Transcript Slide 1

Shoe Power
Ville Kaajakari
Louisiana Tech University
2009
2
Human power
Walking
Pout = 30 W
Wheelchair
Pout = 20 W
•We can “parasitically” take 1% of the human power without
noticeable effect.
•With 33% conversion efficiency, this translates to 100 mW of
electrical power
Ville Kaajakari, Louisiana Tech University
3
Nike + iPod Sport Kit:
do you want to charge your shoes periodically?
Ville Kaajakari, Louisiana Tech University
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Desired properties for a shoe power generator
Ideal transducer is:
- Low cost and ecological (plastic)
- Soft for shock absorption
- Simple design. No complex bimorphs.
- Piezoelectric (no voltage bias needed)
- Light weight (6 g)
- Output measured in voltages and
milliwatts (and not millivolts
and microwatts).
Power generator
Ville Kaajakari, Louisiana Tech University
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Integrated transducer and rectifier/regulator
Polymer
transducer
Rectifier and regulator.
Efficiency > 70%
demonstrated
Size
reference
Factory installed shock absorber.
Power generating
shock absorber.
Ville Kaajakari, Louisiana Tech University
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First shoe prototype with integrated power generator
Power per
step: 3 mJ
• DC rectified power output
deliver to a storage capacitor.
• Substantial power output
demonstrated with average
power output being 2 mW per
shoe.
• Further optimization possible
to obtain higher powers.
• Steps can be detected for zero
velocity updating for more
accurate IMU.
Ville Kaajakari, Louisiana Tech University
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LED demonstration
Ville Kaajakari, Louisiana Tech University
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Power conversion challenge
• Piezotransducer is a high impedance source
=> high voltages (50-500 V) but low currents
(~100 μA) are generated
• Applications require low voltage (~3 V) and
modest current (1-10 mA)
• No commercial converters available:
– Inductor based “buck” converters work for
transformation ratios up to ten. Efficiency drops
quickly for higher transformation ratios.
– Point of reference: MIT demonstrated 17.6% efficiency
for their shoe power generator.
Ville Kaajakari, Louisiana Tech University
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Results on power converter
Charge cycle
70% efficiency demonstrated for
conversion from 120 V to 3.5 V!
Input current
Load cycle
0.8
Output current
Efficiency
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
C1
0
V1  100 V
C2
Wake up
P = 10 µW
Control
P = 0.2 mW
CN
V1
N
 3V
V2 
1
2
3
4
5
6
Load voltage [V}
Energy stored in a battery or
supercapacitor (Dr. Scott Gold)
Ville Kaajakari, Louisiana Tech University
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Conclusions
• Low cost shoe power generator has been
demonstrated.
• Current prototype demonstrates 2 mW of power.
• Custom power regulation circuit with high
effieciency.
• Future research focused on:
– Non-shoe applications
– Film optimization and more efficient rectifier/regulator
– Commercialization
Ville Kaajakari, Louisiana Tech University