Ultrasonic Characterization, Simulation of Porous Metal in the Interest of High Frequency Applications

Porous materials exist widely and play an essential role in many industries and in daily life. Industrial areas where they can be easily found are energy management, vibration suppression, thermal insulation, fluid filtration, and sound absorption. The introduction of pores in a material makes it possible to modify the properties of the initial material. These changes generate or reinforce desired properties, which are not observed or exhibited in a limited way in the original material. In particular, the variation of the structural properties of porous materials, such as the porosity and the size of the pores, imply an evolution of the acoustic properties like the acoustic impedance and the acoustic attenuation of these materials. This fact explains why porous materials currently attract a huge attention in the development in the acoustic field to absorb sound noises at low frequencies of the range 2 – 6 kHz and to apply to high frequency domain. In this context, porous metals are relatively new classes of engineering materials. Research is set up to carry out studies on the ultrasonic characterization and the simulation of the porous metals in the interest of high frequency applications. Two important acoustics properties of the materials were determined from measurements in water using two methods: the first is based on an insertion-substitution technique and the second is based on a multiple reflection echoes technique. In both cases, the transit time measurements and the frequency analysis are carried out considering the reflection and transmission coefficients at the interfaces to determine the ultrasonic celerity and the attenuation in the porous material. A simulation model is developed in parallel to evaluate these results. Several porous materials were investigated with the porosity ranging from 25% to 50% with pore size ranging from 1.7μm to 60μm. The acoustic impedance of the porous material depends linearly on the porosity and can be described by a simple model of homogenization of a fluid in a solid matrix. Results show that the acoustic attenuation strongly depends on the porosity and can reach 4.3 dB.mm-1 at 1MHz.