RFID tags can operate without an internal power source, and they are classified into two main types: passive RFID tags and semi-passive (or battery-assisted passive) RFID tags. Both types leverage the energy transmitted by an RFID reader to power the tag and enable communication.
1. Passive RFID Tags:
Power Source: Passive RFID tags do not have an internal power source (like a battery). Instead, they rely entirely on the energy harvested from the radio frequency (RF) signals emitted by an RFID reader.
Energy Harvesting: When a passive RFID tag enters the electromagnetic field of an RFID reader, the tag's antenna absorbs energy from the reader's RF signals. This energy is used to power the tag's integrated circuit (IC) temporarily.
Data Transmission: The tag's IC modulates the signals it receives from the reader, encoding information such as a unique identifier. The modulated signals are then sent back to the RFID reader.
Range: Passive RFID tags have a shorter read range compared to active RFID tags and are typically used for applications where the tag can be in close proximity to the reader.
2. Semi-Passive (Battery-Assisted Passive) RFID Tags:
Power Source: Semi-passive RFID tags incorporate a small battery as an internal power source. This battery is used to power the tag's circuitry, including the microchip and possibly additional features like sensors.
Energy Harvesting: Similar to passive tags, semi-passive tags can also harvest energy from the RFID reader's signals. The harvested energy supplements the power from the battery.
Data Transmission: The tag's microchip modulates and transmits data back to the RFID reader using both the harvested energy and the power from the battery.
Extended Range and Additional Features: Semi-passive RFID tags typically have a longer read range compared to passive tags, and the addition of a battery allows for more consistent performance and the inclusion of extra functionalities.
Both passive and semi-passive RFID tags utilize energy from RFID readers to operate. While passive tags solely rely on harvested energy, semi-passive tags combine energy harvesting with a small internal battery to extend the tag's capabilities and read range.