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In this study, a series of ($1-$x)Li₂MoO₄$\mathrm{}-$xBi_0.4Ce_0.6VO₄ [x = 0.25, 0.35, 0.45, 0.55, ($1-$x)LM–xBCV] microwave dielectric ceramics, capable of being sintered at low temperatures, were synthesized using the solid-phase method. The temperature coefficient of resonance frequency in LM microwave dielectric ceramics was effectively modulated through the incorporation of BCV with tetragonal zirconia phases, resulting in the formation of composite ceramics. This approach led to the development of a low-permittivity ($\epsilon$_r ∼ 12.6) microwave dielectric ceramic material exhibiting a near-zero temperature coefficient (TCF ∼ +0.5 ppm/^∘C). The composite, specifically 0.55LM–0.45BCV, achieved ultra-low temperature sintering below $620^{\circ }$C and demonstrated excellent performance as low-temperature co-fired ceramic materials, with good co-firing compatibility with metallic silver. Furthermore, the volatilization of lithium and bismuth elements was effectively mitigated through the burying sintering process. Which resulted in a substantial enhancement of the $Q\times f$ (Q and f denote the quality factor and the resonant frequency, respectively) value for the 0.55LM–0.45BCV ceramics, achieving an increase of nearly threefold (Q × f$\sim 18,540$GHz). To investigate the application potential of 0.55LM–0.45BCV ceramic, particularly in the context of low-orbit communication satellites, a circularly polarized patch antenna was designed utilizing 0.55LM–0.45BCV ceramic as the dielectric substrate material. The antenna demonstrated a high simulated radiation efficiency of 93.8% and a gain of 4.0dBi at a center frequency of 1.559GHz, indicating its promising applicability in the domain of orbital satellite communication.

Zinc 20-halogenochlorins 2(20-F), 3(20-Cl) and 4(20-Br) were synthesized by halogenation of a chlorophyll a derivative at the 20-position as a model for bacteriochlorophyll (BChl)c, which possesses a methyl group at the 20-position and 20-unsubstituted BChld. Visible spectra in a polar tetrahydrofuran (THF) solution showed that 2-4 were monomeric and the planarity of the chlorin ring, was distorted with increasing bulkiness of the 20-substituent. Visible, circular dichroism and IR spectra revealed that 2-4 self-aggregated to form oligomers similarly with 20-unsubstituted 1 and BChlsc/d in the heterogeneous thin film as well as in homogeneous non-polar solvents (1% (v/v) THF-hexane). Therefore, the in vitro self-aggregates of 2-4 are good structural models for in vivoBChlsc/d self-aggregates, the main antenna components of photosynthetic green bacteria. Fluorescence spectra showed that monomeric 3 and 4 were less emissive than 1 and 2 due to the heavy atom effect which could not be observed in the oligomeric species, indicating that the in vitro aggregates should be promising as functional (light-harvesting) models.

The 3D Finite-Difference Time-Domain (FDTD) method is a powerful numerical technique for directly solving Maxwell's equations. This paper describes its implementation on high speed computers. This technique is used here for the analysis of millimeter wave planar antennas. In our algorithm, Bérenger's Perfectly Matched Layers (PML) are implemented as absorbing boundary conditions to mimic free space. Dielectric and metallic losses are taken into account in a recursive and dispersive formulation. We present the main techniques implemented to optimize the non-sequential program on vector computers. Besides, two parallel supercomputers of different architectures as well as a multi-user network of Sun workstations are used to investigate the parallel FDTD code. The performances obtained on vector/distributed memory massively parallel/hybrid computers show that the FDTD algorithm is ideally suited for the implementations on both vector and parallel computers. Comparisons with experimental results in the millimeter wave frequency band validate our codes.

In this paper, we review the potential applications of single-walled carbon nanotubes in three areas: passives (interconnects), actives (transistors), and antennas. In the area of actives, potential applications include transistors for RF and microwave amplifiers, mixers, detectors, and filters. We review the experimental state of the art, and present the theoretical predictions (where available) for ultimate device performance. In addition, we discuss fundamental parameters such as dc resistance as a function of length for individual, single-walled carbon nanotubes.

