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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

    / , [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 (r) = relative permeability (r) =1 However, are they really installed in air?

    1

    Scenario I Successful identification

    RF energy

    Information

    &

  • 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

    ???

    &

    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

    3

    Tag on an AMC

    Scenario III

    Stronger response from the tag

    Identification successwith a longer reading distance

    Increased reading distance

    &

  • Overview - AMC Idea: Manipulation of reflection phase Reflection phase Perfect electric conductor (PEC): (=180o) Perfect magnetic conductor (PMC): 0 Artificial magnetic conductor (AMC):

    freq. dependent, controllable phase response

    Antenna applications Distance between an antenna & a substrate

    4

    PEC ground

    PMC ground

    frequency

    Reflection phase

    0

    PECAMC

    PMC

    PEC

    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

    &

  • 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

    140 mm

    80 mm

    50 mm

    50 mm

    &

    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.

    6 &

    Reflection coefficient [dB]

    Cavity wall

    Bowtie antenna

    Metallic wingRFID chip

    Recessed hollow cavity

    : 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

    7

    Induced surface conduction current

    density

    x

    y

    xc

    yc

    Cavity wall

    &

    Surface current

    CST Microwave Studio

  • 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 Its very easy to control the reflection phase by varying via offset(loffset),

    (even with the fixed length of the cell)

    8 &

    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

    9

    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

    140 mm

    80mm 50 mm

    50 mm

    &

    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

  • 10

    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

    &

    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

    11

    Surface current density on the AMC &

    Surface current

    Via Via

    Applications: long range & dual bands

    CST Microwave Studio

  • 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

    12

    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

    &

  • 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

    13 &

    Antenna design 3:RFID tag antennas using AMCsOverview - RFIDOverview - RFIDOverview - RFIDOverview - AMCApplications: long rangeApplications: long rangeApplications: long rangeApplications: long range & dual bands 10Applications: long range & dual bandsApplications: long range & dual bandsPerformance comparisonConclusions

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