What is RFID (Radio-Frequency IDentification)?
RFID (Radio-Frequency Identification) designates the contact-free data exchange between an RFID transponder and an RFID writer/reader device. The RFID writer/reader device builds up a magnetic or electromagnetic field for data transmission purposes, which supplies the RFID transponder with energy. As long as the RFID transponder remains within the electromagnetic field of the RFID writer/reader device, data can be exchanged. Information can be read out from the chip in the RFID transponder, but also new data can be stored on the chip.
Fig.: Data exchange between the RFID-transponder and the RFID-reader
How is the RFID-transponder built up?
Basically, RFID transponders can be provided in virtually all forms, materials, sizes and colors. Their specific construction depends upon the way they are used. The common feature inside all the different RFID transponders is that there are two components. Inside, each RFID transponder consists of at least one microchip and one printed, laid or etched antenna. The chip and the antenna (also called inlay) are very sensitive which means that its resistance to mechanic, thermal and chemical impacts is limited. Consequently, an application-specific “package” of these electronic components becomes necessary. The simplest packaging form is the RFID-label. That´s sufficient for many applications.
Yet using this packaging, the chip is protected only by a simple foil or a paper layer. If you need something more stable and robust, we recommend packing the electronics into a laminated card. And if event that´s not enough, which is especially the case of industrial applications, the sensitive inlay (= chip + antenna) should be cast into a plastic cover which represents the most robust packaging form that lasts most and has the lowest sensitivity.
Fig.: Characteristic memory organization
The „single chip“ transponder consists of a substrate containing an antenna and a chip, with the short term for these being called inlay. The transponder system consists of a transponder, a reader, software and an application process including the respective service.
How much information can be stored on an RFID-Transponder/Chip?
The chip memory size depends upon the way of use as well. Commonly used memory sizes range between 4 byte and 8 kByte. In the simplest, which is mostly the case of electronic article surveillance, even a 1 bit memory may be used. To draw a parallel – a 4 byte memory can store merely one unique number (Unique ID=UID), whereas a n 8 kByte memory stores 4 typewriter pages consisting of 30 lines à 60 characters. Apart from storage facilities, there are also other chip functions available, such as write protection, PIN-rights, data content encoding, cryptographic functions and many more. The individual specifications depend upon the application and the necessary security level.
How does an RFID-transponder reply?
Inductive coupling principle of a LF and a HF transponder:
The sender emits an electromagnetic field created by an antenna reel which is in turn received by the transponder. Power is the being induced in the transponder reel via induction. This power supplies the energy that runs the transponder. The targeted and timed attenuation of the power via chip circuits can trigger an own signal. This field change is registered by the sender and serves for digital communication purposes.
The „EM backscatter“ principle for UHF transponders:
The sender emits an electromagnetic field via antennae that´s received by the transponder. Power is the being induced in the transponder reel via induction. This power supplies the energy that runs the transponder. The transponder modulates the carrier signal which is then received by the sender for communication purposes.
Active and passive RFID-transponders - a fundamental decision
There are two basic transponder types – active and passive ones. Active RFID transponders have an own energy supply system, e.g. an integrated battery and can transmit data over a longer distance (of up to 100 m). Passive RFID transponders receive their energy for the data transmission merely from the electromagnetic field of the RFID-writer-reader.
Furthermore, there is an intermediary type represented by the semi-active or semi-passive transponders that on the one hand do have an own power source, yet they do not function as a sender themselves. The RFID transponder power supply is carried out via a battery and consequently, it´s not necessary to rely on the performance of the electromagnetic field, yet the reply is being created through modulating the field which does not strengthen the field further.
Fig: RFID-transponder types
Passive RFID-transponders can be subdivided into 3 different categories:
Data can be written on read-only-transponders for one time, yet it is not possible to add information subsequently, to erase it or to overwrite it.
- Write-Once, Read Many (WORM):
Data can be written WORM-transponders only once. Afterwards, these data can only be read out, yet not overwritten any more.
- Read and Write:
Read and Write-transponders provide for unlimited writing and changes of the contents stored. By defining a write protection, even these transponders can be blocked both for reading and writing from a certain point onwards.
