Touch-Programmable Metasurface for Various Electromagnetic Manipulations and Encryptions.

Previous programmable metasurfaces integrated with diodes or varactors require external instructions for field programmable gate arrays (FPGAs), which usually rely on computer-inputs or pre-loaded algorithms. But the complicated external devices make the coding regulation process of the programmable metasurfaces cumbersome and difficult to use. To simplify the process and provide a new interaction manner, a touch-programmable metasurface (TPM) based on touch sensing modules is proposed to realize various electromagnetic (EM) manipulations and encryptions. By simply touching the meta-units of the TPM, the state of the diodes can be changed. Through the touch controls, the TPM can achieve independent and direct manipulations of meta-units and efficient inputs of coding patterns without using a FPGA or other control modules. Various coding patterns are demonstrated to achieve diverse scattering-field control and flexible near-field EM information encryptions, which verifies the feasibility of the TPM design. The presented TPM will have wide application prospects in imaging displays, wireless communications, and EM information encryptions.

Ultraviolet-sensing metasurface for programmable electromagnetic scattering field manipulation by combining light control with a microwave field.

Combining digital information science with metasurface technology is critical for achieving arbitrary electromagnetic wave manipulation. However, there is a scarcity of contemporary scholarly studies on this subject. In this paper, we propose an Ultraviolet (UV) sensing metasurface for programmable electromagnetic scattering field manipulation by combining light control with a microwave field. The active sensing of UV light and the real-time reaction of the scattering are achieved by integrating four UV sensors on the metasurface. On the metasurface, a UV sensor ML8511 and a voltage driver module are coupled to control each row of the Positive-Intrinsic-Negative (PIN) diodes. Due to the light sensing capability of the UV sensor, the on or off state of the PIN diode integrated into the programmable metasurface can be switched efficiently through the change of light. When the incident wave changes, various discrete data are transmitted to the FPGA. Then the FPGA performs the corresponding voltage distribution to control the state of the PIN diode. Finally, different metasurface coding sequences are generated to realize different electromagnetic functions. As a result, the spatial distribution of sensing light by sensors can be used to determine the electromagnetic field and connect sensing optical information with the microwave field. The simulation and measured results show that this design is feasible. This work provides a dimension for electromagnetic waves modulation.

Light-controllable metasurface for microwave wavefront manipulation.

Applying multiple physical fields to artificial manipulate electromagnetic waves is a highly stirring research. In this paper, we creatively combine light control with microwave scattering, realizing an optically coding metasurface for beam deflection based on anomalous reflection. A photoresistor and a voltage-driven module are connected to control each row of PIN-diode-loaded unit cells, endowing the reflection phase of the elements with a strong dependence on light. Owing to the high sensitivity of photoresistor, the digital element state "0" or "1" can be switched effectively via light variation sensed by the photoresistor. By modulating the light signal, the arrangement of digital elements can be reprogrammed, generating the specific scattering field. Therefore, the electromagnetic field can be determined by the spatial distribution of light, which induces the connect with the optical information and microwave field. The simulated and experimental results demonstrate the feasibility of our design. This light-steering approach provides a dimension for electromagnetic wave modulation.

Liquid metal metasurface for flexible beam-steering.

In this paper, we propose a reconfigurable metasurface based on liquid metal for flexible beam-steering. The Gallium alloy with low melting temperature (about 30°C) is employed for easy structure reconfiguration. By designing specific dimension of cavity, we make the liquid metal in it easily form into desired sizes, to generate distinct phase responses. Two metasurface elements with four phase responses are designed, simulated and measured. Based on the above elements, various scattering fields can be realized within our design. We present four schemes to achieve single- and dual-beam fields with different beam-deflecting angles. The measured results show great agreement with the simulations, validating our design. In addition, every two columns of the metasurface are grouped into a single composite form, which promises a customizable combination for metasurface pattern. Compared to the previous reconfigurable works for metasurfaces, the method via liquid metal possess lower cost, easier fabrication, and will further enrich the manipulation method for metasurfaces.

Optically Transparent Metasurface Absorber Based on Reconfigurable and Flexible Indium Tin Oxide Film.

In this paper, we present a flexible, breathable and optically transparent metasurface with ultra-wideband absorption. The designed double layer of indium tin oxide (ITO) films with specific carved structure realizes absorption and electromagnetic (EM) isolation in dual-polarization, as well as good air permeability. Under the illumination of x- and y-polarization incidence, the metasurface has low reflectivity and transmission from about 2 to 18 GHz. By employing ITO film based on polyethylene terephthalate (PET), the presented metasurface also processes the excellent flexibility and optically transparency, which can be utilized for wearable device application. In addition, the dual-layer design enables mechanically-reconfigurable property of the metasurface. The transmission and reflection coefficients in two polarizations show distinct difference when arranging the different relevant positions of two layers of the metasurface. A sample with 14*14 elements is designed, fabricated and measured, showing good agreement with the simulation results. We envision this work has various potentials in the wearable costume which demands both EM absorption and isolation.

Dual-functional tunable coding metasurface based on saline water substrate.

In this paper, a dual-functional tunable coding metasurface is presented at X band based on water substrate, which can realize two different functions of specific scattering pattern and absorption at two different frequency ranges. Besides, by changing the salinity of the saline water substrate, the absorption performance in high frequency can be tuned, while the scattering pattern in low frequency remains unchanged. A coding element is designed with small water cavity in it. Three coding sequences with different radiation patterns are designed to verify these functions, and one of them is fabricated and measured. Experimental results have good accordance with our simulations, which demonstrates our schemes. We believe this work can not only broaden our design manner of metasurfaces, but also have plenty potential applications in biological and medical detection domain.