Magnetic Shield Influence on Wireless Power Designs

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Chris Burket presents Magnetic Shield Influence on Low Power Wireless Power Designs as part of the International Wireless Power Summit 2013 in Austin, Texas.

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Magnetic Shield Influence on Wireless Power Designs

  1. 1. Magnetic Shield Influence on Low Power Wireless Power Designs Presented by: Chris T. Burket Sr. Marketing Engineer - TDK chris.burket@us.tdk.com 714-934-7373
  2. 2. Shield and Coil Assembly Basics
  3. 3. Wireless Power Summit - 2013 Magnetic Induction System Example
  4. 4. Wireless Power Summit - 2013 • • • • • • Design Issues of Coil Assemblies Required inductance value (key to coupling/resonance) • Permeability of magnetic shield • # of turns • # of winding layers Saturation current of shield material (Bs of material) Stability of inductance value (both inductive and resonance applications) • Over temp • Over current • Due to proximity to battery • Due to end application packaging Coil type selection • Litz, bifilar, single strand wire, PCB coils, flex printed circuit, etc. • Gauge, Cu weight • Cost vs. performance between PCB coils and wire coils Coil winding diameter (ID – inner diameter) Coil wire (windings) proximity issues (resonance applications)
  5. 5. Wireless Power Summit - 2013 Role of Magnetic Shields • “u” value helps determine inductance value of coil assembly • Completes the magnetic loop path between Tx – Rx coil assemblies (1/2 transformer per side) • Shapes the magnetic flux field • Maintains (encapsulates) magnetic flux field in between 2 parallel shields  improving coupling/efficiency • Keeps magnetic flux field from escaping out top/bottom and thus getting into the battery area (or other metal objects) causing Eddy current losses  heat build up  reduction of inductance  reduction of coupling  loss of efficiency • u’ and u” (u’/u” or Q) greatly influenced by shield material  critical for resonance technologies • Helps keep the Ls value constant in various environments
  6. 6. Wireless Power Summit - 2013 Role of Magnetic Shields
  7. 7. Wireless Power Summit - 2013 Magnetic Field Analysis
  8. 8. Wireless Power Summit - 2013 Inductive System Losses ~ Equal Thirds Courtesy of TI
  9. 9. TDK Shield Material Comparison
  10. 10. Wireless Power Summit - 2013 TDK Material Comparison TDK currently uses 6 main shield materials for Tx, Rx coils used in WPC, PMA and resonant applications: • FK2 – Ni-Zn solid ferrite or pre-cracked (used for most inductive Tx coil assemblies, small size Rx coil assemblies) • FK5 – Ni-Zn ferrite sheet, pre-cracked, Rx side • FJ3 – Ni-Zn ferrite sheet, pre-cracked, Rx side (used for NFC combo coils, inductive and resonant applications) • FJ7 – Ni-Zn ferrite sheet, pre-cracked, Rx side for magnetic resonant applications in the 6.78 MHz range • MS2 – powdered iron sheet, pre-cracked, Rx side (used in high saturation applications) • MS6 – polymer material impregnated with powdered iron, Rx side (used for ultra-thin applications)
  11. 11. Wireless Power Summit - 2013 Material Comparison
