抄録
Our 21st century will face to a sustainable society, which requires
(a) usage of non-toxic materials,
(b) disposal technology of existing hazardous materials,
(c) new energy source creation, and
(d) energy-efficient device development.
Electric components such as motors and transformers are mostly based on electromagnetic transduction at present. With reducing their size (power level less than 30W), these electromagnetic components reduce their efficiency drastically due to the Joule heat in the thin coil wire (i.e., the resistivity in the coil becomes significant). Thus, piezoelectric actuators and transducers having much less losses are highly focused in the 21st century. In the past 30 years, most of the researches have concentrated on realizing higher displacement and electromechanical coupling factors from the piezoelectrics. An example from this approach created single crystals based on Pb(Zn1/3Nb2/3)O3-PbTiO3, which was discovered by our group, and now have become widely researched for medical and underwater applications.
Piezoelectric devices seem to be all-around contributors and a key component to the above mentioned four R&D areas in the sustainable society. Some of the efforts include:
(a) Since the most widely used piezoelectric lead zirconate titante (PZT) ceramics will be regulated in less than 10 years in Japanese and European communities 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 be easily 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) We demonstrated an energy recovery system on a hybrid car from its engine's mechanical vibration to the fuel cell for electric charging. Also, a self-powered remote light switching system has also been developed using piezoelectric bimorphs.
(d) 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.
The key problem in the novel piezoelectric materials and the above four application devices from the high power's viewpoint is found in heat generation, which limits the generative energy density, leading to limited compactness and lower efficiency of the devices.
