The noise attenuation effect of aluminum Foam is determined by its unique structural features. Aluminum foam has a high porosity and a high interconnected pore rate, which allows sound waves to enter and be absorbed easily, meeting the structural requirements of typicalsound-absorbing materials. Additionally, the foam's metallic properties, such as high thermal conductivity and high vibration frequency, also contribute to sound wave absorption. The mechanism of its sound attenuation can be explained in two ways.
The Energy Dissipation Theory
When sound waves enter the pores of the foam, they cause the air within the pores to vibrate, which in turn causes the fibers of the foam to vibrate. Because the internal metal fibers of the aluminum foam are interconnected, they form a network that restricts each other's movement, causing the vibrations to be dampened and converted into heat.
At the same time, the friction between the vibrating air and the pore walls also converts mechanical energy into thermal energy. This heat is rapidly conducted away through the network of metal fibers and then dissipated into the surrounding air through convection, thereby attenuating and consuming the sound energy.
The Noise Source Control Theory
This theory is based on the principle of small-hole muffling. Aluminum foam has a large number of three-dimensional interconnected micropores. When a gas stream flows through these pores, the large stream is broken up into countless smaller, finer streams (much like a large column of water is dispersed when it flows through a sieve). This rapid dispersion of the gas stream reduces the outlet pressure and prevents or weakens the turbulence in the gas, thereby controlling the impact noise from high-speed airflow. This is also the reason why many common mufflers use perforated plates.
Experimental Findings
Relevant experiments show that aluminum foam has a good noise attenuation effect on noise ranging from 125 Hz to 16 kHz. The sound attenuation effect improves as the frequency increases.
1.For high-frequency noise above 1 kHz, the average reduction is 25 to 35 dB, with a maximum of 46 dB.
2.For medium- and low-frequency noise below 1 kHz, the average reduction is 15 to 25 dB, with a maximum of 36 dB.
This indicates that it has a good sound attenuation effect on medium- and low-frequency noise, which is particularly significant for solving the difficult problem of noise in these frequency ranges.
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