Yong-Joe Kim

Low frequency acoustic energy harvesting using PZT piezoelectric plates in a straight tube resonator

A novel and practical acoustic energy harvesting mechanism to harvest traveling sound at low audible frequency is introduced and studied both experimentally and numerically. The acoustic energy harvester in this study contains a quarter-wavelength straight tube resonator with lead zirconate titanate (PZT) piezoelectric cantilever plates placed inside the tube. When the tube resonator is excited by an incident sound at its acoustic resonance frequency, the amplified acoustic pressure inside the tube drives the vibration motions of piezoelectric plates, resulting in the generation of electricity. To increase the total voltage and power, multiple PZT plates were placed inside the tube. The number of PZT plates to maximize the voltage and power is limited due to the interruption of air particle motion by the plates. It has been found to be more beneficial to place the piezoelectric plates in the first half of the tube rather than along the entire tube. With an incident sound pressure level of 100 dB, an output voltage of 5.089 V was measured. The output voltage increases linearly with the incident sound pressure. With an incident sound pressure of 110 dB, an output voltage of 15.689 V and a power of 12.697 mW were obtained. The corresponding areal and volume power densities are 0:635 mW cm 2 and 15:115 W cm 3 , respectively. (Some figures may appear in colour only in the online journal)

Partial sound field decomposition in multireference near-field acoustical holography by using optimally located virtual references

It has been shown previously that the multiple reference and field signals recorded during a scanning acoustical holography measurement can be used to decompose the sound field radiated by a composite sound source into mutually incoherent partial fields. To obtain physically meaningful partial fields, i.e., fields closely related to particular component sources, the reference microphones should be positioned as close as possible to the component physical sources that together comprise the complete source. However, it is not always possible either to identify the optimal reference microphone locations prior to performing a holographic measurement, or to place reference microphones at those optimal locations, even if known, owing to physical constraints. Here, post-processing procedures are described that make it possible both to identify the optimal reference microphone locations and to place virtual references at those locations after performing a holographic measurement. The optimal reference microphone locations are defined to be those at which the MUSIC power is maximized in a three-dimensional space reconstructed by holographic projection. The acoustic pressure signals at the locations thus identified can then be used as optimal “virtual” reference signals. It is shown through an experiment and numerical simulation that the optimal virtual reference signals can be successfully used to identify physically meaningful partial sound fields, particularly when used in conjunction with partial coherence decomposition procedures.

Planar nearfield acoustical holography in moving fluid medium at subsonic and uniform velocitya)

Nearfield acoustical holography (NAH) data measured by using a microphone array attached to a high-speed aircraft or ground vehicle include significant airflow effects. For the purpose of processing the measured NAH data, an improved nearfield acoustical holography procedure is introduced that includes the effects of a fluid medium moving at a subsonic and uniform velocity. The convective wave equation along with the convective Eulers equation is used to develop the proposed NAH procedure. A mapping function between static and moving fluid medium cases is derived from the convective wave equation. Then, a conventional wave number filter designed for static fluid media is modified to be applicable to the moving fluid cases by applying the mapping function to the static wave number filter. In order to validate the proposed NAH procedure, a monopole simulation at the airflow speed of Mach=-0.6 is conducted. The reconstructed acoustic fields obtained by applying the proposed NAH procedure to the simulation data agree well with directly-calculated acoustic fields. Through an experiment with two loudspeakers performed in a wind tunnel operating at Mach=-0.12, it is shown that the proposed NAH procedure can be also used to reconstruct the sound fields radiated from the two loudspeakers.

