Perfect Absorption Research Articles

Ultranarrowband Chiral Absorbers in the Visible Region Based on Brillouin Zone Folding Metasurfaces.

Chiral perfect absorbers that enable the handedness-dependent near-unity absorption of circularly polarized light are highly desirable for enhancing various chiral interactions. However, the experimental realization of ultranarrowband absorbers with extreme chiral responses remains challenging. Here, we realize such chiral absorbers by incorporating Brillouin zone folding and mirror symmetry breaking in the design of planar dielectric metasurface. When the metasurface is backed by a reflection mirror, strong chiral absorption with ultranarrow line width can be achieved in the normal direction. We experimentally achieve a substantial differential absorptance of 0.75 with an ultranarrow line width of 1.4 nm in the visible region. Furthermore, by leveraging handedness-dependent strong field enhancement, high levels of chiral emission with a luminescence line width of 1.75 nm are demonstrated from quantum dots coated on the absorber surface. Our findings may unlock interesting opportunities in chiral photodetectors, optical filters, nonlinear optics, light sources, and quantum photonic devices.

Design and validation of ultra-compact metamaterial-based biosensor for non-invasive cervical cancer diagnosis in terahertz regime.

Cervical cancer belongs to the most dangerous types of cancers posing considerable threat to women's survival. It is most often diagnosed in the advanced stages as precancerous lesions are often symptom-free and difficult to identify. Microwave imaging, especially in terahertz (THz) range, is a convenient and noninvasive cancer detection tool. It enables characterization of biological tissues and discrimination between healthy and malignant ones. This study presents a novel triple-band biosensor based on metamaterials (MTMs). By leveraging unique properties of MTMs, the proposed biosensor operates as a perfect absorber. It exploits resonant modes in the THz spectrum to achieve remarkable sensitivity. Meticulous selection of the sensor geometry and dimensions enables efficient miniaturization. Meanwhile, utilization of frequency-domain data to detect refractive index changes improves resolution of cancerous tissue identification. Extensive numerical investigations corroborate its ability to carry out reliable early-stage cervical cancer diagnosis. This includes identification of the spatial extent of the malignant tissue. Excellent electrical properties of the sensor are accompanied by its compact size, which is highly desirable for non-invasive and portable applications.

Polarization-independent ultranarrow ultraviolet graphene perfect absorption for temperature controlled high-performance optical switch

We demonstrate a tunable polarization-independent ultranarrow perfect absorption (PA) in a hybrid metasurface consisting of graphene-dielectric nanodisk-metal mirror in the ultraviolet (UV) range. Through near-field interactions between the optical dissipation of graphene and surface plasmon polaritons supported by Al2O3 nanodisk array on UV mirror, the UV Fano-like absorption peak can reach 99.92% with linewidth as low as 3.4 nm, which is predicted by the impedance matching theory and a Fano model. Furthermore, a dynamic tuning of the UV PA and the associated high-performance optical switch are achieved via temperature change of the encapsulated ethanol. Importantly, the modulation depth of almost 100%, the ultralarge modulation intensity of about 2.5×106 and the on/off ratio of 63 dB are reached for the graphene-based switch by a thermal control. Our work holds potential applications on the UV graphene based light modulators such as high-precision optical switch and nanodevices.

A simple ultra-broadband metamaterial solar perfect absorber with highly efficient photothermal conversion performance

A simple ultra-broadband metamaterial solar perfect absorber with highly efficient photothermal conversion performance

Robust carbon nanotube composite coatings for perfect absorption in harsh environmental applications

Robust carbon nanotube composite coatings for perfect absorption in harsh environmental applications

Simulation study on ultra-wideband and ultra-narrowband switchable terahertz metamaterial absorbers based on deep neural networks

