Actuator Materials

There are five key trends in the recent development of actuator materials: “Performance to Reliability”, “Hard to Soft”, “Macro to Nano”, “Homo to Hetero” and “Single to Multi-functional”. First of the materials trends, the worldwide toxicity regulation is accelerating the development of Pb-free piezoelectrics as a replacement for conventional PZTs. Second, high power piezoelectrics with low loss have become a central research topic from the energy-efficiency improvement viewpoint; that is to say, “real (strain magnitude) to imaginary performance (heat generation reduction)”. Third, we are facing a revival of the polymer era from the 1980s because of its elastically soft superiority. Larger, thinner, lighter and mechanically flexible human interfaces are a current necessity in portable electronic devices, leading to the development in elastically soft displays, electronic circuits, and speakers/microphones. Polymeric and polymer-ceramic composite piezoelectrics have been revived and commercialized. PZN-PT or PMN-PT single crystals have become a focus due to the rubber-like soft piezo-ceramic strain after 40 years of discovery. In the MEMS/NEMS area, piezo MEMS is one of the miniaturization targets for integrating piezo actuators in a micro-scale device, aiming at bio/medical applications for maintaining human health. “Homo to hetero” structure change is also a recent research trend: stress gradient, in terms of space, in a dielectric material exhibits piezoelectric-equivalent sensing capability (i.e., “flexoelectricity”), while electric-field gradient, in terms of space, in a semi-conductive piezoelectric material can exhibit bimorph-equivalent flextensional deformation (“monomorph”). New functions can be realized by coupling two effects. Magnetoelectric devices (i.e., voltage is generated by applying magnetic field) were developed by laminating magnetostrictive Terfenol-D and piezoelectric PZT materials, and photostriction was demonstrated by coupling photovoltaic and piezoelectric effects in PLZT. This “Actuator Materials” Section provides various new or improved materials’ information to the whole actuator community.

Keywords

• piezoelectrics
• magnetostrictor
• shape memory material
• elastomer
• composite
• strain hysteresis
• material loss
• heat generation