With the development of inkjet-/3D-/4D-printing additive manufacturing technologies, flexible 3D substrate with complex structures can be patterned with dielectric, conductive and semi-conductive materials to realize novel RF designs. This paper provides a review of state-of-the-art additively manufactured passive RF devices including antennas and frequency selective surfaces (FSS), couplers, where origami-inspired structure enables unprecedented capabilities of on-demand continuous frequency tunability and deployability. This paper also discusses additively manufactured active RF modules and systems such as inkjet printed RF energy harvester system with high sensitivity and efficiency for Internet of Things (IoT), smart cities and wireless sensor networks (WSN) applications, inkjet-printed RF front ends, and inkjet-printed mm-wave backscatter modules.

The microelectromechanical system (MEMS) quasi-end-fire array antenna based on a liquid crystal polymer (LCP) substrate is designed and fabricated in this paper. The maximum radiation direction of the antenna tends to the cone axis forming an angle less than 90${}^{\circ }$, which satisfies the proximity detection system applied at the forward target detection. Furthermore, the proposed antenna is fed at the ended side in order to save internal space. Moreover, the proposed antenna takes small covering area of the proximity detection system. The proposed antenna is fabricated by using the flexible MEMS process, and the measurement results agree well with the simulation results. This is the first time that a conical conformal array antenna is fabricated by the flexible MEMS process to realize the quasi-end-fire radiation. A pair of conformal MEMS array antennas resonates at 14.2 GHz with its mainlobes tending to the cone axis forming a 30${}^{\circ }$ angle and a 31${}^{\circ }$ angle separately, and the gains achieved are 1.82 dB in two directions, respectively. The proposed antenna meets the performance requirements for the proximity detection system which has vast application prospects.

Antenna fingerprinting is critical for a range of physical-layer wireless security protocols to prevent eavesdropping. The fingerprinting process exploits manufacturing defects in the antenna that cause small imperfections in signal waveform, which are unique to each antenna and hence device identity. It is an established process for physical-layer wireless authentication with proven usage systems in terrestrial systems. The premise relies on accurate signal feature discovery from a large set of similar antennas and stable fingerprint patterns over the operational life of the antenna. However, in space, many low-cost satellite antennas suffer degradation from atomic oxygen (AO). This is particularly a problem for nano-satellites or impromptu temporary space antennas to establish an emergency link, both of which are designed to operate for a short time span and are currently not always afforded protective coating. Current antenna fingerprinting techniques only use Support Vector Machine (SVM) and Convolutional Neural Networks (CNNs) to take a snap-shot fingerprint before degradation, and hence fail to capture temporal variations due to degradation. Here, we show how we can perform robust antenna fingerprinting (99.34% accuracy) for up to 198 days under intense AO degradation damage using Recurrent Neural Networks (RNNs). We compare our RNN results with CNNs and SVM techniques using different signal features and for different Low-Earth Orbit (LEO) satellite scenarios. We believe this initial research can be further improved and has real-world impact on physical-layer security of short-term nano-satellite antennas in space.

A UHF-band RFID system handling many RF tags has some advantages over a bar code system such as simultaneous multi-reading and long read range. Especially, it has been strongly desired by the logistics and the retail industries for efficiency of operation. Recently, user-friendly RFID systems are being studied. We focused on a gate system using RFID technologies. If the tag moving direction can be recognized at the RFID gate system, it will be very useful for the efficiency of inventory management and the checking of pilferage or shoplifting. In this paper, new methods of tag moving direction detection using the difference of passing time of two antennas without expensive external sensors is proposed and evaluated. Two methods are proposed for the specific procedure. The first one is to detect the time when the received power goes over the preset threshold. The second one is to estimate the aimed time using the maximum likelihood approach. Some experimental results of these methods are also shown and their feasibility is proved.

