RFID Reader Deployment FAQs Volume 1

June 11, 2011

In this first post of frequently asked questions regarding deployment of passive UHF RFID in challenging scenarios, I will answer two questions:
Q1. What are the current countermeasures to combat reader to reader and reader to tags interferences for UHF RFID?

Q2: What would be your advice for best practices while installing UHF RFID system in the environment full of metal objects?

A1. As many of us experienced in actual deployments of RFID systems are aware, there is a difference between how one reader performs in an environment with all variables being controlled (movement of forklifts, location of tagged items, etc.) and the “real world environment” where none of these are controlled.

For UHF readers which are EPC GEN 2 compliant, there is a Dense Mode of operation which should allow for numerous readers in an environment. However, what has had to happen in the past is that the installer or integrator has to configure for worst case and give up a lot of potential performance. In a reader, configuring for worst case means selecting one of the over 256 available configurations (reader modulation, pulse width, tag to reader link frequency, Pulse Interval Encoding ratio, etc.) or, more typically, just going with the reader’s default (static) settings which are, again, usually configured for worst case.

The flip side is to optimize configurations for highest throughput based on the given conditions (usually controlled) in a pilot test (usually a single or a few readers) which works great, amazing throughput/tag read rate – the installer collects their check and moves on. Now, the environment changes – metallic shelves are installed or moved, forklifts are moving in and out of read zone, overhead lights are turned off and on throughout the day, more readers are installed…you get the picture.

Enter the Impinj Speedway Revolution reader with the Autoset feature – the ability to monitor the environment as well as connected antennas and tag reads to optimize configuration of all these variables in real time.
You can see an example here:
http://www.screencast.com/t/ZqzlPjIIQu

Q2: What would be your advice for best practices while installing UHF RFID system in the environment full of metal objects and very high humidity?

A2: I shiver at UHF RFID installs which are full of metal objects because it leads to a highly changing RF environment (those RF signals bouncing everywhere!); sometimes it works in the favor of reading desired tags and sometimes not. What usually happens is that an installer configures for worst case reading at a portal or chokepoint which usually means higher power and sensitivity which leads to stray reads due to reflective nature of metal in the environment.

The answer here is a combination of the AutoSet feature so that the reader can adjust reader and tag communication settings according to the environment but also zone control – defining a read zone and eliminating strays. UHF RFID has gotten really good at reading tags, often 99.x % performance, what happening now is reading too many tags! That is, reading tags outside the desired read zone.

Of course there are the usual ‘knobs’ on the reader to adjust (transmit power and receive sensitivity) but the often-overlooked additional factor is reader antennas with narrow beamwidth to create constrained read zones.
If only a limited range is required (i.e. < 50cm), you can use UHF near field tags and reader antennas like the Impinj Brickyard or Mini-Guardrail:
http://www.impinj.com/products/rfid-reader-antennas.aspx

For longer range, like in a dock door application, a typical circular-polarized patch antenna has a 6dB beamwidth of 90 degrees – this means that is a tag is located at a 45 degree angle on either side of it, it will be read at around half the maximum distance.
For example, if you have a highly sensitive tag (say, one using Impinj Monza 4 IC) and are using maximum allowed transmit power with highest reader sensitivity setting on the Impinj Speedway Revolution reader, and you find that the maximum read range directly in front of the antenna is 16 meters, then when tags are off at a 45 degree angle, the read range will be 8 meters, not a very constrained read zone!

So, you might want to consider something like the Impinj xPortal which uses Dual Linear Phased Array (DLPA) technology and has a horizontal read zone of only 60 degrees (3dB).
http://www.impinj.com/Speedway_xPortal_Reader.aspx
If you require an even tighter beamwidth antenna, there is the MT-263020 from MTI Wireless which has only 30 degrees beamwidth.

Lastly is the option to use some shielding material such as RF absorbing foam or cloaks and adjusting antenna angles – the problems with these two approaches to constraining a read zone are that, especially in an industrial or warehouse environment, the shielding may get damaged or destroyed and antennas get knocked or bumped out of alignment (or the retaining clamp simply comes loose); so, as much as possible, use hardware and configurations that are not too dependant, if at all, on these.

