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We explore steel-mesh structures, which are commercially available as insets of chemical particle filters, in terms of their metamaterial properties below 1 THz, including both single- and multi-layer structures. Their pass-band characteristics are very similar to those reported for hole arrays in metal films, exhibiting power transmission as high as 88% for the lowest transmission band of single-layer structures. The transmission minima are explained in terms of the Rayleigh-Wood anomaly. The phase properties of the transmitted THz pulses reveal negative group delays of several picoseconds, i.e., abnormal group velocities, in spectral regions between pass-bands. [ABSTRACT FROM AUTHOR]

Abstract The progress in the technology of manufacturing new materials increases the usage of Terahertz (THz) region, which is considered as the last explored region of electromagnetic spectrum. In biological, chemical, sensing and detecting applications THz region is started to be used widely. We proposed a unique fishnet metamaterial (MTM) absorber and metasensor that can be used to detect and characterize new materials which are produced for THz region. First of all, the reflection and absorption characteristics of fishnet MTM were analyzed. Perfect absorption was achieved by 97.3% absorption rate and with assisting from electric field and surface current distributions we explained the electromagnetic theory behind the frequency resonances. For sensory application, the material that is going to be detected was added as a single and double overlayer (OL) to proposed fishnet MTM and fishnet MTM absorber sensor. The shifts in the resonant frequencies were observed for the change in permittivity and thicknesses of the OL materials. From the analysis of resonant shifts it is proved that the proposed structure shows high sensing ability in THz region. [ABSTRACT FROM AUTHOR]

In this paper, a novel fishnet metamaterial structure is designed and analyzed under different material combinations and under different active controlling techniques. The results indicate that, the proposed fishnet metamaterial has a single resonance with double negativity at 0.39 THz when quartz substrate and aluminum is utilized in the design. Moreover, when the metallic parts are replaced with YBCO, the proposed design also exhibits double negativity with a stronger resonance and can be used as a switch between the double negative and single negative modes if the temperature is altered. In addition to these, when substrate (quartz) is replaced with MgO, the resonance shifts from 0.39 THz to 0.26 THz and shows double negativity. Moreover, switching properties under illumination can also be obtained when the silicon is utilized in the design (MgO-YBCO combination). According to these results, it is found that, in the case that the conductivity of silicon exceeds a certain value, the character of the resonance changes from double negative to the single negative mode. [ABSTRACT FROM AUTHOR]

In this paper, a new multiband metamaterial absorber design is proposed and the numerical characterization is carried out. The design is composed of three layers with differently sized quadruplets in which the interaction among them causes the multiband absorption response in the infrared frequency regime. In order to characterize the absorber and explain the multiband topology, some parametric studies with respect to the dimensions of the structure are carried out and the contributions of the quadruplets to the absorption spectrum are analyzed. According to the results, it is found that the proposed metamaterial absorber has five bands in the infrared frequency regime with the absorption levels of: 98.90%, 99.39%, 86.46%, 92.80% and 97.96%. Moreover, the polarization dependency of the structure is examined and it is found that the design operates well as a perfect absorber with polarization independency in the studied frequency range. [ABSTRACT FROM AUTHOR]

In this paper, a dual-band high-frequency metamaterial absorber based on patch resonator is designed and analyzed for solar cells. In order to obtain a metamaterial absorber, metal-semiconductor-metal layers are combined. The results of the designed structure are shown in the infrared and visible ranges of solar spectrum. Structural parameters and dimensions of the device have a significant importance on the performance of the designed absorber. The simulations are carried out with full-wave electromagnetic (EM) solver based on the finite integration technique. In the first simulation, the constitutive parameters of the structure are selected as constant in which the metamaterial absorber has 99.99% absorption at 558.75 THz and 99% absorption at 216.75 THz. When the structure parameters are designed again according to Drude model, the second simulation results show that the metamaterial absorber has 99.96% absorption at 514.5 THz and 99.63% absorption at 197.25 THz. Moreover, the second simulation results show that the proposed design is also polarization and incident angle insensitive. Furthermore, the structure is enhanced by the integration of the graphene layer(s). In addition, the fractional bandwidths (FBW) for the resonances are also calculated to show the quality of the absorber. As a result, the proposed metamaterial absorber based on patch resonator and its enhancement with graphene present high absorption in the infrared and visible ranges and can be used in many metamaterial and solar applications. [ABSTRACT FROM AUTHOR]

This paper suggests a metamaterial (MTM) absorber structure to be used for efficiency improved solar cell. The proposed MTM absorber consists of the topmost three concentric circular ring resonators, and a ground metal plane sandwiched to the top layer with a dielectric spacer. Numerical simulation and theoretical (interference theory) studies on the proposed design show a wideband with near-perfect (>99%) absorption response in the visible frequency region of the solar spectrum. Thermal characterization of the suggested design is also conducted in order to investigate its absorption capability at different temperatures. The proposed MTM absorber design is believed to be an outstanding candidate toward high-efficiency solar photovoltaic cell. [ABSTRACT FROM AUTHOR]