Supported by deep neural networks (DNNs), a simulation study on an ultra-wideband (UWB) to ultra-narrowband (UNB) switchable terahertz metamaterial absorbers (THz MAs) was designed and optimized. By leveraging the phase transition properties of vanadium dioxide (VO2), the device achieves nearly perfect absorption, switching between UWB and UNB modes. Finite element analysis was used to simulate and analyze the constructed model. Simulation results indicate that when VO2 is in its metallic state, the device functions as a UWB absorber with an absorption bandwidth of 11.54 THz over the 3.88–15.42 THz range, achieving an absorption rate exceeding 90% and a relative bandwidth (RBW) of 119.6%. When VO2 is in its insulating state, the device switches to a UNB absorber, reaching an absorption rate close to 100% at 13.927 THz. In this state, material detection was conducted, revealing that the device has a maximum refractive index sensitivity (S) of 0.33 THz/RIU and a corresponding quality factor (Q) of up to 515.8, enabling high sensing functionality. Its absorption performance is insensitive to TE and TM polarizations. Additionally, the effects of incident and polarization angles on the operating characteristics were studied. The proposed absorber demonstrates excellent polarization insensitivity, angle stability, and UWB and UNB advantages, offering valuable insights for new multifunctional THz device research. It holds significant application potential in short-range wireless THz communication, ultra-fast optical switching, sensing, transient spectroscopy, and electromagnetic stealth.

Dual-function terahertz metamaterial absorber based on microfluidic structures

In recent years, terahertz metamaterial sensors have shown great potential in label-free biosensing; yet, the detection of high-absorption liquid samples that are sensitive to terahertz waves remains a significant challenge. In this study, a dual-function absorber capable of dynamically switching between broadband absorption and high-sensitivity sensing is proposed based on the microfluidic technology and phase change characteristics of vanadium dioxide (VO2). Compared with traditional terahertz microfluidic sensors, this structure differs in that it incorporates a VO2 film as a separation layer in the sensor cover plate and a VO2 square resonator on top. This configuration not only exhibits high-sensitivity sensing but can also function as an absorber for broadband absorption. When VO2 is in the metallic state, the structure acts as a broadband absorber with an absorption rate exceeding 90% across the 1.09–3.02 THz range. When VO2 is in the insulating state, the structure functions as a microfluidic sensor, achieving an absorption rate above 99.9% at 1.438 and 2.068 THz, with nearly perfect absorption and refractive index sensitivities of 532 and 785 GHz/RIU, respectively; the quality factor is 17.6 and 23.5, respectively, indicating excellent sensing performance. Moreover, due to the symmetry of the metal micro-structured layer and the VO2 square resonator, the device exhibits polarization insensitivity and stability at large incident angles. In summary, this structure significantly broadens the applications of traditional absorbers and sensors and holds promise for future applications in electromagnetic cloaking, energy harvesting, and biomedical detection.

Sound absorption and enhancement mechanism of hierarchical slit-embedded Helmholtz resonators

Abstract In this paper, the low frequency sound absorption structure based on Helmholtz resonator (HR) is deeply studied. The influence of hierarchical structure design on the broadband sound absorption is emphatically discussed. Through the introduction of the embedded slits and hierarchical structures, we design a new and efficient hierarchical slit-embedded HR (HSEHR) for sound absorption. This structure not only inherits the advantages of the classic HR, but also realizes the effective sound absorption(α > 0.97) in a lower frequency(225 Hz) range through the interaction of the embedded slit and the hierarchical structure. More interestingly, the thickness of HSEHR is only 1/50 of the corresponding wavelength. In order to verify the sound absorption effect of HSEHR, we have carried out a lot of theoretical analysis and numerical simulation. The results show that HSEHR has excellent sound absorption performance in the low frequency range, and with the introduction of the hierarchical structure, the sound absorption peak moves to a lower frequency, and a higher sound absorption coefficient is obtained. We also found that by adjusting the structural parameters of HSEHR (such as the depth and width of the primary embedded slit.), its resonance frequency can be precisely controlled. So it can better match the target noise frequency and improve the sound absorption efficiency. In addition, genetic algorithm is used to optimize the structural parameters of HSEHR to further improve its sound absorption performance. The optimization results show that HSEHR optimized by genetic algorithm has better sound absorption performance in the broadband low frequency range. It achieves excellent sound absorption at 260–480 Hz. The sound absorption coefficient is up to 0.92, which is infinitely close to perfect sound absorption. It provides an excellent solution to the noise problem.

