Passive UHF Sensor Tags Will Help Drive RFID Growth

By Mikel Choperena

The radio frequency identification industry has moved from technology demonstration to mass implementation, allowing for new breakthrough solutions, such as battery-free sensors, to emerge.

Those of us who have been close to the radio frequency identification industry for some time have gotten used to hearing that RFID was booming year after year, only to see adoption fail to grow as initially expected. As is not uncommon for many other technologies, RFID has gone through hypes and has faced criticism. We have all attended many RFID-related conferences and events at which manufacturers' main focus has been to demonstrate technology feasibility to RFID strangers.

A walk around the RFID Journal LIVE! 2013 conference and exhibition provided a clear indication that those days are now over. End users no longer talked about the technical performance of readers or tags, but about how to best use the technology for their businesses. This, of course, has been a gradual change, like that of most successful breakthrough technologies.

The United States has contributed to the current status with high-volume RFID deployments, while Europe has opted for slower adoption in a wider variety of industries and solutions. This growth has resulted in a technology maturity that is slowly transforming into successful business.

Along with technology maturity, the RFID industry has begun providing new solutions to meet technological challenges. As clear examples, passive ultrahigh-frequency (UHF) tags that can be attached to metal are already very robust, and new solutions for liquid are also being announced. What's more, new real-time location system (RTLS) technologies are being developed with sharper accuracies, and smaller form-factor antennas are being deployed.

However, there is one idea that started a long time ago, the development of which had completely halted for some time: wireless passive sensors. We have witnessed very interesting solutions involving wireless sensor networks with active tags using such technologies as ZigBee or Bluetooth, and there are some pretty advanced solutions available with battery-assisted passive technology as well. Energy-harvesting systems are also being developed, though they still require some development time before they can be widely used. Passive low-frequency (LF) and high-frequency (HF) RFID sensors are actually being utilized in a number of applications, but these have a big disadvantage: Their communication range is just a few millimeters.

The idea of using UHF RFID for passive sensing has long been in discussion. Successful prototypes have been developed over the years—such as the WISP platform, with the great work undertaken to develop a full passive UHF RFID sensor tag (see Intel, University Researchers Develop Power-Storing Passive Tags)—but none of these ever went as far as market applications.

The current RFID technology status and the growth it is experiencing have revived interest in long-range passive sensors. While temperature-monitoring sensors have always been the typical models introduced—primarily due to the RF IC and the temperature sensor sharing the same complementary metal-oxide semiconductor (CMOS) manufacturing technology—there are new battery-free sensors available, such as pressure sensors, orientation sensors (using a three-axis accelerometer) or switches.

One company focused on battery-free sensor tag solutions is Farsens, where I work. Farsens has developed battery-free UHF RFID sensor tags that are compatible with commercial EPC Gen 2 RFID readers and can provide read ranges in excess of 1.5 meters (5 feet). Currently, my firm offers four types of sensor tags—temperature, pressure, orientation and switches—in a variety of antenna designs and sizes, to adapt performance to a particular application. They can also be encapsulated in an IP67 or IP68 casing for usage within harsh environments.

The main advantage of such sensors is that they operate without batteries, thereby allowing for a wide range of opportunities using different sensor types in applications for which accessibility is restricted, or in which the use of batteries is not recommended. Typical examples of applications per sensor type include:

Temperature sensor: switchgears and cold chain monitoring
Pressure sensor: gas piping systems and container liquid level
Three-axis accelerometer: "this way up" applications and movement detection

Farsens is currently developing tags containing humidity, ambient light or gas sensors, as well as analog sensors, such as strain gages or thermocouples. I expect passive sensor tags to be part of the RFID technology success story.

Mikel Choperena is the business development manager at Farsens, a manufacturer of ultra-low-power digital sensors and long-range passive UHF RFID sensors.