The SmartShelf is an RFID reader enabled shelf. The project goal was to research various strategies to understand and influence the customers’ decision behavior during the process of buying items in a retail store. The SmartShelf is a technology to reveal customers’ interactions with a product item in an unobtrusive way.
Features: The SmartShelf is able to determine the position of RFID tags as well as to determine specific actions, e.g. add a new tag, removing a tag, change the position of a tag on the shelf.

Technology

The SmartShelf comprises a RFID reader array of 144 single coils. An antenna consists of 4 coils. This configuration forms an acceptable homogenous reading field. This was found by conducting a series of experiments. The antennas are connected to 3 reader units serving 12 antennas each. The units were build by TecO using the 125KHz EM Marin compatible single chip reader from IB Technologies. All reader units work in parallel and report back to a master unit.

Each reader units functions as follows:
1. Switch antenna 1 on single chip reader, read try, switch antenna 1 off
2. Switch antenna 2 on single chip reader, read try, switch antenna 2 off
…
12. Switch antenna 12 on single chip reader, read try, switch antenna 12 off
13. Communicate with master
14. start with 1. again

In average a single read on an antenna is about 130ms. Since the readers work in parallel an acceptable response time for reading all 36 antennas can be achieved. However, the single chip reader does not support collision detection, i.e. if two neighbouring antennas are read by different reading units, a collision may occur and a RFID tag cannot be read out. Therefore all reading units need to synchronize their reading procedure. In this implemetation the reading units read every second line of antennas in parallel leaving one line space in between to avoid the read collisions. After finishing the line of antennas, they applied a barrier synchronization and continued afterwards with the next line.

When all antennas were read the results are reported back to the master unit which creates the overall matrix of seen RFID tags. This can be queried by an external PC system. Applications may aggregate this information to determine the position of a RFID tag on the shelf.

Applications

During the project different applications were developed. One example is the Plan-O-Gram compliance monitoring. In retail stores there exists usually a policy that items of various kinds are not allowed to be mixed. One line of items of the same kind must not contain an item of another type. The Plan-O-Gramm compliance application informs store staff if items get mixed accidentially through the interaction of customers with the items.Other applications are out-of-stock prevention and theft prevention.

Further Readings

The Smartshelf was presented as demonstrator on SAPPHIRE 2002, as demonstrator on Pervasive 2002 and as a full paper on IWSAWC 2003. Daniel Spanagel extended the SmartShelf in his master thesis under my guidance with Load-Cell technology. More details can be found on his page.