• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.10
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• pp.71-79
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• 2006

Swirl injector with multi-stage tangential entry was analyzed to suppress high-frequency combustion instability in Liquid Rocket Engines. In order to analyze the effect of swirl injector as an acoustic absorber, swirl injector was regarded as a quarter-wave resonator and it's damping capacity is verified in atmospheric temperature. It has a finite mode of vibration and natural frequencies which can be tuned to the natural frequencies of a model combustion chamber. The interior air core shape of injector is more stable in the case of using the swirl injector with multi-stage entry than with single-stage entry. Also, when the swirl injector with multi-stage entry is used, tuned-injector length for unstable mode is well agreed with the calculated length. From the experimental data, it is proved that if the interior air core shape of swirl injector is stable, the fine tuned swirl injector can decrease the unstable mode of model chamber effectively and increase the damping rate.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.125-129
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• 2000

In this paper, We designed and fabricated C-band bandpass filter using dielectric resonators. From waveguide cutoff frequency which applied the region between adjacent dielectric resonators, the height of cavity is determined. The cavity's diameter is determined to the twice of dielectric resonator's diameter considering the conductor loss. The resonant frequency of the DR-cavity is calculated with travelling wave mode analysis. Conventionally, circular cylindrical dielectric resonator is analysed by Cohn's model which use the evanescent mode in the region between dielectric resonator wall and circular cavity wall, which is an approximated method. The external quality factor, Q$_{ex}$ has found with simulation result using Ansoft's Maxwell simulation tool. The designed filter using dielectric resonators with dielectric constant of 45 has the passband center at 5.065GHz. The bandpass filter using dielectric resonators have about 1dB insertion loss. 20MHz bandwidth and more than 30dB attenuation at f$_{0}$$\pm$15MHz.z.z.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.3
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• pp.209-214
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• 2017

A plane-wave incident upon asymmetric multi-layered dielectric grating as well as symmetric grating structure generates space harmonics. Selected space harmonics among those harmonics can undergo strong resonance scattering variations known as GMR(guided-mode resonance). In this paper, to clarify these effects, the field propagation and dispersion curve inside the grating region are analyzed by using a rigorous equivalent transmission-line theory(RETT) based on eigenvalue problem. The results show that, at the peak of a scattering resonance, the reflected mode is almost identical to a leaky wave that can be supported by the grating structure. Thus, it confirms to be occurred GMR effect associated with the free-resonant character of leaky waves at asymmetric multi-layered dielectric gratings. Quantitative simulation results illustrating the behavior of typical gratings are given, and the special case of normal incidence is discussed for TE and TM modes.

• Journal of Advanced Navigation Technology
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• v.9 no.2
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• pp.147-155
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• 2005

In this paper, we propose that three uniform coplanar waveguides(CPWs), such as a conventional, finite grounded(FG), and grounded(G) CPWs, can be coupled with a $TE_{01{\delta}}$ mode dielectric resonator(DR) for a parallel resonant characteristic as a microstrip line coupled with the DR. Coupling characteristics have been investigated by placing the DR on a dielectric support above the CPWs and by moving the DR away from the center of a slot of the CPWs to the ground plane. FEM simulation(HFSS) results in terms of S-parameters agree well with measurement results. Finally, unloaded Q values of the DR coupled with the three uniform CPWs are compared with those of the DR coupled with a microstrip line. The comparison shows that the DR coupled with the three CPWs has higher unloaded Qs than that coupled with a microstrip line and that the GCPW case has the highest unloaded Qs.

• Journal of Biosystems Engineering
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• v.36 no.1
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• pp.23-32
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• 2011

In this work, the finite element method was used to investigate the shifts of resonance frequencies and quality factor of whispering-gallery-mode (WGM) for an opto-fluidic ring resonator (OFRR) biosensor. To describe the near-field radiation transfer, the time-domain Maxwell's equations were employed and solved by using the in-plane TE wave application mode of the COMSOL Multiphysics with RF module. The OFRR biosensor model under current study includes a glass capillary with a diameter of 100 mm and wall thickness of 3.0 mm. The resonance energy spectrum curves in the wavelength range from 1545 nm to 1560 nm were examined under different biosensing conditions. We mainly studied the sensitivity of resonance shifts affected by changes in the effective thickness of the sensor resonator ring with a 3.0 mm thick wall, as well as changes in the refractive index (RI) of the medium inside ring resonators with both 2.5 mm and 3.0 mm thick walls. In the bulk RI detection, a sensitivity of 23.1 nm/refractive index units (RIU) is achieved for a 2.5 mm thick ring. In small molecule detection, a sensitivity of 26.4 pm/nm is achieved with a maximum Q-factor of $6.3{\times}10^3$. These results compare favorably with those obtained by other researchers.

