The lab focuses on research involving Acoustic Black Hole & Aeroacoustic Metamaterials, Fan Noise, Vibration Analysis, and various other areas listed under the professor's interests.

파동에너지(소음/진동) 제어 연구실은 음향 블랙홀 및 항공 음향 메타 물질, 팬 소음, 진동 분석 및 교수의 관심사 아래 나열된 기타 다양한 영역과 관련된 연구에 중점을 둡니다.

Vortex-shaped acoustic black holes in rotational arrangement for low-frequency vibration suppression

Ventilated acoustic metamaterial for noise insulation in a duct with non-uniform cross sections

Spontaneous emission decay and excitation in photonic time crystals

Phononic crystals with non-quantized Zak phases for controlling interface state frequencies

Concave-shaped acoustic black holes with asymmetric arrangement for suppression and amplification of structural vibration

Enhancement of acousto-optic interaction using a phoxonic cavity with structural hierarchy

Broadband sound absorption using hybrid resonators with embedded necks and micro-perforations in parallel

Complex-valued impedance tiles to reduce noise emanating through openings in mechanical systems

Near-perfect sound absorption using hybrid resonance between subwavelength Helmholtz resonators with non-uniformly partitioned cavities

Palm-sized, vibration-insensitive, and vacuum-free all-fiber-photonic module for 10−14-level stabilization of CW lasers and frequency combs

Design of aluminum plate phononic crystals with wide bandgaps via free-form shape optimization using deep neural networks

Topological interface states in deep-subwavelength phononic beams

On the control of the absorption of an acoustic black hole by using attached point supports

Lightweight soundproofing meta-panel for separate wide frequency bands

Machine learning-enabled development of high performance gradient-index phononic crystals for energy focusing and harvesting

Broadband sound absorption using multiple hybrid resonances of acoustic metasurfaces

Realization of an acoustic metalens exhibiting broadband high transmission

Vibration damping of plates using waveguide absorbers based on spiral acoustic black holes

Acoustic metaliners for sound insulation in a duct with little flow resistance

Ultra-wide low-frequency band gap in a tapered phononic beam

Nonplanar metasurface for perfect absorption of sound waves

Wave-based analysis of the cut-on frequency of curved acoustic black holes

Bandgap characteristics of phononic crystals in steady and unsteady flows

Analytic study on pressure drop and heat transfer characteristics for low Reynolds number flow in spirally finned tubes

Modal and forced response analysis of vehicle systems with latent vibration modes due to hydraulic mounts

Wave-based analysis of dual acoustic black holes for anechoic termination of shock testing devices

Hierarchical phononic crystals for filtering multiple target frequencies of ultrasound

Broadband low-frequency sound absorption by periodic metamaterial resonators embedded in a porous layer

Experimental validation of vibration damping using an Archimedean spiral acoustic black hole

Exact solution of Euler-Bernoulli equation for acoustic black holes via generalized hypergeometric differential equation

A general recipe for nondispersive optical activity in bilayer chiral metamaterials

Linear frequency conversion via sudden merging of meta-atoms in time-variant metasurfaces

Hierarchically structured metamaterials with simultaneously negative mass density and Young's modulus by using dynamic homogenization

Perfect sound absorption using ultra-thin metasurface based on hybrid resonance and space-coiling

Dual-frequency sound-absorbing metasurface based on visco-thermal effects with frequency dependence

Analytic solutions of the friction factor and the Nusselt number for the low-Reynolds number flow between two wavy plate fins

Effect of compressibility and non-uniformity in flow on the scattering pattern of acoustic cloak

Vibration damping using a spiral acoustic black hole

Stochastic rules for predator and prey hunting and escape behavior in a lattice-based model

Evaluation of rapid cell division in non-uniform cell cycles

A mathematical model for the territorial competition of the subterranean termites Coptotermes formosanus and Reticulitermes flavipes (Isoptera: Rhinotermitidae)

Effects of tunnel structures of two termite species on territorial competition and territory size

The number of points on elliptic curves y^2=x^3+Ax and y^2=x^3+B^3

A simulation model for the study on the forest fire pattern

Characterization of fish schooling behavior with different numbers of Medaka (Oryzias latipes) and Goldfish (Carassius auratus) using a Hidden Markov Model

