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Different forms of RFID technology have been in development for decades. Basic forms, such as identification, friend or foe (IFF), were in development and used during World War 2. RFID work continued through the years, with much of the basis for today's technology being developed during the 1970s and 1980s. However, cost inhibitors and a general lack of standardization made widespread implementation of RFID technology a significant challenge. As technology has advanced, the ability to fabricate small, cheap, disposable “tags” has created a huge boom for this market, making the realization of widespread use an obtainable goal for a variety of applications. Regardless of the end application, a number of test requirements exist for the RFID system. Understanding what these requirements are and how to address them can be key to the successful use of RFID.

Despite its early conception, RFID technology has only recently come into widespread use. Current applications are constantly growing, and include inventory control, animal tracking, building access, and toll road payment — just to name a few.

The applications listed below demonstrate some of the most prevalent uses of the technology today.

1. Product tracking/inventory control

   Passive RFID tags can be used within individual products and on pallets to track the movement of goods in a range of sizes (e.g., a truck, pallet or individual item). Unlike traditional barcodes, RFID tags work within a proximity. In other words, the reader does not actually need to “see” the tag. This fact greatly decreases the amount of time it takes to do store and warehouse inventory. Readers often read the response for several tags responding at once, which also reduces the time it takes to do inventory. Because it is simply a proximity reading, the human error of physically counting or scanning each product is also eliminated.

2. ID badges and access control

   Similar to product tracking, proximity readers can grant access to users with an RFID badge that is allowed. Each badge can be set to have a standard or unique data response, depending on the level of security needed in different situations. These badges are used in much the same way as a magnetic strip, reader or barcode, but they are more durable because they require only proximity instead of physical contact with the readers.

3. Transportation payments

   RFID readers for toll plazas are typically active readers, using battery power only when they receive a “wake up” signal from a reader. Because active tags are used, the close proximity of inventory tracking or ID badges is not needed, and tag reading at distances of up to a couple hundred feet can be achieved. This allows the information to be collected without requiring the user to slow down from typical highway speeds. These same readers are being used in trials as a way to measure drive times. Here, readers are set up at multiple points along the roadways and data is collected as a means of monitoring the drive time throughout a trip.

   Related to the technology found in ID badges, many areas are going to systems with optional RFID payment options. This allows users to bypass the long lines that often develop during times of heavy use.

4. Animal identification

   Many small pet owners have begun implanting their pets with passive RFID tags. The tags have a unique identification number that can be recalled if a pet is brought into a veterinarian or humane society with a reader. Once the ID number has been obtained, a database search can be conducted to locate the corresponding personal information (e.g., name, home address and telephone number) of the owner, who can then be contacted.

5. More applications

   The technology for RFID continues to grow with more uses being developed all the time. Below are a few of the more interesting uses that are being explored or are already in use:

   • tracking airline luggage;
   • automatic passport ID;
   • human implantation; and
   • tickets to concerts/sporting events.

The primary components of an RFID system are the antenna, transponder/tag and transceiver/reader. When a passive transponder receives a signal from a reader, the tag is activated by a small portion of the RF signal. It then reacts according to the absorption parameters of its transmitter to reflect back the found data to the reader via backscattering (Figure 1).

RFID applications challenge engineering measurements in many ways; particularly in the analysis of transient signals, bandwidth-critical modulations and backscattered data. Swept-tuned spectrum analyzers with a fast auto-tune function and built-in vector signal analysis, oscilloscopes, power meters and logic analyzers are used for wireless development tests in R&D and manufacturing environments.

Government bodies around the world regulate the test requirements of RFID signals in the power, bandwidth and frequency domains. These regulations tend to protect users and other devices from harmful interference, ensuring that transmitters do not crosstalk or compete with neighbor channels of additional users across the band. RFID systems operate with simple modulation and coding/decoding algorithms that can be spectrally insufficient. Therefore, a large RF bandwidth for a given transition rate is needed where the data being transmitted must be configured in a serial information stream — further complicating the coding and decoding processes.

