基于超材料的微波双波段吸收器

基于闭合双环单元结构, 设计、仿真、测试了对偏振无依赖性的双波段超材料吸收器. 实验结果表明, 该设计在频率4.06 GHz和6.66 GHz存在两个显著吸收峰, 吸收率分别为99.60%和95.83%, 并且在入射角达到50°时, 吸收率仍然保持在83%以上. 由于单元结构具有旋转对称性, 使得该吸收器对偏振不敏感, 能同时实现横电波和横磁波的双波段吸收. 吸收频率决定于闭合环大小, 调节闭合环尺寸能够灵活实现特定频率的吸收. 这些优点使我们的设计在多频谱成像、热辐射探测等应用中表现出较大的潜力.     

Numerical study of metamaterial absorber and extending absorbance bandwidth based on multi-square patches

A simple design of metamaterial absorber (MA) was proposed based on a periodic array of metal patch at microwave frequencies. Our design could exhibit absorption of 99.9% confirmed by numerical simulation. Such high narrowband absorption which mainly based on strong electric and magnetic resonances overlapping in a certain frequency range and perfect impedance-matched (z = 1) to the free space. Numerical simulations demonstrate that the MA could achieve very high absorptivity at wide angles of incidence for both transverse electric (TE) wave and transverse magnetic (TM) wave. The absorption band of our device is effectively extended by patterning multi-square patches of different dimension elements with appropriate geometrical parameters in a co-planar. Finally, the composite MA is only 0.4 mm thick, with a maximum absorption of 99.8% at 15.8 GHz, and a full width at half maximum (FWHM) bandwidth of 2 GHz by numerical simulation, which may have potential applications in the detection of explosives and stealth.     

Low-frequency and broad band metamaterial absorber: design, fabrication, and characterization

We report a metamaterial absorber (MA) with a broad absorption band in the frequency region of 2–4 GHz, whose thickness is not limited to the quarter-wavelength. Theoretical and experimental results show that the absorber has two adjacent absorption apexes at 2.24 and 3.46 GHz, respectively, which are both related to the electric and magnetic resonances of the metamaterial. The absorption is over 68% in the whole wave band of 2–4 GHz provided the thickness of 4 mm. The distributions of the surface currents and the power loss density indicate that the surface currents produced by the electric and magnetic resonances are strongly consumed by the resistive patches. This low-frequency absorber has potential applications in many scientific and martial fields.     

A metamaterial absorber with direction-selective and polarisation-insensitive properties

This paper reports the design of a metamaterial absorber with direction-selective and polarisation-insensitive property.Both theoretical and simulated results reveal that the absorber has a distinct absorption point with direction selectivity at 7.48 GHz,which is related to the resonance of the metamaterial and is not influenced by the polarisation.The retrieved impedance indicates that the impedance of the absorber can be tuned to approximatively match the impedance of the free space on one side and not to match the impedance of the free space on the other side.This design can result in the minimal reflectance,the minimal transmission and the highest absorbance at the absorption frequency.The distribution of the power loss indicates that the absorber is an excellent electromagnetic wave collector:the wave is first trapped and reinforced in certain specific locations,and then mostly consumed.The distribution of the surface current is consistent with the design,the retrieved impedance and the distribution of the power loss.This absorber may have applications in many scientific and technological areas.     

Ultra-wideband water-based metamaterial absorber with temperature insensitivity

The natural water has frequency dispersion and its permittivity is also related to temperature, which are important factors to design temperature insensitive absorber at microwave frequency. Here, a water-based metamaterial absorber which is fabricated by 3D-printing is proposed. The absorber can perform stably at different temperatures and it also shows 90% absorption in the frequency range of 7.9–21.7 GHz. The experiment proves that the absorber can work at a wide incident angle and is polarization insensitive. Based on these features, the water-based absorber could be applied to various electromagnetic scenarios such as stealth technology and electromagnetic compatibility in temperature-variable environment.     

一种极化不敏感和双面吸波的手性超材料吸波体

基于手性结构设计了一种极化不敏感和双面吸波的超材料吸波体.该吸波体的结构单元由手性结构和介质基板组成.仿真的电磁波正、反向入射时超材料吸波体的吸收率表明:该吸波结构的正、反面是互易的,具有双面吸波特性.仿真的不同极化角下超材料吸波体的吸收率表明:该超材料吸波体具有极化不敏感特性.仿真的不同入射角下超材料吸波体的吸收率表明:该超材料吸波体的入射角较窄.仿真的吸波体单元的表面电流和磁能密度分布表明:电、磁场之间存在交叉耦合,吸波与手性有关.仿真的不同损耗情况下超材料吸波体的吸收率表明:基板的介质损耗在吸波过程中起主导作用,金属的电阻热可以忽略不计.该超材料吸波体可能在要求双面吸波的领域中具有潜在的应用. 关键词： 极化不敏感 双面吸波 手性结构 超材料吸波体     

