An eight-element sequentially rotated crescent-slot-coupled dielectric resonator antenna array for WIFI applications

In this communication, the author presents an eight-element sequentially rotated (SR) circularly polarized (CP) dielectric resonator antenna (DRA) for operation in the IEEE 802.11a standard. A novel resonating element composed of a crescent slot (CS) used to excite a rectangular dielectric resonator (RDR) is proposed that has two orthogonal modes ${\mathit{TE}}_{1\delta 1}^y$ and ${\mathit{TE}}_{\delta 21}^x$ as required for CP radiation. An SR series–parallel geometry is used to prototype the array feed network to allocate the array elements to symmetrical positions. The phase progression of each element was 45° along the array, and the signal magnitude was distributed evenly based on the binomial theory to enhance the antenna performance. The prototyped SR array had a size of $46\times 46\times 0.813$ mm³ and was measured and characterized in order to authenticate the design. The resonance bandwidth (S₁₁ ˂ −10 dB) was found to be 14.28% with a 3 dB axial ratio (AR) of 17.7% for right-hand CP. The gain varied from 15.71 to 16.26 dBi within the operating band. The size, gain, and impedance bandwidth of the proposed array make it a potential candidate for devices operating in the IEEE 802.11a band.     

Pilot-aided 1 × 2 and 2 × 2 space-time line code systems with transmit antenna selection

The space-time line code (STLC), which has been recently proposed in the literature, assumes fully known channel state information at the transmitter and not the receiver. However, the effective channel gain is still required at the receiver to coherently detect $M$-ary quadrature amplitude modulation ( $M$QAM) symbols. In this paper, we propose pilot-aided STLC systems, which do not require the effective channel gain at the receiver to detect the $M$QAM symbols. In order to further improve the error performance of the proposed schemes, we present the pilot-aided STLC systems with transmit antenna selection (TAS). Using a more direct and simpler approach, we derive the average symbol error probability (ASEP) of the coherent $1\times 2$ STLC systems with TAS, which represents the lower bound of the pilot-aided $1\times 2$ STLC systems with TAS. For comparison, in a similar manner, we also derive the ASEP of the coherent $2\times 2$ STLC systems without TAS, which represents the lower bound of the pilot-aided $2\times 2$ STLC systems. For pilot-aided $1\times 2$ STLC systems with TAS, the gap between the simulated symbol error rate (SER) and the derived theoretical ASEP lower bound is very small. For a given number of transmit antennas, the simulated SER and theoretical ASEP also show that the error performance of the pilot-aided $2\times 2$ STLC systems with or without TAS is superior to the pilot-aided $1\times 2$ STLC systems with TAS by at least 1.8 dB.     

Axial ratio bandwidth improvement of compact planar monopole antenna with dual-band and dual-sense

A small size, dual-band and dual-sense monopole antenna is proposed to improve the axial ratio bandwidth (ARBW). The proposed antenna is considered on a low-cost lossy FR4 substrate with parasitic strips (PSs) and partial ground plane of half guided wavelength dimensions. The dimension of the antenna in terms of wavelength is $\mathbf{0.27}{\mathit{\lambda }}_{\mathbf{0}}\mathit{\times }\mathbf{0.29}{\mathit{\lambda }}_{\mathbf{0}}\mathit{\times }\mathbf{0.02}{\mathit{\lambda }}_{\mathbf{0}}$, where ${\mathit{\lambda }}_{\mathbf{0}}$ is the wavelength at the lowest resonant frequency. The circularly polarized (CP) mode is created for strong orthogonal electric fields ${\mathit{E}}_{\mathit{X}}$ and ${\mathit{E}}_{\mathit{Y}}$. The obtained phase difference (PD) between two electric fields ${\mathit{E}}_{\mathit{X}}$ and ${\mathit{E}}_{\mathit{Y}}$ is varied from ${\mathbf{86}}^{°}$ to ${\mathbf{96}}^{°}$ under ARBW. The achieved ARBW is 3.68–3.8 GHz, 4.84–12.58 GHz, and impedance bandwidth (IBW) is 3.51–3.82 GHz and 4.28–15 GHz. The applications of the proposed antenna are International Telecommunication Union (ITU) for 5G, C-band IEEE 802.11a wireless local area network (WLAN) at 5 GHz (5.15–5.825 GHz) and X-band wireless systems.     

