Zhiping Yin

The illegal operation of unmanned aerial vehicles (UAVs) has raised significant public safety concerns, especially the challenge of identifying UAV operators in complex electromagnetic environments. This article proposes an optimized local maximum method for extracting multiple UAV flight control signals. The proposed method employs a novel four-stage processing framework, enabling it to operate effectively under low signal-to-noise ratio (SNR), multisignal interference, and spectral overlap conditions. First, the time–frequency transformation effectively distinguishes time-varying flight control signals from stationary white Gaussian noise using a discrete short-time Fourier transform (STFT). Next, an improved multilevel local maximum method enhances the capture capability of weak signals when multiple signals coexist. Furthermore, a dynamic frequency block update mechanism groups flight control signal points into blocks, leaving image transmission signals and noise scattered. Finally, by calculating the kurtosis for each frequency band, irrelevant noise blocks are filtered to keep flight control signals with a steep waveform. Experimental results demonstrate that the proposed method outperforms traditional methods in various scenarios. Moreover, through data flow reconstruction and hardware parallelism, the method is efficiently deployed on a field-programmable gate array (FPGA) platform. This not only accelerates processing speed but also significantly reduces storage requirements and computational load, providing a feasible solution for practical engineering applications.

The azimuth resolution of real aperture radar (RAR) is limited by the effective beamwidth of the antenna. Based on the convolution relationship between target scatterings and the antenna pattern in the traditional model, the azimuth resolution can be improved by deconvolution methods. However, due to the low-pass nature of the antenna pattern, the radar observation matrix is of great ill-conditioning, thus, direct deconvolution is sensitive to noise which will be detrimental to azimuth resolution enhancement. In this paper, a RAR two-channel antenna pattern design method is proposed where we mitigate the ill-conditioning of the radar observation matrix from the perspective of designing the antenna pattern, while the traditional methods improve the super-resolution capability with algorithms. Firstly, we elicit the reconstruct probability to analyze the reconstruction performance, however, which is not suitable for the antenna pattern design. Hence, inspired by the deconvolution theory, we propose four metrics to reflect the ill-conditioning of the radar observation matrix and use them to characterize the reconstruct probability with the random forest algorithm. Besides, we use their relationship as the objective function to obtain the optimally-designed antenna pattern with the particle swarm algorithm. Considering the feasibility of the antenna pattern, we also approximate the theoretical solution with beam assignment. Simulations verify the proposed method for robustness enhancement with different algorithms both on the traditional convolution model and the Doppler-convolution model, and higher reconstruct probability, lower Mean Squared Error(MSE), fewer entropy and higher target-to-clutter ratio(TCR) are also demonstrated in real scene from publicly available dataset.

This work presents a pixelated liquid-crystal-driven terahertz (THz) reconfigurable intelligent surface (RIS) with a vertical cross structure. The RIS array is composed of two metal metasurfaces with a liquid crystal (LC) embedded in between, having a 2-bit phase resolution. Each pixel subarray is independently controlled with a low voltage of 3.5V, using film-on-glass (FOG) technology integrated into quartz. The dynamic beam scanning in the two-dimensional plane can be realized by real-time encoding of subarrays under the control of a 2-bit digital coding sequence. A RIS prototype composed of 32 ×32 elements was manufactured and measured. The experimental results show that the device achieves 100° beam scanning with 1° of angular precision at 345 GHz. This device is expected to be useful in various applications, such as high-precision imaging, next-generation wireless communication, and other information systems.

reconfigurable intelligent surface (RIS) have received significant attention in the field of communication and wireless networks, due to their numerous advantages, such as low cost, low energy consumption, miniaturization, programmability, and ease of deployment. This article proposes an RIS based on liquid crystal (LC) for constructing wireless communication systems. Tunable LC embedded between metal microstructures supported by quartz substrates allows for precise control of the reflected wave phase. The experimental results demonstrate that RIS has more than 360° of phase modulation capability and four stable digital coding states at the optimal operating frequency of 100.2 GHz. In addition, the RIS has a 100° beam scanning capability, providing a solid foundation for tracking and targeting during communications. The communication capability of RIS was then demonstrated in the sub-terahertz band by constructing a 16QAM constellation diagram test system and a video real-time transmission system with varying deflection angles. Our work provides excellent solutions for communication and wireless network applications in the millimeter wave and terahertz (THz) frequency bands.

