In this work, we experimentally implemented square-root higher-order topological insulators (HOTIs) in topological electric circuits with decorated Su–Schrieffer–Heeger (SSH) lattice. Due to the square-root operation, the corner states of the square-root HOTIs typically appear on the finite energy. Through theory and experiments, the corner states in both the parent and square-root HOTIs models, as well as their spectrum connection, were demonstrated. Our work not only experimentally substantiates the existence of square-root higher-order topology in decorated SSH lattice model, from the perspective of electric circuits, but also extends the possibilities for observing various topological phases in acoustic and mechanical systems.

In this paper, a broadband vortex beam generator based on the graphene metasurface reflectarray is demonstrated in terahertz region. The designed graphene metasurface reflectarray structure realizes the generation of orbital angular momentum vortex wave with topological charges of l=±1, l=±2 and l=±3 ranging from 2 to 2.4 THz by modulating the chemical potential and the radius of the graphene unit. Moreover, all of the vortex beam with topological charges of l=+1, l=+2 and l=+3 have a high purity in the range from 2 to 2.4 THz. Our finding shows that the graphene metasurface reflectarray structure might find applications in the fields of broad band vortex wave devices in THz domains and also provide new insights into innovative low-profile devices in the wireless communication.

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Fractional Fourier transform (FrFT) is a kind of generalized Fourier transform and linear frequency modulation signals can be well focused after FrFT. Meanwhile motion error is an important factor affecting SAR (synthetic aperture radar) resolution, aiming at the problem that the effect of error elimination is not obvious in processing non-stationary motion error using the conventional SAR imaging algorithm, FrFT is combined with two-step motion compensation technique and wavenumber domain imaging algorithm in this paper. Simulation results and imaging results of real SAR data show that the proposed algorithm indeed eliminates the influence of motion error effectively. (the real SAR data provided by Institute of Electronics, Chinese Academy of Sciences).

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