• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.165-168
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• 2000

Engine noise is one of the major causes of the interior noise, and so has been studied in various ways in recent days. Recently air induction noise has been extensively studied to reduce the engine noise. Conventional method to reduce the noise is adding several resonators to the induction system. However this causes a reduction of engine output power and an increase of fuel consumption. Thus in this study, the feasibility of applying the active noise control to the induction system is studied to the overcome the above disadvantage.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.426-430
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• 2001

Conventional smart foam is not applicable to active noise control in a duct having flow. Thus, this paper presents a ring-type smart foam as an alternative. The ring-type smart foam consists of polyurethane acoustic foam of lining shape and PVDF film embedded in the foam. The embedded PVDF element acts as an actuator to reduce noise at lower frequencies and the foam absorbs noise at higher frequencies. A feedforward adaptive filtered-x LMS controller is used to minimize the signal from the error microphone. Experiments are executed to reduce broadband and tonal noise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.883-884
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• 2012

This study deals with design and application of silencer to reduce the exhaust noise, especially at the low frequency range below 200 Hz which is main contribution for the bridge wing noise and the external noise of ships. The designed silencer is composed of side branch resonator, Helmholtz resonator and absorbing material. The resonating frequencies of resonators are set to be the firing order frequencies of the generator engine. Based on the on-board measurement result, it is verified that the designed silencer can effectively reduce the exhaust noise of generator engine.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.1
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• pp.34-41
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• 2001

Semiconductors performing digital clocking are a main source of radiated emission noise. Therefore, the most secure method of reducing emission noise is to reduce emission radiated from semiconductors; an application of an absorber to the surface of semiconductors is one of these methods, too. However, in reality, it is difficult to achieve as much effect of noise reduction as expected by using only absorber. It is confirmed by experiment in this paper that a loop area within chip has no correlation with radiated emission noise and it is clarified why the existing absorber fails to achieve a satisfactory effect of emission noise reduction. Besides, a new type of chip coating absorber has been developed which can cover up to semiconductor out lead by using ferrite coating material of ferrite/epoxy acrylate substance using only permeability loss out of electromagnetic wave reduction characteristics of materials. As a result of evaluating radiated emission noise by applying this coating absorber to semiconductor device, it could be confirmed that emission noise decreased from about 3 ㏈ up to 20㏈ depending on frequency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.168-171
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• 2005

The present study describes the prediction of the flow induced noise level of a high-speed rotating hexagonal disk and proposes the way how to reduce it. Since a hexagonal disk, which is used in the laser printer and named a polygon mirror, has six sharp comers, there are low and high pressure regions on each of six edges when it rotates. Therefore, the Pressure difference generates three dimension flow field and causes aerodynamic noise. The Ffowcs-Williams and Hawkings(FWH) method is employed for the analysis. We have measured the sound pressure levels and compared them with the computational results. The calculated sound pressure levels agree well with the experimental results. We modified the shape of the edges of a hexagonal disk to reduce the noise level and confirm their effects through numerical computation.

• Journal of Power Electronics
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• v.19 no.1
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• pp.296-306
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• 2019

The flyback topology is being widely used in power adapters. The coupling capacitance between primary and secondary windings of a flyback transformer is the main path for common-mode (CM) noise conduction. A Y-cap is usually used to effectively suppress EMI noise. However, this results in problems in space, cost, and the danger of safety leakage current. In this paper, the CM noise behaviors due to the electric field coupling of the transformer windings in a flyback adapter with synchronous rectification are analyzed. Then a scheme with balance winding is proposed to reduce the CM noise with a transformer winding design that eliminates the Y-cap. The planar transformer has advantages in terms of its low profile, good heat dissipation and good stray parameter consistency. Based on the proposed scheme, with the help of a full-wave simulation tool, the key parameter influences of the transformer PCB winding design on CM noise are further analyzed. Finally, a PCB transformer for an 18W adapter is designed and tested to verify the effectiveness of the balance winding scheme.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.5
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• pp.357-363
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• 2003

There have been lots of studies on noise transmission analysis and noise reduction In ducts. In order to reduce the noise transmission in ducts. active noise cancellation techniques have often been employed and a rotation shaft with blades has sometimes been suggested. These Ideas were not successfully commercialized because of the limitation of real life such as size or application difficulties. This study investigated how a rotational shaft with blades could reduce the noise transmission in a duct. To do so, an assembly of the shaft and the $haft housing was built In the middle of a duct. and the clearance between the blades and the housing was 0.2 mm. The noise reduction was experimentally evaluated with respect to the number of blades. the rotation speed, and the rotation or stop. This paper showed that the noise reduction resulted in about 14∼19 dBA regardless of the three test conditions only If the blades always blocked the duct. And. the noise reduction increased due to the higher number of blades and the lower speed of the shaft.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.4
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• pp.897-904
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• 2011

In this paper, a novel circuit topology of a low-noise amplifier tunable at 1.8GHz band for PCS and 2.4GHz band for WLAN using a CMOS active inductor is proposed. This circuit topology to reduce higher noise figure of the low noise amplifier with the CMOS active load is analyzed. Furthermore, the noise canceling technique is adopted to reduce more the noise figure. The noise figure of the proposed circuit topology is analyzed and simulated in $0.18{\mu}m$ CMOS process technology. Thus, the simulation results exhibit that the noise performance enhancement of the tunable low noise amplifier is about 3.4dB, which is mainly due to the proposed new circuit topology.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1891-1895
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• 2003

Switch-mode power supplies (SMPS) have become a major source of conducted electromagnetic interference (EMI) which is the combination between differential mode (DM) noise and common mode (CM) noise. This paper presents the conducted EMI reduction approach in flyback switched mode power supply by rerouting for circuit balance to reduce common mode noise. And differential mode noise can be reduce by adding $c_x$ capacitor across the input power line, and passive element to the gate drive of switching device MOSFET to slow down the switching times. This combination of our approach is the effective way to reduce the conducted EMI and it is also a cost effective for product design

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.49-53
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• 2008

This study deals a way to reduce the transformer noises. The first step is to identify the source of the transformer noises. The second step is obtaining the vibration characteristics of transformer; its natural frequencies and mode shapes. Based on these information, an method to reduce the vibration of transformer can be found. The cause of transformer noises is mainly due to the magnetostrictive vibration of a core which is made of ferromagnetic substances. It is well known that the magnetostrictive vibration of a core is unavoidable, and a way to reduce the transformer noise by structural design is needed. It requires understanding the vibration characteristics. The natural frequencies and the mode shapes of transformer are analyzed by performing the modal testing.