When a hypersonic vehicle reenters the Earth's atmosphere, plasma sheath generated by its collision with ambient air affects electromagnetic (EM) wave propagation. To understand such effects is very important for design of communication, telemetry, and satellite navigation systems. In this paper, transmission coefficient investigated using finite-difference time-domain (FDTD) method. The moving-window (MW) technology employed to reduce massive computational resources required large model....

Abstract In this letter, an ultra‐thin triple‐band metamaterial absorber with high absorptivity in each band of operation is presented. The unit cell the proposed structure consists outer circular metal ring and inner Jerusalem cross on top a thin dielectric substrate backed by metallic ground plate. Simulation responses exhibit that polarization insensitive has stable performance to oblique incidence angles for both TE TM polarizations. A simple equivalent circuit model multi‐reflection...

A new architecture for designing a tuneable wideband absorber using an active frequency selective surface (AFSS) is presented. The proposed AFSS composed of 2‐D periodic array two opposite directional anchor‐shaped metal strips printed on dielectric substrate with no metallic screen the back side, where positive–intrinsic–negative diodes as components are embedded between each strips. Biasing at different voltages to turn ON and OFF diodes, structure can react switchable transmissive...

Thermoacoustic imaging (TAI) is a non-ionizing, high-contrast and high-resolution modality for biomedical applications. The resolution of the reconstructed image by traditional algorithm, such as back-projection (BP), dependent on input microwave pulse width. In this work, it experimentally demonstrated that quality images based compressive sensing (CS), novel algorithm can reconstruct using fewer measurements, largely independent width which taken into account when building dictionary....

The design of metamaterial absorbers (MMAs) using deep learning (DL) models typically involves the construction a large dataset through time-consuming full-wave simulations (FSs). In this letter, an efficient shrinking method is proposed that employs both electromagnetic (EM) theory and DL to enhance efficiency. impact each MMA on training model estimated equivalent circuit (ECM) by analyzing gradients parameters with respect training. Impact sampling then used construct smaller while still...

An active metamaterial absorber with electrical control of both polarisation and frequency is presented. The unit cell the proposed consists an outer circular ring inner Jerusalem cross two pin diodes mounted between. Tuning ON/OFF states, absorption response structure can be switched between performances. As biasing OFF, a dual‐band polarisation‐independent characteristics achieved. Although regarding to ON state, polarisation‐dependent performance exhibited. Specifically, same still...

In this letter, a shifted double-sided frequency selective surface (FSS) with miniaturized unit cells is proposed to achieve superior performance in angular insensitivity. Two identical FSS screens mounted on both sides of thin substrate have lateral displacement relative each other. We shed light into effect shifting by investigating current and field distributions, present the operating principles along equivalent circuit model. The whole structure has lower profile (a thickness 0.001λ,...

Owing to its intrinsic advantages of favorable contrast and spatial resolution, microwave-induced thermoacoustic imaging (TAI) has drawn great attention in biomedical applications, such as breast cancer detection. Many experimental studies have demonstrated the promising potential TAI. Several TAI modeling also been published that facilitate design optimization systems. However, validation results is rarely seen; thus it highly desirable prove effectiveness approach. In this letter, approach...

The transverse focal shift (TFS) is a phenomenon that the maximum of focused field does not occur at geometrical focus, but moved short distance transversely in plane. In this paper, TFS vortex beams high numerical aperture system investigated. Four typical types incident are selected and intensity distributions vortices behaviors region discussed analytically numerically. It found there three main parameters, topological charge, initial positions vortices, semiaperture angle influencing...

Abstract A novel low‐radar cross section (RCS) microstrip antenna with radiation performance and volume maintained is proposed in this paper. Different from other RCS reduction methods, the applies shaping method on frequency selective surface (FSS) ground plate to achieve further reduction. In order obtain effect of subtracting square slots, an normal FSS designed as reference antenna. The modified slotted shows more significant compared range 4 7.5 GHz, maximum 14.62 dBsm at 4.22 GHz. And...

