Piezoelectric Devices for Sustainability Technologies

Abstract

Our 21st century will face to a “sustainable society”, which requires (a) usage of non-toxic materials, (b) disposal technology for existing hazardous materials, reduction of contamination gas, (c) environmental safety monitoring, (d) new energy source creation, and (e) energy-efficient device development. Electric components such as motors and transformers are mostly based on electromagnetic transduction at present. With reducing their size, these electromagnetic components reduce their efficiency drastically due to the Joule heat in their thin coil wire. Thus, piezoelectric actuators and transducers with much less losses are highly sought after in the 21st century. Piezoelectric devices seem to be all-around contributors and key components to the above mentioned five R&D areas in the sustainable society. Some of the efforts include: (a) Since the most widely used piezoelectric lead zirconate titanate (PZT) ceramics will be regulated in less than 10 years in the world due to their toxicity (Pb2+ ion), lead-free piezoelectric ceramics based on (K,Na)(Ta,Nb)O3 and (Bi,Na,Ba)TiO3 have been developed with performance equivalent to the PZTs. (b) Since hazardous organic substances such as “dioxin” can easily be dissolved by the irradiation of ultrasonic energy in water, a new technology for safe disposal of dioxin using high-power piezoelectric transducers has been developed. (c) Similar to radio-active rays, magnetic rays may also increase the brain cancer patients. Thus, sensitive environmental magnetic noise detectors with magnetostrictive-piezoelectric composites have been developed. (d) We demonstrated an energy recovery system on a hybrid car from its engine’s mechanical vibration to the fuel cell for electric charging. A self-powered remote light switching system has also been commercialized using piezoelectric bimorphs. (e) Micro ultrasonic motors based on piezoelectrics demonstrated 1/20 reduction in the volume and weight and a 20 time increase in efficiency of the conventional electromagnetic motors with equivalent output power. We also demonstrated compact and highly-efficient high-voltage supplies with piezoelectric transformers, which have been widely commercialized for laptop backlight inverter applications. After the piezoelectric fundamentals, this paper describes leading piezoelectric materials, devices, and drive/control methods, relating with the above “sustainability” technologies, aiming at further research expansion in this area.