Several ways and means have been established for the conversion of mechanical energy into electricity, generally by way of electromagnetic induction, static-electricity generation, or piezoelectric materials. Vibration-based mechanical energy is ever-present in the environment and readily accessible. The harvesting of mechanical energy by piezoelectric materials, specifically, has seen increased focus in research of late, locally and abroad. The capability of piezoelectric materials to directly convert mechanical energy into electricity presents possibility for integration with other applications. Harvesting and converting mechanical energy could facilitate the operation of technology under environments in which other energy sources, such as solar or wind, are not available.
New technologies with adaptable functionalities and performance are essential. These new technologies require active and adaptive interactions between devices. Electricity generation and energy storage have always been two distinct processes that are achieved through separated physical units. Recently, the direct conversion of mechanical energy into simultaneously stored chemical energy has brought energy generation and storage together and resulted in integrated self-charging power cells. These can be charged up by mechanical deformation and vibration from the environment, providing an innovative approach for developing mobile power sources for portable electronics.
Lead zirconate titanate has always been the material that is used for mechanical energy harvesting. However, the fragile nature of ceramic and its fusion with lead creates several concerns, one being that it can break relatively easily. Unless this is controlled by dampening or pre-biasing, it can lead to rapid failure. Conversely, piezoelectric zinc oxide nanowires have demonstrated capacity in the harvesting of mechanical energy in various nanogenerator configurations. They exhibited potential as a sustainable, efficient and environmentally friendly power source.
Several piezoelectric products are manufactured and sold in South Africa. These include;
- piezo sensors – discs which sense velocity sensitive impact and/or can be wired as buzzers to play melodies;
- perimeter intrusion detection systems – piezoelectric acoustic sensor cable that detect the noises and vibrations that occur during an intrusion attempt. Piezoelectric sensor cable is applied to the fabric or structure being protected. Audible signals and vibrations generated during an attack are picked up by the sensor cable and converted into electrical signals;
- piezo switches – in contrast to conventional switches, they have no moving mechanical parts, making them extremely resilient and capable of enduring millions of actuations.
Research is ongoing in some academic institutions in South Africa as scientists seek to utilise piezoelectric energy. In an M.Eng Dissertation submitted to University of Pretoria, Department of Mechanical and Aeronautical Engineering, E.F. Williams explores the design and analysis of a practical large-force piezoelectric inchworm motor with a novel force duplicator. This technology is a new and novel embodiment for a piezoelectric utilisation. The essence of the emerging research and applications, using piezoelectric potential in new devices, relies on the coupling between strain-induced polarisation and semiconductor properties in piezoelectric semiconductor materials.
We expect piezotronics enabled technological advances in sensing, human-electronics interfacing, robotics, biomedical therapy, prosthetics, bioimaging, and optical microelectromechanical systems. Piezotronic nanodevices and integrated systems exhibit potential in achieving technology advancement that can deliver new solutions and enable increased capabilities.