The paper proposes an ultra-narrow band graphene refractive index sensor, consisting of a patterned graphene layer on the top, a dielectric layer of SiO2 in the middle, and a bottom Au layer. The absorption sensor achieves the absorption efficiency of 99.41% and 99.22% at 5.664 THz and 8.062 THz, with the absorption bandwidths 0.0171 THz and 0.0152 THz, respectively. Compared with noble metal absorbers, our graphene absorber can achieve tunability by adjusting the Fermi level and relaxation time of the graphene layer with the geometry of the absorber unchanged, which greatly saves the manufacturing cost. The results show that the sensor has the properties of polarization-independence and large-angle insensitivity due to the symmetric structure. In addition, the practical application of testing the content of hemoglobin biomolecules was conducted, the frequency of first resonance mode shows a shift of 0.017 THz, and the second resonance mode has a shift of 0.016 THz, demonstrating the good frequency sensitivity of our sensor. The S (sensitivities) of the sensor were calculated at 875 GHz/RIU and 775 GHz/RIU, and quality factors FOM (Figure of Merit) are 26.51 and 18.90, respectively; and the minimum limit of detection is 0.04. By comparing with previous similar sensors, our sensor has better sensing performance, which can be applied to photon detection in the terahertz band, biochemical sensing, and other fields.

/pdf/design-of-ultra-narrow-band-graphene-refractive-index-sensor-15gyt2xt.pdf

Design of Ultra-Narrow Band Graphene Refractive Index Sensor

A four-band terahertz tunable narrow-band perfect absorber based on a bulk Dirac semi-metallic (BDS) metamaterial with a microstructure is designed. The three-layer structure of this absorber from top to bottom is the Dirac semi-metallic layer, the dielectric layer and the metal reflector layer. Based on the Finite Element Method (FEM), we use the simulation software CST STUDIO SUITE to simulate the absorption characteristics of the designed absorber. The simulation results show that the absorption rate of the absorber is over 93% at frequencies of 1.22, 1.822, 2.148 and 2.476 THz, and three of them have achieved a perfect absorption rate of more than 95%. We use the localized surface plasmon resonance (LSPR), impedance matching and other theories to analyze its physical mechanism in detail. The influence of the geometric structure parameters of the absorber and the incident angle of electromagnetic waves on the absorption performance has also been studied in detail. Due to the rotational symmetry of the structure, the designed absorber has excellent polarization insensitivity. In addition, the maximum adjustable range of absorption frequency is 0.051 THz, which can be achieved by changing the Fermi energy of BDS. We also define the refractive index sensitivity (S), which is 39.1, 75.4, 119.1 and 122.0 GHz RIU−1 for the four absorption modes when the refractive index varies in the range of 1 to 1.9. This high-performance absorber has a very good development prospect in the frontier fields of bio-chemical sensing and special environmental detection.

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

High sensitivity active adjustable graphene absorber for refractive index sensing applications

We propose a broad band and high absorption adjustable ideal absorber. The whole structure is Cr-Ge-Si 3 N 4 -Ti from bottom to top. The simulation results show that three resonant absorption modes are generated at 9.15 μm, 10.68 μm and 15.17 μm, with absorption rates of 92.1%, 97.3% and 95.2%, respectively. The bandwidth of the absorber is broadened by adding a lossy dielectric layer. Then, the control variables of the structural geometry parameters of the absorber were studied respectively to obtain the best optimization parameters. Since then, comparisons of different underlying microstructures have confirmed the uniqueness of our structure. Finally, we simulate the absorption of the absorber in different polarization modes with varying incident angles. In addition, the performance of previous work and our absorber are compared. These studies show that our absorber has active tunability, polarization and incident angle sensitivity, and high absorption bandwidth. • The results of FDTD theory show that the absorber based on MDM structure has high absorption bandwidth and three resonant absorption peaks in the mid-infrared band, which indicates that the absorber has wavelength selectivity. • By tuning the geometric parameters of the absorber structure, the active tuning of the absorber in a wide range is realized. • The absorption of the absorber under the change of incident angle and polarization mode is simulated, and it is determined that the absorber is insensitive to polarization and incident angle. • By adding a lossy dielectric layer, the bandwidth of the absorber can be broaded. Long wavelength infrared (LWIR) wideband absorption is an important target in the research of middle infrared band. In this work, we study the absorption characteristics of Cr-Ge-Si 3 N 4 -Ti metamaterial absorber based on nanowire cross surrounding. The absorber has polarization independence when the light wave is incident vertically. Due to the coupling of surface plasmon resonance and the intrinsic absorption of lossy material, the numerical simulation calculation shows that the bandwidth with absorptivity greater than 90 % reaches 7.23 μm, and the average absorptivity in the LWIR band (8.98–16.21 μm) is 94.1 %. The absorption spectrum can be adjusted independently by changing the geometric parameters of the structure. Moreover, the absorber has excellent incident angle insensitivity in TE and TM modes. The designed absorber is simple in structure, easy to configure, and suitable for infrared imaging, thermoelectronic devices and thermal detection applications. 