Independently tunable dual-channel angle-sensitive narrowband perfect absorber

Independently tunable dual-channel angle-sensitive narrowband perfect absorber

Tunable perfect absorber in the short-wave infrared band based on ITO nonlinear metasurface with enhanced optical response

A polarization-sensitive nonlinear metasurface of antenna-indium tin oxide (ITO) coupled structure has been meticulously designed to enhance the nonlinear response with strong coupling between the localized surface plasmon resonance (LSPR) of gold nanoantenna and the epsilon-near-zero (ENZ) mode of the ITO film. This metasurface exhibits a broadband spectrum (∼730 nm) and a large nonlinear index coefficient n2 of 1.41 cm2/GW, which is approximately 520 times greater than that of a single-layer ITO film. Additionally, we have engineered a perfect absorber using an ITO nonlinear metasurface, with a 38 nm absorption bandwidth ranging from 1085 nm to 1123 nm, achieving near-perfect absorption, with a maximum absorption rate of up to 94% in the short-wave infrared band. These findings offer a promising foundation for the development of ultra-compact and large nonlinear optical devices.

Electronic CPA‐Laser Having Enhanced Sensitivity and Tunability

AbstractExceptional point degeneracies, which are spectral singularities of non‐Hermitian systems, have been widely utilized for building optical, mechanical, or electrical sensing systems with much larger responses than those utilizing Hermitian degeneracies. However, such systems suffer from enhanced noise, which negates the enhanced response and thus does not provide any improvement in signal‐to‐noise ratio. Recently, the coherent perfect absorber (CPA)‐laser, which also utilizes non‐Hermitian singularity, has been used in sensing systems resulting in better noise robustness and enhanced responsivity. Nonetheless, CPA‐laser (CPAL) implementation requires all system parameters to be immutable, which hinders progress toward their practical use for sensing purposes. Here, a tunable electronic CPA‐laser is reported that overcomes these obstacles providing ultrahigh sensitivity as validated in the experiments for monitoring arterial pressure and respiration. This CPAL sensing scheme utilizes inductive coupling between gain and loss sub‐components and thereby the whole system can be decomposed into an active reader and a passive sensor, which enables better tunability and performance compared to previously reported CPAL systems. Moreover, the proposed CPAL system exhibits better performance compared to exceptional point‐based systems having a similar circuit structure. This research paves the way for exploring electronic CPAL for sensing applications and may have a profound impact on the next‐generation, ultrasensitive electromagnetic sensing system.

Switching from perfect absorption to plasmon induced transparency in graphene-vanadium dioxide metamaterials with high sensitivity

Abstract A multifunctional metamaterial, composed of patterned graphene layer atop the dielectric and vanadium dioxide (VO2) layer has been proposed. It can switch from a perfect absorption to plasmon induced transparency (PIT) as the VO2 transits from the metallic state into the dielectric state. By adjusting graphene’s Fermi energy, the perfect absorption can be finely tuned from a single-band to a dual-band. PIT occurs when the VO2 is in the dielectric state and the transparency window blue-shifts with a higher Fermi energy. Notably, it demonstrates the sensing ability and the resonant peaks embody a linear tendency with different substrates or embedding solutions. Thus, our findings not only provide new perspectives on the innovative design of multifunctional metamaterials but also underscore their potential applications in filters, optoelectronic detectors, and environmental monitors.

Broadband negative refraction based on a pair of anti-parity-time structures

Abstract An anti-parity-time(A-PT) symmetric system, of which the refractive index satisfies n( - x) = - n*(x), can present intriguing scattering properties like continuous coherent perfect absorption(CPA) spectrum and laser spectrum, which are symmetric to each other in the parameter space. In this work, an acoustic parity-time(PT) symmetric system consisting of two A-PT symmetric structures is introduced to realize a broadband negative refraction. When the two A-PT symmetric structures are at their CPA mode and laser mode respectively, the PT symmetric system can display its unidirectional negative refraction property. As the two A-PT structures we design here have a broadband CPA and laser modes, the PT symmetric negative refraction system would be broadband. Besides, the exceptional point(EP) of the proposed PT-symmetric system corresponds to the CPA point and laser point of its two components, and it's unidirectionally transparent on broadband as well.

