Kohei Motoo

Piezoelectric Vibration-Type Tactile Sensor Using Elasticity and Viscosity Change of Structure

We propose a new tactile sensor utilizing piezoelectric vibration. This tactile sensor has a high sensitivity, wide measurement range, pressure resistance, flexibility, and self-sensing function. This tactile sensor comprises two piezoelectric materials. One is used for the vibration of the sensor element and the other is used for the measurement of the change in mechanical impedance induced by an external force. We achieved the wide measurement range by implementing two ideas. One was to apply the external force to the sensor element through an elastic body and the other was to use two or more modes of vibration. Moreover, for the elastic body, it is preferable to use a material whose elasticity and viscosity are easily changed by an external force, such as a gel. In this study, first, this tactile sensor was analyzed, and then its characteristics were derived. The analytical results qualitatively corresponded to the experimental results. Next, a prototype tactile sensor was fabricated and evaluated. The evaluation results showed that this tactile sensor can measure a pressure of 2.5 Pa or less and a pressure of 10 kPa or more and its pressure resistance is 1 MPa or more.

Touch sensor for micromanipulation with pipette using lead-free (K,Na)(Nb,Ta)O3 piezoelectric ceramics

In the field of applied microbiology, a touch sensor for micromanipulation with a pipette is needed. Therefore, we previously developed a touch sensor using Pb(Zr,Ti)O3 (PZT). The piezoelectric material is used for vibration of the pipette and for measurement of the change in mechanical impedance caused by the pipette tip contacting the object being measured. However, the lead included in PZT can cause environmental problems. Therefore, in the present work, we developed a touch sensor using lead-free (K,Na)(Nb,Ta)O3 (KNNT) ceramics, which are strong candidates for lead-free piezoelectric ceramics. In this study, characteristics of a touch sensor utilizing piezoelectric vibration were theoretically derived. The results show that the piezoelectric constant d31 is very important: the higher the mode of vibration, the smaller the tip amplitude; the lower the mode of vibration, the higher the sensitivity. Also, the higher the elasticity or viscosity of the object in contact with the sensor, the higher the sens...

Piezoelectric properties of lead-free CaBi4Ti4O15 thin films

CaBi4Ti4O15 (CBTi144) thin films are evaluated for use as lead-free thin-film piezoelectrics in microelectromechanical systems. CBTi144 thin films were prepared on Pt substrates by dip coating a precursor solution of metal alkoxides. We fabricated a piezoelectric bimorph actuator using those films and analyzed the displacement induced by the electric field. Young’s modulus was measured by the vibrating-reed technique and the piezoelectric constant d31 was derived by analysis of bending displacement and measurement of displacement-voltage curve. The measurements revealed that the CBTi144 films had a large piezoelectric constant d31 of 32pm∕V.

Generation of Concentration Gradient from Two-Layered Flow with High-Speed Switching Microvalve

Mixing two liquids and generating a concentration gradient in a microchannel are important in biochemistry. In a microchannel, mixing is limited by molecular diffusion due to the constraints of the laminar flow. Therefore, it is important to reduce the length of the mixing path for a quick mixing. One of the techniques for reducing the mixing path is sequential segmentation. A concentration gradient is generated by producing a wave-like pattern along the microchannel direction. In this technique, the high frequency vibration of the liquid-liquid interface is generated to form a wave-like pattern for mixing along a short channel length. High frequency switching of the fluid flow is achieved by employing the newly developed microvalve using tailor-made multilayer piezoelectric actuators (TAMPA) that is compact and low-cost yet produces large displacements and forces. This paper details the concept for the concentration gradient generation method. Next, a microvalve (20×15×15mm) was designed and produced using TAMPA (8.5×10×10mm), Finally, a concentration gradient in two-layered flow was generated with the microvalve. As a result, the generation of a concentration gradient in two-layered flow with active mixing was achieved in a high-speed fluid (120 mm/s, Re = 14.4). Moreover, the concentration gradient was controlled by adjusting the input voltage to TAMPA.

Tailor-made multilayer piezoelectric actuator having large displacements and forces produced from lead-free piezoelectric ceramics

We propose tailor-made multilayer piezoelectric actuators (TAMPA) having large displacements and large forces. In existing piezoelectric actuators, production of small, low-cost actuators having large displacements and large forces is difficult to achieve. We solved this problem by combining two bimorph-type piezoelectric elements with both ends simply supported, and stacking several elements on top of each other. Moreover, TAMPA is a tailor-made actuator whose displacement to force ratio can be varied widely by adjusting the size of the bimorph-type piezoelectric elements even when the total size of the actuator is kept constant. In this study, the bimorph-type piezoelectric element was analyzed, and the relationship between the displacement and the force under fixed conditions was experimentally determined. The relationship between the displacement and the force of TAMPA was theoretically derived. The analytical results showed that a TAMPA having dimensions of approximately 10times10times10 mm is capable of generating displacements of several hundred mum or the force of several N. A prototype was produced and its performance was evaluated. These results agreed well with the analytical results, confirming the validity of the analytical results. Finally, because the lead in PZT can cause environmental problems, a TAMPA was produced that used (K,Na)(Nb,Ta)O3 piezoelectric ceramics instead of PZT