Ultra long infrared metamaterial absorber with high absorption and broad band based on nano cross surrounding

In this paper, a dual-parameter sensor based on surface plasmon resonance (SPR)-photonic crystal fiber (PCF) is proposed, which can be applied in detecting the magnetic field and temperature. In this sensor, two elliptical channels are designed on both sides of the fiber core. The left channel (Ch 1) is coated with gold film and filled with magnetic fluid (MF) to achieve a response to the magnetic field and temperature using SPR. The right channel (Ch 2) is coated with gold film as well as Ta2O5 film to improve the SPR sensing performance. Finally, Ch 2 is filled with polydimethylsiloxane (PDMS) to achieve a response to the temperature. The mode characteristics, structural parameters and sensing performance are investigated by the finite element method. The results show that when the magnetic field is in the range of 50-130 Oe, the magnetic field sensitivities of Ch 1 and Ch 2 are 65 pm Oe-1 and 0 pm Oe-1, respectively. When the temperature is in the range of 17.5-27.5 °C, the temperature sensitivities of Ch 1 and Ch 2 are 520 pm °C-1 and 2360 pm °C-1, respectively. By establishing and demodulating a sensing matrix, the sensor can not only measure the temperature and magnetic field simultaneously but also solve the temperature cross-sensitivity problem. In addition, when the temperature exceeds a certain value, the proposed sensor is expected to achieve dual-parameter sensing without a matrix. The proposed dual-parameter SPR-PCF sensor has a unique structure and excellent sensing performance, which are important for the simultaneous sensing of multiple basic physical parameters.

Two-channel photonic crystal fiber based on surface plasmon resonance for magnetic field and temperature dual-parameter sensing.

A series of magnetic composites of sodium polyacrylate and polyacrylamide copolymer [Fe3O4@SiO2@P(AANa-co-AM)] were prepared. The investigation showed that the adsorption efficiency of Pb(II) was the best when the acrylamide/acrylic acid (AM/AA) mass ratio of composites was 5:5. Therefore, the composite of this ratio was selected as the adsorbent to systematically adsorb Pb(II) in aqueous solution. Static adsorption of Pb(II) to the magnetic composites in aqueous solutions was investigated by varying the solution pH and the concentration of Pb(II). The adsorption kinetics and isotherms model of Pb(II) on the Fe3O4@SiO2@P(AANa-co-AM) composites followed a pseudo-second-order model and the Langmuir isotherm model, respectively. When the temperatures were 298.15, 308.15, and 318.15 K, the maximum adsorption capacities of Fe3O4@SiO2@P(AANa-co-AM) composites were 237.53, 248.14, and 255.10 mg/g, respectively. The thermodynamic study of adsorption showed that the adsorption of Pb(II) on Fe3O4@SiO2@P(AANa-co-AM) composites was a spontaneous endothermic process. The X-ray photoelectron spectroscopy (XPS) analysis showed that the adsorption of Pb(II) was due to the chelation between -COO- and Pb(II). After four adsorption-desorption cycles, the adsorbent can still maintain a high adsorption capacity.

Preparation of Fe3O4@SiO2@ P(AANa-co-AM) Composites and Their Adsorption for Pb(II).

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Preparation of Fe3O4@SiO2@ P(AANa-co-AM) Composites and Their Adsorption for Pb(II).