A four-band and polarization-independent BDS-based tunable absorber with high refractive index sensitivity

Li R., Zheng Y., Luo Y., Zhang J., Yi Z., Liu L., Song Q., Wu P., Yu Y., Zhang J.

In this paper, we have investigated an absorber based on two-dimensional hexagonal graphene array and theoretically propose a calculation method for the approximate conductivity of graphene in the terahertz band and its correction term, and we also theoretically explain the phenomenon of blue-shift of the absorption spectrum with increasing graphene chemical potential. The finite difference time domain (FDTD) method shows that this absorber has the advantages of exciting high absorption rate, multi-band, tunable and high figure of merit (FOM). By discussing the analysis of different graphene geometries, we demonstrate the optimality of this result. The bottom layer of our absorber is composed of an Au reflection layer, and the middle layer is a silicon oxide dielectric layer. Four hexagonal two-dimensional graphene is placed at the top. Taking this as the basic unit, an array can be formed. Our absorber has a simple structure, which simplified the processing technology and saves the processing cost greatly. In the near-infrared band from 1600 nm to 1900 nm, our absorbers have absorption peaks of 99.70%, 99.25% and 99.82% at 1667.19 nm, 1691.71 nm and 1773.20 nm, respectively. In addition, the resonance wavelength of the absorber can also be adjusted by adjusting the chemical potential and refractive index of the silicon dioxide layer. The absorber also has the features of polarization and angular insensitivity. Our simulation results show that our absorber's absorption spectrum will change significantly as the ambient refractive index changes, and based on this, we can calculate the sensitivity and the figure of merit (FOM) of our model. We finally calculated the best FOM for the three peaks of our absorber (sorted by resonance wavelength from short to long) is 90.93, 90.96, 107.34, and the sensitivity is 290.25 nm/RIU, 309.95 nm/RIU, 318.50 nm/RIU, respectively. Thus, we trust that our absorbers can be widely used in Near-infrared thermal radiation, optical detector and Near-infrared sensors. • A concise method for deriving the approximate conductivity of graphene in the terahertz band is proposed, and its correction term is given. • A theoretical explanation for the blue-shift phenomenon of absorption spectra when the chemical potential of graphene increases. • By FDTD simulation, the absorber has three perfect narrow band absorption peaks. • The absorption property can be turned by controlling chemical potential or relaxation time. • The wave absorber has extremely high FOM.

Chen X., Zhou Y., Han H., Wang X., Zhou L., Yi Z., Fu Z., Wu X., Li G., Zeng L.

Core–shell Fe 3 O 4 @C magnetic nanoparticles which are of great interest for research have a widely applied prospect. However, people know little about the optical and magnetic properties of the small-size Fe 3 O 4 @C nanoparticles due to the difficulty of uniformly coating small size Fe 3 O 4 nanoparticles. In this paper, the influence of carbon shell coating on the optical and magnetic properties of small size Fe 3 O 4 nanoparticles was presented. Carbon coating can strengthen the absorption intensity in the UV–visible light region through the introduction of oxygen defects on the surface of the nanoparticles by nitric acid treatment. Fe 3 O 4 and Fe 3 O 4 @C nanoparticles both display typical superparamagnetic behavior in the high-temperature regime and a blocked state at low temperature from hysteresis loop, zero-field cooled and field cooled curves. Carbon coating reduce the surface uniaxial anisotropy, thus the average blocking temperature decreases from 59 K of Fe 3 O 4 nanoparticles to 50 K of Fe 3 O 4 @C nanoparticles. • Fe 3 O 4 @C nanoparticles exhibit a wide range of light absorption in the UV-visible region. • Fe 3 O 4 @C nanoparticles display typical superparamagnetic behavior in the high-temperature regime. • Fe 3 O 4 @C nanoparticles have a blocked state at temperature lower than 50 K. • Fe 3 O 4 @C nanoparticles have lower average blocking temperature because carbon coating can reduce the surface anisotropy.

Xiong H., Li D., Zhang H.

