(Part 1 of a 2-part series)

As new Radio Frequency (RF) identification and location awareness technologies emerge, the differences among the growing list of options becomes increasingly difficult for potential users to understand. Deciphering which technologies are right for your organization, applications, and use-cases can be challenging. Often, those responsible for improving productivity, asset utilization, safety or other key operational metrics have heard that RF identification or location awareness technology can help, but they’re not sure where to start.

Here are some simple fundamentals of Radio Frequency Identification (RFID) and Real-Time Location Systems (RTLS) and how they can work together to help you start your journey toward using RF technology to improve your organization’s operational performance.

RFID Technology

RFID technology works by detecting electromagnetic fields transmitted by small electronic tags attached to objects. There are two main types of RFID – Passive RFID, which has no battery in the tag, and Active RFID, which has a battery in the tag.

The most common RFID applications use readers mounted in fixed locations to detect tags as they move within the detection or scan range of a reader. Mobile handheld readers/scanners can also be used to read RFID tags. Usually the intent, as the acronym implies, is to “identify” an object; what is it, what is the SKU number, what is the serial number, how many items are in the box, and so on.

Depending on the quantity and locations of the readers, some general location awareness information about the tagged object may be derived from the RFID scan. If there is some location awareness, the information is often not current (real time) and represents the last known location of the tagged object, that is, the general location of the object the last time a transmission was received from its tag.

Passive RFID

Passive RFID technology uses tags that are unpowered, with no battery in the tag. This makes the tags very cheap to manufacture and eliminates any concerns about battery life or battery charging. Passive tags can also be very thin or small, enabling them to be embedded with products, if the materials are RF transparent. Shown below, passive tags are available in multiple frequency ranges that roughly correspond to read ranges enabling a variety of applications.

 

Frequency Typical Read Range

(varies)

Example Application
Low Frequency (LF) 125 – 134 KHz 5 feet or less Car Immobilizer
High Frequency (HF) & Near-Field (NFC) 13.56 MHz 3 feet or less Access Control
Ultra High Frequency (UHF) 865 – 960 MHz 30 feet or less Asset Management

When a passive RFID tag moves into the proximity of an associated RFID reader, the tag circuit produces a response to the an electromagnetic field transmitted by the reader. The same reader, or potentially other nearby readers, then picks up the signal from the tag registering the serial number of the tag and associating the presence of the tag with that reader. Passive tags can only produce a signal and be detected when near an energizing reader. All other times, they are silent/dead and in an unknown location.

Active RFID

Active RFID technology uses tags powered by batteries. This internal power source enables the tags to transmit longer distances, and the readers do not have to transmit an electromagnetic field to energize the tags. There are two major types of active RFID tags.

Transponders – Active transponder tags only transmit after receiving a triggering signal from a reader. This enables the tag to be silent most of the time significantly extending battery life.

Beacons – Active beacon tags transmit on a regular interval. This is appropriate for applications requiring more continuous visibility of tagged object activity. Depending on the application, the tag transmit power level may need to be reduced to conserve battery life, resulting in a reduced read distance.

Some common active tag frequencies and example applications are shown below.

 

Frequency Typical Read Range

(varies)

Example Application
Very High Frequency (VHF) 433 MHz 1,500 feet or less Container Tracking
Ultra High Frequency (UHF) 915 MHz 3 feet or less Logistics
Super High Frequency (SHF) 2.45 GHz 300 feet or less Asset Location

Active RFID tags send out signals every few seconds or minutes depending on how frequently an update is required to satisfy the needs of the application. Once one or more readers hears a tag, the tag is identified as being near a reader or readers and enables the system to register the presence of the tag and associated object.

RTLS Technology

With both Passive and Active RFID technologies, the system is aware of the presence or absence of a tag with respect to a reader or set of readers that hear the tag or have heard it. Determining the location of a tag is limited to results such as:

  • Tag A1 is somewhere near Reader 17 at the back of Room 12.
  • Tag B2 passed between Reader 6 and Reader 7 at the door into Room 37, but is silent now.
  • Tag C8 has not been heard for 4 hours.

In contrast, RTLS, or Real-Time Location Systems, enable you to know continuously in real time the location of a tag, with the location accuracy ranging from centimeters to meters, depending on the specific RTLS technology used. Examples of some RF-based RTLS technologies are shown below. The main difference is in the frequency or band and other RF signal characteristics of the tags and readers used. Some RTLS systems, such as those developed by PLUS, can receive and process location data streams from a variety of RTLS sensor sources, not even necessarily RF-based.

RTLS Position Data Examples:

  • Bluetooth®
  • Zigbee®
  • Mesh (varies)
  • WiFi (regular timing)
  • WiFi – FTM (fine timing measurement)
  • Ultra-Wideband (UWB)
  • GPS
  • Cellular

Like Active RFID, RF-based RTLS solutions use battery powered tags attached to the objects that need to be monitored. Objects can be assets, vehicles, tools, work-in-process inventory, personnel, and so on. The physical format of RTLS tags varies depending on the use case (rugged inventory tags, personnel badge tags, externally powered vehicle tags, hard hat mounted personnel tags, etc.)

Like Active RFID, RF-based RTLS tags transmit a signal that is heard by multiple readers placed throughout a specific environment (manufacturing facility, sports stadium, office building, restaurant/bar, soldier training facility). Signals received by readers are combined, processed and analyzed in software using several different means, such as RSSI (received signal strength indication), TOF (time of flight) or TDOA (time difference of arrival). Complex location solving and filter algorithms enable the determination of the location of each tag continuously in real time. Each RTLS tag has a unique serial number and is associated with a single object in the system database.

As you can see, RFID and RTLS have many similarities, but are very different and each industry and use case benefit from each technology in a unique way. In our next post, “Integrating RFID and RTLS into a single application,” learn how PLUS is integrating RFID data into our Location Engine to create a new, integrated application for organizations who want to use RFID within an RTLS platform.

For more information about our RTLS platform, contact our team.