On the performance of energy harvesting-assisted Nth best relay cooperative networks in Nakagami-m fading

We study the energy harvesting (EH)-assisted system model based on the performance of a dual-hop cooperative communication system that is subjected to Nakagami- $m$ fading. Through the partial relay selection method, the selection of $N$th best relay (BR) is performed among $M$ amplify and forward (AF) relays, which can harvest energy from radio frequency signals. At the receiver, the selection combining scheme is considered to select between the signals of $N$th best relaying path and the direct path. For this considered system, we compute the closed-form expressions of outage probability (OP) and the average symbol error rate (ASER) for higher order quadrature amplitude modulation (QAM) techniques, especially for rectangular QAM, cross QAM, and hexagonal QAM. Further, a new moment-generating function expression is obtained which is used to derive the ASER expression related to the generalized non-coherent modulation technique. We also give the asymptotic expression of OP to find out the diversity order. Furthermore, we study the effect of fading parameters, $N$th BR, and other factors on system behavior. Finally, we verify the derived expressions with Monte Carlo simulations.     

Path loss model based on exponential water cycle algorithm for wireless sensor network

Wireless sensor networks (WSNs) are frequently employed in the agriculture field to improve the quality and crop yield. The WSN might reduce the quality of the communication link because of the absorption, dispersion, and attenuation through the leaves of plants. Therefore, estimating the path loss due to signal attenuation before WSN deployment is crucial for the smooth operation of the network. In this research paper, three innovative path loss models are defined based on the MATLAB curve fitting tool: polynomial water cycle (PWC), exponential water cycle (EWC), and Gaussian water cycle (GWC) algorithm. Here, the path loss between the router node and the coordinator node is modeled on the basis of the received signal strength indicator (RSSI) and time of arrival (TOA) measurements in a sugarcane field. The correlation coefficient between the RSSI measurement and the distance must be increased to create a precise path loss model. This paper integrates the exponential, polynomial, and Gaussian functions with the water cycle algorithm (WCA) to evaluate the optimal coefficients that would lead to precise path loss models. The performance of the proposed models that determines the optimum linear fit between RSSI and distance is validated using the correction coefficient $R^2$. The results show that the proposed path loss model is superior to existing path loss models. The correlation coefficient $R^2$ of the proposed EWC model is 0.9993, whereas the existing PE-PSO, LNSM, and PSO-Exponential models yield 0.98, 0.87, and 0.93, respectively. Also, the proposed models attain the best mean absolute error (MAE) of 0.2187, 0.2951, and 0.3457 dBm for EWC, PWC, and GWC algorithms, respectively.     

Spectrum sensing performance of wireless cognitive radio sensor network with hard-decision fusion over generalized α−μ fading channels

The analysis of spectrum sensing performance of energy detection (ED)-based wireless cognitive radio sensor network (ED-WCRSN) with hard-decision combining (HDC) is presented in this paper. Particularly, several network parameters are derived to estimate the performance of ED-WCRSN, considering channel errors, noise, and generalized $\alpha -\mu$ fading. In the considered network, first, cognitive radio sensor (CRS) senses a primary user (PU), gets sensing data, and then uses an ED to make a local binary decisions about PU's active or inactive status. In both sensing and reporting channels, the channel error probability is also taken into account. Next, HDC technique is used at control center (CC) to combine the locally obtained decisions, and a final decision about the status of the PU is made. To do so, first, the expression for the novel and analytical, which incorporates noise and $\alpha -\mu$ fading, detection probability in a CRS is derived and validated using Monte Carlo simulations in MATLAB and using an experimental setup. Then, utilizing derived mathematical expressions, closed-form expressions of an average error rate (AER), optimal numbers of CRSs, and detection thresholds under noisy and $\alpha -\mu$ fading conditions are developed. The substantial influence of channel and network factors is assessed using receiver operating characteristics (ROC), complementary ROC, and AER. Finally, the impacts of channel and network parameters on ED-WCRSN performance are explored. For numerous parameters of the considered network, the optimal values detection threshold and number of CRSs are also found.     

