A novel approach for infrared (IR) energy harvesting through the integration of a resonating metasurface with a metal-insulator-metal (MIM) nano-rectenna is presented. The absorption of IR radiation at 28.3 THz is significantly enhanced through the localization of surface plasmons with the integration of a periodic metasurface on the top of the log spiral MIM rectenna. Additionally, a ground plane is introduced on the backside of the structure to further enhance absorption characteristics. Extensive characterization analysis of the antenna's absorbed E-fields for incident 28.3 THz radiation is conducted with and without the integrated metasurface using full-wave numerical simulation. Also, the rectification properties (I/V, resistivity, and responsivity) are studied with variations in metal (Au, Al, Ag, and Cu) and five different insulators (Al2O3, Cu2O, Ta2O5, TiO2, and ZnO) types. The results demonstrate that the presence of the metasurface enhances the absorbed IR E-field by the rectenna to levels of 80–90%. Furthermore, exceptional harvesting performance, including E-field, current density, resistivity, and rectification efficiency (responsivity), is achieved with the asymmetric Au-ZnO-Cu and Au-ZnO-Ag MIM and metasurface rectenna structures. The proposed design strategies can lead to the development of highly efficient IR energy harvesters in the future.

An eight-element antenna system operating at sub 6 GHz is presented in this work for a future multiple-input multiple-output (MIMO) system based on a modified E-slot on the ground. The modified E-slot significantly lowers the coupling among the antenna components by suppressing the ground current effect. The design concept is validated by accurately measuring and carefully fabricating an eight-element MIMO antenna. The experimentation yields higher element isolation greater than −21 dB in the 3.5 GHz band and the desired band is achieved at −6 dB impedance bandwidth. The E-shape slot occupies an area of 17.8 mm × 5.6 mm designed on an FR-4 substrate with dimensions of 150 mm × 75 mm × 0.8 mm. We fed the I-antenna element with an L-shape micro-strip feedline, the size of the I-antenna is 20.4 × 5.2 mm2, which operates in the (3.4–3.65 GHz) band. Moreover, our method obtained an envelope correlation coefficient (ECC) of <0.01 and an ergodic channel capacity of 43.50 bps/Hz. The ECC and ergodic channel capacity are important metrics for evaluating MIMO system performance. Results indicate that the proposed antenna system is a good option to be used in 5G mobile phone applications.

This article presents an eight-element tri-band Multiple Input Multiple Output (MIMO) antenna system for future handheld devices. The suggested antenna system consists of a main and sideboards. The feed lines are connected on the main board while the antennas are placed on sideboards, two on each side separately. The total dimension of the main board is $150\times 75$ mm2, and the sideboard is $150\times 7$ mm2. The antenna resonates at three distinct 5G allocated bands of 3.1-3.7 GHz, 4.47-4.91 GHz, and 5.5-6.0 GHz with impedance bandwidths of 600 MHz, 440 MHz, and 450 MHz, respectively. The antenna system provides pattern and spatial diversity characteristics with radiation and total efficiency of 78% and 62% and peak gain of 5.8 dBi. The MIMO system is fabricated, and the measured results are found to be in good agreement with the simulations. The isolation among radiating elements in all resonating bands is found to be >16 dB. The vital MIMO performance parameters such as envelope correlation coefficient (ECC) is less than 0.2 for any two antenna array meeting the required standard of less than 0.5 alongside the mean effective gain or MEG ratio of any two antenna meeting the required standard of less than 3 dB for power balance and optimal diversity. The Channel Capacity (CC) is found to be 41.1 bps/Hz, approximately 3 times that of $2\times $ 2 MIMO operations.

This article presents the design of an array of rectennas operating at 28.3 THz for infrared (IR) energy harvesting applications. The basic element of the array consists of a Vivaldi-dipole rectenna composed of two arms made with different conductors (gold and titanium). A metal-insulator-metal (MIM) tunnel diode is used to rectify the THz ac current. The proposed MIM diode consists of a very thin layer of Al2O3 sandwiched between the two metal electrodes. Arrays of two, three, and four rectennas are investigated. The improvement of the energy captured by coupling several elements in the same structure with a common gap is also investigated. This array architecture, without feeding network, may reduce the number of rectifying diodes and, therefore, decrease losses and increase the overall efficiency. Finally, it has been found that the four-elements rectenna array has a maximum electric field intensity of 62.4 × 104 V/m at 28.3 THz.

