Study On Absorbing Properties Of Foam Core Sandwich Composites

This paper describes a new type of composite material that both absorbs electromagnetic wave and supports structural loads.The material is an advanced plastic foam sandwich composite incorporating radar absorbing materials. Our design enables the foam sandwich to be strong, thin and light, while achieving wide-spectrum absorption requirements, providing broad prospects for application.This paper studied the effect of radar absorbing material (RAM) distribution in composites and concentration of RAM on absorbing properties of polyurethane (PU) foam and polyvinyl chloride (PVC) foam sandwich composite. The complex permittivity and permeability of RAM was measured by the coaxial method, and the reflection losses of composites in the frequency range 8-18 GHz were measured using the free space technique. Next, the optimum distribution and concentration of RAM were confirmed. Finally, the impact resistance of PU foam sandwich composite and PVC foam sandwich composite were compared.The main results were:1. The RAM in each layer of multi-layered composite functions differently. For example MnO2 is more suitable for the surface layer, due to its impedance matching with air; while graphite is better for underlying absorption material to improve the electromagnetic wave loss rate. A small quantity of RAM in the PU foam also can improve the absorption of electromagnetic waves;2. The optimum concentration of MnO2 in surface layer was 15%, while the optimum concentration of graphite in the underlying layer was 35%;3. Higher density foam has a smaller cell diameter, which extends the path of electromagnetic wave propagation in the foam, increasing the absorption of the composite;4. Comparison of the impact resistance of PU sandwich composite with PVC sandwich composite found little difference at low impact energy. With increasing impact energy, the PVC sandwich composite performed better.In conclusion, PU sandwich composites have good absorbing properties, while PVC foam sandwich composites have good impact resistance. In practical application, the choice between the two depends on the weighting of each requirement. This study may guide the choice in design and application.