Interdisciplinary team from three universities will seek to create “piezoelectrics on steroids.”
Artificial limbs that can perform a variety of complex tasks by more closely mimicking natural movement and levels of strength and high-tech military equipment powered by every step a soldier takes are just two of the many innovations that may arise through the work of a research team based at the University of Houston Cullen College of Engineering.
The group is led by Mechanical Engineering Professor Pradeep Sharma and consists of Ramanan Krishnamoorti of the Cullen College’s Department of Chemical & Biomolecular Engineering, Boris Yakobson of Rice University, and Zoubeida Ounaies of Texas A&M University. Together they have been awarded a $1.22 million grant from the National Science Foundation to develop a novel class of meta-materials that, like piezoelectrics, generate electricity when placed under physical stress, even though none of the constituent materials are themselves piezoelectric.
Naturally occurring, piezoelectrics generate an electrical charge when placed under stress such as bending or pushing. If exposed to an electrical charge, they will develop stress that could lead to movement if the system is unconstrained. They are widely used in high-tech applications ranging from military, medical and aerospace devices to more common consumer products. Cellular telephones, for example, rely on piezoelectrics for their vibrate function.
Natural piezoelectric materials, while plentiful, have their limits—there are only a few types of such materials, each with a set percentage at which they convert mechanical energy to electrical energy (and vice versa). In general, if an application requires level of energy conversion not found in these materials, a composite consisting of piezoelectrics and non-piezoelectrics must be made. Often these composites, while functional, are not ideal for the tasks they are assigned.
Using a theory inspired from related works by researchers from Penn State University and developed by Sharma, however, this team of researchers, utilizing nanoscale effects, will combine a soft dielectric material (materials that are natural insulators) with other harder materials (such as ceramics) in such a way that, like piezoelectrics, they yield an electrical charge when put under stress.
This is made possible, Sharma said, because of the scale at which the researchers will be working. At the nano-level, where one nanometer equals 1 billionth of a meter, certain properties of materials are more pronounced, while others are suppressed.
“The real applications of this technology are going to come from the fact that you don’t have to depend on existing piezoelectrics,” Sharma said. “You can create materials, using certain nanoscale effects, that give higher energy conversion. These are basically piezoelectrics on steroids.”
One possibility application of these piezoelectrics is in the next generation artificial limbs. Using existing piezoelectrics, it is difficult to construct prosthetics that offer a full range of motion and are strong enough to lift heavy objects or support a large amount of weight. The highly customizable piezoelectrics being developed by this research team could enable the creation of prosthetics that come closer to offering both the flexibility and the strength of real limbs.
These materials could also find use in military applications. A strip of these new piezoelectrics placed in the boot of a soldier would generate electricity with every step. That energy could be used to power the increasing number of devices with which individual soldiers are equipped.
Other possible applications could involve putting these new piezoelectric materials in a roadway and generating electricity from the pressure of automobiles riding over them; the development of actuators (devices that open and close when exposed to an electrical current) that are much more sensitive and able to make small adjustments to the size of their opening; and medical diagnostic tools that can determine not just the presence of a pathogen, but also the concentration.
“We’re getting rid of nature’s limitations on piezoelectrics,” said Sharma. “Nature has given us just a couple of these materials. With this method we can design specific properties, making them much more effective. We can fine tune it to meet certain needs.”