Mathematical investigations on branch length similarity entropy profiles of shapes for various resolutions

Quantitative analysis of fish schooling behavior with different numbers of Medaka (Oryzias latipes) and Goldfish (Carassius auratus)

Analysis of the responses of termites to tunnel irregularity

Butterfly species identification by branch length similarity entropy

Characterizing temporal patterns in swimming activity of Caenorhabditis elegans

A simulation model for the study of the territorial behavior of subterranean termites

Suppression of scar formation in a murine burn wound model by the application of non-thermal plasma

Simulation study of territory size distributions in subterranean termites

Simulation model for dual-species biofilm growth in hydrodynamic flow

A constraint condition for foraging strategy in subterranean termites

Acoustic diffraction by a finite airfoil in uniform flow

Exact and useful formulas of generalized gamma functions occurring in finite diffraction theory

Radiation characteristics of noise generated by steady loading on rotating blade

Perfect sound absorption of ultra-thin metasurface based on hybrid resonance and space-coiling

Palm-sized, vibration-insensitive, and vacuum-free all-fiber-photonic module for 10− 14-level stabilization of CW lasers and frequency combs

Wonju Jeon

This study starts with a simple question: can the vibration of plates or beams be efficiently reduced using a lightweight structure that occupies a small space? As an efficient technique to damp vibration, the concept of an acoustic black hole (ABH) is adopted with a simple modification of the geometry. The original shape of an ABH is a straight wedge-type profile with power-law thickness, with the reduction of vibration in beams or plates increasing as the length of the ABH increases. However, in real-world applications, there exists an upper bound of the length of an ABH due to space limitations. Therefore, in this study, the authors propose a curvilinear shaped ABH using the simple mathematical geometry of an Archimedean spiral, which allows a uniform gap distance between adjacent baselines of the spiral. In numerical simulations, the damping performance increases as the arc length of the Archimedean spiral …

The energy of an electromagnetic wave is converted as the wave passes through a temporal boundary. Thus, effective temporal control of the medium is critical for frequency conversion. Here, we propose rapidly time-variant metasurfaces as a frequency-converting platform and experimentally demonstrate their efficacy at terahertz frequencies. The proposed metasurface is designed for the sudden merging of two distinct metallic meta-atoms into a single one upon ultrafast optical excitation. This sudden merging creates a spectrally designed temporal boundary on the metasurface, by which the frequency conversion can be achieved and engineered. Interestingly, the time delay between the abrupt temporal boundary and the input terahertz pulse is found to be strongly related to the phase of the converted wave as well as its amplitude. As the proposed scheme does not rely on the nonlinearity, it may be particularly …

We propose an acoustic metasurface for perfect absorption at dual frequencies within a compact space. Meta-molecules of the metasurface contain four subwavelength meta-atoms whose cavities are coiled by three foldings. The meta-atoms comprising a meta-molecule have slightly different neck sizes to obtain hybrid resonances at desired frequencies. In order to consider an effect of coiled spaces in the meta-atoms, we use equivalent straight cavities with an effective length in an analytical model. By using the analytical model, metasurfaces are optimally designed for perfect absorption at desired frequencies. The experimental results show that a λ/23-metasurface exhibits over 99% energy absorption at 294 Hz and 406 Hz. Furthermore, we define another optimization problem to minimize the thickness of the metasurface for perfect absorption at two desired frequencies. The experimental results show that a λ/32 …

Broadband absorption of the audible sound wave at low frequency has been achieved by using periodic acoustic metamaterial resonators (AMRs) embedded inside a porous layer. A single AMR embedded in a porous layer could reach perfect absorption (PA) at the resonance frequency, and it can be easily tuned by adjusting the inner radius of AMR. With four AMRs in the porous layer, a high absorption (> 80%) is obtained in the frequency range from 180 Hz to 550 Hz, while the thickness of the porous layer is only 1/10 of the relevant wavelength at 300 Hz. The broadband and high absorption performances are due to the interferences of the low-frequency resonances of the AMRs and the energy trapping between the AMRs and the rigid backings. The finite element simulations are experimentally validated. Moreover, the broadband low-frequency absorption is robust under various oblique incidence even at large …

