by Marina Buzzi, Marco Conti and Daniele Vannozzi
Radio-frequency identification (RFID) and sensor technologies are now enabling the Internet of Things. Ultra High Frequence (UHF) RFID readers and passive tags can be valuable tools for emerging pervasive services since they allow tags to be read at distances ranging from one-half to few meters, depending on antenna power, size and polarization. However, UHF has limits due to RF reflection, shadowing and absorption. Our experimental study investigates the feasibility of UHF RFID for reliable and efficient retrieval of archived documents.
Radio-frequency identification (RFID) uses radio waves to permit the automatic identification of objects, people and animals. It consists of two components, readers and tags; the tags store information that can be retrieved by readers. Tags may be passive, active (battery-powered) or semi-active. Passive tags are especially convenient since they are small, cheap and potentially can last infinitely.
The DocSearch project is underway in Pisa, Italy, at the Istituto di Informatica e Telematica of the Italian National Research Council. It aims to develop a tool for improving the efficiency of the ccTLD ".it" Registry which assigns and manages domain names under the country code Top Level Domain "it". Specifically, the goal of the project is to aid Registry staff to answer customer questions regarding paper documents submitted as part of a registration request. The operator needs an efficient method to retrieve the original document(s) referred to by the customer from among thousands of documents. The DocSearch project is thus developing a tool that exploits RFID technology. Each document is archived with an RFID tag and the document data and tag id are stored in a database. Using RFID technology the operator can easily find the correct document even if the document was stored in the wrong place.
When applying RFID technology, the reliability of the reading is crucial. Raw RFID data are large-volume streams characterized by duplicate, missed and ghost reads. Therefore, data filtering and aggregation are necessary in order to extract reliable data.
UHF tag reading can be challenging depending on object composition, packaging, and tag size and placement. It is facilitated by motion. Three issues affect UHF reading: reflection, shadowing and absorption:
- metal reflects RF (however an appropriate insulation between tag and object can improve reading)
- shadowing is present when several tags are placed very close to one another and their antennas mask each other, and this decreases the read rate
- liquids (such as water) absorb RF and hinder tag reading.
The DocSearch project began in 2008 with a feasibility study aimed at measuring the reliability of UHF tag reading applied to document search. In the feasibility study we tested both multiple reads and single search. Multiple simultaneous reads (usually called inventory mode/command) make it possible to discover multiple tags in the antenna field at the same time, by using an anti-collision search algorithm. In order to verify the amplitude of the shadowing problem, we tested the worst case when each document consists of a single paper sheet and all sheets are piled in a folder. We carried out experiments in several configurations with different spatial positioning of tags. The best result was achieved by applying a thin dielectric substrate, which separates the tag from the page (increasing distance between tags). In this configuration the mean read percentage was 85% (see Table 1).
|% success||Tag identified||Reads||Time in sec|
Looking for a specific tag is less critical. The success percentage is almost 100% when searching a 50-document folder (see Table 2).
|% success||Tag identified||Num tests||Time in sec|
Since single document retrieval is the main operation in our scenario, the feasibility study indicates that UHF RFID is a suitable technology for efficient document localization; thus we have developed a procedure for the storage and retrieval of documents using RFID technology. Currently a preliminary prototype (developed in C# language) is available for testing on a WorkAbout Pro 2 palm (Psion Teklogix) integrating an RFID reader (CAEN/Intel technology), with Win Mobile 6 OS. Documents were tagged with ALN 9540 "Squiggle" (Alien Technology). The development environment is .NET, Visual Studio 2005 and SQL server 2005.
IT NIC: http://www.nic.it/
Marina Buzzi, Marco Conti, Daniele Vannozzi, IIT-CNR, Italy