What are the different taxonomies of RFID tags? part 2

The second part of this FAQ focuses on how RFID tags are categorized based on frequency bands and the presence/absence of microchips in RFID tags. While the classification based on frequency is well known, it helps practicing engineers to know about chipless RFID tags.

Types of RFID Tags based on frequency bands

Categorizing RFID tags based on frequency bands is very common. Figure 1 shows how the RFID tags can be divided into various categories based on frequency. The main categories are:

Low-frequency (LF)
High-frequency (HF)
Ultra-high frequency (UHF)

LF RFID systems operate between 125/134 kHz and offer a short reading distance of up to 30 cm. They support a data reading speed of 10 kbps and are commonly used in medical applications, such as patient access control, animal identification, and equipment inventory management. Their limited range and low data speed suit them for secure, short-range communication.

HF RFID systems commonly operate at 13.56 MHz, providing a reading range of around 1 m. These systems are known for their high reading speed but require a line of sight for effective communication. Additionally, they are generally more expensive than LF systems due to their advanced capabilities.

UHF RFID systems operate in the 850 to 960 MHz frequency range, offering a 3 to 5 m reading distance. Depending on the modulation technique, they support data transfer rates ranging from 40 to 640 kbps. These systems are popular for inventory management and supply chain applications due to their longer range and faster data communication.

Figure 2 illustrates the working principles of LF/HF and UHF RFID tags. The RFID reader generates an electromagnetic field using a reader coil when the RFID system operates at the LF/HF range. This field induces a current in the tag coil of the RFID microchip, enabling communication through inductive coupling. The communication range is usually short due to the near-field interaction between the coils.

When operating at the UHF range, the RFID reader sends power and data to the tags through electromagnetic waves. The tags receive the signal and respond by backscattering the data to the reader. UHF RFID systems operate over longer distances due to far-field communication, allowing multiple tags to be read simultaneously.

Types of RFID tags based on microchips

With the emerging trends in chipless RFID tags, the RFID tags can also be classified into chipless and chipped RFID tags, as illustrated in Figure 3.

Chipless RFID tags

Chipless RFID tags do not contain microchips. Instead, their operation is based on backscattering and retransmission. They operate at higher frequencies (3 GHz to 60 GHz), allowing compact designs but limiting range and material penetration.

These tags use a broad frequency spectrum, enabling multiple tags to be read simultaneously, although they require advanced signal processing. They consume less power (below 10 mW), making them cost-effective but limiting their communication range to around 5 ft.

Chipless RFID tags are highly affected by noise and interference due to low signal power, impacting performance in noisy environments. They lack handshaking protocols, reducing data security. Their working principle relies on backscattering and retransmission of incident electromagnetic waves, encoding data in the reflected signal’s variations. The leading chipless RFID technologies are based on printed electronics, EM scattering, and surface acoustic waves (SAW).

These tags are ideal for cost-sensitive applications such as basic inventory tracking, retail anti-theft systems, access control, and localized tracking where short-range and lower security are acceptable.

Chipped RFID tags

Chipped RFID tags contain an application-specific microchip that stores and processes information, enabling advanced functionalities like encryption and data storage. They operate at lower frequencies (125 kHz to 5.875 kHz), providing better materials penetration but slower data rates.

These RFID tags work within the UHF range, ensuring long-range communication and fast data transfer. They require higher power levels (3 to 4 W or more), resulting in stronger signals and longer reading distances of up to 18 ft with antenna arrays.

Thanks to robust signal power and error correction, chipped RFID tags are less affected by noise and interference. They support advanced communication protocols like hash chain, three-way handshake, and DASH7 for secure data transmission.

Their working principle is based on antenna loading, enabling complex data encoding. Due to their reliability and long-range capabilities, these tags are widely used for theft prevention, traffic management, biomedical applications, and location tracking.

Summary

Knowing how RFIDs are grouped by power source, frequency, and microchip presence helps engineers make better systems by letting them make decisions that balance cost and performance. Even though these groups are connected, each focuses on a different part of functionality. This helps engineers choose the best combination for each application.