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pigsabusiveElectronics - Devices

Nov 29, 2013 (3 years and 8 months ago)

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INTRODUCTION

:

RFID makes it possible to give each product in a grocery store its own unique identifying
number, to provide assets, people, work in process, medical devices etc. all with individual
unique identifiers
-

like the license

plate on a car but for every item in the world. This is a vast
improvement over paper and pencil tracking or bar code tracking that has been used since the
1970s. With bar codes, it is only possible to identify the brand and type of package in a grocery
s
tore, for instance. Furthermore, passive RFID tags (those without a battery) can be read if
passed within close enough proximity to an RFID reader. It is not necessary to "show" the tag to
the reader device, as with a bar code. In other words it does not r
equire line of sight to "see" an
RFID tag, the tag can be read inside a case, carton, box or other container, and unlike barcodes
RFID tags can be read hundreds at a time. Bar codes can only read one at a time. Some RFID
tags can be read from several meter
s away and beyond the line of sight of the reader. The
application

enables an almost
-
parallel reading of tags.


HISTORICAL BACKGROUND

:

The history of radio frequency engineering can be traced to 1864 when James Clerk Maxwell
predicted the existence of ele
ctromagnetic waves, of which microwaves are a part, through
Maxwell’s equations.

By 1888, Heinrich Hertz had demonstrated the existence of electromagnetic waves by building
an apparatus that produced and detected microwaves in the UHF region, the radio fre
quency
selected by the Auto
-
ID Center at MIT for its passive RFID initiative a century and a half later.

Radio frequencies, like other physical signals in nature, are analog, as is also the

case for voltage,
urrent
, pressure, temperature, and velocity. Radio frequency waves and radar radiation connect
interrogators and tags via ‘‘inductive coupling’’ or ‘‘backscatter coupling’’ as will be analyzed
in depth by Marlin Mickle in ‘‘Resolution and Integration of HF & UHF
’’. The first RFID
applications were developed in conjunction with radar technology at the height of the Second
World War, for Identification Friend or Foe (IFF) systems, where the RF transponder (tag) and
interrogator (reader) were designed to detect frie
ndly airplanes. A precursor to passive RFID was
the electronic article surveillance (EAS) systems deployed in retail stores in the 1970s that used
dedicated short
-
range communication (DSRC) RF technology for anti
-
theft detection. Auto
-
ID
RFID technology bu
ilds on automated data capture (AIDC) barcode

standards for identifying
products that, together with the standardization of

shipping container dimensions, have so
dramatically lowered the cost of transportation

in recent decades
. Companies that seized the

opportunity to optimize

their supply chains with this technology have become some of the largest
companies

in the world, including such retailers as Wal
-
Mart, Metro, Target, and

Carrefour.

The best
-
known and most widespread use of AIDC barcode technology
has been in consumer
products, where the Universal Product Code (UPC) was developed in response to grocery
industry requirement
s in the mid 1970s
. Where barcodes are widely used in these networks
today, RFID systems are now

being installed to expedite non
-
line
-
of
-
sight data capture using RF
to read the electronic product code (EPC) on RFID tags.


One area where history can help us to avoid ‘‘reinventing the wheel’’ is in human
resources planning for what RF background is useful for implementing low
-
power

RFID
systems today. By contrast, the RF engineers who have worked in more recent RF domains
such as cellular telephony

and

wireless LANs are accustomed to working at much higher power levels and with more
host processing capabilities in cell phones than are present in tiny RFID tags.
The success is

related in
to
bringing radar

technicians from the airplane manufacturing side
of the
business to design their

RFID infrastructure
.
In addition to the challenging physics of
generating low
-
power electromagnetic

UHF signals to wake up passive RFID tags to
transmit their ID in the original
.



THE COMPONENTS OF THE BASIC RFID SYSTEM:


Radio
-
frequency identification involves the hardware known as
interrogators

(also known as
readers
), and
tags

(also known as
labels
), as well as RFID
software

or RFID
middleware
.

Most RFID tags contain at least two parts: one is an
integrated circuit

for storing and processing
information,
modulating

and
demodulating

a
radio
-
frequency

(RF) signal, and other specialized
functions; the other is an
antenna

for receiving and transmitting the signal.

A basic RFID system consists of three components:




An antenna or coil



A transceiver (with decoder)



A transponder (RF tag) electronically programmed

with unique information









The
antenna

emits radio signals to activate the
tag

and to read and write data to it.



The reader emits radio waves in ranges of anywhere from one inch to 100 feet or more,
depending upon its power output and the
radio frequency

used. When an
RFID tag

passes
through the
electromagnetic zone, it detects the reader's activation signal.



The reader decodes the data encoded in the tag's integrated circuit (silicon chip) and the
data is passed to the host computer for processing
.




The purpose of an RFID system is to enable d
ata to be transmitted by a portable device,
called a tag, which is read by an RFID reader and processed according to the needs of a
particular application. The data transmitted by the tag may provide identification or location
information, or specifics abo
ut the product tagged, such as price, color, date of purchase, etc.
RFID technology has been used by thousands of companies for a decade or more. . RFID
quickly gained attention because of its ability to track moving objects. As the technology is
refined,
more pervasive
-

and invasive
-

uses for RFID tags are in the works.

A typical RFID tag consists of a microchip attached to a radio antenna mounted on a
substrate. The chip can store as much as 2 kilobytes of data.

To retrieve the data stored on an RFID
tag, you need a reader. A typical reader is a device
that has one or more antennas that emit radio waves and receive signals back from the tag.
The reader then passes the information in digital form to a computer system.

