Study On Design And Performance Of The Microwave Absorption Composite Coatings Based On Polyurethane

The morphology and electromagnetic characteristics of carbon black (CB), carbonyl iron (CIP), Fe-Si-Al (FSA), ferrite (FP), and Nano-carbonyl iron (nmCIP) were performed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vector network analyzer (VNA), and the electromagnetic wave absorbing mechanism of these absorbents were analyzed. Polyurethane (PU) based microwave absorbing coatings were manufactured with aluminium (Al) sheet or polrvinyl chloride (PVC) sheet as baseplate. The effects of absorbents content, complex method, special coating structure and different baseplate on absorbing properties of coatings were studied meticulously. The results show that:CB considered as a resistive-type absorbent, is easy to be polarized and form conductivity networks in the internal of composites, which could attenuate microwave via resistance loss, multiple scattering and leak-conductivity effect between conducting particles. CIP、n FSA、 FP are all absorbents based on magnetic loss, attenuating microwave via natural resonance and eddy-current loss. nmCIP is a magnetic nanoparticle, which possesses a new way to attenuate microwave with the special size and microwave effect.As the increasing absorbent content, the reflection loss (RL) peaks of Al-based coatings with CB、 CIP、FSA、 FP as absorbent respectively, shift towards low-frequency region. However, the impedance matching between coatings and atmosphere become very poor when the absorbent content rises above a certain threshold, and most of the electromagnetic wave will be reflected on the surface of coatings, accompanying the weak absorbing performance. Among of these coatings, FP/PU composite coating with a mass ratio of6:1displays the best absorption properties, exhibiting a minimum RL value of-30.7dB at13.8GHz and an effective RL (RL≤-10dB) band of9.5GHz (8.5-18GHz).The compound with different absorbents can enhance the absorption properties. nmCIP is an absorbent with efficient magnetic-loss and low density, compounded with CB could widen the effective absorption band of composite coatings; compounded with CIP, FSA, or FP could modify the effective absorption band obviously.The microwave absorption properties of discontinuous CIP/PU Al-based composite coatings are much better than common plate structural coatings. The absorption band of RL<-10dB widens from2.2GHz to3.6GHz, and the absorption band of RL≤-8dB widens from3.2GHz to13GHz. Compared with the Al-based coatings, the RL curves of PVC-based coatings with the same composition show two absorption peaks in the measurement range of2-18GHz, which perform much weaker absorption properties as a whole, but even better absorbing abilities in the low-frequency region. Among of these coatings, CIP/PU composite coating with a mass ratio of7:1exhibits a minimum RL value of-13.3dB at2.15GHz and an effective RL (RL≤-10dB) band of0.3GHz (2-2.3GHz). Through varying the thicknesses of PVC sheet and composites, the simulated coatings could achieve the effective RL (RL<-10dB) in the range of2-6GHz.