In architectural design, few materials compare to the degree of use of concrete. Due its high compressive strength and economic efficiency, concrete excels in architectural applications. While impressive, concrete has shortcomings in its acoustic absorption properties and ability to be used sustainably. To address both concerns, the proposed solution is to introduce waste wood fibers into concrete's composition. Due to wood's fibrous nature, acoustic absorption can be bolstered while improving sustainability by recycling waste wood products. While manufacturing wood infused concretes and measuring acoustic absorption is not difficult, it is time consuming and resource intensive. Therefore, a model to estimate acoustic absorption coefficients of fiber-infused concretes is developed to aid in bypassing the need for experimental trial-and-error. The model utilizes the Delany-Bazley (DBz) and Johnson-Champoux-Allard-Lafarge (JCAL) models to predict acoustic absorption coefficients of given fiber-infused concretes. The DBz model provides an estimate of the characteristic impedance and wave number of a sample based on a power-law relationship that considers sound medium and airflow resistivity. The DBz model estimates are then refined by the JCAL model using estimated viscous and thermal properties of the sample. Finally, using these refined acoustic property estimates, the acoustic absorption coefficients are estimated. Using varying wood-infused concrete samples, results are experimentally verified using an impedance tube and absorption coefficients are calculated using the transfer-function method. After comparing estimated and measured absorption values, the current model was found to have the potential of providing a relative comparison of acoustic performance between compositions. However, estimated values were not accurate, nor considered representative of samples. Further, multiple aspects of the model could be improved to better represent different concrete compositions in model estimations.

The primary goal of this work is to measure the acoustic properties of a surface in situ. This generally involves sound pressure measurements and a calculation of the acoustic reflection factor of a surface, which may then be used to calculate the acoustic impedance or the acoustic absorption coefficient. These quantities are of use in acoustic simulations, architectural design, room acoustics and problems in noise control. It is of great interest to determine the performance of a particular surface where it is used, as opposed to measurements conducted in a laboratory. In situ measurements are not trivial, caution must be taken to ensure that high signal-to-noise levels are achieved and that the reflections of sound from the measurement environment are taken into consideration. This study presents five measurement methods that may be applied in situ. The acoustic absorption coefficient is calculated for each method on various surfaces spanning the whole range of absorption. Emphasis is placed on frequency resolution, in order to determine absorption characteristics in the bass region (50 Hz to 200 Hz). Advantages and disadvantages of each method are demonstrated and discussed. Finally, the in situ implementation of the surface pressure method is presented and measurements are made in order to test the limitations of this approach.

The primary goal of this work is to measure the acoustic properties of a surface in situ. This generally involves sound pressure measurements and a calculation of the acoustic reflection factor of a surface, which may then be used to calculate the acoustic impedance or the acoustic absorption coefficient. These quantities are of use in acoustic simulations, architectural design, room acoustics and problems in noise control. It is of great interest to determine the performance of a particular surface where it is used, as opposed to measurements conducted in a laboratory. In situ measurements are not trivial, caution must be taken to ensure that high signal-to-noise levels are achieved and that the reflections of sound from the measurement environment are taken into consideration. This study presents five measurement methods that may be applied in situ. The acoustic absorption coefficient is calculated for each method on various surfaces spanning the whole range of absorption. Emphasis is placed on frequency resolution, in order to determine absorption characteristics in the bass region (50 Hz to 200 Hz). Advantages and disadvantages of each method are demonstrated and discussed. Finally, the in situ implementation of the surface pressure method is presented and measurements are made in order to test the limitations of this approach.

