Wide-angle metamaterial absorber with highly insensitive absorption for TE and TM modes.

Being incident and polarization angle insensitive are crucial characteristics of metamaterial perfect absorbers due to the variety of incident signals. In the case of incident angles insensitivity, facing transverse electric (TE) and transverse magnetic (TM) waves affect the absorption ratio significantly. In this scientific report, a crescent shape resonator has been introduced that provides over 99% absorption ratio for all polarization angles, as well as 70% and 93% efficiencies for different incident angles up to [Formula: see text] for TE and TM polarized waves, respectively. Moreover, the insensitivity for TE and TM modes can be adjusted due to the semi-symmetric structure. By adjusting the structure parameters, the absorption ratio for TE and TM waves at [Formula: see text] has been increased to 83% and 97%, respectively. This structure has been designed to operate at 5 GHz spectrum to absorb undesired signals generated due to the growing adoption of Wi-Fi networks. Finally, the proposed absorber has been fabricated in a [Formula: see text] array structure on FR-4 substrate. Strong correlation between measurement and simulation results validates the design procedure

Metasurfaces for ultrathin optical devices with unusual functionalities

Metamaterials are artificial materials that are made from periodically arranged structures, showing properties that cannot be found in nature. The response of a metamaterial to the external field is defined by the geometry, orientation, and distribution of the artificial structures. Many groundbreaking discoveries, such as negative refraction, and super image resolution has been demonstrated based on metamaterials. Nevertheless, the difficulty in three-dimensional fabrication, especially when the operating band is located in the optical range, hinders their practical applications. As a two-dimensional counterpart, a metasurface consists of an array of planar optical antennas, which locally modify the properties of the scattered light. Metasurfaces do not require complicated three-dimensional nanofabrication techniques, and the complexity of the fabrication is greatly reduced. Also, the thickness of a metasurface can be deep subwavelength, making it possible to realize ultrathin devices. In this thesis, geometric metasurfaces are utilized to realize a series of optical devices with unusual functionalities. Phase gradient metasurface is used to split the incident light into left-handed polarized (LCP) and right-handed polarized (RCP) components, whose intensities can be used to determine the polarization state of the incident light. Then we propose a method to integrate two optical elements with different functionalities into a single metasurface device, and its overall performance is determined by the polarization of the incident light. After that, a helicity multiplexed metasurface hologram is demonstrated to reconstruct two images with high efficiency and broadband. The two images swap their positions with the helicity reversion of the incident light. Finally, a polarization rotator is presented, which can rotate the incident light to arbitrary polarization direction by using the non-chiral metasurface. The proposed metasurface devices may inspire the development of new optical devices, and expand the applications of metasurfaces in integrated optical systems

An Integrated 3D-Printed Lens with Ultra-Wideband Flower-Shaped Stub Antenna for Ethanol-Water Mixture Characterization

This paper presents a 3D-printed hemispherical lens integrated with flower-shaped stub antenna for liquid-mixture characterization. The proposed lens antenna is designed, fabricated, and integrated with the ultra-wideband planar antenna. A high impact polystyrene (HIPs) is selected to design the 3D-printed lens antenna by using the fused deposition modelling (FDM) technique, due to low loss 3D-printed material. The optimum the dimensions of the lens antenna are obtained by using the 3D EM Simulation CST Studio, which is used to investigate the performance of the antenna, e.g., gain, radiation pattern and reflection coefficient. To discriminate the liquid content in ethanol-water mixture, the level of the transmission coefficient (S21) is detected. The proposed sensor system offers various preferable features, e.g., non-destructive method and non-contact measurement. Five samples, e.g., 60%, 65%, 70%, 75%, and 80% ethanol in the ethanol-water mixtures, are measured and performed to generate the extraction model. The proposed sensor also offers other advantages, e.g., real-time monitoring and no life-cycle limitation

Instrumentation development of innovative radio-devices to improve the coming cycles of radio astronomy observations

Radio astronomy represents one of the most useful tools for investigating celestial objects such as sychrontronic emissions from quasar , molecular clouds in the interstellar medium, and a black hole event horizon . All this is possible due to the great sensitivity that astronomical receivers can achieve, and the high angular resolution that can be reached using interferometric techniques. However, despite the great effort made, radio astronomy is not exempt of limitations that prevent it from deploying its maximum capability in terms of resolution. Atmospheric phase fluctuations, mainly induced by turbulent currents, are primarily responsible. Failure to correct these phase fluctuations will impede that the maximum potential of radio astronomy can be realized. In this thesis work, a novel solution to solve the drawbacks related to phase fluctuations in high frequency observations is presented. The ALMA telescope in Chile , has been selected as a target. The idea is to use an external optical system at room temperature, which can illuminate a low and a high frequency receiver, simultaneously. In this way, the solution for the phase fluctuation can be transferred from low to high frequency, thus, extending the maximum baseline for interferometric observations at high frequencies

Antenna Systems

This book offers an up-to-date and comprehensive review of modern antenna systems and their applications in the fields of contemporary wireless systems. It constitutes a useful resource of new material, including stochastic versus ray tracing wireless channel modeling for 5G and V2X applications and implantable devices. Chapters discuss modern metalens antennas in microwaves, terahertz, and optical domain. Moreover, the book presents new material on antenna arrays for 5G massive MIMO beamforming. Finally, it discusses new methods, devices, and technologies to enhance the performance of antenna systems

