, changes impedance of
interrogator’s antenna and consequently modulates voltage across antenna port.
A Reader constantly analyzes this voltage and retrieves data from voltage
modulation depth. NFC tags are mainly the same as HF RFID tags but with
advanced security measures and communication protocol.
Ultra High Frequency (UHF) and Super High Frequency (SHF)
Chip Tags use a backscatter modulation by re-radiating a small fraction of RF
power received from an interrogator. In contrast with HF tags, UHF transponders
provide longer communication range but they are more susceptible to surrounding
objects. Practically any object can change electro-magnetic wave distribution
around transponders and drop delivered power below tag activation level.
Another class of passive transponders is a Chipless. There
are two bases for their operation: Surface Acoustic Wave (SAW) technology (Time
Domain) and Ultra Wide Band (UWB) Chipless Tags (Frequency Domain). SAW
transponders are bulky. They have only a unique ID but provide a longest
communication range and high resilience to EMI/RFI among passive tags. UWB chipless
tags are under development phase. They have relatively large dimensions and as
of today have up to 32 bits data for ID. That simplicity is in exchange for
lower noise immunity.
Active transponders have enhanced capabilities and the
highest communication range that is limited practically by available battery
capacity and FCC regulations. They are actually transceivers (sharing the same
hardware for receiving, generating and transmitting RF signals) with large
memory size, high reception sensitivity, selectivity, noise immunity and strong
transmitting RF power. They are very resistant to environmental impact and
surrounding objects, not even to mention the influence of identifiable objects.
CAPABILITY
1. RF wave
penetration and reception through the majority of opaque materials
2. Tag
Re-writable memory enables building Decentralized DB
3. Tag Unique,
unchangeable ID data
4. In case of
battery-supported version, Tag’s IC can include a micro CPU to form a data
logger with variety of sensors: pressure, gas, temperature, etc.
CHALLENGES & ISSUES
1. Field
Activated, Chip Tags
·
Reception sensitivity and re-radiation efficiency
strongly depend on instant
spatial location and proximity to surrounding electro-mechanical objects and
other tags
·
Susceptibility to EMI/RFI and low noise immunity
·
Range loss because of variation of minimum activation
RF power level and its increase over time
·
Overestimation of Battery-Supported Tags capabilities
2. Surface
Acoustic Wave Devices: SAW Chipless Tags
·
Non-rewritable Very small memory size
·
Bulky but with relatively strong re-radiated signal
3. UWB Chipless
Tags (Multi-Resonance Antenna)
·
Very small, non-rewritable memory size
·
Relatively large size but very inexpensive and
practically printable
4. Active Tags
·
Bulky and expensive but can last years with high
redundancy of data acquisition and long operating range
·
Malfunctions related to Battery temperature range
unmatched to the rest of Tag electronics
·
Communication interruptions observed for Tags with
replaceable battery caused by environment conditions.
5. NFC Tags
NFC protocol has enabled
installation of NFC Readers in a Smartphone. With this phone, users have a
complete interrogator in their hands allowing for new powerful applications of
Auto-ID.
·
The same challenges as for other RFID Tags
· NFC Tags need higher RF power than conventional HF RFID tags.
RFID Readers (Transceivers)
RFID Transceiver
(aka Reader) is a second key component of RFID system. For by-directional data
exchange with Active Tags, transceivers have a classical Transmitter-Receiver structure.
In contrast, Readers for Passive RFID (LF, HF and UHF) must provide Constant
Wave to simultaneously energize transponders and decode data received from them.
RFID Readers can have stand along or embedded antennas. There are a few Reader
versions available: handheld, stationary and modules for integration in products.
The stationary Readers can have up to 16 antenna ports. The mobile type usually
includes an antenna, display and a keypad as well for entering and retrieving
data. Readers for NFC, beside the main ID function, are capable of supporting a
data link with other Readers enabling a highly secured, bi-directional
interface. A mass possession of smart phones with NFC radically enlarges and
simplifies a number of RFID applications.
CAPABILITIES:
·
Generation
of RF power with Digital adjustment of dynamic range for corresponding
frequency band
·
Fast
DSP for authentication of group of transponder in the field of an antenna using
anti-collision algorithm
·
Activation
of passive (or waking-up of active) transponders and simultaneous data
communication with them
·
Interfacing
with peripheral equipment over LAN
CHALLENGES
& ISSUES
·
Low
Read/Write rate
·
Configuration
and management of multiple Readers
·
Low
sensitivity and number of tags differentiation associated with Antenna
impedance deviation
·
Insufficient
RF power
Interrogator Antennas
An antenna and RFID Reader form together an Interrogator. This combination performs two functions. It provides a Reader-Transponder data exchange and delivers power for Field Activated (aka Passive) RFID Transponders. An antenna is the most critical component of any RF system. It can improve or degrade the entire system performance. RFID frequency band, available RF power and an operational level are three major factors defining an antenna’s type, structure and dimensions.
Antennas for Long and Short Range RFID
An Antenna-Transponder interaction changes significantly depending
on their separation distance.
At close proximity, transponders are in Near-Field of an
antenna and at long range – in Far-Field.
Whether transponders are in antenna’s Far-Field or Near-Field
is determined by wavelength, dimensions of transponder and antenna, distance
apart, and their alignments. While in Far-Field, transponders are practically
not affecting an antenna. In contrast, being in Near-Field, transponders form
with antenna a new composite structure. This new device has a set of
characteristics unrelated to conventional antennas. The terms like
Polarization, Directivity, Beam width, Gain are not valid any more.
