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May 17, 2022

The “Secret” to Ensuring Accuracy and Repeatability in RFID Testing – Properties of an RFID Test Chamber

When our customers think of where measurement accuracy and repeatability in a tag testing setup originate from, they usually mention things like output power resolution, power setting accuracy, measurement distance measured down to a millimeter, angular alignment, and high quality matched antennas, test grade RF cables, etc…  My claim is, and it’s not even a bold claim, but more like a friendly reminder, that the most significant factor in achieving result repeatability and comparability is actually the environment.

So, what is the best route to a great environment? Well, clearly, the best solution is to use a closed and controlled environment like an anechoic cabinet specifically designed for RFID measurements. At Voyantic, the most iterated and refined cabinet is the C50. It is also the smallest of the offered cabinets, supporting the TIPP/ARC compatible four antenna measurement layout.

  

ARC / TIPP antenna arrangement and the C50 cabinet

Test Distance

The C50 name comes from the 50cm nominal measurement distance and the circular arrangement of the antennas. The choice of the distance is a sweet spot to be as close as possible for best accuracy and dynamic range, but far enough to be in an accurate enough representation of a  far-field for most average-sized tags, tagged items, and item stacks. Any further attempt to still reduce the distance rapidly ends up in the antennas not physically fitting anymore or just coupling into each other as they would sit in each other’s reactive near field.

The Cabinet Size

When you add on top the 50cm test distance the size reserved for the test object, clearance for the Fresnel zone, the volume required by the UHF range pyramid absorbers optimized for each wall, and the outer shielding, you still actually end up with a reasonably sized package. The C50 chamber totals to dimensions of 1,55m x 1,50m x 1,05m. This typically doesn’t sound important in any way, until one is planning the location for the cabinet and the transport route up to the very spot. These dimensions have not evolved by accident but rather designed from experience so that the cabinet would fit through as many door openings, narrow corridors, and elevators as possible. Also, the total weight remains in the 200kg range, making it movable by a few sturdy RFID test engineers without renting any additional equipment.  

A Sturdy RFID Engineer

Low Reflections

One of the hardest parameters to get right is the level of unechoicity. It wouldn’t be too hard in a totally empty space, but as the item under test requires a computer-controlled rotatable platform withstanding over 10kg of weight and still being totally stealthy, things get a lot trickier. The rotation mechanism and the support platform should not provide alternative radio paths from the antenna to the tag which could create a multipath situation and decrease the accuracy.

Turntable Design

To achieve the required stealth properties, anything bulky, parallel, and flat should be avoided. Also, electrically conductive materials must be avoided at all costs, except for the shortest of screws.  This means that conventional mechanical design is thrown right out of the window and other approaches are needed. Our chambers have fully ceramic bearing structures, Kevlar belts, fiberglass axles, Nylon bolts, and numerous foam structures. Most other structural parts are carefully designed from polyamide with most of the material hollowed out and any parallel and straight lines broken to reduce the RF footprint as much as possible.

Components in the chamber are designed to minimize any RF reflections.

To see the full range of available Voyantic anechoic chambers, download our R&D Solutions Catalogue ›

Download R&D Solutions Catalogue

Learn more about the Voyantic Tagformance® Pro system, accessories, and test chambers!

By combining RAIN RFID and NFC testing into one compact test device, our all-new Tagformance Pro is a true all-in-one tool for anyone either developing or using RFID technology.

Jun 30, 2020

Adaptive Front-Ends Are Here to Stay

中文版 Chinese version

Impedance Matching

Matching the transponder antenna well to the chip impedance has always been the cornerstone of a well-performing UHF tag. For antenna designers, it is lightly frustrating that each chip brand and model seemed to have their unique impedances, therefore various versions of the same antenna are needed for different chips models.

On the other hand, from the chip designers’ point of view, it must have been frustrating that the tag antenna is never comfortably operating in free space, but always attached to various materials needing different tuning to operate optimally again.