A novel wideband fractal-shaped MIMO antenna for brain and skin implantable biomedical applications

A novel fractal-shaped wideband multiple-input multiple-output (MIMO) antenna is proposed for brain and skin implantable applications. This antenna works in the 2.4–2.48 GHz band of industrial, scientific, and medical (ISM) standards. The fractal-shaped wideband MIMO antenna is miniature in size with a footprint of $0.13\mathrm{\lambda }\times 0.06\mathrm{\lambda }\times 0.01\mathrm{\lambda }$. Rogers RT/Duroid 6010 high-dielectric substrate material is used to fabricate the optimized design in order to validate the implantable MIMO antenna structure. The same high-permittivity substrate material has been used as a superstrate. Experiments were carried out in brain and skin-mimicking gel at 2.45 GHz in the ISM band. The proposed antenna has a peak gain of −21.3 dBi at 2.45 GHz. High isolation (>20 dB) between two MIMO ports is attained. The proposed antenna achieves a fractional bandwidth of 36.76% and an impedance bandwidth of 1.02 GHz. According to IEEE safety regulations for 1- and 10-g tissues, the computed maximum specific absorption rate (SAR) is safe bound.     

Performance analysis of intelligent reflecting surface-assisted mobile wireless networks subjected to generalized Gaussian noise

Different from the prior works, this paper presents the performance analysis of an intelligent reflecting surface (IRS)-assisted communication link in a static and mobile scenario impaired by Rayleigh fading and additive white generalized Gaussian noise (AWGGN). Precisely, the IRS is configured as an intelligent access point, and the mobile behavior of the nodes is characterized by the random waypoint (RWP) model. To this end, closed-form expressions of average bit error rate (BER), average channel capacity (ACC), and outage probability (OP) in both static and mobile scenarios are obtained. To gain further insight into the system performance at high signal-to-noise ratio (SNR), asymptotic expressions are obtained. Moreover, the effect of the number of reflective elements ( $N$) and the shaping parameter ( $\lambda$) on the system performance is thoroughly studied. The results indicate that introduction of IRS leads to significant improvement in the overall system performance. The derived results are corroborated with Monte Carlo simulations.     

Anisotropic Phonon Response of Few‐Layer PdSe2 under Uniaxial Strain

PdSe₂, an emerging 2D material with a novel anisotropic puckered pentagonal structure, has attracted growing interest due to its layer‐dependent electronic bandgap, high carrier mobility, and good air stability. Herein, a detailed Raman spectroscopic study of few‐layer PdSe₂ (two to five layers) under the in‐plane uniaxial tensile strain up to 3.33% is performed. Two of the prominent PdSe₂ Raman peaks are influenced differently depending on the direction of strain application. The $A_g^1$ mode redshifts more than the $A_g^3$ mode when the strain is applied along the a‐axis of the crystal, while the $A_g^3$ mode redshifts more than the $A_g^1$ mode when the strain is applied along the b‐axis. Such an anisotropic phonon response to strain indicates directionally dependent mechanical and thermal properties of PdSe₂ and also allows the identification of the crystal axes. The results are further supported using first‐principles density‐functional theory. Interestingly, the near‐zero Poisson’s ratios for few‐layer PdSe₂ are found, suggesting that the uniaxial tensile strain can easily be applied to few‐layer PdSe₂ without significantly altering their dimensions at the perpendicular directions, which is a major contributing factor to the observed distinct phonon behavior. The findings pave the way for further development of 2D PdSe₂‐based flexible electronics.     

