The passive tags antenna coil receives the signal from the reader

Working with RFID Tags • Chapter 3 57

Table 3.2 UHF Frequency Bands Allocated for the RFID Systems Around the Globe

■ Can the tag initiate the communication?

■ Does the tag have its own power source?

1. The passive tag’s antenna (or coil) receives the signal from the reader.

2. The antenna sends the signal to the IC.

58 Chapter 3 • Working with RFID Tags

■ Size and range Because there is no battery, passive tags tend to be smaller in size and have a shorter read range compared to active tags.

■ Depending on the frequency range at which a passive tag is operating, a passive tag may have a read range from 2 millimeters to about 5 meters.

■ The passive tags are simpler and cheaper and therefore more popular.

■ Operation Because a semipassive tag can transmit a response signal only if it gets adequate power from the reader, its operating principle is very similar to that of a passive tag.

■ Size and range Because a semipassive tag has its own battery, it is larger than the passive tag. For the same reason, it can produce a stronger signal, which can transmit across a longer distance, resulting in a larger read range compared to a passive tag.

Working with RFID Tags • Chapter 3 59

initiate communication. On the other end of the spectrum is the tag type that contains the battery and can initiate communication; this tag is called an active tag.

■ Size Because of their power sources (batteries), active tags are the largest in size. Typical sizes are (1.5 × 3) × 0.5 inch3. However, with the advancement of technology, the smallest active tags could be the size of a coin.

■ Read range Because an active tag has its own power source for circuitry and for generating signals, it can achieve the greatest read range. Some active tags have the ability to send a signal across a distance of 1 km. However, confi ned to standards and regulations, many active tags have read ranges of tens of meters. Due to its larger read range, an active tag can be integrated with a global positioning system (GPS) to pinpoint the exact location of an object.

■ Beacons A beacon is a tag that emits a signal at predetermined intervals. Beacons are mostly used in real-time locating systems (RTLS). Possible applications for beacons include the following:

■Tracking parts in large manufacturing facilities

Active tags usually operate in the UHF and microwave frequency ranges

(455 MHz, 2.45 GHz, and 5.8 GHz) and have read ranges from 20 to 100 meters.

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NOTE

NOTE

The EPC is a group of coding schemes for tags defi ned by the standard called Generation 2. These coding schemes are designed to meet the wide spectrum of needs of various industries while guaranteeing uniqueness of codes for all tags that comply with the standard. The EPC was originally the creation of the Massachusetts Institute of Technology (MIT) Auto-ID Center, a consortium of over 120 corporations and university research labs.