The search for a clean, reusable source of energy has caused a spike in interest in the exploration of piezoelectricity. Further research into its uses has significantly increased in the last few years.
Piezoelectricity takes advantage of the charges in a piezoelectric crystal (such as quartz). An exerted force causes internal dipole moments and net positive and negative charges develop on each surface of the crystal. This voltage can be collected in batteries and several applications for piezoelectricity are already widely used, such as piezoelectric sensors, which use the produced voltage to output a display reading of the force exerted. [1]
Currently, smaller projects have been exploring new applications for piezoelectric energy. Numerous piezoelectricity nightclubs in Europe have sprung up in recent years, advertising their use of piezoelectricity-charged batteries to power their establishments. There are also efforts to create mobile energy sources with piezoelectric fabrics, allowing for energy to be collected from more than just footsteps-- including heartbeats, ambient noises, and airflow. [2] Furthermore, researchers are experimenting in harvesting piezoelectricity for bigger projects and could even turn ordinary highways and roadways into power stations. [2]
Piezoelectric materials are used to obtain energy from exerted forces or vibrations. The deformation of the material produces an internal dipole moment, which in turn, produces an electrical charge across its surfaces. This process is reversible -- when an electric current is run through the material, its shape also changes. The polarity of charge results in an alternating current (AC), which is then converted into direct current (DC). The converted current is then used to charge a capacitor or a battery, which can store the energy for later use. [3]
In 1989, LA times released an article: "Piezo: Tough Plastic With a Sensitive Side : Technology: A high-tech super-polymer is tough, clear, able to withstand harsh environments--and it can sing." Scientists believe piezoelectricity may one day harness the ocean's vast power. The L.A. Times article explained: "With [piezoelectric PVDF], electric current is what moves in and out. And because electricity can easily be shunted through wires and then to nearby or remote circuitry, the new plastic forms the heart of increasingly more sensors, switches and other devices." [4] Since then, the use of piezoelectric sensors has unmistakably increased. However, researchers have recently been looking to expand the use of piezoelectric materials beyond sensors and are extremely interested in storing the electricity produced.
The School of Materials Science and Engineering of the Georgia Institute of Technology in Atlanta, Georgia has presented research in harnessing the "energy from vibration or disturbance originating from footsteps, heartbeats, ambient noise and airflow" in order to "explore innovative technologies that work at low frequencies (such as <10 Hz) and that are based on flexible soft materials". [2] The researches have explored techniques that employ piezoelectric zinc oxide nanowires grown radially around textile fibers. Through brushing the nanowires on the entangled fibers, piezoelectric energy is created. The researchers have established a methodology for turning wind and body movement into energy through interactions with the fabric. [2]
Another project in Japan attempts to fully utilize the power of human movement. Rubber sheeting floor tiles embedded in front of ticket turnstiles contain piezoelectric mats, putting the 400,000 people that pass through Tokyo Station to good use. The same concept at the Shibuya Station, also in Tokyo, allows its patrons to contribute to the collection of energy; Soundpower Corp has installed a "Power Generation Floor" in the station and on an average weekday, 2.4 million passengers step over this floor. "'An average person, weighing 60 kg, will generate only 0.1 watt in the single second required to take two steps across the tile,' said Yoshiaki Takuya, a planner with Soundpower Corp. 'But when they are covering a large area of floor space and thousands of people are stepping or jumping on them, then we can generate significant amounts of power.' Stored in capacitors, the power can be channeled to energy-hungry parts of the station, he said, including the electrical lighting system and the ticket gates." [4]
The use of piezoelectricity for sensors is widely accepted; however, doubt still remains concerning its efficiency as a direct source of energy. Because of the sheer amount of force it takes to generate a very small amount of electricity, many believe that piezoelectricity will never have large-scale applications. However, in examples like the train stations in Japan, the individually insignificant footsteps of people add up to enough electricity to power the lighting systems and gates. It would seem this potential is too great to ignore -- and that future research into piezoelectricity as a prospective power source is well worth the effort.
© Brenda Ou. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] J. Fraden, Handbook of Modern Sensors: Physics, Designs, and Applications, (Springer, 2004).
[2] Y. Qin, X. Wang and L. W. Wang, "Microfibre Nanowire Hybrid Structure for Energy Scavenging," Nature 451, 809 (2008).
[3] I. Amato, "Piezo: Tough Plastic With a Sensitive Side," Los Angeles Times, 4 Dec 89.
[4] J. Ryall, "Japan Harnesses Energy from Footsteps," The Telegraph, 12 Dec 08.