For a long time, it has been known that impedance tuning does not need to be a permanent compromise, but can be actively re-tuned. This has been the norm in many wireless communications and roughly ten years ago this was introduced to UHF RFID as well. The first company to open the game was RFMicron with their ”Chameleon technology” in the Magnus® family of chips.

The early chips had a 5-bit tuning register, giving 32 different and successive tuning states, wherefrom the chip chose the optimal. Since the register value could be read back, the biggest value proved not to be the improved tuning, but the information of how much was tuned. This was turned into a clever way of performing RFID sensoring and later chip versions had an improved resolution of a 9-bit tuning register.

Today, several mainstream RFID chip providers utilize self-adapting front-ends for the small performance gain it provides. Most notable companies utilizing this are Impinj and NXP. Here we are going to see how this alters the tag performance and how to gain visibility into this.

Visibility Into Tuning

First, let’s take a look into the Monza® R6B chip. Examining the memory map in the datasheet, it clearly tells that there are three bits in the reserved memory where you can read the current suggested tuning state. In addition, there is a single bit, by which adaptive tuning can be disabled.

Part of the Monza® R6B datasheet

So, to set the feature on or off in Tagformance® for testing, the simplest way is to perform any write test with the correct write parameters. Reserved memory, Word pointer 4, and write the last bit high/low to deactivate/activate the tuning. The current state can be verified by reading the same memory.

Write parameters for turning the adaptive tuning off. The memory map of the Monza® R6B reserved memory showing the change (in red) where the disable bit was activated. Read parameters to point to the three tuning bits to read back the current tuning state.

Below is a threshold of the tag both with the tuning activated and disabled. With the adaptive tuning activated, the area of optimal performance is seen to increase by +/- 10MHz for this particular inlay design. To monitor the used tuning state, do the sweep with the READ command and the correct read settings for the chip. This gives the ability to select “response data” from the drop-down menu to see what data the chip responded with to the READ. In this case, you can see the tuning goes from 4 to 0 in the ~20MHz stretch from 880MHz to 900MHz.

Sweeping a tag using a READ command while monitoring the tuning state.

How About the UCODE®?

The UCODE® 8 family from NXP works in quite a similar manner. The tuning state can be read back from the memory by pointing to the correct location as stated in the datasheet. The deactivation of the feature needs more involvement. It seems a non-zero access password needs to be set for the tag, and then the setting bit needs to be “toggled” in the secured state using the proper WRITE command as the BLOCKWRITE will not do it. As the UCODE® has fewer tuning steps, you can sometimes spot from the tuning curve the points where the impedance was changed. It’s as if the curve consists of a few cut-n-pasted curves. Well, because it kind of is.

A close-up of a threshold sweep of a UCODE® 8 based label revealing the discrete tuning steps.

Conclusion

Automatically adaptive tag ICs are here to stay. It might be that the advantage they provide is a little slim at the moment, but if there is a performance gain to be had, why not take it? For the antenna designer and tag producer, it is valuable to be able to also switch the tuning off when needed, to easier judge the antenna itself, perhaps against a simulation.

Alternatively monitoring the read response data “stepping diagram” is a simple tool to see if the design is functioning as it should. Eager to chat more about tag design with us? Feel free to contact our RFID experts HERE.

May 15, 2020

A Major Upgrade for Aerospace RFID Testing

中文版 Chinese version

日本語版 Japanese version

During this COVID-19 pandemic, as most airplanes are stuck on the ground and several large airplane orders have been canceled, aerospace is probably not considered the hottest market for RAIN RFID. However, eventually, this situation will pass, and more airplanes will be built. When that happens, the aerospace industry will be more ready than ever to use RAIN RFID, due to recent standardization work.

