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Nov 30, 2016

Vehicle RFID Tags – Big Benefits with Some Challenges

中文版 Chinese version

Electronic Vehicle Identification (EVI) is a perfect match for RAIN RFID (UHF RFID) technology. Once a vehicle is tagged, the possibility to identify the vehicle remotely enables a lot of applications and services. While vehicle tagging is of high interest, it is not the easiest task. In the past few months I have worked with some vehicle tagging projects and learned that the application requires some special attention from technology providers.

EVI Tag Types

The EVI tags come in different forms. Most common EVI tag types are

  • windshield tags attached to the windshield inside the car; and
  • license plate tags mounted on license plates outside the vehicle.

There are some specific design issues related to both of these tag types.

License plate tags must be on-metal tags, and very durable. They must survive weather conditions and car washing. Also, the position and the mounting angle are rarely ideal for readers. The natural best reading direction is straight backward (or forward), and at low height. In many applications the goal is to identify a vehicle approaching an identification point, for example an access gate or a road toll collection point. Reading would preferably be done from above or from side with an angle.

Windshield tags provide better reading angle. The challenge is to design a tag that works well with all possible windshields, regardless of the windshield’s angle, thickness, material, embedded technologies and type and proximity of the windshield frame to the tag position.

Both passive and semi-passive tags are commonly used. The semi-passive tags are battery powered; more of those can be read in earlier Voyantic Blog post.

EVI Tag Applications

Once the tagging is successful, it is easy to find use for the tags. Applications include road toll collection, tracking vehicle registrations and inspections, tracking tax payments, and parking control. Many of the applications are initially set for government purposes. Once the tags are in place, they can also be used in various value added applications of the private sector. Even if the tag is initially placed for registration, it can be used as a parking permit and gate access permit of a housing community.

Performance Testing of EVI Tags

A car is a special case of a tagged item. There are components that reflect RFID signals, absorb or block the signals, and may even resonate with RFID frequencies. These effects are different to different reading angles, they vary when a tag is attached to different position in a vehicle, and may even change when a tag’s mounting orientation changes. At Voyantic we have assisted several companies in defining test methods and processes for optimizing the EVI tag performance.

With the Voyantic Tagformance Pro system it is possible to test the sensitivity, tuning and backscatter signal strength of the car tag. The Tagformance system is an essential tool for evaluating effects of reading angles and mounting positions. The system can also be used for optimizing the EVI tag performance, finding optimal tag positions in the cars, and for finding optimal reader antenna positions for the applications.

Learn How to Test EVI Tags with Tagformance Pro

Download our application note to learn how to avoid the pitfalls of EVI tag testing!

Oct 31, 2016

RAIN RFID Tag Read Range: Opinion or Fact?

中文版 Chinese version

Creating a tagging solution for passive RAIN RFID tags to a particular application starts with understanding the application specific requirements. That involves plenty of process engineering, but also typically discussions around the expected read range between tagged items and reader antennas. The read range is impacted by several factors and many start the cooking process by looking at the properties of RAIN RFID tags.

Tag datasheets carry plenty of information: protocol, operating frequency, chip type, memory utilization, physical size and much more. Amongst all information on datasheet, I reckon tag dimensions and read range are typically the first ones checked. Both are relatively easy values to understand, although the first one is a fact, and the second more an opinion. In the following I explain how to interpret the tag read range right.

Classic Approach: Take a Tag and Walk Away

The simplest way to get an idea of the read range is to place a reader to the end of a hall, take a tag and walk away from the reader antenna to see how far the tag can still be successfully read. In this kind of empirical test the result is not a fixed distance under which the reading would always be successful, but instead the result typically varies as below:

Result of a “walk away” read range measurement using a lower end RFID reader. What would you choose for a read range value?

Obviously such a result leaves a problem: how to interpret the results? What in fact is the read range in this case? A bigger problem is that the result is actually a synthesis of so many factors, such as reader properties, tag alignment, other objects in the environment, illumination in the hall, settings in the reader… So, what was it again you wanted to see?

Very few halls, office spaces or basements are stable enough to reproduce the test from day to another with the same test result. Therefore, key delivered value of this approach is merely the physical exercise, and most vendors don’t use these results in their tag datasheets.

