• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.2
• /
• pp.53-58
• /
• 2004

In this paper, the low-phase dual-band VCO, by adding switching circuit with PIN diode at feedback loop of the oscillation part having negative-resistance, is realized. In order to reduce the phase noise of the VCO, PBG structure applied to the ground plane of the resonator. When applying for PBG structure, output power is -9.17㏈m and phase noise is -102㏈c/Hz at 5.25㎓, output power is -5.17㏈m and phase noise is -101㏈c/Hz at 1.8㎓, respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1996.10a
• /
• pp.266-271
• /
• 1996

Optimal design of disk shaped piezoelectric actuator and sensor mounted on the plate structure is studied for the control of noise radiated fro the structure. The sensor signal is returned to the actuator through negative gain. Finite element modelling is used for the plate structure and the disk shaped piezoelectric sensor and actuator. The objective function is the total radiated sound power and the design variables are the locations and sizes of the piezoelectric actuator and sensor. The optimal is performed at the resonance and the off resonance frequency and the results show good noise reduction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1997.10a
• /
• pp.445-450
• /
• 1997

Optimal design of a piezoelectric smart structure is studied for cabin noise control. A cubic shaped acoustic cavity with a flat plate which covers one side is taken as the problem. The sensor signal is returned to the actuator through a negative gain. The acoustic cavity is modeled using the modal approach which represents the pressure fields in the cavity as a sum of mode shapes of the cavity with unknown coefficients. By using orthogonality of the mode shapes of the cavity, finite element equation for the structure with the influence of the acoustic cavity is derived. The objective function is the average pressure at a certain region, so-called silent zone, in the cavity and the design variables are the locations and sizes of the piezoelectric actuator and sensor. The optimal design is performed at several frequencies and the results show a remarkable noise reduction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2009.10a
• /
• pp.473-477
• /
• 2009

In general, the softer the stiffness of a linear vibration isolator the better the performance of isolation can be achieved. However, the stiffness of the isolator cannot be made too soft because it needs a sufficient stiffness to hold the load. This is the most critical limitation of a linear vibration isolator. Recently, a HSLDS (High-Static-Low-Dynamic-Stiffness) magnetic vibration isolator was proposed to overcome this fundamental limitation. The suggested isolator utilizes two pairs of attracting magnets that that introduces negative stiffness. Previously, this new type of vibration isolator was merely introduced and showed a possibility of practical use. In this paper, detailed dynamics of the HSLDS magnetic isolator are studied using computer simulations. Then, the isolation performance is examined for various design parameters to aid the practical use.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2009.10a
• /
• pp.321-321
• /
• 2009

This paper presents quasi-zero-stiffness (QZS) characteristic of a passive isolator using flexures under compression force. The passive isolator consists of a positive stiffness element (a vertical coil spring) and a negative stiffness element (flexures under compression force), and their proper combination of the positive and negative stiffness elements can produce both substantial static and zero dynamic stiffness, so called QZS. Firstly, a nonlinear dimensionless expression of a flexure under compression force is derived. A dynamic model of the passive isolator is developed and numerical simulations of its time and frequency response are performed. Then, undesirable nonlinear vibration is quantified using a period doubling bifurcation diagram and a Poincare's map of the isolator under forced excitation. Finally, experiments are performed to validate the QZS characteristic of the passive isolator.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.20 no.1
• /
• pp.92-97
• /
• 2010

In general, the softer the stiffness of a linear vibration isolator the better the performance of isolation can be achieved. However, the stiffness of the isolator cannot be made too soft because it needs a sufficient stiffness to hold the load. This is the most critical limitation of a linear vibration isolator. Recently, a HSLDS(high-static-low-dynamic-stiffness) magnetic vibration isolator was proposed to overcome this fundamental limitation. The suggested isolator utilizes two pairs of attracting magnets that introduces negative stiffness. Previously, this new type of vibration isolator was merely introduced and showed a possibility of practical use. In this paper, detailed dynamics of the HSLDS magnetic isolator are studied using computer simulations. Then, the isolation performance is examined for various design parameters to aid the practical use.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2014.06a
• /
• pp.173-175
• /
• 2014

In this paper, we compare a bit error rate performance with channel estimation for terrestrial cloud transmission systems in order to provide an advanced research. Since terrestrial cloud transmission systems experience co-channel interference from one or more transmitters, they have to operate under negative signal-to-noise ratio.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.05a
• /
• pp.202-207
• /
• 2002

This paper deals with a novel shunted actuator, which has a capability to suppress multi-mode vibration amplitudes by using a pair of piezoceramic patches. In order to describe the characteristic behaviors of shunted dampers connected with a series and a parallel resistor-negative capacitive branch circuit, the stiffness ratio and loss factor with respect to the non-dimensional frequency are considered. To obtain a guideline model of a piezo/beam system connected with a series and a parallel resistor-negative capacitor branch circuit, the governing equations of motion is derived through Hamiltons principle and a piezo sensor equation as well as a shunt damping matrix is developed. The theoretical analysis shows that the shunted actuator developed in this study can significantly reduce multiple-mode vibration amplitudes simultaneously over the whole structural frequency range.

• Journal of Sensor Science and Technology
• /
• v.29 no.3
• /
• pp.180-186
• /
• 2020

In this study, we applied edge-pulse modulation to prevent the flicker of light-emitting diode (LED) light in a visible light identification system. In the visible light transmitter, positive pulses were transmitted at the edges of the low-to-high transition points, and negative pulses were transmitted at the edges of the high-to-low transition points of the non-return-to-zero (NRZ) data waveforms. In the visible light receiver, the NRZ waveforms were regenerated by making low-to-high and high-to-low transitions at the point of the positive and negative pulses, respectively. This method has two advantages. First, it ensures that the LED light is flicker-free because the average optical power of the LED was kept constant during data transmission in the transmitter. Second, the 120 Hz optical noise from the adjacent lighting lamps was easily cut off using a simple RC-high pass filter in the receiver.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11b
• /
• pp.866-870
• /
• 2001

Measurement techniques for in-duct acoustic source parameters can be classified into the direct method and the load method, according to whether it utilizes an extra external source or not. It is reported that the load methods yield the negative source resistance and the purpose of this paper is to clarify that the time-varying nature of the source is the main cause of this physically implausible result. For this purpose, the direct and load methods for measuring the source characteristics of a simplified fluid machine are simulated using the time domain numerical analysis. In the numerical simulations, the method of characteristics is employed and the source characteristics are calculated from the resultant data. It is shown that the load method results in negative source resistance for some frequencies, whereas the direct method yields positive values for all frequencies considered. It is found that the result of load method is quite sensitive to the change of cylinder pressure or valve profile in contrast to the direct method.