This study reports the design of a dielectric resonator (DR) metasurface-based terahertz biosensor for rapid and accurate detection of different kinds of viruses (H1N1, SARA-COV-2, etc.). The characterization of the sensor is done by analyzing its absorbance properties with and without the presence of the H1N1 virus layer of different concentrations and electrical properties in the frequency range of 2.4 THz to 3 THz. A full-wave EM model of the sensor is designed using CST MWS software. The geometrical parameters of the proposed biosensor, as well as its dielectric constant of the virus swab, are varied to achieve good performance with an absorption level close to 1 (100%). A significant change in the resonating pick-up frequency owing to the variation in the effective refractive index of the realized sensor ensures the detection and classification of the different concentrations of the same or different viruses. The presented design could be used for the rapid detection of viruses with the added advantages of contactless, label-free, and accurate identification of different concentrations of viruses.

This work presents the design and analysis of a novel metal-insulator-insulator-metal (MIIM) rectenna with an added meta lens on top of it for efficient and robust infrared (IR) energy harvesting at 28.3 THz. To ensure maximum transfer of the captured IR radiations by an antenna with better impedance matching, the log-spiral antenna terminals are used as rectenna electrodes while two different insulators are placed between its feeding terminals to form the MIIM rectenna. A split ring-based resonating metasurface is designed and placed on the top of the MIIM rectenna to focus the incoming electromagnetic radiations. The characterization of the MIIM rectenna with added meta lens, in terms of absorbed E-field, is performed for the four different work function metals (gold aluminum, silver, and copper) as well as four combinations of aluminum oxide, titanium oxide, zinc oxide, and copper oxide as insulators. The focusing of illuminating IR radiations by the integrated meta lens to the rectenna structure enhances its field-capturing characteristic by more than 400% as compared to conventional structures. In addition, the proposed design shows improved rectification properties in terms of better impedance matching and rectification efficiency, particularly for the best configuration of Au-Al2O3-Cu2O-Cu rectenna with added metasurface. Future applications of this study include the development of efficient IR energy harvesting systems for remote sensing, wireless communication, and other IoT devices.

Abstract Metasurface tuning is performed using different ways for a wide range of applications. This study presents the design of a thermally‐tuned all‐dielectric reconfigurable metasurface. A microfluidic channel, filled with different concentrations of tellurium–selenium (Te‐Se) alloy, is added on the top of the elliptical dielectric resonator (EDR) unit cell of the considered metasurface. The electrical properties of used semiconductor alloy are varied in the range of 400 to 700°C (steps size of 100°C). The impact of thermal tuning on the reflection and transmission characteristics of the designed metasurface is analyzed in the frequency range of 20–30 GHz using COMSOL Multiphysics. Obtained results demonstrated that the realized metasurface exhibits reconfigurable behavior in terms of variations in the reflection and transmission characteristics with a change in either temperature or concentrations of selenium and tellurium. The wider bands with high reflection and low transmission frequency bands are obtained with lower concentrations of selenium and tellurium for all operating temperatures.

The oil and gas industry requires accurate sensors to control fluid flow in pipelines during the production process from horizontal and near horizontal wells. The extracted crude oil is usually a multiphase mixture of oil, water, and gas, and the accurate measurement of the ratio of each multiphase within the pipeline is an important parameter to manage wells efficiently by maximizing the hydrocarbons that can be extracted. Various methods have been developed for determining the phase ratio including mechanical, optical, X-ray or gamma ray, ultrasound, nuclear magnetic resonance (NMR), and rarely microwave techniques. However, these methods do not permit the knowledge of the real-time evolution of the phase ratio and are less precise. Here, we propose and develop by simulation two microwave systems, in horizontal and vertical polarizations, to choose the optimal configuration for crude pipeline imaging applications. First, the pipeline containing crude oil was modeled and its thermal and dielectric properties are proposed. Then, the antennas array performances were optimized and assembled to the pipeline. Different numbers of antenna elements were successfully investigated using CST simulation in both vertical and horizontal polarizations to find the optimal number of antenna elements for the pipeline applications.