Laboratory vs. Real Life Performance

RFID measurement systems characterize tags at high precision after which read range is calculated based on a few assumptions. Laboratory measurements themselves are often performed in shielded and anechoic chambers to remove other variables from the test results, which greatly improves the value of the data and the repeatability of the test process.

Theoretical read range of two RAIN RFID tags designed for different applications. Tag 2 shows better max read range at the FCC band, but is too highly tuned to efficiently cover the whole band. Despite of its shorter read range, Tag 1 as a broadband design seems like a more reliable choice.

This kind of measurement does not emulate effects of environment where tags are used. Experts talk of multipath propagation and path loss, and some others may talk of reflections, shadowing and interior design. No matter which definition is used, the environment is the grand source of differences between laboratory and real life performance.

Practical Difference of ERP and EIRP

Theoretical read range values plotted by the Tagformance system are based on the Tag Performance Parameters and Test Methods Version 1.1.2, 2008, EPCGlobal Inc. For the read range standard specifies 35dBm EIRP transmit power to be used in the calculation. 35dBm EIRP transmit power equals 33dBm ERP power. 33dBm ERP equals 2W and 35dBm EIRP equals 3.28W. If maximum power 4W EIRP is allowed, as in the FCC band, theoretical read range results can be obtained by adding 11% on the figures shown in the Tagformance software.

Forward Limited Read Range Is Not a Safe Assumption Anymore

As tag dimensions shrink and tag ICs become more sensitive, readers often become the limiting factor of read range. A reader with more sensitive receiver is able to pick up a tag’s reply from greater distance. When read range is analyzed it is typical to separate read range to forward (up) and reverse (down) links.

Picture below shows forward and reverse read range curves, which are calculated using 1W ERP transmit power, 2dBi antenna gain and -65dBm receiver sensitivity.

Separated forward, reverse and resulting read range curves. For ETSI range forward and reverse curves are equal, but for FCC range read range is reverse link limited – a reader with more sensitive receiver would improve read range on FCC band.

Tag Close Coupling Issues to Be Addressed by TIPP

As tagging spreads to new product categories in the retail industry, small tagged items are often brought into close proximity to each other. Just think about items boxed for transport. Especially when the distance between tags is less than 3 cm, the tags start to couple with each other.

The close coupling effects will be considered in the upcoming GS1 TIPP global standard. Stay put for Juho Partanen’s upcoming blog post regarding these issues!

From Opinions Back to the Facts

As you saw from the above, the read range is a factor of many issues. As you work yourself through the tag and reader datasheets with the aid of expert tools and good standards, you can connect the dots with relative ease. This process transforms opinions into facts.

I’d appreciate your comments and suggestions around these topics. New perspectives are always welcome.

Learn How to Test the Read Range with Tagformance

Download our application note “Read Range Test with Voyantic Tagformance” to learn how easy it is to test the read range!

Jul 29, 2016

Battery Assisted Passive (BAP) Tags – Do You Know Your Reader Receiver Sensitivity?

中文版 Chinese version

One of my customers in Taiwan is developing battery-assisted passive (BAP) tags. He called me recently and asked why the read range that they reach with their RFID reader is only a quarter (1/4) of the distance that they measure with their Tagformance RFID measurement system. I answered him with another question: “Do you know your reader receiver sensitivity…?”

What Is a BAP Tag?

A BAP tag has an on-board battery to power its IC, but like a passive tag, it does not have an active transmitter. BAP tags are generally used to reach longer read ranges than what passive tags can provide, or for logging some physical quantity when a reader is not present. As known, the typical limiting factor for the read range of a passive tag is the forward link. In other words, the read range of a normal passive tag is determined by how far the passive tag can be powered or activated, i.e., the tag sensitivity is the limiting factor. Therefore, by default designing the passive tag to receive power from an on-board battery as a BAP tag, read range could be increased.

However, since the on-board battery is only used to power-on the RFID IC or to increase the BAP tag sensitivity, the battery does not really increase the tag backscatter power. As a result, the return link will become the limiting factor for the read range of a BAP tag. In order to fully realize the maximum read range of a BAP tag, the reader receiver sensitivity becomes crucial.

