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RFID DESIGN STUDIES

Explore the applications and design challenges of RFID systems, including electronic toll collection, access control, animal tracking, and inventory control. Learn about impedance matching techniques for hybrid loop and dual cross-dipole antennas.

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RFID DESIGN STUDIES

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  1. RFID DESIGN STUDIES Dr. KVS Rao Intermec Technologies Everett, WA, USA Prof. Raj Mittra Pennsylvania State University University Park, PA, USA.

  2. Electronic Toll Collection Access Control Animal Tracking Inventory Control Tracking Runners in Races! Applications

  3. Introduction Radio Frequency Identification (RFID) System - Background Information • Applications of RFID • High Frequency (13.56MHz) • Supply Chain • Wireless Payment • Libraries Book ID • Ultra High Frequency (902 – 928 MHz) • Supply Chain • Sensors • Libraries • Microwave Frequency (2.45GHz) • Supply Chain • Sensors • Electronic Toll Payments

  4. Small Size Planar UHF Frequency Allocation Europe 866-869 MHz North America 902-928 MHz Impedance Matching ASIC Chip: High Capacitive Value, Small Resistive Value Environmental Conditions Design Challenges

  5. Characteristic Impedance Power 3-Dimensional Radiation Patterns Maximum Directivity Antenna Parameters where Umax is the radiation intensity in maximum direction, and Prad is the total radiated power. where Za = Ra + j Xa is the antenna impedance, and Zs = Rs + j Xs is the source impedance.

  6. Hybrid loop antenna • Length of the antenna ~ one operating wavelength in free space • Outer loop terminated by inner loop  size reduction • Simple structure (one layer of dielectric substrate) • Antenna impedance must be highly inductive Top View of the antenna

  7. Hybrid loop antenna (cont‘d) • Realize a high value for the inductance by: • Changing the loop area (L ~ A) • Changing the length of the perimeter Top View of the modified antenna

  8. Hybrid loop antenna : First design • Perimeter of the loop antenna : 244 mm • Size used by the antenna : 39 x 40 (mm) • Resonance frequency : ~0.5 GHz and 1.26 GHz • Reactance +300 Ω at 1.01 GHz Input Impedance

  9. Hybrid loop antenna : First design (cont‘d) • Not omnidirectional Pattern in the xy-plane  Non strictly symmetry of the geometry Far Field Pattern (normalized) xy-plane xz- (blue) and yz-(red) plane

  10. Hybrid loop antenna : Parametric study • Li = 16 (red graph) mm  Li= 10 mm (blue graph) • Perimeter  , Loop area  : L  • Perimeter 244 mm  232 mm Changing the length of the inner loop Li

  11. Hybrid loop antenna : Parametric study • Wi = 28 (red graph) mm  Wi= 30 mm (blue graph) • Perimeter  , Loop area  : L  • Perimeter 248 mm  252 mm Changing the width of the innerloop Wi

  12. Hybrid loop antenna (cont‘d) • Current distribution : small current in the top part of the antenna  small influence on the inductance  Meandering Far Field Pattern and Current distribution at 910 MHz

  13. Meandered Hybrid loop antenna Top View of the meanderd antenna • Perimeter 252 mm  302 mm • Maximum percentage at 910 MHz

  14. Hybrid Loop Antenna • Length of the antenna has a greater effect on the input impedance more than does the loop area • Meandering technique reduces the size of the antenna • Small percentage power delivered to the antenna  attributable to very small resistive part of the input impedance • The developed design did not prove to be too useful OBSERVATIONS

  15. Dual cross-dipole • Meandering dipole  size reduction • Cross-polarization sensitivity  dual dipole • Ground plane  can act as reflector  gain  Top and Side Views of the Antenna Structure

  16. Dual cross-dipole : Design#1 Input Impedance • Length of the antenna : 218 mm ~0.66 λ (at 910 MHz) • Area used by the antenna : 51 x 51 (mm) • Reactance is too small in the desired frequency  Length of the antenna  • Resistive part is again very small

  17. Dual cross-dipole : Design#2 • “Load bar“ is added • Length of the antenna : 258 mm ~ 0.78 λ (at 910 MHz) • f300 at 900 MHz Top View

  18. Dual cross-dipole : Design#2 • ~80 % of the power is delivered to the antenna • Narrow bandwidth (10.5 MHz more than 50 % is delivered) • Min. AR  3 dB (860 MHz – 960 MHz) Far Field Pattern/Power delivered to the antenna/ Axial Ratio