Achieving broadband sound absorption in low-frequency ranges using thin acoustic materials has been a long-standing and challenging problem in acoustics. When using the existing acoustic materials such as porous and fibrous materials, they are inevitably thick for low-frequency sound absorption. In this study, we propose a thin acoustic metasurface for broadband absorption of low-frequency sound by using hybrid resonances at multiple target frequencies. Supercells of the proposed metasurface are partitioned into multiple unit cells, and each of them is composed of two adjacent subwavelength Helmholtz resonators for perfect sound absorption based on hybrid resonance at each target frequency. When the hybrid resonance is derived, the unit cell exhibits perfect sound absorption at the target frequency with the lower Q-factor than the existing absorbing structures with same thicknesses. To take this …

Vibration damping in a thin structure can be effectively achieved by using an acoustic black hole (ABH), which is a straight wedge-shaped structure with power-law profile. However, it is difficult to apply the straight ABH to industrial system due to space limitations. In this study, we show that a spiral ABH whose baseline is rolled into an Archimedean spiral configuration can be an alternative for the straight ABH when an installation space for the ABH is limited. The spiral ABH is manufactured through a wire electric discharge machining, and its damping performance is validated experimentally. The experiments show large reductions of resonance peaks when compared to a reference uniform beam, indicating that the spiral ABH effectively reduces the structural vibration in the beam structure. Rolling the baseline into the spiral curve causes eigen-frequency shifts, but there is little difference in the damping performance …

We investigate theoretically an acoustic metasurface with a high absorption coefficient at two frequencies and design it from subwavelength structures. We propose the use of a two-dimensional periodic array of four Helmholtz resonators in two types to obtain a metasurface with nearly perfect sound absorption at given target frequencies via interactions between waves emanating from different resonators. By considering how fluid viscosity affects acoustic energy dissipation in the narrow necks of the Helmholtz resonators, we obtain effective complex-valued material properties that depend on frequency and on the geometrical parameters of the resonators. We furthermore derive the effective acoustic impedance of the metasurface from the effective material properties and calculate the absorption spectra from the theoretical model, which we compare with the spectra obtained from a finite-element simulation. As a …

We propose a waveguide absorber (WGA) based on an acoustic black hole (ABH) to damp vibrations in plate structures. The proposed WGA is composed of a spiral ABH and a rod connecting it to the surface of the plate. The geometrical dimensions of the WGA are determined, such that it has a lower cut-on frequency than a given target range of frequencies, by using a recently developed impedance method for curved ABHs. We then optimize the location of attachment and direction of the WGA on a simply supported uniform plate to minimize the peak levels of its surface-averaged mobility. The strategy used to find its optimum location and direction is based on an analysis of structural intensity that provides the distribution and direction of elastic wave energy propagating in the plate. The results of simulations and experiments show that large reductions of resonance peaks could be achieved below 500 Hz by …

Acoustic black hole (ABH), a thin wedge-shaped structure tapered according to the power-law of power ( m ) greater than or equal to two, has received much attention to the researchers in wave dynamics due to its potential as a light and effective absorber of elastic waves propagating in beams or plates. In this paper, the Euler-Bernoulli equation for the ABH is reformulated into the form of a generalized hypergeometric differential equation for m > 2. Then, the exact solution is derived in terms of generalized hypergeometric functions ( p F q ) where p = 0 and q = 3 by dividing the power m into four cases. The derived exact solution is in linearly independent and regular form for arbitrary m . In addition, by using the exact solution, the displacement field of a uniform beam with an ABH and the reflection coefficient from an ABH are calculated to demonstrate the applicability of the present exact solution. This paper aims …

We propose a tapered phononic beam with a broad low-frequency band gap for flexural waves. A unit cell of the phononic beam consists of two identical uniform parts and a thickness-and width-varying part sandwiched between them. Thickness and width profiles and uniform beam length are controlled to change the shear and rotational stiffnesses of the phononic beam, changing the starting and ending frequencies of the first band gap. By identifying the effects of those geometrical parameters on band structures, we determine the parameter values that enable the phononic beam to yield an ultra-broad and ultra-low band gap from 3.6 Hz to 237.9 Hz with a small lattice constant of λ/25. For experimental realization, a finite phononic beam with three unit cells is fabricated by wire electric discharge machining and its displacement transmission is measured through impact hammer tests. Particularly low transmission of …