BAP – Battery Assisted Passive – Tag

The Performance of a BAP Tag

When evaluating the performance of an RFID tag, the starting point is usually measuring the sensitivity of the tag as a function of frequency. The graph below shows the Tagformance Pro’s Threshold Sweep measurement results of one BAP tag. As can be seen, the theoretical read range for this BAP tag is close to 37 meters at 930 MHz. That is a lot; the read range of a good passive tag is around 10 meters.

Sensitivity of a BAP RFID Tag Measured with Tagformance Pro

But the forward link read range above is only the theoretical upper limit of the read range that can be reached. Below we use the Tagformance Pro’s Read Range measurement functionality to test the BAP tag with different reader parameter settings. The radiated power is set at 2W ERP. The yellow curve below shows that the read range is about 19 meters at 930 MHz if the reader receiver (RX) sensitivity is -85 dBm.

Read Range of a BAP Tag Measured with Tagformance Pro; 2W ERP & -85 dBm Sensitivity

By changing the reader sensitivity in the Tagformance software, we can see what reader sensitivity would be needed to reach the theoretical read range maximum. This situation is shown in the yellow curve below. The reader sensitivity required to reach the 37-meter read range is -97 dBm.

Read Range of a BAP Tag Measured with Tagformance Pro; 2W ERP & -97 dBm Sensitivity

From my experiences, it may not be easy nowadays to find a reader with the RX sensitivity of -97 dBm. Therefore, in order to reach the read range of 37 meters, I have suggested my customer redesign the BAP tag’s antenna to make the tag having stronger backscatter power and use a higher sensitivity reader if possible.

Reader receiver sensitivity is getting more attention in the RFID market after the increase of tag sensitivity both in BAP tags and normal passive tags. This means that the limiting factor for the read range is the return link. Receiver sensitivity is the key to optimizing the read range. Interestingly, most system integrators and even UHF reader suppliers do not know how to measure the receiver sensitivity. Voyantic’s Readformance reader tester is designed to tackle this challenge.

How to Measure Reader Receiver Sensitivity?

Do you want to learn how to measure the receiver sensitivity of RFID readers? Download the Voyantic Readformance datasheet

Dec 11, 2015

This Doesn’t Look Right – Should I Contact Technical Support?

What do you do if, one morning, a new light with some strange symbol is suddenly lit on your car’s dashboard? You probably pull over and start browsing the car owner manual. You may be a little worried. Did I do something wrong? Can I fix this myself, or does the car need to be serviced? How long will I need to survive without my car?
In the same way, your Tagformance, the RFID test system that you typically use every day may have a problem you need to solve. You may already be an experienced user, or maybe you have just recently started to work with the system. When a new error message pops up or you get unexpected measurement results, it’s just like with your car. What’s wrong? Should I contact Voyantic Technical Support?

The answer to the last question is yes. You should.

*‘No such thing as a stupid question’ is a common phrase with a long history, and it makes perfect sense to me. *

If you have a problem with anything, and there is a possibility to get it solved quickly by asking someone who can help you, why shouldn’t you? The one who asks the “stupid question” may be doing a service to everyone, including the vendor, by pointing out a visible improvement to the product.

Here are some more or less typical situations where you might wonder if you should contact the vendor or just carry on. Uncertainty: You are performing measurements that look nice and smooth, but deep down, you are still wondering whether the results are correct? Is there some bias in the device? Am I measuring the right way? By contacting Voyantic Technical Support, we can verify if the device is OK by comparing the reference tag measurement results with the same measurement setup. We can also measure your sample tags and give a second opinion of the results and maybe give pointers on what else you can measure from your tags.

Differences between sites: You may have a colleague in the next room or on the other side of the globe doing the same measurements that you are. The equipment may be the same, the setup may be identical, but still, your results don’t match completely. For example, you get a theoretical read range value of 11 meters, and your colleague measures 10 meters. One meter sounds like a lot, but is it after all? By looking at the measurement data, we can verify whether the difference is something to worry about, or if it fits into production variation and typical measurement accuracy. Other factors, such as temperature, may cause a difference. The effect of temperature is described in more detail in an Application Note, which can be downloaded here. While visiting the site, you may find other Application Notes worth reading too.

