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The purpose of this paper is to investigate the sound absorption by modeling for the aluminum foam produced by press infiltration casting.

First use Johnson-Allard-Champoux (JAC) model to calculate the sound absorption coefficient of the present aluminum foam, and then improve it after finding its deviation from the experimental data, so as to get an improved model that could have a good agreement with the experimental result.

Using JAC model to calculate the sound absorption coefficient of the present aluminum foam, it is found that the model may have a good agreement with the experimental data only for the sound wave frequency below the absorption peak frequency, but a large deviation from the experimental result for the sound wave frequency above this frequency.

Improving JAC model by means of two factors, i.e., the absorption peak frequency and the specific surface area, the resultant improved model could be in good agreement with the experimental data.

This paper aims to present a data-processing methodology combining kernel change detection (KCD) and efficient global optimization algorithms for solving inverse problem in eddy current non-destructive testing. The main purpose is to reduce the computation cost of eddy current data inversion, which is essentially because of the heavy forward modelling with finite element method and the non-linearity of the parameter estimation problem.

The KCD algorithm is adapted and applied to detect damaged parts in an inspected conductive tube using probe impedance signal. The localization step allows in reducing the number of measurement data that will be processed for estimating the flaw characteristics using a global optimization algorithm (efficient global optimization). Actually, the minimized objective function is calculated from data related to defect detection indexes provided by KCD.

Simulation results show the efficiency of the proposed methodology in terms of defect detection and localization; a significant reduction of computing time is obtained in the step of defect characterization.

This study is the first of its kind that combines a change detection method (KCD) with a global optimization algorithm (efficient global optimization) for defect detection and characterization. To show that such approach allows to reduce the numerical cost of ECT data inversion.

This paper aims to propose to study the control of tube parameters in terms of diameter, separation between adjacent tubes and length, on delay and power dissipation in single-walled carbon nanotube (SWCNT) bundle interconnect for VLSI circuits.

The paper considers a distributed-RLC model of interconnect. A CMOS-inverter driving a distributed-RLC model of interconnect with load of 1 pF. A 0.1 GHz pulse of 2 ns rise time provides input to the CMOS-inverter. For SPICE simulation, predictive technology model (PTM) is used for the CMOS-driver. The performance of this setup is studied by SPICE simulation in 22 nm technology node. The results are compared with those of currently used copper interconnect.

SPICE simulation results reveal that delay increases with increase in separation between tubes and diameter whereas the reverse is true for power dissipation. The authors also find that SWCNT bundle interconnects are of lower delay than copper interconnect at various lengths and higher power dissipation due to dominance of larger capacitance of tube bundle.

The investigations show that tube parameters can control delay and this can also be utilized to decrease power dissipation in SWCNT bundle interconnects for VLSI applications.

The purpose of this paper is the design and experimental investigation of compact hybrid sound-absorbing materials presenting low-frequency and broadband sound absorption.

The hybrid materials combine microchannels and helical tubes. Microchannels provide broadband sound absorption in the middle frequency range. Helical tubes provide low-frequency absorption. Optimal configurations of microchannels are used and analytical equations are developed to guide the design of the helical tubes. Nine hybrid materials with 30 mm thickness are produced via additive manufacturing. They are combinations of one-, two- and four-layer microchannels and helical tubes with 110, 151 and 250 mm length. The sound absorption coefficient of the hybrid materials is measured using an impedance tube.

The type of microchannels (i.e. one, two or four layers), the number of rotations and the number of tubes are key parameters affecting the acoustic performance. For instance, in the 500 Hz octave band (α₅₀₀), sound absorption of a 30 mm thick hybrid material can reach 0.52 which is 5.7 times higher than the α₅₀₀ of a typical periodic porous material with the same thickness. Moreover, the broadband sound absorption for mid-frequencies is reasonably high with and α₁₀₀₀ > 0.7. The ratio of first absorption peak wavelength to structure thickness λ/T can reach 17, which is characteristic of deep-subwavelength behaviour.

The concept and experimental validation of a compact hybrid material combining a periodic porous structure such as microchannels and long helical tubes are original. The ability to increase low-frequency sound absorption at constant depth is an asset for applications where volume and weight are constraints.

This paper aims to study the design and characterization of a 3D printed tetrakaidecahedron cell-based acoustic metamaterial. At present, the mitigation of low-frequency noise involves the utilization of spatially demanding materials for the absorption of sound. These materials lack the ability for targeted frequency control adjustments. Hence, there is a requirement for an approach that can effectively manage low-frequency noise using lightweight and durable materials.

The CAD model was created in SolidWorks and was manufactured using the Digital Light Processing (DLP) 3D printing technique. Experimental study and numerical simulations examined the metamaterial’s acoustic absorption. An impedance tube with two microphones was used to determine the absorption coefficient of the metamaterial. The simulations were run in a thermoviscous module.

The testing of acoustic samples highlighted the effects of geometric parameters on acoustic performance. Increment of the strut length by 0.4 mm led to a shift in response to a lower frequency by 500 Hz. Peak absorption rose from 0.461 to 0.690 as the strut diameter was increased from 0.6 to 1.0 mm. Increasing the number of cells from 8 to 20 increased the absorption coefficient and lowered the response frequency.

DLP 3D printing technique was used to successfully manufacture tetrakaidecahedron-based acoustic metamaterial samples. A novel study on the effects of geometric parameters of tetrakaidecahedron cell-based acoustic metamaterial on the acoustic absorption coefficient was conducted, which seemed to be missing in the literature.

