Inc easing o RFID sys em ead ange
171
INCREASING OF RFID SYSTEM READ RANGE
P. Ves enický
Depa men o Con ol and In o ma ion Sys ems, Facul y o Elec ical Enginee ing,
Uni e si y o Žilina, Uni e zi ná 1, 010 26 Žilina, Slo akia
e-mail: pe e . es enicky@ el.u c.sk
Summa y
This pape desc ibes some compu a ions needed o inc ease RFID sys em ead ange wice wi hou any changes
in RFID eade . The inc easing o ead ange is done only by p ope selec ion o RFID ma ke pa ame e s – coil diame e and
numbe o u ns. Ano he way – gene a ing s onge magne ic ield om eade – can no be used because equi emen s o
some limi a ions gi en by alid s anda ds mus be aken in o accoun .
1. INTRODUCTION
Two yea s ago he pape s [1] and [2], which
desc ibe solu ion o some echnical p oblems o
digi al RFID ma ke and eade (loca o )
de elopmen we e published. Pa ame e s o
de eloped loca o a e ully compa able wi h simila
equipmen s p oduced in USA and Ge many. Ma ke
can be loca ed om dis ance o 2 m and
iden i ica ion code om RFID chip in ma ke can be
ead om dis ance o 1.5 m.
This pape analyzes possibili ies how o
inc ease he ead and localiza ion anges wice ( om
1.5 m o 3 m) because some enginee ing ne wo ks
(mos ly wa e and sewe age pipes) ma ked by RFID
ma ke s a e bu ied mo e han 3 m unde g ound
su ace. A he same ime alid s anda ds which
limi magne ic ield in ensi y gene a ed by loca o
mus be obse ed so ha he equipmen could be
ope a ed unde Gene al License VPR-06/2005
issued by Telecommunica ion O ice o Slo ak
Republic.
2. LIMITS FOR THE RADIATED
MAGNETIC FIELD
Fo RFID applica ions in used equency band
om 80 o 150 kHz nex s anda ds and egula ions
a e accep ed:
• Gene al License VPR-06/2005 issued by
Telecommunica ion O ice o Slo ak
Republic
• Recommenda ion ERC/REC 70-03, annex
9, issued by ERC (Eu opean
Radiocommunica ions Commi ee)
• Decision ERC/DEC/(01)13 issued by ERC
• S anda d ETSI EN 300 330-1 issued by
ETSI [3].
Tab. 1. Magne ic ield limi s a 10 m dis ance
F equency
[kHz] HMAX
[dBµA/m]
HMAX
[µA/m]
83.0 42.0 125.9
101.4 42.0 125.9
121.6 58.8 871.0
134.0 58.4 831.8
145.7 37.7 76.7
The limi s o adia ed magne ic ield measu ed
a 10 m dis ance om loca o an enna and o
di e en wo king equencies a e shown in Tab. 1.
These limi s conside an enna adius
LT
=0.1 m.
3. MAGNETIC FIELD GENERATED BY
LOCATOR
T ansmi e an enna o loca o gene a es
magne ic ield wi h in ensi y
322
)(2
)( x
SIN
xH
LT
LTLLT
L
+
=
π
[A/m] (1)
whe e indi idual symbols deno e:
- ansmi e coil numbe o u ns N
LT
=50
- diame e o ansmi e coil
LT
=0.1 m
- a ea o ansmi e coil S
LT
=0.0314 m
2
- ansmi e coil cu en I
L
=0,5 A
- dis ance om ansmi e coil x
These pa ame e s we e chosen so ha limi s
gi en in Tab. 1 a e ul illed, i. e. H
L
(x)=42 dBµA/m
o x=10 m o all wo king equencies (no e: o
equency 145.7 kHz he limi is lowe ed o 37.7
dBµA/m). Dependence o in ensi y H
L
(x) on
dis ance x is shown in nex g aph (Fig. 1) and i
gi en limi s mus be ul illed, he in ensi y canno be
in luenced by any means.
Fig. 1. Magne ic ield in ensi y gene a ed by loca o .
