![]() investigated the membrane-based acoustic metamaterials with the honeycomb structure and found that low frequency noise reduction could be significantly improved. explored the transmission loss of honeycomb sandwich structures with attached gas layers and impedance mismatch of gasses were shown to be an effective means to decrease the sound transmitted across a sandwich panel. Ruzzene found that sandwich beams with honeycomb topology were generally more effective for vibration and sound transmission reduction applications. analyzed the sound absorption characteristics of a panel sound absorber with a honeycomb structure in its back cavity, and found that the peak value increased along with the peak frequency decreased with a thin honeycomb. found the variation in the resistance of the porous honeycomb had a significant impact on the acoustic attenuation when the face sheet resistance had given a value. designed a new honeycomb core by the increase of the stiffness of the panel to improve the noise transmission loss at low frequencies, the results showed the honeycomb panels had higher transmission loss at the frequencies between 100 and 200 Hz due to higher stiffness and damping. explored the sound insulation of honeycomb sandwich panels and found that the noise transmission reduced by adding the honeycomb stiffened structure and damping materials. discussed some dynamical properties of sandwich structures with honeycomb and foams core by using Hamilton's principle. developed an expression for the modal density of honeycomb sandwich panels with orthotropic face sheets from a fourth-order equation which was modified from the governing equation for a symmetric laminate by including the shear flexibility of the core. Additionally, the acoustical effect of honeycombs back with sound absorbing systems has also been studied, particularly for porous absorbent materials. It is important to understand the relation between acoustic properties and structures in order to protect the occupants in aircraft and vehicle cabins from the noise of the power plants. In addition to their good lightweight stiffness properties, they are also useful in impact absorption, low energy loss elastomeric materials, thermal management and sound reduction. Honeycomb sandwich panels have been increasingly used instead of metal structures for the construction of aircraft and spacecraft due to their high stiffness-to-weight ratios. It is possible to obtain various properties and desired performance by varying the honeycomb structure, the thickness and the material of the face sheet. Honeycomb sandwich panel is formed by adhering two face sheets with a low-density honeycomb core. Honeycomb sandwich panels are used in the aerospace, automotive industry and other transport sectors for their high mechanical performance per unit weight, high energy-absorption capability and low density,. Especially, the STL difference reaches the maximum at around 20 dB at frequencies below 3.0 kHz. The advantage of glass fiber assembly for improving the STL of honeycomb sandwich panel is particularly clear at frequencies below 4.5 kHz. ![]() Random glass fiber assembly with the fine fibers has the best STL in the all testing samples. STL can be improved by the increase of the fiber content. The experiment results indicate that the first resonance frequency of SAC disappears along with the improvement of the second resonance frequency by reducing the fiber diameter or increasing the fiber content. Sound absorption coefficient (SAC) and sound transmission loss (STL) are determined by a B&K impedance tube. Effect of glass fiber assembly with different filling shapes (random and fiber ball), fiber diameter, fiber content and air-layer on acoustic properties are explored. A new composite structure (glass fiber assembly-filled honeycomb sandwich panel) is prepared in order to improve the acoustic properties.
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