UHF RFID Tag
UHF tags work well in manufacturing environments and warehouses. They are commonly used in airline baggage, container and trailer tracking coupled with fleet management.
Screen-printed flexible RFID antennas with moderate gain and small linear dimensions were developed using different printing techniques. They were then tested for wireless functionality by measuring RSSI vs. distance for three types of printed RFID tags.
Low-frequency (LF)
Low-frequency (LF) RFID tags operate in the 30 KHz to 300 KHz band, most commonly around 125 KHz. LF systems have very short read ranges and slower data transfer rates than higher frequencies, but they are less sensitive to interference from electromagnetic energy. This makes them suitable for use in moist environments, and LF transmissions can pass through most non-metal materials. LF systems are most often used in access control and livestock tracking applications.
LF tags can be either passive or active. Passive tags do not have their own power source and rely on the inductive coupling of reader antennas to transmit a signal that the tag reflects back (this is called “backscatter”). Active LF tags require a RF downlink from the reader to activate a microcontroller within the device, which then transmits its information (typically 96 bits) to the reader. LF RFID tags can be either read-only or read/write devices.
High-frequency (HF) RFID has a greater read distance than LF tags but is still limited to a few inches. This makes it better suited for RTLS, which requires continuous monitoring of assets that are not easily moved. It is also the technology of choice for item-level tracking and is the basis of the NFC standard for smart card payments and proximity cards (such as those used in hotel rooms). Other HF RFID applications include credit card identification, ticketing payments, library books and airline baggage.
High-frequency (HF)
HF RFID tags operate at higher frequencies and typically have a much longer read range than LF tags. They use radiative coupling to power and communicate with interrogators via radio waves. However, these radio waves are reflected, diffraction, or refraction by objects and liquids in the vicinity, which causes multiple signal paths to reach the receiver, resulting in multipath effect. This can cause varying tag readability or even loss of communication between the tags and the interrogator. To minimize multipath effect, HF RFID tags have directional antennas and may require a longer reading distance than LF RFID tags.
Typical applications for HF RFID tags include smart cards, library books, airline baggage, and asset tracking. These tags HF RFID Tag and interrogators have relatively low cost due to their simpler antenna design. However, HF RFID tags do not support anti-collision protocols.
Passive HF RFID tags are very affordable and easy to manufacture, making them the most popular option for many organizations. These tags work well with metals and liquids, can be used to track items in a variety of environments, and have excellent memory capacity. However, they cannot be easily read while attached to products containing water or animal tissue, because water absorbs the frequency of the radio wave.
UHF RFID tags are most commonly found in enterprise-wide asset management applications, and they offer a wide range of benefits for companies seeking to link digital and physical experiences. These tags have a longer reading range than HF RFID tags and can support more complex communication protocols.
Ultra-high-frequency (UHF)
UHF RFID tags operate on the 860-to-960-megahertz frequency range. They are popular for items that require high read ranges such as jewelry. They are also used in inventory management, tracking metal assets and returnable transit item (RTI) applications.
UHF RF waves have a shorter wavelength than LF waves, so they can pass through most materials except water and dense metals. This makes them less prone to interference from conductive materials like metal and plastics that interfere with data transmission between the tag and reader. The broader read ranges and fast transfer speeds of UHF tags make them popular for commercial processes, such as tool monitoring and IT network management and sprint timing.
Passive and semi-passive UHF tags are available for the EPC Class 1 Gen 2 standard, ISO 18000-6C, or simply “Gen 2.” There are passive tags that perform well across the entire 860-to-960 band as well as those optimized for different sub-bands. The majority of Gen 2 tags on the market are passive. Active RFID tags are available as well, which have a battery and proactively beacon at predetermined intervals, requiring the tag to be within range of an active reader.
These tags can have higher costs than comparable passive technologies due to the battery, but they are more durable and have extra sensors that improve performance in liquids and near animals and human bodies. They can be more susceptible to electromagnetic interference from cell phones and other wireless devices that share the RF spectrum with UHF systems, so these tags should not be placed in close proximity to them.
Active
The frequency of the radio waves used to communicate with an RFID tag determines its read range. A lower frequency (LF or HF) has longer wavelengths and offers shorter read distances while a higher frequency (UHF or RAIN RFID) uses shorter, high-energy wavelengths that provide greater read ranges. The higher frequencies HF RFID Tag are also more sensitive to materials such as metals and liquids that disrupt the signal1.
Active HF RFID tags have their own internal power source, typically batteries, to send information-carrying signals. They’re often used in real-time location tracking systems to locate objects, such as wheelchairs at a hospital or large containers on a shipping dock. These tags are typically more expensive than passive RFID tags, starting around $25 apiece and climbing to $100 per tag.
There are two main types of active HF RFID tags: transponders and beacons. Transponders are “awaken” when a reader signals them, and then they transmit a signal with their stored data. Because they don’t emit any signals at other times, these tags conserve battery life.
Beacons, on the other hand, emit a signal at regular intervals to continuously broadcast their location. They’re most often used in real-time locating systems to track large objects such as wagons, containers or products that need to be controlled over long periods of time. These tags require more expensive reader antennas to maintain adequate coverage, but they do offer the advantage of continual data transmission that can help with a system’s performance monitoring.
