Co-authors: Toni Heijari, Turo Rantanen & Mikko Lähteenmäki

The tag and the reader

The picture below shows a basic model about how a tag and a reader communicate with each other. In case of passive UHF RFID, the basic idea is that the tag receives all the energy it needs from the radio frequency wave that the reader is sending. Therefore, a passive tag does not need a power source of its own.

To understand how the demo and tag writing actually work, you need to understand how the tag itself works.

EPC Global Class-1 Gen-2 UHF RFID tags consist of 4 memory areas, which are called banks. These banks are numbered from 0 to 3. The banks and their purpose are described below.

Bank 3 is the user memory, which usually is empty before the tag is written. Apparently, all the tag types have the 3rd bank, but the bank does not necessarily have a memory. Bank 3 can be used for various purposes. A retailer can use it to add product information such as the type of the product, for instance the type of the product (trousers), color (black) and size (36). When a customer is asking for black trousers in size 36, the retailer can use a tag locating application with a mobile RFID reader and thus search all the available options from all collections and brands in the store with the requested parameters. When  the information has been written to the tag itself, the RFID readers can operate without connecting to the business information system. Therefore, the search can be carried out rapidly. EPC can be created in a way that it already includes information about the product, meaning that in some products the retailer can see the collection, type of garment, color and size of an item from the EPC. With this kind of an EPC it is possible to search based on some parts of code (for example 02 for trousers, 01 for black, and 03 for size 36) and search only for tags including those parts in the EPC. Here the reader asks the tags filling the condition to respond for calling. By doing this only the tags that have that part of the EPC code are replying. In this way the search can be done more rapidly compared to not using filtering at first place. It is also possible that the tag can send two different kinds of information. These so-called near-field memory tags tell their EPC as answer when read from a long distance, but in a short distance change the memory area and tell some other information about the tag. There is also a tag which contains areas for public and private information. Here the user can set the area used.

The content of the tag itself varies between different users. Depending on the operation that a company runs and depending on the need to recognize tags, the content of the tag varies. Retailers who distribute products from several suppliers tend to look for the supplier to create the tag similarly to how they operate with barcode these days. On the other hand especially vertical retailers looking to replace barcodes with RFID tags may initially insert the numeral series of the barcode which will form a part of the EPC in the tag.

Technical blog post about more practical tips to tag writing!