Multicavity structures with triply periodic minimal surface for broadband and perfect sound absorption manufactured by laser powder bed fusion

Multicavity structures with triply periodic minimal surface for broadband and perfect sound absorption manufactured by laser powder bed fusion

Chiral Light-Matter Interactions with Thermal Magnetoplasmons in Graphene Nanodisks.

We investigate the emergence of self-hybridized thermal magnetoplasmons in doped graphene nanodisks at finite temperatures upon being subjected to an external magnetic field. Using a semianalytical approach, which fully describes the eigenmodes and polarizability of the graphene nanodisks, we show that the hybridization originates from the coupling of transitions between thermally populated Landau levels and localized magnetoplasmon resonances of the nanodisks. Owing to their origin, these modes combine the extraordinary magneto-optical response of graphene with the strong field enhancement of plasmons, making them an ideal tool for achieving strong chiral light-matter interactions, with the additional advantage of being tunable through carrier concentration, magnetic field, and temperature. As a demonstration of their capabilities, we show that the thermal magnetoplasmons supported by an array of graphene nanodisks enable chiral perfect absorption and chiral thermal emission.

Perfect absorption of molecular vibration enabled by critical coupling in molecular metamaterial

Perfect absorption of molecular vibration enabled by critical coupling in molecular metamaterial

Simulation of terahertz tunable seven-band perfect absorber based on high frequency detection function of Dirac semi-metallic nanowires

In this work, a tunable perfect absorber in the terahertz range is designed based on Dirac semimetal nanowires, featuring high sensitivity, quality factor, and dual functionality. The absorber achieves perfect absorptions across seven bands in a range of 0—14.5 THz: <i>f</i><sub>1</sub> = 5.032 THz (84.43%), <i>f</i><sub>2</sub> = 5.859 THz (96.23%), <i>f</i><sub>3</sub> = 7.674 THz (91.36%), <i>f</i><sub>4</sub> = 9.654 THz (99.02%), <i>f</i><sub>5</sub> = 11.656 THz (93.84%), <i>f</i><sub>6</sub> = 12.514 THz (98.47%), and <i>f</i><sub>7</sub> = 14.01 THz (97.32%). To ensure structural stability during design, the periodicity of the wire array structure is carefully considered. Verification of the absorber’s performance is conducted through the calculation of impedance matching. The analyses of the surface electric field and magnetic field at resonance frequency elucidate the underlying physical mechanisms governing the absorber’s characteristics. The values of quality factor (<i>Q</i>) for the seven resonance points are computed, with a maximum <i>Q</i> of 219.41. Further investigations by changing the external refractive index show that the maximum sensitivity value and the figure of merit (FOM) value are 5421.43 (GHz/RIU) and 35.204 (1/RIU), respectively. Then, by discussing the influence of key parameters on the device, we conclude that the device can achieve the choice of dual fixed performance. Dynamic modulation capabilities are demonstrated by changing the Dirac semimetal’s Fermi energy. Additionally, by changing the incident angle of the external electromagnetic wave, it is found that the device has good stability in the medium frequency band and low frequency band, but it is greatly affected by the external incident angle in the high frequency band, thus necessitating careful consideration in practical applications. In conclusion, the proposed absorber holds significant promise for imaging, sensing, and detection applications, providing the valuable insights for designing optoelectronic devices.

A perfect ultra-wideband solar absorber with a multilayer stacked structure of Ti-SiO2-GaAs: structure and outstanding characteristics.

In this paper, we introduce an entirely new solar absorber design-a multi-layer periodic stacked structure. Through coupling effects, this design has perfect ultra-wideband absorption characteristics. The absorber structure is composed of four absorption units with varying cycle lengths, which are cyclically stacked on the surface of the refractory metal Cr. Each cycle encompasses three-layer nanosheets of Ti-SiO2-GaAs. We verify through finite difference time domain method (FDTD) simulations that the absorber achieves an absorption efficiency of 97.8% within the wavelength range of 280 nm to 3000 nm, with an average efficiency of 96.6% under the AM1.5 standard solar spectrum. The absorber can achieve such a remarkable absorption effect because of surface plasmon resonance (SPR) and Fabry-Pérot resonance effects. At 1500 K, this structure exhibits a thermal radiation efficiency of up to 97.83%. Furthermore, the design is not affected by polarization and it is less affected by the incident angle of the light source. These absorption spectra remain consistent regardless of whether it is in the TE or TM mode. Even when the angle of incidence is increased to 60 degrees, the absorption efficiency remains high. Its unique structure and excellent performance characteristics provide higher solar energy efficiency. These outstanding features enable solar absorbers to have broad application potential in improving solar energy efficiency.