Missing features: Different Tagformance measurement options are enabled with the license file. We can create license files where any measurement option can be enabled for a given time. So, if you think that one or more options could be useful for your work, we can enable the option for a trial period. To name a few;

  • Scripter is a great tool to automate your daily measurement routines and reduce the human error from the results.
  • The Tagformance has two Application Programming Interfaces, APIs, that enable you to write your software that uses the Tagformance device. The LabVIEW API is a perfect match for LabVIEW users, and the DLL API serves users of other programming languages.
  • Memory management is a brand new tool for one of the hot topics, sensor tags, for example. With Memory management, it is possible to verify changes of any memory address content within seconds.

Memory Management

All this said, do not hesitate to contact us! In most cases, it is a win-win situation where you will get your problem solved or a question answered, and we get valuable feedback, which will help us in making our products even better. We are here to help you – send us a message!

Aug 14, 2015

Tagged-Item Grading Helps Retail UHF RFID Projects

Retail and the retail supply chain are among the most significant users of UHF RFID technology. However, retail RFID projects are not the most simple ones. Items in retail come in all shapes, sizes, and materials. They are shipped in different boxes and stored and displayed on all kinds of racks, shelves, and tables. Also, different readers are used in various applications: logistics tracking, inventory count, RFID EAS, POS, and so on. I was involved in several retail RFID projects, and I have seen how complicated the performance optimization can be.

GS1 Tagged-Item Performance Protocol (TIPP) was developed to help retail RFID by making buying and selling tags easier. But what do the TIPP guidelines mean, and what kind of testing is required?

Goal: Accuracy in Inventory Counting

The purchase of RFID tags for retail items used to be complicated. The goal is simple: to have good counting accuracy (read rate) and a long and controlled read range. But I have seen how simple read range and counting accuracy requirements turn into a complicated mess of lengthy and costly field testing and piloting. Tags and readers are often selected separately, and system-level optimization is left to a trial-and-error process, if not entirely forgotten.

One approach used to be describing various use cases in detail and relying on the suppliers and technology providers to deliver tags that would work in all of the applications. The supplier was accountable for performance but had in practice minimal possibilities to achieve the goal.

Another strategy was to test extensively and to list accepted tags for different product categories. That way, the supplier was no longer accountable but was forced to buy specified tags without a possibility for price competition.

Finally, when using TIPP, the supplier is accountable for performance, and also has all the tools needed for delivering and verifying it.

Tagged- Item Grading Makes Retail RFID Projects Easier

The Tagged Item Performance Protocol makes buying and selling tags easier. The idea is familiar with many goods, from engine oils to clothes. It is a lot easier for a buyer to purchase shoes of size 41 than to provide a list of different measures of the foot. And it is a lot easier for the supplier to produce, stock, and sell shoes with a few different sizes than to verify that the unique requirements of each customer are met.

Similarly: it is easier to buy and sell tagged items performing according to a grade S05B than to list and verify all relevant performance requirements individually. As a result, a retailer’s list of requirements could be, for example:

  • items to be tagged with UHF RFID tags with C1G2 protocol
  • tagged items following GS1 Format & Symbol Placement for the Electronic Product Code guideline with C1G2 protocol
  • performance according to GS1 TIPP S05B grade
  • coded with SGTIN-96.

Now there is no longer a need to describe in detail which RFID tags to use and how to place them. Also, the suppliers and tag providers don’t need to guess what the use case description means from an RF performance point of view. TIPP translates complex system-level requirements into simplified component level pass/fail verification that any vendor can handle themselves.

The Voyantic Tagged-Item Grading System is 100% aligned with the GS1 Tagged-Item Performance Protocol (TIPP). The system automates TIPP grade validation and testing and provides results quickly and easily. It also enables TIPP grade audits to be performed by anyone. The Voyantic Tagged-Item Grading System is available as a complete turn-key setup.

Want to learn more? Read more about the GS1 TIPP guideline and the Voyantic Tagged-Item Grading System! Don’t forget to download our handy tool for evaluating read ranges with different RFID readers and tags with various TIPP grades below!

Download a Tool for Evaluating Read Ranges

Download a handy tool for evaluating read ranges with different RFID readers and tags with various TIPP grades. In the tool you can select a TIPP grade, input reader parameters, and see what kind of read range is expected from the system.