Lab 9 - RFID Basics


Background -

RFID tags have three main forms, active, passive and semi-passive.  We will be dealing with passive tags in this lab.  A system based on passive tags works by having a reader send radio signals out, which are received by any tags within range.  The tags are constructed such that the antenna captures some of the reader's signal and uses that power to backscatter information from an embedded chip, which the reader then receives.  The backscattered information could be an ID number stored in the tag.  There are a number of different frequency ranges RFID tags can operate over giving varying ranges of operation and different propagation properties.  Our setup uses the longest range variety and operates in the ISM band at approximately 900 MHz. 

We will use two antennas in this lab, a simple dipole antenna and a directional circularly polarized antenna. 

Procedure -

Make sure the RFID reader card is inserted and the dipole antenna is attached to antenna port A and the directional antenna is attached to port B.  Start the MPR Demo software.  Set the inventory duration to 1 second in the drop-down menu along the top of the window.  Select antenna A at the maximum power of 27 dBm.  Position a class 1 RFID tag around the antenna and take inventories with the tag at various distances and orientations relative to the reader antenna.  At what range can you still read tags?  What orientation gives the best or worst range?  What angle relative to the plane of the antenna gives the best or worst range? 

Repeat the above procedure for the directional antenna (antenna B).  Try class 0 tags for both antennas.  Do you notice any difference? 

Put something non-metalic underneath the antenna to prop it up off the table.  How does this change range?  If you put obstacles inbetween the reader and the tags, how does the range change?  Can you read the tags at all? 

Can you discover any "dead areas" due to fading? 

Analysis -

What differences do you see in your results between the two antennas? Make plots of distance for given angles and orientations for each antenna to  show the difference. 

If barcodes can be used to hold the same amount of information as an RFID tag, why would a manufacturer change their inventory tracking system from barcode-based to RFID-based?  What kind of applications can you think of for the RFID system used in this lab, given the range and angle of operation?  Which antenna should be used?

References -

RFID kit user manual.