Developing a perfect absorber based on metamaterials (MTMs) is a promising technique towards improving the efficiency of solar photovoltaic cells. In this study, a novel MTM‐based perfect absorber (MPA) is proposed for solar cell applications, which exhibits an excellent single‐band with high absorption rate of 99.7% in visible frequency regime (resonance frequency of 614.4 THz) with an outstanding absorption bandwidth of 15.5%. The proposed design presents a high symmetry flexibility which makes it easy to fabricate. Besides, the simulation results for the defined different incident angles and different polarisation (transverse electric and transverse magnetic) confirm the quality of the proposed design by showing how insensitive it is to both the defined incident angles (normal and oblique incident) and different polarisation angles of electromagnetic wave. The parametric study on dielectric spacer shows the tunability characteristic of an intended MPA structure. The proposed MPA design is a good candidate for fabrication of high‐efficiency solar cell operating in a visible frequency range. [ABSTRACT FROM AUTHOR]

Developing a perfect absorber based on metamaterials (MTMs) is a promising technique towards improving the efficiency of solar photovoltaic cells. In this study, a novel MTM-based perfect absorber (MPA) is proposed for solar cell applications, which exhibits an excellent single-band with high absorption rate of 99.7% in visible frequency regime (resonance frequency of 614.4 THz) with an outstanding absorption bandwidth of 15.5%. The proposed design presents a high symmetry flexibility which makes it easy to fabricate. Besides, the simulation results for the defined different incident angles and different polarisation (transverse electric and transverse magnetic) confirm the quality of the proposed design by showing how insensitive it is to both the defined incident angles (normal and oblique incident) and different polarisation angles of electromagnetic wave. The parametric study on dielectric spacer shows the tunability characteristic of an intended MPA structure. The proposed MPA design is a good candidate for fabrication of high-efficiency solar cell operating in a visible frequency range. [ABSTRACT FROM AUTHOR]

A new metamaterial absorber is designed and characterized numerically for the harvesting of solar energy. The design is composed of three layers in which the interaction among them gives rise to the plasmonic resonances. The main operation frequency range of the proposed structure is chosen to be the visible regime. However, the design is also analyzed for the infrared and ultraviolet regimes. In order to characterize the absorber, some parametric studies with respect to the dimensions of the structure are carried out. According to the results, it is found that the proposed metamaterial absorber has 98.2 % absorption capability at 445.85 THz and 99.4 % absorption capability between 624 and 658.3 THz. Moreover, the polarization dependency of the structure is examined and it is found that the design operates well as a perfect absorber with polarization independency for the studied frequency range. As a result, the proposed metamaterial absorber can be used for solar energy harvesting as it provides multiple perfect absorption bands in the visible regime. [ABSTRACT FROM AUTHOR]

Since the discovery of metamaterial absorber to the present days, several designs were proposed which display single-, dual-, and multiple-bands absorption responses in almost all regions of solar spectrum. However, little work has been done for wide-band metamaterial absorber in the visible frequency range. Hence, a novel wide-band metamaterial perfect absorber (MPA) based on concentric Circular Ring Resonator (CRR) topology is proposed for the application to improve the absorbance of solar photovoltaic cells for the visible frequency region. The proposed design consists of three basic components as resonators, ground metal, and dielectric spacer. The geometrical parametric study is conducted in order to investigate the flexibility of the proposed MPA structure. The design flexibility also analyzed by the polarization angle insensitivity character, in which the proposed design provides the perfect absorption for different angles of the incident electromagnetic wave as well as for TE and TM polarized waves. [ABSTRACT FROM AUTHOR]

This paper proposes a metamaterial absorber design for solar energy harvesting using a simplified and symmetric structure. A unit cell of this design consists of three important layers namely, the bottom metallic layer, which is gold lossy, the intermediate layer: made of a lossy dielectric material that is gallium arsenide and patches which formed by a combination of gold and gallium arsenide. These three important layers are being carefully arranged at the top of a dielectric spacer. The geometric structure was being examined for its contribution towards absorption characteristics. The simulation results show outstanding dual-bands absorption (99.96% and 99.37%) in the visible frequency regime of electromagnetic wave. Due to the excellent symmetric nature of the proposed structure, its absorptance capacity exhibits polarization insensitivity for a wide range of incident angles for electromagnetic radiation. [ABSTRACT FROM AUTHOR]

The design and characterization of perfect metamaterial absorbers (MAs) based on simple configurations including square- and triangle-shapes, which operate in X-band frequency region are numerically and experimentally investigated. The proposed MAs provide perfect absorption with the polarization angle independency. In X-band waveguide, the absorption rates are 99.69% and 99.97% at the resonance frequencies of 10.57 GHz and 10.93 GHz for the square- and triangle-shaped MAs, respectively. In addition, the same configurations are numerically tested under free space boundary conditions to compare and discuss the obtained results. The suggested MAs enable myriad potential application areas for security and stealth technologies in X-band including wireless communication. [ABSTRACT FROM AUTHOR]