  19. Dual cross-dipole : Parametric study • Decreasing h, increases the resonance frequency • By varying the height, input impedance can be adjusted for a good matching Influence of the height of the antenna

  20. Dual cross-dipole : Parametric study Influence of the dielectric constant Input Impedance and new design • Increasing the dielectric constant , drops the resonance frequency  length of the antenna • Area used by the antenna was decreased ~ 19 % by using a higher dielectric (4 instead of 2.2 ) • Max. Power delivered to the antenna was sligthly higher for the case with the higher dielectric constant (79 % vs 86 % ) • Bandwidth wasn‘t influenced

  21. Dual cross-dipole : New design New design/Power delivered to the antenna • Area used by the antenna reduced ~ 35 % compared to the inital design (second case) and ~21 % compared to the previous case • Max percentage for the power plot : ~81 % (79 % second case / 86 % previous case) • Bandwidth didn‘t change

  22. Inductively coupled Feed • Strength of the coupling depends on h2 and the size of the loop • Inductive coupling modeled by a transformer • Analyzing the input impedance by varying the size and shape of the loop Top View and structure

  23. Inductively coupled Feed (cont‘d) Changing length of the loop • Increasing the loop size, increase the inductance • With this method the reactance increases ~200 Ω • Two operating range frequency • Antenna size needs to be adjusted (increased)

  24. Inductively coupled Feed (cont‘d) • Same experiment as before (changing the size of the loop) • For one design we realized a very high percentage of power delivered (98 % at 899 MHz) • Bandwidth was narrow Changing the shape of the feeding loop

  25. Inductively coupled Feed (cont‘d) • Narrow bandwidth • Operating frequency can be varied by changing the size of the feeding loop • Antenna size must be increased to operate in the desired frequency range if we use a square loop. OBSERVATIONS

  26. Antenna Measurement Top View of the antenna

  27. Input Impedance Comparison : Measurement et Simulation

  28. Field Pattern normalized (910 MHz) - Comparison Measurement Simulation • Anechoic chamber not ideal for 910 MHz • Different feeding part (balun for measurement) • Infinite substrate size used for simulation

  29. PLATFORM-TOLERANT RFID DESIGNS

  30. Dual-Band PIFA Design ASIC Chip: Zc=10-j160 [W] at 867 MHz Zc=10-j150 [W] at 915 MHz Zc=10-j145 [W] at 940 MHz

  31. Dual-Band PIFA Design • Dual-band Frequency Operation • Open-Ended Stub • Gap Dimension and Stub Dimension Used to Tune • Platform Tolerance • Dominating Horizontal Current Distribution • Widening Short, Vertical Inductance Reduced, Antenna Lowered

  32. Dual-Band PIFA Design • Mounting Materials • Dimensions • 900 mm x 900 mm • (4 x 4) • Thickness=13 mm • Cardboard (er=2.5) • Glass(er=3.8) • Plastic(er=4.7)

  33. Impedance [867/915 MHz] Dual-Band PIFA Design

  34. Power (867 MHz) Power (915 MHz) Power (940 MHz) No Material 83.49 64.92 74.07 Cardboard 54.53 86.28 80.5 Amount Increased -28.96 21.36 6.43 No Material 83.49 64.92 74.07 Glass 54.81 80.72 72.9 Amount Increased -28.68 15.8 -1.17 No Material 83.49 64.92 74.07 Plastic 58.3 85.72 72 Amount Increased -25.19 20.8 -2.07 Power Dual-Band PIFA Design

  35. Radiation [867 MHz] Dual-Band PIFA Design No Material Cardboard Glass Plastic

  36. Directivity (867 MHz) Directivity (915 MHz) Directivity (940 MHz) No Material 1.6841 1.832 1.8815 Cardboard 1.928 2.0704 2.3425 Amount Increased 0.2439 0.2384 0.461 No Material 1.6841 1.832 1.8815 Glass 2.4053 2.8135 3.9153 Amount Increased 0.7212 0.9815 2.0338 No Material 1.6841 1.832 1.8815 Plastic 2.9936 3.4036 4.1411 Amount Increased 1.3095 1.5716 2.2596 Conclusions Dual-Band PIFA Design