Does Salt Concentration Matter? New Insights on the Intercalation Behavior of PF6−${\rm{PF}}_6^ - $ into Graphite Cathode for the Dual-Ion Battery

A high-concentration electrolyte is favored in dual-ion batteries (DIBs) due to the lower onset potential for anion intercalation, higher specific discharge capacity, and better oxidation stability. Inspired by the correlation between the high-concentration electrolytes and localized high-concentration electrolytes, it is suspected that it is not the salt concentration but the solution structure of the electrolyte that determines the intercalation behavior of anion into graphite cathode. To prove the viewpoint, a series of electrolytes are prepared by controlling the salt concentration or solution structure and the intercalation behavior of $P{F}_6^{-}$ within the graphite cathode is investigated in Li||graphite and graphite||graphite cells. It is found that $P{F}_6^{-}$ anions exhibit similar onset potentials and specific discharge capacities in the electrolytes with different salt concentrations but similar solution structures. This study provides a new perspective on designing promising electrolytes for DIBs, which can accelerate the further exploitation of high-performance DIBs.     

Performance analysis of satellite link using Gaussian mixture model under rain

The evolution of communication systems to the next generation, for example, B5G and 6G, demands an ultrareliable performance regardless of weather conditions. Such ultrareliable system design will require that the effects of adverse weather events on the communication system have to be computed more accurately so that physical layer compensation should be optimally and dynamically adaptive to such events. The performance of satellite links is severely affected by dynamic rain attenuation, and thus, accurate and reliable modeling of performance parameters is essential for dynamic fade countermeasures, especially above 10 GHz. In this work, we model the energy per bit to noise spectral density ratio ( $E_b/N_0$) using Gaussian mixture (GM) model during rainy events. The developed mathematical expression is used to accurately model the average $E_b/N_0$, bit error rate (BER), outage probability, and ergodic channel capacity of the link. The average BER, upper bound on BER, and average ergodic capacity of an M-ary phase shift keying scheme (MPSK) using the GM model of $E_b/N_0$ are derived to evaluate the performance of the link under such weather impairments. We then show the numerical results and analysis using the GM model of the measured $E_b/N_0$ data obtained with the AMoS-7 satellite at a site located in Israel.     

The approach of hybrid adaptive coupling synchronization among N Lorenz systems and its application in secure communication for multi-unmanned aerial vehicle formation

In this paper, it is proposed that a hybrid global adaptive coupling synchronization scheme among $N$ Lorenz chaotic dynamical nodes to realize the secure communication system between base station and multi-unmanned aerial vehicle (UAV) formation. The specific method is that the feedback drive–response synchronization is utilized for first two nodes of base station and the leader of multi-UAV formation, and the nodes of all UAVs are coupled by unidirectional adaptive coupling synchronization according to a directed link in ad hoc network of multi-UAV formation. It is demonstrated that the asymptotic stability of the proposed hybrid adaptive coupled synchronization by constructing the Lyapunov function. In this way, the encrypted information formed by plaintext information masked into the chaotic sequence generated by the chaotic dynamical node of base station; meanwhile, it is fed back into the base station node as the drive system. On the other hand, encrypted information is forwarded to the leader node as the response system for decryption. The feedback driver–response synchronization is used to realize secure communication between the base station and the leader of multi-UAV formation. Meanwhile, secure communication among its leader and followers is achieved through the unidirectional adaptive coupling synchronization in the network. This strategy ensures the multi-UAV formation decrypting encrypted information synchronously and effectively improves the security, consistency, and overall performance of their commands.     

Multipoint Defect Synergy Realizing the Excellent Thermoelectric Performance of n‐Type Polycrystalline SnSe via Re Doping