An optimization method for terahertz metamaterial absorber based on MOPSO

Metamaterials can freely control terahertz waves to obtain the desired electromagnetic characteristics by designing the geometry and direction of the unit structure, which is widely used in sensing, communication and stealth technology in radar. The traditional design of terahertz metamaterial absorber usually requires continuous structural adjustment and a large number of simulations to meet the expected requirements. The process is heavily dependent on the experience of researchers, and the physical modeling and simulation solution process is time-consuming and inefficient, which has greatly hindered the development of metamaterial absorbers. Therefore, deep learning has been used to predict the structural parameters or spectra of metamaterial absorbers due to its powerful learning ability. However, when designing a new structure, a large number of training samples need to be reprepared, which is time-consuming and not universal. Particle swarm optimization can quickly converge to the optimal solution through the sharing and cooperation of individual information in the group, without prior preparation. Therefore, this paper proposed a fast design method of terahertz metamaterial absorber based on multi-objective particle swarm optimization algorithm. Taking a new center symmetric absorber structure composed of four L as an example, the structure parameters are optimized to achieve fast automatic design of metamaterial absorber. The multi-objective particle swarm optimization takes the absorptivity and quality factor as independent targets to design the structure parameters of the absorber, realizes the dual-objective optimization of the absorber, and overcomes the shortcoming of the multi-objective conflict that PSO cannot solve. The optimally-designed absorber achieves perfect absorption at 1.613THz with a quality factor of up to 319.72 and a sensing sensitivity of 264.5GHz/RIU when used for refractive index sensing. In addition, the causes of absorption peaks are analyzed in detail using impedance matching, surface current, and electric field distribution. By studying the polarization characteristics of the absorber, it is found that it is not sensitive to polarization, which is more stable in practical application. In summary, the multi-objective particle swarm optimization algorithm can realize the design according to the demand, reduce the experience requirement of researchers in the design of metamaterial absorber, improve the design efficiency and performance, and have great application potential in the design of terahertz functional devices.

Research on thermal resistance Performance: Broadband solar absorber based on laminated circular ring − disk microstructure

This paper presents a laminated circular-ring-disk (CRDS) solar microstructure absorber constructed based on heat-resistant metals. This absorber achieves an ultra-broadband absorption with a bandwidth of 2171.68 nm in the near-ultraviolet to mid-infrared band, and has three absorption peaks with absorption rates exceeding 96 %, with peak wavelengths of 342.09 nm, 1215.40 nm, and 2032.86 nm respectively. With the finite-difference time-domain method (FDTD), we detected that the average absorption efficiency of this absorber under Atmospheric mass of 1.5(AM 1.5) conditions is as high as 96.05 %, and the average energy loss is only 3.95 %. Meanwhile, the research results of the electric field distribution of the CRDS microstructure show that CRDS effectively promotes the surface plasmon resonance effect between the laminated metal materials. Combined with the research on the top micro-absorption structure materials, we finally determined the structural parameters of the CRDS structure absorber and selected heat-resistant metals nickel (Ni), chromium (Cr), and titanium (Ti). On this basis,we focused on the thermal radiation performance of the absorber and found that it has good adaptability to high-temperature environments. Finally, by comparing the Transverse Electric Wave(TE) and Transverse Magnetic Wave(TM) polarization conditions with the sweep parameter diagrams of 0°-60°, we found that the absorber has excellent angle insensitivity. In view of the above discussions, the CRDS microstructure absorber has good thermal stability, angle insensitivity, and can achieve ultra-broadband perfect absorption from the near-ultraviolet to the mid-infrared band, and has broad application prospects.