Antennas for LF & HF RFID
LF and HF RFID antennas radiate strong magnetic fields and
consequently couples with transponders. When transponders are in an antenna
field, data exchange between them goes by antenna impedance modulation concurrently
supplying energy to transponders and supporting their functioning.
A conventional antenna is a tank resonating at 125-135 kHz
for LF and 13.56 MHz for HF RFID. LF antennas have a form of wire wounded large
or small coils with resonance frequency tuning and impedance matching
components. Dimensions depend on desirable range and required operational
conditions.
HF antennas have a lower than LF antennas inductance and
usually are planar, often in the form of PCB traces, including tuning and
impedance matching components. Using flexible ferrite materials one can easy
modify distribution or concentration of a coil’s Magnetic Flax for spatial
selectivity.
Antennas for
UHF RFID
Antennas for UHF RFID work with Field-Activated transponders
(aka Passive Tags) at relatively long-range applications. Often used term “backscattering”,
which incorrectly burrowed from Radar Engineering, implies a reflection of RF
waves back to the direction from which they have come. A process of getting a
response from tags after interrogator had sent a request is based on reception of
signals, which have been re-radiated back by transponders, and not reflected.
At closely spaced transponder-antenna, the mechanism of
getting tags’ response mainly changes from re-radiation to electro-magnetic
coupling, which is similar to LF & HF technology.
For UHF RFID long range Interrogators, the most popular antenna is a planar patch type or an antenna array and ceramic antennas. These antennas provide coverage for multiple transponders located in antenna field. An antenna can have Linear or Circular Polarization. Linearly polarized antennas to be efficient require some specific transponders alignment, whereas circularly polarized antennas are agnostic to transponders orientation but less power efficient.
CAPABILITIES:
·
Impedance
bandwidth and gain are in spec and independent from operation conditions
·
RF
power delivered to transponders is higher than their activation power
CHALLENGES & ISSUES
·
Antenna
provides an excessive power density and violates a limit specified by country
·
Antenna
beam widths at E and H planes are incompliant with applied RF power
Spatially Selective Antennas
The distinctive class of HF and UHF antennas, called Spatially Selective Antennas (SSA), remains practically a single choice for RFID applications that require identification of small and single targeted transponder among closely spaced others. Spatial selectivity is an antenna feature that allows activating a targeted transponder with high RF power margin and disabling neighboring transponders. There are two typical operation conditions for Item-Level Identification. A first case is static, when an alignment and separation distance between an antenna and transponder remains unchanged. The second one is dynamic, when both an alignment and separation distance are changing during an operation.
SSA for HF RFID
HF RFID SSA
provide RF power for transponders by a concentrated or directed magnetic flux.
It is relatively easy to focus this flux for a small area using flexible
ferrite patches. The patches definitely change original resonant circuits and
their frequency tuning and impedance matching require some correction.
Sometimes, shields with a window can help in selective identification of small
and closely spaced transponders having some specific form-factor. A different
transponder type will need a fabrication of modified shield configuration.
SSA for UHF RFID
A
transponder coupling with UHF RFID antenna at close proximity is
electro-magnetic or inductive-capacitive. Both components of RF wave energize a
transponder. A solution to achieve spatial selectivity is to use loaded
transmission lines and coplanar waveguide structures. Tuned to resonance, they
provide relatively short, power efficient encoding area but have a narrow
bandwidth. Tapered lines and guides increase antenna’s bandwidth.
These
antennas can have very wide bandwidth when their characteristic impedance is
equal to system impedance, but power efficiency is much lower in comparison
with resonant antennas.
A UHF antenna can have a ring form to increase wave magnetic component or consists of a matrix of encoding elements.
CAPABILITIES:
·
Maintain
specified characteristic impedance for all transponder alignments and
positioning
·
Provide
RF power to a transponder exceeding its activation level at least for 3 dB
·
Allows
for an operation with wide range of transponder form factors
·
Bandwidth
is wider than 860-960 MHz
·
US
and EU Restrictions Compliant
CHALLENGES & ISSUES
·
Low
encoding rate
·
Parasitic
encoding of non-targeted transponders
·
Limited
options for a transponder orientation and its positioning
·
Excessive
emission
RFID Printers
An RFID
Printer is the fourth essential component of any RFID system. Smart Labels and
RFID Smart Cards in addition to embedded transponders, usually need to have
human readable information. RFID Printer-Encoders are making fast processing of
multiple labels and cards automatically. The most popular RFID printers’
form-factors are Mobile, Desktop, and Tabletop. Specifications on numerous HF
and UHF Printer-Encoders can help selecting a matching printer. However, if you
want to get a printer with best Performance/Price ratio for your application
case, you will have to consider a few more parameters beyond specifications.
CAPABILITIES:
·
Effective
completion time of Printing & Encoding
·
Minimum
Label Length & Minimum Pitch
·
Varieties
of embedded transponder types
·
Limitations
of tags placement inside labels and cards
·
Automatic
RFID printer settings (RF power and encoding position)
·
Encoding
in Batch Mode
·
Operation
in US, EU, and other regions without HW/SW changes
CHALLENGES
& ISSUES
·
Low
successful encoding rate
·
Inability
to use smart media made not for specific printer
·
Encoding
errors associated with improper label/card position
·
Long
time requires to re-set printer to work with different tag types
·
Missing
encoding of some labels
·
Wrong
encoding of not targeted labels
·
Parasitic
label encoding (re-encoding) outside the printer
·
Interference
with other neighboring printer-encoders