  12. 12. Wireless Power Summit - 2013 Material Comparison – Ferrite Based
  13. 13. Wireless Power Summit - 2013 Material Comparison – Powdered Iron Based
  14. 14. Magnetic Induction Shield Influence Comparison
  15. 15. Wireless Power Summit - 2013 Magnetic Shield Influence on System Performance 1) Efficiency of coil w/ battery for a WPC Tx A1/WR-4832 Rx coil system 2) Efficiency vs shield thickness w/ and w/o battery vs material 3) Efficiency using WPC Tx A1 w/ and w/o magnet (same Tx coil) vs material 4) Efficiency vs. Rx Ls value 5) Efficiency vs. Rx coil size 6) Efficiency vs. distance between Tx-Rx coils 7) Rs (Rac) of multi-strand Litz wire vs. single strand wire vs. frequency 8) Cracked vs. non-cracked sheet efficiency 9) Efficiency of coil w/ Cu sheet for a WPC Tx A1/WR-3832 Rx coil system
  16. 16. Wireless Power Summit - 2013 1 - 3) Efficiency vs. Shield Material vs. Shield Thickness • Tested with WPC Tx/A1 coil, output current at 0.7A
  17. 17. Wireless Power Summit - 2013 WPC A1 Magnet Impact on Performance
  18. 18. Wireless Power Summit - 2013 1 - 3) Efficiency vs. Various Shield Materials Test with Tx/A1 coil, output current is 0.7A • 80.0 75.0 Efficiency(%) FK5(48x32xt0.3) FK5(48x32xt0.5) 70.0 FJ3(48x32xt0.25) FJ3(48x32xt0.5) 65.0 MS2(48x32xt0.3) MS2(48x32xt0.5) MS6(48x32xt0.25) 60.0 MS6(48x32xt0.5) 55.0 50.0 Only Coil with Magnet w/o Battery w/o Magnet with Battery with Magnet with Battery
  19. 19. Wireless Power Summit - 2013 4) Efficiency vs. Ls Value Using 3 different shield materials for Rx coil, varying windings  inductance Tested with Tx/A1 coil, output current at 0.7A FJ3(44x40xt0.3) MS6(44x40xt0.25) MS2(48x32xt0.5) Ls(uH) Efficiency(%) Ls(uH) Efficiency(%) Ls(uH) Efficiency(%) 23.1 65.6 19.7 63.4 12.6 70.8 21.8 66.3 18.8 62.9 11.8 70.8 20.4 66.9 17.7 63.7 10.8 70.6 19.1 66.2 16.9 63.7 9.5 69.1 16.1 66.4 14.5 62.7 8.0 67.6 11.6 63.8 12.1 60.9 10.0 61.6 9.6 55.1 80.0 75.0 Efficiency(%) • • 70.0 FJ3(44x40xt0.3) MS6(44x40xt0.25) MS2(48x32xt0.5) 65.0 60.0 55.0 50.0 5.0 7.0 9.0 11.0 13.0 15.0 Ls(uH) 17.0 19.0 21.0 23.0 25.0
  20. 20. Wireless Power Summit - 2013 5) Efficiency vs. Rx Coil Size All data is with battery. (Battery size is 54 x 83 x t2.9 mm) All sheet thickness at t=0.5mm Tested with Tx/A1 coil, output current at 0.7A MS2(with MS2(w/o FK5(with FK5(w/o Magnet) Magnet) Magnet) Magnet) 4832size 68.5 71.1 68.9 71.7 3832size 66.3 70.3 58.0 71.6 3030size 61.3 65.2 57.5 65.9 80.0 75.0 Efficiency(%) • • • 70.0 MS2(with Magnet) MS2(w/o Magnet) 65.0 FK5(with Magnet) FK5(w/o Magnet) 60.0 55.0 50.0 4832size 3832size 3030size
  21. 21. Wireless Power Summit - 2013 6) Efficiency vs. Distance Between Tx-Rx Coils Tested with Tx/A1 coil, output voltage at 5V • Distance(mm) 2.4 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 MS2(38x32xt0.5) Efficiency(%) 71.7 71.7 71.1 70.2 69.5 69.2 69.1 68.7 68.0 66.6 0.0 MS2(48x32xt0.5) MS2(38x32xt0.5) with Battery MS2(48x32xt0.5) with Battery Efficiency(%) 72.8 72.8 72.6 72.4 72.1 71.2 70.8 70.6 69.1 68.3 0.0 Efficiency(%) 68.9 68.9 67.6 67.6 65.8 63.5 63.5 62.6 60.3 56.4 0.0 Efficiency(%) 72.1 71.7 70.7 69.8 68.3 67.4 65.6 63.9 61.1 58.5 0.0 80.0 75.0 Efficiency(%) MS2(38x32xt0.5) 70.0 MS2(48x32xt0.5) MS2(38x32xt0.5) with Battery 65.0 MS2(48x32xt0.5) with Battery 60.0 55.0 50.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 Distance between Tx-Rx(mm) 8.0 9.0 10.0 11.0 12.0
