RFID: Radio Frequency IDentification Basics

  RFID: Radio Frequency IDentification Basics

  Now, It is coming in order to talk about RF Identification. RFID – what does it mean, some theory, main purpose, sample identification systems?  


  Often, mainly in the near past, the identification systems are corresponding basically with Barcode Labels, which are part of optical recognition IDs. 

  The Scanning head emits Laser lines through a specially shaped Prism, lighting the bar-code label and reading the reflected image via a linear CCD Matrix. 

  The Maximal reading distance is a few / up to 5 meters. 



   With an advance in technologies, grows and is necessary for large distance Identification. In the ’80s was developed a new technology for remote identification, was patented in 1983, and it was named RFID. The main purpose is to identify, locate and track people, animals, and assets.

   Unveiling the name’s letters as an abbreviature, means: Radio Frequency IDentification is pointing to the use of electromagnetic waves.

   A device – named TAG, represented as a black box has two main stages:

  • Antenna Stage:
    • Twisted or Printed Matched Powering Antenna/inductor with Discrete or Printed Capacitor, forming а determined frequency tuned Parallel LC Loop.
  • MCU Stage:
    • Managing The Read-only or Read/Write dual directional Communication. 

   The genius aspects of this unique technology can be divided into two parts:

  • Remote powering the TAG device,
  • The Unique TAG Information reading way.

Powering the TAG device:

   Almost all TAGs actually don’t need a powering battery. They derive all necessary energy for proper hardware functioning over the air, more specifically from the electromagnetic field, generated by the RFID Reader.

   Using the phenomenon of the LC pair Resonance, the target device – TAG is extracting little power from the transmitting reader circuitry. It is enough to power the internal hardware of the TAG device. 

Reading the TAG Information:

  The ID Data into the passive -Read-Only and active -ReWritable TAGs is a Crypted. For example, in describing the main principles we will use the simplest 125KHz TAG.

  As we already said the TAG device has an antenna loop part and an MCU part. Precisely Matched to an operating frequency antenna loop is deriving all necessary power to supply MCU Part, within surplus. A Transmitted By the Reader RF Signal is called a “Carrier”. 

While the Carrier RF Signal is existing and is interruptable, and, there is a TAG in the useful range of the RF Field of the reader, there is a continuous reading of the CODE stored by the TAG’s Manufacturer.

  We Can look at the magnetically coupled Reader Coil and TAGs Antenna Coil as a Transformer with Primary and Secondary Coils. The weak, but real magnetic coupling makes possible the way of corresponding between the Reader and TAG. 

The Typical Reading “Handshake”:

  • The RFID reader generates continuously an RF
    carrier sine wave, and is watching for a modulation
    existence. When Reader detects a modulation in its RF field, 
    it indicates the presence of an RFID TAG.
  • The Reader’s RF field powering the TAG. Once the tag gets an enough
    power for operating, it manipulates the carrier sine and begins clocking its MCU data to an output
    switching transistor – normally connected across
    the coil terminals.
  • The Corresponding MCU Data, using the self-extracted RF Field clock is managing the output transistor – shunting the coil,
  • Shunting the coil causes a slight change in the amplitude of the carrier,
  • The Reader detects these dampenings into an amplitude of the carrier, using peak-detectors, and extracts bitstream data for the next stage of identification used methods.

Data Modulation:

   Data Modulation can be of three different types:

  • Direct Amplitude modulation,
  • FSK – Frequency Shift Keying,
  • PSK  -Phase Shift Keying,


PIC. 1  Different Data Coding waveforms


PIC. 2  Visual Representation of FSK Modulated Signal


PIC. 3  Visual Representation of PSK Modulated Signal

Different Kinds of RFID TAGs:

  The simplest way to divide the TAGs is by using the bandwidth of their working frequencies. Different Kinds of Tags is working in different frequency ranges, using different communication protocols, standards, ways of encrypting data, etc. 

  You can see the TAGs separated into a few groups – By Frequency | Max Reading Distance:

  • 120-150 kHz LF-Low Frequency | up to 10cm,
  • 13.56 MHz HF-High Frequency | up to 1m,
  • 433 MHz UHF-Ultra High Frequency | from 1m to 100m,
  • 865-868 MHz, 902-928 MHz UHF-Ultra High Frequency | from 1m to 2m,
  • 2.45-5.80 GHz  Microwave | from 1m до 2m,
  • 3.1-10 GHz  Microwave | up to 200m,


  For the sake of completeness, we will say a few words about another similar technology.


   Talking about the Identification of things, e.g. the articles into an electronic devices store. Some people will notice, the NFC is using the same frequency as HF TAGs. But, there are a few main differences between RFID and NFC. 

   The Near Field Communication Devices are using the same 13.56 MHz HF Frequency Band as the HF TAGs:

  • Work at the truly near distance – max 5cm from the reading device, 
  • Using a Fast Dual Directional communication, adequate for fast P-2-P detection and connection, enable transferring large size Files,
  • In every single moment is possible only one NFC Communication,


ID Printer:


HID Programmer:



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