Design of a metamaterial based on an S-shaped resonator surrounded by a ground frame and excited by using a feeding transmission line on microstrip technology is presented. Since the resonator, ground frame, and its excitation mechanism are all realized on a microstrip, its characterization can be carried out using common laboratory equipment without needing any waveguide components or plane-wave-illumination techniques. The structure presented here may be realized on any microstrip and does not require special materials. The resonator and ground frame are both on the same side of the microstrip, thus the proposed topology may also be populated with active and passive microwave components, and hybrid active, passive, or reconfigurable microwave circuits may be realized. In metamaterial designs that require plane wave illumination, usually many numbers of periodic unit cells are needed; however, in our design, only one cell is capable of achieving metamaterial properties. The constitutive parameters of the metamaterial are retrieved and compared to demonstrate the agreement between simulations and measurements. The proposed topology is also demonstrated in a sensor application, where simulated and measured results agree well. Thus, it can be realized using standard microwave technology and used for numerous applications where metamaterial properties are needed. [ABSTRACT FROM AUTHOR]

In this paper, we have designed, simulated, and analyzed a microwave biosensor based on chiral metamaterials (MTMs) to detect pig biological tissues which are widely used as a trial for medical explorations and researches. There are various types of biosensor structures based on MTMs in the literature. However, only a limited number of study is conducted on biosensors based on chiral MTMs; therefore, our study is one of the pioneer works for this type of research. The proposed diamond-shaped resonator-based structures are numerically investigated and analyzed in detail in the microwave frequency regime. The results are in good agreement which lead us to conclude that our structure can be easily used as an effective instrument for biosensing applications in medical technologies. [ABSTRACT FROM PUBLISHER]

A metamaterial absorber that effectively harvests solar energy is being proposed in this paper using a simple and high flexible structure. The proposed structure unit cell comprises of three vital layers. The ground metallic plane, an intermediate dielectric spacer while patches are wisely prepared on the top of a dielectric spacer. Geometrical parameters of the proposed metamaterial is studied in order to get insight on their impact for the absorption behaviour of the structure. The results from simulation provides two excellent absorption resonance (99.96% and 99.37%) in the visible spectrum range of electromagnetic wave. Due to the excellent symmetry of the proposed metamaterial design, its absorption coefficient is polarisation insensitive for a wide range of incident angles of electromagnetic radiations. [ABSTRACT FROM AUTHOR]

The efficiency of solar photovoltaic (PV) cells has been one of the major problems impeding its global adoption as one of the sustainable substitutes to fossil fuel based technologies. Metamaterial (MTM) based solar cells offer an opportunity towards increasing the system efficiency by enhancing the total absorbed solar radiation incident on this device. In this study, a nanostructure-based MTM perfect absorber has been designed and simulated. By adjusting geometrical parameters and MTM structure properties, nearly perfect dual-band absorptions have been obtained with 99.99% and 99.90% absorption at 543.75 THz and 663.75 THz, respectively. The proposed structure is simple and more flexible for scaling, which helps achievement of multiple-band absorption. Implementation of the intended MTM structure can effectively lead to the realization of more efficient PV solar cells. [ABSTRACT FROM AUTHOR]

An alternative design of left-handed (LH) metamaterial (MTM) for waveguide configurations is presented with sensor and absorber applications. The LH structure is based on two identical circular ring resonators connected with a wire strip. Both simulation and experimental results show that the planar MTM has an LH resonance at ∼9.9 GHz. Surface current and magnetic field distributions at the resonance are also presented to show the LH behavior of the structure in detail. In addition, a parametric study based on the gap size of the structure is also provided in order to present the dependency of the LH resonance. Next, the sensing process is presented with respect to the thickness, position, and dielectric constant variations of the superstrate layer located in front of the material surface. Finally, the absorption application of the structure in X-band is shown, and the results show that the absorber behaves as a perfect absorber with an absorption rate of 99.99%. As a result, the proposed structure can be used in many MTM applications, such as sensor, absorber, and soon. [ABSTRACT FROM AUTHOR]

A microwave metamaterial (MTM) based on H-shaped resonator in a waveguide configuration is introduced and investigated both numerically and experimentally for X-band frequencies. The proposed model is designed and fabricated on both sides of the substrate and exhibits strong magnetic resonance at around 10.5 GHz. Additionally, it has very simple design which improves and simplifies the fabrication process. Besides, only one single slab is used in the simulation and experiment which provides a reduction in the number of the required samples with respect to its free space and/or waveguide counterparts. The effective medium theory is employed for the characterization of the structure, and the left-handed region is identified using the simulation and experimental data. The measured results are in good agreement with the simulated ones which show that the proposed MTM operates well and can be used in waveguide miniaturization and waveguide-based applications such as antennas, filters, sensors, imaging systems, and so on. To validate this, sensor and absorber applications are selected and the simulation results show that the proposed devices operate well with a good efficiency under the defined conditions. [ABSTRACT FROM AUTHOR]

