RFID tag antennas using AMCs

14 Pages·2016·1.28 MB·English

by  Dongho Kim

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]
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 (ε ) = relative permeability (µ ) =1
r r
 However, are they really installed in air?
Successful identification
Scenario I
Information
RF energy
안테나 & 전자파 응용 연구실 1
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
Scenario II Identification failure Shorted current
No response
y
(or very poor
d
o r)
b e response )
t
c a
i w from the tag
l
l
a r
??? t o
e (
M
안테나 & 전자파 응용 연구실 2
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
Identification success
Scenario III
with a longer reading distance
Stronger response from the tag
Increased reading distance
Tag on an AMC
안테나 & 전자파 응용 연구실 3
Overview - AMC
 Idea: Manipulation of reflection phase
Reflection phase
 Reflection phase
PEC
 Perfect electric conductor (PEC): π (=180o) fixed π
phase
 Perfect magnetic conductor (PMC): 0 λ
PMC
 Artificial magnetic conductor (AMC):
0
freq. dependent, controllable phase response
AMC
 Antenna applications PEC
−π
 Distance between an antenna & a substrate
frequency
Constructive interference condition
PEC ground
h  h  (=)  2m
2m  1 2m  1
h    
2 4
PMC ground
h  h  (=0)  2m
2m m
h    
2 2
안테나 & 전자파 응용 연구실 4
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.
Single-band application
RFID tag antenna
cavity
(Fairly simple geometry)
(Recessed volume
in a metallic object)
Strap type
Higgs-2 chip:
910 MHz band (Korea, USA)
11-j130 Ω
80 mm
50 mm
140 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
안테나 & 전자파 응용 연구실 5
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.
Recessed hollow cavity Reflection coefficient [dB]
Bowtie antenna
Cavity wall
RFID chip
Metallic wing
모델링: CST Microwave Studio
안테나 & 전자파 응용 연구실 6
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
Induced surface
conduction current
y
density
x
Surface current y
c
CST Microwave Studio 사용
Cavity wall
x
c
안테나 & 전자파 응용 연구실 7
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(l ),
offset
(even with the fixed length of the cell)
Reflection coefficient [deg]
CST MWS
Unit cell of AMC
안테나 & 전자파 응용 연구실 8
Applications: long range & dual bands
 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
Dual-band application
RFID tag antenna
Cavity + AMC ground
(Fairly simple geometry)
869 MHz band (European)
Strap type
910 MHz band (Korea, USA)
Higgs-2 chip:
11-j130 Ω
80
mm 50 mm
50 mm
140 mm
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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