InTech-Design Fundamentals and Advanced Techniques of Rfid Antennas
Antenna design 3:RFID tag antennas using AMCs
Transcript of Antenna design 3:RFID tag antennas using AMCs
Antenna design 3:RFID tag antennas using AMCs
Dongho Kim, Professor, Ph/DAntennas & EM applications Lab., Sejong University
안테나 / 전자파응용연구실, 세종대학교[email protected]
Overview - RFID Normal operation of RFID antennas Applications: identification, management, tracking, etc. Almost all tags are designed for stand-alone operation in air Air has relative permittivity (εr) = relative permeability (µr) =1 However, are they really installed in air?
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Scenario I Successful identification
RF energy
Information
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Overview - RFID Problem of conventional RFID tag antennas Tags do not properly operate on metallic surfaces or high dielectric
materials, Why not? On a metallic platform: antenna surface current is shorted out On a high dielectric platform: antenna input impedance severely varies
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Identification failure
No response (or very poor
response )from the tag
Met
allic
bod
y(o
r wat
er)
Shorted current
???
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Scenario II
Overview - RFID How can we increase reading distances? Platform (or product)-tolerant tags are needed Artificial magnetic conductor (AMC) is the right technique for our problem , which increases recognition distance with the minimum influence of various
platforms
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Tag on an AMC
Scenario III
Stronger response from the tag
Identification successwith a longer reading distance
Increased reading distance
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Overview - AMC Idea: Manipulation of reflection phase Reflection phase Perfect electric conductor (PEC): π (=180o) Perfect magnetic conductor (PMC): 0 Artificial magnetic conductor (AMC):
freq. dependent, controllable phase response
Antenna applications Distance between an antenna & a substrate
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PEC ground
PMC ground
frequency
Reflection phase
−π
π
0
PECAMC
PMC
PEC
λ
fixed phase
Constructive interference condition
(= ) 2
2 1 2 12 4
h h m
m mh
(=0) 2
2
2 2
h h m
m mh
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Applications: long range Provides a much longer reading distance Based on a creative idea of impedance matching
Using coupling effects between the tag and the cavity Installing the tag in the metallic cavity
Target applications: large objects such as metallic containers, cars, trains, aircrafts, etc.
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RFID tag antenna(Fairly simple geometry)
Single-band applicationcavity
(Recessed volumein a metallic object)
910 MHz band (Korea, USA)
Strap type Higgs-2 chip: 11-j130 Ω
140 mm
80 mm
50 mm
50 mm
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Reference: D. Kim et al, “A passive RFID tag antenna installed in a recessed cavity in a metallic platform,” IEEE Trans. Antennas Propagat., vol.58, no.12, pp.3814-3820, 2010
Applications: long range Provides a much longer reading distance Based on a creative idea of impedance matching
Using coupling effects between the tag and the cavity Installing the tag in the metallic cavity
Target applications: large objects such as metallic containers, cars, trains, aircrafts, etc.
6안테나 전자파 응용 연구실&
Reflection coefficient [dB]
Cavity wall
Bowtie antenna
Metallic wingRFID chip
Recessed hollow cavity
모델링: CST Microwave Studio
Applications: long range Effect of the cavity size Longer length (in the x-direction) increases a resonant frequency Longer length (in the y-direction) decreases a resonant frequency , which can be explained parasitic inductance and capacitance
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Induced surface conduction current
density
x
y
xc
yc
Cavity wall
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Surface current
CST Microwave Studio 사용
Applications: long range & dual bands
Design of the AMC cells Using offset vias reduced cells we can accommodate the AMC
cells in the cavity
Control the reflection phase It’s very easy to control the reflection phase by varying via offset(loffset),
(even with the fixed length of the cell)
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Reflection coefficient [deg]
Unit cell of AMC
CST MWS
Changing coupling effect from the bottom surface of the cavity Installing an AMC on the bottom of the cavity
Varies phase values of the wave reflected from the AMC By selecting appropriate reflection phase of the AMC, we can make the tag resonate
another frequency of interest At the two frequencies of interest, we can obtain the same phase values
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RFID tag antenna(Fairly simple geometry)
Dual-band applicationCavity + AMC ground
869 MHz band (European)910 MHz band (Korea, USA)
Strap type Higgs-2 chip: 11-j130 Ω
140 mm
80mm 50 mm
50 mm
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Applications: long range & dual bands
Reference: D. Kim et al, “Dual-band long range passive RFID tag antenna using an AMC ground plane,” IEEE Trans. Antennas Propagat., vol.60, no.6, pp-2620-2626, 2012
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Changing coupling effect from the bottom surface of the cavity Installing an AMC on the bottom of the cavity
Varies phase values of the wave reflected from the AMC By selecting appropriate reflection phase of the AMC, we can make the tag resonate
another frequency of interest At the two frequencies of interest, we can obtain the same phase values
안테나 전자파 응용 연구실&
Cavity wall
Bowtie antenna
AMCs
Reflection coefficient [dB]
Metallic wing
Applications: long range & dual bands
Reference: D. Kim et al, “Artificial magnetic conductor loaded long range passive RFID tag antenna mountable on metallic objects,” Electronic Letts., vol.50, issue 5, pp. 335-336, 2014
Effect of the AMC ground plane At the three different resonant frequencies The antenna shows the same overall phase value of about 90 degrees.
Surface current density of the AMC
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Surface current density on the AMC안테나 전자파 응용 연구실&
Surface current
Via Via
Applications: long range & dual bands
CST Microwave Studio 사용
Performance comparison
Items
Simulation Experiment
Max. gain
Best matching(Min. VSWR)
Max. induced power
Distance increase
(prediction)
Max. reading distance
AlienALN-9540 2.1 dB 1.1 @ 915 MHz -3.67 dBm 1.0
(reference) 6.5 m
Proposed tag (single band) 7.1 dB 1.2 @ 912 MHz 1.44 dBm 3.2 20.9 m
Proposed tag (dual bands)
6.74 dB 1.03 @ 864 MHz 1.35 dBm 2.93 22.75 m
6.46 dB 1.23 @ 910 MHz 1.05 dBm 2.90 23.74 m
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Performance evaluation Reference tag: commercial Alien ALN-9540 Experimental environment
RFID tester: commercial TESCOM TC-2600A Reader: ALR-9800 reader with transmitted
power of 30 dBm
Experimental results
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Conclusions Using the controllable behavior in reflection phase of AMCs,
it’ s possible to Fabricate RFID tag antennas that are platform tolerant Extend the recognition distance (by using a recessed metallic cavity) Make the tag operate at two different frequencies
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