Many structural acoustic and vibration designs rely extensively on materials that are light-weight, stiff, and highly damped. Advanced materials such as metallic foams can be engineered to achieve these properties in order to control sound and vibration for a variety of aerospace, maritime, and ground transportation applications. In this work, the structural and acoustic properties of commercially available and digitally designed metallic foams are analyzed through numerical and experimental methods. Furthermore as a post-manufacturing process, metallic foams can be engineered in order to preferentially alter the microstructure and achieve material property enhancements. In this work, the following engineering methods are proposed and investigated: plastic deformation and material saturation. When a metallic foam is plastically deformed, the foam's porosity and pore shape are dramatically altered. This transformation in microstructure can lead directly to changes in bulk properties. In this work, a method for triaxial hydrostatic compression of metallic foams is proposed and demonstrated experimentally. The structural properties of transformed foams are tested using a load cell with digital image correlation. Transformed foams exhibit higher compliance, higher toughness, and a reduced Poisson ratio. Measurement and analysis of acoustic properties indicate that the transformed foams can absorb significantly more sound than the conventional samples of equal thickness in the test range of 0.25 - 4.50 kHz. Due to their open-cell microstructure, metallic foams can be filled with saturating materials. In this work, metallic foams saturated with viscous liquids are investigated for reducing vibration transmissibility in a structure. For the best performing saturated foam subject to a transient excitation, an order of magnitude increase in damping ratio is measured. Additionally, a composite foam (consisting of metallic foam saturated with polyurethane foam) is fabricated to enhance acoustic properties. For the best performing composite foam at normal incidence, the sound absorption coefficient is improved by a factor of 6 near 0.60 kHz and by a factor of 2 up to 4.5 kHz. Lastly, two methods for estimating acoustic absorption in metallic foams are presented which utilize finite element analysis and boundary layer theory. The proposed methods are discussed for commercially available foams as well as for representative digital designs. Limitations and assumptions of the methods pertaining to size scales and boundary layer features are addressed.

No / Hemp concrete is an attractive alternative to traditional materials used in building construction. It has a very low environmental impact, and it is characterized by high thermal insulation. Hemp aggregate particles are parallelepiped in shape and can be organized in a plurality of ways to create a considerable proportion of open pores with a complex connectivity pattern, the acoustical properties of which have never been examined systematically. Therefore this paper is focused on the fundamental understanding of the relations between the particle shape and size distribution, pore size distribution, and the acoustical properties of the resultant porous material mixture. The sound absorption and the transmission loss of various hemp aggregates is characterized using laboratory experiments and three theoretical models. These models are used to relate the particle size distribution to the pore size distribution. It is shown that the shape of particles and particle size control the pore size distribution and tortuosity in shiv. These properties in turn relate directly to the observed acoustical behavior.

No / Clinkers of high alumina cements are separated into three granular formulations with particle sizes in the range 0.6-0.71 mm, 0.71-1.18 mm and greater than 1.18 mm. These are used to manufacture consolidated samples of porous concrete in an autoclave. The acoustic and microscopic properties of loose and consolidated porous samples of concrete are investigated using both experimental methods and mathematical modelling. Values of porosity, flow resistivity, tortuosity and parameters of the pore size distribution are determined and used to predict closely the sound speed, acoustic attenuation and normal incidence absorption coefficient of these materials. It is shown that high alumina cements do not require additional binders for consolidation and that the structural bonds in these cements are developed quickly between individual clinkers in the presence of water. The hydration product build-up during the consolidation process is insignificant which ensures good acoustic performance of the consolidated samples resulting from a sufficient proportion of the open pores. The value of porosity in the consolidated samples was found to be around 40%, which is close to that measured in some commercial acoustic absorbers. This work provides a foundation for the development of acoustically efficient and structurally robust materials, which can be integrated in environmentally sustainable concrete and masonry structures.

