Currently, RFID products are categorized by their operating frequencies into low frequency (LF), high frequency (HF), and ultra-high frequency (UHF), with different products meeting various standards across these ranges. Different frequency bands result in distinct characteristics for RFID products. Sensors can be either passive or active. Below, we provide a detailed overview of the characteristics of passive sensors at different frequencies and their main applications.
1. Low Frequency (125 KHz to 134 KHz)
RFID technology initially saw widespread use at low frequencies. This frequency band operates via inductive coupling, where there is transformer coupling between the reader coil and the sensor coil. The alternating magnetic field from the reader induces a voltage in the sensor’s antenna, which is rectified and can be used as a power supply. The magnetic field can be well-defined, but it diminishes rapidly with distance.
Characteristics:
Sensors in this frequency range are more expensive than those in higher frequencies.
- 1. The typical operating frequency for low-frequency sensors ranges from 120 KHz to 134 KHz, with TI’s frequency set at 134.2 KHz. The wavelength at this frequency is about 2,500 meters.
2. Aside from interference from metal, low-frequency signals can penetrate almost any material without reducing the read range.
3. Readers operating at low frequencies do not require special permissions globally.
4. Low-frequency products come in various packaging options, some of which are expensive but offer over 10 years of lifespan.
5. Although the magnetic field diminishes rapidly, it produces a relatively uniform read/write zone.
6. Data transmission rates in this band are slower compared to other RFID frequencies.
7. Sensors in this frequency range are more expensive than those in higher frequencies.
Main Applications:
- Livestock management systems
- Vehicle anti-theft and keyless entry systems
- Marathon race timing systems
- Automated parking and vehicle management systems
- Automated fuel payment systems
- Hotel door lock systems
- Access control and security management systems
International Standards:
- ISO 11784: Coding structure for livestock RFID applications
- ISO 11785: Technical concept for livestock RFID applications
- ISO 14223-1: Air interface for livestock RFID
- ISO 14223-2: Protocol definition for livestock RFID
- ISO 18000-2: Defines the physical layer, anti-collision, and communication protocols for low frequency
- DIN 30745: European standard for waste management applications
2. High Frequency (13.56 MHz)
At this frequency, sensors no longer require coils for antenna creation and can instead use etched or printed antennas. The sensor typically operates via load modulation. This involves toggling the load resistor on the sensor, which modulates the voltage in the reader’s antenna. Data is transferred by controlling the load, allowing information to be sent from the sensor to the reader.
Characteristics:
- 1. The operating frequency is 13.56 MHz, with a wavelength of around 22 meters.
- 2. The signal can penetrate most materials except metals, though the read range may decrease. Sensors need to be placed at a distance from metal objects.
- 3. This frequency is globally recognized and free from special restrictions.
- 4. Sensors typically come in the form of electronic labels.
- 5. The magnetic field diminishes rapidly but still provides a relatively uniform read/write zone.
- 6. Systems at this frequency support anti-collision features, enabling simultaneous reading of multiple tags.
- 7. Some data can be written to the tags.
- 8. Data transmission speeds are faster than in the low-frequency band, and the cost is moderate.
Main Applications:
- · Library management systems
- · Gas cylinder management systems
- · Clothing production and logistics management systems
- · Prepaid meter systems
- · Hotel door lock management
- · Large conference attendee tracking
- · Fixed asset management
- · Pharmaceutical logistics management
- · Smart shelf management
International Standards:
- · ISO/IEC 14443: Defines proximity IC cards with a maximum read distance of 10 cm.
- · ISO/IEC 15693: Defines vicinity IC cards with a maximum read distance of 1 meter.
- · ISO/IEC 18000-3: Defines the physical layer, anti-collision algorithm, and communication protocols for 13.56 MHz systems.
- · 13.56 MHz ISM Band Class 1: Defines EPC-compliant interface for 13.56 MHz.
3. Ultra-High Frequency (860 MHz to 960 MHz)
UHF systems transfer energy via electric fields. The energy in the electric field diminishes more slowly compared to magnetic fields, though the read zone is harder to define. This band allows for long-range reading, with passive tags reaching up to 10 meters, typically operating through capacitive coupling.
Characteristics:
- 1. Global definitions for this frequency band vary. Europe and parts of Asia define 868 MHz, North America defines 902 to 905 MHz, and Japan suggests 950 to 956 MHz. The wavelength in this band is around 30 cm.
- 2. Output power is globally regulated, with the U.S. defining 4W and Europe defining 500mW, though Europe may increase this to 2W EIRP.
- 3. UHF waves cannot penetrate many materials, particularly water, dust, fog, or other suspended particles. Unlike HF tags, UHF tags do not need to be separated from metal objects.
- 4. UHF tag antennas are usually long and rectangular, with both linear and circular polarization designs to meet different application needs.
- 5. While UHF allows for long read distances, the read zone is difficult to define.
- 6. UHF supports high data transmission rates, allowing large numbers of tags to be read in a short time.
Main Applications:
- · Supply chain management
- · Production line automation
- · Airline baggage management
- · Container management
- · Railway cargo management
- · Logistics management systems
International Standards:
- · ISO/IEC 18000-6: Defines the physical layer and communication protocol for UHF; includes Type A and Type B air interface definitions, supporting read/write operations.
- · EPCglobal: Defines the electronic product code structure and UHF air interface, including protocols like Class 0, Class 1, and UHF Gen2.
- · Ubiquitous ID: A Japanese standard defining UID encoding structures and communication management protocols.