SnSe has attracted much attention due to the excellent thermoelectric (TE) properties of both p‐ and n‐type single crystals. However, the TE performance of polycrystalline SnSe is still low, especially in n‐type materials, because SnSe is an intrinsic p‐type semiconductor. In this work, a three‐step doping process is employed on polycrystalline SnSe to make it n‐type and enhance its TE properties. It is found that the Sn_0.97Re_0.03Se_0.93Cl_0.02 sample achieves a peak ZT value of ≈1.5 at 798 K, which is the highest ZT reported, to date, in n‐type polycrystalline SnSe. This is attributed to the synergistic effects of a series of point defects: $V_{\mathrm{Se}}^{\mathrm{..}},{\mathrm{Cl}}_{\mathrm{Se}}^{.},V_{\mathrm{Sn}}^{,,},{\mathrm{Re}}_{\mathrm{Sn}}^{\times },{\mathrm{Re}}_{}^0$. In those defects, the $V_{\mathrm{Se}}^{\mathrm{..}}$ compensates for the intrinsic Sn vacancies in SnSe, the ${\mathrm{Cl}}_{\mathrm{Se}}^{.}$ acts as a donor, the $V_{\mathrm{Sn}}^{,,}$acts as an acceptor, all of which contribute to optimizing the carrier concentration. Rhenium (Re) doping surprisingly plays dual‐roles, in that it both significantly enhances the electrical transport properties and largely reduces the thermal conductivity by introducing the point defects, ${\mathrm{Re}}_{\mathrm{Sn}}^{\times },{\mathrm{Re}}_{}^0$. The method paves the way for obtaining high‐performance TE properties in SnSe crystals using multipoint‐defect synergy via a step‐by‐step multielement doping methodology.     

3D Reconstruction of Sawtooth 180° Tail-to-Tail Domain Walls in Single Crystal BiFeO3

Previous studies of single crystal BiFeO₃ have found a dense domain structure with alternating sawtooth and flat domain walls (DWs). The nature of these domains and their 3D structure has remained elusive to date. Herein, several sections taken at different orientations are used to examine the structure in detail, concentrating here on the sawtooth DWs using diffraction contrast transmission electron microscopy, electron diffraction, and aberration-corrected scanning transmission electron microscopy (STEM). All DWs are found to be 180° type; the flat walls have head-to-head polarity while the sawtooth DWs are tail-to-tail with peaks elongated along the polar [111] axis, formed by neutral ($11\overline{2}$) DW facets and slightly charged facets with orientations close to ($3\overline{2}1$) and ($\overline{2}31$). The neutral DW facets are Ising type and very abrupt, while the charged DW facets have mixed Néel/Bloch/Ising character with a chiral nature and a width of about 2 nm.     

2D Porous Polymers with sp2‐Carbon Connections and Sole sp2‐Carbon Skeletons

2D porous polymers with a planar architecture and high specific surface area have significant applications potential, such as for photocatalysis, electrochemical catalysis, gas storage and separation, and sensing. Such 2D porous polymers have generally been classified as 2D metal–organic frameworks, 2D covalent organic frameworks, graphitic carbon nitride, graphdiyne, and sandwich‐like porous polymer nanosheets. Among these, 2D porous polymers with sp²‐hybridized carbon ( $C_{s{p}^2}$) bonding are an emerging field of interest. Compared with 2D porous polymers linked by B? O, C?N, or C?C bonds, $C_{s{p}^2}$‐linked 2D porous polymers exhibit extended electron delocalization resulting in unique optical/electrical properties, as well as high chemical/photostability and tunable electrochemical performance. Furthermore, such 2D porous polymers are one of the best precursors for the fabrication of 2D porous carbon materials and carbon skeletons with atomically dispersed transition‐metal active sites. Herein, rational synthetic approaches for 2D porous polymers with $C_{s{p}^2}$ bonding are summarized. Their current practical photoelectric applications, including for gas separation, luminescent sensing and imaging, electrodes for batteries and supercapacitors, and photocatalysis are also discussed.     

