Query: design broadband absober

title: Design of a Broadband Tunable Terahertz Metamaterial Absorber Based on Complementary Structural Graphene
abstract: We present a simple design for a broadband tunable terahertz (THz) metamaterial absorber (MMA) consisting of a complementary cross oval shaped graphene (CCOSG) structure and dielectric substrate placed on a continuous metal film. Both numerical simulation and theoretical calculation results indicate that the absorbance is greater than 80% from 1.2 to 1.8 THz, and the corresponding relative bandwidth is up to 40% Simulated electric field and power loss density distributions reveal that the broadband absorption mainly originates from the excitation of continuous surface plasmon resonance (SPR) on the CCOSG. In addition, the MMA is polarization insensitive for both transverse electric (TE) and transverse magnetic (TM) modes due to the geometry rotational symmetry of the unit cell structure. Furthermore, the broadband absorption properties of the designed MMA can be effectively tunable by varying the geometric parameters of the unit cell and chemical potential of graphene. Our results may find promising applications in sensing, detecting, and optoelectronic related devices.

title: Design of broadband graphene metamaterial absorbers for permittivity sensing at mid infrared regions
abstract: In this paper, a tunable broadband metamaterial absorber (MA) based on graphene is investigated theoretically and numerically at mid infrared regions. Compared with the previously reported multiband graphene based MAs, a broad bandwidth of 11.7 THz with the absorption over 90% is obtained in the proposed MA, which is composed of a Jerusalem cross (JC) metal encrusting into the slot graphene layer in the top layer. The results show that the origin of broadband absorption is caused by coupling effect between metal and graphene, and this effect is explained by the two mode waveguide coupling theory. The tunability of MA is achieved via changing the external gate voltage to modify the Fermi energy of graphene. Further results show that the proposed MA can be used as the permittivity sensor with a high absorption. This work indicates that the proposed MA has the potential applications with respect to sensors and infrared absorbers.

title: The design of ultra broadband selective near perfect absorber based on photonic structures to achieve near ideal daytime radiative cooling
abstract: Passive cooling, which cools without any electricity input, has had a great impact on global energy consumption. The recent progress on radiative cooling has many potential applications in efficient passive cooling. During the day, this strategy uses the maximized infrared emissivity via the atmospheric transparency windows for radiating heat and minimizing solar absorption. However, the realization of daytime radiative coolers with ideal selective mid infrared emissivity is still a great challenge. Here, we firstly design and numerically demonstrate a near ideal radiative cooler operating below the ambient temperature, achieving both broadband selective emissivity in the infrared atmospheric window and extremely low absorption in the entire solar spectrum, realizing a net cooling power exceeding 122 W/m 2 at ambient temperature. The cooling effect can still persist under significant nonradiative heat exchange conditions. The design of multi layer all dielectric micropyramid structure in this work not only solves the shortcoming of poor mid infrared selectivity in planar photonics device, but also overcomes the disadvantage of high solar absorption in metal/dielectric metamaterials. The comparisons of physics mechanism between this multi layer all dielectric structure and previously reported multi layer metal/dielectric structure also are investigated clearly. Thus, this study can help pave the way for designing ideal daytime radiative coolers.

title: Design of a Tunable Ultra Broadband Terahertz Absorber Based on Multiple Layers of Graphene Ribbons
abstract: We propose and numerically demonstrate an ultra broadband graphene based metamaterial absorber, which consists of multi layer graphene/dielectric on the SiO2 layer supported by a metal substrate. The simulated result shows that the proposed absorber can achieve a near perfect absorption above 90% with a bandwidth of 4.8 Thz. Owing to the flexible tunability of graphene sheet, the state of the absorber can be switched from on (absorption 90% to off (reflection 90% in the frequencies range of 3 7.8 Thz by controlling the Fermi energy of graphene. Moreover, the absorber is insensitive to the incident angles. The broadband absorption can be maintained over 90% up to 50deg. Importantly, the design is scalable to develop broader tunable terahertz absorbers by adding more graphene layers which may have wide applications in imaging, sensors, photodetectors, and modulators.

title: Design of a Broadband Polarization Reconfigurable Fabry Perot Resonator Antenna
abstract: In this letter, a broadband polarization reconfigurable Fabry Perot (FP) resonator antenna is presented for WLAN/WiMAX applications. The open air filled FP cavity is constructed by a partially reflective surface (PRS) layer directly placed over a fully reflective ground plane. A two element patch array is employed to serve as a feeder. To achieve polarization reconfigurability, the feeding antenna is designed to have the capability of switching between horizontal linear polarization (HP) and vertical linear polarization (VP) by controlling the <sc>on/off</sc> states of four pairs of p i n diodes. By combining the frequency resonances of the FP cavity and the feeding antenna, the proposed FP resonator antenna obtains broadband performance. Furthermore, the proposed antenna achieves a broadband 3 dB gain bandwidth by designing the PRS layer to have a reflection phase with positive slope over as wide a frequency band as possible. The proposed antenna was fabricated and experimentally characterized. Measurements demonstrate that it achieves a 10 dB impedance bandwidth of 21<inline formula><tex math notation="LaTeX" /tex math>/inline formula> ranging from 2.2 to 2.72 GHz, which can well cover WLAN/WiMAX band of operation. The 3 dB gain bandwidths of 12.5<inline formula><tex math notation="LaTeX"/tex math>/inline formula> and 14.6<inline formula><tex math notation="LaTeX"/tex math>/inline formula> are obtained with peak realized gains of 15.1 and 14.8 dBi for the HP and VP, respectively.