The purpose of this paper is to investigate the acoustic properties of needle-punched nonwovens produced of bamboo, banana and hemp fibers blended with polyester (PET) and polypropylene (PP) as they are supportive enough to minimize sound transmission inside the automobiles.

Textile materials like bamboo, banana and hemp blended with PET and PP in the ratio of 35:35:30 were applied to make the web. The needle-punching technique was applied to each web for three times to form a full nonwoven textile composite. The concept of PET/PP blend with natural fibers was to enhance the consistency and thermoform propensity of the composites. When nonwoven textile composites were placed in between a sound source and a receiver, they absorbed annoying sound by dissolving sound wave energy. Sound absorption coefficient was measured by the impedance tube method as per ASTM C384 Standard. Bamboo/PET/PP composite showed the highest absorption coefficient in most of the frequencies.

Physical and comfort properties were tested for the composites and it was noticed that bamboo/PET/PP composites with its compressed structure showed a better stiffness value, lesser thermal conductivity, lesser air permeability, better absorption coefficient and highest sound transmission loss compared to other two composites. At 840 Hz, the absorption coefficient of bamboo/PET/PP remained in satisfactory level but it was inferior by 20 percent in banana/PET/PP. Conversely at more frequencies like 1,680 Hz, there was a decrease from the target level in all the nonwovens composites, which could be enhanced by raising the thickness of the nonwovens, and all these properties of bamboo/PET/PP were considered appropriate for controlling noise inside the vehicles.

This research will provide facilities to decrease noise inside the vehicles. It will improve the apparent value of the automobiles to the traveler and also provide a sensible goodwill to the manufacturer.

This research will open several ways for the development of different nonwoven composites, particularly for the sound absorption and will open possible ways for the scholars to further study in this field.

THE last decade has seen great progress in the development of the electronic flash tube and there are today few scientific or engineering projects which do not employ the tube as a high‐speed photographic light source to secure data which cannot otherwise be obtained. Aeronautical research is no exception; the technique of flash photography was accelerated during the war years, both in this country and America, primarily to meet the many and varied problems which arise in aircraft engineering.

The purpose of this paper is to research the morphologies of the oxide films formed on the internal surfaces of water wall tubes in a 600 MW furnace at 300° while using CPT, CT, AVT(R) and AVT(O) water chemistry. In these water chemistry conditions, a layer of oxide film spontaneously forms in the furnace wall which could prevent corrosions in boiler water directly contact with the inner tube and reduce the probability of tube perforation.

The different morphologies, specific functions and distribution in the oxide film were identified by electrochemical workstation, XRD, SEM and EDAX.

It is concluded that metal surface was rugged and had deep corrosion in CPT. Ions penetrated into the oxides of large particles with gaps and intergranular corrosion occurred in CT conditions. In AVT(R), the oxide film uniformly covered on the metal surface played a protective role, but could be easily washed away by solution. The oxide film formed in AVT(O) was similar to AVT(R), but the difference is that large solid particles of Fe₂O₃ cover the outermost oxide film, which prevents the oxide film from being taken away by the flowing solution. In consequence, the degree of corrosion sustained by the tube walls is lowest in the case of AVT(O).

The results can provide reference for reducing the high temperature corrosion of metal in the actual operation.

At present, piezoelectric impedance technology has been used in the study of wood damage monitoring. However, little effort has been made in the research on the application of piezoelectric impedance system to monitor the change of wood moisture content (MC). The monitoring method of wood MC is used by piezoelectric impedance technique in this study.

One piezoceramic transducer is bonded to the surface of wood specimens. The MC of the wood specimens increases gradually from 0% to 60% with 10% increments; the mechanical impedance of the wood specimen will change, and the change in the mechanical impedance of the structure is reflected by monitoring the change in the electrical impedance of lead zirconate titanate. Therefore, this paper investigates the relationship between wood MC change and piezoelectric impedance change to verify the feasibility of the piezoelectric impedance method for monitoring wood MC change.

The experiment verified that the real part of impedance of the wood increased with the increase of wood MC. Besides, the damage index root mean square deviation is introduced to quantify the damage degree of wood under different MC. At the same time, the feasibility and validity of this experiment were verified from the side by finite element simulation. Finally, MC monitoring by piezoelectric impedance technique is feasible.

To the best of the authors’ knowledge, this work is the first to apply piezoelectric ceramics to the monitoring of wood MC, which provides a theoretical basis for the follow-up study of a wide range of wood components and even wood structure MC changes.

One of the recent applications of fabrics is to use them for sound insulation. Accordingly, due to their low production cost and low relative density, fabrics have drawn attention in some of the industries such as the automotive and aircraft industries. The present study is aimed to investigate the effects of the fiber cross-section, porosity, thickness of samples and fuzzing of the knitted fabric on the sound absorption coefficient.

In the present study, fabrics with three different stitch densities were knitted by yarns consist of three different forms of fiber cross-section shapes (circular, elliptical and plus-shaped). In this work, the sound absorption coefficient of knitted fabrics was investigated with regard to the different fiber cross-sections and structural parameters using an impedance tube.

As indicated by the obtained results, the cross-section, porosity, thickness and mass per unit area of the fabrics were the determinant factors for the sound absorption coefficient. In addition to, the sound absorption coefficient and porosity were shown to have an inverse relationship.

A section of the present paper has been allocated to the investigation of the effect of the fiber cross-section and fuzzing of fabric on the sound absorption of plain knitted fabrics.