• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1037-1044
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• 2007

In an attempt to determine the correlations between the input acoustic impedance and the variations of the physical characteristics of the terminal elements, a five-lobe branched tube-network is mathematically developed and experimentally simulated using a lung simulator. The model takes into account some realistic conditions such as varying cross-sectional areas, flexible wall properties and branching. The effects of airway constrictions expressed by lobe stiffness variations on the impedance are determined for a range of frequencies up to 256 Hz. It is concluded that the developed model is capable of non-invasively predicting various physiological changes in the airway passages.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.462-465
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• 1995

In this research a 2-dimensional motion producer based on two linear motors was developed. When the tester provides some motion through the level attached to the upper moving part of the motion producer, it provides the arbitrary intertia, damping and stiffness characteristics without actual change in physical structure of the motion producer. That is, the active impedance is implemented by controlling input currents supplied to the linear motors. A PID controller with feedforward loop was used to control the currents and pre-processing of input velocity and accleration singals from the encoder and the current singnal from the motor driver circuit are conducted to improve the performance.

• Journal of electromagnetic engineering and science
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• v.2 no.1
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• pp.45-49
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• 2002

This paper presents the basic characteristics of a forced resonant type EMI dipole antennas for frequencies below 80 MHz in which two reactance elements are used for the impedance matching at the fined point. The input impedance of the short dipole less than half-wavelength is controlled by the properly determined loading position and the value of loading reactance. The numerical results show that the small-sized EMI dipole antenna with loller antenna factors for frequencies below 80 MHz can be realized by the reactance loading. In case tole proposed center driven forced resonant type EMI dipole antenna with 0.3 λ length is loaded from the center, the input impedance is matched at feed line with 50 $\Omega$, and hence the antenna has lower factors in the frequency range of 30 to 80 MHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.2
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• pp.167-177
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• 1996

The cutoff frequencies of a double ridged rectangular waveguide are calculated by applying the modal analysis to its cross-section. And the characteristic impedance of its $TE_{10}$ mode is evaluated in a frequency range of 6 to 18 GHz. When both ends of a linearly tapered rectangular wa- veguide consists of single and double ridged rectangular cross-sections, the equivalent nonuniform transmission line of its $TE_{10}$ mode is solved numerically. It is shown that the input impedance at its single ridged terminal becomes nearly constant in the wide bandwidth.

• Journal of Korea Multimedia Society
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• v.21 no.9
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• pp.1068-1075
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• 2018

We propose a method for driving loudspeakers from class D audio power amplifiers in current mode, instead of in conventional voltage mode, which was impossible with the feedback circuitry. Unlike analog audio amplifiers, Class D audio power amplifiers have signal delay between the input and output signals, which makes it difficult to apply the feedback circuitry for current-mode driving. The idea of the pre-distortion scheme used for the compensation of the non-linearity of RF power amplifiers is adapted to remedy the impedance variation effect of the loudspeakers for current driving. The method uses the speaker model for the pre-distorter to compensate for the speaker impedance variation with frequency. The simulation and test results confirms the validity of the proposed method.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.14 no.1
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• pp.17-25
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• 2014

This paper presents the formulation of an impedance controller for regulating the contact force with the environment. To achieve an accurate force tracking control, uncertainties in both robot dynamics and the environment require to be addressed. As part of the framework of the proposed force tracking formulation, a neural network is introduced at the desired trajectory to compensate for all uncertainties in an on-line manner. Compensation at the input trajectory leads to a remarkable structural advantage in that no modifications of the internal force controllers are required. Minimizing the objective function of the training signal for a neural network satisfies the desired force tracking performance. A neural network actually compensates for uncertainties at the input trajectory level in an on-line fashion. Simulation results confirm the position and force tracking abilities of a robot manipulator.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.7
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• pp.89-94
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• 2013

This paper presents a method of simulating the protection effects of surge protective devices(SPDs) depending on the protective distance and types of input impedance of load to be protected. In order to analyze the protective performances of voltage-limiting type SPDs associated with the reflection and oscillation phenomena, the terminal voltage across load being protected and the residual voltage of SPDs were simulated by using EMTP model as functions of the protective distance and types of input impedance of loads. As a consequence, SPDs should be installed by taking into account the protective distance and input impedance of loads to achieve reliable protection of electrical and electronic equipment from lightning and switching surges. It is expected that the simulation method proposed in this paper could be practically used in design for installing SPDs in low-voltage distribution systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.4
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• pp.323-329
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• 2003

In this paper, the method of material constants extraction in a thin-film bulk acoustic resonator(FBAR) using a genetic algorithm(GA) is proposed. The material constants are extracted from the input impedance of a FBAR by a GA optimizer. The characteristics of the FBAR input impedance affected by the material constants were studied to decide the fitness function for GA. As a result, the fitness was estimated by the series- and parallel -resonance frequencies and the FBAR bandwidth, as determined from the input impedance of the FBAR. A flowchart for the GA and a procedure fur the proposed extraction method are explained in detail, and the results of the material constants extraction are presented.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.5
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• pp.612-619
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• 2013

This paper proposes an early diagnosis technique for the stator-turn fault (STF) in an interior permanent magnet (IPM)-type brushless DC (BLDC) motor using the impedance parameter. We have analyzed the varying characteristics owing to the STF through various experiments and the finite element method (FEM). As a result, we have presented a simple method for fault detection. This technique can be applied without requiring a fast Fourier transform (FFT) and the calculation of the negative-sequence impedance. The fault detection system works on the basis of the comparison the measured impedance with the database impedance. The variations in the characteristics owing to the STF as well as the proposed technique have been verified through the simulation and experiment.

• Journal of Sensor Science and Technology
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• v.27 no.6
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• pp.374-379
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• 2018

The piezocomposite transducer is widely used because it is highly efficient in transforming electric energy into mechanical energy, and its frequency range is broader than that of other types of ultrasound transducers. A general piezocomposite transducer is composed of an acoustic lens, impedance matching layers, piezoelectric materials, and backing layers. When an input voltage is applied to a piezoelectric material as an active material, it generates sound waves while vibrating. At that time, an impedance matching layer helps the sound waves to propagate forward while reducing the impedance mismatch that may occur at the interface between the active material and its front material. The impedance mismatch has a negative effect on the signal of an ultrasound transducer; thus, it is important to design a matching layer to overcome the issue. In this study, an optimized feature of a matching layer with gradient properties is studied. An objective function is defined to minimize both the average and the deviation of the reflection coefficients that are functions of the frequencies. As a result, an improvement in the signal characteristics with respect to the sensitivity and bandwidth is reported.