Tokyo Tech News
January 31, 2010
Miniaturised ultrasonic motors (USMs) driven with piezoelectric ceramics could soon be used to operate the zoom lenses of small digital cameras in mobile phones. They are superior to other motors in the mini-motor area because their efficiency is not affected by their size, but most USMs in the market are driven with ceramics called lead zirconate titanates (PZTs), which contain more than 60 % lead by weight.
In order to protect the environment, it is hoped that the lead-based ceramics in USMs could be replaced by lead-free ceramics. However, the piezoelectric properties of lead-free ceramics may not be sufficient to drive certain systems, in particular the traditional, so-called longitude mode (d33) applications.
Now, Takaaki Tsurumi and colleagues at Tokyo Institute of Technology have successfully made ultrasonic motors driven with lead-free piezoelectric ceramics, by using a different mode called the shear mode (d15).
The motors were fabricated by a three-step process. Firstly, the researchers designed the shear mode USMs, using finite element analytical software for modeling and simulation to decide on the optimum design. Then, they studied the crystallography of lead-free ceramics in order to learn how to enhance the shear mode and choose the ceramics with the best properties. Finally they built and tested the shear mode USMs.
The researchers successfully made three kinds of USMs driven with lead-free ceramics using the shear mode, and achieved a highest speed of 486 revolutions per minute. Their work reveals both academic and practical insights into the shear mode of lead-free piezoceramics. It provides a possible basis for actual application of lead-free piezoceramics as replacements for lead-based PZT ceramics, thereby helping to protect the environment.
Figure caption: A miniature ultrasonic motor (USM) built using lead-free ceramics.
Graduate School of Science and Engineering Metallurgy and Ceramics Science