A demonstration of useful electric energy generation from piezoceramics in a shoe

Abstract

The feasibility of harnessing electric energy using piezoelectric inserts in a sport sneaker has been demonstrated. Continuing in that spirit, this thesis compares regulation schemes for conditioning the electric energy harnessed by a piezoceramic source imbedded in a shoe insole. Two off-line, dc-dc direct converter hybrids (buck and forward) are proposed and implemented to improve the conversion efficiency over previously demonstrated conditioning schemes. A rigid, bimorph piezoceramic transducer was developed and integrated into an off-the-shelf orthopedic insert. The insert consists of two THUNDER™ PZT unimorphs connected in parallel and mounted on opposing sides of a Be-Cu backplate. The bimorph absorbs the energy of the heel strike and lift during walking, thereby inducing a charge differential across the faces of the PZT. The energy stored in this charge is removed at its peak and converted into a useful form using a high-frequency switching technique. The power conditioning circuitry consists of the following stages: Rectification, high-frequency switching (and step-down transformation), CMOS "555" timing and switcher control, low-side output filtering, load stage on/off control, and output regulation. Finally, it is important to note that, although the proposed conditioning scheme was designed for the transducer developed herein, it could be applied to any similar low-frequency, piezoelectric source.