• Journal of Sensor Science and Technology
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• v.26 no.4
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• pp.235-238
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• 2017

In this study, the design of a tri-axis micromachined gyroscope is proposed and the vibration characteristic of the structure is analyzed. Tri-axis vibratory gyroscopes that utilize Coriolis effect are the most commonly used micromachined inertial sensors because of their advantages, such as low cost, small packaging size, and low power consumption. The proposed design is a single structure with four proof masses, which are coupled to their adjacent ones. The coupling springs of the proof masses orthogonally transfer the driving vibrational motion. The resonant frequencies of the gyroscope are analyzed by finite element method (FEM) simulation. The suspension beam spring design of proof masses limits the resonance frequencies of four modes, viz., drive mode, pitch, roll and yaw sensing mode in the range of 110 Hz near 21 kHz, 21173 Hz, 21239 Hz, 21244 Hz, and 21280 Hz, respectively. The unwanted modes are separated from the drive and sense modes by more than 700 Hz. Thereafter the drive and the sense mode vibrations are calculated and simulated to confirm the driving feasibility and estimate the sensitivity of the gyroscope. The cross-axis sensitivities caused by driving motion are 1.5 deg/s for both x- and y-axis, and 0.2 deg/s for z-axis.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.7
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• pp.462-468
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• 2018

The piezoelectric energy harvesting characteristics of a trapezoidal cantilever generator with lead zirconate titanate (PZT) laminate were investigated with various Ag inner electrodes. The piezoelectric mode of operation was a transverse mode by using a planar electrode pattern. The piezoelectric cantilever generator was fabricated using trapezoidal cofired-PZT/Ag laminates by five specimens of 2, 3, 4, 7, and 13 layers of Ag. As the number of Ag electrodes increased, impedance and output voltage at resonant frequency significantly decreased, and capacitance and output current showed an increasing tendency. A maximum output power density of $7.60mW/cm^3$ was realized for the specimen with seven Ag layers in the optimal condition of acceleration (1.2 g) and resistive load ($600{\Omega}$), which corresponds to a normalized power factor of $5.28mW/g^2{\cdot}cm^3$.

• Journal of Power Electronics
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• v.19 no.2
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• pp.403-412
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• 2019

Aiming at the problems of large dv/dt and di/dt in traditional single-ended converters and high electromagnetic interference (EMI) noise levels, a single-ended isolated converter using the secondary resonance technique is proposed in this paper. In the proposed converter, the voltage stress of the main power switch can be reduced and the voltage across the output diode is clamped to the output voltage when compared to the conventional flyback converter. In addition, the peak current stress through the main power switch can be decreased and zero current switching (ZCS) of the output diode can be achieved through the resonance technique. Moreover, the EMI noise coupling path and an equivalent model of the proposed converter topology are presented through the operational principle of the proposed converter. Analysis results indicate that the common mode (CM) EMI noise and the differential mode (DM) EMI noise of such a converter are deduced since the frequency spectra of the equivalent controlled voltage sources and controlled current source are decreased when compared with the traditional flyback converter. Furthermore, appropriate parameter selection of the resonant circuit network can increase the equivalent impedance in the EMI coupling path in the low frequency range, which further reduces the common mode interference. Finally, a simulation model and a 60W experimental prototype of the proposed converter are built and tested. Experimental results verify the theoretical analysis.

• The Journal of the Acoustical Society of Korea
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• v.27 no.5
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• pp.215-220
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• 2008

The kerfs between arrayed piezoelectric elements in a medical ultrasonic transducer or a piezoelectric composite transducer are generally filled by polymeric materials. The boundary condition of the elements for lateral mode vibration is changed according to the kerf-filling materials, so that the resonance frequency for longitudinal mode of the transducer is also varied. In this study, to investigate the resonance frequency variation for an arrayed transducer experimentally, the piezoelectric vibration elements of $14mm{\times}0.22mm{\times}0.44mm$ were fabricated and those were linearly arrayed. And, the resonance frequencies were measured for three cases of kerf-filling condition, non-filling and two different kinds of epoxy filling. Conclusively, it is confirmed that the resonant frequency variation shows the similar tendency with the theoretical one for the longitudinal mode.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.1110-1113
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• 2002

A Single-Stage Single-Switch power-factor- correction(PFC) AC/DC Converter with universal input is presented in this paper. The PFC Converter can be achieved based upon the continuous current mode(CCM). The switch has less current and voltage stresses over a wide range of load variation so that a low voltage rating device can be used. The presented converter features high power factor high efficiency, and low cost. An 90W prototype was implemented to show that it has 70% efficiency with low voltage stress over universal line input.