This paper presents a reconfigurable broadband transmissive-type linear cross-polarization converter (LCPC) based on liquid crystal (LC) metasurfaces. The proposed structure exhibits broadband linear cross-polarization conversion capabilities and asymmetric transmission (AT) effects, with the ability to tune the operational bandwidth by adjusting the applied bias voltage. Experimental results demonstrate that, without external biasing, the structure can achieve linear cross-polarization conversion functionality with polarization conversion ratio (PCR) ˃0.97 over the frequency range of 107.8 to 133.6 GHz. Additionally, the AT effect can be realized within the same frequency band. When a saturated bias voltage of 8 V is applied, the operational bandwidth shifts to 101.7 to 129.3 GHz, resulting in a tuning rate of approximately 4.4%. Compared with tranditional grating-based three-layer structures, the proposed design, features low cost, simple configuration, and tunable linear cross-polarization conversion and AT effects, providing new possibilities for practical applications that require flexible operation across varying frequency bands in fields such as wireless communication and imaging.

This paper presents a flexible and broadband metamaterial absorber (MA) with a sandwich structure for W-band absorption. The MA uses a thin FR4 material as the dielectric layer and incorporates multiple patches of varying sizes as the top pattern layer. By optimizing the dimensions and arrangement of the metal patches, an average absorption rate exceeding 94% is achieved across the 75–110 GHz frequency range, effectively covering the entire W-band. The MA, with a thickness of only 0.22 mm and a weight less than 600 g/m², is polarization-insensitive and maintains high absorption for TM waves within an incident angle of 45°. The structure is simple, low-cost, and compatible with PCB fabrication processes. The experimental results align well with the simulations and demonstrate effective absorbing performance in conformal applications, offering a new solution for flexible millimeter-wave absorption.

This paper presents a reconfigurable polarization converter based on the liquid crystal (LC) terahertz metasurface. The proposed structure shows unique ability in achieving the conversion from linearly polarized (LP) waves to selective cross-polarized waves or circularly polarized (CP) waves within a wide frequency range. Experimental results demonstrate that, within the frequency region of 318.0 to 375.6 GHz, the metasurface can achieve the conversion from LP waves to cross-polarized waves without external biasing. However, when a saturated biasing voltage of 8 V is applied, the y-LP waves can be converted to right-handed circularly polarized (RHCP) reflection waves. Similar phenomenon is observed for x-LP incidence, as the x-LP waves were converted to left-handed circularly polarized (LHCP) wave in reflection. Unlike previously reported single-function metasurface polarization converters, the proposed design offers a new approach for achieving wideband reconfigurable multifunctional polarization conversion with a cost-effective solution, opening up possibilities for its application in the field of terahertz sensing and communication.

In this paper, a low-cost, robust, and highly sensitive microfluidic sensor is proposed, leveraging a complementary split-ring resonator (CSRR) operating at microwave frequencies. The sensor design incorporates a U-shaped microfluidic tunnel within each unit cell structure, facilitating the identification of various liquid samples with minor dielectric constant variations through spectrum measurement. The measurement results indicate a resonant frequency shift of 1.54 GHz is achieved for a change in the dielectric constant of 1, and the capability of the microfluidic sensor in detecting several common oils is experimentally demonstrated. Moreover, a liquid constant temperature circulation system is included in this design, and the test error induced by the fluctuation of liquid temperature, which contributes to most of the measurement error, can be reduced significantly. Due to its robustness and high sensitivity, this passive metasurface-based microfluidic sensor provides promising potential for liquid sample detections with minor dielectric constant variations.

In this paper, we propose a novel approach for circular Multiple-Input Multiple-Output (MIMO) array imaging, termed the Partial Equivalent Method (PEM), aimed at sidelobe suppression. In our method, the imaging process of the circular MIMO array is initially decomposed into bistatic circular synthetic aperture radar (BCSAR) components with different bistatic angles. Components with larger bistatic angles produce equivalent channels whose wavenumber spectra are concentrated near zero frequency, leading to significant broadening of the main lobe in the corresponding point spread function (PSF). In traditional MIMO imaging, each transmit–receive antenna pair is considered an equivalent channel, and all these channels are utilized for imaging. However, components with large bistatic angles, when integrated into the MIMO imaging output, result in increased sidelobe levels. To address this issue, we employ the PEM to restrict the range of equivalent channels. This method selectively retains effective channels generated by components with specific bistatic angles, effectively mitigating the adverse effects of BCSAR components with larger bistatic angles. Through point target simulations, electromagnetic simulations, and practical experiments, we demonstrate that the PEM significantly reduces sidelobes and enhances image quality in circular MIMO array imaging.