Abstract: We report the design, characterization and experimental verification of a perfect metamaterial absorber (MA) based on rings and cross wires (RCWs) configurations that operate in the microwave regime. The suggested MA provides perfect absorption with incident angle and polarization independencies which can be used for various shielding applications. Maximum absorption rate is at for simulation and at for experiment, respectively. The experimental results of the fabricated prototype are in good agreement with the numerical simulations. We also present a numerical analysis in order to explain physical interpretation of MA mechanism in detail. Moreover, a sensor application of the proposed MA is introduced to show additional feature of the model. As a result, proposed MA enables myriad potential applications in S band radar and medical technologies. [Copyright &y& Elsevier]

Reflection and transmission properties of a new type of frequency selective surface (FSS) made of zigzag metallic elements placed periodically on a dielectric substrate are investigated theoretically for arbitrary polarisation. The electric field integral equation technique with the subdomain overlapping piecewise sinusoidal basis functions are employed to compute the unknown current coefficients induced on the metallic elements. The zigzag FSS arrays act as a low-pass filter in S-(1- 5 GHz), X-(8-12 GHz) and Ku-(12-18 GHz) bands. Owing to multiple resonances the zigzag FSS arrays can be used in multiband frequency applications. Between the resonances there exist transmission windows that allow full energy transfer. By removing the first and third arms, the power reflection coefficient of three-arm zigzag FSS is compared with a freestanding strip FSS, and it is compatible with the measured and calculated results found in the literature. [ABSTRACT FROM AUTHOR]

Abstract: Numerical simulation and experimental analysis of a novel metamaterial using periodic passive planar structure composed of Λ-shaped inclusions are presented. Experimental and computational results are shown to be in very good agreement. The Λ-shaped inclusions operate as magnetic resonators providing negative permeability behavior as a result of the magnetic resonance arising from the self and mutual coupling of the inclusions. Issues related to the unit cell dimension versus operation wavelength are also addressed. The proposed design allows the metallization to be non-nested as opposed to the usual split-ring-resonators. Furthermore, specific permeability values at the frequency of interest can be easily established by changing the inclusion dimensions providing extra flexibility to control the electromagnetic response of the structure. The proposed design and its variations enable myriad applications such as super-lens for free-space microwave-focusing as well as creating double-negative metamaterials by combining the structure with a conducting strip. [Copyright &y& Elsevier]

The electric and magnetic resonances of anisotropic broadside-coupled triangular-split-ring resonators are studied for different incident wave excitations. It is shown that the higher order modes exist in both electric and magnetic resonances. It is observed that the incident electric field couples to the magnetic resonance of the designed structure under different excitations. Multiple resonance features due to the anisotropy of the structure are found in the case of different excitations and the nature of these resonances can be regulated as either an electric or a magnetic mode for different frequencies. In this way, a resonant effective permittivity or permeability can be obtained. Hence, controllable properties of the constitutive material parameters (i.e. electric or magnetic resonances, negative values, etc.) can be determined by changing the incident wave excitation. [ABSTRACT FROM AUTHOR]

Abstract: A dual-band and polarization-independent fishnet metamaterial for the sub-THz frequency range is proposed and investigated. Dual-band modes have two resonances in which the first one is fixed as a left-handed mode and the second one can be arranged as a left-handed or single-negative mode. We select the character of second resonance by the choice of substrate properties. The metamaterial features of the structure are analyzed using the scattering data and confirmed by applying Kramers–Kronig relations. The characteristic features are also verified by the current distribution at the inner metallic surfaces of the structure. The influence of substrate modifications is studied and the effect of this change on resonances is discussed. The design of a dual-band and polarization-independent sub-THz metamaterial presented here can serve as a model and guide to realize tunable fishnet metamaterials for other frequency regimes. [Copyright &y& Elsevier]

Reflection and transmission analysis due to the interaction of electromagnetic waves with a frequency dispersive double-negative slab are investigated in detail. In particular, the reflection and the transmission coefficients are found and defined. The incident field is assumed to be a plane monochromatic wave of transverse magnetic polarization. Imposing the boundary conditions at the interfaces, the transmission and the reflection coefficients at each interface can be obtained. Numerical results are presented for both cases of transverse magnetic and electric waves to show the effects of the incidence angle, the frequency, and the structure parameters on the reflection and the transmission coefficients. [ABSTRACT FROM AUTHOR]

Terahertz region has become very attractive for new applications however, the materials that work in this region are very limited. Within the aim of providing a new instrument that can be used in this field, we designed and analyzed a new metamaterial (MTM) absorber and MTM absorber sensor for Sub-Terahertz region. As a first step, the structure was designed and the electromagnetic response of the design was analyzed. The perfect absorption with 99.9% absorption rate was achieved for the resonant frequency at 0.12 THz. After finding the resonant frequencies and absorption rates, the surface current and electric field distributions at resonance frequencies were gathered and then described. As a second step, sensory application of the proposed structure has been conducted. The material to be detected was added to the top of the structure as an overlayer (OL). The changes in reflection resonances by the mean of shift in resonant frequency and change in amplitude have been investigated as a function of the permittivity, thickness and loss tangent of the OL. As a result of that study, we proved that this unique MTM absorber can be used for detecting materials in Sub-THz regime. [ABSTRACT FROM AUTHOR]

