Piezoelectric Powershoe Insert

Piezoelectric Energy Scavenging In Shoes
Joe Paradiso, Nate Shenck

Goal: To develop a rugged piezoelectric shoe insert and complementary conditioning electronics for unobtrusive, parasitic harvesting of the compression energy normally lost while walking....

Energy is readily available at two locations in a shoe.

Layup.GIF (3106 bytes)

Curvature and relaxation at the ball of the foot, and Heel strike displacement at the heel cup

Previous ML demonstrations of Energy Scavenging in the Shoes:

PVDF_stave.GIF (45611 bytes)

The Media Lab PVDF flexible film stave

THUNDER(tm) PZT unimorph with power conditioning electronics, 12-bit encoder and RFID transmitter

The implants are unobtrusive and do not affect the gait of the bearer. They generated 20-80 mW of peak power (1-2 mW average) during brisk walk and were demonstrated in a low-power, wireless application:

Store charge over several footsteps
When capacitor full, discharge through:

regulator, 12-bit encoder, 310 Mhz ASK transmitter

Transmits 12-bit digital RFID from shoe to vicinity every 3-5 steps
Enables smart building to track occupant location

Work continues... ML working with TTT consortium member, Draper Laboratory:

Develop a rugged, self-contained insert
Efficient conditioning electronics

Undetectable and interchangeable when imbedded in an insole package:

Bimorph Insole from below

A bimorph PZT design, connected in parallel, doubles the source power and cuts source impedance.

Power measurements at 1.1 Hz

Power conditioning: Must regulate very high-voltage, low-frequency, micro-power, capacitive source... "Direct Discharge" is lossy

High-frequency switcher ---> to "impersonate" an impedance match
Step-down transformer ---> keeps the high side high (E=1/2CV²)!!
Super-high impedance sensing of primary waveform ---> sleep cycle
Bootstrapping

Hybrid "Forward-Converter" topology

This work in progress; thesis will be completed in early May '99.