  22. 22. Wireless Power Summit - 2013 7) Rs of Multi-strand Litz Wire vs. Single Strand Wire at 100 KHz Using Tx/A1 coil structure Inner coil diameter set to φ8.0 mm for both. • • Wire type (wire dia mm) Sheet No of Turn Outer size of coil(mm) Ls (uH) Rs (Ω) Q Single (φ0.45mm) FK2(1mm) 24 φ31.2 17.17 0.41 25.29 FK2(1mm) 26 φ33.0 21.09 0.47 26.90 Litz wire (φ0.08mmx30) FK2(1mm) 24 φ41.0 20.25 0.23 52.80 FK2(1mm) 26 φ44.0 24.76 0.26 56.90 2.0 24 1.8 1.6 Litz wire(φ0.08mmx30) - 24 Turns 22 20 Litz wire(φ0.08mmx30) - 26 Turns 18 Single(φ0.45mm) - 24 Turns 16 Single(φ0.45mm) - 26 Turns 14 Litz wire(φ0.08x30mm) - 24 Turns 1.4 Rs(Ohm) Inductance(μH) 26 1.2 Litz wire(φ0.08x30mm) - 26 Turns 1.0 Single(φ0.45mm) - 24 Turns 0.8 0.6 Single(φ0.45mm) - 26 Turns 0.4 12 0.2 0.0 10 50 100 150 200 Frequency(kHz) 250 300 50 100 150 200 Frequency(kHz) 250 300
  23. 23. Wireless Power Summit - 2013 8) Cracked vs. Non-cracked Shield Efficiency • • • Using FJ3 material, shield size 43.5 x 39.5 x t0.3 mm Tested with battery Tested with Tx/A1 coil, output current at 0.7A
  24. 24. Wireless Power Summit - 2013 9) Efficiency of Coil w/ Cu Plate • • Using Rx coil/WR-383250 (MS2) Test with Tx/A1 coil, output current is 0.7A
  25. 25. Magnetic Resonance Shield Influence
  26. 26. Wireless Power Summit - 2013 Magnetic Resonance Shield Influence • • • • • Key parameters in resonance system are coupling (typically K < 0.5) and Quality Factor (Q) of the coil assemblies. K depends on: • u’ of material, some minimum value, above which, limited impact • Coil winding dimensions • Shield dimensions/area • Distance between coil assemblies Q depends on: • Size/shape, configuration of shield • u’, u” of shield material • Frequency of application • Type of coil used, winding proximity, coil pattern for field shaping • Operating power level Figure of merit value of is used to determine coil parameters Higher Q material/coils, allow for use over broader range of distances
  27. 27. Emerging Applications Technical Challenges
  28. 28. Wireless Power Summit - 2013 15-30W Application Issues • Targeting tablets, notebooks, laptops, power tools, appliances • Higher current applications need higher Bs shield material to reduce saturation effects • AC resistance (Rac) is critical for reducing losses  typically Litz wire, I2 x Rac losses create heat problems • Adding thin sheet of higher “Bs” value magnetic material for handling higher current/preventing saturation is an option • Shield size important to ensure good coverage over battery, other critical components • Thickness limitations per end application affect performance
  29. 29. Wireless Power Summit - 2013 Typical Coil Assembly Stack-up – 20W Rx Example
