• Proceedings of the KSME Conference
• /
• 2001.06d
• /
• pp.890-895
• /
• 2001

Pressure resonance frequency that is caused in the combustion chamber can be interpreted to acoustic analysis. Until now the pressure resonance has been assumed and calculated to a disc type combustion chamber that neglected the combustion chamber height because the knock occurs near the TDC(top dead center). In this research FEM(fine element method) has been used to calculate the pressure resonance frequency inside the experimental engine combustion. The reduce error of the resonance frequency obtained by FEM has decreased about 50% compared to the calculation of Draper's equation. Due to the asymmetry in the shape of the combustion chamber that was neglected in Draper's equation we could find out that a new resonance frequency could be generated. To make the experimental results equal we could know that the speed of sound that satisfies Draper's equation was selected 13% higher than all the pent-roof type combustion considered.

• Journal of the Korean Wood Science and Technology
• /
• v.33 no.4 s.132
• /
• pp.15-22
• /
• 2005

The acoustic properties of various coatings for stringed musical instruments made were investigated. The applied coatings were urethane topcoat, oil stain, natural varnish, cashew and UV-curable epoxy coating. Acoustic properties of coatings inferred from a resonance frequency and a damping measured by FFT analyzer and tan ${\delta}$ measured by DMTA. Acoustic properties from resonance frequency and damping were analyzed. Optimum coating for stringed instruments was determined by viscoelastic properties and acoustic properties of coating.

• Investigative Magnetic Resonance Imaging
• /
• v.2 no.1
• /
• pp.50-57
• /
• 1998

MR acoustic sound or noise due to gradient pulsings has been one of the problems in MRI, both in patient scanning as well as in many areas of psychiatric and neuroscience research, such as brain fMRI. Especially in brain fMRI, sound noise is one of the serious noise sources which obscures the small signals obtainable from the subtle changes occurring in oxygenation status in the cortex and blood capillaries. Therfore, we have studied the effects of acoustic or sound noise arising in fMR imaging of the auditory, motor and visual cortices. The results show that the acoustical noise effects on motor and visual responses are opposite. That is, for the motor activity, it shows an increased total motor activation while for the visual stimulation, corresponding(visual) cortical activity has diminished substantially when the subject is exposed to a loud acoustic sound. Although the current observations are preliminary and require more experimental confirmation, it appears that the observed acoustic-noise effects on brain functions, such as in the motor and visual cortices, are new observations and could have significant consequences in data observation and interpretation in future fMRI studies.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.2 no.2
• /
• pp.59-72
• /
• 1994

For a panel contribution of the passenger vehicle compartment, a model was created for acoustic analysis of the passenger vehicle compartment and through the acoustic normal modal analysis, frequencies and mode shapes of the resonance modes were calculated. Also, the contribution analysis of each panel was executed using acoustic reciprocal theorem, and through this analysis, normalized responses at the particular point indicate the relative contribution of each panel for generating noise and vibration

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.05b
• /
• pp.283-286
• /
• 2000

In this study, the acoustic transducer of a thin circular disc-type with PZT/Metal was manufactured. The piezoelectric transducer with 200kHz resonance frequency was designed by considering the sharp directivity and the sound pressure. The dielectric and piezoelectric properties of 0.5 weight percent $MnO_2$ and NiO doped $0.1Pb(Mg_{1/3}Nb_{2/3})O_3-0.45PbTiO_3-0.42PbZrO_3$ ceramics were investigated aiming at acoustic transducer applications. Also, the acoustic characteristics of a thin circular disc-type with metal-piezoceramics have been Investigated.

