wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

Radio Frequency Identification 8-9
FIGURE 8.8
Active RFID reader to be inserted in a PDA for the tourism industry.
saved by directing the tag to sleep for an extended period, wake up momentarily, listen to the broadcast,
and go back to sleep unless it is summoned. Once woken up, a reader-tag linkage is established via
energy stored in the battery. A fast response is observed because there is no need to accumulate energy
from the incoming wave. Using pager technology, a tag with one CR2025 battery could run for months
without battery replacement, such as the RFID system for a tourist group (Figure 8.8) and the RFID tag
for mountain hikers with GPS and GPRS capabilities (Figure 8.9), both of which are prototype systems
developed at the City University of Hong Kong.
Sometimes, waking up periodically remains unnecessary because there is no reader in the vicinity.
This scenario is often found in a vehicle-based RFID tag, such as the toll-payment label on the windshield
glass. Addressing this scenario, an application-specific integrated circuit (ASIC) has been tailormade
to wake up under the illumination of a strong electromagnetic field. Surprisingly, most ASICs
available in the market use a low frequency 125.kHz signal in the wake-up process, and the sensitivity
ranges from 100.μV rms to 1.mV rms . Other than the wake-up mechanism, the instruction set is similar to
that of a pager-tag; therefore, an equally fast response is observed.
FIGURE 8.9
RFID locator for mountain hikers with GPS and GPRS capabilities.
© 2011 by Taylor and Francis Group, LLC