Triple-Band Metamaterial Inspired Antenna for Future Terahertz (THz) Applications

For future healthcare in the terahertz (THz) band, a triple-band microstrip planar antenna integrated with metamaterial (MTM) based on a polyimide substrate is presented. The frequencies of operation are 500, 600, and 880 GHz. The triple-band capability is accomplished by etching metamaterial on the patch without affecting the overall antenna size. Instead of a partial ground plane, a full ground plane is used as a buffer to shield the body from back radiation emitted by the antenna. The overall dimension of the proposed antenna is 484×484 μm2. The antenna's performance is investigated based on different crucial factors, and excellent results are demonstrated. The gain for the frequencies 500, 600, 880GHz is 6.41, 6.77, 10.1 dB, respectively while the efficiency for the same frequencies is 90%, 95%, 96%, respectively. Further research has been conducted by mounting the presented antenna on a single phantom layer with varying dielectric constants. The results show that the design works equally well with and without the phantom model, in contrast to a partially ground antenna, whose performance is influenced by the presence of the phantom model. As a result, the presented antenna could be helpful for future healthcare applications in the THz band

An Additive 3D-Printed Hemispherical Lens with Flower-shaped Stub Slot Ultra-Wideband Antenna for High-Gain Radiation

This paper presents a 3D-printed hemispherical lens integrated with a planar ultra-wideband (UWB) antenna. The flower-shaped stub slot UWB antenna is made of 0.8-mm FR-4. The operating frequency of the UWB covers 3.10 GHz - 11.6 GHz with a nominal gain at zero degrees of 1.74 dBi. To enhance the UWB antenna’s high-gain radiation, a 3D-printed additive hemispherical lens is designed and fabricated from acrylonitrile butadiene styrene (ABS). The electrical properties, i.e., relative permittivity and loss tangent, of ABS are 2.66, and 0.003, respectively. Four different lens radii (8 mm, 10 mm, 12 mm, and 14 mm) are chosen to investigate the gain of the antenna. In all four cases, the 3D-printed lens is fixed in place in front of the UWB antenna with an optimum gap of 3 mm chosen to reduce the wave reflection between the lens and source antenna. Based on the measurement results, the reflection coefficient, S11, of four conditions still covers the UWB frequency range. The nominal gain at zero-degree values for lens radii of 8 mm, 10 mm, 12 mm, and 14 mm are 3.43 dBi, 4.22 dBi, 4.73 dBi, and 5.18 dBi, respectively. The proposed additive 3D-printed dielectric lens antenna also offers many advantages, i.e., ease of design and assembly, low-cost fabrication, and size reduction for high-gain antennas. Furthermore, the high-gain antenna provides a narrow half power beamwidth, which can be implemented to increase the resolution of the imaging system

Structural Analysis of Nano Core PCF With Fused Cladding for Supercontinuum Generation in 6G Networks

The Sixth Generation (6G) networks have identified the use of frequency range between 95 GHz and 3 THz with a targeted data rate of 1 Terabytes/second at the access network for holographic video applications. As is demands broadening of spectrum at the core network, this paper proposes a Supercontinuum Generation (SCG) through photonic crystal fiber (PCF) as it provides excellent broadening of the optical spectrum. Discussed in the paper is supercontinuum generation at high pumping power as per the standards specified by the International Telecommunications Union. The proposed PCF is designed with silicon nanocrystal core and the cladding microstructures is arranged in a fusion approach to effectively optimize the optical parameters such as dispersion, nonlinearity, birefringence, group-velocity dispersion, and confinement loss. The fused cladding comprises of a flower-cladding assembly in which air-holes arrangement is inspired from petals in a pleated structure. Such arrangement is shown here to provide high nonlinearity and negative dispersion for high power supercontinuum generation. The novel nanocore assembly with improved structural constraints delivers a non-linearity of 6.37 × 106 W−1 km−1 and a negative dispersion of −142.1 (ps/nm-km) at 1,550 nm. Moreover, a supercontinuum spectrum is generated using different pulse widths ranging from 350 to 650 ps with 25 kW pump power for PCF lengths of 10 and 15 mm

Tapered Plasmonic Nanoantennas for Energy Harvesting Applications

In this chapter, novel designs of tapered-dipole nanoantennas are investigated for energy harvesting applications. A full systematic analysis for the proposed structure is presented where the harvesting efficiency, return loss, radiation pattern, and near-field enhancement are calculated using a finite-element frequency domain solver. Simulation results show that the proposed nanoantennas can achieve a harvesting efficiency of 60% at a wavelength of 500 nm where the antenna input impedance is matched to that of fabricated rectifying devices. Additionally, the cross-tapered nanoantenna offers a near-field enhancement factor of 252 V/m, which is relatively high compared to previously reported nanoantennas. The spatial and spectral resonance modes are investigated, and the simulation results indicate the ability of the cross geometry to be utilized in color-sorting applications. Moreover, the particle swarm optimization technique is adapted to configure the proposed designs for maximum performance