A Vivaldi dipole rectenna system for infrared (IR) energy harvesting is investigated. First, a parametric study on the Vivaldi dipole antenna is performed to collect the maximum electric field between the Vivaldi poles. The antenna arms were optimized to achieve a high-efficiency rectenna system. The two arms of the antenna were formed using two different metals, that is, gold and titanium. These two metals have different work functions, which facilitate the diode operation through tunneling at zero bias. The two arms of the Vivaldi dipole are overlapped, and a suitable insulator layer is injected in the overlapped area to form the metal-insulator-metal (MIM) diode. The MIM diode is an ideal candidate for this operation as it works without any bias, provided the two metals have different work functions. For rectenna operation, it is crucial that the rectifying diodes should work without any aid of external bias. The Al2O3 is the insulator layer of the MIM diode. We have chosen Al2O3 because it has a low dielectric constant at terahertz frequency regime, which allows us to match the operational cut-off frequency, that is, 28.3 THz. A parametric study of the Al2O3 insulator layer is performed to increase the captured received intensity. At the end, the nano-antenna operates at a frequency band of [26 horizontal ellipsis 30 THz] to harvest IR energy from the environment with good efficiency and demonstrate its capacity to capture incident waves and obtain high-intensity values within its gap. It is a development that could eventually boost electricity generation.

This study presents, for the first time, a novel design of ultra‐wideband (UWB), circularly polarized and highly directive log‐spiral THz photoconductive antenna. The proposed antenna is simulated in High Frequency Structure Simulator using gold as the antenna electrode material which is backed by a quartz substrate (εr = 3.78, tan δ = 0.0001) and hemispherical silicon‐based lens with a diameter of 140 μm. A comprehensive detailed parametric study of the antenna design parameters is performed in the frequency range of 1 to 6 THz for the optimal design of the developed antenna structure. The optimal antenna structure with integrated lens has UWB characteristics with −10 dB impedance bandwidth of 5 THz and 3 dB axial ratio bandwidth of around 4 THz. The observed directivity and half‐power beam width of the presented design varies in the range 5 to 12 dBi and 34° to 62°, respectively, for the frequency range of 1 to 4 THz. The wideband, high directivity as well as high‐efficiency (>50%) characteristics of the proposed design make it a favorable choice for the THz sensing and imaging applications.

In this paper, we present a compact array of 4 printed dipole antennas with ground plane, operating at 2.7 GHz and 5.2 GHz, designed for base station applications. First, the elementary printed dipole antenna, selected for its small size and good performances, is described. However, this kind of structures cannot cover two bands at the same time, which justify our proposal of a 4-elements network. Next, the 4-elements array is simulated, optimized, and measured to proof its performances with good agreement between the measurements and simulations. The measured gain of the 4-dipoles array is 4.21 dBi and 6.15 dBi for both operating frequencies 2.7 GHz and 5.2 GHz, respectively.

In this work a novel design of an ultra-wideband and highly directive Vivaldi photoconductive antenna (PCA) is reported for the first time for the THz sensing and imaging applications. The optical-to-THz conversion efficiency for the enhanced directivity of the reported PCA is enhanced by adding a hemispherical silicon-based lens with the PCA gold electrode and quartz substrate (Epsilon r = 3.78, tan delta = 0.0001). The optimization of the antenna design parameters is performed in CST MWS for the frequency range of 1-6 THz. The design antenna has UWB -10 dB impedance and 3-dB AR bandwidths of 6 THz, maximum directivity of 10 dBi and maximum total radiation efficiency of > 40%.

Metamaterial-inspired electric-and magnetic-based near-field resonant parasitic (NFRP) elements are electrically coupled to a coaxial-fed printed monopole to realize an electrically small, ka = 0.49 (lambda(0)/9.41 x lambda(0)/14.11 x lambda(0)/104.18) Huygens source antenna that operates at the GSM1800 frequency. The electric NFRP element is a meander patch; the magnetic element is a Capacitively Loaded Loop (CLL). The individual electric-and magnetic-based antennas were studied numerically to ensure they had overlapping frequency behavior near the GSM frequency 1.8 GHz; high radiation efficiency; and very good matching to their 50 Omega sources. They were combined together and retuned to create a three metal - two dielectric layer Huygens source antenna. A 20 nH inductor was inserted between the driven monopole and the SMA connector in order to enhance the input impedance matching. A prototype of this antenna was fabricated and experimentally characterized. The measurements confirmed the Huygens source nature of the prototype antenna.

