Tie Jun Cui's research while affiliated with University of Alaska Southeast and other places

Dual‐polarization programmable metasurfaces can flexibly manipulate electromagnetic (EM) waves while providing approximately twice the information capacity. Therefore, they hold significant applications in next‐generation communication systems. However, there are three challenges associated with the existing dual‐polarization programmable metasurfaces. This article aims to propose a novel design to address them. First, the design overcomes the challenge of element‐ and polarization‐independent controls, enabling more powerful manipulations of EM waves. Second, by using more energy‐efficient tunable components and reducing their number, the design can be nearly passive (maximum power consumption of 27.7 mW), leading to a significant decrease in the cost and power consumption of the system (at least two orders of magnitude lower than the power consumption of conventional programmable metasurfaces). Third, the design can operate in a broad bandwidth, which is attractive for practical engineering applications. Both the element and array of the metasurface are meticulously designed, and their performance has been carefully studied. The experiments demonstrate that 2D wide‐angle beam scanning can be realized. Moreover, secure communication based on directional information modulation can be implemented by exploiting the metasurface and an efficient discrete optimization algorithm, showing its programmable, multiplexing, broadband, green, and secure features.

Programmable metasurfaces show enormous potential in real-time electromagnetic (EM) manipulation and their stable responses to variable EM waves including incident angle and polarization changes are crucial for related applications. However, the demonstrated programmable metasurfaces are commonly considered in normal-incident waves with fixed polarization; how to achieve stable performance in more realistic scenarios of wide-angle and full-polarized wave incidences is still a challenge. Here, we propose and realize a wide-angle and full-polarization programmable metasurface, which can generate stabilized amplitude and phase responses at both transverse electric (TE) and transverse magnetic (TM) oblique incidences. These are achieved by introducing metallic walls around the metasurface element to reduce element coupling, which greatly improves the angular stability of its reflection responses. The mechanisms of angular insensitivity are analyzed comprehensively, and as a proof of concept, obliquely-incident beam steering, large-angle beam scanning and oblique vortex beam emitting are demonstrated on this programmable metasurface. Both the simulation and experimental results demonstrate that the programmable metasurface can operate well at both TE and TM wide-angle oblique incidences in the upper half space. Our work offers an actual route for improving the angular stability and polarization insensitivity of metasurfaces, which could push them one step closer towards more complicated applications.

Wireless networks are undergoing a transformative shift, driven by the crucial factors of cost effectiveness and sustainability. Digital coding metasurfaces (DCMs) might play a key role in realizing cost-effective digital modulators by harnessing energy embedded in electromagnetic waves traversing through the air. Integrated sensing and communication (ISAC) optimize power and spectral resources by combining sensing and communication functionalities on a shared hardware platform. This article presents a tutorial-style overview of the applications and advantages of DCMs in ISAC-based networks. Emphasis is placed on the dual-functionality of ISAC, necessitating the design of DCMs with simultaneously transmitting and reflecting (STAR) capabilities for comprehensive space control. Additionally, the article explores key signal processing challenges and outlines future research directions stemming from the convergence of ISAC and emerging STAR-DCM technologies.

Circuits can provide a versatile platform for exploring new physics, particularly in probing the topological phases within complex geometries. Fractals, celebrated for their intricate, self-similar duality, and noninteger dimensions, particularly those embedded in complex manifolds, remain uncharted in this context. In our research, we implement Sierpiński fractal topological insulators within reconfigurable fractal topological circuits while expanding the scope to include the cylindrical and toroidal structures. Our approach is grounded in consistency theory and reinforced through experimental verification, confirming the presence of unconventional higher-order topological phenomena referring to the abundance of topological edge and corner modes. Intriguingly, the quantity of these edge and corner modes is proportional to the volume modes relative to the system size, with an exponent aligning with the Hausdorff fractal dimension of the Sierpiński carpet. This study paves the way for a deeper exploration of topological modes within fractal geometries, potentially unlocking new avenues in topological physics.

High-power electromagnetic (EM) waves can directly modulate the parameters of nonlinear varactor diodes through the rectification and Kerr effects without relying on external sources. Based on this principle, we propose a power-modulated reconfigurable nonlinear device based on spoof surface plasmon polariton (SSPP) waveguide loaded by varactor diodes, without applying DC power supply or feed circuit. Increasing the input power level reduces the effective capacitance of the varactor diode, leading to a blueshift in the cutoff frequency of the SSPP waveguide. This feature can be employed to realize the switching on/off of the input signal depending on the signal power. On the other hand, the transmission state of a low-power signal can be controlled by inputting another independent high-power EM wave simultaneously. Increasing the power of the control wave will enable the low-power signal within a wider bandwidth switched from off to on states. Experimental results are presented to show the excellent performance of the power-modulated reconfigurable SSPP device. This method can reduce the system complexity and provide inspiration for reconfigurable all-passive multifunctional devices and systems.