Gradient-index (GRIN) phononic crystals (PnCs) offer an excellent platform for various applications, including energy harvesting via wave focusing. Despite its versatile wave manipulation capability, the conventional design of GRIN PnCs has thus far been limited to relatively simple shapes, such as circular holes or inclusions. In this study, we propose a GRIN PnC comprising of unconventional unit cell designs derived from machine learning-based optimization for maximizing elastic wave focusing and harvesting. A deep neural network (NN) is trained to learn the complicated relationship between the hole shape and intensity at the focal point. By leveraging the fast inference of the trained NN, the genetic optimization approach derives new hole shapes with improved focusing performance, and the NN is updated by augmenting the new dataset to enhance the prediction accuracy over a gradually extended range of …

The curved acoustic black hole (ABH), a thin structure with a curved baseline and a thickness that tapers according to a power law, has been proposed and investigated numerically and experimentally as a candidate for an effective and compact absorber of flexural waves. To understand physically the wave motions within a curved ABH and to utilize a spiral ABH in practical applications, systematic investigations of the effects of geometrical parameters such as the curvature or the damping-layer thickness are needed, as well as a theoretical approach to facilitate fast and accurate calculations. In this paper, we propose a wave-based theoretical method and investigate the “cut-on frequency” of a curved ABH, the frequency from which waves start to propagate within the ABH, using this method. The governing equation of the wave motion is derived using Hamilton's principle, and the solution of the governing equation …

We previously developed a shape recognition methodology that uses “branch length similarity” (BLS) entropy, which is defined as a simple branching network consisting of a single node and branches. The simple network is referred to as a “unit branching network” (UBN). Our approach involves obtaining BLS entropy profiles from UBNs created by joining each pixel in the outline of a shape with every other pixel in the shape's border. The profiles successfully characterize the shapes by comparing their BLS entropy profiles. Presently, we modified this approach to facilitate its application to butterfly species identification by partitioning and weighting the entropy profile. As a test, we identified the butterfly species Colias erate, Parnassius bremeri, Eurema hecabe, Gonepteryx rhamni, and Papilio maackii. Each species group consisted of 10 specimens. We used wing shape to identify a species. We extracted evenly …

We propose a metaliner that can insulate the duct noise for various grazing flow speeds with little flow resistance. The metaliner, whose unit cell consists of two different Helmholtz resonators with subwavelength scales, is placed underneath the duct. In order to predict sound insulation and absorption of metaliner in a duct with flow, an effective impedance model of the metaliner is established by considering the effect of flow. We present a design procedure for a metaliner with high transmission loss for various flow speeds. Experiments show that designed metaliners exhibit transmission loss above 45 dB/m within±5% of the target frequencies of 500 and 1000 Hz for different flow speeds of 0, 17, and 34 m/s. We investigate the effects of flow on sound absorption as well as sound insulation for probing the applicability of the metaliner to various environments where noise should be suppressed at both the upstream and …

During the last decade, most of acoustic cloak research has been done within a theoretical framework in which the medium is at rest. However, such an acoustic cloak cannot preserve its unique properties or functions to make an object acoustically invisible in the presence of flow. In this study, we propose a theoretical framework to accurately investigate the effect of compressibility and non-uniformity in flow on the scattering pattern of acoustic cloak. In the formulation, the wave operator is coupled with the non-uniform velocity vector, and the equivalent source terms due to mean flow are divided into the compressibility effect and the non-uniformity effect with their own physical meanings. Numerical simulation shows the difference in far-field directivity between previous and present formulations. The polarity of the equivale﻿nt s﻿ources ﻿in the present formulation shows hexapole and skewed quadrupole patterns for non …

