What is HF RFID?

High-frequency (HF) RFID is considered one of the older forms of RFID technology and utilizes induction or near field coupling as the means for reading/writing data to transponders or tags. Data transponders or tags are placed onto objects that can be edited (read/write) through automated RFID readers or handheld scanners.

The designation of HF refers to the radio frequency at which the readers function, 13.56 MHz.

When to use HF RFID?

Automated HF RFID solutions work well in short read ranges (less than 2 feet). Once the system is in place, special attention to how the tags are presented to the readers is needed.

Benefits from HF RFID

Since data can be edited directly through RFID readers, it is easy to keep track of changing information, such as the completion of production tasks, with the object.

With the short read range, there is far less interference with the surrounding area, making installation much faster than the UHF RFID readers to achieve the desired results.

Challenges of HF RFID

One challenge with HF RFID is that it uses close-range inductive coupling between transponders and readers, making it hard to have multiple tags working together. If the requirement involves deploying multiple tags concurrently, alternative technologies should be explored. Moreover, the HF RFID technology’s susceptibility to interference from metal or other grounding sources presents another obstacle. Metal nearby or between the units can obstruct the inductive coupling process, rendering it ineffective.

The inductive coupling field created by the HF RFID reader includes a primary field which normally is meant to be used for the RFID application. However, the HF RFID reader also produces secondary fields, also referred to as side lobes. These secondary fields must be considered during application planning to ensure that the fields are not picking up adjacent tags or interfering with any moving tag applications.

Additionally, while HF RFID allows for reading and writing lots of data, it is not very fast due to its lower transmission rate in comparison to other RFID technologies operating in higher frequency bands. This can pose challenges when dealing with large amounts of data and necessitates careful consideration of both the data volume and the available transfer time. This is particularly an issue with applications where the tag is moving during the reading/writing process. Generally, application planners must balance the need for reading/writing data with the need of production throughput.

What is UHF RFID?

Ultra-high frequency (UHF) RFID technology utilizes radio propagation or backscatter as the means for reading/writing data to transponders or tags. Worldwide harmonization efforts have been made to make UHF RFID globally compatible for the efficiency benefits of intercompany supply chains. Because different countries have differing radio spectrum allocations, UHF RFID tags are often, but not always, designed to function in multiple radio bands. In FCC regulated jurisdictions, UHF RFID operates in the radio spectrum between 902 MHz and 928 MHz. While this band range provides UHF RFID systems with larger read ranges and higher data transfer rates than the LF or HF RFID, for instance, it transfers less data overall.

The UHF RFID readers can be programmed to filter out unwanted tags and tuned to reduce the number of missing and duplicate errors within the system.

When to use UHF RFID?

Automated UHF RFID solutions work well for variable positioning and long-range reading applications. With the ability to read multiple tags at a time, it can be a tool for lIot tracking and other Industry 4.0 applications.

It is important to note that large metal objects and liquid containers inside the read field can create issues with reflected fields and holes. Completing site surveys can help to identify and mitigate these issues early on.

Benefits from UHF RFID

While UHF RFID systems do require additional programming compared to HF RFIDs, they offer a lot more flexibility in how the tags are presented to the readers.

Challenges of UHF RFID

Unlike the simple close proximity reading environment of HF RFID, the reading environment or “interrogation zone” of UHF RFID requires very careful planning. Interrogation zone design is heavily influenced by the application and the physical environment in which the interrogation zone is to be located.

Depending on the application, an interrogation zone may require multiple antennas or even multiple readers. Applications with multiple antennas may require the use of cable splitters and/or multiplexers. Application designers will need to consider the power transmission levels, cable losses, insertion losses of connectors and splitters, antenna gains, and regulatory limitations. This process is often referred to “Link Budgeting”. Proper, and legal, interrogation zone design is best accomplished by experienced and qualified application designers.

Before interrogation zone design is performed, proper transponder/tag selection must be made. Tag selection is nontrivial. Poorly selected tags can cause an UHF RFID application to fail to achieve investment objectives. Some tag selection considerations include the required size of the tag, method of attachment to the tracked item, orientation of the tag with respect to the orientation of the radiating field of the antennas, and environmental considerations such as exposure to heat, harsh chemicals, etc. Other tag selection considerations include electronic product code (EPC) and user memory needs, read/write sensitivities and speeds, and the capability of being killed or locked.

Perhaps, the main challenges of UHF RFID are the many unexpected and normally unseen effects to the radio wave propagation from reader to tag and back from tag to reader. UHF RFID radio waves can be reflected by metal obstacles and absorbed by liquid obstacles. Multipath propagation is when broadcasted signals from the reader (and the tag by consequence) arrive at the receiver part of the reader (or the tag) from different directions. When these signals arrive in phase with each other they create a condition referred to as constructive interference. When this constructive interference occurs outside of the planned interrogation zone, this can cause the reading of unexpected tags. When these signals arrive out of phase with each other they can create a condition referred to as destructive interference. When this destructive interference occurs inside of the planned interrogation zone, this can cause dead zones to emerge where expected tags are not able to be read or written. One way to visualize destructive interference is to consider the interrogation zone as a block of Swiss cheese where the dead zones are the holes in the cheese.

There are many more challenges and considerations to evaluate in planning a successful UHF RFID application. The use of experienced and qualified UHF RFID application designers will be necessary except for the rarest and simplest applications.

What is RTLS?

Real-time locating system (RTLS) focuses on tracking the location of an item. Tags are attached directly to the object, and a network of locating devices are placed around the work area to triangulate the position of the object.

The locating device network can be customized with as many devices as needed in order to establish the necessary accuracy across the work area.

When to use RTLS?

From finding tooling and important equipment to automated guided vehicles (AGVs) and production racks, RTLS helps you find what you are looking for, geographically speaking.

Items will only be tracked within work areas that are covered by the network of devices. Once an item leaves the network area, it will no longer be tracked.

Benefits from RTLS

The location accuracy of an RTLS system can range from several yards to a few inches depending on the application.

Basic information can be manually connected to the tags through additional programming to meaningfully track the items through the work area.

Challenges of RTLS

A key challenge for RTLS is the cost of the infrastructure which are the various gateways which perform the locating functions of the transponders. Generally, the finer the locating resolution required the higher the number of gateway devices that are needed. Each gateway will require power and networking back to a central controller/server. Oftentimes gateways need to be installed in a location where there is not an existing suitable mounting option. In these cases, application designers must include the addition of poles or bridges to mount the needed gateways. For some applications, these new poles or bridges could be unacceptable physical interferences to existing operations. Careful consideration must be made by the application designers to ensure that the locating resolution is not too fine nor too coarse making the balance between RTLS application capability versus overall RTLS cost of ownership.

Another challenge for RTLS is selecting the right technology for the physical area of the application. For instance, in FCC regulated jurisdictions the use of ultra-wide band (UWB) is generally limited to indoor applications since the FCC prohibits UWB transmitting devices from being permanently mounted outdoors.

Another common downside is that the RTLS transponder is generally an active device meaning that it requires a power source. This requires plant operators to regularly review battery levels and replace discharged batteries to maintain operations. Further due to limited onboard memory and data transmission norms, RTLS transponders are often used only as asset identifiers and not as data carriers. However, newer RTLS technologies are allowing for applications that require more on-device data storing.