报告题目：Intri 活动暨光电子器件与系统教育部重点实验室高水平学术报告51：铁氧体电磁屏蔽材料晶格调控的研究 nsic Lattice Tuning to Architected Composites: Absorption-Dominated EMI Shielding with Ni-Modified Ferrites and thin polymeric EMI shield.

报告人：Dr. Atta Ur Rehman, 香港大学

时 间：2025.10.27（周一）下午3:30

地 点：粤海校区南校区致原楼1206

邀请人：曾昱嘉 教授

报告简介：

The proliferation of wireless systems, IoT devices, and next-generation 5G/6G networks has dramatically heightened concerns surrounding electromagnetic interference (EMI), which threatens the reliability, security, and safety of modern technologies. Emerging research further associates long-term exposure to high-frequency electromagnetic fields with potential biological effects, underscoring the urgent need for advanced EMI shielding solutions that safeguard both device performance and public health.

EMI shielding effectiveness is fundamentally determined by a material’s electrical conductivity (σ) and magnetic permeability (μ), with reflection and absorption losses governed by their interplay. Ferrimagnetic Fe₃O₄ is widely utilized for its simultaneous AC conductivity, dielectric response, and magnetic loss characteristics, yet its intrinsic electromagnetic properties are rarely tuned prior to composite integration. Addressing this gap, we investigated low-level cation substitution in Fe₃O₄ of the form M₀.₀₁Fe₂.₉₉O₄ (M = Mn, Ni, Cu, Zn). Among these, Ni incorporation led to the most significant enhancement in shielding effectiveness, raising attenuation from ~10 dB to ~22 dB[1], with absorption dominating over reflection. This improvement is attributed to increased dielectric constant, electrical conductivity, and saturation magnetization (Mₛ), consistent with facilitated small-polaron hopping between Fe²⁺↔Fe³⁺ sites, strengthened by Ni substitution. These changes collectively elevate both dielectric and magnetic loss tangents, thus maximizing absorption-dominated shielding.

We validated these findings in a parallel study of Ni₀.₀₁₋ₓZnₓFe₂.₉₉O₄, reaffirming that even modest Ni additions can substantially modify the electromagnetic properties of magnetite toward absorption-driven attenuation[2]. Extending this strategy to BaFe₁₂O₁₉, we observed analogous enhancements in dielectric and conductive properties [3], suggesting that targeted cation substitution across both spinel and hexaferrite families can strengthen intrinsic dissipation channels. Further, by integrating optimized Fe₃O₄ nanoparticles with mesocarbon microbeads and carbon nanotubes, we achieved composite shielding effectiveness exceeding 65 dB, demonstrating the synergy of magnetic and conductive pathways in amplifying loss mechanisms.

1. A.U. Rehman, M. Atif, S. Baqi, A. Ul-Hamid, U. ur Rehman, W. Khalid, Z. Ali, F.C.-C. Ling, M. Nadeem, Enhancement in the electromagnetic shielding properties of doped M0.01Fe2.99O4 magnetite nanoparticles (M=Mn2+,Ni2+,Cu2+,Zn2+), Journal of Alloys and Compounds, 960 (2023) 171051.

2. A.U. Rehman, M. Atif, U.u. Rehman, H. Wahab, F.C.-C. Ling, W. Khalid, A. Ul-Hamid, Z. Ali, M. Nadeem, Tuning the magnetic and dielectric properties of Fe3O4 nanoparticles for EMI shielding applications by doping a small amount of Ni2+/Zn2+, Materials Today Communications, 34 (2023) 105454.

3. M. Atif, H.U. Husnain, A.U. Rehman, U. Younas, T. Rafique, W. Khalid, Z. Ali, M. Nadeem, Enhancement in the dielectric and magnetic properties of Ni2+–Cu2+ co-doped BaFe11Cu1−xNixO19 hexaferrites (0.0 ≤ x ≤ 1.0), RSC Advances, 14 (2024) 6883–6895.

报告人简介：

Dr. Atta UR Rehman is an accomplished early career researcher specializing in electromagnetic interference (EMI) materials and advanced nanostructures. He graduated with distinction, earning both BS and MS degrees as the top student in academic and research performance, and received a fully funded PhD scholarship at Air University, Pakistan. His doctoral work on EMI absorbing materials was conducted at the Pakistan Institute of Nuclear Science and Technology (PINSTECH) and enriched by international research at the University of Hong Kong (HKU) under the IRSIP program.

Dr. Rehman has over eight years of hands-on research experience in the synthesis, characterization, and application of magnetic, dielectric, and EMI materials. With 21 peer-reviewed publications, over 300 citations, and an H-index of 10, Dr. Rehman’s research has demonstrated both quality and impact in the field. His current work at HKU as Senior Research Assistant focuses on transparent EMI shielding for medical applications, exemplifying his ability to address technological challenges through innovative approaches. Additionally, as Director of Technology R&D at Jiazhen Technology, China, Dr. Rehman actively bridges academia and industry, facilitating the translation of scientific advances into practical solutions.