Palvig Michael Forum, Breinbjerg Olav, Willatzen Morten
J Opt Soc Am A Opt Image Sci Vis. 2014 Sep 1;31(9):1912-8. doi: 10.1364/JOSAA.31.001912.
In order to obtain a benchmark for electromagnetic energy harvesting, we investigate the maximum absorption efficiency by a magneto-dielectric homogeneous sphere illuminated by a plane wave, and we arrive at several novel results. For electrically small spheres we show that the optimal relative permeability and permeability of materials where ϵ(r)', μ(r)'≥1 is (1+i3) independent of sphere size, while that of metamaterials is (-2+iδ), where the imaginary part δ decreases strongly with decreasing sphere size. For larger spheres we show that while maximum absorption efficiency occurs at the resonances of the spherical modes, there exists a wide plateau of high absorption efficiency when material intrinsic impedance is constant; in the case of free-space intrinsic impedance and electrical radius κ=1, the absorption efficiency becomes 2.8. The investigation is analytic/numerical and based on the Lorenz-Mie theory combined with the optical theorem.
为了获得电磁能量收集的基准，我们研究了平面波照射下磁电介质均匀球体的最大吸收效率，并得出了几个新颖的结果。对于电小尺寸球体，我们表明，对于介电常数ϵ(r)'、磁导率μ(r)'≥1的材料，最佳相对磁导率和磁导率为(1 + i√3)，与球体尺寸无关，而对于超材料则为(-2 + iδ)，其中虚部δ随球体尺寸减小而急剧下降。对于较大的球体，我们表明，虽然最大吸收效率出现在球形模式的共振处，但当材料本征阻抗恒定时，存在一个宽的高吸收效率平台；在自由空间本征阻抗和电半径κ = 1的情况下，吸收效率变为2.8。该研究是解析/数值的，基于洛伦兹-米氏理论并结合光学定理。