Identification of Acoustic Characteristics of Honeycomb Sandwich Composite Panels Using Hybrid Analytical/Finite Element Method

For the purpose of identifying the acoustic characteristics of honeycomb sandwich panels, finite element method (FEM), combined with boundary element method (BEM), has been widely used. However, the latter approach is not always applicable to high frequency analyses since it requires a large number of FEM/BEM meshes. In order to reduce computational resources and modeling times, a hybrid analytical/finite element method (HAFEM) is described that uses a finite element approximation in the thickness direction, while analytical solutions are assumed in the plane directions. Thus, it makes it possible to use a small number of finite elements, even for high frequency analyses. By using the HAFEM, the wave transmission, propagation, and radiation characteristics of the honeycomb sandwich panels are investigated. The proposed HAFEM procedure is validated by comparing the predicted transmission loss (TL) results to the measured ones. Through the use of the HAFEM model of a honeycomb sandwich panel, it is shown that the structural responses of the panel converge asymptotically to flexural waves in the low audible frequency region, core shear waves in the high audible to ultrasonic frequency region, and skin flexural waves in the high ultrasonic frequency region. Coincident frequencies occur at the transition region from the flexural to core shear wave behaviors. From the TL sensitivities of various panel design parameters, the most dominant design parameters contributing to the TL results are determined as a function of frequency. In order to improve the acoustic performance of the honeycomb sandwich panel while satisfying weight and strength requirements, a new double core honeycomb sandwich panel is designed to have the same mass per unit area as the baseline single core panel but have a larger equivalent flexural stiffness than that of the baseline panel.

Acoustic Energy Harvesting Using Quarter-Wavelength Straight-Tube Resonator

Although there have been significant efforts in harvesting environmental energy, our environment is still full of wasted and unused energy. As clean, ubiquitous and sustainable energy source, acoustic energy is one of the wasted energies and is abundant in our life. Therefore, it is of great interest to investigate acoustic energy harvesting mechanism as an alternative to existing energy harvesters. In this study, in order to harvest acoustic energy, piezoelectric cantilever beams are placed inside a quarter-wavelength straight-tube resonator. When the straight-tube resonator is excited by an incident wave at its acoustic eigenfrequency, an amplified acoustic resonant wave is developed inside the tube and drives the vibration motion of the piezoelectric beams. The piezoelectric beams have been designed to have the same structural eigenfrequency as the acoustic eigenfrequency of the tube resonators to maximize the amount of the harvested energy. With a single beam placed inside the tube resonators, the harvested voltage and power become the maximum near the tube open inlet where the acoustic pressure gradient is at the maximum. As the beam is moved to the tube closed end, the voltage and power gradually decrease due to the decreased acoustic pressure gradient. Multiple piezoelectric beams have been placed along the centerline of the tube resonators in order to increase the amount of harvested energy. Due to the interruption of acoustic air particle motion caused by the beams, it is found that placing piezoelectric beams near the closed tube end is not beneficial. The output voltage of the piezoelectric beams increases linearly as the incident sound pressure increases.Copyright

Wave‐number domain representation of tire vibration

In the work to be described here, wave‐number decomposition techniques have been used to study tire vibration. In the experimental component of this work, a tire was driven radially at a point on its treadband. Measurements of the resulting radial treadband vibration were made at approximately 200 points around the treadband circumference by using a laser Doppler velocimeter. From an inspection of the resulting space‐frequency data, it was possible to identify the frequency ranges in which the tire responded either modally or nonmodally. Further, by performing a circumferential wave‐number decomposition of the space‐frequency data, the propagation characteristics of the wave types that contributed to the response of a tire could be determined. It was observed that a small number of circumferentially propagating waves combine to control the response of a tire in both low‐ and high‐frequency ranges. The cut‐on and propagation characteristics of these waves are closely related to propagating waveguide modes ...

Effects of fluid medium flow and spatial temperature variation on acoustophoretic motion of microparticles in microfluidic channels.

