Retracted Article: A versatile strategy for alternately arranging the foam ratio layers of multilayer graphene/thermoplastic polyurethane composite foams towards lightweight and broadband electromagnetic wave absorption.

A broadband electromagnetic wave (EW) absorbing material should possess both wider effective absorption bandwidth and lower minimum reflection loss, depending on good impedance matching between the absorber and air and strong attenuation of EW. In this study, single-layer graphene/thermoplastic polyurethane (TPU) composite foams with different foam ratios and alternating multilayer graphene/TPU composite foams with different numbers of layers were prepared. Not only was the EW-absorbing mechanism of these composite foams examined, but also the relationship between the EW-absorbing properties and the number of layers were investigated. The single-layer sample S-5 with good impedance matching characteristics and S-3 with strong EW attenuation characteristics were selected as the constituent layers to design alternating multilayer graphene/TPU composite foams. Compared to the single-layer sample 4L-C (4L-C is defined as the monolayer sample S-4 with a thickness of 9 mm), the 4L alternating multilayer graphene/TPU composite foams could achieve more than 90% EW absorption in a wide frequency band of 8.5 GHz, and its minimum reflection loss was as low as -37.67 dB, which are very beneficial for its use as a lightweight, flexible electromagnetic wave absorbing material (EWAM) for broadband absorption. More importantly, the absorption of the obtained alternating multilayer composite foams could be simply modulated not only by the absorber thickness, but also by the number of layers to satisfy the applications in different frequency bands.