As always, any feedback from readers is encouraged.

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Determine RFID Tag Direction and Velocity using Phase Data

June 3, 2011

It is not a new concept to use the reported phase from a UHF GEN 2 RFID tag to calculate direction of travel as well as velocity. Phase data can also be used to filter out stray tag reads, assuming the stray reads are static/non-moving tags while desired tags are in motion (i.e. through a portal), using an approach known as TD-PDOA (Time Domain Phase Difference of Arrival).

Here are a couple of resources to help you with implementing this technique. The first is a white paper which gives an overview and some theory on this approach and why it is the best versus some other options:
Phase Based Spatial Identification of UHF RFID Tags

Next is an application note from Impinj which gives some practical specifics on using the Speedway Revolution reader to get the phase data from the tag and how to use it to calculate velocity (and thus direction of travel):
Use of Phase Data with Impinj Speedway Revolution

The latest version of firmware for the Speedway Revolution reader from Impinj will also allow you to read out doppler frequency directly. However, you actually need to slow down the read rate such that using that particular approach to measure tagged items moving at a walking or even forklift pace is not very practical.

Remember that phase resolution and time window are inversely related; you need a very long time window (packet length) to get down to the few Hertz of doppler resolution required at UHF frequencies and typical velocities. So, for most applications, utilizing phase data is the best approach.


UHF RFID Reader Designs: Achieving FCC Part 15 Certification

April 3, 2011

I was watching this video the other day on “How to Build an RFID Reader“; while it’s interesting to see how compact and prevalent UHF RFID reader modules have become, they missed one of the biggest challenges which is achieving certification from the regional authority to operate the reader in question.

This post will focus on deciding how to implement a UHF EPC GEN 2 RFID reader design (902 to 928 MHz) and, if necessary, the steps needed to get it certified for use in the United States by the Federal Communication Commission (FCC) under Code of Federal Regulations (CFR) 47 part 15.

Module or System-on-chip design?
If you plan on developing an RFID reader the first consideration should be whether to design your own from scratch by using an RFID reader-on-a-chip like the Impinj Indy series reader chips or if you should integrate a ready-made, pre-certified module like those from Thingmagic.

Cost considerations
A pre-built and certified RFID reader module costs on the order of $250 to $300 and requires an additional $50 or so in additional parts (i.e. power supply, connectivity module, heat sink, casing, etc.) to have a ready-for-market product. An RFID reader-on-chip typically costs somewhere around $40 and usually includes a Bill of Materials (BOM) which can be used to build a complete module. A good electronic contract manufacturer should be able to build a complete module using this BOM for around $100 each. In either case, there will be an additional cost for antennas.

The decision needs to be made based on a calculated profit point consisting of two key factors: volume and time-to-market. If your volume is going to be in the hundreds or even low thousands, it probably does not make sense to go through the long development, test and certification cycle of a reader-on-chip. Development time using a reader chip is on the order of at least 6 months and can be a year or more depending on how much modification you choose to do to the supplied firmware and BOM; a reader module will be significantly faster but the tradeoff is in terms of flexibility in form-factor design and implementation.

Some specific costs associated with taking a reader through design, test and certification are:
1. Test equipment – while an FCC-approved lab will be doing all the final test, you will need some to verify design and prototype board build as we as for pre-compliance testing. this will typically include at least a spectrum analyzer and Vector Network Analyzer (VNA).

2. Certification costs (for various regions): certification for FCC costs around $6000. If you plan to sell in other regions you will need to pay for certification for each of those regions; Canadian certification costs about the same as FCC, whereas to get certification for your device to operate in the European market (ETSI) you will need to allow for around $10,000. Reader modules are typically pre-certified and do not require additional testing but you would need to confirm this with the manufacturer.

