Hyonho Chong

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.

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%.

Driving Characteristics of the Thin-Type Ultrasonic Motor Using Microcontroller

This paper represented driving characteristic of a thin-type ultrasonic motor by fabricating and utilizing two kinds of drivers which could generate sinusoidal wave, square wave, respectively. A thin brass plate was used as a cross shaped vibrator and sixteen ceramic plates were attached on upper and bottom side of the brass plate. From the thin stator, elliptical displacements of the four contact tips were obtained. When two harmonic voltages which have 90° phase difference were applied to the ceramics, the symmetric and anti-symmetric displacements were generated at inside of the tips to make the elliptical motion. A finite element analysis (ATILA) was used for simulating the motional pattern of contact tips of the stator. The characteristics of the motor such as speed, torque, and current consumption were measured by applying sinusoidal waves through driving equipment which composed of function generator and power amplifier. As a result, the speed and the torque changed linearly at both driving frequency of 88.6 ∼ 87.6[kHz] and voltage of 24∼36[V]. Two-drivers which generate sinusoidal waves and square waves were designed and compared through some experiments in order to be put to practical use. In conclusion, the drivers had similar characteristic of speed-torque at alike frequency and voltage range. The square wave driver was recommended to control the motor linearly among two drivers by reason of practical use and simplification of driver.

Effects of K Nonstoichiometry in (Bi0.5K0.5+x )TiO3 Ceramics

K nonstoichiometry effects in (Bi0.5K0.5+x )TiO3 (BKT) ceramics were studied with K contents varying in the range of −8≤ x ≤+1 mol% from the stoichiometric K0.5. Within the range tested, a single BKT phase region was found to be at −1≤ x ≤+1 mol% and secondary phases started emerging with further K deficiency. Despite the formation of secondary phases, BKT perovskite with tetragonal symmetry was retained at all compositions. For nonstoichiometric BKT perovskite, a composition dependent structure property relation was observed; a decrease in tetragonality (c/a) caused piezoelectric coefficient (d 33) enhanced while depolarization temperature (Td ) reduced and vice versa.

Design of a Nib-Shaped Ultrasonic Motor for Auto-focusing Camera

In this paper, a newly designed nib-shaped ultrasonic motor was proposed. The motor can be easily designed and fabricated as a small actuator due to its simple structure composed of a nib-shaped elastic body frame and two ceramics. Also, the motor is expected to be used as small actuator for auto-focusing camera by designing the size of the motor less than 10[mm], because the ultrasonic motor has general merit of generating high torque in spite of low speed. When two sinusoidal sources with phase difference of 90 degrees are applied to two ceramics, the elliptical displacement is generated at contact tip of the motor. To define vibration shapes and output characteristics of the motor, design parameters were chosen and the modeling of the motor was conducted by using ANSYS 11.0, FEM(Finite Element Method) Program. Elliptical motions of the contact tips of the stator were consistently obtained at resonance frequency. Characteristics of the motor such as frequency, speed, torque, and pre-load were measured by using the driving system and measurement equipment. From the fabricated prototype motor, high rotational speeds were obtained by applying relatively low voltages. Speed and torque were increased linearly by increasing the voltage

Characteristics of the Piezoelectric Generator Using Circular Type Bender

The Piezoelectric generator for energy harvesting is usually using rectangular type unimorph or bimorph. In this paper, the characteristic of the piezoelectric generator which has a circular type bender was studied for more efficiently converting the mechanical energy to electrical energy than the rectangular type. The generator consisted of circular type vibrating plate, thin piezoelectric ceramics, stub and mass. The generator was simulated with FEM(finite element method) program as changing size of each part. When the radius of the piezoelectric ceramics and the elastic body were increased and the diameter of the vibrating plate was increased, the resonant frequency was decreased. And the output voltage was increased when the radius of the elastic body was increased. The output voltage was also affected by the distance which is the mass position from center of unimorph. The piezoelectric generator was fabricated from these simulated results. The output power was 4.3[mW] when the weight of mass was 7.2g.

Study on the new type of piezoelectric actuator utilizing smooth impact drive mechanism

ABSTRACT In this paper, the linear piezoelectric actuator utilizing smooth impact drive mechanism (SIDM) was proposed. It is easy to fabricate an actuator because of the simple structure of a bimorph type piezoelectric ceramic cantilever without any rotators or sliders. The cantilever, called as leg, was composed of four rectangular ceramics which were attached on the surfaces of an elastic body. Finite Element Analysis (FEA) was used to optimize the driving characteristics of the actuator. When bipolar rectangular wave with different durations for positive and negative voltages was applied, the piezoelectric actuator was moved by a stick-slip driving mechanism. The actuator was driven by two successive motions of actuator legs, slow forward and rapid backward movement. The driving characteristics of the prototype actuator were measured by the laser Doppler vibrometer.

A Study on Generating Characteristics of Circular Unimorph-Type Piezoelectric Transducer

On this paper, a circular unimorph-type piezoelectric transducer was proposed and studied. The transducer was fabricated by attaching a circular-shaped PZT ceramic to a circular plate of brass and output characteristics of the fabricated transducer were then analyzed and measured by changing driving points where the mechanical vibrations were applied. Two conditions depending on the location of vibration were respectively defined as a center forced model and an edge forced model. The resonance frequency and output voltage of the models were simulated by using ANSYS, a FEM(finite element method) program. Based on the results of the analyses, the vibration experiment was conducted and the output characteristics then measured through measurement equipment. As a result, the maximum output characteristics of two models were respectively generated at each resonance frequency and the resonance frequency of the center forced model was lower than the edge forced model.

Design and Fabrication of a Thin-Type Ultrasonic Motor

In this paper, the characteristics of a thin-type ultrasonic motor generating elliptical displacements analyzed by FEM are presented, and then fabrication of the motor is then described. The structure of the motor consists of sixteen ceramic pieces attached to the upper and bottom surfaces of an elastic body. The principle of the motor is to apply alternating voltages which have a 90 phase difference to the attached ceramics, and then elliptical displacements are generated at four edges of the elastic body. Then the rotor is moved by the elliptical displacements. In the case of a ceramic thickness of 1.5, the highest speed was obtained at 79 kHz. In the case of a ceramic thickness of 2 mm, the highest speed was obtained at 77.5 kHz. Consequently, the speed and torque of the ultrasonic motor (USM) increased linearly with increasing applied voltage.

Piezoelectric and Dielectric Properties of (Bi0.5K0.5+x Li y )TiO3 Ceramics

Dielectric and piezoelectric properties of (Bi0.5K0.5+xLiy)TiO3 ceramics were studied in the range of x = −8–1 and y = 0–5 mol% of the stoichiometric K0.5. Secondary phases were not observed within −1 ≤ x ≤ 1 but started emerging at x ≤ −2 mol%. A tetragonal perovskite structure was maintained at all compositions despite the formation of secondary phases with K deficiency. Piezoelectric coefficient (d33) was improved due to K-vacancies facilitating domain walls movement and was further enhanced due to the microstructure improved with the tetragonality optimized by Li addition. Depolarization temperature (Td), on the other hand, depressed with K deficiency and Li addition.