• The absorption bandwidth and intensity not only can be controlled by Fermi energy of BDS, but also can be tuned by temperature of water. • Tunable mechanism of the proposed dual-controlled absorber is to utilize the permittivity of water can be adjusted by temperature. • DS can be controlled by Fermi energy. • Field analyses are introduced to analyze and elucidate the physical origin of broadband absorption. A dual-tunable broadband metamaterial absorber based on bulk Dirac semimetal (BDS) and water is proposed in the terahertz (THz) region. Different from the traditional single controlled absorber, this proposed absorber can be adjusted by temperature and Fermi energy level. Simulation results indicate that the absorptance greater than 90% is achieved in the frequency range of 3.05 to 6.35 THz under normal incidence, when the temperature of the water and Fermi energy level of BDS are adjusted at 15 ℃ and 30 meV, respectively. Compared with the absorber without injected water or no BDS pattern, the bandwidth with absorptance over 90% has been significantly improved. Moreover, absorption bandwidth and intensity can be controlled independently or jointly by adjusting the temperature of the water or the Fermi energy of BDS instead of redesigning the devices. The mechanism of the proposed dual-controlled absorber is explained by utilizing the permittivity of water can be adjusted by different temperatures, and BDS can be controlled by employing the Fermi energy. Field analysis is introduced to investigate and elucidate the physical origin of broadband absorption. Based on the remarkable performance, our results may have potential applications in the thermal detectors and terahertz imaging areas.

Bao Z., Wang J., Hu Z., Chen Y., Zhang C., Zhang F.

In this paper, we propose novel absorbers with periodic stacking of graphene metasurface based on multilayer film structures. The proposed structure is delicately simulated by using the commercial finite element method (FEM). We combine equivalent circuit model (ECM) with parameter inversion to achieve new method to analyse the physical mechanism of selective absorption. The results show that four gradually decreasing peaks of ultra-high absorption are formed within 0-1.1THz, and the maximum absorptance is near 100%. Numerical simulation and theoretical calculation are in good agreement. Due to the symmetry of the structure and the locality of SPR, the proposed structures are insensitive to the incident angle and polarization state of incident light. By changing the Fermi level of graphene, the coordination of the device is realized. By changing the height of the dielectric material to change the resonance frequency, the working frequency band is increased from 0-1.1THz to 0-1.9THz, and the four absorption peaks become three, which are used as sensor applications. The sensitivity of the sensors is 50GHz/RIU, the coefficient of determination value (R2) obtained by linear fitting is 0.9989, and the value of the limit of detection (LOD) is 5.9 ×10-5RIU. The results show that our proposed devices have great potential in the practical application of terahertz technology absorbers and refractive index sensors.

Zhang R., Zhang R., Wang Z., Li M., Li K.

Diabetes is one of the biggest health problems in the world; in order to control blood in modern biological detection and analysis, most of them use the method of label determination to realize the detection. This method usually needs to modify and label the samples in advance. This pretreatment process is not only complex, time-consuming, and slow in response, but also has a great risk of damaging and polluting the samples to be tested, which seriously limits the detection accuracy [1, 2]. In order to realize the real-time detection and analysis of biological targets without label, high precision, and high sensitivity, the design of liquid refractive index sensor based on terahertz metamaterials is carried out in this paper. Based on terahertz technology and artificial periodic structure design of metamaterials, a liquid refractive index sensor with high precision, high sensitivity, and high stability is successfully designed. Then, based on the equivalent medium theory, the absorption characteristics of the sensor are studied; it is proved that the sensor has excellent polarization-insensitive and wide-angle incident characteristics. It can complete the detection of biological targets in most polarization modes and electromagnetic wave environment with various incident angles, and maintain perfect absorption at the resonance frequency of the sensing structure. The displacement of the resonance absorption peak is 102 GHz, the displacement sensitivity is 51 GHz/RIU, and the detection accuracy is 0.0196 RIU/GHz, which can realize the detection of minimal refractive index change; the average absorption index is high, which is 99.98%, and the displacement of absorption peak has an excellent linear relationship with the change of refractive index, and the linear fitting degree is 98.788%. Through data analysis, it is found that the sensor structure also has a strong bandwidth and absorption stability, which has a certain practical application value in the detection and analysis of biological targets. It provides a new idea for the real-time detection and analysis of biological liquid analytes with no label, high precision, and high sensitivity. Finally, through the data analysis, the change law of the sensor absorption characteristics with different physical dimensions is revealed, which lays a theoretical foundation for the future sensor structure optimization and the improvement of sensing accuracy and sensitivity.

Li Z., Yi Y., Xu D., Yang H., Yi Z., Chen X., Yi Y., Zhang J., Wu P.

We design a four-band terahertz metamaterial absorber that relied on the block Dirac semi-metal (BDS). It is composed of a Dirac material layer, a gold reflecting layer, and a photonic crystal slab (PCS) medium layer. This structure achieved perfect absorption of over 97% at 4.06 THz, 6.15 THz, and 8.16 THz. The high absorption can be explained by the localized surface plasmon resonance (LSPR). And this conclusion can be proved by the detailed design of the surface structure. Moreover, the resonant frequency of the device can be dynamically tuned by changing the Fermi energy of the BDS. Due to the advantages such as high absorption, adjustable resonance, and anti-interference of incident angle and polarization mode, the Dirac semi-metal perfect absorber (DSPA) has great potential value in fields such as biochemical sensing, information communication, and nondestructive detection.