Control and Flexibility
Going with a from-scratch design allows you more freedom in terms of form factor and implementation. Often reader chip manufacturers will supply the MAC source code to do a complete custom build of control firmware giving you the ultimate in design and implementation flexibility. That being said, it is wothwhile to confirm that a reference design with a Bill of Materials (BOM) is included in the purchase of the reader chip development kit.

Speaking of implementation, be sure to factor in software development; confirm with reader chip or module manufacturer that a Software Development Kit (SDK) is available in the programming language(s) and platform that you prefer developing in.

Steps for FCC Approval
Should you decide to move forward with a design implementation, here’s some details on getting FCC part 15 approval once you have functional prototypes made:
1. Lab selection – my advice is to select a full service test lab which will file all the paperwork for you in addition to the technical testing. Basically a one-stop-shop whereby you submit your reader and some paperwork and in return you have an FCC certification number and ready to go to market. Here is the link to search the dtabase of FCC accredited test labs:
https://fjallfoss.fcc.gov/oetcf/eas/reports/TestFirmSearch.cfm

2. Registration (Federal Registration Number)
After selecting a lab, you will need to register your device and get a Federal Registration Number (FRN), this can be completed on-line using this link: https://fjallfoss.fcc.gov/coresWeb/publicHome.do

3. Once you have the FRN, you will need to obtain a Grantee code using form 159
http://www.fcc.gov/Forms/Form159/159.pdf

Submitting Device for Testing
When submitting your device to the testing lab for certification, you will need to include:
a. Letter appointing the test lab – lab should be able to provide an example of this
b. FCC ID code of the unit (first three digits are grantee code, last 14 are up to you)
c. Sketch of FCC label location and dimensions
d. Block diagram showing all clock oscillators and their frequencies – reason being that one key test (and the most difficult to pass) is that for spurious emissions. This test is performed starting at the lowest frequency radiated by the device, notice I did not say transmitted but, rather, radiated – so this includes clock frequencies.
e. Full schematics
f. User’s manual
g. A brief, non-technical description of the device and method of operation
h. A sample of the device for testing and photos

Design Confidentiality
All the documentation submitted for FCC approval is a matter of public record. You can file with the FCC to request confidentiality under 47 CFR 0.459
http://fjallfoss.fcc.gov/oetcf/kdb/forms/FTSSearchResultPage.cfm?id=41731&switch=P

For additional information, you may wish to contact the FCC directly.
Federal Communications Commission
Office of Engineering and Technology
7435 Oakland Mills Road
Columbia, MD 21046
Phone: (301) 362-3000
E-mail: labhelp@fcc.gov


RFID “Electronic Pickpocketing”

February 26, 2011

Interesting story on “electronic pickpocketing” or “skimming” as it’s sometimes called:

http://www.kdvr.com/news/kdvr-coloradans-more-likely-to-be-victims-of-electronic-pickpocketing-20110224,0,4065996.story 

One solution would be if credit card designers used an approach that required the user to enable the tag like this “secure touch” technology demo video shows.

Here we see that unless touched in a certain spot, the card is unreadable. In this demo it is being read at quite a distance once activated but it’s technically an easy approach to limit the range when activated to avoid ‘snooping’.

Vodpod videos no longer available.


UHF RFID Readers Safest for Pacemakers

April 11, 2010

Research was conducted by the U.S. Food and Drug Administration’s (FDA) Center for Devices and Radiological Health on how RFID readers affect pacemakers and implantable cardioverter-defibrillators (ICDs).

The findings show that the readers in the LF band produced the most significant reaction; 67 percent of all pacemakers tested showed EMI interference from these devices at a maximum distance of 60 centimeters (24 inches) between the interrogator and the pacemaker. And 47 percent of all ICDs tested showed interference at a maximum distance of 40 centimeters (16 inches).

During HF exposure, an adverse reaction was observed for 6 percent of all pacemaker tests when the maximum distance was 22.5 centimeters (9 inches), and 1 percent of all ICD tests when the maximum distance was 7.5 centimeters (3 inches).

But the UHF readers produced no measurable reaction from either the pacemakers or the ICDs.

Read the full report by click on the link: RFID Readers Impact on Pacemakers and ICDs