The effects of voids and recesses on the transmission loss of honeycomb sandwich panels

Sandwich honeycomb composite panels are lightweight and strong, and, therefore, provide a reasonable alternative to the aluminum ring frame/stringer architecture currently used for most aircraft airframes. One drawback to honeycomb panels is that they radiate noise into the aircraft cabin very efficiently provoking the need for additional sound treatment which adds weight and reduces the material’s cost advantage. A series of honeycomb panels was made which incorporated different design strategies aimed at reducing the honeycomb panels’ radiation efficiency while at the same time maintaining their strength. The majority of the designs were centered on the concept of creating areas of reduced stiffness in the panel by adding voids and recesses to the core. The effort culminated with a reinforced/recessed panel which had 6 dB higher transmission loss than the baseline solid core panel while maintaining comparable strength.