  30. 30. Wireless Power Summit - 2013 20W Rx Examples without IFL10M 0.1mm TDK EX1 TDK EX2 with IFL10M 0.1mm TDK EX3 TDK EX4 Sharp Inquiry φ35 WLC Coil total Thickness [mm] WLC Coil wire WLC Outer Coil size [mm] WLC Inner Coil size [mm] WLC Turn WLC Ls @100kHz [uH] WLC Rs @100kHz [Ohm] WLC Q @100kHz 1.0mm (FK2) 1.62 0.4mm Copper Wire φ32.8 φ10 WLC Sheet thickness [mm] φ35 1.0mm (FK2) WLC Outer Size [mm] 2.91 0.08mm x 50 φ33.8 φ7.9 15Ts/1Layer Total 2Layer 24.68 23.25 17.06 19.11 0.16 0.27 0.60 0.76 101.88 55.54 18.27 16.29 26 1. Only Coil 2. WPC A1 Tx 3. WPC A1 Tx + Batt. 4. WPC A1 Tx + Cu. 1. Only Coil 2. WPC A1 Tx 3. WPC A1 Tx + Batt. 4. WPC A1 Tx + Cu. 1. Only Coil 2. WPC A1 Tx 3. WPC A1 Tx + Batt. 4. WPC A1 Tx + Cu. 24.32 19.84 12.93 15.40 0.46 0.49 0.87 1.08 32.09 25.57 9.33 9.21 φ35 1.0mm (FK2) + 0.1mm (IFL10M) 1.72 0.4mm Copper Wire φ32.8 φ10 26 24.41 20.52 14.76 16.08 0.48 0.51 0.79 0.90 32.01 25.55 11.39 10.77 φ35 1.0mm (FK2) + 0.1mm (IFL10M) 3.01 0.08mm x 50 φ33.8 φ7.9 15Ts/1Layer Total 2Layer 24.86 24.41 19.38 20.95 0.16 0.28 0.51 0.67 103.21 55.26 24.33 19.54
  31. 31. Issues With Small Diameter Rx Coils
  32. 32. Wireless Power Summit - 2013 Rx Coil << Tx Coil • Number of turns need to be higher to achieve required inductance value  DCR is higher • Typically target higher inductance  higher coupling  higher efficiency (for inductive) • Typically, more turns on smaller shield requires smaller diameter wire to be used  DCR is higher • Higher “u”, lower Bs material is used in order to boost inductance • Typically have height restriction  higher wire gauge, thinner shield • Current levels are usually lower  Rac not as critical • Q winding diameter  Q is lower (key to magnetic resonance)
  33. 33. Multiple Winding Coils
  34. 34. Wireless Power Summit - 2013 Dual Mode Coils – The Latest Trend • • • • • • WPC + PMA (Dual Mode coils) WPC and/or PMA + resonance WPC and/or PMA + resonance + NFC (13.56 MHz) WPC or PMA + NFC (Combo coils) WPC + PMA can use same shield material, issue on resonance caps WPC or PMA + resonance, issue on optimizing shield material at 100300 KHz and 6.78 MHz. One or both may be reduced in efficiency. Dual Mode Coils Combo Coils
  35. 35. TDK’s Wireless Power Products
  36. 36. Wireless Power Summit - 2013 What is TDK Capable of Doing? • Supplier of ferrite, powdered iron and polymer cores/shields for: • Inductive applications (WPC, PMA, others) • Resonant applications (A4WP, others) • Supplier of coil assemblies (shield + windings) • Standard and custom for low power (up to 20W currently) • Wire and PCB based coils • Supplier of dual mode (WPC+PMA or WPC or PMA + resonant coil) and combo coils (WPC or PMA + NFC) • Supplier of materials • Ferrite “tiles” which are glued/pieced together to make large sheets (up to the KW range) • Shields for applications where the windings are in other format (flex circuit, PCB, etc.) • Supplier of complete modules
  37. 37. Wireless Power Summit - 2013 Custom Coil Assemblies Custom coils will be considered on a case by case basis, depending on many business factors. TDK is current supporting:       WPC applications PMA applications A4WP applications Witricity PowerByProxi Others

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