Page 340 - Mechatronics for Safety, Security and Dependability in a New Era

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sends commands to tag which then responds to the reader by backscattering its identification data. The
identification data is modulated into the backscattered electromagnetic wave using load impedance
modulation (Finkenzeller, 2003). The components of an RFID system are presented in Figure 1.

At present, one of the biggest challenges is tagging objects that are totally made of or contain
conductive materials in their structure. Conductive materials next to antennas operating at UHF
spectrum affect the performance of the antennas for example by lowering the radiation efficiency and
changing the resonance frequency. Conductive materials also reflect the electromagnetic wave
radiated by the antenna and therefore they affect the radiation pattern and radiation directions of the
antenna (Raumonen et al., 2003). In addition, the conductive materials attenuate the incident
electromagnetic wave and therefore the electromagnetic wave does not propagate well or at all
through the conductive material (Reitz, Milford & Christy, 1993).
Cigarette cartons, which contain ten individual cigarette packs, have been a difficult object to identify
using RFID technology because the individual packs are wrapped with aluminium foil. This foil
contains thin layer of paper coated with 0.25 /.im thick layer of pure aluminium that is highly
conductive. The aluminium layer is coated with very thin polyester layer. The structure of a cigarette
carton and an individual cigarette pack are presented in Figure 2.
Data
RFID Reader Clock Transponder
RFIDReader
f (i.e. Tag)
Reader Antenna Energy
F ten erAnte
Tag’s Antenna
Application
Application
(PC,Host
(PC, Host
Object
Computer) Object
Computer)
1: The components
Figure 1: The components of an RFID system
of an RFID system
Figure
Aluminium foil
Two layers of cigarette packs
_ _ _
—

Figure 2: A cigarette carton and a cigarette pack

Conventional label-fabricated RFID tags do not work with enough reliability when attached to a
cigarette carton. Therefore, a novel tag design using microstrip patch antenna integrated on a cigarette
carton was designed. The cigarette carton with individual packs was used as a substrate material of the
microstrip patch antenna and the dimensions of the antenna structure were designed to fit on the
carton and at the same time to achieve the 915 MHz resonance frequency. 915 MHz is the UHF center
frequency used in RFID in North and South America.