Composition and Reading Process of RFID Systems
I. System Components
A typical RFID system consists of three main parts:
Reader / Interrogator
Responsible for generating the radio frequency (RF) field and communicating with tags. The reader initiates commands, receives tag responses, and exchanges data with the host or backend system.
Electronic Tag (Tag / Transponder / Smart Label)
Composed of an antenna and a chip, it stores a unique identifier and business-related data. Depending on the power supply method, tags can be classified as:
Passive Tag: No internal battery; operates entirely using the RF energy emitted by the reader.
Semi-passive Tag: Contains a battery to power internal circuits, but communication still relies on RF signals.
Active Tag: Equipped with its own power source, can actively transmit signals, and supports longer communication ranges.
Backend System (Host / Backend System)
Receives data uploaded from the reader for parsing, storage, business logic processing, or system integration. Typical applications include inventory management, identity authentication, and transaction statistics.
II. Typical RFID Tag Reading Process
1. Reader Transmits RF Field
The reader continuously emits a carrier signal at a set frequency, forming an RF energy field. For passive tags, this field provides both communication and operating power.
2. Tag Detection and Power-Up
When a tag enters the RF field, its antenna receives energy and activates the chip, switching it from standby to active mode. Active or semi-passive tags enter the communication phase directly.
3. Anti-collision and Selection
When multiple tags are present in the reading area, the system runs an anti-collision algorithm (such as ALOHA or tree-based querying) to distinguish and identify each tag sequentially, preventing signal interference.
4. Session Establishment / Protocol Activation
In some protocols (e.g., ISO/IEC 14443), the reader and tag go through selection and activation steps (SEL, ANTICOLL, SELECT) to establish a temporary session that identifies the current communication tag and maintains session context.
5. (Optional) Authentication and Key Exchange
Whether authentication is required depends on the application:
General identification (e.g., logistics, inventory) usually reads the tag ID directly without authentication.
Security-sensitive applications (e.g., access control, e-tickets, payments) require mutual authentication using symmetric or asymmetric encryption (such as 3DES or AES) to verify legitimacy and establish an encrypted channel, preventing cloning or eavesdropping.
6. Data Exchange (Read/Write Operations)
After authentication, the reader sends read/write commands. The tag responds with data or confirms successful writing. In high-frequency systems (13.56 MHz), communication often uses APDU (Application Protocol Data Unit) command-response formats.
7. End of Communication
Once data transmission is complete, the reader deactivates the session, and the tag returns to sleep mode. The reader then uploads the parsed data to the backend system for further processing.
III. Key Points of Information Exchange
Connection Establishment:
RFID communication is generally connectionless, though most protocols employ a short-term session mechanism to maintain context during a communication cycle.
Authentication Requirement:
Depends on the application. Security applications require strong authentication and encryption, while general identification tasks typically do not.
Anti-collision Capability:
Modern readers are equipped with anti-collision mechanisms, enabling simultaneous detection and sequential interaction with multiple tags.
IV. RFID Frequency Bands and Categories
Globally, RFID operates in ISM (Industrial, Scientific, and Medical) bands. Common frequency ranges and corresponding categories include:
Low Frequency (LF): ~125–134 kHz
Suitable for short-range applications with strong penetration (e.g., animal implants, low-frequency access cards).
High Frequency (HF): 13.56 MHz
Widely used for smart cards, NFC, e-tickets, and short-range reading.
Ultra High Frequency (UHF): ~860–915 MHz (depending on region)
Suitable for long-range and high-speed tag recognition (e.g., logistics pallets, workshop tracking).
Microwave Frequency: 2.4 GHz, 5.8 GHz, etc.
Used in specialized or specific environmental applications.
