Available Technology

Variable-Depth, Multi-Layer Liner for Aircraft Noise Reduction

New design significantly improves control of the acoustic properties of liners used for aircraft noise reduction
Conventional broadband acoustic liners are generally limited to two layer configurations, with the internal septa placed at a constant depth for ease of manufacturing. This constant-depth constraint limits the ability of the liner to achieve broadband noise absorption needed for todays aircraft. In this design, the number of internal septa along with their respective insertion depths and DC flow resistance are carefully selected to achieve optimum broadband sound absorption over a targeted frequency range. These liners provide more precise control of the acoustic impedances and therefore increased sound absorption over a broad frequency range.
Patent Abstract: 
NASA Langley Research Center has developed a new approach for designing aircraft liner cores for noise reduction. These liner cores are comprised of multiple honeycomb-shaped chambers, each of which may contain one or more embedded porous septa. By varying the resistance and insertion depth of the septa between adjacent honeycomb core chambers, the number of tuning frequencies is increased for the full liner. High resistance septa can also be used to change the effective chamber depth. Together, these design features cause the acoustic liner to absorb sound over a broad frequency range.

Increased sound absorption resulting in noise reduction


Commercial aircraft

Military aircraft

Other places where engine noise could be a concern

Patent Number: 
Internal Laboratory Ref #: 
Patent Status: 
Patent Issue Date: 
February 21, 2018
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