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RFID tag antennas using AMCs PDF

14 Pages·2016·1.28 MB·English
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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] 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 안테나 & 전자파 응용 연구실 9

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Applications: identification, management, tracking, etc. Successful identification On a metallic platform: antenna surface current is shorted out between an antenna & a substrate. 4. PEC ground. PMC ground frequency . Reference: D. Kim et al, “Dual-band long range passive RFID tag antenna
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