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HOW FASTAGS WORK WITHOUT A POWER SOURCE?THE MAIN COMPONENT OF FASTAG IS AN RFID WHICH HARNESS ENERGY FROM INCOMING WAVES AND USES BACKSCATTER TECHNIQUE TO COMMUNICATE WITH RFID READER.

FASTag is a reloadable tag that enables automatic, contactless deduction of toll charges. It is operated by the National Highways Authority of India (NHAI) and the National Payments Corporation of India (NPCI). By using Radio Frequency Identification (RFID) technology, it allows vehicles to pass through toll plazas without stopping for cash transactions.

The Core Technology: RFID

FASTag works on Passive RFID (Radio Frequency Identification) technology.

• The Tag: Affixed to your vehicle’s windshield, the tag contains a microchip and an antenna. It is “passive” because it doesn’t have its own battery; it remains dormant until it enters the range of a reader.
• The Reader: Installed at the toll plaza canopy, the reader emits radio waves at a specific frequency (865–867 MHz in India).
• The Interaction: As your vehicle approaches (usually within 20–30 feet), the radio waves from the reader provide enough energy to “wake up” the chip in your tag. The tag then reflects back a unique 13-digit identification code.

Step-by-Step Working Process

The entire transaction, from scanning to the barrier opening, typically takes less than a few seconds.

1. Detection and Scanning:When your vehicle enters the FASTag lane, the overhead RFID reader scans the tag on your windshield. It captures the Tag ID and the Vehicle Class (e.g., Car, Bus, or Truck).

2. Validation (The NETC Mapper):The toll plaza system sends this Tag ID to the NETC Mapper (a central database managed by NPCI).The Mapper performs three critical checks:

• Validity: Is the tag authentic and not tampered with?
• Status: Is the tag active, or has it been blacklisted (due to low balance or fraud)?
• Mapping: Which bank issued this tag?

3. Fare Calculation and Debit Request:Once the tag is validated, the toll plaza’s “Acquirer Bank” calculates the toll rate based on your vehicle class.It then sends a “Debit Request” through the NPCI switch to your Issuer Bank (the bank where you bought the FASTag).

4. Transaction and Notification:The Issuer Bank debits the amount from your linked prepaid wallet or bank account.Once successful, a confirmation is sent back through the system to the toll plaza.

• Barrier Opens: The boom barrier lifts automatically.
• SMS Alert: You receive an instant SMS on your registered mobile number with the amount deducted and your remaining balance.

RFID Fastag Design Concept

The design of a FASTag is optimized for durability, high-speed detection, and security.

Physical Components

• Integrated Circuit (Microchip): A tiny silicon chip that stores the unique ID and handles data processing.
• Antenna: A thin, conductive coil (usually aluminum or copper) that receives radio waves and transmits data. Its shape is specifically designed to work through glass.
• Substrate (Encapsulation): The chip and antenna are embedded between layers of protective, weather-resistant material (PET or paper) to withstand sunlight, rain, and heat.

How RFID emits Signals without battery or internal power source?

The internal circuitry of the tag follows a specific process to turn a radio wave into usable electricity.Instead of “broadcasting” a new signal like a radio station, the tag acts more like a smart mirror that reflects the reader’s own signal back in a coded way.in physics trick is called Backscatter Communication.

Backscatter Communication-The Mirror Analogy:Imagine a person standing in a dark field holding a powerful flashlight (the Reader), and you are standing far away holding a mirror (the FASTag). You have no light of your own, but you can see the flashlight’s beam. To send a message, you don’t turn on a lamp. Instead, you quickly cover and uncover the mirror with your hand.The person with the flashlight sees a “flickering” reflection. If you cover the mirror for “0” and uncover it for “1,” you have just sent a digital message using their energy.

Here is how Fastag RFID performs backscatter communication.

1. Antenna Reception: The incident radio wave from the reader hits the tag’s antenna, creating an Alternating Current (AC).
2. Rectification: The tag’s microchip contains a Rectifier (usually a bridge of diodes) that converts the oscillating AC signal into a steady Direct Current (DC).
3. Voltage Boosting: Because the energy from radio waves is often very weak (in millivolts), a Voltage Multiplier is used to step up the voltage to a level high enough to “wake up” the microchip (typically around 1.2V to 1.5V).
4. Storage: A tiny internal Capacitor acts like a temporary battery, smoothing out the power so the chip doesn’t shut down during minor signal fluctuations.
5. Impedance Switching: The FASTag’s microchip contains a tiny transistor (an electronic switch) connected across the antenna.When the switch is open, the antenna is “matched” to the chip. It absorbs most of the incoming energy to keep the chip powered.When the chip closes the switch (short-circuits the antenna), the antenna becomes highly reflective. It “bounces” the radio wave back toward the reader.
6. Creating the Signal: By switching between these two states thousands of times per second, the tag creates a “pulse” in the reflected wave. The reader detects these tiny changes in the reflection and decodes them as the 13-digit FASTag ID.