Adap%ve Impedance Matching for Magne%cally Coupled Resonators

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Brenda McKenzie
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1 Adap%ve Impedance Matching for Magne%cally Coupled Resonators Ben Waters, Alanson Sample, Joshua Smith University of Washington Department of Electrical Engineering Sensor Systems Research Group 1 PIERS 2012, Moscow 11/17/12

2 Sensor Systems Research Group Wireless Power WERL (Intel) WISP WARP FREE-D Robotics PR-2 Sensory Robotics Security New Sensors Electric Field Pretouch FiberFingerprint 2

3 Magne%c Resonance Coupling Technology 4-element systems High-Q resonators Volume charging Benefits Adaptation RF Amplifier Drive Loop Tx Coil Rx Coil Load Loop Load or Device Efficiency Orientation Range 3

Challenges with Adapta%on Techniques for Commercial Applica%ons Frequency tuning Technique: Dynamically control operating frequency for maximum S 21

4 Challenges with Adapta%on Techniques for Commercial Applica%ons Frequency tuning Technique: Dynamically control operating frequency for maximum S 21 Limitation: Frequency tuning exceeds government regulated bandwidths Critically Coupled Over Coupled Under Coupled Efficiency Distance (cm) Frequency (MHz) 4

5 Need for Adap%ve Impedance Matching Z MCR changes as a function of k 23 Z MCR and Z RECT have complex input impedance Z RECT changes as a function of input power and load condition Goal: Achieve constant efficiency behavior at a single frequency Tx Resonator Rx Resonator Z IN,SYS Z MCR Z RECT Z LOAD AIM Network AIM Network R S R L V S k 23 5

6 AIM Network Topology π-match Enables wideband impedance matching Additional degree of freedom from quality factor of matching network Desirable topology for switchable capacitor bank Critical Coupling Resonator Input 13.56MHz (Ω) # Under-coupled Over-coupled r S C S L m C L π-match AIM network R L + r L + jx jx L L k 23# 6

7 Enable Automa%c, Fast Switching Goals Pre-determine AIM network component values Define the impedance of each block in the impedance path Include as many non-idealities as possible Accurately model complete system performance Two methods explored Method 1: Ideal Conjugate Matching Algorithm Method 2: Parasitic Match Optimization Algorithm 7

8 Algorithm 1: Ideal Conjugate Match Overview 1. Calculate Z MCR for a range of k 23 Z MCR C 1 C 4 L m R S V S I 1 I 2 I 3 I 4 C S C L R L + C R p1 R 2 C 3 p2 R p3 R R L r S r L + jx p4 jx L L L 1 L 2 L 3 L 4 M 12 M 34 8 M Select inductor value L m for π-match network 3. Calculate Q M, C S, and C L for Z MCR at each k 23 Q M = 1+ r (r + r ) l l s + 2r r l l r s L 2 2 m ω L m2 ω 0 L m2 ω 0 C S = 1 r s ω 0 C L = Q M r l ω 0 r s (1+ Q 2 M ) 1 r l

9 Algorithm 2: Parasi%c Op%miza%on TX π-match MCRs RX π-match L π L π R S V S C S1 C L1 C S2 C L2 R L + jx L 1. Extract S2P parameters [Y] C S1 + r p [S] L π [Y] C L1 + r p [S] MCR [Y] C S2 + r p [S] L π [Y] C L2 + r p 2. Perform matrix transformations C S1 + r p L π C L1 + r p MCR C S2 + r p L π C L2 + r p 3. Multiply cascaded ABCD matrices R s System R L + jx L 4. Perform matrix transformation for system S-matrix with complex termination impedances [S] System 5. Apply constrained non-linear optimization algorithm to maximize S 21 9 [S 21,max ] C S1,2, C L1,2

10 Algorithm Comparisons 1. Ideal Conjugate Match Advantages Fast computation time Simulates ideal performance Disadvantages Topology-specific computations Neglects parasitic effects Less accurate match to experimental results 2. Parasitic Optimization Advantages Accurately models experimental results Easily accommodates new matching network topologies Disadvantages Slower computation time Difficult to perform live calculations 10

11 Model Results and Experimental Valida%on 50Ω Termination Impedances Ideal Conjugate Match Algorithm Parasitic Optimization Algorithm with overlaying experimental results 11

12 Single Sided vs. Double- Sided Matching At long range, every form of AIM outperforms frequency tuning At long range, no adapta%on and frequency tuning perform iden%cally 12

13 Effect of Inductor Selec%on Inductor selection in matching network can be used to achieve better performance for a specific WPT range. L M (nh) 13

14 Questions? Contact Thank You Sensor Systems Research Group University of Washington, Seattle WA 14

Lecture 14 Date:

Lecture 14 Date: 18.09.2014 L Type Matching Network Examples Nodal Quality Factor T- and Pi- Matching Networks Microstrip Matching Networks Series- and Shunt-stub Matching L Type Matching Network (contd.)