HF RFID Tag
HF RFID Tag have lower costs than other frequencies and are less sensitive to liquids. They use near-field inductive coupling to gain power and communicate with interrogators.
This paper demonstrates screen-printed passive UHF RFID tags with temperature sensors on flexible substrates that operate on meandered monopole and folded dipole antennas. The antennas have small linear dimensions and moderate gain, making them suitable for integration with everyday objects.
HF Antennas
HF RFID Tags are typically passive, with little or no battery. They transmit data by backscattering RF signals from the antenna. HF tags are more mature than UHF, offering faster data transfer and limited issues with liquids and metals.
Compared to LF tags, HF tags have simpler antenna designs. They are usually made of a copper, aluminum, or silver coil with three to seven turns. This makes them relatively cheap to manufacture, and they are often thinner than LF tags so they can be incorporated into standard-sized labels, tickets, or documents.
More advanced HF RFID systems use directional antennas, such as yagi and quad designs, to concentrate the transmitted signal (like a flashlight beam). This increases read range and reduces interference from nearby objects. However, these directional antennas are very expensive, as they require large, high-powered transmitters, and they require a receiver with an equally strong transmission pattern (to counteract the received signal from the direction of the antenna).
When tuning HF RFID antennas, the first step is to measure the inductance and complex impedance of the coil. This can be done with a network analyzer that spans a wide frequency range, such as 12 to 15 MHz. It is also important to consider the physical and environmental look of where the antenna will be deployed. For example, a long cable between the network analyzer and the tag will introduce its own impedance and may impact performance.
HF Transponders
High-frequency (HF) transponders power and transmit data to RFID readers via inductive coupling. They have a very small footprint, with antennas of three to seven turns, allowing for a low cost and small form factor. This technology has a high data transfer rate and limited issues with liquids and metals, making it ideal for item-level applications such as document management, casino chips and playing cards, laundry, jewelry, and retail inventory tracking.
HF RFID systems use the same transmission method as LF, but operate at higher frequencies to allow for greater data transmission and a larger read range. The increased data transmission speed also makes HF tags more versatile than other passive technologies, but they are not ideal for every industrial application. HF signals occupy the same space as electromagnetic waves used by cell phones, Wi-Fi, and Bluetooth devices, which can cause interference.
Unlike LF systems, which have a well-defined operating range and are not affected by the presence of metal in their environment, HF systems can be disrupted by metal objects, which can interfere with the signal. This makes the choice of the operating environment a HF RFID Tag critical element in tag selection, as it will affect the performance and reliability of an RFID system. The choice of a HF system also depends on the needs of a specific operation, such as how long it will be in use and whether the tags will need to be exposed to harsh environments.
HF Readers
HF tags use electromagnetism to power themselves and communicate with readers. When the tag is within range of a reader’s antenna, electromagnetic waves strike the antenna and induce an electric current that powers the tag’s integrated circuit (IC) to “turn it on”. This turns the tag into a broadcasting source of data, which can then be read by the RFID reader’s antenna. HF tags are the most common type of RFID tags in the world, and they operate in the 3 MHz to 30 MHz frequency band. They’re often used with Near Field Communication (NFC) technology for electronic ticketing, payment, and data transfer.
HF ISO-18000-3 mode 2 tags are also popular for item-level applications like document management, casino HF RFID Tag chips and playing cards, laundry, and jewelry, as well as on-the-shelf retail and warehouse inventory tracking. Their ability to read tightly stacked and densely packed items makes them perfect for supply chain applications, like warehouse and showroom floor asset tracking.
Unlike LF RFID, which can’t track metal objects or items containing water, HF waves are less likely to be affected by these factors. This means that HF tags can be easily read through plastic, plexiglass, and other materials that LF RFID cannot. They can even be used with conductive metals, such as aluminum and stainless steel. They’re also more cost effective than UHF RFID systems and have a wider reading range than LF RFID, making them ideal for countless new applications.
HF Sensors
HF sensors work with HF RFID tags by using the inductive coupling method to power and communicate with them. This technology uses magnetic flux to create a read zone that is omnidirectional, meaning it covers the entire area around it evenly.
This makes it well-suited for retail and item-level tracking, CD & DVD tagging, library books and airline baggage management. It also works well with metals and liquids.
Due to their ability to track assets and people in real-time, HF RFID systems are used worldwide. They keep tabs on products as they make their way through a supply chain, and can identify everything from casino chips to cattle to marathon runners.
Engineers at the Auto-ID Lab at MIT are turning RFID toward a new function: sensing. They’ve developed an HF RFID tag-sensor configuration that detects spikes in glucose levels and wirelessly transmits the information.
Another factor to consider in selecting a tag and system is data transfer speed. LF, HF and UHF all have different transmission speeds that will impact how fast the reader can receive and deliver data to users. The higher the frequency, the faster the tag can transmit, but this comes with some tradeoffs. For example, high-frequency waves can more easily be disrupted by obstacles and materials like metals and liquids.
