Sumiaki Kishimoto

Miniature Cantilever-Type Ultrasonic Motor Using Pb-Free Multilayer Piezoelectric Ceramics

A Miniature cantilever-type ultrasonic motor was fabricated using multilayer piezoelectric ceramics (MLPC) made of (Sr,Ca)2NaNb5O15 (SCNN), a Pb-free piezoelectric material, and the electrical driving properties were investigated. The displacement of SCNN-MLPC was 177 nm at 100 V, which was 10-fold the voltage of MLPC made of Pb(Zr,Ti)O3–Pb(Ni,Nb)O3–Pb(Zn,Nb)O3 (PZT). The ultrasonic motor using SCNN-MLPC started to rotate at 3.8 Vp–p, and showed the following characteristics: a revolution speed of Ω0=517 rpm, a torque of T0=1.4 µN m, and an efficiency of η=7% at 13.4 Vp–p. The power consumption, in this case, was 0.3 mW, which is not so high. On the other hand, an ultrasonic motor of the same form made of PZT-MLPC showed Ω0=610 rpm, T0=1.6 µN m, and η=9% at 1.9 Vp–p, and the same power consumption as the SCNN motor. That is, it was found that the SCNN motor was not so different from the PZT motor in terms of their characteristics; however, the SCNN motor needed 10 times as high a voltage as the PZT motor in electrical driving. In conclusion, it can be said that we succeeded in realizing a miniature cantilever-type ultrasonic motor using Pb-free MLPC.

Double-Mode Miniature Cantilever-Type Ultrasonic Motor Using Lead-Free Array-Type Multilayer Piezoelectric Ceramics

We studied the following to improve the characteristics of the lead-free ultrasonic micromotor. A double-mode miniature cantilever-type ultrasonic motor was fabricated using array-type multilayer piezoelectric ceramics (A-MLPC) of (Sr,Ca)2NaNb5O15 (SCNN) such as lead-free piezoelectric materials, and the electrical driving properties were investigated. The A-MLPC integrated multilayer piezoelectric ceramics (MLPC) arrayed in a 2 ×2 matrix. By using A-MLPC, double-mode bending vibration of the stator vibrator can be realized easily, and the quality factor of the vibrator increased. Furthermore, with the improvement of the piezoelectric properties of the SCNN, the electromechanical coupling coefficient of the vibrator increased. As a result, we succeeded in improving the driving properties of the motor. In particular, the driving voltage of SCNN motor decreased to 1/10 of the previous study, and this motor is similar to Pb(Zr,Ti)O3–Pb(Ni,Nb)O3–Pb(Zn,Nb)O3 (PZT) one in terms of properties by applying 3 times higher voltage than that required for the PZT one. The SCNN motor started to rotate at 0.3 Vp–p and showed such characteristics as revolution speed of 730 rpm, torque of 0.7 µN m, and efficiency of 3.5% at 1.6 Vp–p. It appeared that the SCNN motor was able to rotate by a lithium-ion cell used in the mobile equipment without an amplifier circuit.

Investigation of displacement property and electric reliability of (Li,Na,K)NbO3-based multilayer piezoceramics

In this study, lead-free multilayer piezoceramics with Pd inner electrodes were fabricated, and their displacement properties and electric reliabilities were investigated. The Li0.06Na0.52K0.42NbO3 multilayer piezoceramic exhibited a high displacement (S max/E max = 350 pm/V at 5 kV/mm) but a low resistivity (1.3 × 108 Ωcm at 100 °C). On the other hand, the additive-modified Li0.06Na0.52K0.42NbO3 multilayer piezoceramic exhibited both high displacement (S max/E max = 330 pm/V at 5 kV/mm) and high resistivity (1.2 × 1012 at 100 °C), and the breakdown voltages of the two piezoceramics were 4 and 16 kV/mm, respectively, at 100 °C. The observed improvement in electric reliability can be attributed to the refinement of the microstructure of Li0.06Na0.52K0.42NbO3 after the use of additives. Furthermore, the additive-modified Li0.06Na0.52K0.42NbO3 multilayer piezoceramic also showed a markedly higher resistivity than previously reported multilayer piezoceramics with Ag/Pd, Cu, and Ni inner electrodes, since the dispersion of elemental Ag and the generation of oxygen vacancies during the sintering process was prevented in the former case.