The stretched coordinate (SC) perfectly matched layer (PML) absorbing boundary in cylindrical system is implemented using the bilinear transform technique. proposed PML performs much better attenuating low frequency evanescent waves as compared to conventional UPML (anisotropic medium). Numerical results show efficiency of algorithm.

To break through the limitation of harmonic loss on transmission bandwidth, a novel frequency-selective rasorber (FSR) for wideband is present in this article. The FSR composed two subsets: an absorption-transmission (A-T) and transmission-absorption (T-A) rasorber. A-T generates lower absorption band with suppression, resulting multioctave low insertion (IL) window. suppression principle resistive sheet described analyzed detail, corresponding equivalent circuit model developed to further...

A hybrid weighted Fourier transform and relaxation (hybrid-WRELAX) method applied to Loran-C skywave delay estimation is presented. The performance of this demonstrated compared with the spectrum analysis method. hybrid-WRELAX has been proved provide higher accuracy estimate delay. Results testify conclusion using off-air data.

A high precision algorithm is proposed to estimate the Enhanced Loran skywave delay, which based on an Extended Invariance Principle Weighted Fourier transform and Relaxation (EXIP-WRELAX) algorithm. It innovation application of interference estimation in receiver. Compared with existing algorithms, this has higher accuracy lower computational complexity. Simulation results show that reduces estimated error from ∼1000 50 m. At same time, accurate search over entire frequency domain avoided,...

Thermoacoustic imaging (TAI) is an emerging promising hybrid modality for biomedical imaging. High spatial resolution of TAI conventionally accomplished by utilizing a short exciting microwave pulse, but squeezing the pulse simultaneously degrades signal-to-noise ratio (SNR) thermoacoustic image. There usually tradeoff between and SNR. Compressive sensing (CS), novel algorithm signal recovery, introduced into to obtain images whose resolutions are largely independent width. In this work,...

A miniaturized periodic element for constructing bandpass frequency selective surface (FSS) independent of incident angles and polarizations is presented.An interdigital resonator (IR) with one extending finger to connect the two separate parts capacitor explored achieve parallel resonance.The equivalent circuit model (ECM) electric field distributions are introduced explain performance FSS.The whole structure has only layer possesses a low profile (a thickness 0.001 5 , where represents...

In this paper, we proposed a dynamically tunable broadband microwave absorber based on active frequency selective surface (AFSS). The unit cell of the AFSS is composed PIN diode and two reverse anchor patches. When bias voltage changed between 0.6 0.78 V, reflection coefficient can be less than -10 dB from 7 to 13 GHz, absorbing band tuned within specific range. fabricated light, thin enough achieves broad tuning bandwidth. It has potential applied in smart radar materials.

A modified Sierpinski fractal broadband antenna for multiband application is investigated, simulated, and measured in this paper. The perturbed patch the groundplane are employed to obtain wider bandwidth at resonance frequencies. implemented antenna, with nearly omnidirectional radiation pattern, has been designed a total dimension of 50.8×69×1.6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . According results, it can be seen that...

This study proposes a high precision algorithm to estimate the Enhanced Loran skywave delay. It is based on artificial neural network. The establishes network model between receiving signal and propagation By training large number of data, can more accurately reflect relationship an innovative application delay estimation in system, especially low signal‐to‐noise ratio (SNR) environments. experimental results show that accuracy this about hundreds nanoseconds condition normal SNR. us SNR,...

The polarization properties of a strongly focused, unpolarized, partially coherent beam with circular coherence are studied in this Letter. It is found that the degree (DoP) focal plane can be adjusted, not only by initial and semi-aperture angle, but also through an annular pupil due to unusual source. Our results show for incident beam, field go from almost unpolarized state fully polarized along radial distance, although length very short. Through adjusting width pupil, DoP on average...