Olcay Altintas

Multi-band polarization independent cylindrical metamaterial absorber and sensor application

A multi-band perfect metamaterial absorber (MA) based on a cylindrical waveguide with polarization independency is numerically presented and investigated in detail. The proposed absorber has a very simple configuration, and it operates at flexible frequency ranges within the microwave frequency regime by simply tuning the dimensions of the structure. The maximum absorption values are obtained as 99.9%, 97.5%, 85.8%, 68.2% and 40.2% at the frequencies of 1.34 GHz, 2.15 GHz, 3.2 GHz, 4.31 GHz and 5.41 GHz, respectively. The numerical studies verify that the proposed model can provide multi-band perfect absorptions at wide polarization and incident angles due to its rotational symmetry feature. We have also realized sensor and parametric study applications in order to show additional features of the suggested model. The suggested MA enables myriad potential applications in medical technologies, sensors and in defense industry etc.

Design of a wide band metasurface as a linear to circular polarization converter

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.

Metamaterial absorber-based multisensor applications using a meander-line resonator

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 meander-line 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.

Wideband metamaterial absorber based on CRRs with lumped elements for microwave energy harvesting

ABSTRACT A novel metamaterial absorber structure is designed and characterized for microwave energy harvesting. The suggested structure is composed of two circular ring resonators with different dimensions. Due to harvesting application of the proposed structure, the main operation frequency of the suggested structure lies in WIMAX and satellite communication frequency bands and surrounds our environment. The optimum dimensions of the suggested structure are obtained through parametric study by genetic algorithm in order to realize wideband absorption and harvesting response. Simulation results show that the metamaterial-harvester-based resistive loads are useful to absorb and convert microwave energy for the operation frequency. The simulated harvested power across the resistors has been found greater than 0.4 W, which corresponds to 80% efficiency between 7.8 and 14 GHz. In addition, polarization dependence and angular stability of the proposed harvester are investigated at operation frequency to support the simulation of an experimental study for S-parameter measurement. Therefore, simulation and experimental study results show that the proposed design with good absorption and harvesting characteristics can be operated in WIMAX and satellite communication frequency bands.

Design of a dual band metamaterial absorber for Wi-Fi bands

The goal of this work is to design and fabrication of a dual band metamaterial based absorber for Wireless Fidelity (Wi-Fi) bands. Wi-Fi has two different operating frequencies such as 2.45 GHz and 5 GHz. A dual band absorber is proposed and the proposed structure consists of two layered unit cells, and different sized square split ring (SSR) resonators located on each layers. Copper is used for metal layer and resonator structure, FR-4 is used as substrate layer in the proposed structure. This designed dual band metamaterial absorber is used in the wireless frequency bands which has two center frequencies such as 2.45 GHz and 5 GHz. Finite Integration Technique (FIT) based simulation software used and according to FIT based simulation results, the absorption peak in the 2.45 GHz is about 90% and the another frequency 5 GHz has absorption peak near 99%. In addition, this proposed structure has a potential for energy harvesting applications in future works.

Fire detection behind a wall by using microwave techniques

In this work, detection of the fire location behind a wall by using microwave techniques is illustrated. According to Planck’s Law, Blackbody emits electromagnetic radiation in the microwave region of the electromagnetic spectrum. This emitted waves penetrates all materials except that metals. These radiated waves can be detected by using directional and high gain antennas. The proposed antenna consists of a simple microstrip patch antenna and a 2×2 microstrip patch antenna array. FIT based simulation results show that 2×2 array antenna can absorb emitted power from a fire source which is located behind a wall. This contribution can be inspirational for further works.