Radio frequency identification (RFID) is an integral part of our life, which increases productivity and convenience. It is the term coined for short-range radio technology used to communicate mainly digital information between a stationary location and a movable object or between movable objects. This RFID system uses the principle of modulated backscatter where it can transfer the data from the tag to the reader. The tag generally reads its internal memory of stored data and changes the loading on the tag antenna in a coded manner corresponding to the stored data. RFID is a technology, which spans systems engineering, software development, encryption etc., and thus there are many engineers involved in the development and application of RFID and at present the shortage of technical and business people trained in RFID is hampering the growth of the industry.

The history of RFID

Radio-frequency identification technology, based on the reader/tag paradigm, is quickly permeating several aspects of everyday life. The electromagnetic research mainly concerns the design of tag antennas having high efficiency and small size, and suited to complex impedance matching to the embedded electronics. Starting from the available but fragmented open literature, this paper presents a homogeneous survey of relevant methodologies for the design of UHF passive tag antennas. Particular care is taken to illustrate, within a common framework, the basic concepts of the most-used design layouts. The design techniques are illustrated by means of many noncommercial examples.

/pdf/the-art-of-uhf-rfid-antenna-design-impedance-matching-and-8181kp44t2.pdf

The art of UHF RFID antenna design: impedance-matching and size-reduction techniques

This paper presents a method for measuring signal backscattering from RFID tags, and for calculating a tag's radar cross section (RCS). We derive a theoretical formula for the RCS of an RFID tag with a minimum-scattering antenna. We describe an experimental measurement technique, which involves using a network analyzer connected to an anechoic chamber with and without the tag. The return loss measured in this way allows us to calculate the backscattered power and to find the tag's RCS. Measurements were performed using an RFID tag operating in the UHF band. To determine whether the tag was turned on, we used an RFID tag tester. The tag's RCS was also calculated theoretically, using electromagnetic simulation software. The theoretical results were found to be in good agreement with experimental data

Theory and measurement of backscattering from RFID tags

In this paper, an overview of near field UHF RFID is presented. This technology recently received attention because of its possible use for item-level tagging where LF/HF RFID has traditionally been used. We review the relevant literature, discuss basic theory of near and far field antenna coupling in application to RFID, and present some experimental measurements.

An Overview of Near Field UHF RFID

Radio Frequency IDentification (RFID) is intended to supplant legacy (optical) bar code scanning technology found in many logistic and retail applications. RFID is distinguished by inexpensive, low power and compact form factor tags, whose longevity and efficacy are predicated on using passive communication techniques and on-tag power harvesting. Such tags employ backscatter modulation, which does not require any active RF components. As a result, backscatter has become an attractive design choice for short-range communications in power constrained wireless sensor networking scenarios. The purpose of this work is two-fold. First, it aims to expose backscatter communication as an emerging topic to a communication systems-theoretic audience. Since backscatter modulation and on-tag power harvesting efficiency are coupled, it is necessary to re-examine notions of power and spectral efficiency from an energy-constraint perspective; this leads to novel coded modulation schemes for future RFID systems. Further, we investigate RFID MIMO systems where the channel fading encountered has different statistics than the classical Rayleigh fading model. In turn,the trade off between diversity order and spatial multiplexing gains are distinct from wide-area MIMO.

— Invited Paper — Backscatter Communication and RFID: Coding, Energy, and MIMO Analysis

An electronic identification system which uses modulated backscatter from an RF beam-powered tag is described. A subcarrier is used in the return signal format to allow separation from the background clutter and to allow use of a novel method to avoid RF phase problems.

Short-range radio-telemetry for electronic identification, using modulated RF backscatter

A unique system of identifying animals so that a computercompatible digital code number can be automatically recognized by electronic methods is described. The transponder attached to the animal is passive and has an unlimited life. It provides a means of measuring body temperature in animals in addition to providing identity. The characteristics of the system and its potential in animal health control are discussed. (25 figures) (auth)

R.W. Freyman

Papers

Short-range radio-telemetry for electronic identification, using modulated RF backscatter

Electronic animal identification and temperature monitoring.