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Printing Technologies Make Their Mark in Radio Frequency Identification

(June 2006) posted on Tue Jun 27, 2006

Learn about the function and construction of RFID tags and how screen printing and other imaging methods are used to produce these devices.


By Wim Zoomer

click an image below to view slideshow

Currently RFID tags are seeing increased use for logistic and supply- chain management by postal and courier services, the food industry, the medical care and the pharmaceutical industries, and libraries, as well as in access management and toll collection, airline baggage handling, cattle identification, document tracking, and product authentication or anti-counterfeiting. To protect clothing against counterfeiting and theft, some companies are even working on means to print RFID antennas directly on textiles.

Types of RFID tags

RFID tags come in two forms: passive and active. Passive RFID tags require activation by means of the reader system before transmitting the data they carry. Active RFID tags are provided with a battery, which enables them to transmit signals independently. For this article, we will focus only on passive RFID systems, which are the most common type.

The antennas of passive RFID tags can generate an inductive or a capacitive signal. An inductive antenna is able to convert a magnetic field into an electrical signal, or the other way around. These antennas look like a wound coil. The counterpart is the capacitive antenna. This antenna is not susceptible to electromagnetic energy, but only electrical signals. A capacitive antenna is recognizable by its dipole shape (Figure 1).

The frequency of the electromagnetic radiation determines the read distance that the tag will support. The minimum read distance required to collect the data is a major influence on the design of RFID antennas for specific applications.

RFID tags can be based on a number of frequency bands, such as low frequency (LF), high frequency (HF), ultra-high frequency (UHF), and microwave (Table 1).

 

Table 1 Frequency of RFID Tags
Band
Frequency
Read/write distance
LF
125 kHz
less than 20 in.
HF
13.56 MHz
approximately 3 ft
UHF
862-950 MHz
16 ft or more
Microwave
2.45 GHz and 5.8 GHz
approximately 3 ft

The read and write distance of RFID tags ranges from 4 in. (10 cm) to more than 16 ft. (5 m).

LF antennas support a frequency of 125 kHz. They consist of coiled copper wire that is wound 200 times or more. LF tags are used for relatively short read distances—not exceeding 20 in. (50 cm). Common applications for LF tags include access control (i.e., door-entry/security cards) and identification of cattle and other livestock.


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