Back in 2015, I wrote about the aerospace industry as the pioneers of RFID:

“The aerospace industry realized that they need standardization for flyable tags as early as 2006. That is when a group of experts in the field decided to develop a standard under SAE International. SAE AS5678, “Passive RFID Tags Intended for Aircraft Use”, was born … In addition to environmental testing, the standard also describes RF performance tests for the tags. The standard described a very professional and well repeatable measurement methodology. But even more interestingly, the standard divided tag performance into performance grades, somewhat similarly to what the GS1 TIPP standard would do for the retail industry in 2015.”

Fast forward to 2020, in February, SAE published the third version of the standard, AS5678B Passive RFID Tags Intended for Airborne Equipment Use. So, what’s new in the standard revision?

The changes are mostly related to how the performance grades are defined. In earlier versions of the standard, tags were graded based on their read range, determined from their sensitivity. And that makes perfect sense: In 2006, the sensitivity of RFID chips wasn’t that great, and read range was nearly always limited by power delivery to the tag. Nowadays, that is not always the case. As the sensitivity of tags has improved, in more and more cases the return link from the tag to the reader may limit read range. This is reflected in the new standard revision; in AS5678B, the grades are determined by both minimum read sensitivity and minimum backscatter.

To give an example, for a tag to be classified for Grade X, the sensitivity of the tag on a metal plate has to be better than -12 dBm, and its backscatter strength needs to be at least -23 dBm. That corresponds to an expected read range of 6 m. But that’s not all. Because airplanes are expected to cross borders, and radio regulations are different in different parts of the world, this performance is required throughout the global RAIN RFID range of 865 to 930 MHz.

There is one more new element in the standard. It is no longer sufficient for one individual tag to pass a grade – a statistical element is introduced. A total of 30 tags needs to be tested, and their performance variation must be below a level defined in the standard.

Overall, I am quite happy with the new standard revision. With the new backscatter criteria, it is well in line with the development of the industry. The backscatter is required to be quite strong which means that most readers are able to read tags that meet the criteria – and that is probably a good approach. In addition, the statistical test brings a hint of a quality aspect to the standard.

As a final thought, there is one thing that I find curious about AS5678. No one is openly advertising to offer test services according to this standard. Customers often contact me to ask for a service provider. Some tag makers are obviously either testing their tags themselves or having them tested somewhere. Probably most of them use an external lab for the environmental testing and do the RFID part with their own Tagformance system).

But wouldn’t it make sense to have a one-stop-shop for AS5678B testing?

If you think that a lab that you know should start offering these tests, please let us know. If they already have the environmental part, we would be happy to help with the RFID part.

Learn How to Test UHF RFID Tags in the Aerospace Industry

Download The Essential Guide for UHF Tag Testing in Aerospace

Feb 21, 2020

Optimizing Counting Reliability With Well-Designed Reader Zoning

中文版 Chinese version

At RFID&WIoT Tomorrow 2019, Erik van Noort from Avery Dennison stopped by a Voyantic booth. He introduced a recently launched ShieldSense™ RFID blocking material. The material is for reader zoning and aimed to help system integrators in building better RAIN RFID systems.

After sharing some ideas, we decided to write an article explaining the reader zoning and how to use Voyantic Tagformance to check not only if the zoning works, but how well the zoning works. In this piece, we introduce the ShieldSense™ material with the Tagformance test results.

What Is Reader Zoning?

Reader zoning is a common challenge when building RAIN RFID systems. You want to scan tags in one area, but don’t want to read tags from another area nearby. For example, at a loading dock, it is essential to know that the item passes a specific gate and goes to the correct truck, and not to the next truck a few feet away.