  37. Environmental ChangeDual-Band PIFA Design • Cardboard Box • 900 mm x 900 mm • 4 x 4 • Thickness=13 mm • Metal sheet • 450 mm x 450 mm • 2 x 2 • Height from Cardboard was Varied from 0 mm-20 mm Radiation [867 MHz] Metal 20 mm Under Cardboard No Metal

  38. Power (867 MHz) Power (915 MHz) Peak Directivity (867 MHz) Peak Directivity (915 MHz) No Metal 54.53 86.28 1.928 2.0704 Metal 0 mm 76.6 80.7 3.3105 3.0219 Amount Increased 22.07 -5.58 1.3825 0.9515 Power (867 MHz) Power (915 MHz) Peak Directivity (867 MHz) Peak Directivity (915 MHz) No Metal 54.53 86.28 1.928 2.0704 Metal 10 mm 91.08 73.11 3.1872 3.0167 Amount Increased 36.55 -13.17 1.2592 0.9463 Power (867 MHz) Power (915 MHz) Peak Directivity (867 MHz) Peak Directivity (915 MHz) No Metal 54.53 86.28 1.928 2.0704 Metal 20 mm 73.25 76.82 3.2213 3.0599 Amount Increased 18.72 -9.46 1.2933 0.9895 Environmental Change Dual-Band PIFA Design

  39. No Material Glass Directivity (867 MHz) Peak Directivity (867 MHz) Peak Directivity (915 MHz) Directivity (915 MHz) Original GP Original GP 2.4053 1.6841 1.832 2.8135 1 Inch Larger 1 Inch Larger 2.5102 2.3265 2.3131 2.6094 2 Inch Larger 2 Inch Larger 2.9178 2.9306 2.918 3.0237 3 Inch Larger 3 Inch Larger 2.7375 3.6696 3.7427 2.7357 10 Inch Larger 10 Inch Larger 3.7178 4.5087 4.1891 4.4954 Cardboard Plastic Directivity (867 MHz) Peak Directivity (867 MHz) Peak Directivity (915 MHz) Directivity (915 MHz) Original GP Original GP 2.9936 1.928 2.0704 3.4036 1 Inch Larger 1 Inch Larger 2.9787 2.6915 3.0035 2.7059 2 Inch Larger 2 Inch Larger 3.0787 3.2191 2.9965 3.2618 3 Inch Larger 3 Inch Larger 3.1907 3.1032 3.3583 3.0408 10 Inch Larger 10 Inch Larger 4.6297 3.0544 2.9356 4.687 Ground Plane Optimization Dual-Band PIFA Design

  40. Ground Plane Optimization Dual-Band PIFA Design

  41. Inductively-Coupled Feed Loop PIFA Design • Impedance Matching • Inductively Coupled Feed Loop • Gap dimension between loop and radiators is used to tune • Designed to match Zc=10-j150 [W] at 915 MHz • Platform Tolerance • Reduced Current on Ground Plane

  42. Inductively-Coupled Feed Loop PIFA Design • Mounting Materials • Dimensions • 200 mm x 200 mm • ( x ) • Thickness=5 mm • Cardboard (er=2.5) • Glass with No Loss(er=3.8) • Glass with Loss(er=2.5) and Loss Tangent 0.002

  43. Power 915 MHz [%] Power 940 MHz [%] Average Gap 9 mm 9.09 4.39 6.74 Gap 9.25 mm 86.09 41.45 63.77 Gap 9.5 mm 77.38 34.50 55.94 Gap 9.75 mm 15.28 13.00 14.14 Optimization of Impedance in Free Space

  44. Directivity (915 MHz) Directivity (940 MHz) No Mounting Material 3.47 3.3 Cardboard (er=2.5) 3.43 2.94 Amount Increased -0.04 -0.36 Directivity (915 MHz) Directivity (940 MHz) No Mounting Material 3.47 3.3 Glass No Loss (er=3.8) 3.4 3.25 Amount Increased -0.07 -0.05 Directivity (915 MHz) Directivity (940 MHz) No Mounting Material 3.47 3.3 Glass With Loss (er=2.5) and loss 0.002 3.36 3.3 Amount Increased --0.11 0 Directivity & Radiation 867 MHz No Material 867 MHz Cardboard

  45. Optimization of Impedance for Cardboard

  46. Impedance Inductively-Coupled Feed Loop PIFA

  47. Impedance Inductively-Coupled Feed Loop PIFA

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