Vanadium dioxide (VO2) is a promising candidate for electronic and optical switching applications in the terahertz frequency range due to the metal to insulator transition (MIT). In this study, the use of VO2 patterned as a metamaterial surface or coupled as a homogeneous layer with a metallic metamaterial surface on top is investigated in terms of performance. High-quality VO2 thin films were deposited on c-cut sapphire substrates by using the dc magnetron sputtering technique. A change in resistivity by a factor of 104 MIT in VO2 was observed allowing to investigate its use as a controllable metamaterial. The layer was patterned using a unique geometry (four-cross shaped) that operates in the THz frequency range. To understand its performance as a tunable THz filter, the four-cross structure fabricated from VO2 is compared to one fabricated from Au on VO2 bare film using UV lithography and ion beam etching techniques. The spectral performances of metamaterials were assessed using THz-Time Domain Spectroscopy (THz-TDS) and results were compared with simulations based on CST Microwave Studio. Absence of the resonant effects in the purely developed VO2 device, while clear observation of the MIT behavior shows the strong dependency of the inductive and/or capacitive effects of the four-cross structure on conductivity of the surface metamaterial, which is clearly observable for the Au-based device. In the latter case, the resonant transmittance of the filter can be effectively modulated by change in temperature. [ABSTRACT FROM AUTHOR]

In this work, a new multiband terahertz metamaterial absorber is designed and characterised by numerical simulation method. In addition, the utilisation of the proposed absorber as a sensor is also investigated. The dielectric and thickness sensing characteristics are analysed. The proposed multiband metamaterial absorber has the ability for utilising the terahertz region up to 2 THz. According to the results, it is found that the proposed absorber is capable of sensing unknown materials and material thickness with any of its five absorption bands. The sensitivity of the proposed sensor is 6.57 GHz / unit sensitivity for dielectric sensing and 7.66GHz/μm for thickness sensing. [ABSTRACT FROM AUTHOR]

In this paper, a sensor structure operating in the microwave frequency band is used and it is aimed to determine whether fuel samples are branded or not. In the literature, the studies on the sensor applications of metamaterials (MTMs) have increased considerably in recent years. However, this study, unlike other studies, focuses on determining the changes in electromagnetic parameters of different fuel samples at X band frequencies. For this purpose, the electromagnetic properties of the branded and unbranded fuel samples are measured experimentally. Then, simulation studies are carried out using the experimental results and the dimensions of the resonators are optimized to determine the most suitable structure. Fabrication of MTM sensor structure is then performed using optimized dimensions. Finally, the experimental study is carried out using the sensor structure. [ABSTRACT FROM AUTHOR]

Abstract Exploration of the perfect combination between metamaterials (MTMs) and plasmonics has paved the way of the new innovations in electromagnetic and communication engineering, especially in sub-THz spectroscopy. In order to contribute to such developments, plasmonic resonances in sub-THz fishnet MTM on the basis of complementary hexagonal resonator structure is investigated in this paper. The design, in which method of removing hexagonal structure is applied, has been performed based on finite simulation technique. Five distinct plasmonic resonances are determined at some of the specific frequency spots where interactions between electron plasmas and incident electromagnetic waves can be observed. The proposed material can be employed in several subtopics of electromagnetic engineering such as high pass filters and antenna applications. Furthermore, thanks to the THz wave confinement property of this plasmonic structure, incident THz waves can be controlled efficiently and therefore, the proposed MTM can be tailored at THz spectroscopy and imaging, localization of the THz wave and energy, sensors and photonics applications, effectively. [ABSTRACT FROM AUTHOR]

Emerging nanotechnologies have revealed carbon nanotubes (CNTs) as one of the best materials with immense potential. Considering the outstanding physical, mechanical, electrochemical, thermal, and optoelectronic properties of CNTs, extensive studies have been reported assessing their applications in several disciplines. This paper presents a broad review of the studies in the literature that address the contribution of CNTs in terms of their applications as different parts of solar cells such as photoelectrode, photoconductor, top and back electrode, replacement of indium tin oxide (ITO) as transparent conducting electrode (TCE) in a variety of photovoltaics such as silicon, organic, polymer and dye-sensitized with their subsequent efficiencies. [ABSTRACT FROM AUTHOR]

A wide-band (6,5) single-walled carbon nanotube metamaterial absorber design with near unity absorption in the visible and ultraviolet frequency regions for solar cell applications is proposed. The frequency response of the proposed design provides wide-band with a maximum of 99.2% absorption. The proposed design is also simulated with (5,4), (6,4), (7,5), (9,4), and (10,3) chiralities, and results are compared to show that the proposed design works best with (6,5) carbon nanotube (CNT) but also good for other chiral CNTs in the visible and ultraviolet frequency region. The geometric structure was carefully analyzed for its contribution to the absorption behavior. The absorber design is highly flexible and capable of keeping the wide-band with high absorption. Due to the excellent symmetric characteristics of the proposed design, which provides polarization independency under normal incidence (transverse electromagnetic mode), the proposed metamaterial absorber is a good candidate for the solar cell application, where absorbance can be kept high with respect to the polarization angle. [ABSTRACT FROM AUTHOR]

