Preface

Abstract

Preface The concept of smart materials was conceived in the 1980s due to the requirements of advanced performance and built-in intelligence for modern mechanical systems. Since then, the study of intelligent material systems and structures has become a very active research area in engineering and science. Across the wide spectrum of engineering materials, a number of them are considered to be `smart' in the literature. Typical examples include shape memory alloys (SMA), piezoelectric ceramics (PZT) and polymers (PVDF), magnetostrictive (MS) and electro/magneto-rheological (ER/MR) materials. In particular, piezoelectric materials perform relatively well in both sensing and actuation. Therefore, this type of material has attracted substantial attention from researchers in academia and industry. In recent years, it seems that research on piezoelectric materials within the realm of smart materials and structures has been overwhelmingly focused on the analysis of structural control. In fact, there are many other mechanical systems using piezoelectric materials as sensors and actuators. Typical examples are acoustical and ultrasonic devices. However, such applications are usually studied by researchers in physics and electrical engineering and may not be known to colleagues working in the area of smart materials and structures. In view of this, a special issue on piezoelectric actuators was proposed. The main theme of this special issue is ultrasonic motors. The ultrasonic motor earned its name from operating in the ultrasonic frequency range. The mechanisms for motion are structural vibration and mechanical friction. The major advantages of ultrasonic motors include: low-speed/high-torque performance, compact size and low noise. Both rotary and linear motors can be implemented. The earliest version of an ultrasonic motor was invented in the 1970s. Since the introduction of a newer generation driven by travelling waves in the 80s, ultrasonic motors have gained considerable interest from industrialists, especially in Japan. In addition to ultrasonic motors, a few other piezoelectric actuators and related subjects are included in this special issue. The contributed papers may be classified into the following four categories: Introduction and overview Design, development and system characterization Materials, mechanics and analysis Engineering applications Since diversity is another objective of this special issue, the papers were sought from nine different countries/regions to cover various applications. The Editor of this issue wishes to thank all authors who contributed papers and all reviewers for their hard work. Appreciation is also due to the Editor-in-Chief, Professor Vijay K Varadan, for his continuous support and encouragement. The assistance of Ms Debra Witherite is also acknowledged. It is our intention to make this special issue a comprehensive and informative reference to researchers in related fields. It would be our best reward to see colleagues in the community of smart materials and structures expand their research horizons in the near future. S-W Ricky Lee Guest Editor Department of Mechanical Engineering Hong Kong University of Science and Technology