The detection of emerging technologies is vital for R&D managers and policymakers; hence, the bibliometric approach to analyzing papers and patents was developed. In this study, we proposed a new method, the research classification schema (RCS). We used citation network analysis to classify technologies into four categories: change-maker, breakthrough, matured, and incremental. Each technology is then plotted on the RCS based on its publication profile. A case study in the field of antennas was undertaken to evaluate the relevance and effectiveness of the RCS. The RCS method demonstrates the usefulness of the identification process of promising technologies, and therefore, the convenience of target designing research projects in universities and companies. We also discussed the effect of the resolution limit of clustering algorithms on the RCS to improve reliability.

Thermoacoustic imaging (TAI) is an emerging high-resolution and high-contrast imaging technology. In recent years, metal wires have been used in TAI experiments to quantitatively evaluate the spatial resolution of different systems. However, there is still a lack of analysis of the response characteristics and principles of metal wires in TAI. Through theoretical and simulation analyses, this paper proposes that the response of metal (copper) wires during TAI is equivalent to the response of antennas. More critically, the response of the copper wire is equivalent to the response of a half-wave dipole antenna. When its length is close to half the wavelength of the incident electromagnetic wave, it obtains the best response. In simulation, when the microwave excitation frequencies are 1.3GHz, 3.0GHz, and 5.3GHz, and the lengths of copper wires are separately set to 11cm, 5cm, and 2.5cm, the maximum SAR distribution and energy coupling efficiency are obtained. This result is connected with the best response of half-wave dipole antennas with lengths of 11cm, 4.77cm, and 2.7cm under the theoretical design, respectively. Regarding the further application, TAI can be used to conduct guided minimally invasive surgery on surgical instrument imaging. Thus, this paper indicated that results can also guide the design of metal surgical instruments utilized in different microwave frequencies.

Traditional approaches to connectivity in sensor networks are based on the omnidirectional antenna model which relies on the assumption that the sensors send and receive in all directions. Current technologies make possible the utilization of sensors with directional antenna capabilities whereby the sensors send and/or receive along a sector of a predefined angle (or beam-width). Although several researchers in the scientific literature have investigated the impact of directional antennae on network throughput, energy consumption, as well as security very little is known concerning the effect of directional antennae on its connectivity. In this paper, we introduce for the first time a new sensor model with each sensor being able to transmit in any one of k directions, for some fixed k, and explore the algorithmic limits and potential of such a directional antenna model. More specifically, given a set of n sensors in the plane, we consider the problem of establishing a strongly connected ad hoc network from these sensors using directional antennae. In particular, we prove that given such set of sensors, each equipped with k, 1 ≤ k ≤ 5, directional antennae with any angle of transmission, these antennae can be oriented in such a way that the resulting communication structure is a strongly connected digraph spanning all n sensors. Moreover, the transmission range of the antennae is at most times the optimal range (a range necessary to establish a connected network on the same set of sensors using omnidirectional antennae). The algorithm which constructs this orientation runs in O(n) time provided a minimum spanning tree on the set of sensors is given. We show that our solution can be used to give a tradeoff on the range and angle when each sensor has one antenna. Further, we also prove that for two antennae it is NP-hard to decide whether such an orientation exists if both the transmission angle and range are small for each antennae.

In this paper, we investigate the possibility of using the heterogeneous materials, with cuboid metallic inclusions inside a dielectric substrate (host) to control the effective permittivity. We find that in the gigahertz range, such a material demonstrates a significantly larger permittivity compared to the pure dielectric substrate. Three principal orientations of microscale cuboid inclusions have been taken into account in this study. The highest permittivity is observed when the orientation provides the largest polarization (electric dipole moment). The detrimental side effect of the metallic inclusion, which leads to the decrease of the effective magnetic permeability, can be suppressed by the proper choice of shape and orientation of the inclusions. This choice can in fact reduce the induced current and hence maximize the permeability. The dissipative losses are shown to be negligible in the relevant range of frequencies and cuboid dimensions.