The new perfect metamaterial absorber (MA) based on square resonator with gap configuration is numerically (for GHz and THz frequency regime) and experimentally (for GHz frequency regime) presented and investigated. The proposed MA has a simple configuration which introduces flexibility to adjust its metamaterial properties and easily rescale the structure for other frequency regimes. In addition, polarization and incident angle independencies of the proposed model are analyzed for the THz frequency regime. The suggested structure could achieve very high absorption at wide angles of polarization and incident angles for both transverse electric and transverse magnetic waves. At resonance frequencies, absorption results are realized around 99.99% at 5.48 GHz and 99.92% at 0.865 THz for their respective frequency regimes. Besides numerical results in GHz and THz frequencies, experimental results are also obtained for GHz frequency regime. The proposed MA and its variations enable myriad potential applications in areas such as defense systems, communication, stealth technologies, and so on. [ABSTRACT FROM AUTHOR]

• Novel multiband (9,4) polarization insensitive nanotubes based metamaterial absorber. • Absorption of the energy in multiband scale with unique design. • Simplicity of the design, ease of the fabrication and the ability to absorb more energy. • Good candidate for the photovoltaic energy generation. A novel multiband (9,4) polarization insensitive metamaterial (MTM) absorber structure based on the vertical nanotubes composited with the silicon dielectric material is proposed in this research. Multiband polarization insensitivity is achieved through the unique geometrical configuration of the design, which provides almost unity absorption in the visible and ultraviolet regions from 300 THz to 1000 THz. The proposed design is selected due to the simplicity of the construction, ease of fabrication and the ability to absorb almost perfectly under changing geometrical parameters. The electromagnetic response of the design is simulated for four maximum absorption peaks at 394.3 THz, 514.9 THz, 632.8 THz, and 773.2 THz with the corresponding absorption rates of 99.8%, 98.35%, 96.66%, and 80.60%, respectively. The sensitivity of the polarization angle of the MTM absorber has also been investigated, which verifies that the current design is insensitive to the different polarization angles. The flexibility of the proposed design has also been investigated by altering the geometrical components, materials, and the dimensions, and it is confirmed that the proposed MTM absorber design provides high absorption rates under all considered circumstances. The MTM absorber designs is found to be capable of improving the efficiency of the solar cell. The implementation of these MTM absorbers in the solar cells can significantly improve the absorption rate by reducing the reflection and transmission. MTM is validated by both prior art investigation and the different solver such as FEM and FIT. Results of interface theory model and simulations are compared against one another, which show good agreement yielding reliable and accurate estimations. [ABSTRACT FROM AUTHOR]

In this paper, a rectangular split ring resonator-type metamaterial (MTM) sensor application is demonstrated in order to examine concrete materials. First, different types of concrete materials including carbon steel fiber with the purity ratio of 0.5%, 1% and 1.5% were prepared by using cement and water and their electrical properties were determined via Nicolson–Ross–Weir tehcnique. After that, compatible MTM-based sensor structure was designed and proposed. In order to find out the effect of the humidity on the concrete material, all samples were kept in the water pool for 28 days, the samples were then taken out and the temperature effect on the concrete materials was observed by increasing the heat up to 30 ∘ and 70 ∘ in the oven. The simulated resonance frequency shifts were observed at 910 MHz for concrete material sensor, 120 MHz for humidity sensor validation and 400 MHz for temperature sensor applications. By having large bandwidth in different fiber contents and validating the physical sensor applications as temperature and humidity, it was shown that the proposed study has novelty in the area of MTM-based sensor applications when it is compared with current state-of-the-art. [ABSTRACT FROM AUTHOR]

Chiral metamaterial-based sensor is designed for sensing the change in substance ratio of chemical substances when combined with distilled water. These samples have been prepared with 10%, 50% and 90% volume fraction of methanol, ethanol, acetone, ammonia and isopropyl alcohol. The complex permittivity of the prepared samples has been measured by Agilent 85070E dielectric probe kit and compared with the simulations. In the proposed design, linear shifts with the frequency bands of more than 100 MHz are observed in different measurements. For different material sensing, pure samples have been used and their reflection coefficient measurement results have been presented. Unique side of this study is that the structure provides very clear and sensitive results and presents a new approach to the microfluidic sensor applications by using the sample holder. [ABSTRACT FROM AUTHOR]

A novel multiband metamaterial absorber (MTMA) is proposed which is capable of well presenting a polarization-insensitive and wide incident angle stability in the microwave frequency range. The proposed MTMA comprising two vertically stacked asterisk-based copper resonators separated by dielectric layer of flame retardant type four and backed with a thin copper film. High-frequency structure simulator was used to simulate the absorber and to depict surface current distribution. The results showed that the absorber is operated at three narrow bands with high absorptivity of about 92, 100 and 100% at frequencies of 2.75, 4.3 and 9.5 GHz, respectively. The position of the resonant peaks can be effectively tuned by adjusting the geometry parameters of the structure, thereby achieving a multiband, polarization-independent and wide-angle absorber. The designed structure is important for the application of sensors, thermal images and in constructing broad multiband signals for electromagnetic compatibility/interference. [ABSTRACT FROM AUTHOR]

