Radio frequency identification devices (RFID), originally intended to identify agricultural equipment and livestock, are nowadays present in daily life everywhere: car immobilisers, access control, airport luggage handling, contactless cards, anti-theft tags etc.
Electronic RF identification devices in the 125 kHz, 134 kHz and 400 kHz frequencies use inductors as antennas both to receive and transmit in active (battery-powered) transponder devices and to power the circuit in passive transponders.
Passive transponders
A passive transponder consists of a parallel-resonant tuned LC circuit connected to an ASIC. The 125 kHz LC tuned circuit both powers the ASIC, which includes a full-wave rectifying circuit, and receives the modulated signal of the reader or primary coil. Once the modulated signal is decoded, the ASIC sends a ROM-recorded code to the LC circuit, operating now as a transmitting antenna.
Passive transponder ICs can usually be 'Read-only' or 'Read-write' devices. PSK or FSK modulation is often used, as well as many other safety features such as encryption, random generated security codes, etc. These passive devices can be read or written millions of times with a handheld reader from a certain distance. This is known as reading distance and depends on reader coil size, or rather, the intensity of the magnetic field created by the reader primary coil and, what is very important, transponder coil sensitivity, measured in mV/mT.
The sensitivity is the parameter that determines how much voltage can be induced in the transponder ASIC by a known magnetic field. The higher the sensitivity, the longer the reading distance. There are other factors influencing the reading distance such as coupling factor, Q factors of the primary and secondary inductors and ASIC power consumption.
Types
Passive transponder devices are manufactured with multiple sizes and shapes such as glass tubes for animal and pet identification, plastic moulded bricks for car immobilisers and access control or flat tags for industrial applications. Each one of these applications needs a different type of inductor: ferrite wound rod inductors with flying leads for glass tubes, SMD ferrite inductors to be picked and placed on leadframe for plastic moulded bricks or flat coreless coils with circular, oval or elliptical shapes for flat tags and contactless cards.
Automotive electronic security and safety systems are currently introducing extended features of transponder technology to ensure car-theft will never happen. Car keys are no longer so easy to copy and not even mechanical - they are electronic systems integrating RF encrypt immobilising and remote door opening based on SMD transponder inductors.
A step further is the car Keyless Entry System, consisting of a three-axis sensitive card that can stay in one's pocket or wallet while entering a car and starting it. Tyre pressure monitoring systems and wheel rotation detection are also common applications.
Fastron's SMD Ferrite and Alumina wound inductors for transponders are specially designed and produced to fulfil these tough requirements of new automotive RFID applications. These transponder and reader coils are suitable for all existing transponder IC manufacturers.
With its base in Germany, Fastron has expanded into a multinational group. Fastron is certified in ISO/TS 16949, ISO 9001 and ISO 14001.
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