A numerical modeling method for accurately predicting the acoustophoretic motion of compressible microparticles in microfluidic devices is presented to consider the effects of fluid medium flow and spatial temperature variation that can significantly influence the acoustophoretic motion. In the proposed method, zeroth-order fluid medium flow and temperature, and first- and second-order acoustic fields in the microfluidic devices are first calculated by applying quadratic mapping functions and a second-order finite difference method (FDM) to perturbed mass, momentum, and energy conservation equations and state equation. Then, the acoustic radiation force is obtained based on the Gorkovs acoustic radiation force equation and applied to the Newtons Equation of Motion to calculate the microparticle motion. The proposed method was validated by comparing its results to a commercial software package, COMSOL Multiphysics results, one-dimensional, analytical modeling results, and experimental results. It is shown that the fluid medium flow affects the acoustic radiation force and streaming significantly, resulting in the acoustic radiation force and streaming prediction errors of 10.9% and 67.4%, respectively, when the fluid medium flow speed is increased from 0 to 1 m/s. A local temperature elevation from 20 °C to 22 °C also results in the prediction errors of 88.4% and 73.4%.

Acoustophoretic force-based compressibility measurement of cancer cells having different metastatic potential

Mechanical properties of cells such as compressibility are regarded to be different as cancer cells progress into metastatic state. Traditional methods for measuring mechanical properties of single cells such as AFM and micropipette aspiration require labor-intensive procedures and can cause damage to cells due to direct contact, thus unsuitable for high-throughput measurement. Acoustophoretic force exerted on particles under acoustic-standing-waves depends on the particle and medium’s vibro-acoustic properties. Thus, cells with different mechanical properties show different mobility under acoustic resonant field, which can be analyzed to decipher the mechanical properties of cells. Here we present a high-throughput, single-cell-resolution, cell compressibility measurement approach based on acoustic-standing-wave-induced force, and the finding that head and neck cancer cells having different metastatic capacities show noticeable differences in compressibility. The acoustophoresis chip has a straight flow ...

Three-dimensional visualizations of open fan noise fields

Fan noise is a dominant component of noise fields radiated from high-speed turbomachinery such as turbofan engines. For the purpose of understanding fan noise generation and propagation characteristics, a Nearfield Acoustical Holography (NAH) procedure is applied to visualize the three-dimensional sound fields radiated from a 4-blade test fan operating at 4.3, 4.7, and 5.1 kRPM. Here, a generalized planar NAH description including a partial field decomposition technique is described. The fan radiates strong tonal noise components at the 1st Blade Passing Frequency (BPF) and its higher harmonics. NAH reconstruction frequencies are selected at the 1st, 2nd, and 4th BPFs. It is shown that reconstructed sound fields can be used to identify the sound source locations and radiation patterns of the fan. For example, at the 1st BPF, a composite sound source that consists of 8 monopoles and rotates at the fan rotation speed is identified at the leading and trailing edges of blade tips. The latter finding leads to the modeling of the fan noise source as a combination of monopoles that rotates at the fan speed. At the 2nd and 4th BPFs, the sound sources of monopole type are mainly identified at the blade surfaces and edges. The reconstructed supersonic sound intensity fields indicate that the farfield noise radiations from the fan can be modeled by using a single off-centered monopole. The total sound power level calculated from the reconstructed active sound intensity fields on the source surface is dominant at the 1st BPF and decreases as the BPF increases: e.g., the total sound power levels are 96, 85, and 72 dB for the 1st, 2nd, and 4th BPFs, respectively.

Numerical modeling for analyzing microfluidic acoustophoretic motion of cells and particles with application to identification of vibro-acoustic properties

Microfluidic, acoustophoretic cell/particle separation has gained significant interest recently. In order to analyze the motion of cells/particles in the acoustophoretic separation, a one-dimensional (1-D) analytical model in a “static” fluid medium has been widely used, while the effects of acoustic streaming, viscous boundary layers, and 2-D and 3-D geometries are usually not considered. Therefore, it is not sufficient to accurately predict the cell/particle motion. Thus, a numerical modeling procedure for analyzing the acoustophoretic cell/particle motion is presented to include the aforementioned effects. Here, the first-order acoustic pressure and the second-order acoustic streaming velocity are first calculated by using a high-order finite difference method. Then, acoustophoretic force is calculated based on the acoustophoretic force equation proposed by Gorkov and is applied to the Newton’s equation of motion to calculate the motion of cells/particles. Through various simulations, the effects of ac...