Microstructured piezoelectric shoe power generator outperforms batteries

by Ville Kaajakari, Ph.D.
Assistant Professor, Louisiana Tech University

Energy harvesting is an attractive way to power MEMS sensors and locator devices such as GPS; however, the power harvesting technologies often fall short in terms of power output.  For example, vibratory MEMS generators might give out only microwatts of electrical power.  While this may be sufficient for emerging ultra low power sensors, many current applications require milliwatt power levels.  As an example, commercially available running sensors for shoes consume over 100 uW of electrical power and requirements for GPS locators are even higher.

Piezoelectric transducers generate electrical charge when compressed.  This makes piezoelectric materials especially advantageous for power harvesting as they do not require bias voltage for operation.  In principle, a piezoelectric transducer together with two rectifying diodes is sufficient for generating dc output voltage.

The shoe power generator that our group has developed is based on a low-cost polymer transducer that has metallized surfaces for electrical contact.  Unlike the conventional ceramic transducers, the plastic-based generator is soft and robust matching the properties of regular shoe fillings.  The transducer can therefore replace the regular heel shock absorber with no loss in user experience.

A significant challenge in harvesting piezoelectric energy is that piezoelectic materials are optimal for generating high voltages but provide only a low current output.  The polymer used in the shoe transducer provides over 5 mJ of energy per step but at voltages too large (>50 V) to be directly used in low power sensors.  A breakthrough in piezoelectric power generation is the new voltage regulation circuits that we developed at Louisiana Tech University that efficiently converts the piezoelectric charge into a usable voltage.  A conversion circuit coverts the high voltage to a regulated 3 V output for charging batteries or for directly powering electronics at better than 70% conversion efficiency.  Combined with the polymer transducer, the regulation circuit gives time-averaged power of 2 mW per shoe during a regular walk.

The generated power output can be compared to typical storage capacity of 30 mAh for lithium coin/button cells -- with an average current consumption 0.5 mA, a miniature coin cell is depleted in less than three days whereas the shoe power generator gives power output as long as the user keeps walking.  The total energy output can therefore easily surpass conventional batteries.  In addition to running sensors and inertial navigation, the show power generator can be used to power RF transponders, GPS receivers, and locator tags that require a milliwatt power source.

Copyright 2010 MEMS Investor Journal

Comments

[Polaris1927]

What a great invention based on piezoelectricity. It goes to show that people like yourselves continue to enhance the discoveries of the great Pioneers like the Curie brothers.

May your tribe increase!

[SVE]

Wow this is great. We could charge all our home appliances while walking around the house, thereby getting rid of our nasty electric bills!

[s.kathirvel]

great invention
a little further it can be used to power an e-scooter both wheels as shoes at 45kms it will produce more power connection to charger is not that problem so many ways available

[R Bhosale]

Question really is - how does one store this power generated? Or supply to devices? I guess you will need to plug in a battery into your shoe and charge it or have cables running from the shoe to your pockets?
Same goes for the car - how do you transport this energy generated from the Tires to the battery or any other device for that matter?

I think embedding these devices into a road makes a lot sense too!

[darshan]

can we charge mobile by this?
which specific crystals are used for this purpose?
please give some technical details for this.

[DrBill3]

Just a reality check...The energy needed to charge all your home appliances by walking around would be far greater than would be required by simply doing the house work by hand.

[aditya]

sir can these devices implement on floors to store large amount of energy if yes please guide me as i am curious to work upon it.

[Stu Burroughs]

Is it possible to buy one of these shoe generators?