Introduction of Research
Walking Assistive SystemIn order improve QOL for elderly people; supporting the mobility function is promising technology. This research is concerning the walking assistive system including clarifying the walking mechanism itself. Our proposal is to utilize the ultrasonic motors (USM) which poses light weigh, compact dimensions, powerful output, back drivability and high-efficiency. The advantages of our project is not only installing the USMs but also developing original control system related to preload-control method. From the view of smart sensing, the motion sensors signal are collecting and analyzed using artificial intelligence technology for reasonable control for supporting elderly people’s walking behavior.
Double Parabolic refLectors wave-guided high-power Ultrasonic tranSducers (DPLUS)In ultrasound therapeutics, to solve the bioeffects using conventional High Intensity Focused Ultrasound (HIFU) and to achieve powerful ultrasound supply using alternative Minimally Invasive Treatments (MIT), we invent Double Parabolic refLectors wave-guided high-power Ultrasonic tranSducers (DPLUS). Parabolic focusing technique (powerful ultrasound generation) and waveguide technique (miniaturization) are innovatively combined in this research. It is the first time to successfully introduce double parabolic reflectors for focusing and guiding powerful ultrasound into waveguides. The waveguide possesses double parabolic reflectors, the first parabolic reflector is to increase the contact surface area between PZT and waveguide to enhance the energy input and focus ultrasound, and the second parabolic reflector is to transfer the focused ultrasound to an enhanced plane-wavefront ultrasound for high power transmission. We validate our proposal by numerical simulation (FEMTET, PZFlex), analytical calculation (propagation modes, output fields), and experiments. In the future, our DPLUS can be promisingly applied to ultrasound imaging, ultrasound microscopy, cell capture, etc.
Miniaturized R-SIDM actuator / Resonant frequency controlAs one of promising miniaturized piezoelectric actuator, we are studying on the SIDM (Smooth Impact Drive Actuator). The driving principle is based on asymmetric piezoelectric motion, namely slow expansion and quick returning motion. Due to inertia of the slider, slip-stick phenomena is induced, which results in unidirectional frictional motion of the slider. In this study, we proposed to realize this asymmetric motion by combining two resonant vibration motions to reduce the input voltage. For this purpose, the resonant frequency ratio must be controlled to be 1:2. As a result of low-voltage operation, temperature increase is eliminated. To realize this RSIDM (Resonant type SIDM) operation, the resonant frequency ration should be controlled precisely. During operation, the temperature increase and the nonlinear piezoelectric vibration affect this ratio. To overcoming this problem, we proposed the resonant frequency control system was developed. In general, the piezoelectric material is utilized for driving the transducer; however, in this study, the resonant frequency controlling piezoelectric parts were introduced. By changing the electrical boundary condition for these parts, the resonant frequency of the stator transducer can be adjusted during actuator operation.
Hydrothermal MethodPiezoelectric materials are promising for miniaturized actuator or sensors due to its simple mechanism for energy conversion. For developing these elemental technologies, large thickness of the piezoelectric films is strongly required. Compared to sol-gel method, sputtering, CVD, the hydrothermal method has various unique advantages. An important feature is its low temperature deposition, 150 degree C which is more than 450 degree C lower than the conventional methods. In addition, the hydrothermal method enables to deposit the film on the three dimensional substrate because the process is carried out based on the chemical reaction in solution. Until now, by using the hydrothermal method we realized the micro piezoelectric actuator, ferroelectric memories and so on. Recently, we succeeded in increasing the thickness larger than 10 micro meters by developing the ultrasonic assist hydrothermal method. By irradiation ultrasonic power during the hydrothermal process, the larger thickness and smooth surface profile were confirmed. As target materials, PZT and environmental friendly material such as (KNbO3) type piezoelectric materials are studying in this project.
Evaluation of Nonlinear Piezoelectric VibrationFor developing the high-power ultrasonic devices, such as medical ultrasonic knives and ultrasonic motors, nonlinear piezoelectric vibration must be taken into consideration. When the piezoelectric material is excited with large amplitude, complicated phenomena appear, such as the increase in heat generation, the change in resonance frequency, the vibration speed / current jump phenomenon (Figure 1).
In this research, focusing on the influence of higher order elasticity, nonlinear modeling and quantitative evaluation for piezoelectric high power characteristics were conducted. In the nonlinear piezoelectric equivalent circuit model (Fig. 2b), the parameters of the single-plate piezoelectric vibrator (Fig. 2a) are examined and nonlinear mechanical stiffness was introduced. As a next step, for considering a distributed parameter model (Fig. 3), transfer matrix method was improved by putting nonlinear vibration parameters. These modeling enabled to study on the influence of heat generation and the practical ultrasonic transducer such as Langevin transducer. Our evaluation method is quite important for the material development process, for example finding the suitable piezoelectric materials for high power ultrasonic devices. Now, we are trying to find such materials in environmental friendly materials.