Yong Han Liu

We propose a new design of polarization insensitive sensing for Direction of Arrival (DoA) achieved by programmable metasurface with independent control of dynamic phase under dual‐polarization. The unit cell of metasurface is constructed by multi‐layer structure mainly including one dual‐polarization patch for receiving of spatial electromagnetic (EM) signal with any polarization and two programmable phase shifters for each polarization. All of the EM power collected from each unit cell will be concentrated by one power‐combining network integrated in the middle layer of metasurface to acquire the total receiving signal corresponding to each polarization. Accordingly, the spatial sensing matrix composed of diverse receiving patterns can be generated by randomly controlling the programmable phase shift in each unit cell, and the DoA estimation will be actualized by utilizing the compressive sensing method due to the information received from each polarized port. One prototype of metasurface is fabricated and measured, the DoA estimation in the azimuth plane of single source and two sources under different polarization states have been solved precisely under the center frequency of 4.8 GHz with a relative bandwidth of 8%.

A novel method for achieving the ultra‐wideband 2‐bit phase control by switchable circuit for programmable reflectarray is proposed. The microstrip line based active circuit is composed of three PIN diodes for dynamically selected four different reflective loads of open, short, capacitive and inductive characteristics respectively, and the theoretical calculation about the reflective phase of proposed circuit model can verify the basic method is correct. For considering the design of the ultra‐wideband reflectarray, the tightly coupling dipole (TCD) element is introduced for the ultra‐wideband electromagnetic wave receiving or radiating. And the co‐simulation of the period unit cell, launched by TCD structure and the measurement data from fabricated switchable circuit has shown the good results of 2‐bit phase control from 1.8 to 4.2 GHz with the relative bandwidth of 2.33:1.

The switching or continuous operations which are digital or analog manipulations for periodic electromagnetic (EM) structures have developed rapidly to achieve sufficient designs of manipulating spatial wave. However, achieving phase control over an ultra-wideband has always remained a challenge, restricting its applications. Here, we propose a new method to realize large phase shift beyond 270 degrees with relative bandwidth of 112%, utilizing joint digital-analog control. The frame of “EM receiving - reconfigurable circuit - EM re-radiating” for designing unit cell of reflector is applied. Tightly coupled dipole is preferred to realize ultra-wideband EM receiving/re-radiating. By programmable switching four PIN diodes to control different transmission paths and continuously tuning varactors to change capacitance, large reflection phase shift within ultra-wideband can be jointly accomplished. The method of co-simulation, combining simulation results of passive EM textures with measured data of fabricated circuit, can acquire good performance of reflection phase manipulation both at phase coverage and working bandwidth. A prototype of reflector with frequency-adaptive module has been measured. The automatic and customized variation of reflection phase can be actualized without human intervention by proposed intelligent reflector according to the frequency of incident wave from 0.55 to 1.95 GHz.

The control of electromagnetic (EM) radiation and scattering under shared aperture has always been research hotspots, and the method of time multiplexing by electric switching to select the radiation or scattering function is usually used in the former designs. Here, we propose a new method to achieve the synchronous and independent manipulation of EM dynamic radiation and scattering under same frequency and EM polarization by applying new active metasurface without function switching. For each unit cell of presented metasurface, the device of transistor circuits owning the capability of unidirectional transmission and reverse isolation is introduced, and varactor-based programmable phase shifters with 360-degree coverage are employed in both chains of radiation and scattering for dynamic phase compensation to accomplish the active control of spatial waves in real time. The cascaded architecture is preferred to realize the design of active unit cell, all of passive components and active devices are analyzed and optimized using field-circuit co-simulation. Further, one prototype of active metasurface is fabricated and good measured performances that the synchronous and independent control of dynamic radiation and scattering beams in the far field has been actualized under the center frequency of 2.85 GHz with a relative narrow bandwidth of 6 %.

