Chapter 7: Seeing the Invisible: The Site Assessment
6. Using the radar graph option in the spreadsheet program, convert the
The result should look something like the graph on the right in Figure 7-5. The graph on the left is a perfect RF field in a vacuum. The informa- tion you are interested in is how these two figures are different.
Putting your results to use
The Full Faraday Cycle Analysis and the RF path loss contour map are also the perfect blueprint for setting up other aspects of an optimal RFID network architecture. With those two tests completed, you can move on to the next key steps in deploying your RFID network:
You can choose the best reader to fit your needs.
You can set up the optimal configuration of those readers.
You can verify and test the readers once they are set up.
The RF path loss contour map is an important tool for designing your reader interrogation zone. The ideal zone should be an equal bubble around the center pole (the left graph in Figure 7-5).
40 50
40 30 20 10 0 30
20 10 0
902 MHz 915 MHz 928 MHz Figure 7-5:
The perfect RF field graph and a typical RF test graph.
You now need to compensate for any areas within that bubble that do not have equally powerful signal strength. If an area where you decide to set up an antenna is particularly weak, that will be a difficult area for tags to receive enough energy to power back a signal.
A passive RFID tag requires about 100 microwatts of power (or –10 dBm) to generate enough power and backscatter a signal to the receiving antenna of a reader. If you want to avoid problems of reading across multiple interroga- tion zones (like from one dock door to another), you need to make sure your power levels are below the –10 dBm level. This can be done by adjusting the power or shaping the field with antenna choice and direction or with shield- ing between the dock doors. Chapter 9 explains the specifics of reader setup and testing.
For example, if you refer to the graph on the right in Figure 7-5, you see that the signal reaching the point that represents 225 degrees is much weaker (or closer to the center) than the other points in the chart. The signal is weaker because something is either absorbing or deflecting the signal away from this area.
It is up to the reader configuration to compensate for this loss. To counteract that loss, the antenna located on that side of the dock door needs additional power compared to the other dock doors.
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Chapter 7: Seeing the Invisible: The Site Assessment
Chapter 8
Testing One, Two, Three:
Developing Your Own Lab
In This Chapter
Gathering the equipment you need to build a lab Figuring out the best location and design for your lab Developing standard lab tests and evaluating the results
Imagine yourself in the woods of Switzerland back in the year 1307. You’ve got to shoot an apple off your son’s noggin’ or die. Do you just go out to your local sporting goods store, pick up a bow, and take a shot? Of course not, and neither would William Tell. He spent hours honing his skills and cre- ating and testing bow designs before he became the expert marksman who let that famous shot fly. How do you hone your skills and create perfect designs for RFID before you make a huge investment in your production system? By putting together a well-planned and -organized lab. That is your key to becoming the William Tell of the RFID world.
As I mention throughout this book, understanding physics holds the key to a successful RFID deployment. But physics can be a fickle thing: Because you can’t see how radio frequency waves change and behave, you have to find other means for knowing what happens with certain combinations of hard- ware, antennas, tags, and products. The best way to glean useful information is by having a consistent environment in which you can execute a repeatable process. A repeatable and consistent testing methodology allows you to change one variable at a time and compare results to understand the physics behind RFID.
Not only does a quality lab help you to choose equipment, design, and processes, but it is also a great place for your RFID team to discover new technologies and try new equipment in a low-risk, nonproduction environ- ment. You save money by testing equipment and identifying what will work best for your RFID network before making a large financial investment in that equipment, and you can separate marketing hype from reality. The lab can also pay for itself quickly if you have a lot of items to test for tag placement and tag type — also known as SKU testing.(SKUstands for stock-keeping unit.) And lastly, a lab is also a great tool for getting the CEO excited about RFID.
This chapter takes you through the five steps of setting up a world-class lab and gives you some examples of test procedures you can use to compare equipment before making a buying decision. I tell you what equipment you must have, what is nice to have, and what is icing on the cake. In addition, I describe some of the test procedures we’ve refined at the ODIN technologies labs and explain how you can apply your lab results and knowledge to the real world.
To Lab or Not to Lab
Stop — before you spend any more time reading this chapter, you need to understand the three options for testing products, evaluating equipment, and trying different RFID configurations:
Use a third-party lab. Third-party labs are great if you’re testing just a few products or want the latest information on readers, antennas, and tags. As I write this book, three principal labs do scientific testing for RFID and also test for hire:
• Met Labs (www.metlabs.com)
• The University of Kansas, anchoring the consortium called the RFID Alliance Lab (www.rfidalliancelab.org)
• ODIN technologies lab, which has been doing RFID the longest and produced the first head-to-head comparison of RFID readers and tags (www.odintechnologies.com)
Build your own in-house RFID lab. The benefit of having your own lab is that you can maintain control over the testing, especially if you are concerned with competitors seeing a preview of new products or pack- aging. You also build a great amount of internal knowledge around the technology. The drawback is the initial expense and the operating cost to keep a lab running, train people, and recruit good talent.
Use hybrid approach. In this case, a qualified consultant or existing lab sets up a lab for you. You use their testing software, services, and proto- cols to get the benefit of their intellectual capital but still maintain control and build knowledge.
Beyond a Swanky White Lab Coat: The Tools You Need for Successful Testing
Before setting up a lab, you need to think about what tools you need for a successful lab environment. If you’re setting up a lab on your own, you need some of this equipment in order to build the lab. If you’re using an outside firm to help you set up a lab, ask which of the following devices they plan on including. So get out your checkbook and let’s go shopping. First, here are the must-haves:
An assortment of RFID readers that have
• The ability to read Class 0, Class 1, and Generation 2.0 tags
• The ability to read multiple protocols
• Integrated printers
An assortment of linear and circular polarized antennas — both directional and omnidirectional (many will come with the readers, others can be ordered directly from Cushcraft or Sensormatic) A mixture of RFID tags
An application server and database server Several hubs — USB, RS-232, and RS-485 Several serial-to-Ethernet converters An assortment of zip-ties and plastic bands 1-inch thick colored tape
25 feet of 2.5-inch PVC pipe Ten 2.5-inch 90-degree PVC joints Four 2.5-inch PVC T-joints Four camera tripods
If you’re aren’t yet familiar with the different readers, antennas, and tags, flip to Chapter 5, where I explain these in more detail.
The following list shows the tools that are nice to have, but that are not entirely necessary. (I explain these in more detail in Chapter 7.)
Lab-grade spectrum analyzer that can operate up to at least 1.5 GHz Lab-grade signal generator that can operate up to at least 1.5 GHz RF power meter with power head for frequencies up to 1.5 GHz and up
to 5 watts of power
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