LF, HF and UHF-transponder - Which frequencies are being used here?
There are three different frequency bands into which RFID systems are classified:
Low Frequency (LF = 125kHz)
This freely accessible frequency band is characterized by low transmission rates and short transmission distances. Mostly, the construction of these systems is cheap and easy to handle and exempt from registration as well as charges. The RFID transponders make use of the electromagnetic waves nearfield and are supplied with energy via inductive coupling. The advantage is that the RFID transponders in this frequency band are relatively resistant towards metals or fluids which makes them appropriate for being used in animal identification.
High Frequency (HF 13,56 MHz)
The HF can be universally used and is characterized by high transmission rates and high tact frequencies. The respective RFID transponders operate at an HF frequency of 13.56 MHz – which is a short wavelength requiring only a few antenna windings. Consequently, the RFID antennae can be smaller and simpler. This makes it possible to use etched or printed antennae, which in turn means that the inlays (=chip + antenna) may be manufactured as a continuous reel, and this significantly simplifies the subsequent processing as far as large production numbers within a role-to-role process are concerned.
Ultra High Frequency (UHF 860 – 950 MHz subdivided into partial bands)
These systems do have very high transmission rates and ranges. Due to the shorter wavelengths, a dipole is sufficient as an antenna instead of a reel, the field spreading is sufficient as far as ray optics is concerned, and this in turn provides for a targeted spreading. Also UHF-transponders are predominantly being manufactured as foils which is beneficial for processing large quantities in a role-to-role process. Using a support battery for energy supply purposes (semi-passive transponders) is sensible in some applications due to the ranges that are anyway high, in order to increase these ranges further. We also have to mention within this context that some frequency bands in the microwave spectrum have not yet been made accessible in a financially cost-effective manner and furthermore, they may be subject to local approval restrictions. For example, the FCC UHF-frequency band around 915 MHz has not yet been approved in Europe. Currently, discussions are taking place about making parts of this frequency band accessible for RFID purposes. The ETSI UHF-frequency band around will remain as it is.
Fig.: Wave propagation display (electric and magnetic waves) in the near field and remote field
Fig.: Defining the near field and remote field area
RFID transponder read range
Frequency band: 1 Hz - 30 MHz
Range: 0 - 1 cm
RFID-transponders have to be inserted into a reader or their position during the reading process has to be exactly defined. Thanks to the close coupling, the RFID transponder can be provided with larger amounts of energy, yet we have to bear in mind that the transmitted energy is growing in proportion to the rising frequency. The data transmission between the RFID transponder and the RFID reader can be carried out via inductive or capacitive coupling. Apps requiring the highest safety level are managed this way.
Frequency band: between 100 and 135 kHz, 6.75 MHz, 13.56 MHz and 27.125 MHz
Range: up to 1 meter
Just as in the case of all remote-systems, data transmission is provided for by inductive coupling. As the RFID-transponder energy supply is carried out passively, the energy transmitted from the magnetic field of the reader is sufficient to run the chip.
Frequency band: Microwave spectrum: 1 m – up to 10 m
Data transmission is carried out via the so-called backscatter process, yet the energy transmission is merely sufficient for sending a wake-up- or a sleep signal. A support battery is needed for supplying the RFID transponder chip with energy or for preserving the stored data. Toll systems would be conceivable as an area of application.
Fig.: Read-range and communication method of the different frequency bands
Advantages of using RFID-transponders
• Every chip has a unique serial number that´s assigned only once throughout the entire world (UID or TID). This guarantees a clear assignability on the individual product level and provides for a full-range product individualization.
• Re-writable data memory in the chip which in turn provides for flexible data management directly on the product. The information on the RFID data carrier can be changed, erased or amended at any time. Product, maintenance, manufacture or service data are available directly at the product.
• The communication that´s carried out between the RFID data carrier and the writer-reader system without a visual contact requirement provides for ruggedness against dirt through being placed on protected places, and also for an invisible integration into existing products and for a simplified process optimization.
• The high speed of the communication equals a 100 % first pass rate in the case of bar-codes.
• Reading several RFID data carriers at one moment and in one work step (bulk capturing) speeds up the processes .