Intelligent voice interaction offers a flexible and powerful way to connect individuals with smart devices beyond our expectations. The real-time nature of voice communication enables smart devices to comprehend the user language, execute the corresponding instructions, and facilitate seamless communications, transforming our lives in unprecedented ways. Owing to self-adaptive and reprogrammable functionalities, information metasurface (IMS) opens up a new avenue for smart home and smart cities. To further enhance the intelligence of IMS, we propose an IMS system via intelligent voice interaction and information processing. The voice interaction enables the efficient remote control on the IMS in a flexible, convenient, touchless manner. Leveraging speech recognition, speech synthesis, target detection, and communication technologies, the IMS system achieves automatic beam manipulation capabilities for wireless information transmissions and wireless power transfers. The IMS system is designed to operate in two distinct modes: instruction mode, wherein the user instructs the operations, and autonomous mode, wherein the automatic detections govern the actions, in which seamless mode switching through the voice commands is supported. Users can flexibly achieve precise control over the functions of the intelligent metasurface system through voice interaction at a distance, without the need for close-range manual touch control, which greatly simplifies the operation difficulty and is particularly suitable for remote control and complex application scenarios. A series of experiments, including wireless video transmissions and wireless power transfers are conducted to demonstrate the flexibility and convenience of the IMS system. The incorporation of intelligent voice interaction technology with the IMS presents a novel paradigm for the applications of programmable and information metasurfaces.

In this letter, a miniaturized Vivaldi antenna based on a fan-out wafer-level packaging (FOWLP) process with a single redistribution layer is proposed. A step-by-step design procedure for the proposed antenna is presented. By introducing the slots and semicircular-shaped loads, its low-end cut-off frequency is extended from 35.28 to 24.04 GHz, leading to a size reduction of 31.8% when normalized to the lowest operating frequency. Moreover, a wideband low-pass coplanar waveguide to slotline transition is proposed for antenna feeding, in which a folded split ring resonator and etching periodic slots are added to reduce the transition insertion loss above 40 GHz. Prototypes of the proposed antenna and back-to-back (BTB) coplanar waveguide to slotline transition were fabricated and measured. The measured return loss of the BTB transition is better than 13.4 dB from dc to 67+ GHz, and the insertion loss of a single transition is below 0.95 dB. The measured |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | of the proposed antenna is less than −10 dB from 23 to 67+ GHz with 4.5–7.1 dBi measured gain and >84% simulated efficiency.

The traditional sea clutter simulation techniques encounter challenges in effectively balancing dynamic simulation, coupling effects, and construction cost management. To tackle these issues, we propose an experimental platform to simulate the sea clutter in real time using space-time-coding digital metasurfaces. Specifically, we use deep learning techniques to construct an encoding retrieval library with angle-insensitive characteristics. Combing the library with the desired clutter sequences generated by the zero memory nonlinearity approach (ZMNL), we can obtain the corresponding space-time-coding sequences for the simulation platform. To validate the proposed approach, we generate two correlated clutter signals following the Weibull and lognormal distributions under the illumination of monochromatic electromagnetic plane waves. Experimental results exhibit robust conformity with the theoretical values, demonstrating the dependability and stability of the proposed approach. These findings highlight the significant potential of our methods in various domains, including radar sensing and countermeasures.

Realizing the wireless environmental sensing is another desired function of reconfigurable intelligent surface (RIS), in addition to enhancing the performance of wireless communication systems. In this paper, we design a holographic RIS-aided computational imaging system, which consists of a transmitter, a holographic RIS, a rectangular target and a receiver. Here, the target is composed of a series of discrete segments, each of which possesses a constant scattering density. The sensing task of the proposed system is to estimate the scattering densities of the target, which corresponds to the term computational imaging . The term holographic means that the RIS is modeled as a physically continuous surface with a physically continuous phase shift pattern, which can be approximately considered as as having massive (possibly infinite) number of elements within a finite space. Both the RIS and the target are subject to the electromagnetic boundary conditions, whose scattered fields are computed by the equivalent current method and the physical equivalent. Based on the computed scattered fields of the target, we derive the pathloss of the proposed system. In order to perform the imaging, we alter the phase shift pattern of the RIS such that the main energy of its scattered fields is focused towards different segments of the target successively, which then produces multiple measurements of the scattering densities and simultaneously ensures a low pathloss. After all measurements are completed, the scattering densities of the target can be estimated with the observed measurement vector and the reconstructed sensing channel, i.e., the computational imaging is accomplished. Simulation results show that the proposed imaging strategy performs well if the system parameters are designed properly.