Fig. 4: Surface-wave-assisted nonreciprocity in focusing.
From: Surface-wave-assisted nonreciprocity in spatio-temporally modulated metasurfaces
a Measured reflected field power at ω+1 in the forward off-axis focusing experiment (kin = 0). b Calculated snapshot of the reflected electric field distribution for the reverse scattering process \(( - \nabla \varphi _{\bar n = + 1}^{{\mathrm{focus}}},\omega _{{\mathrm{in}}} + {\mathrm{\Omega }}) \to ( - 2\nabla \varphi _{\bar n = + 1}^{{\mathrm{focus}}},\omega _{{\mathrm{in}}})\) for the infinite-sized STMM. The black line represents the time-averaged Poynting vector for the same scattering process. c Measured power at ωin in the far-field for the reverse process is mainly confined within the wedge-shaped region. Data at given radii of the arc sector correspond to different locations \(\ell\) of the monopole source. Indicated are the calculated main directions of radiative emission from the right and left edges of the STMM and angles subtended between their crossings with the arc and its center, respectively given by \(\alpha _{\mathrm{R}}^{{\mathrm{th}}} = + 53.27^\circ\) and \(\alpha _{\mathrm{L}}^{{\mathrm{th}}} = - 20.36^\circ\). The measured scanning angles for the main peaks on the right-side and left-side are \(\alpha _ + ^{{\mathrm{exp}}} = ( + 54 \pm 1)^\circ\) and \(\alpha _ - ^{{\mathrm{exp}}} = ( - 26 \pm 1)^\circ\). d Same as c but as a function of the scanning angle and \(\ell\). Parameters are xf = 6 cm and zf = 15 cm \((\ell _f = 16\,{\mathrm{cm}})\). In all panels ωin = 2π × 6.9 GHz and Ω = 2π × 50 kHz.
