Hiremath, Kirankumar R

In this article, a wire based metamaterial absorber is capped with dielectric absorber to achieve bandwidth enhancement. The unit cell of the designed absorber consists of copper wires, placed on the metal back FR4 sheet and dielectric absorber is located on the top of wire elements. The simulated return loss shows two resonant modes, one due to the dielectric absorber and other due to wire based metamaterial absorber. By optimizing the design parameters, the resonant peaks are tailored to achieve a bandwidth of more than 6 GHz for 10 dB return loss in TE polarization. The electric field and power loss densities are plotted to present the origin of the absorption peaks.

In this work, absorption properties of spatially disordered metamaterials are analysed using numerical simulations. For this purpose, position randomness is introduced in a supercell, which transforms a periodic metamaterial structure into a random metamaterial structure, where the constituent resonators are interacting with each other. It is demonstrated that the disorder can be used to enhance the absorption bandwidth. This enhancement is obtained due to the coupling among the nearby resonators, which results in broadening of collective resonance. The proposed disordered metamaterial absorbers also exhibit polarisation-insensitivity and have wide-band absorption for both normal and oblique incidences, which makes them a promising candidate for a variety of applications.

This work presents experimental results of scattering studies in spatially random metamaterial absorbers fabricated by randomly distributed conducting circular patches on a dielectric substrate having a conducting ground plane. It has been showed that due to the random distributions of distances between the resonators, there are many coupled resonances, resonating at different wavelengths, resulting in a wider absorption bandwidth. For the validation of experimental results, numerical simulations were carried out and a good degree of agreement was found between them.

We carried out a detailed balance calculation of quantum dot sensitized solar cell based on widely used TiO2 as electron transport material and polysulfide electrolyte as hole transport material, considering the finite electrochemical potential level for these layers. The findings suggest that detailed balance efficiency decreases much faster for higher band gap quantum dots absorber as compared to that of ideal electron and hole transport layers. The detailed balance efficiency values are close to 20% without carrier multiplication for Eg near exciplex quantum dots, closer to experimental observation with finite Ediff limitation and without considering carrier multiplication, much smaller than the ideal case, which is close to 30% for ideal open circuit voltage. Thus, the present study shows the impact of limited/finite electron and hole transport material energy levels in designing QDSSCs, towards more realistic photovoltaic efficiency values.

CdTe quantum dots were synthesized using water as a solvent medium. Synthesized quantum dots were used to integrate into TiO2 nano-porous electrode using a combination of linker assisted direct adsorption and chemical bath deposition process. Sensitized electrodes were characterized to understand their physical and optical properties for photovoltaic application.

The work presents a simple and novel design approach to extend the bandwidth of existing Dielectric Material Based Microwave Absorber (DMBMA). The design comprises planar square patches of DMBMA placed periodically on a metalbacked FR4 sheet. For demonstration purpose, the DMBMA is synthesized by adding conducting carbon fillers in polyurethane matrix, and its electromagnetic parameters are measured in X-band. A single reflection null is observed in DMBMA owing to λ/4 resonance. In comparison, the bandwidth of 8GHz (10-18 GHz) is achieved for -10 dB reflection for square patch based DMBMA. The thickness of proposed absorber is 2.75mm. An additional resonant mode is observed due to capacitive coupling between the square patches. The enhanced bandwidth is attributed to the overlapping of λ/4 resonance and induced coupling mode. A good agreement between the simulated and measured data is observed.

In this paper, a simple design strategy is proposed for obtaining broadband, polarization insensitive metasurface, for radar cross section (RCS) reduction. Two different unit cells, circular patch and square ring structures are chosen as basic meta-atoms. For significant enhancement of RCS reduction bandwidth, sixteen supercells comprised of the variation of the two unit cells are distributed randomly in a checkerboard setting, resulting in a diffused backward scattering. The proposed metasurface have a wide-band, polarization insensitive RCS reduction spectra.

In this paper, a simple design strategy is presented for designing broadband, polarization insensitive metasurface for radar cross section (RCS) reduction. Two different unit cell structures, circular patch, and loop are chosen to enhance the phase bandwidth. Different phase gradient supercells are designed by positioning these unit cells in a specific phase gradient direction. The eight supercells are then randomly distributed in a checkerboard pattern for further diffusing the incident wave. The proposed metasurface significantly reduce the RCS and demonstrate features such as polarization insensitivity and wideband operational bandwidth.

In this paper, the absorption properties of resonant patch absorbers are analyzed using the quality factor approach. The total quality factor contributing from both the dissipative quality factor and radiative quality factor is deduced. The resonant circular patch absorbers are studied under the influence of position randomness with increasing filling factor. It is observed that by introducing position disorder, it is possible to enhance the absorption bandwidth of the otherwise periodic circular patch resonant absorbers. This enhancement in absorption bandwidth is obtained due to the coupling among neighboring resonators, which results in broadening of collective resonances. The designed disordered resonant patch absorbers also exhibit polarization insensitivity for oblique incidences for both polarizations. In addition, square patch absorbers are also investigated under the periodic and disordered setting. It is found that the enhancement in the bandwidth of the disordered absorber structures is independent of the shape of the patch resonators, and depends solely on the coupling among the neighboring resonators.

The work presents an inventive, simple and implementable design approach to enhance the bandwidth of conventional Salisbury Screen Microwave Absorber (SSMA). Theoretically, the maximum fractional bandwidth of SSMA for FR4 substrate with an optimum sheet resistivity of 308 Ω/sq for –10 dB reflection is nearly 42.1%. In comparison, the bandwidth for square patch based SSMA is 59.7% with the same thickness. The design comprises square patches of SSMA placed periodically on a metal sheet. The square patches consist of an FR4 substrate and a 200 Ω/sq resistive sheet. A single reflection null is observed in the SSMA due to λ/4 resonance whereas in the proposed absorber an additional resonant mode is introduced due to coupling between the nearby patches. The simultaneous overlapping of the λ/4 mode and the additional coupling mode results in bandwidth extension. The close agreement between the simulation and measurement data is observed.