Broadband and ultra-low reflection metamaterial absorber embedded with magnetic materials

In this study, we design, prepare and characterize a broadband, ultra-low reflectivity and incidence angle-insensitive metamaterial absorber. The design of this absorber not only provides a novel idea for the design of broadband absorbers, but also enhances the application prospects of metamaterial absorbers. By introducing FeSiAlp/epoxy magnetic composite and optimizing the structural parameters, the absorption performance of the metamaterial absorber has been significantly improved. The effective absorption bandwidth (bandwidth with reflectivity less than −10dB) is increased by 3.4 times from 2.19 GHz to 7.49 GHz, and the RL_min (minimum reflection loss) value reaches −38.31 dB at 17.83 GHz, that is the absorption rate reaches 99.99%. Meanwhile, the experimental results also verify the simulation design results. Therefore, the absorber not only plays the characteristics of strong absorption of metamaterial, but also absorbs the advantages of broadband of magnetic material.     

Microelectromechanical systems bimaterial terahertz sensor with integrated metamaterial absorber

This Letter describes the fabrication of a microelectromechanical systems (MEMS) bimaterial terahertz (THz) sensor operating at 3.8 THz. The incident THz radiation is absorbed by a metamaterial structure integrated with the bimaterial. The absorber was designed with a resonant frequency matching the quantum cascade laser illumination source while simultaneously providing structural support, desired thermomechanical properties and optical readout access. Measurement showed that the fabricated absorber has nearly 90% absorption at 3.8 THz. A responsivity of 0.1°/μW and a time constant of 14 ms were observed. The use of metamaterial absorbers allows for tuning the sensor response to the desired frequency to achieve high sensitivity for potential THz imaging applications.     

A dual-band polarization insensitive metamaterial absorber with split ring resonator

A dual-band polarization insensitive absorber has been proposed . Unlike the previous dual band absorber composed of composite structures, only one square metal ring with a slit at the middle of each side can be used to achieve the dual-band absorption. The calculated results show two distinct absorption peaks of 0.96 at 10 GHz and 0.99 at 20 GHz. In addition, the positions of the two peaks are strongly influenced by the width of the slit (g). More importantly, the absorptions of the two peaks keep higher than 0.9 while g changing. The dual-band absorber may have many potential applications in scientific and technological areas because of its excellent absorption characteristics and concise structure.     

An ultra-thin dual-band wide-angle polarization-insensitive metamaterial absorber with near-unity absorbance

In this paper, a dual-band metamaterial absorber (MMA) with wide-angle and polarization-insensitivity is proposed. The MMA consists of two copper layers with a layer of FR-4 between them. And its top layer consists of a cross-shaped resonator and a square ring resonator. The calculation result demonstrates that there are two distinct absorption peaks, whose absorptivity are 99.933% at 3.8441 GHz and 99.99% at 9.1094 GHz. And its thickness is only 1.34% of the wavelength of the lowest absorption frequency. The dual-band MMA shows polarization-insensitivity for normal incident wave and shows high absorptivity in a wide incident angle for both TE and TM polarization wave. In addition, we discuss the working mechanism. The influences of main parameters on the dual-band MMA's absorption are also analyzed. The proposed ultra-thin MMA has simple structure and high absorptivity, which has many potential applications, such as thermal radiometer, detection sensor, stealth technology.     

Frequency-locked tunable LD laser with a broad bandwidth

Using lock-in amplifer and proportional, integral, and derivative (PID) electric circuit, the frequency of diode laser is stabilized on a highly mechanical stable Fabry-Perot (FP) cavity transmission peak. When the frequency locking system is on, the frequency tunable range of the laser is about 4 GHz around the D1 transition of Rb. The laser frequency tuning is implemented by scanning the FP cavity length. The fluctuation of frequency of the output laser is less than 1 MHz, and the drift of the center frequency is less than 1.5 MHz in 1.5 min. This system has great potential of the application in the experimental investigation of the interaction between light and atoms, especially, for the case of far off the atomic resonance.     

High-speed and broad optical bandwidth silicon modulator

A high-speed silicon modulator with broad optical bandwidth is proposed based on a symmetrically configured Mach–Zehnder interferometer.Careful phase bias control and traveling-wave design are used to improve the high-speed performance.Over a broadband wavelength range,high-speed operation up to 30 Gbit/s with a 4.5 dB–5.5 dB extinction ratio is experimentally demonstrated with a low driving voltage of 3 V.     

