Piezoelectricity—the charge that gathers in solid materials in response to strain—has piqued the interest of entrepreneurs and scientists alike.
A number of materials are piezoelectric, including topaz, quartz, cane sugar, and tourmaline. That means a charge begins accumulating inside these materials when pressure is applied. Piezoelectrics are already commonly used in a number of applications. Quartz clocks, for example, rely on piezoelectricity for power, as do many sensors, lighters, and actuators. But these are the old uses for piezoelectricity. Scientists today have much more interesting piezoelectric plans in mind.
One of the most popular uses for piezoelectricity in the past few years relies on roads and sidewalks. It all started in 2008 with Club Watt, a dance spot in the Netherlands dubbed the world's first sustainable dance club. The club installed piezoelectric materials in its dance floor to turn patrons' moves into electricity that is used to change the color of the floor's surface.
After Club Watt, the piezoelectric floors kept coming. A Tokyo railway station installed a piezoelectric floor that uses kinetic energy to generate 1,400 kW of energy per day—enough to power ticket gates and displays. Toulouse, France, recently became the first city to put pressure-sensitive piezoelectric modules on the sidewalk, generating enough energy to power streetlamps. And the United Kingdom plans to install power-generating tiles on London streets to light up bus stops and pedestrian crossings.
Piezoelectrics are also increasingly becoming common on roads. In 2009, a British supermarket installed kinetic road plates that collect energy from customers driving over road bumps in the store parking lot. The road plates are pushed down by vehicle weight, which creates a rocking motion that turns generators. The system is used to power the supermarket's checkout lines.
In Israel, a company called Innowattech is installing strips of asphalt embedded with piezoelectric materials. According to the company, the generators could produce 1 MWh of electricity from a four lane highway, or enough to power 2,500 homes.
The technology just keeps getting better, too. Last year, Princeton University researchers combined silicone and nanoribbons of lead zirconate titanate to create PZT, an ultra-efficient piezoelectric material that can convert up to 80 percent of mechanical energy into electricity. PZT is 100 times more efficient than quartz. It's so efficient, in fact, that the material could be used to harness energy from the minute vibrations found in items like shoes and clothing. That means a piezoelectric-equipped shirt could potentially charge up your cell phone after a day of activity.
Piezoelectric sidewalks, roads, and clothing items haven't taken off in a big way quite yet, but they probably will soon. As we become more reliant on having fully-charged gadgets with us at all times, a shirt or pair of shoes that can prevent a device from dying will be incredibly valuable.