Tae-Gone Park

Effects of Bi nonstoichiometry in (Bi0.5+xNa)TiO3 ceramics

Effects of Bi nonstoichiometry on (Bi0.5+xNa)TiO3 (BNT) ceramics were investigated at x=−1–+2 mol % of Bi0.5 covering Bi deficiency and excess. At all compositions, rhombohedrally symmetric BNT perovskite formed without secondary phases. Increasing x caused smaller grains. Higher piezoelectric coefficient (d33) but lower depolarization temperature (Td) occurred at Bi excess than at Bi deficiency and vice versa. Leakage current at room temperature decreased with decreasing x. Electrical conductivity of the stoichiometric BNT (x=0) from 700 to 900 °C increased with decreasing partial oxygen pressure from 1 to 10−5 atm suggesting n-type conductivity at elevated temperatures.

Effects of Na nonstoichiometry in (Bi0.5Na0.5+x)TiO3 ceramics

Effects of Na nonstoichiometry in (Bi0.5Na0.5+x)TiO3 ceramics were investigated in the range of x=(−5)−(+1) mol % of Na0.5. A rhombohedral perovskite structure was maintained at all compositions with no secondary phases. Grain size decreased with Na nonstoichiometry. Piezoelectric coefficient (d33) increased from 74 pC/N at x=0 up to 91 pC/N at x=−3.5 then dropped with further Na deficiency. Depolarization temperature (Td), on the other hand, decreased from 190 °C at x=0 down to 112 °C at x=−3.5 then increased. Rhombohedral lattice distortion (90−α) decreasing with Na deficiency was a key factor for the variation in d33 and Td.

notRoles of lattice distortion in (1−x)(Bi0.5Na0.5)TiO3-xBaTiO3 ceramics

Structure property relations in (1−x)(Bi0.5Na0.5)TiO3-xBaTiO3 ceramics were investigated at x=0–10 mol %. A solid solution with either rhombohedral or tetragonal symmetry was confirmed with a morphotropic phase boundary (MPB) at x=5–7 mol %. Grains became small with increasing x possibly due to grain boundary pinning by BaBi′–BaNa•. Lattice distortion was a key factor affecting piezoelectric coefficient (d33) and depolarization temperature (Td). Both rhombohedral 90−α and tetragonal cT/aT lattice distortion became smaller toward the MPB causing poling by field and depoling by temperature to become easier subsequently resulting in higher d33 but lower Td, and vice versa.Structure property relations in (1−x)(Bi0.5Na0.5)TiO3-xBaTiO3 ceramics were investigated at x=0–10 mol %. A solid solution with either rhombohedral or tetragonal symmetry was confirmed with a morphotropic phase boundary (MPB) at x=5–7 mol %. Grains became small with increasing x possibly due to grain boundary pinning by BaBi′–BaNa•. Lattice distortion was a key factor affecting piezoelectric coefficient (d33) and depolarization temperature (Td). Both rhombohedral 90−α and tetragonal cT/aT lattice distortion became smaller toward the MPB causing poling by field and depoling by temperature to become easier subsequently resulting in higher d33 but lower Td, and vice versa.

Characteristics of the First Longitudinal-Fourth Bending Mode Linear Ultrasonic Motors

Linear ultrasonic motors using a combination of the first longitudinal mode and the fourth bending mode were designed and fabricated. The driving characteristics of the motors, which were composed of a straight metal bar bonded with piezoelectric ceramic vibrators as a driving element, were measured. Unimorph and bimorph ceramic vibrators were attached on three kinds of metal bars for constructing the stators of the linear motors. As results, motors made with the bimorph ceramic vibrators had higher velocity than motors of the unimorph vibrators. As a metal bar for stator, magnesium alloy, which has lower elastic coefficient than aluminum alloy, was better for the motors.

Piezoelectric and Dielectric Properties of Lead-Free (1-x)(Bi0.5K0.5)TiO3-xBiFeO3 Ceramics

Dielectric and piezoelectric properties of lead-free (1-x)(Bi0.5K0.5)TiO3-xBiFeO3 ceramics prepared by a conventional solid-state reaction method were studied in the range of x = 0∼40 mol%. A tetragonal perovskite structure was maintained at x = 0∼10 mol% forming a solid solution between (Bi0.5K0.5)TiO3 and BiFeO3 with no secondary phase. Piezoelectric coefficient (d33) increased from 31 pC/N at x = 0 mol% to 64 pC/N at x = 6 mol% and then decreased with further addition of x. Depolarization temperature (Td) gradually decreased with increasing x from 302°C at x = 0 mol% to 163°C at x = 20 mol% and slightly increased up 180°C at x = 40 mol%.