• International Journal of Precision Engineering and Manufacturing
• /
• v.9 no.2
• /
• pp.28-33
• /
• 2008

In a scanning electron microscope (SEM), outside acoustic noise causes image noise that distorts observations of the specimen being examined. A SEM that is less sensitive to acoustic noise is highly desirable. This paper investigates the image noise problem by addressing the mode shapes of the base plate and the transmission path of the acoustic noise and vibration. By arranging the position of the rib, a new SEM base plate was developed that had twisting as the 1st and 2nd modes. In those two twisting modes, vibration nodes existed near the center of the base plate where the specimen chamber is placed. Less vibration was transmitted to the chamber and to the specimen by the twisting modes compared to bending ones, which are the 2nd and 3rd modes for a rectangular plain base plate. An SEM with the developed base plate installed exhibited a significant reduction of image noise when exposed to acoustic noises below 250 Hz.

• KIEAE Journal
• /
• v.9 no.6
• /
• pp.81-87
• /
• 2009

The purpose of the present study is to establish structural noise analyzing method for apartments building floor with structural-acoustic coupling analysis modeling. Noise through floor in the room is recognized as a significant problem with the consequence that noise isolation technique has been studied in the various fields of industry. From among noise factors, resonance sound is the main reason for solid noise of the floor, which is occurred by mechanical vibrations of the acoustic boundary line and the change of velocity. To analyse this phenomenon, numerical computation methods are provided in many fields, In this study, evaluation method for slab is established using finite element method, and a case study for analyzing acoustic phenomenon was suggested. The results show that numerical method, especially F.E.M, has a good approximation to predict noise at floors.

• Journal of Advanced Marine Engineering and Technology
• /
• v.24 no.4
• /
• pp.515-525
• /
• 2000

A new acoustic field visualization technique is introduced in this study. Small particles of which density is small enough to follow up the air used for the noise field visualization. In order to quantify the noise, PIV(Particle Imaging Velocimetry) has been constructed. When the driving frequency is in the vicinity of the resonance frequency of the simplified 2-dimensional muffler system, an acoustic streaming is shown and of which velocity distribution is obtained through PIV technique. It is experimentally proved that the present technique is able to visualize and quantify the acoustic fields.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.23 no.2
• /
• pp.167-175
• /
• 2013

The wave propagation characteristics of an acoustic metamaterial composed of periodically repeated one-dimensional Helmholtz resonator array was investigated considering the effects of dimensional changes of the resonator geometry on the transmission coefficient and band gap. The effective impedance and transmission coefficient of the acoustic metamaterials are obtained based on the acoustic transmission line method. The designed acoustic metamaterials exhibit band gaps and negative bulk modulus that are non-existent properties in the nature. The band gap of the acoustic metamaterial is strongly dependent on the geometry parameters of Helmholtz resonators and lattice spacing. Also, a new type of metamaterial that is periodically constructed with two different resonators was designed to open the local resonance band gap without change of Bragg scattering.

• Applied Microscopy
• /
• v.50
• /
• pp.25.1-25.11
• /
• 2020

Scanning acoustic microscopy (SAM) or Acoustic Micro Imaging (AMI) is a powerful, non-destructive technique that can detect hidden defects in elastic and biological samples as well as non-transparent hard materials. By monitoring the internal features of a sample in three-dimensional integration, this technique can efficiently find physical defects such as cracks, voids, and delamination with high sensitivity. In recent years, advanced techniques such as ultrasound impedance microscopy, ultrasound speed microscopy, and scanning acoustic gigahertz microscopy have been developed for applications in industries and in the medical field to provide additional information on the internal stress, viscoelastic, and anisotropic, or nonlinear properties. X-ray, magnetic resonance, and infrared techniques are the other competitive and widely used methods. However, they have their own advantages and limitations owing to their inherent properties such as different light sources and sensors. This paper provides an overview of the principle of SAM and presents a few results to demonstrate the applications of modern acoustic imaging technology. A variety of inspection modes, such as vertical, horizontal, and diagonal cross-sections have been presented by employing the focus pathway and image reconstruction algorithm. Images have been reconstructed from the reflected echoes resulting from the change in the acoustic impedance at the interface of the material layers or defects. The results described in this paper indicate that the novel acoustic technology can expand the scope of SAM as a versatile diagnostic tool requiring less time and having a high efficiency.