SOME EXAMPLES OF THE USE OF THE RFI
D:

Security and Access Control


RFID has long been used as an electronic key to control who has access to office buildings or
areas within office buildings. The first access control systems used low
-
frequency RFID tags.
Recently, vendors have introduced 13
.56 MHz systems that offer longer read range. The
advantage of RFID is it is convenient (an employee can hold up a badge to unlock a door,
rather than looking for a key or swiping a magnetic stripe card) and because there is no
contact between the card and

reader, there is less wear and tear, and therefore less
maintenance.


As RFID technology evolves and becomes less expensive and more robust, it's likely that
companies and RFID vendors will develop many new applications to solve common and
unique busines
s problems.


FREQUENCY RANGE:

Because RFID systems generate and radiate electromagnetic waves, they are justifiably classified
as radio systems. The function of other radio services must under no circumstances be disrupted
or impaired by the operation of RFID systems. It is particularl
y important to ensure that RFID
systems do not interfere with nearby radio and television, mobile radio services (police, security
services, industry), marine and aeronautical radio services and mobile telephones.

The need to exercise care with regard to o
ther radio services significantly restricts the range of
suitable operating frequencies available to an RFID system. For this reason, it is usually only
possible to use frequency ranges that have been reserved specifically for industrial, scientific or
med
ical applications or for short range devices. These are the frequencies classified worldwide
as ISM frequency ranges (Industrial
-
Scientific
-
Medical) or SRD frequency ranges, and they can
also be used for RFID applications.

Frequency ranges for RFID
-
Systems

frequency range

C
omment

allowed fieldstrength /
transmission power


< 135 kHz

low frequency, inductive
coupling

72 dBµA/m max

3.155 ... 3.400 MHz

EAS

13.5 dBµA/m

6.765 .. 6.795 MHz

medium frequency (ISM),
inductive coupling

42 dBµA/m

7.400 ..

8.800 MHz

medium frequency, used for
EAS (electronic article
surveilance) only

9 dBµA/m

13.553 .. 13.567 MHz

medium frequency (13.56
MHz, ISM), inductive
coupling, wide spread usage
for contactless smartcards
(ISO 14443, MIFARE,
LEGIC, ...), smartlabels
(ISO
15693, Tag
-
It, I
-
Code, ...)

60 dBµA/m

26.957 .. 27.283 MHz

medium frequency (ISM),
inductive coupling, special
applications only

42 dBµA/m

433 MHz

UHF (ISM), backscatter
coupling, rarely used for RFID

10 .. 100 mW

865 .. 868 MHz

UHF (RFID only),
Listen
before talk

100 mW ERP

Europe only

865.6 .. 867.6 MHz

UHF (RFID only), Listen
before talk

2W ERP (=3.8W EIRP)

Europe only

865.6 .. 868 MHz

UHF (SRD), backscatter
coupling, new frequency,
systems under developement

500 mW ERP,

Europe only

902 ..

928 MHz

UHF (SRD), backscatter
coupling, several systems

4 W EIRP
-

spread spectrum,
USA/Canada only

2.400 .. 2.483 GHz

SHF (ISM), backscatter
coupling, several systems,

4 W
-

spread spectrum,
USA/Canada only

2.446 .. 2.454 GHz

SHF (RFID and AVI
(automatic vehicle
identification))

0.5 W EIRP outdoor

4 W EIRP, indoor

5.725 .. 5.875 GHz

SHF (ISM), backscatter
coupling, rarely used for RFID

4 W USA/Canada,

500 mW Europe



DIFFERENTS CIRCUITS:



Low path filter:




High path filter:




pass band filter:




Functional

block diagram

of an RFID tag
:






Principle

of the oscillator
:

An oscillator

is an amplifier

(A)

that uses

a

feedback loop

(B).

The portion of

output signal

fed back

as input

is in phase with

the input signal
.

If

(A
) introduces
a phase shift
of

180

then (
B)
must

also introduce

a phase shift of

180
.






The output voltage

can be written
:


Also


So we obtain:


This result

shows

that the gain

H

may

become infinite

depending on the

gain of the

feedback
loop
.

In this case it

is possible to
have

an

output signal in

the

abscence

of the

input signal.

For

oscillations

must:

1)

the total phase shift

of the loop

must be

exactly between

0

and 360.

2)

the total gain

of the loop

must be 1

or

| AB |

= 1.




O
ther oscillators

(
colpitts


oscillators)
:





Hartley oscillators

:





pont de wien

oscillators

:







The types of

modulation:

AM

MODULATION
:


Carrier



information to send




Expression of the signal

:


Ration modulation

:





AM MODULATION EXAMPLE
:








FM MODULATION:

the frequency

of a

sinusoidal

signal

is modified

according to a

baseband

signal
.




PM MODULATION
:




the signal

also


We obtain:


The PM modulator is shown as:





REFERENCES:


http://www.aimglobal.org/technologies/rfid/what_is_rfid.asp

http://fr.wikipedia.org/wiki/Filtre_passe
-
bas

http://tel.archives
-
ouvertes.fr/docs/00/38/97/76/PDF/khouri_memoire.pdf

http://users.polytech.unice.fr/~pmasson/Enseign
ement/Oscillateurs%20et%20radio%20Cours%20
-
%20Projection%20
-
%20MASSON.pdf

http://users.polytech.unice.fr/~pmasson/Ensei
gnement/Oscillateurs%20et%20radio%20Cours%20
-
%20Projection%20
-
%20MASSON.pdf