RFID | RFxValue

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.

back to top

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

back to top

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

back to top

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

back to top

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

back to top