Tag design challenges the efficiency of the data transfer. This is due mainly to poor precision timing sources on board the tag, stringent bandwidth requirements and the need for high RF power transmission to activate the tag under anti-collision protocols to allow reading of all tags in the required field of view.

Regulatory testing, standards conformance and optimization protocols must be guaranteed at all times. Additionally, RFID technologies challenge manufacturers and users with several uncommon engineering measurement needs such as transient signals, bandwidth-inefficient modulations and backscattered data.

Performance considerations include speed of tag reading, ability of a tag to operate in a dense reader environment, and distance between the tag and reader. In consumer applications, the speed of the tag-reader communication directly translates into customer acceptance. As an example, consider that RFID-enabled bus passes did not gain wide acceptance until the read time dropped from five seconds to less than 0.5 seconds.

Despite the testing challenges, RFID testing requirements during R&D and manufacturing can be addressed with a combination of an auto-tuned spectrum analyzer, appropriate software, a spectrogram, and tutorials for RFID applications (Figure 2). See Figure 3 for a list of additional equipment needed to optimize the data traffic between the reader (interrogator) and tag in other areas outside the frequency and time domains.

The auto-tuned spectrum analyzer with embedded software and spectrogram can be used to easily analyze the power characteristics of complex RFID transmissions. Such an analyzer can recognize the modulation of a transient RFID signal and obtain the requested measurements of power, frequency and bandwidth via a single-button operation, including rapid frequency-related changes.

These analyzers' different configurations provide the best solution for measurements of spectrally inefficient RFID modulations and their unique decoding needs. Their demodulation and decoding capabilities also solve the measurement needs of transient signals by triggering specific spectral events in a timely manner.

With a color spectrogram in 3-D, the user can monitor in real time and as a trend, the evolution of a transient signal. Also, the automatic setting of threshold and markers on a trace allows the numerical analysis of rapidly changing signals. Finally, a multitrace screen configuration in average, max hold and min hold with markers and detectors allows the identification of frequency segments in which the signal went through the most significant transient changes.

The standard parameters that must be tested during R&D and manufacturing processes are numerous. The three most important ones are as follows:

1. Interrogator (reader)/tag analysis. When integrating an RFID communications system, many signals — digital, baseband, IF and RF — are present. The close proximity of the components is an invitation to crosstalk and can lead to unwanted signals in the signal output.

2. Standard compliance (e.g., EPCglobal class 1-Gen 2 and other ISO 18000 standards) and manual setting of demodulation format, line coding and bit rate control via digital demodulation. This demodulation is possible using vector signal analysis.

3. Burst and CW (interrogator power) time domain analysis.

Figure 4 defines the different parts of an RFID signal. Any RFID interrogator signal can be recorded in the time domain and displayed in a log magnitude format. This is an easy way to see the power envelope of the signal. Multiple markers can be used to measure power or voltage at an instant in time. The time axis can be configured as relative to the beginning of the acquisition record or at the trigger point. As an example, Agilent's 89600 vector signal analyzer software allows users to identify each burst by using number arrow indicators that show whether the signal is from the interrogator or the tag. Users can easily switch between each burst to examine the individual characteristics such as rise and fall times, as well as an overall burst summary table. This information can be seen in Figure 5.

Other typical measurements for RFID systems are:

• test wireless transducer with antenna;

• backscatter power and data testing;

• periodic query to any tag in the area;

• activate-upon-detection testing;

• activate-upon-request testing;

• read range, memory variable query; and

• data stored for collection or passed to the data processor to/from tag.

RFID technology is a rapidly growing segment of the industry. While it is being eyed for use in many applications, testing RFID systems during research and installation phases remains a challenge. Use of the latest generation of auto-tuned spectrum analyzer products and the demodulation capabilities available with vector signal analysis offer a viable means of addressing these challenges and are aiding in the widespread adoption of RFID technology.

Franco Canestri works in Agilent Technologies sales and services GmbH & Co. KG, BÖblingen. He holds a degree in physics from the University of Genova,Italy, with a Ph.D in biophysics from the National Cancer Institute of Milan, Italy. He works as business development specialist for Agilent's spectrum analyzer products out of the Agilent BÖblingen site in Germany.

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