Reader Zoning challenges

  • An apparel store has stock at the backroom
  • Every item in stock should be represented at the shop floor
  • With RAIN RFID it is possible to count and identify every item at the backroom and the shop floor, with a few minutes scan – quick enough to be done several times a day
  • The system can then generate an alert if an item type is not represented on the shop floor
  • Having each item represented on the shop floor is critical. If an item is forgotten, it would never be sold during the season and would have to be either heavily discounted afterward as the last season item, or even wasted

Reader Zoning – Test Without ShieldSense™

Conventional methods for reader zoning are

  • selecting reader antennas with different reading angles
  • planning reader placement
  • adjusting reader power levels
  • using the RSSI filter to prevent stray reads
  • applying RF shielding material aka RF blocking material

For testing the zoning challenge, I designed a simple test environment in our office. In one of our meeting rooms (“Front Room”), I had 100 tags placed on all sides of a cardboard box. In the next room (“Back Room”), behind a wall, there were another 100 tags placed on a similar box.

Photo: Test setup: 100 tags on the box in the Front Room, and another 100 tags in Back Rroom

My goal was to find reader settings that would allow the inventory of the 100 tags in the Front Room without reading any tags from the Back Room. In the test, I used an antenna placed on different locations and orientations in the Front Room. I used the Tagformance population analysis as a test tool. A combination of several test positions would correspond with someone doing an inventory count with a handheld RFID reader.

Results Without RF Blocking Material

There was no antenna placement and orientation in the Front Room with which all of the tags in the Front Room could be read. In typical good positions, 85% – 95% of the tags were scanned. One apparent challenge was that the light wall between the Front Room and the Back Room did not block the RF signal. With antenna orientations that gave the best read results in the Front Room, a good number of tags from the Back Room were also found. In some antenna positions, more tags were found from the Back Room than from the Front Room.

Figure 1: antenna position 1, tags scanned from the Front Room with different power levels

Figure 2: antenna position 1, tags scanned from the Back Room with different power levels

No antenna placement would give a decent amount of readings from the Front Room without giving any readings from the Back Room

Figure 3: antenna position 11, tags scanned from the Front Room with different power levels

Figure 4: antenna position 11, tags scanned from the Back Room with different power levels

Even if 100% reading was not achieved from any single antenna position, a 100% read rate from the Front Room was achieved when two antenna positions were combined. In practice, a 100% read rate would be easy to achieve by a simple handheld reader sweep. But, the combination of two positions gave over 90% rate also from the Back Room.

No power level cut would enable efficient zoning. At any power level with which tags are found from the Front Room, some tags are also found from the Back Room.

There is no difference at backscatter signal strengths from tags in the Front Room and tags in the Back Room. RSSI filter would not be efficient for reader zoning in this scenario.

After the first tests, it was apparent that the task is hard. There was no reading angle where power adjustment or RSSI filter could separate the items. In the test scenario, antenna placement, adjusting reader power, RSSI filter, or any combination of those would not solve the zoning issue.

Reader Zoning – Test With ShieldSense™

For the delight of fellow Voyanticians, I wallpapered part of the Front Room with Avery Dennison’s ShieldSense™ material. After shaking of the numerous “do they make foil hats of that” comments, I did the second part of the testing. I again placed antenna to different positions and tried to find an antenna position where zoning would work. In this test, I also used the Voyantic High-Power kit to boost radiated power beyond normal power levels, up to 39 dB ERP radiated power (antenna in the test had about 8dB gain).

Photo: Test setup without and with temporarily mounted ShieldSense™ (and not the prettiest wallpapering
with test equipment)

Results With RF Blocking Material

The positive effect of ShieldSense™ was apparent immediately. In most antenna positions tags from Back Room were not found

It was also noticed that in the original test scenario, some tags were leaning against the wall, and after applying ShieldSense™, those tags were leaning against the metal surface, making the tags non-readable.

Figure 5: antenna position 1, tags scanned from the Front Room with different power levels, ShieldSense™ in use. Some tags leaning against the wall

Figure 6: antenna position 1, tags scanned from the Front Room with different power levels, ShieldSense™ in use. any tag 10cm from the wall

Figure 7: antenna position 1, tags scanned from Back Room with different power levels, ShieldSense™ in use

There were still read angles that gave some readings from the Back Room when the power level was high enough. Most likely, the read is from reflections, the Front Room was only partially shielded, and in some antenna orientations, the signals have some reflecting paths even if the direct paths are blocked.