Parachute shape ultra-wideband wearable antenna for remote health care monitoring

Wireless body area networks (WBAN) is used to measure patients' health conditions continuously. Different kinds of sensors are required to measure health conditions. When such types of antennas are used on the human body, they are flexible with the movements. The usage of wearable devices is currently increasing in the biomedical field. The presented wearable antenna is suitable for biomedical applications. The presented ultra-wideband (UWB) flexible parachute shape wearable antenna is fabricated on a jeans textile substrate. The prototype antenna has a −10 dB measured impedance bandwidth of 5800 MHz (7 to 12.8 GHz) with average radiation efficiency of 75.28%. The prototype antenna's size is 40 × 40 mm² (1.32 × 1.32 ${\lambda }_0^2$ at centre frequency 9.9 GHz) and a peak gain of 4.5 dB at 12.33 GHz. The fabricated antenna is suitable for biomedical applications in X-band frequencies and can be implemented with a low-cost manufacturing process. The radiating element is made by conductive copper tape. Muscle-equivalent phantoms are used to analyze the body effect on antenna performance. The radiation effect emitted by the presented antenna on the human body is calculated by the specific absorption rate (SAR) value. The maximum SAR value of the proposed antenna is 1.84 W/kg at 12.33 GHz. This leads to promising results for wearable applications related to remote health care monitoring, such as biotelemetry and mobile health with a sensor-driven approach.     

Macroscopic and Microscopic Structures of Cesium Lead Iodide Perovskite from Atomistic Simulations

A first‐principles‐based effective Hamiltonian is developed and employed to investigate finite‐temperature structural properties of a prototype of perovskite halides, that is CsPbI₃. Such simulations, when using first‐principles‐extracted coefficients, successfully reproduce the existence of an orthorhombic Pnma state and its iodine octahedral tilting angles around room temperature. However, they also yield a direct transformation from Pnma to cubic $Pm\overline{3}m$ upon heating, unlike measurements that reported the occurrence of an intermediate long‐range‐tilted tetragonal P4/mbm phase in‐between the orthorhombic and cubic phases. Such disagreement, which may cast some doubts about the extent to which first‐principle methods can be trusted to mimic hybrid perovskites, can be resolved by “only” changing one short‐range tilting parameter in the whole set of effective Hamiltonian coefficients. In such a case, some reasonable values of this specific parameter result in the predictions that i) the intermediate P4/mbm state originates from fluctuations over many different tilted states; and ii) the cubic $Pm\overline{3}m$ phase is highly locally distorted and develops strong transverse antiphase correlation between first‐nearest neighbor iodine octahedral tiltings, before undergoing a phase transition to P4/mbm under cooling.     

ASER analysis of generalized hexagonal QAM schemes for NOMA systems over Nakagami-m fading channels

To achieve high data rates expected from beyond 5G communications, higher-order modulation techniques have been explored. The energy-efficient modulation technique with a high data rate has encouraged researches towards an optimum two-dimensional hexagonal-shaped constellation, namely, hexagonal quadrature amplitude modulation (HQAM). Thus, in this work, we analyze the average symbol error rate (ASER) of HQAM schemes by considering a two-user nonorthogonal multiple access (NOMA) pair. Closed-form expressions for ASER of HQAM schemes for users are derived over generalized Nakagami- $m$ fading channels. Further, for the HQAM constellation feasibility in two-user downlink NOMA systems, the power allocation criterion for the users is presented. Furthermore, the impact of modulation order of the users over the systems ASER analysis is investigated and valuable insights are drawn.     

Background memory-assisted zero-shot video object segmentation for unmanned aerial and ground vehicles

Unmanned aerial vehicles (UAV) and ground vehicles (UGV) require advanced video analytics for various tasks, such as moving object detection and segmentation; this has led to increasing demands for these methods. We propose a zero-shot video object segmentation method specifically designed for UAV and UGV applications that focuses on the discovery of moving objects in challenging scenarios. This method employs a background memory model that enables training from sparse annotations along the time axis, utilizing temporal modeling of the background to detect moving objects effectively. The proposed method addresses the limitations of the existing state-of-the-art methods for detecting salient objects within images, regardless of their movements. In particular, our method achieved mean $J$ and $F$ values of 82.7 and 81.2 on the DAVIS'16, respectively. We also conducted extensive ablation studies that highlighted the contributions of various input compositions and combinations of datasets used for training. In future developments, we will integrate the proposed method with additional systems, such as tracking and obstacle avoidance functionalities.