This paper describes the design of a 5.5:1 bandwidth feed antenna and reflector system, intended for use in hydrogen intensity mapping experiments. The system is optimized to reduce systematic effects that can arise in these experiments from scattering within the feed/reflector and cross-coupling between antennas. The proposed feed is an ultra-wideband Vivaldi style design and was optimized to have a smooth frequency response, high gain, and minimal shadowing of the reflector dish. This feed can optionally include absorptive elements which reduce systematics but degrade sensitivity. The proposed reflector is a deep parabolic dish with $f/d=0.216$ along with an elliptical collar to provide additional shielding. The procedure for optimizing these design choices is described.

The detection of emerging technologies is vital for R&D managers and policy makers; hence, the bibliometric approach to analyzing papers and patents was developed. In this study, we proposed a new method, the research classification schema (RCS). We used citation network analysis to classify technologies into four categories: change-maker, breakthrough, matured, and incremental. Each technology is then plotted on the RCS based on its publication profile. A case study in the field of antennas was undertaken to evaluate the relevance and effectiveness of the RCS. The RCS method demonstrates the usefulness of the identification process of promising technologies, and therefore, the convenience of target designing research projects in universities and companies. We also discussed the effect of the resolution limit of clustering algorithms on the RCS to improve reliability.

The increasing environmental pollution and serious shortage of energy and resources have become big problems in human society in the recent years. Exploration of novel renewable and biodegradable materials based on biomass and construction of biomass-based energy-related applications have received more and more attention. Cellulose is the most abundant biomass on earth. Especially, nanocellulose possesses excellent mechanical, thermal, and optical properties. In this chapter, we review the recent advances in nanocellulose-based energy conversion materials, including piezoelectric materials, loudspeakers, antenna, phototransistors, organic light-emitting diodes (OLEDs), and touch screen.

With the development of inkjet-/3D-/4D-printing additive manufacturing technologies, flexible 3D substrate with complex structures can be patterned with dielectric, conductive and semi-conductive materials to realize novel RF designs. This paper provides a review of state-of-the-art additively manufactured passive RF devices including antennas and frequency selective surfaces (FSS), couplers, where origami-inspired structure enables unprecedented capabilities of on-demand continuous frequency tunability and deployability. This paper also discusses additively manufactured active RF modules and systems such as inkjet printed RF energy harvester system with high sensitivity and efficiency for Internet of Things (IoT), smart cities and wireless sensor networks (WSN) applications, inkjet-printed RF front ends, and inkjet-printed mm-wave backscatter modules.

In this paper, we review the potential applications of single-walled carbon nanotubes in three areas: passives (interconnects), actives (transistors), and antennas. In the area of actives, potential applications include transistors for RF and microwave amplifiers, mixers, detectors, and filters. We review the experimental state of the art, and present the theoretical predictions (where available) for ultimate device performance. In addition, we discuss fundamental parameters such as dc resistance as a function of length for individual, single-walled carbon nanotubes.

Tunka-Rex is a new radio detector for extensive air showers from cosmic rays, built in 2012 as an extension to Tunka-133. The latter is a non-imaging air-Cherenkov detector, located near lake Baikal, Siberia. With its 25 radio antennas, Tunka-Rex extends over 1 km² with a spacing of 200 m and therefore is expected to be sensitive to an primary energy range of 10¹⁷–10¹⁸ eV. Using Trigger and DAQ from Tunka-133, this setup allows for a hybrid analysis with the air-Cherenkov and radio technique combined. The main goal of Tunka-Rex is to investigate the achievable precision in reconstruction of energy and composition of the primary cosmic rays by cross-calibrating to the well understood air-Cherenkov detector. An early analysis proves the detection of air-shower events with dependencies on energy and incoming direction as expected from a dominant geomagnetic emission mechanism.

To arrange the antennas onboard space tracking ship properly to avoid mutual interference, especially between those operating in the same frequency band, mutual coupling needs to be calculated. However, the complexity of conventional electromagnetic algorithm is intolerable and can't solve the problem efficiently. In this paper, a high-frequency asymptotic algorithm is adopted, party with time-domain finite element integration algorithm, to analyze the coupling between marine radar and tracking radar, both operating in S-band. Simulation result and test result show that, for large-scale antennas, the method proposed by us improves the efficiency significantly and computation error is less than 5 dB, which make it to be very applicable in engineering.