Figure 8: antenna position 6, tags scanned from Back Room with different power levels, ShieldSense™ in use

When the power levels and backscatter signal strengths are analyzed, efficient zoning parameters can be found. Using 30dB radiated power and applying -65dBm RSSI filter with a handheld reader

  • would give 5dB safety margin before read rate would drop to below 100%
  • would give 5dB safety margin before tags in the Back Room would wake up
  • about 8dB margin in RSSI until reader would accept the response from Back Room

These safety margins are likely well sufficient for ensuring reliable system performance also in the long run.

I am also convinced that expanding the ShieldSense™ coverage a bit around the corner instead covering just one wall, and applying it permanently instead of the temporary mount I used, the safety margins would increase by some dBs

With ShieldSense™ it is easy to find reader power levels and RSSI filter values with which zoning works, and safety margins are good for getting reliable reads as well as for avoiding stray readings.

About ShieldSense™

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Feb 02, 2018

Sensors, Healthcare IoT and Pigeon Races – Review of RAIN RFID Research in 2017

中文版 Chinese version

Following research activities of RFID is a nice way to keep up with the latest technology developments. Awareness of hot research topics also helps in anticipating the direction of commercial development and new product launches. Here is my take on the published RFID research in 2017. I have included short comments on the research topics, and a number of links to papers published in 2017 that have caught my attention – for one reason or another.

First, a disclaimer: the selection of the introduced research papers and overview is my own. Summaries of the articles are short and written from my personal perspective, the points I raise are not necessarily same as authors’ intentions. When the topic seems interesting, I recommend clicking the link and reading the whole article.

Sensor Tags

RFID sensors continue to be one of the main research areas. The topic is wide – there are a lot of parameters that can be sensed, and the ways to sense ambient conditions are vast. New materials provide new possibilities for sensing, and existing methods have been fine-tuned to solve specific problems.

Healthcare and Wellness

Healthcare and wellness related sensor tag applications is a wide research area on its own. Research is aiming to fulfill the potential of RAIN RFID technology in healthcare. Amount of research related to RFID in healthcare is significant. I expect already growing RAIN RFID use in healthcare to grow even faster in the coming years.

The healthcare RFID sensor applications seem to fall into one of three application categories: implantable, partially implantable and wearable RFID sensors.

Printed Antennas and Tags

Research of printable antennas is in my opinion shifting from basics towards studying mass production possibilities and reliability, although new methods and ink types are also being studied.

Specialty Tags

Embedded and other specialty tags are a continuous and versatile project area. The amazing versatility of the research topics tells about the potential of the RAIN RFID technology, and about the world we live in. Here are some examples:

Contact us and let me hear what you think of the above studies! I would also be happy to guide you how Voyantic test systems can be used in various RFID research projects.

Dec 15, 2017

Testing Against RFID Immunity Makes Medical Devices Future Proof

中文版 Chinese version

Healthcare spending raises steadily as the silver tsunami rolls over societies in East and West. Tightening cost, quality of care and efficiency requirements are some of the drivers that highlight healthcare as one of the strongly growing RFID application areas. RFID improves patient safety, raises operational efficiency and reduces shrinkage.

Healthcare organizations have expressed concerns about medical device immunity against RFID, and the RFID technology vendors and regulatory authorities have been quick to respond. A new immunity test standard has been developed in cooperation with RFID and healthcare stakeholders, and released by AIM. This standard has been recognized by FDA and the first test laboratories are already offering Immunity Testing as a service for Medical Device manufacturers.

Interference May Effect Medical Devices

Healthcare organizations are understandably very cautious about any new RF systems that could risk the functionality or reliability of various medical testing and treatment devices. Research projects were commissioned and some studies – for example van Lieshout et al. – found that RFID can induce incidents with medical equipment.

