Radio frequency identification (RFID) technology dates back to the late 1940s and is responsible for many of the advancements that improve everyday life. From helping drivers pay their tolls quickly to giving pet owners the ability to locate a lost pet and helping shop owners track and control the inventory that leaves their shops and warehouses, RFID plays an important role in the world around us.
At Intermec Technology Inc., our RFID readers, printers, and tags bring intelligent data collection to the global supply chain for a wide variety of applications and environments. Therefore, it is crucial that the testing and verification of the RFID products we develop are as accurate and reliable as possible.
RFID applications have greatly evolved over the past 60 years. Recently, RFID technology has grown tremendously due to developments in integrated circuits and radios, as well as from increased interest from retail industries and government agencies.
Modern RFID systems include an RFID reader and an RFID tag, which is a simple device composed of an antenna and an integrated circuit chip. The reader signal alternates between a continuous wave (CW) and modulated transmissions. The tag sends data during one of the CW periods by switching its input impedance between two states, effectively modulating the backscattered signal.
Cost and Flexibility a Key Requirement
Accurate measurement of wideband tag range is crucial to quality tag design implementation and performance verification. To accurately measure and test our RFID products, we needed a cost-effective system for measuring and analyzing tag read range in wide frequency band. In addition, this system’s GUI needed to be flexible and easily upgradable to meet future demands.
Configuring LabVIEW and PXI for RFID Tag Testing
We created a viable solution using National Instruments products. The system we developed includes an NI PXI-1044 chassis with an NI PXI-8196 embedded controller, which runs a custom LabVIEW application.
First, we place a tag on a piece of material in an anechoic chamber at a fixed distance from a 6 dBi antenna. Then we connect the antenna to the PXI system through a circulator, which separates transmitted and received signals, and a 1 W RF power amplifier.
The LabVIEW application makes the NI PXI-5671 RF signal generator generate and send query commands with desired modulation and coding formats at specified frequencies in the 800 to 1000 MHz band to a UHF RFID tag that can operate under various protocols such as ISO 18000-6B, 18000-6C, and more. Then an NI PXI-5660 RF signal analyzer captures and processes the tag’s response.
During the test, we gradually increase the power of the query command transmitted at each frequency until the PXI-5660 detects the tag response. The detection is performed in the frequency domain by analyzing the spectral content of the signal backscattered from the tag. To increase the speed of testing without sacrificing the desired accuracy, we first perform the power increase in large steps and then repeat the last step with small steps. In our application, step values are 1 dB and 0.1 dB accordingly. The minimum power that makes a tag respond helps us calculate the maximum tag range and other tag parameters such as sensitivity. Using this method, we are also able to gather measurements for different materials and tag orientations.
PXI, LabVIEW Provide Precision, Cost-Effective Options
Our PXI RF hardware, controlled by LabVIEW, offers a cost-effective and flexible modular solution for custom RF systems. In addition, our custom LabVIEW application and its graphical user interface are extremely flexible, making it easy to further customize to meet specific RFID tag testing needs in the future.