This work presents a novel design of a high gain circularly polarized (CP) crossed‐bowtie shaped antenna with cloverleaf arms which exhibits a wideband impedance match as well as 3dB axial ratio bandwidths. The designed wideband antenna is realized by employing a low‐cost phase shifting mechanism that uses a Metasurface (MTS) superstrate which is placed above the radiating surface of the antenna. A design chart is developed for the determination of the required phase variation based on the distance between MTS and the antenna radiator. Next, the concept of MTS placement above the antennas is extended to the cases of 3x3 and 5x5 cloverleaf‐shaped bowtie antenna arrays, with the goal of improving the gain and sidelobe levels (SLLs). The study includes a systematic analysis of the variation in gain and SLL of CP antenna arrays as we change the number of elements of the superstrate.

A frequency reconfigurable fractal antenna for wireless communication application is presented in this paper. Three RF switches are incorporated into the antenna design to achieve frequency reconfigurability. The proposed antenna is designed and simulated using the HFSS code and then fabricated. The experimental results confirm the numerical simulation and demonstrate that integrating the RF switches improves the antenna flexibility and enables us to switch the antenna from single-band to dual-band as well as to a multi-band state with minimal design complexity and high degree of miniaturization.

This work presents a novel chipless radio frequency identification (RFID) tag design method for Latin alphabets. Unlike the traditional complicated geometry tags, this new method uses a compact printable alphabet letters which additionally offers the advantage of efficient real time recognition of the transmitted data visually along with radio frequency (RF) waves. In this study, alphabet letters (a, b and c) are realized using copper etching on thin dielectric substrate (TLX-8) backed by a ground plane. The original signature of the radar cross section (RCS) frequency response reflected by letter, displays dips corresponding to the presence of individual letters. The tag has been simulated, fabricated and measured in a mono-static radar system using Vivaldi dual polarized antenna in frequency band ranging from 6 to 13 GHz. A robust detection has been reached with very good agreement between the experimental and simulated results in both co- and cross-polarizations.

This work presents a novel technique for designing chipless radio frequency identification (RFID) tags which, unlike the traditional tags with complex geometries, are both compact and printable. The tags themselves are alphabets, which offers the advantage of efficient visual recognition of the transmitted data in real-time via radio frequency (RF) waves. In this study, the alphabets (e.g., a, b and c) are realized by using copper etching on a thin dielectric substrate (TLX-8) backed by a ground plane. It is shown that the original signature of the frequency response of the backscattered radar cross-section (RCS) of the letter, displays dips that are unique to the individual letters. The tags have been simulated, fabricated and their monostatic cross-sections have been measured by using a dual-polarized Vivaldi antenna in the frequency band ranging from 6 to 13 GHz. The study also includes, for the first time, a detailed analysis of the impact of changing the shape of the tag owing to variation in the font type, size, spacing, and orientation. The proposed letters of the alphabet are easily printable on the tag and provide an efficient way to visually recognized them and, hence, to detect them in a robust way, even with a low coding density of 2.63 bit/cm(2). The advantages of the proposed novel identification method, i.e., utilization of the both co- and cross-polar RCS characteristics for the printable clipless RFID tags are the enhancement of the coding density, security and better detection of the alphabet tags with different fonts by capturing the tag characteristics with better signal to noise ratio (SNR). Good agreement has been achieved between the measured and simulated results for both co- and cross-polarized cases.

This paper proposes a frequency reconfigurable notched-band UWB antenna design, which is capable of wide band rejection. We begin with a conventional reconfigurable modified-square monopole printed antenna and insert a U-shaped slot to create the rejection band. Next, we add two identical SMV1249 varactor diodes with variable capacitances in the created slots to tune the rejected band. We modify the capacitances, which, in turn, controls rejected band by controlling the reverse bias voltage applied across the varactor diodes. The proposed structure has been simulated, optimized, fabricated and experimentally tested. Good agreement has been achieved between the simulation and measurement results. Experimental results show that when the bias voltage is varied from 0 to 7 V, the antenna can be reconfigured to achieve various rejection frequency bands, and to maintain good impedance match as well as stable radiation patterns over the explored frequency band ranging from 1 to 6 GHz.

To enhance the reliability of motor imagery based brain-computer interface, we present a study that considers subject-based optimization of feature extraction and classification. In particular, wavelet-based feature extraction performed on different bands was optimized over available selections of wavelet family, length and number of decomposition levels. Likewise, the classification step considers three general families of classifiers whose parameters are optimized in a similar manner. Such optimization was performed for each subject whereby processing parameters are selected based on the best performance obtained in the training session. We report the results obtained from applying this approach to the BCI competition 2008 dataset 2b (Graz) and demonstrate that such optimization provides results that outperform previous methods.