Nemati A., Wang Q., Ang N.S., Wang W., Hong M., Teng J.

Zhou F., Qin F., Yi Z., Yao W., Liu Z., Wu X., Wu P.

An ultra-wideband solar energy absorber composed of a Ti ring and a SiO2–Si3N4–Ti thin film is proposed. It was found that the absorption efficiency of the absorber was over 90% with a broadband of 3683 nm.

Li Z., Yi Z., Liu T., Liu L., Chen X., Zheng F., Zhang J., Li H., Wu P., Yan P.

We designed a perfect absorber based on bulk Dirac semi-metallic. The minimum bandwidth is 0.02 THz, the maximum quality factor is 106, and the maximum refractive index sensitivity is 0.1525 THz RIU−1. The device can be tuned by Fermi level.

Wang Y., Yi Y., Xu D., Yi Z., Li Z., Chen X., Jile H., Zhang J., Zeng L., Li G.

A tunable terahertz (THz) narrowband absorber in view of bulk Dirac semimetal (BDS) is designed in this paper. The tunable terahertz absorber's basic unit comprises BDS, intermediate medium, and metal substrate. The BDS has good surface conductivity and the Fermi energy of that is flexible tunable, and the good surface conductivity might make controlled by Fermi energy. The absorption characteristics of the designed absorber are simulated by the finite integral time domain technique. The calculation results show that the designed absorber achieves ideal absorption in 139.97 μm, 163.52 μm, 247.76 μm bands, and the absorption rate is more than 0.96, which realizes ideal narrowband absorption and dynamic tuning. We find that the absorption peaks are flexible and adjustable by changing the Fermi energy of BDS, and the frequency adjustability of the absorber is analyzed. In addition, the effects of different structural parameters on the absorption efficiency and the absorption performance at different incident angles are studied. These results show that, compared with traditional metamaterials, Dirac semimetallic absorbing materials can tune the resonant frequency more effectively, even without reconstructing the structure, which has great application value in many fields, and provide a new reference for future research.

Chen Z., Chen H., Yin J., Zhang R., Jile H., Xu D., Yi Z., Zhou Z., Cai S., Yan P.

This paper propose a perfect absorber with multi-band, adjustable, high figure of merit (FOM) and high sensitivity is based on single-layer patterned graphene surface plasmon resonance (SPR). The wave absorber is composed of a patterned graphene structure etched in a circular shape in the middle and a bottom metal film separated by a SiO2 dielectric layer. It has simple structural features and can greatly simplify the manufacturing process. In the mid-infrared band of 3 μm ~ 5 μm, the numerical results of FDTD method show that the absorbers have three perfect absorption peaks, which are λ1 = 3275.31 nm, λ2 = 3706.12 nm and λ3 = 4481.76 nm, respectively. The absorption rates are 99.44%, 98.22% and 99.10%, respectively. The resonant wavelength of the absorber can be tuned by controlling the Fermi energy level and relaxation time of the graphene layer. In addition, the wave absorber is insensitive to polarization and can keep high absorption in a wide range of incident angles from 0° to 50°. At last, we explore the sensitivity and FOM of the absorber by changing the environmental refractive index. The results show that the sensitivity of its three resonance absorption peaks is 666.75 nm/RIU, 760.50 nm/RIU and 907.88 nm/RIU (RIU is the per refractive index unit), and the FOM is 86.82, 53.03 and 56.14, respectively. Therefore, we believe that the absorber can be used in the fields of narrow-band thermal radiation, narrow-band light detection and narrow-band sensor.

Abdelsallam A., Gaafar A., Abdalla M.

In this paper, a submillimetric/THz metasurface polarization/oblique independent absorber is designed and characterized. The absorber is designed using a periodic arrangement of a modified split ri...

Kim R.H., Huang C., Luan Y., Wang L., Liu Z., Park J., Luo L., Lozano P.M., Gu G., Turan D., Yardimci N.T., Jarrahi M., Perakis I.E., Fei Z., Li Q., et. al.

Wu T., Shao Y., Ma S., Wang G., Gao Y.

