Beomjin Kim

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.

Epitaxial Ba0.5Sr0.5TiO3 thin films for microwave phase shifters

Abstract A tunable phase shifter was fabricated with epitaxial Ba0.5Sr0.5TiO3 (BST) thin film and gold coplanar waveguide. BST thin film of the thickness ∼0.5 μm was deposited by laser ablation on the MgO(OOl) single crystalline substrate. Gold electrode of the thickness ∼2 μm was prepared by the sequence of thermal evaporation, electroplating, and wet etching. Epitaxial quality of the BST thin film was confirmed by X-ray diffraction. The microwave performance of phase shifter was measured at room temperature in the frequency range of 8–12 GHz, and with applied bias voltage of up to 30 V. Effect of Mn dopant in the epitaxial films was also considered.

Electrically Tunable Phase Shifters With Air-Dielectric Sandwich Structure

Abstract : Electrically tunable microwave phase shifter was developed by inserting dielectric slab and piezoelectric actuator inside a waveguide. Air-dielectric sandwich structure of dielectric material and thin air gap was placed inside a waveguide, where the thickness of air gap is controlled by the actuator. Small changes in the ratio between the thickness of dielectric material and air gap induce significant changes in the effective dielectric constant of the air-dielectric sandwich structure. Phase shifts of 20 ^ 200 degrees were realized with the dielectric materials such as (Mg, Ca)TiO3 while the thickness of air gap is changed between 0 to 30 micrometers by piezoelectric control. Since the dielectric ceramics has very small loss (tan delta ^ 10 (exp-4)) and the air gap has practically no loss, the total structure shows low insertion loss.

Non-resonant, electrode-less method for measuring the microwave complex permittivity of ferroelectric thin films

A procedure is described for measuring the complex permittivity of dielectric thin films with relatively large dielectric constants (e: about 102–104) and considerable losses (tan δ: about 10−3–1). The ferroelectric films studied here are deposited on a relatively low-e dielectric substrate and placed in the centre of a rectangular waveguide parallel to the direction of wave propagation. The dielectric constants and losses of thin films are determined not by the shift of the resonant peak, but by numerical analysis of measured scattering parameters using a vector network analyser. The proposed method does not require electrode deposition on the film surface, and provides the natural properties of the film without complications due to conductive electrodes and their interfaces.

Design and driving characteristics of ultrasonic linear motor

Abstract This paper gives results on theoretical and experimental studies about an ultrasonic linear motor using a combination of the first longitudinal and the fourth bending mode. Four pairs of stacked PZT ceramic plates were bonded both on and bottom sides of a straight aluminum bar as driving elements. The length of the aluminum bar was calculated by the classical beam theory. The size and attaching positions of the ceramic plates and the projections were determined by a finite element method. The velocity and the static thrust of the motor were measured by changing the voltage of input source.

Waveguide technique for ferroelectric bulk and film microwave study

Non-resonant waveguide method is presented to study materials with large dielectric constant ϵ. The enhanced method is based on network analyzer use and combines benefits of all known techniques. An additional custom calibration procedure is employed. Gathering redundant data of scattering parameter frequency dependence accompanied with curve fitting data processing is implemented. To increase microwave penetration into studied large-ϵ specimen, a low-ϵ matching dielectric plate is adapted. The influence of air gaps between specimen and waveguide is studied and errors eliminated. Higher-order mode propagation conditions analysis is considered. Waveguide partial tilling is studied and applied as a new electrode-less technique for ferroelectric thin film study. Experimental results of reference materials investigation are presented.

Non-Resonant Waveguide Technique for Measurement of Microwave Complex Permittivity of Ferroelectrics and Related Materials

A waveguide method is developed to study the materials with relatively large dielectric constants at microwave range. Basically, the method is similar to the previous waveguide methods represented by short-circuit line and transmission/reflection measurement methods. However, the complex permittivity is not determined by the shift in resonance frequencies, but by numerical analysis of measured scattering parameters. In order to enhance microwave penetration into the specimen with relatively large permittivity, a dielectric plate with lower permittivity is employed for impedance matching. The influences of air gap between the specimen and waveguide wall are evaluated, and the corresponding errors are estimated. The propagation of higher order modes is also considered. Experimental results for several reference ceramics are presented.