Previous studies have shown that not only are piezoelectric materials feasible for energy
harvesting, they are feasible as an energy harnessing medium in shoes during walking.
Continuing in that vein, this thesis provides new designs to better apply mechanical stress
and achieve higher power output. Two points of stress during walking were used for
energy harvesting. 1.) The heel of the shoe, for when a person’s foot first lands on the
ground during the initial stage of the step. 2.) The ball of the shoe, for the curling
motioning of the foot as the person propels forward finishing a step.
A flexible, multilayered insole was developed for the ball of the shoe operation and
integration into the sole of a specially selected “street shoes”. The insole consists of six
layers of PVDF sheets, three sheets per side, adhered to a thick but flexible Nylon core.
The PVDF absorbs the mechanical compression or tension stress, depending on the side they are on, thereby creating a charge differential across the surface of each sheet. A
rigid, reversed clamshell piezoceramic transducer was developed and integrated into the
heel of the same shoe. The insert consists of two Thunder PZT unimorph connected in parallel and mounted inside a steel housing to facilitate optimal force transference. The inherent capacitive property of the piezoelectric materials and its very low frequency
of operation (~ 1Hz or 1 step per second), allows for very little current to be extracted through conventional full-wave rectifier harvesting circuit. Due to previous research
success with resonating an inductor in series with the piezoelectric source, an energy
harvesting circuit coined “Synchronized Switch Harvesting on Inductor” SSHI was
utilized to increase power output. However, due to the inability to correctly synchronize
the switching circuit and lack of proper piezoelectric source modeling, SSHI circuit only
provided marginal improvement in power output ~10-20% as oppose to previous study
demonstrating 250%+ output. Nevertheless, by using only full-wave rectifier harvesting
circuits, the new PVDF insole and PZT insert designs have propelled harvestable energy
to 11-13mW from one shoe, with a combined generation of 22-26mW for both shoes.