A bifunctional broadband absorber in the terahertz band based on patterned bulk Dirac semimetal (BDS) and strontium titanate (STO) is proposed. The properties of the absorber are investigated using the finite-difference time-domain (FDTD) method. The results show that the width of absorption can be modulated from 0.59 THz to 0.7 THz when the Fermi energy of the BDS is independently shifted from 40 meV to 50 meV. By tuning the temperature from 250 K to 400K, the center frequency of the broadband absorption spectrum can be changed from 1.311 THz to 1.505 THz, and the absorption bandwidth broadens from 0.66 THz to 0.81 THz. In addition, the simulation results show that the absorber is insensitive to electromagnetic wave polarization, and can still maintain a stable broadband absorption effect when the oblique incidence is within 40° for TE and TM modes. Based on the impedance matching theory, the physical mechanism of the broadband absorption is analyzed theoretically. This work can provide an alternative way to design high-performance multifunctional tunable terahertz devices.

Dai Z., Manjappa M., Yang Y., Tan T.C., Qiang B., Han S., Wong L.J., Xiu F., Liu W., Singh R.

Zhou W., Zhang Y., Qin X., Huang Y., Huang Z., Xu N., Wang B.

Li L., Chen F.

Zeng Z., Liu H., Zhang H., Cheng S., Yi Y., Yi Z., Wang J., Zhang J.

Wang Q., Liu L., Cui N., Li Q., Gao B.

Fang R., Zhang X., Song B., Zhang Z., Zhang L., Song J., Yao Y., Gao M., Zhou K., Wang P., Lu J., Shi Y.

Chang F., Wang Q., Kuang K., Peng W.

Abstract Metamaterial absorbers have significant effects and great potential for applications in a variety of important sciences and technologies, including infrared imaging, thermal emitters, electromagnetic shielding, and photodetectors. However, conventional absorbers with a single function are difficult to meet the growing demand of devices, especially for the situations where the absorption and polarization are simultaneously required in infrared detection. If the polarization absorption function is realized by integrating absorption and polarization elements, it will lead to a large overall system size and slow response time. To solve this problem, we propose a dual-band polarization-selective metamaterial perfect absorber, whose maximum absorptions at resonant wavelengths of λ 1 = 2.824 μ m and λ 2 = 7.622 μ m are 99.99% and 99.88%, respectively. The absorber exhibits strong polarization sensitivity, absorbing TM-polarized incident light and reflecting TE-polarized incident light at the two resonant wavelengths. The extinction ratios of the absorber at the two referred resonant wavelengths are 90.9 and 142.7, respectively. The proposed absorber would be beneficial for infrared polarization detection and imaging.

Sandiman S.A., Mishra N.K.

Maurya V., Singhal S.

Singhal S.

—This paper investigates a dual-side, dual-mode reflective cross-polarization converter for biosensing applications. The converter consists of a polyimide substrate with a modified dumbbell-shaped resonator on one surface and its complementary slot on another. The overall volume is 8.25μm × 8.25μm × 2.47 μm with dual-band operation of 6.39268–7.311692 THz and 9.783001–23.53473 THz for PCR≥80 % for front signal incidence and two full widths at half maximum (FWHM) bands i.e. 11.71594–12.26761 THz & 19.12042–19.87691 THz for back signal incidence. The periodicity is ∼λo/6, and substrate thickness is ∼λo/19 at 6.39268 THz. This device has performance stability for incident angle (θ)≤30o. The performance of this device can be tuned from dual-band operation to single-band by varying the chemical potential of the graphene strip for signal incidence from both sides. This device can classify cancer or tuberculosis-infected cells concerning healthy cells by using the variations in their corresponding refractive indices that lead to changes in the band edge frequencies. This device can differentiate between infected and healthy cells or different refractive indices with a high sensitivity of ∼5 THz/RIU. This device has merits of dual side sensing, wide operating bandwidth, multiple frequencies for sensing purposes, and high sensitivity over previously reported sensors.

Cheng S., Li W., Zhang H., Akhtar M.N., Yi Z., Zeng Q., Ma C., Sun T., Wu P., Ahmad S.

This paper proposes a metamaterial absorption device (MAD) based on Block Dirac semimetal (BDS), which exhibits five band perfect absorption in 5.96 THz, 7.86 THz, 9.84 THz, 11.91 THz, 12.22 THz, the absorption rates of M1-M5 are 0.987, 0.998, 0.997, 0.996, 0.999 and Q-factors are 54.36, 131.06, 61.61, 99.75, 102.58, respectively. The MAD has a three-layer structure consisting of substrate gold, silica, and top layer BDS, where BDS is designed as a cylindrical and circular microstructure. And polarization insensitivity due to the symmetry of the design. According to calculations, the MAD conforms to the impedance matching theory. In the analysis of the electric field diagram, it was revealed that the absorption of electromagnetic waves comes from LSPR and guided mode resonance effects. Based on the characteristics of BDS, this device can be tuned with changes in BDS Fermi energy, while also possessing certain physical tuning capabilities. When exploring the refractive index sensitivity of the device, we found that it has a high refractive index sensitivity. Among them, the sensitivity of M1-M5 is 2000 GHz/RIU, 570 GHz/RIU, 3970 GHz/RIU, 3000 GHz/RIU, and 1000 GHz/RIU, respectively Overall, this device has strong application prospects in sensing fields such as biomedicine.