Several emerging renewable technologies are available to satisfy the current energy demand and to minimize the effect of environmental degradation caused by high consumption of fossil fuels. These technologies are not mature enough to solve this problem but require more time for improving the efficiency, and cost reduction to become the economical alternative of fossil fuels. In this paper Dye-sensitized solar cell (DSSC) has been discussed in detail owing to advancement in the technology. Since each component of DSSC is responsible for a specific function, therefore, comprehensive literature studies has been done on individual section to understand the technology in depth. All the advancement in sensitizer, semiconductors, electrolyte, electrodes, additives, sealing and anchoring groups are included in this review with performance parameter of DSSC. Focus of this article is to provide summary of all available literature since beginning to date. [ABSTRACT FROM AUTHOR]

In this study, we have developed an efficient metamaterial (MTM)-based portable fuel oil sensor in order to distinguish branded and unbranded fuel-oil samples. Electromagnetic properties of the fuel-oil samples are experimentally obtained and these data are defined in numerical analysis to design and test the performance of MTM sensor. Then, simulated MTM-based sensor structure is fabricated and measured to observe the efficiency and agreement to numerical results. Numerical and experimental studies are conducted in the microwave frequencies of 10-11 GHz. The experiment results are in accordance with the simulation ones. It can be seen from the results that the proposed MTM-based sensor can be implemented into the sensor industry for distinguishing the branded and unbranded fuel oil for several frequency regions. [ABSTRACT FROM AUTHOR]

In this study, a novel metamaterial absorber (MA) is designed and numerically demonstrated for solar energy harvesting. The structure is composed of three layers with different thicknesses. The interactions of three layers bring about the plasmonic resonances. Although the main operation frequency of the structure is chosen between 430 and 770 THz, which is the visible light regime, the proposed structure is also investigated in the ultra-violet (UV) region. One can see from the results that the proposed structure carries nearly perfect absorption capacity that is more than 91% at the whole visible light spectrum. The proposed structure even has the absorption capacity of 99% between 556 and 657 THz. In addition, the designed MA is also investigated in terms of its polarization and angle independency. Results show that the proposed structure is independent from the polarization and incident angles. Lastly, the designed structure can be considered to be used in solar energy applications as a harvester since it has an ultra-broadband absorption characteristic in visible light regime. [ABSTRACT FROM AUTHOR]

We propose a microwave imaging structure with GSM, ISM, Wi-Fi, and WiMAX operating frequencies at 1.80, 2.45, and 5.80 GHz, respectively. The suggested structure is based on a microwave antenna-inspired absorber with cavities in resonator layers. Our study, which is validated using simulation and experimental techniques, deals with the absorption of the incident electromagnetic waves at 1.80, 2.45, and 5.80 GHz for creating the image when radio frequency microwave is employed. The above-mentioned three operating frequencies, by which electromagnetic waves are radiated from three different antennas, are read via digital oscilloscope and finally these voltages are converted to 256 gray-leveled pixel values of each cell. During the experimental testing, simulated and tested values complied with each other. Small differences occurred due to calibration and testing errors. The novelty of this study is having image capability with most commonly used frequency bands by absorbing microwave energy. [ABSTRACT FROM AUTHOR]

A new metamaterial absorber (MA) having distinct properties than those given in the literature is investigated. Although several designs have been studied for achieving absorption characteristics in single-band, dual-band and multiple bands within the whole spectrum of solar light, there has been limited number of researches examining the broadband MA in the visible light section of the spectrum. The designed structure is composed of the combination of three layers having different thicknesses including a metallic substrate, dielectric and a metal layer. Due to the sandwich-like structure, it can support the plasmonic resonance. The proposed structure, which provides a maximum absorption level of 99.42% at 579.26 THz, has a high absorption rate of 99% between the frequency band 545 and 628 THz. Numerical results indicate that the proposed structure has perfect absorption which is greater than 90.98% through the whole working frequency band. The dependency of the designed structure on the polarization angle is investigated for different incident angles with TE and TM polarizations as well as the TEM mode. In addition to its potential applications such as solar cells and cloaking, the designed structure can also be considered as a color sensor and an optical frequency sensor. [ABSTRACT FROM AUTHOR]

The analytically obtained algebraic equation systems for the TM/TE-z polarized monochromatic waves scattering from eccentrically layered circular cylinders are ill-conditioned for numerical calculations. Therefore, such ill conditioned systems must be regularized for reliable numerical results. Here, the steps of the regularization of the ill conditioned system obtained for the scattered field from a circular metamaterial cylinder includes three parallel circular cylinders: a dielectric, an impedance and a perfect electric conductor is explained. In the regularization procedure used here each circular boundary brings block(s) correspond to its electromagnetic property and the regularization procedure is done according to this block(s). For this end a system that consists of perfect electric conductor (PEC), impedance, dielectric, and metamaterial cylinders is discussed and thus the steps of a regularization procedure for a general system that has all the type of boundaries in terms of electromagnetics will be explained here. As a result, if a new boundary is included to the system then it is sufficient to locate the blocks related to this boundary suitably. [ABSTRACT FROM AUTHOR]

