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Page 2 of 25 Liu et al. Soft Sci. 2025, 5, 7 https://dx.doi.org/10.20517/ss.2024.69

INTRODUCTION
With the booming growth of the electric industry and wireless communication, particularly the rapid
development of 5G and various intelligent devices, high frequency in the gigahertz range has brought
undesirable electromagnetic (EM) radiation pollution . It is another pollution that is challenging to
[1-6]
[7]
manage after the water, noise, atmosphere, and solid waste . In the telecommunication, radar, military,
aviation, and other scientific implementation areas, etc., EM interference (EMI) can cause delicate electronic
devices to malfunction, severely interfere with signal communication, and hinder the running of smart
facilities and precision instruments, ultimately leading to system failure [8-11] . Moreover, studies show that
exposure to high electromagnetic wave (EMW) density poses risks to human health and increases the
likelihood of diseases [12-16] .

To tackle the above-mentioned problems, the application of EMI shielding materials is an effective
approach [17-20] . The EMI shielding can be realized by reflecting or absorbing EMW. Secondary EM pollution
could arise from the reflecting shielding materials. However, absorbent shielding materials are in high
demand since they primarily absorb EMW and convert them into heat or other energy [21-25] . The
requirement for EMW absorbing materials that are suitable for usage environment and function is
increasing. Generally speaking, the next generation of EM absorbing materials should have light weight,
thin thickness, flexibility, strong absorption capability, outstanding impedance matching, and wide effective
absorption bandwidth (EAB) [22,26-29] . Nowadays, designing efficient EMW absorbers with multifunctionality
is still quite challenging.

The major focus of the fabrication of EMW absorbers is metals, carbon materials, magnetic materials,
conductive polymer materials, MXene, metal-organic frameworks (MOFs), and composite materials [26,30-32] .
Nonetheless, the traditional metal-based EMW absorbing materials have high density and are prone to
corrosion. Carbon materials have low density and good electrical conductivity, but excellent absorbing
materials also need good impedance matching performance. Therefore, carbon materials alone are not an
ideal absorber and need to be improved . Because of their low density, remarkable resilience to corrosion,
[30]
processability, moldability, high design flexibility, and tunable specific shielding capability, polymer-based
materials hold great promise for the creation of advanced EMW absorbers [1,33,34] .

Generally, there are two strategies to improve microwave absorption. The first method is heterointerface
engineering strategy which achieves an excellent impedance matching . Another method is to build
[13]
absorbers with unique structures to increase their capacity to absorb EMW by regulating the surface and
interface properties [26,31,35-39] .

EMW ABSORBING STRATEGY OF POLYMER-BASED MATERIALS
Absorption, reflection, and multi-reflections were the EMI shielding mechanisms. Materials with a
reflection mechanism exhibit high electrical conductivity, where interactions between the EM field and
charge carriers result in EMW reflections . The interactions of magnetic or electric dipoles produce the
[40]
EMW absorption. The pores, interfaces, and flaws generated multi-reflections. In order to obtain
appropriate EMW absorption properties, dielectric/magnetic loss, and impedance matching ought to be
considered [11,21,41] .

The dielectric/magnetic loss and impedance matching of polymer-based EMW absorbers can be adjusted by
cooperating conductive and dielectric components with magnetic material, adjusting the structure, and
constructing heterointerfaces [8,42-44] . Figure 1 is the expected EMW absorbing mechanism of advanced
polymer-based materials with multi-components, designed structures, and heterogeneous interfaces.