Li W., Zhao W., Cheng S., Zhang H., Yi Z., Sun T., Wu P., Zeng Q., Raza R.

Zhou W., Qin X., Chen Y., Zhao Q., Huang Y., Zhou H., Xu N., Wang B.

In this paper, a triple-band metamaterial absorber in the terahertz frequencies is proposed, and its refractive index sensing characteristics are analyzed, where the bulk Dirac semimetal (BDS) periodic array is on top of a photonic crystal slab backed with a metal ground plane. The simulation results show that the absorber achieves three perfect absorption peaks in the range of 3.4–5.2 THz, whose absorption rates are over 96%, and a maximum quality factor (Q) of 74.1. The designed absorber exhibits excellent polarization insensitivity and dynamic tunability; further, the tuning of the Fermi energy level of BDS enables the dynamic adjustment of absorption frequencies and absorption rates of these peaks. By analyzing the distributions of the electromagnetic field and different structural parameters, it is revealed that the absorber mainly dissipates the electromagnetic wave through coupled resonance and localized surface plasmon resonance (LSPR) effects to achieve perfect absorption. Further, the metamaterial absorber shows the capacity to detect analytes with varying refractive indices, and the absorber has a maximum sensitivity S of 405 GHz/RIU with high detection accuracy. This work provides novel design options for triple-band terahertz metamaterial absorbers and their potential applications in refractive index sensing.

Feng S., Yang L., Cai B., Yang W., Wu L., Cheng Y., Chen F., Luo H., Li X.

Rahman S., Ruyhan, Usman M., Noreen S., Farrukh S., Ghfar A.A., Bibi N.

The full-potential linear augmented plane wave with local orbital (FP-LAPW) technique is now used in this approach to better understand the structural, electronic, optical and mechanical properties of simple cubic oxide perovskite. NdLrO3 and NdYO3 compounds are studied by employing the density functional theory (DFT) with CASTEP code for the first time. The lattice parameters are found 4.2462 and 4.2301 Å for NdLrO3 and NdYO3 respectively. Both the compounds have 1.9 eV and 1.4 eV band gap showing the direct band gap nature of both materials. The exchange-correlation (XC) energy has been selected during this investigation with the Local Density Approximation (LDA) approach. We optimize as well as clarify the elastic constants Cij, the bulk modulus B, elasticity modulus G, Young's modulus of stretch Y, and the Poisson ratio v. Every substance shows anisotropic behavior. NdLrO3 and NdYO3 compounds exhibit a direct band-gap nature, as revealed by the electronic band structure computations. These compounds were all classified as semiconductors. To quantify the number of localized electrons in various bands, partial density of states (PDOS) and total density of states (TDOS) were deployed. Both compounds are computed by fitting the dispersion relation of the imagined component. Optical properties showed that these compounds were excellent absorbers of incident radiation. Therefore, it may be assumed that these compounds could be employed in magnetic sensors because of anisotropic magnetic behavior and to capture the ultraviolet range of solar radiations.

Cheng G., Li B., Sun B., Yu Y., Yang W.

A mid-infrared ultra-wideband tunable terahertz absorber based on bulk Dirac semimetal (BDS) is presented. It has a simple three-layer structure: a top BDS metal layer, a middle dielectric layer, and a bottom reflective metal layer. The BDS layer was designed by creating a square cavity and a long rectangular cavity in the center of the BDS rectangle. The long rectangle was then rotated by 90° to form a centrosymmetric cavity. Using CST Studio Suite software, we numerically simulate the absorption characteristics. The simulation results indicate that the absorber achieves a high absorption (>90 %) of about 47.59 THz in the range of 37.5–90 THz when the Fermi energy level is 70 meV. The average absorption exceeds 95 %. In addition, adjusting the Fermi energy level of the BDS alters the absorption bandwidth. The centrosymmetric design of the structure ensures the absorber exhibits insensitivity to different polarization modes and angles of incidence, as well as excellent absorption stability. The designed shock absorber also exhibits excellent tolerance in manufacturing, reducing fabrication challenges and enabling practical applications. In addition, our design possesses the unique ability to modulate light in the mid-infrared band. These remarkable properties position our findings with significant potential in fields such as spectral analysis, optical biosensing technology, infrared sensing, and related applications.