A novel electromagnetic (EM) detection for dynamic targets is proposed by applying metasurface with multiple Direct Current (DC)-based sensing channels in time-domain without complex Radio Frequency (RF) manipulation of receiving aperture. The unit cell for EM receiving is composed of the patch antenna and the rectifier circuit converting input RF signals to DC voltages in real time. Only half of unit cells in metasurface are utilized for receiving echo from objects under the distribution of chessboard pattern with considering both sensing results and cost. The artificial intelligent (AI) technology based on convolutional neural networks (CNNs) is applied to process the collected signals from multiple time-domain DC-based channels, and human gait as typical dynamic target from many models has been successfully classified and identified in our proof-of-concept experiment.

The sensing and detection of electromagnetic (EM) targets by utilizing the metasurface has been the frontier research in recent years. A novel microwave sensor for information sensing of dynamic targets is proposed by applying the space-time metasurface working under a single frequency with multiple Doppler Spectra. For each unit cell of the metasurface, it is composed of a receiving patch antenna and a programmable phase shifter owning the ability of continuous phase manipulation within 360°, enabling the generation of a Doppler spectrum by loading periodic time-modulation signals on the unit cell. The column-control method of metasurface is preferred, and the predesigned Doppler spectrum has been observed by separately allocating different time-modulation signals for each column to map the information of the dynamic target in real time. By using a multimodal fusion-based convolutional neural network (CNN) to process the synchronous microwave and optical data, the dynamic information of human gait has been classified and identified completely in our proof-of-concept measurement by space-time metasurface-based sensor.

The intelligent control of electromagnetic waves by 2D active period structures has become very common in recent years. However, the methods for ultra‐wideband designs are lacking to achieve much more adaptive and flexible manipulation in the frequency domain. Here we propose a new method to realize the independent control of reflection amplitude and phase under ultra‐wideband by using intelligent reflectarray. Each unit cell is composed of a tightly coupled antenna and active circuit to accomplish the receiving or transmitting of spatial wave and signal modulations of amplitude‐phase information respectively. The field‐circuit co‐simulation method is preferred to analyze and optimize the texture. One prototype of the whole reflectarray is fabricated and corresponding measurement results of reflection amplitude with continuous control and reflection phase with 1‐bit switching have been actualized under the working frequencies from 0.6 to 1.6 GHz with the relative bandwidth of 90.9%. Further, one or multiple spectrums (Doppler shift) generated by the time‐modulation phase have been achieved in the ultra‐wideband. Both control of the reflection amplitude and spectrum shifting can be applied to mimic various scattering signals under the ultra‐wideband.

Image reconstruction has become more attractive in electromagnetic (EM) areas, especially when metasurface emerges to introduce various methods for manipulating spatial EM waves. Here, we propose a new method for achieving direct EM imaging in the near field by applying a co-aperture active metasurface combined with nonreciprocal and time-modulation features at a single frequency. In our metasurface design, the transmitting and receiving EM signals can be manipulated independently in each meta-atom by integrating the dual-direction power amplifiers (PAs), which can be regarded as isolators for one-way propagation. In the transmitting aperture, a uniform wavefront is realized to illustrate the imaging plane; in the receiving aperture, the phase shift of 360-degree coverage in each meta-atom is dynamically controlled by time-modulation of different frequencies to establish direct relations between the spatial pixels of the imaging plane and spectra of Doppler shift. A metasurface prototype is fabricated, and several targets composed of metal stripes are successfully reconstructed directly with one co-aperture metasurface at a single frequency in experiments. The good measurement results verify the validity of the proposed method for direct imaging and sensing.

The passive sensing and active control of electromagnetic (EM) waves have always been attractive in electronic and information areas, especially during the intelligent era. Here a new method is presented to achieve the angle sensing of incident wave and adaptive control of backward scattering using the intelligent metasurface. The proposed unit cells have the ability to dynamically manipulate the receiving and reflection of the EM energy respectively. The angle sensing of incident waves can be actualized using the method of compressive sensing based on multiple receiving patterns, which are generated by randomly switching the receiving and reflection states of the unit cells. Afterward, the customized performances of backward scattering waves according to the cognitive incident angle can be realized by controlling the programmable reflective phases of unit cells correspondingly. One prototype composed of the metasurface and the module for sensing and adaptive feedback control is fabricated. The whole intelligent metasurface with customizing the function of retro‐reflection or low scattering is measured without human intervention and the good results acquired can verify the validity of the proposed concept and design.