Solution – Standardized RFID Immunity Testing for Medical Devices

To remove possible RFID related risks and uncertainties, RFID industry took action. With the help of industry organization AIM, a new test standard was created: AIM 7351731. This standard describes methods for testing Medical Electric Equipment and System Electromagnetic Immunity against RFID readers.

U.S. Food and Drug Administration FDA soon recognized the standard. FDA has also started to endorse it for medical device manufacturers submitting new equipment to Premarket notification (PMN) process according to section 510(k) of the FDA rules.

Voyantic was quick to release a solution that conveniently extends EMC laboratories’ existing EMC hardware to support the new AIM standard. Voyantic approach is based on creating the required test commands on a PC software and loading them over Ethernet to vector signal generator (VSG) already in use at the EMC labs. This approach, called Voyantic RFID Immunity Interface, is a quick and cost-efficient way to implement RFID immunity testing, utilizing the facilities and equipment already available.

Do you have any thoughts or questions about the RFID immunity testing? Contact us – I would be happy to discuss this in more detail!

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!

Oct 07, 2016

Recommendation for RFID Reader Testing from RAIN RFID Alliance

中文版 Chinese version

The RAIN RFID Alliance recently published a recommendation for RFID reader sensitivity testing. But why is such a recommendation important for the RFID industry? I was deeply involved in its creation process, and can open up some of the reasoning behind it.

Reader Sensitivity Is Important

It is well known that the performance of a RAIN RFID system depends on

  • reader transmit power,
  • the path loss between the tag and the reader,
  • tag sensitivity,
  • tag backscatter power, and
  • reader sensitivity.

Now there is plenty of information available about tag performance, and tags are typically characterized in detail both in the design phase as well as in production. Measuring path loss (characterizing the environment) is relatively easy as well – simply measure a Voyantic Reference Tag with the Tagformance system in an unknown environment, and the result is the path loss between the reader and the tag (contact Voyantic for more information about the test process). But even though reader sensitivity is one of the main elements defining the overall performance of a RAIN RFID system, it has been given very little emphasis so far.

RAIN RFID Alliance Reader Sensitivity Test Recommendation

Almost all RFID reader datasheets report output power (TX power, radiated power, port power) somehow, but very few reader manufacturers report the receiver sensitivity of their reader. And without the sensitivity information, you can’t really be confident about the reliability of your RFID system. So RAIN RFID Alliance decided to take the initiative and publish a recommendation document “RAIN RFID Reader Sensitivity Testing” to get more companies to report their reader sensitivity.

Now reader sensitivity can be a complicated issue, but only if you let it.

It is well known that sensitivity varies (a little) as a function of the exact frequency, reader transmit power, and the choice of protocol parameters. However, the RAIN RFID Alliance workgroup that developed the recommendation, opted for simplicity and deemed sufficient to report a single sensitivity value. In order to make comparing reported sensitivity values easy, it was also required to report the used test parameters. As a result, RFID system integrators and end users can evaluate the usefulness of the sensitivity data by comparing the test parameters to those of their use case. And if needed, they can request further test data with other parameters.

Voyantic Readformance Reader Tester

Voyantic Readformance – Perfect Match with the RAIN RFID Alliance Recommendation

Voyantic has offered a solution for reader sensitivity testing, the Readformance, for several years. So with our experience in reader testing, it was natural for us to participate in developing the RAIN RFID Alliance test recommendation.

The approach taken in the recommendation was:

Easy and simple testing that anyone can perform without the most expensive test equipment.

This very same approach, combining simplicity and flexibility with fast and low cost testing, is exactly what we had in mind when designing the Readformance back in 2012.

In order to help the RFID industry, and to boost availability of reader sensitivity information, Voyantic is also offering reader sensitivity testing as a service, in addition to selling test equipment. Request a quotation for reader sensitivity testing!

Reader testing performed at the Voyantic lab

Learn How to Test RAIN RFID Reader Performance

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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