A metamaterial-based energy harvesting structure has been designed and experimentally tested in this study. The proposed structure has square and split ring resonators placed in different angles on the back and front sides for compatible multiband operation in energy harvesting. Resonance points have been defined at 900 MHz, 1.37 GHz, 1.61 GHz, 1.80 GHz, and 2.55 GHz, by simulation and experimental methods. These points correspond to Global System for Communication (GSM) 900, GSM 1800, Universal Mobile Telecommunication System (UMTS), satellite navigation, and Industrial Scientific and Medical (ISM) band frequencies. Supporting multiband application in a single structure without changing dimensions or design is one of the properties of this study. To harvest captived electromagnetic energy, an HSMS 2860 Schottky diode has been used. For wireless power transmission efficiency, voltage across the Schottky diode has been measured by a spectrum analyzer in different points experimentally. The maximum obtained voltage across the Schottky diode is 90 mV at 1800 MHz when a 500 mV signal is applied from a 5 cm distance. Simulated and experimental results prove that the proposed structure can effectively be used in GSM, satellite communication, and UMTS electromagnetic bands for energy harvesting and filtering applications. [ABSTRACT FROM AUTHOR]

In this study, we both numerically and experimentally present a metasurface (MS) polarization converter to transform linearly polarized signal into circularly polarized one. The unit cell consists of two rectangular metallic patches placed at the crossed corners of rectangularly arranged inclusions. The results of a full-wave Electromagnetic (EM) simulator are compared to those of free space measurement using two horn antenna at microwave frequency regime. For a linearly polarized antenna, the s-parameters are obtained for both co-polarized and cross-polarized responses. The polarization quality referred to as axial ratio (AR) is expressed by the ratio of these two responses. It is found that, strong polarization conversion activity is obtained with the proposed MS at the frequency of about 3 GHz. As a result, we can generate polarization converter with a wide bandwidth, of interest for microwave filtering, coating, and especially polarization conversion devices. [ABSTRACT FROM AUTHOR]

In this paper, we present a wide band metasurface (MS) polarization converter which converts a linearly polarized signal to a right-handed or left-handed circularly polarized signal both numerically and experimentally. The unit cell of MS has three nested rectangular resonators which have two metallic patches at its crossed corners. The simulated and measured results are achieved by a commercial full wave EM simulator and a vector network analyzer with two horn antennas in microwave frequency regime. The S-parameters are obtained for co-polarized and cross-polarized responses and axial ratio is evaluated by the division of these two responses. The axial ratio is kept below 3 dB for efficient polarization converting activity. Correspondingly, axial ratio bandwidth of 800 MHz is obtained. The proposed MS can easily be fabricated and integrated into many desired applications by proper configurations depending on the application area and frequencies. The proposed MS has potential such as polarization converter with 0.75 efficiency in WiMAX frequency band, PMC-like treatment with a phase reflection around 0 and reflection coefficient nearly unity at some frequency points. Beside this, the three nested rectangle MSs also provide opportunities to design low profile antennas with conversion characteristics. [ABSTRACT FROM AUTHOR]

This study aims to demonstrate the effects of the different boundary conditions on triangular split ring resonator (TSRR)-shaped metamaterials in X band frequency regime. Three different TSSR-shaped metamaterials are designed and simulated in a certain frequency range. TSSR-shaped metamaterials are utilized to show that the use of different boundary conditions may result in completely different electromagnetic responses. Characterization is explained by applying 5 different boundary conditions. To verify simulation results, an experimental study is realized for the unit cell boundary condition. Both experimental and simulation results are complying with each other. For further investigation, electrical energy density and surface current distributions are simulated and discussed. [ABSTRACT FROM AUTHOR]

A metamaterial (MTM) absorber-based multifunctional sensor is numerically and experimentally realized using meander-line resonators. The proposed sensor device can be used to measure pressure, density, and humidity with perfect signal absorption characteristics at the frequency range of X band. The structure consists of a sensor layer sandwiched between two dielectric slabs. The sensor layer is used to detect unknown environmental parameters with respect to the electromagnetic responses of the material under test. A meanderline type resonator is chosen to achieve highly efficient electrical response at the related frequency range. It is well known that an MTM can be efficiently used for sensing purposes in a microwave regime if the absorption characteristic is approximately linear over the certain frequency band. The proposed model is numerically analyzed for pressure, density, and humidity sensing applications. In addition, the experimental study is carried out to prove the sensing ability of the suggested structure in the case of the density sensing application. The meander-line-based MTM absorber can be used in many application areas, such as the agriculture, medical, and defense industries. [ABSTRACT FROM AUTHOR]