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Antenna design 3: RFID tag antennas using AMCs Dongho Kim, Professor, Ph/D Antennas & EM applications Lab., Sejong University 안테나 / 전자파 응용 연구실, 세종대학교 [email protected]

Antenna design 3: RFID tag antennas using AMCs tag antennas...Antenna design 3: RFID tag antennas using AMCs Dongho Kim, Professor, Ph/D Antennas & EM applications Lab., Sejong University

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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

안테나 전자파 응용 연구실&

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

2

Identification failure

No response (or very poor

response )from the tag

Met

allic

bod

y(o

r wat

er)

Shorted current

???

안테나 전자파 응용 연구실&

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

안테나 전자파 응용 연구실&

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

안테나 전자파 응용 연구실&

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.

5

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

안테나 전자파 응용 연구실&

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

안테나 전자파 응용 연구실&

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)

8안테나 전자파 응용 연구실&

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

안테나 전자파 응용 연구실&

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

안테나 전자파 응용 연구실&

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

13안테나 전자파 응용 연구실&