Peizoelectricty is the property of some crystalline materials to generate an electric charge when they are mechanically stressed. The most familiar household application of piezoelectricity is in the gas lighter that you use to light up the cooking gas stove. In this, a spring loaded plunger strikes against a crystal, causing a spark across two electrodes. Another common example is a voice microphone. The pressure of breath on a diaphragm in the microphone causes an electric charge, that is amplified and reproduced through speakers. Peizolectricity was discovered by the French scientists Pierre and Jacques Curie in 1888. The peizolelectric effect is now very widely used in applications like sensors, transducers, medical equipment, inkjet printers etc. In the early days, the crystals used were the naturally occurring quartz or topaz. In recent times, higher potential piezoelectric ceramic crystals have been developed. Scientists and industrial researchers continue to look for new applications for peizoelectricity and are coming up with some interesting new applications for this renewable energy source.
1. Bright Walk illuminates your run on renewable energy
You are familiar with shoes for toddlers that light up and squeak, designed to encourage young children to start walking. In these, the power source is usually a small battery. Alberto Villareal, the Mexican industrial designer, has applied piezoelectricity into running shoes to illuminate the track at night. A piezoelectric sensor is mounted on the heel of the shoe and an electroluminous polymer patch is fitted to the sides of the shoe, that lights up when it gets an electric signal from the sensor on the heel. As the user runs or walks, the piezoelectric sensor generates electric pulses to make the polymer strip glow.
2. French sidewalk generates piezoelectricity to power street lights
The French city of Toulouse has installed 8 piezoelectric modules on a small stretch of a sidewalk, that produces 50-60 watts to power a street light. They adopted this technology from a Dutch company that has installed such modules on the dance floor of a nightclub where the foot impact of the dancers powers strobe lights and music amplifiers.
A similar idea has been tried out at Shibuya, a busy subway station in Tokyo, where a one square meter area at the exit from the station was embedded with piezoelectric sensors. The 900,000 people who walked over the sensors in a one month period generated some 56 kilowatts of power.
Piezoelectric power modules are also being tried out at the check-out counters of Sainsbury’s, the UK retail chain and are planned to be installed at a soccer stadium in Holland.
3. Powering an iPod with your heartbeat could soon be a reality
Scientists at the Georgia Institute of Technology have developed new nano-wire technology, that can generate electricity from very small movements such as the human heartbeat. These nano-wires are made from Zinc Oxide and have a thickness only slightly larger than the human hair. When worn on a person, the very small muscular movements made by the heartbeat or even blood flow is enough for these piezoelectric sensors to generate electricity. The expectation is that this nano-wire technology could, some day, produce enough power to recharge a mobile phone or an iPod. Perhaps of even greater interest would be to power medical devices like implanted pacemakers or a hearing aid.
The benefits
Peizolectricity is a renewable source of energy. The technology is already well-known and has been applied to many devices as noted above. The continuing application of this technology to new applications will push the envelope and perhaps lead to the discovery of new piezoelectric materials.
The increasing awareness of the importance of renewable energy sources should expand the application of piezoelectricity to more applications where you presently use disposable or rechargeable batteries.
The lowdown
The major problem with piezoelectric sensors is the low electric charge they produce. While these are good enough for applications in transducers and sensors, they are unlikely useful in the near term, to be applied for significant or continuous power generation applications. Since the mechanical force application is intermittent (as in the case of the side walk), there is need for a back-up energy source in most applications. The transducers are expensive and the performance also deteriorates with time.
The impact
Piezoelectricity will continue to be used in applications like transducers and sensors where the need is for sensing a mechanical force or displacement and not one for generating power. These applications should be expanded to reduce or eliminate the use of batteries, since spent batteries are already becoming an environmental concern.
Application as a renewable energy source appears to be distant.
