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In this study, we investigate a one-dimensional (1D) unidirectional phononic waveguide embedded within a three-dimensional (3D) hexagonal close-packed phononic crystal, achieved by the introduction of a screw dislocation. This approach does not rely on the non-trivial topological characteristics of the 3D crystal. We discover that this dislocation induces a pair of helical modes, characterized by their orthogonal $x$- and $y$-directional displacements being out of phase by 90 degrees, which results in a distinctive rotational motion. These helical modes demonstrate directional propagation, tightly linked to the helicity of the screw dislocation. Through considerations of symmetry, we reveal that the emergence of these helical modes is governed by the symmetry of the screw dislocation itself. Our findings not only provide insights into the interplay between dislocation-induced symmetry and wave propagation in phononic systems but also open new avenues for designing directionally selective waveguides without relying on the crystal's topological properties., Comment: 13 pages, 4 figures

A varactor-based reconfigurable multifunctional metasurface capable of simultaneous beam steering, polarization conversion and phase offset is proposed in this paper. The unit cell is designed to naturally decompose the incident waves into two equal amplitude orthogonal linear components, and by integrating varactors, the reflection phase of the field components can be engineered from $-180^{\circ}$ to $180^{\circ}$.Taking advantage of the infinite states of the varactors, this design integrates a new function, the phase offset. After simulation validation of its capability, a four-layer $7$ by $6$ unit one-dimensional prototype is fabricated as a printed circuit board. It is experimentally demonstrated that it switches between X/Y and circular polarization with more than $10$ dB cross polarization isolation, while reaching $\pm45^{\circ}$ steering and $\pm180^{\circ}$ phase offset.

Manipulating the electromagnetic (EM) reflection behavior from an arbitrary surface dynamically on arbitrary design goals is an ultimate ambition for many EM stealth and communication problems, yet it is nearly impossible to accomplish with conventional analysis and optimization techniques. In this paper we present a reconfigurable conformal metasurface prototype as well as a workflow that enables it to respond to multiple design targets on the reflection pattern with extremely low on-site computing power and time. The metasurface is driven by a sequential tandem neural network which is pre-trained using actual experimental data, avoiding any possible errors that may arise from calculation, simulation or manufacturing tolerances. This platform empowers the surface to operate accurately in a complex environment including varying incident angle and operating frequency, or even with other scatterers present close to the surface. The proposed data-driven approach requires minimum amount of prior knowledge and human effort yet provides maximized versatility on the reflection control, stepping towards the end form of an artificial-intelligence-based tunable EM surface.

Breaking reciprocity in the microwave frequency range will have important implications for modern electronic systems. Since it usually involves bulky biasing magnets or complex spatial-temporal modulations, exploring a lightweight, all-passive approach becomes intriguing. Starting from a circuit model, we theoretically demonstrate the nonreciprocal behaviour on a transmission line building block creating a strong field asymmetry with a switchable matching stub to enable two distinct working states. After translating to an electromagnetic model, this concept is first proved by simulation and then experimentally verified on a microstrip-line-based diode-integrated metasurface showing nonreciprocal transmission. This printed circuit board design is expected to find various applications in electromagnetic protecting layers, communication systems, microwave isolators and circulators.

Symmetry indicators are a modern tool for characterizing topological phases that require only minimal computational expense but provide an elegant means of designing practical devices. This paper demonstrates how a rotational symmetry indicator can be used to construct and characterize a topologically robust waveguide, which is then verified experimentally on a printed circuit board (PCB) platform. The design takes advantage of the real-space gauge-dependency of the symmetry indicators and adopts a $C_6$ lattice with simple shifts, forming a defect line supporting topological edge modes. It is shown that the modes can realize the same features as previous topological waveguides, but in addition possesses a greater degree of reconfigurability and the unique ability to form a one-way termination. Moreover, the design illustrates the critical role real space information plays in determining the topological properties of photonic crystals, enabling a wider range of possible realizations.

A metallic ring based, diode-integrated, low-profile, power-dependent, reflective metasurface working from 3 GHz to 3.6 GHz is proposed in this letter. Unlike the previous study which shifts a band up and down to change the impedance of the surface, the triggering of the diodes directly transforms the structure from a surface wave supportive state to a self-induced bandgap topology if exposed to high power RF illumination. We demonstrate the concept by conducting the EM-circuit co-simulation and measurements for a 6 by 8 unit 2D prototype. Near field scan experiments verify that the proposed topology works in two distinct states, the ON and OFF state, and high-power measurements prove that the reflection varies with the incident signal power. The highest 10 dB decrement in transmission occurs at 3.3 GHz with 52 dBm illumination. This structure can be used to protect sensitive devices from large signals while otherwise supporting a communication channel for small signals.

Wide-band absorption is a popular topic in microwave engineering to protect sensitive devices against broadband sources. However, the Bode-Fano criterion defines the trade-off between bandwidth and efficiency for all passive, linear, time-invariant systems. In this letter, we propose a broadband absorber beyond the Bode-Fano limit by creating an energy trap using time-modulated switch/diodes. This work starts with an ideal circuit model to prove the concept, followed by two EM realizations - a freuqnecy selective surface (FSS) approach for general bandwidth broadening and a low-profile PCB design. The prototype of the latter is built and measured, demonstrating a Bode-Fano integral larger than one. This approach paves a way to many practical ultra-wide band absorber designs.