Tutorial #103
George Riley
April 2010

A recent nanotechnology breakthrough at Princeton University generates useful amounts of electricity from bodily movements.[1] Potential applications vary from medical implants to mpegs. One such application may provide power for the long-awaited ultimate cell phone.

Background

The electricity is generated by piezoelectric ceramics of lead zirconate titanate (PZT), a high-efficiency piezoelectric material developed in the early 1950s. Piezoelectric materials have dipole crystalline structures which generate an electric potential when mechanically stressed by flexing.

They were discovered in the late 19th century, and since then have served diverse uses ranging from SONAR systems to cigarette lighters. Recent applications include sparks for lighting gas-fired barbeque grills, and ultrasonic obstacle detectors for automobiles.

Problem

The challenge of powering piezoelectrics by internal bodily movements is suitable packaging. The packaging must be flexible enough to bend readily under bodily movements; the packaging must be both bio-safe, to protect the person, and impermeable, to protect the sensor.

Solution

Unfortunately, packaging materials such as rubber and plastics that meet those requirements cannot survive the extremely high temperatures required to crystallize high-output PZT. Fortunately, Professor Michael C. McAlpine and his colleagues at Princeton recently announced an elegant solution.[2]

The PZT is formed in a series of parallel nano-thickness ribbons deposited upon a rigid magnesium oxide substrate. This material has a melting point of 2,852°C, well suited to high-temperature processing. The ribbon form is advantageous, since the power generated is proportional to the length of the PZT.

The substrate is next etched away, and the ribbons are transferred by printing onto silicone rubber sheets, which are both flexible and biocompatible. Conductive leads are deposited on the crystal ribbons to collect and carry away the current.

A second layer of silicone rubber protects the top side of the PZT. Figure 1 shows a sample of silicone rubber with printed ribbons of PZT.

Figure 1. Piezoelectric ribbons on silicone rubber. (Courtesy of Princeton University)

Potential Applications

Applications for flexible energy conversion from bodily motion include both external uses, such as generating electricity for cell phones, and internal uses, such as powering pacemakers or other medical devices.[3]

The Nano Letters abstract states that this technology   ”… may enable a host of exciting avenues in fundamental research and novel applications.”

References

1. Princeton University News Release, “Energy-harvesting rubber sheets could power pacemakers, mobile phones,” posted January 28, 2010; 0127 p.m.

2. “Piezoelectric Ribbons Printed onto Rubber for Flexible Energy Conversion,” Yi Qi, Noah T. Jafferts, Kenneth Lyons, Jr., Christine M. Lee, Habib Ahmad and Michael C. McAlpine, Nano Letters 2010, 10(2), pp 524-528, January 26, 2010

3. “Move Your Body, Power Your Cellphone,” Henry Fountain, New York Times, March 2, 2010.