In general the acoustic wave is used as a detecting tool in the ocean, its application placing a sound source into ocean, then the sound may impinge involves the target by wave propagation in the ocean. Due to the reflection and scattering effect of target, part of acoustic energy will be received by transducer through the path of reflection. The goal of target identification can be achieved by signal processing finally. If a submarine wish to avoid the detection by sonar system , it should attenuate the acoustic energy . Therefore the reflected signal can not be analyzed and distinguished by sonar system .The area of underwater acoustic attenuation has been researched for camouflaging submarine purpose for many years. There are two acoustic energy attenuation methods to reduce the reflective wave and transmitted wave. One is active attenuation control, which is to understand how the destructive interference of incident acoustic wave could be achieved for acoustic energy attenuation purposes. The other one is passive acoustic attenuation technique, which rely on the attenuation performance of underwater acoustic material to reduce the acoustic energy of incident wave. To be evaluated the acoustic absorption efficiency of material. Although the efficiency of active attenuation control is better compared with passive acoustic attenuation technique, the development of active attenuation control have not been highly pursued in the commercial market for underwater application, due to the limitations in piezo-composite technology. The cost of installation and maintenance is also higher in active control. This thesis studied the acoustic absorptive material based on passive acoustic attenuation technique . It could be attenuated the acoustic energy and spectrum of reflection and transmitted wave. Therefore, the signal can not be analyzed and distinguishing by sonar system. According to Alberich acoustic absorption coating, their designs have the inherent problem of degradation under hydrostatic pressure and temperature. Thus, the objective of this thesis is to study the characteristics of the acoustic absorptive material at various water depth where the hydrostatic pressure are different. To measure the characteristics of acoustic material, an experimental system is setup, and the standard measuring method and criterion is also studied for future experimental reference. Furthermore, the different measurement parameters are discussed for accuracy of experimental results. There are five specimens tested in this experiment. The specimens are mainly made of neoprene and sawdust mixture and marked as A1¡BA2¡BA3¡BA4¡Band A5 respectively. The composites of these specimens are analyzed by x-ray diffraction meter. The physical properties and the acoustic absorption in airborne were measured before underwater hydrostatic pressure applied on these specimens. The physical properties show that the impedance of these specimens is very close to acoustic impedance of the water. Therefore, the specimen may be considered an acoustic isolator in the air. To reduce the boundaries interference, such as reflection, diffraction and scattering signal. The pulse sound is used as sound source in this underwater experiment. Moreover, the gating system is applied to capture the proper signals for analysis. The echo reduction and insertion loss are measured in the 11 to 30 kHz frequency region for acoustic absorption evaluation in this experiment. The performance of experiment is found that specimen has the echo reduction about 10 dB and the insertion loss about 15 dB at 1 bar hydrostatic pressure. But when the hydrostatic pressure was increased to 5 bar, the echo reduction and insertion loss were both decreased by 3 dB. In addition, when the hydrostatic pressure was loaded at 10 bar, the echo reduction was decreased by 8 dB, and the insertion loss was decreased by 5 dB. It became evident that the efficiency of acoustic absorption is degraded under the higher hydrostatic pressure.

This diploma thesis deals with the determination of the material acoustic absorption in an impedance tube. The aim of the work is to propose a measuring experiment and to design measuring device with the intention of reducing costs. The aim is to carry out a measuring experiment on a manufactured measuring device. The results of the experiment are evaluated in terms of meeting the requirements formeasuring device. The results of the tested materials are compared with the values from the supplier.

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This thesis is concerned with developing porous materials from tyre shred residue and polyurethane binder for acoustic absorption and thermal insulation applications. The resultant materials contains a high proportion of open, interconnected cells that are able to absorb incident sound waves through viscous friction, inertia effects and thermal energy exchanges. The materials developed are also able to insulate against heat by suppressing the convection of heat and reduced conductivity of the fluid locked in the large proportion of close-cell pores. The acoustic absorption performance of a porous media is controlled by the number of open cells and pore size distribution. Therefore, this work also investigates the use of catalysts and surfactants to modify the pore structure and studies the influence of the various components in the chemical formulations used to produce these porous materials. An optimum type and amounts of catalyst are selected to obtain a high chemical conversion and a short expanding time for the bubble growth phase. The surfactant is used to reduce the surface tension and achieve a homogenous mixing between the solid particulates tyre shred residue, the water, the catalyst and the binder. It is found that all of the components significantly affect the resultant materials structure and its morphology. The results show that the catalyst has a particularly strong effect on the pore structure and the ensuing thermal and acoustical properties. In this research, the properties of the porous materials developed are characterized using standard experimental techniques and the acoustic and thermal insulation performance underpinned using theoretical models. The important observation from this research is that a new class of recycled materials with pore stratification has been developed. It is shown that the pore stratification can have a positive effect on the acoustic absorption in a broadband frequency range. The control of reaction time in the foaming process is a key function that leads to a gradual change in the pore size distribution, porosity, flow resistivity and tortuosity which vary as a function of sample depth. It is shown that the Pade approximation is a suitable model to study the acoustic behaviour of these materials. A good agreement between the measured data and the model was attained.