RFID Systems

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Date
2009
Authors
Safaa herz-Allah
Alaa Fatayer
Suzan Rabayaa
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Abstract
          Radio Frequency Identification (RFID) systems use radio frequency to identify, locate and track people, assets and animals. Passive RFID systems are composed of three components a reader (interrogator), passive tag and host computer. The tag is composed of an antenna coil and a silicon chip that includes basic modulation circuitry and non-volatile memory. The tag is energized by a time-varying electromagnetic radio frequency (RF) wave that is transmitted by the reader. This RF signal is called a carrier signal. When the RF field passes through an antenna coil, there is an AC voltage generated across the coil. This voltage is rectified to result in a DC voltage for the device operation. The device becomes functional when the DC voltage reaches a certain level. The information stored in the device is transmitted back to the reader. This is often called backscattering.        By detecting the backscattering signal, the information stored in the device can be fully identified. There are two classes of RFID device depending on type of memory cell: (a) read only device and (b) read and write device. The memory cell can be made of EEPROM or FRAM. EEPROM is based on CMOS silicon and FRAM is based on ferroelectric memory. Since CMOS process technology has been matured, the EEPROM can be produced relatively at lower cost than the FRAM device. However, FRAM based RFID device consumes less power which is desirable for low power device. Therefore, it is known as a good candidate for the future RFID device, if its manufacturing cost becomes compatible to that of the CMOS technology. Because of its simplicity for use, the passive RFID system has been used for many years in various RF remote sensing applications. Specifically in access control and animal tracking applications.       In recent years, there have been dramatic increases in application demands. In most cases, each application uses a unique packaging form factor, communication protocol, frequency, etc. Because the passive tag is remotely powered by readers RF signal, it deals with very small power (~ w). Thus, the read range (communication distance between reader and tag) is typically limited within a proximity distance. The read range varies with design parameters such as frequency, RF power level; readers receiving sensitivity, size of antenna, data rate, communication protocol, current consumptions of the silicon device, etc. Low frequency bands (125 kHz-400 kHz) were traditionally used in RFID applications. This was because of the availability of silicon devices. Typical carrier frequency readers transmitting frequency) in todays applications range from 125 kHz-2.4 GHz.       In recent years, the applications with high frequency (4-20 MHz) and microwave (2.45 GHz) bands have risen with the advent of new silicon devices. Each frequency band has advantages and disadvantages. The 4-20 MHz frequency bands offer the advantages of low (125 kHz) frequency and microwave (2.4 GHz) bands. Therefore, this frequency band becomes the most dominant frequency band in passive RFID applications.       Our device uses an antenna coil to power the RFID tag embedded in our Cornell ID's and read the induced response pic 16f877 microcontroller which runs the actual security program. In addition to interactions with the ID cards, the system is in contact with an administrator computer via a serial communications link.
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