The enhancement of light-matter interaction for monolayer graphene is of great importance on many photonic and optoelectronic applications. With the aim of perfect ultraviolet trapping on monolayer graphene, we adopt the design of an all-dielectric nanostructure, in which the magnetic resonance of optical field is combined with an ultraviolet mirror. The physics inside is revealed in comparison with the conventional plasmonic perfect absorber, and various influence factors of absorption bands are systematically investigated. In the ultraviolet range, an optimized absorbance ratio up to 99.7% is reached, which is 10 times more than that of the suspended graphene, and the absorption bands are linearly reconfigurable by angular manipulation of incident light. The scheme for perfect ultraviolet trapping in a sub-nanometer scale paves the way for developing more promising ultraviolet devices based on graphene and potentially other 2D materials.

In this article, we present an efficient phaseless inverse source method (PISM) to reconstruct equivalent sources on a printed circuit board (PCB) using magnitude-only single-plane near-field scanning. The equivalent source distribution reconstructed by the conventional source reconstruction method requires accurate near-field magnitude and phase information, but phase measurement is difficult in many cases due to inaccuracy and complexity. In order to describe the inverse problem between phaseless fields and radiation sources, a nonlinear cost function based on surface integral equations is established. The cost function of the PISM is rapidly minimized by an iterative optimization and regularization technique for nonlinear ill-posed systems. The proposed method gives the characterization of PCBs both for diagnostic tasks of radiation sources and the near-field radiation behavior prediction when the phase information is missing. It also shows excellent robustness in tackling with various near-field data and noises. Both numerical examples and laboratory experiments are given to verify the effectiveness of the proposed method.

In this article, we present a new diagnostic technique for printed circuit boards (PCBs) and integrated circuits (ICs). This technique consists of an array-probe scanning system and the phaseless inverse source method with a joint regularization. Different from the single probe scanning system, a ground plane for array probes is applied to protect the RF transmission path from interference by other radiation in the array probes scanning system. In order to consider the influence of both PCB ground and array probes ground on electromagnetic near-field distributions, we use the method of moments to solve the surface integral equations in the forward problem. In the inverse problem, we establish a nonlinear cost function between the magnitude-only fields and equivalent sources. Because of the ill-posedness of the inverse problem, an efficient iterative method with a joint regularization framework is applied to reconstruct the equivalent sources on the source plane above the PCB ground. Different levels of noise are added to the simulated data to validate the algorithm. Laboratory experiments and numerical examples show the effectiveness of the proposed method.

In practical hardware platforms such as FPGA orDSP, the FFT operation is based on a length of $2^{L}$ . However, due to the system limitation, the length of sampled signal would be not equal to $2^{L}$ . Thus, zero-padding is performed on the signal before FFT operation. Most traditional sinusoidal frequency estimation methods are for signals without zero-padding. When applying these methods to the zero-padded signal, the performances would degrade. To solve this problem, a novel frequency estimation method for zero-padded signal is proposed in this paper. In the proposed method, by using the analytical expression of the DFT signal after zero-padding, an amplitude ratio function is defined between the two DFT samples nearest to the true frequency. Based on the monotonic property of the ratio function, Newton-Raphson method or bisection search is used to estimate the residual frequency. Two implementation flows are proposed, with similar performance and computational complexity. Experimental results show that the proposed method achieves better RMSE performance than the traditional methods. More importantly, the proposed estimation method can be applied to both the zero-padded signal and the non-padding signal.

In this paper, a systematic design strategy of polarization-insensitive, broadband, and high-efficiency metasurface is reported, and the proposed metasurface has excellent performance in holographic imaging. First, we utilize a multi-objective differential evolution algorithm to rapidly design a high-performance meta-atom group, capable of achieving a reflected amplitude (efficiency) exceeding 0.91 (83%) within the bandwidth of 8.21-17.50 GHz. Subsequently, a wideband phase distribution method is proposed for calculating the imaging phase map. Guided by the phase map, the meta-array is designed for the generation of letter-shaped images under distinct polarization excitation across the entire bandwidth. Finally, calculations, simulations, and experiments collectively verify the effectiveness of the systematic design strategy utilized in holographic imaging. The metasurface sample has the capability to generate letter-shaped images at varying heights with an imaging efficiency over 62.8%. The proposed method can be employed to achieve the unrestricted distribution of electromagnetic wave energy in three-dimensional space, encompassing applications such as wireless charging, data storage, and microwave imaging.

Compared with the traditional time division multiple access - multiple input multiple output (TDMA-MIMO) radar, Doppler division multiple access - multiple input multiple output (DDMA-MIMO) radar enables the design of orthogonal waveform in Doppler domain instead of in time domain. Thus DDMA-MIMO radar performs well in long range radar application. However, it suffers from Doppler ambiguous and energy defocus of the target spectrum in DDMA-MIMO radar, and as a result the target detection performance degrades. To tackle these problems, a target detection algorithm based on multiple subbands coherent-accumulation (MSCA) is proposed in this paper. First, the empty-band is inserted into the Doppler domain by modifying the phase modulation of the transmitting antennas. Based on the periodic extension of Doppler in DDMA-MIMO system, a coherent accumulation and Doppler ambiguity mitigation method based on subband correlation is proposed. By exploiting the low energy characteristic of the empty subband, this method compares the energy of accumulated subband after MSCA to extract the real velocity of target. It also solves the problem of Doppler ambiguity caused by the period extension of target velocity. Besides, the proposed method can improve the detection performance, avoiding the target being drowned by noise. Simulation and real data results show that the proposed method can effectively alleviate the Doppler ambiguity, improve the target detection performance under low signal-to-noise scenarios.