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Shoe Power

Shoe Power. Ville Kaajakari Louisiana Tech University 2009. Human power. Walking P out = 30 W. Wheelchair P out = 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.

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Shoe Power

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  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

  3. Nike + iPod Sport Kit: do you want to charge your shoes periodically?

  4. Desired properties for a shoe power generator • - 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). Ideal transducer is: Power generator

  5. Integrated transducer and rectifier/regulator Polymer transducer Rectifier and regulator. Efficiency > 70% demonstrated Size reference Factory installed shock absorber. Power generating shock absorber.

  6. 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. First shoe prototype with integrated power generator Power per step: 3 mJ

  7. LED demonstration

  8. 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.

  9. C1 C2 Control P = 0.2 mW Wake up P = 10 µW CN 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 0.7 0.6 0.5 Efficiency 0.4 0.3 0.2 0.1 0 0 1 2 3 4 5 6 Load voltage [V} Energy stored in a battery or supercapacitor (Dr. Scott Gold)

  10. 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

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