RFID tags got you covered!

Diverse options provide flexible platform for electronic security and identification applications

BY MICHAEL KAWA, Contributing Editor

After spending the day in Canada recently, I headed back to the United States through my local border crossing. At the entry gate, and before looking at my ID, the border patrol agent surprisingly greeted me by name. He then took my ID, gave it a quick glance and asked me some basic security questions before letting me go on my way.

While the crossing appeared mostly routine, it was not. This had been my first opportunity to use an enhanced driver’s license (EDL) as a cross-border travel document. My new state-issued EDL contains an embedded radio frequency identification (RFID) tag, which stores a unique reference number specifically assigned to me.

As I approached the border gate, the tag number was read remotely by an RFID reader and used to retrieve my corresponding records from a secured EDL database. Before I pulled up to the agent’s window, my personal information, photograph, and tag travel history were already being displayed on the agent’s security console for processing and review.

Fig. 1: U.S. Customs and Border Protection use RFID tTags in enhanced drivers lEnhanced Drivers Licenses and U.S. passports for security and iPassports for Security and Identification. (Photo courtesy of the Times Colonist .)

This early identification system is just one application of RFID technology. In this instance, its use is invisible to travelers but it provides the border agent with a quick and secure means of verifying their identity and citizenship. The fast processing promotes smooth traffic flow while the extra layer of discreet security increases protection from false or problematic entry.

RFID technology

RFID is a wireless technology used to communicate with electronic tags which are attached or embedded in an object or living thing for the purposes of identification or tracking. They are used in a wide variety of security and identification applications spanning several industries including military, transportation, manufacturing, and retail.

An EDL for travel documentation is one example of an item that can be tagged. Other items include badges for access control, car windshields for auto tolling, smart cards for contactless payment, store products to prevent shoplifting, and inventory goods for monitoring the supply chain.

An RFID system is made up of an RFID tag (or transponder) that stores data and an RFID reader (or interrogator) that polls and reads the data from the tag and sends it to a local display, storage device, or external system for processing.

The RFID tag consists of an integrated circuit (IC) that typically supports memory storage, communication, control logic, and encode/decode functions. It also contains an antenna to transmit and receive data. The devices can be passive, active, or battery-assisted passive (BAP).

Tag types

Passive RFID tags contain no on board power and must draw it from the antennas using the nearfield of the RFID reader. When the tag enters the RF field generated by a reader, the incident electromagnetic field generated by the antenna coil supplies power to the IC. It then modulates the RF field and transmits the stored information to the reader. The effective operating range of passive tags is limited, but with no battery and zero maintenance, they can be manufactured to very minute sizes and can have virtually unlimited life.

Fig. 2: Passive tag operation. (Diagram Courtesy of Priority 1 Design [www.priority1design.com.au].)

Active RFID tags have their own battery, which supplies power to the IC and antennae. They actively transmit and receive on their own and do not need to be in the near-field of the RFID reader to operate. This allows them to communicate at much greater distances.

Internalized power also allows active tags to integrate sensors and other components into the package to perform specialized functions such as monitoring or independent control. The added circuitry makes them physically larger than passive tags and more expensive to manufacture. They also stop operating when the battery dies. This limits tag life and adds maintenance costs if the battery is designed to be replaced.

In applications where the performance of passive tags is too limiting and the expense of active tags is too much, a growing alternative is BAP or semi-passive RFID tags. These devices use a smaller battery (relative to active tags) to supply power to the IC portion of the tag. Power from the near-field of the RFID reader is mainly used to energize the antenna to establish contact and modulate the signal.

The communication process is similar to that of passive tags, but BAP tags use most of the harvested energy from the nearfield rather than just a small portion for modulation. This creates a stronger and more reliable signal that can extend the tag range and increase readability.

Most current BAP tags use leading edge thin-film battery (TFB) technology to supply power to the IC. These batteries have a high energy density, a long cycle life, and can be recharged. They also have an extremely small form factor. TFBs are thin, lightweight, and can be adapted to any shape, making them ideal for the diverse nature of RFID tag applications.

On BAP devices, the TFB is active only when in range of the reader. This allows it to conserve power and prolong life. As their performance specs continue to increase, TFBs are also being used in active tag designs more and more.

Operating frequencies

RFID tags and their corresponding reader can be designed to operate at different frequencies depending on the application needs and operational environment. Design considerations include the type of tag used (active or passive), the number and rate of tags to be read, the distance and obstacles between tag and reader, whether the tags are stationary or moving, and local regulations limiting power levels or frequencies.

The most commonly used bands are low frequency (125 to 135 kHz), high frequency (13.56 MHz), ultra-high frequency (850 to 900 MHz) and microwave (2.45 GHz, 5.8 GHz.) Generally, the higher the band, the faster the transmission rate and longer the operating range. However, each band has its own benefits and drawbacks. For example, ultra-high-frequency tags have excellent range but their signal can reflect off metal surfaces. In applications with dense metallic structures, one solution could be to use a lower-frequency tag with an acceptably smaller range due to its better signal penetration through metal.

Fig. 3: The Tres active RFID tag from RFID, Inc. operates at 433.92 MHz and has a maximum read range of over 600 ft. It can be used to provide automated vehicle identification and perimeter security.

Sensor integration

A key area of development in RFID technology is integration with sensor technologies. RFID tags incorporating sensors not only can provide information on an objects identity and location but can provide data on the condition of the object and its immediate surroundings. These devices can be used to monitor parameters such as temperature, vibration, humidity, pressure, and light exposure.

Sensors can be added to a tag as a separate component or can be directly embedded in the IC design. When used with passive or BAP tags, sensors are active only when in range of the reader. When used with active tags, sensors can use the independent power and control of the tag for more extensive operations like data logging or active real-time monitoring. In both cases, the tags can be used as a single node or deployed en masse to form wireless sensor networks.

To facilitate the extra power requirements, energy harvesting can be used to supply power to the sensors or to the battery if it is rechargeable. The technology allows the tag to acquire energy from the surrounding environment using ambient sources such as solar, vibration and motion in addition to the RF field. This enables tags to become not only self-contained but self-sustaining. ■