Design of a Piezoelectric Energy-Harvesting Shock Absorber System for a Vehicle

Only ∼20% of a vehicles fuel consumption is used for overcoming air drag force and friction with the road. Vibration energy produced during driving is dissipated by shock absorbers in the vehicle suspension. A new Piezoelectric Energy-Harvesting Shock Absorber (PEHSA) system for vehicles has been developed to act as an energy harvester that converts vibration energy to electrical energy. Cylindrical piezoelectric transducers are combined with the cylinder of the shock absorber to generate electricity from changes in fluid pressure produced by piston vibrations. A multiphysics simulation was performed using COMSOL Multiphysics to determine the characteristics of the PEHSA system.

Generating characteristics of a cross-shaped piezoelectric generator depending on elastic body material and leg length

The dependence of the generation characteristics of a cross-shaped piezoelectric generator on the material and leg length of the elastic body was studied. The generator consisted of a centrosymmetric thin cross-shaped elastic body and four rectangular piezoelectric ceramics that were attached to the upper surfaces of the four legs of the elastic body. Vibrations from a vibrating source were applied to the center of the elastic body. The centrosymmetric structure of the cross-shaped generator guarantees more stable and multiplied generation than a cantilever-type generator since the four legs of the generator resonate at the same frequency. The resonance and output characteristics of the generator were analyzed by using a finite element method (FEM) program. Generators were fabricated on the basis of analysis results and attached to a frequency controllable vibrator for determining their output characteristics. Further, experimental results were compared with simulated results. The speed of sound in the materials depends on the Young’s modulus and density of the materials. Accordingly, the resonance frequency of the generator decreased with a decrease in the velocity of sound in the material. The resonance frequency of the generator also decreased with an increase in the leg length. By changing the generator parameters, the resonance frequency of the generator can be controlled.

Design and Fabrication of Three Touch Point Thin Ultrasonic Rotary Motor

A novel structure three touch points thin ultrasonic rotary motor has been proposed to enable the actuator to use in small mobile equipment. A thin stator of simple structure is advantageous to use in tight spaces. Also, three points of contact enables to stable driving. Twelve ceramics plates were attached on upper and bottom side of the metal plate. When three phase alternating current sources are applied to the stator, elliptical displacements are generated at three inner edges of the stator. Modeling of the ultrasonic motor was done and the displacement characteristics were defined by using finite element analysis program. The effectiveness of the proposed design was verified by experiments. Characteristics of the motor such as speed, and input voltage were measured by using the driver and measurement equipment. Maximum displacement was appeared at frequency of minimum impedance. The resonance frequency was inversely proportional to the ceramic length. The maximum speed of 220 [rpm] was obtained at the resonance frequency, 76.4 [kHz]. The speed increase somewhat linearly with increasing applied voltage.

Effects of A-Site Nonstoichiometry on Dielectric and Piezoelectric Properties of Pb-Free (Na0.53+x K0.47)(Nb0.55Ta0.45)O3 Ceramics

(Na0.53+x K0.47)(Nb0.55Ta0.45)O3 (NKNT) ceramics prepared by a solid state process were investigated at 0 ≤ x ≤ 0.02 to determine the effects of Na content in NKNT ceramics. With Na nonstoichiometry, piezoelectric properties were varied but grains were all cube-like perovskites with no impurity phases. Piezoelectric coefficient (d 33) was sensitive to Na content while polymorphic phase transition (PPT) temperature was not. PPT temperature between orthorhombic and tetragonal phases (T O-T) was around room temperature within the compositional range tested. The highest d 33 obtained was 330 pC/N at Na0.545 (x = 0.015) increased from 310 pC/N at Na0.53 (x = 0), which was due to the morphotropic phase boundary (MPB) effect around (Na0.53K0.47) of NKNT ceramics.

Generating Characteristics of a Cantilever-Type Unimorph Piezoelectric Generator Depending on the Material and Mass

Structure of a cantilever-type unimorph piezoelectric generator was proposed and designed so as to allow the generator to resonate at frequencies lower than commercial frequencies. This generator is capable of generating amount of voltage its despite low frequency and simple fabrication that result from its simple structure. In this paper, the resonance characteristics of the generator depending on significant parameters were determined through a modal analysis and the influence of each parameter was analyzed to define each its level of sensitivity on the high output characteristics using ANSYS, a FEM program. The generators resonated at frequencies lower than 60 [Hz], as determined through the FEM results. The generating characteristics were then defined by implementing vibration experiment and comparing the results with those from the analysis. The resonance frequency and output power depending on changes in the mass and material were determined by the analysis.