Lightweight Electromagnetic Absorption Performance and Size Effect of Ni@PPy Composites Based on Hollow Glass Microspheres

Abstract

Lightweight and broadband microwave absorbers are highly desirable for practical electromagnetic protection, yet achieving strong absorption at low density and reduced thickness remains challenging due to the trade-off between impedance matching and attenuation capability. Herein, a lightweight multilayer core–shell absorber (HNP) was constructed using hollow glass microspheres as the core, combined with a nickel-based intermediate shell and an outer polypyrrole layer to enhance conductive networks and interfacial polarization. By tuning the cavity size, systematic structure–property–performance relationships were established. With increasing cavity size, the permittivity is significantly enhanced, leading to improved dielectric and conductive losses. Notably, the absorber maintains an ultralow density of ~0.32 g·cm⁻³. As a representative system, HNP-110 exhibits loading-dependent absorption behavior. At 10 wt%, a minimum reflection loss (RL_min) of −51.39 dB is achieved at 10.88 GHz with a thickness of 2.7 mm, along with an effective absorption bandwidth (EAB) of 5.28 GHz. At 15 wt%, the EAB further expands to 5.44 GHz while maintaining strong absorption. Excessive loading (20 wt%) leads to impedance mismatch and performance deterioration. Mechanistic analysis reveals a transition from polarization-dominated to conduction-dominated loss, with optimal impedance matching (|Z_in/Z₀| ≈ 1) achieved at 10–15 wt%, enabling efficient broadband absorption.