Time-modulated metasurfaces (TMMs) can achieve extraordinary manipulation of electromagnetic (EM) waves and hold remarkable potential in future information fields. However, many limiting factors, including angular stability, polarization insensitivity, and conformal ability, remain unconsidered for the TMM. Moreover, it is a significant challenge to achieve independent control of orthogonal polarization via the TMM while achieving conformal structure. In this article, a flexible multifunctional TMM (MTMM) with polarization control for conformal applications is proposed to manipulate the spectrum distribution. It can simultaneously achieve amplitude, polarization, and frequency control in a single structure with excellent angular stability and conformality. A Doppler effect with multiple discrete frequency components is implemented based on fast temporal modulation. Furthermore, a conformal MTMM for radar application is explored. It possesses the advantage of manipulating radar echo signals in a wide-angle domain. The modulation effect of the conformal MTMM on the radar is analyzed in detail. Multiple discrete false harmonic peaks are generated. Finally, the MTMM characteristics are tested, and the radar experiments are performed, verifying the validity of the structural design and theoretical method.

The discovery of electromagnetic (EM) metasurfaces has significantly advanced the free manipulation of EM waves. Further, the harmonic phenomena based on time-modulated metasurfaces (TMMs) have received much attention in communication and radar detection applications, which can reduce the efficiency of radar target detection. However, existing research on time-varying metasurface has neglected its potential to manipulate the scattering characteristics of polarized radar targets. When a linear polarization wave is incident on a metasurface, it will be reflected into two orthogonal polarization states of EM waves, thus directly affecting the polarized scattering of the target. Active Polarization conversion metasurfaces (APCM) can manipulate the polarization of electromagnetic waves, aligning well with polarimetric radar. In this work, a dual-polarization radar target feature manipulation (Pol-TFM) method based on APCM is proposed, which enables manipulation of the harmonic and energy distribution of radar echo signals in multiple polarization channels. Through this processing, virtual targets generated by harmonic effects become observable on the dual-polarized high resolution range profile (HRRP). This method also allows for the position manipulation of the virtual targets. Finally, echo signal experiments are conducted in dual-polarimetric channels to verify the effectiveness of the proposed method.

This paper demonstrates a miniaturized flexible multifunctional active frequency selective surface (MAFSS) with excellent angular stability and polarization insensitivity. The proposed structure consists of two metal layers printed on a thin, flexible substrate to achieve curved surface conformal capability. The PIN diodes are welded on two metal layers. By independently switching the bias voltage of PIN diodes, four working states and two functions, including electromagnetic switching and polarization selection, are realized. The unit cell takes itself as a bias feeder to excite the PIN diodes, avoiding the negative impact of the additional feeding network on the overall performance. A spiral wire-based miniaturization technique is utilized to achieve excellent angular stability in the planar and conformal states. On this base, a double-layer symmetrical structure based on the via-connected metal strips is designed to realize polarization insensitivity. The miniaturized unit size can reach 0.082λ ₀ ×0.082λ ₀ ×0.005λ ₀ at the center resonance frequency. The flexible MAFSS prototype is measured in planar and conformal states. The measured operating bandwidth with transmission coefficient difference greater than 10 dB is 2.8 GHz (5.2 GHz ~ 8 GHz). The measured and simulated results have good consistency, demonstrating the effectiveness of the proposed structure.

The time-varying Phase-Switched Screen (PSS) has demonstrated significant potential for modulating radar target features, owing to its exceptional capabilities in harmonic generation and control. However, most existing studies focus on single-dimensional target features, with limited investigation into joint modulation of two-dimensional or higher-dimensional features. In this article, a time-domain digital coding PSS system is proposed. By applying 1-bit periodic phase modulation, the spectral energy of the incident electromagnetic wave is redistributed across multiple harmonics, thereby simultaneously influencing the detection of range and velocity features by linear frequency modulated (LFM) pulse-Doppler (PD) radar. Through precise control of the energy and frequency-domain distribution of these harmonics, radar false targets exhibiting coupled range-velocity features can be synthesized in the feature space. Leveraging this coupling characteristic, the method enables flexible feature modulation, including electromagnetic cloaking, range modulation, Doppler modulation, and range-Doppler two-dimensional joint modulation. Simulations demonstrate the effectiveness of the approach, revealing that the primary false targets remain detectable even at low signal-to-noise ratios (SNR), despite a reduction in the number of the effective false targets. Finally, a practical counter-measure experiment conducted in a microwave anechoic chamber further validates the feasibility and effectiveness of the proposed method.

In this paper, a dual-band terahertz absorber with two passbands is proposed. The absorber is composed of periodic patterned graphene arrays on the top of a SiO ${}_2$ substrate and a frequency selective surface (FSS) on the bottom of the substrate. The simulated results indicate that there are two absorption bands (absorption greater than 90%) ranging from 0.54 to 0.84 THz and 2.13 to 2.29 THz. It is almost transparent to incident waves (transmission greater than 50%) below 0.19 THz and between 1.3 and 1.67 THz with a center frequency of 1.49 THz. The absorber has a good tolerance to the transverse electric (TE) and transverse magnetic (TM) polarized wave oblique incidence, and the transmission rate of the passbands remains greater than 50% within 70 degrees. Moreover, the absorption rate of the absorber can be tuned by the chemical potential of graphene. The structure with absorption and transmission properties has potential applications in filtering, sensing, detecting and antenna stealth.