Ad ances in Elec ical and Elec onic Enginee ing
172
4. VOLTAGE INDUCED INTO MARKER
The magne ic ield wi h in ensi y gi en by (1)
induces in o ma ke ol age
)()( xHSNQxU
LMMMM
µω
=
[V] (2)
whe e
- ma ke coil numbe o u ns N
M
=35
- ma ke a ea S
M
=0.0314 m
2
- quali y ac o o LC ci cui Q
M
=70
- pe meabili y µ=4π.10
-6
H/m
- ci cula equency ω=637 k ad/s
Nex g aph shows dependency o ol age U
M
(x) on
dis ance x. A 1.5 m he ol age is 2.26 V and his
alue is su icien o supplying he RFID chip bu in
dis ance x=3 m he ol age is insu icien (only 0.28
V). Ra io o hese wo alues is
(
)
( )
96,7
3
5,1 =
M
M
U
U
Fig. 2. Vol age induced in o ma ke
and he e o e o co ec supplying o RFID chip a 3
m dis ance he induced ol age mus be 8 imes
inc eased. Analysis o o mula (2) shows ha i can
be done only by inc easing o numbe o u ns N
M
and/o a ea S
M
. The quali y ac o canno be
inc eased o he sake o uned LC ci cui pa asi ic
ea u es and o equi ed equency bandwid h, µ and
ω a e cons an and H
L
(x) is limi ed by s anda d [3].
5. CHANGE OF COUPLING FACTOR
BETWEEN MARKER AND LOCATOR
COILS AND ITS INFLUENCE ON
INDUCTIVITY
The coupling ac o depends on geome ical
a angemen o bo h coils (Fig. 4) and is gi en by
o mula (3) [4, 5], whe e
M
is ma ke coil adius and
θ is angle be ween coils.
Acco ding o (3) he coupling ac o a dis ance
x=1.5 m is k(1,5)=2,94.10
-4
and o x=3 m he alue
o k(3)=3,70.10
-5
, i. e. i is 8 imes smalle (Fig. 3).
I we wan o keep he coupling ac o a longe
dis ance he ma ke adius
M
in (3) mus be 4 imes
inc eased.
2
3
22
22
).(.
cos..
)(
x
xk
LTMLT
MLT
+
=
θ
[-] (3)
Fig. 3. Coupling ac o
θ

M
LT
x
Fig. 4. Geome ical a angemen o coils.
The induc i i y o ci cula coil is (acco ding o
[4])








=
0
9,1
ln...
NL
M
MMM
µ
[H] (4)
whe e
0
is conduc o adius. I he coil adius
M
is 4
imes inc eased he induc i i y is inc eased by ac o
4.ln4 i. e. 5.55 imes. I he o iginal induc i i y has
o be kep , i mus be compensa ed by numbe o
u ns N
M
dec eased by ac o 5.55
1/1.9
i. e. 2.46
imes.
6. CONCLUSION
Fo doubling RFID ma ke ead ange om 1.5
m o 3 m hese changes a e needed:
• The ma ke diame e mus be 4 imes
inc eased ( om o iginal alue o 20 cm o
80 cm).
• Numbe o u ns mus be dec eased 2.46
imes ( om o iginal alue o 35 o 14
u ns).
Inc easing o RFID sys em ead ange
173
Then he induced ol age (2) a dis ance 3 m will be
1.82 V. This is su icien o co ec supplying o he
RFID chip. Nei he he coupling ac o (3) no
induc i i y (4) will no be essen ially changed.
Expe imen al es ing o big ma ke has no been
pe o med ye and will be done in u u e.
Ano he ques ion is p ac ical usabili y o so big
ma ke – manipula ion, mechanical esis ance,
equi emen o wide exca a ion e c. and p ice.
REFERENCES
[1] Ves enický, P.: Op imiza ion o Selec ed RFID
Sys em Pa ame e s. AEEE 3, 2004, No. 2,
pages 113-114. ISSN 1336 – 1376) 483.
[2] Ves enický, P.: Solu ion o Some Technical
P oblems in Ma ke and Ma ke Loca o
De elopmen . Communica ions 6, 2004, No. 4,
pages 103-106, ISSN 1335-4205
[3] Final d a ETSI EN 300 330-1 V1.5.1.
Elec omagne ic compa ibili y and Radio
spec um Ma e s (ERM); Sho Range De ices
(SRD); Radio equipmen in he equency ange
9 kHz o 25 MHz and induc i e loop sys ems in
he equency ange 9 kHz o 30 MHz; Pa 1:
Technical cha ac e is ics and es me hods
[4] Geh ing, U., Roz, Th.: RFID made easy. EM
Mic oelec onic-Ma in SA. Ma in, Swi ze land,
2000
[5] íž, R., Ško pil, V.: ADSL Coppe Loop
P equali ica ion. P oceedings o he
In e na ional Con e ence "Resea ch in
Telecommunica ion Technology 2000". VSB-
TU, Os a a, 2000. Pages 13 – 16. ISBN 80-
7078-817-8