Tomoki Funakubo

Ultrasonic Linear Motor Using Multilayer Piezoelectric Actuators

In order to lower operating voltage and improve the lifetime of an ultrasonic linear motor, we have developed an ultrasonic oscillator with multilayer piezoelectric actuators. Multilayer piezoelectric actuators are operable at low voltage. However, the tensile strength of the multilayer piezoelectric actuator is small. Therefore, the multilayer piezoelectric actuators are build within an elastic body to lower the tensile stress with a compressive preload. Elliptical oscillations are generated by synthesizing two degenerated modes, a first longitudinal mode and a second flexural mode, with π/2 phase difference. As a result of estimating the characteristics of the ultrasonic linear motor with the ultrasonic oscillator, the operating voltage of 10 Vp-p, maximum thrust force of 8 N and lifetime of over 5000 hours have been obtained.

Characteristics of 10 mm Multilayer L1-F2 Mode Vibrator and Application to a Linear Motor

In the present paper we discuss a small-sized multilayer L1-F2 mode vibrator and its application to an ultrasonic linear motor. In an attempt to reduce both the size and the driving voltage of an L1-F2 mode vibrator, we constructed a multilayer L1-F2 mode vibrator whose inner electrodes are simply divided into two. Test results clarified that the multilayer L1-F2 mode vibrator exhibits two resonance modes; namely, a first longitudinal mode and a second flexural mode, and that an amplitude of vibration velocity is sufficiently large for application to a linear motor. Specific merits of our multilayer L1-F2 mode vibrator are that the driving voltage is low (5 Vrms), owing to multilayer construction, and that the vibrator is small (10 ×2.5 ×2 mm: W×H×D), owing to the simple construction of the inner electrodes. Additionally, the present study revealed that an ultrasonic linear motor using the multilayer L1-F2 mode vibrator exhibits superior performance in practical application.

Characteristics of Multilayer Piezoelectric Actuator Made of High Q Material for Application to Ultrasonic Linear Motor

Recently, we have developed a low voltage drive ultrasonic linear motor using a L1-F2 double mode stator vibrator made of multilayer piezoelectric actuators (MPAs). However, when the linear motor was continuously driven, the temperature rise of the stator vibrator was over 20°C. This is mainly because the MPA used by us is made of a low Q piezoelectric material (soft material MPA), which is usually applied due to its large piezoelectric coupling coefficient. Therefore, in order to reduce heat generation of the MPA, we tried to apply a MPA made of high Q piezoelectric material (hard material MPA), which has been little applied to date. As a result, it is clarified that the temperature rise of the hard material MPA is far less than that of a soft material MPA and therefore the temperature rise of the stator vibrator using the hard material MPA is also far less than that of the stator vibrator using a soft material MPA. Additionally, in this paper, it is reported that performances of the ultrasonic linear motor composed of hard material MPA are superior in practical application.

Cross-coupling Properties of Ultrasonic Phased Array Probe.

The frequency dependence of cross-coupling is described for a phased array probe developed for sector-scanning endoscopic ultrasonic diagnosis. The sweep frequency range is set from 0.5 MHz to 10.5 MHz for a 48-element phased array transducer with a center frequency of 5 MHz. Cross-coupling measurements were carried out on various piezoelectric elements at different positions in the probe. The relationship between the cross-coupling and the position of piezoelectric elements as determined by the measurements shows good agreement with the results of static-mode finite-element method (FEM) calculations.