title: Materials and design of nanostructured broadband light absorbers for advanced light to heat conversion.
abstract: Light to heat conversion systems have been attracting growing research interest in the last few decades, due to their highly intriguing photothermal properties and their wide applications ranging from biomedical applications to solar energy harvesting to mechanical actuators. In general, because the light to heat conversion efficiency depends strongly on the absorbing material, significant efforts have been focused on fabricating broadband light absorbers. However, there are several challenges associated with the design and fabrication of light absorbers, such as minimizing heat loss, and optimizing the broadband light absorption and omnidirectional light absorption. Thus, the rational design of enhanced light absorbers is critical to achieve efficient light absorption over a broad wavelength range. In this paper, we introduce the basic theory of light absorption and heat transfer, then summarize fundamental understanding of representative light to heat conversion agents including carbon based, semiconductor based and plasmonic metal based materials and structures, and highlight state of the art structural designs towards the development of broadband light absorbers. In addition, the practical applications of these materials and designs are also discussed.

title: Design of a Photo Excited Switchable Broadband Reflective Linear Polarization Conversion Metasurface for Terahertz Waves
abstract: We present a photo excited switchable broadband reflective linear polarization conversion metasurface for terahertz waves. The unit cell structure of the switchable polarization conversion metasurface is composed of metallic disk and split ring resonator (together named as DSRR) integrated with semiconductor photoconductive silicon (Si) placed over the continuous films. The electric response of the photoconductive Si filled in the gap of the DSRR can be tunable through a pump beam with different optical power. The simulation results indicate that the polarization conversion ratio (PCR) of the compound metasurface without pump beam is greater than 80% in the frequency range of 0.65 1.58 THz, and the PCR is up to 99% at resonances frequencies of 0.69 THz, 1.01 THz and 1.42 THz, respectively. The numerical simulation results are in good agreement with the theoretical predictions based on the interference theory. Furthermore, the broadband PCR can be tunable continuously with the changes of Si conductivity by adjusting the pump optical power. Moreover, the surface current distributions of the unit cell structure with different Si conductivity at the resonance frequency are discussed to illustrate its physics mechanism. Thus, our design can find potential applications in many areas, such as remote sensors, reflector antennas, and radiometers in terahertz region.

title: Design of Metamaterial Absorber using Eight Resistive Arm Cell for Simultaneous Broadband and Wide Incidence Angle Absorption
abstract: In this paper, a broadband metamaterial (MM) absorber is presented for X band applications. A novel eight resistive arm (ERA) cell is proposed as an MM unit cell to achieve both broadband absorption and wide incidence angles. The proposed ERA cell is designed using equivalent circuit model and full wave analysis in order to achieve an absorption ratio higher than 90% in the range of 8.2 13.4 GHz. The experimental results indicate that the absorptivity was greater than 90% in the range of 8 13 GHz for all polarization angles under normal incidence. Under oblique incidence, the measured absorptivity was greater than 90% in the range of 8.2 12.2 GHz up to 60deg and in the range of 9.2 12 GHz up to 65deg in the transverse electric (TE) mode. In the transverse magnetic (TM) mode, the measured absorptivity was higher than 90% in the range of 9.5 12.4 GHz when the incidence angle was varied from 0deg to 60deg and remaining a 90% absorption bandwidth in the range of 10 12 GHz up to 65deg. Compared to other broadband MM absorbers, the proposed MM absorber exhibited the widest incidence angles in both TE and TM modes.

title: Inverse design and demonstration of an ultracompact broadband dual mode 3 dB power splitter.
abstract: An ultracompact broadband dual mode 3 dB power splitter using inverse design method for highly integrated on chip mode (de) multiplexing system is proposed and experimentally demonstrated. A dual mode convertor based on subwavelength axisymmetric three branch waveguide is utilized to convert TE0 and TE1 to three intermediate fundamental modes. The axisymmetric topology constraint of the nanostructures enables the optimized device to achieve a strict 50:50 splitting ratio over a broad wavelength range from 1.52 to 1.60 um. The fabricated device occupied a compact footprint of only 2.88 um x 2.88 um. The measured average excess losses and crosstalks for both modes were respectively less than 1.5 dB and 20 dB from 1.52 to 1.58 um for both TE0 and TE1, which are consistent with the numerical simulations.

title: Multi scale design of electromagnetic composite metamaterials for broadband microwave absorption
abstract: The microwave absorbing composites embedded with magnetic dielectric lossy components including spherical carbonyl iron (CI) and multi wall carbon nanotubes (MWCNT) were fabricated by a two step molding method. By manipulating the content of CI and MWCNT for adjusting complex permittivity and permeability, the as prepared composites were used to optimize the electromagnetic composite metamaterials (ECMs) for broadband absorption. The multi scale ECMs achieved 8 dB absorption in 2 40 GHz and 10 dB absorption within the 30 GHz bandwidth, where the minimum reflectivity of 55 dB was found at 14.8 GHz. It is found that the magnetic and dielectric loss materials are responsible for attenuating the electromagnetic energy, while the structure of the metamaterials are mainly linked with the broadband absorption via impedance match improvement and electromagnetic field manipulation. The results suggest that multi scale design for ECMs is an attractive avenue to enhance microwave absorption performance via utilizing ternary composites and tailoring geometrical sizes for absorption resonance.