This study proposes an acoustic metasurface composed of Helmholtz resonators coupled with micro-perforations to achieve perfect sound absorption with a low Q- factor. A key feature of the metasurface is the parallel arrangement of an embedded neck and a micro-perforated panel within a single unit cell. This geometrical configuration facilitates the generation of hybrid resonance, leading to perfect absorption at the target frequency, in which the metasurface dimensions are significantly smaller than the corresponding wavelengths. To guide design choices, a theoretical model is introduced to outline the frequency-dependent effective impedance of the resonators, thereby aiding in specifying the geometric parameters required for impedance matching with the ambient air. Experimental validation for a unit cell fabricated using three-dimensional printing confirms the efficacy of the metasurface at a target frequency of …

Hierarchically structured phononic crystals are proposed for filtering multiple frequency bands. The advantages of using structural hierarchy come from its multiscale periodicity and the increased number of controllable parameters, which contribute to open multiple bandgaps in broadband frequency ranges and adjust the positions of those bandgaps. By deriving a transfer-matrix-based theoretical formula, hierarchical phononic crystals are designed that filter the frequency bands for randomly selected frequencies in the ultrasonic range of 20 kHz to 10 MHz. Their wave-filtering capability is demonstrated by using numerical simulations with consideration of material loss. By comparing the transmittance spectra of the hierarchical phononic crystals with those of conventional ones, the structural hierarchy of the former is shown to be advantageous in filtering multiple frequency bands.

We propose a lightweight soundproofing meta-panel that suppresses noise in separate wide frequency bands. The meta-panel has a multi-scale lattice structure sandwiched by two thin membranes. High sound isolation over a wide frequency range is achieved by inducing negative effective material properties of the meta-panel. Unlike a single-scale lattice structure, in which total transmission is unavoidable at certain frequencies due to resonances of the membranes, the meta-panel isolates sound waves effectively in separate wide bands with the aid of multiple reflections within the multi-scale lattice structure. A sound transmission loss exceeding 16.7 dB was realized within the range 100–1750 Hz by a meta-panel sample fabricated via three-dimensional printing. Aiming at practical applications in electric cars, we evaluated the insertion loss of the meta-panel in a box-shaped structure for dual-band noise which …

Suppression of hypertrophic scar generation in an animal model by treatment with plasma is reported. Contact burn following mechanical stretching was used to induce scar formation in mice. Exposure to the plasma tended to reduce the scar area more rapidly without affecting vitality. The treatment resulted in decreased vascularization in the scar tissue. Plasma-treated scars showed mild decrease in the thickness of hypertrophic tissues as shown by histological assessment. Finally, we showed that plasma treatment induced cell death and reactive oxygen species generation in hypertrophic scar fibroblast. All of the results support that plasma treatment can control scar generation.

Compact and robust frequency-stabilized laser sources are critical for a variety of fields that require stable frequency standards, including field spectroscopy, radio astronomy, microwave generation, and geophysical monitoring. In this work, we applied a simple and compact fiber ring-resonator configuration that can stabilize both a continuous-wave laser and a self-referenced optical frequency comb to a vibration-insensitive optical fiber delay-line. We could achieve a thermal-noise-limited frequency noise level in the 10 Hz–1 kHz offset frequency range for both the continuous-wave laser and the optical frequency comb with the minimal frequency instability of 2.7× 10− 14 at 0.03-s and 2.6× 10− 14 at 0.01-s averaging time, respectively, under non-vacuum conditions. The optical fiber spool, working as a delay reference, is designed to be insensitive to external vibrations, with a vibration sensitivity of sub-10− 10 (1/g …

Wave Energy Control Lab

교수님 소개

전원주

연구실 소개

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Vortex-shaped acoustic black holes in rotational arrangement for low-frequency vibration suppression

Ventilated acoustic metamaterial for noise insulation in a duct with non-uniform cross sections

Spontaneous emission decay and excitation in photonic time crystals

연구실 보유 특허

대학별 입시끈

우리 연구실 모집

교수님 소개

전원주

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Vortex-shaped acoustic black holes in rotational arrangement for low-frequency vibration suppression

Ventilated acoustic metamaterial for noise insulation in a duct with non-uniform cross sections

Spontaneous emission decay and excitation in photonic time crystals

연구실 보유 특허

최근 3년간 연구실적 높은 연구실

대학별 입시끈

우리 연구실 모집