Computational and experimental verification of a wide-angle metamaterial absorber

A metamaterial absorber is computed numerically and measured experimentally in a 150-THz~300-THz range.The measured absorber achieves high absorption rate for both transverse electric(TE) and transverse magnetic(TM) polarizations at large angles of incidence.An absorption sensor scheme is proposed based on the measured absorber and the variations of surrounding media.Different surrounding media are applied to the surface of the absorption sensor(including air,water,and glucose solution).Measured results show that high figure of merit(FOM) values are obtained for different surrounding media.The proposed sensor does not depend on the substrate,which means that it can be transplanted to different sensing platforms conveniently.     

Modeling for multi-resonant behavior of broadband metamaterial absorber with geometrical substrate

Despite widespread use for extending absorption bandwidth, the coexistence and coupling mechanism of multiple resonance is not well understood. We propose two models to describe the multi-resonant behavior of a broadband metamaterial absorber with geometrical-array substrate(GAS). The multi-resonance coupling of GAS is well described by logarithmic law. The interaction between metasurface and GAS can further broaden the absorption bandwidth by generating a new resonance which coexists with original resonances in substrate. The proposed models can thoroughly describe this multiple-resonance behavior, highlighting guidelines for designing broadband absorbers.     

Wide bandwidth acoustic transmission via coiled-up metamaterial with impedance matching layers

Many acoustic metamaterials suffer from a narrow bandwidth transmission because of the impedance mismatch at the airmetamaterial interface. In this paper, a two-dimensional impedance-matched metamaterial with broadband transmission performance is investigated. The impedance matching layer is introduced for a gradient variation of effective impedance from the inlet of the unit to the outlet. The effective medium theory and corresponding effective model are used to explain the underlying mechanism. The improved energy transmission of our designs is demonstrated by experiment and numerical simulation within a broad frequency bandwidth over 6 kHz. Our impedance-matched design can be used to enhance sound absorption, which is expected to present improved acoustic performance in the applications of acoustic damper and muffler.     

A broadband,polarisation-insensitive and wide-angle coplanar terahertz metamaterial absorber

Broadband terahertz metamaterial absorbers have attracted considerable attention due totheir significant potential for practical applications. These absorbers are usuallystacked in several differently shaped or sized subunits to form a unit cell, making theirfabrication quite troublesome. A simple design for broadband metamaterial absorbers istherefore urgently needed. Herein, we propose a coplanar broadband andpolarisation-insensitive perfect absorber formed by two patterned square metallic ringswith a dielectric layer on top of a metallic ground plane. The full width at half maximum(FWHM) of the device can be up to 42% (with respect to the central frequency), which is 2times greater than that of a single-layered structure. This property is retained well fora very wide range of incident angles. The two patterned square rings resonating atdifferent but similar frequencies leads to the broadband absorption. Moreover, ahybridised resonance model is proposed to analyse the origin of the resonance bandwidth.The results of this metamaterial absorber design appear to be very promising for solarcell, detection and imaging applications.     

高Q值超薄完美吸波体设计方法研究

为了增强完美吸波体的吸波性能,提出了一种高Q值超薄完美吸波体的设计方法. 该方法将基片集成波导技术与一般完美吸波体设计方法有机结合,通过合理添加金属过孔实现了高Q值的完美吸波体设计. 利用该方法设计出了厚度0.0065λ、半波功率带宽5.8%的完美吸波体,其吸波率Q值为33.9,比普通完美吸波体吸波率Q值提升了20%以上;其1.5和3 dBsm的雷达散射截面缩减Q值分别提高了54%和67%以上;同时该方法消除了传统设计中的频率偏移问题. 实测与仿真结果表明所设计的吸波体具有高Q值特征,也具有良好的雷达散射截面缩减效果,散射截面缩减最高达14 dBsm. 仿真和实测验证了设计方法的可靠性. 关键词： 基片集成波导技术 频率偏移 吸波率 雷达散射截面     

低雷达散射截面的超薄宽带完美吸波屏设计研究

提出了一种基于PMA单元结构的超薄宽带完美吸波屏设计方法. 该方法将多层拓展带宽的技术与单层多谐振方法有机结合, 实现带宽拓展的同时, 保持了完美吸波屏结构简单、无集总元件的特点, 易于实际加工和应用. 以双层三谐振超薄宽带完美吸波屏为例, 结合其等效电路, 理论上验证了所设计吸波屏的吸波机理, 同时验证了方法的有效性. 仿真分析该吸波屏具有低雷达散射截面、极化不敏感和宽入射角的特征. 仿真和实测结果表明: 该吸波屏在厚度为0.01 λ的条件下, 具有14.1%的半波功率带宽;-3 dBsm的雷达散射截面缩减带宽为18.9%, 在法线方向的最大缩减量为23 dBsm, 在法向±40°内具有较好的雷达散射截面减缩效果. 关键词： 完美吸波屏 宽带 雷达散射截面 等效电路