CONFORMAL WIRELESS
BATTERY PROJECT
SD1003
Advisor:
Ben Braaten
Team members:
Casey Brossart
Chris Pickett
Matt Lommen
Matt Sandbakken
Summary
Problem Requirements Design Impedance Matching Testing Power requirements Budget
The Problem
Charging a battery without being hooked into the grid.
Why Wireless?
Environmental Considerations Mobility Energy Costs
Requirements
Design a wireless battery charger Operate at 2.4 GHz Create a DC output voltage Uses high frequency laminate
Block Diagram
Voltage Doubler
Uses configuration capacitors and Diodes
Rectifies AC input to DC output
Voltage Doubler Workings
Schematic
Lommen’s Microstrip Calculator
Allows all active components to be mounted on the top side of the board
Susceptible to cross-talk and unintentional radiation Calculates W or Z0 given H and εr
Important to match the characteristic impedance of microstrip line to that of the source. Maximum power is delivered Improves signal-to-noise ratio Reduces amplitude and phase errors
Initial Design
Impedance Matching (Tuning)
Z0 ZL
Matching Network
Impedance Matching (Tuning) Normalizing the impedance:
zL=ZL/Z0
We assumed ZL=15-j150We assumed Z0=50zL=0.3-j3
Impedance Matching (Tuning)Note that zL lies outside the 1+jx circle on
the Smith Chart. Because of this, the following configuration for the matching network should be used.
Impedance Matching (Tuning)
X=±[RL(Z0-RL)]^(1/2)-XL
B=±{[ (Z0-RL)/RL]^(1/2)}/RL
Two solutions possible for both B and XPositive X implies an inductorNegative X implies a capacitorPositive B implies a capacitorNegative B implies an inductor
Impedance Matching (Tuning) For positive values
jX=jωLjB=jωC
For negative valuesjX-j/ωCjB=-j/ωL
Test Board
Trial and Error
4.5pF (4 - 1pF + 0.5pF in parallel) 10pF 0.5pF 2.864 -10.24.5pF (4 - 1pF + 0.5pF in parallel) 10pF 5pF 2.75 -6.674.5pF (4 - 1pF + 0.5pF in parallel) 5pF 5pF 2.761 -7.174.5pF (4 - 1pF + 0.5pF in parallel) 5pF 20pF 2.747 -8.67open 5pF 20pF 2.06 -5.15open 5pF 10pF 2.114 -7.54open 5pF 5pF 2.154 -18.59open 5pF 2pF 1.648 -4.01open 10pF 10pF 2.027 -9.42open 20pF 10pF 1.999 -9.495pF 10pF open 2.63 -11open 10pF 5pF 2.09 -22.111nH 10pF 5pF 2.1897 -20.3211nH 5pF 5pF 2.26 -32.111nH 2pF 5pF 2.485 -6.9711nH 3pF 5pF 2.4 -14.1
PI Network Center Freq dBTrace to GND (doubler side) Trace in Series Trace to GND (antenna side) (GHz)
Trial and Error Results
Power Requirements
Power Requirements
Attenuation (dBm) Attenuation (mW) Potential across LED (V)2.4 GHz 2.45 GHz
-2 0.630957344 1.449 1.404-1 0.794328235 1.536 1.4990 1 1.619 1.5741 1.258925412 1.648 1.6252 1.584893192 1.669 1.6533 1.995262315 1.685 1.6764 2.511886432 1.702 1.6925 3.16227766 1.714 1.7079 7.943282347 1.763 1.766
Using the 11nH - 3pF - 5pF matching network
Power Requirements
Friis Transmission Equation
Project Status
Project Status
Tasks remainingRefine impedance matching techniquesVerify operation with antenna installedCharge a AAA batteryExplore flexible substrates
TimelineWant to be charging a battery within the first
4 weeks of next semesterFlexible substrates are a secondary
objective
Budget
Part Quantity Retail CostExpected
CostTotal Cost Notes
AAA Rechargable NiMH Batteries
2 packs (8 batteries)
$10.88/pack $10.88/pack $21.76 Walmart;
Energizer
AA Rechargable NiMH Batteries
2 packs (8 batteries)
$14.84/pack $14.84/pack $29.68
Walmart; Battery Biz
Total $51.44
Part QuantityRetail Cost
Expected Cost
Total Cost Notes
2.4 GHz wireless-G router 1 $41.99 $41.99 $41.99
Ebay
Capacitors (.1pF to 150pF)
750 (various sizes) $83.65 Digikey/
Mouser
Inductors (11nH) 20 $6.01 Digikey
RF Detector 4 VBR 0.3 pF 100 $0.68 $0.68 $68.00
Mouser
Mica 2.4 GHz SMD Antenna 5 $11.20 $11.20 $56.00
Antenova
Rogers duroid 5880 1 sheet $0 $0 Provided
by BenTotal $255.65
Remaining Purchases
Summary
Two PCBs createdInitial prototype including antennaTest board including SMA input
Impedance matching completedNeed to refine this processNeed to incorporate antenna
