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A novel wideband folded dipole antenna (FDA) with stable radiation patterns under multiresonant modes is proposed in this communication. First, by lengthening and widening the driven strip of an FDA, the input resistance of its 1st- and 3rd-order modes declines significantly. Second, the driven and non-driven strips are further widened at a fixed ratio to achieve better impedance matching. Third, a pair of open-slot loops (OSLs) is advisably added to compress the resonant frequency of the 5th-order mode close to that of the 3rd-order mode for bandwidth improvement. Finally, a prototype is fabricated to provide experimental verification of the idea, and measured results show that the proposed FDA has a bandwidth of about 82% from 1.72 to 4.10 GHz, which exhibits a good agreement between measurement and simulation. In particular, the proposed FDA obtains stable radiation patterns in the entire operating band. [ABSTRACT FROM AUTHOR]

A variety of novel orbital angular momentum (OAM)-based communication or sensing systems have attracted much attention over the past decade, the superiority is brought about by nothing other than its orthogonality or vorticity. Plane spiral OAM (PSOAM) mode-group (MG) technique as a reconfigurable beamforming method can be used for building a multiple-in-multiple-out (MIMO) system to achieve the reduction in subchannel correlation, which benefits from the spiral phase distribution within the mainlobe. However, the demultiplexing process still depends on the MIMO algorithm, in which the receiver complexity is same as the conventional MIMO systems. In this article, a PSOAM MG orthogonal multiplexing communication link at the X-band using partial arc sampling receiving (PASR) scheme has been demonstrated experimentally. The MG channels have a good isolation of about 15 dB, and the existing performance can ensure the reliable 16-QAM wireless transmission. Besides, a real-time dual-channel video transmission experiment has been carried out to verify the channel isolation caused by MG’s orthogonality intuitively. More importantly, the demultiplexing procedure using the PASR scheme can be implemented by simple analog phase shifting operation with a lower receiver complexity compared with the conventional MIMO systems. [ABSTRACT FROM AUTHOR]

This article proposes a scalable dual-polarized antenna using the compact cavity and slot-dipole hybrid structure for omnidirectional radiation. For the horizontal polarization, an open-ended cavity is uniformly excited at its TE1/2,0,0 mode to achieve omnidirectional coverage. Based on this thin cavity, a hybrid structure with slots and parasitic dipole stub pairs is designed for vertical polarization, providing an omnidirectional pattern in the azimuthal plane. The measured results show that dual-polarized radiations with port isolation higher than 25 dB and gain variations lower than 2.7 dB are achieved in the band of 2.39–2.49 GHz, covering the frequency band of wireless local area network (WLAN) system. Moreover, to validate the scalability of the proposed antenna, a cascaded array is contrived to realize high-gain omnidirectional radiation. Compared with the existing works, the proposed omnidirectional dual-polarized antenna has the advantages of both compact volume and array scalability, exhibiting promising usage for high-gain router applications. [ABSTRACT FROM AUTHOR]

In this article, for the first time, the shielding of orbital angular momentum (OAM) waves by a cavity with apertures is evaluated. This is particularly interesting because the distinguishing feature between the OAM modes is their phase distribution in space, and, hence, shielding effectiveness is a mode-dependent phenomenon. A perfectly electrically conducting cavity with multiple apertures and two OAM antennas, inside and outside the cavity, is investigated using a method of moments based tool. The behavior of OAM waves is analyzed by comparing the transmission between the OAM arrays for different cases, including their field patterns in front of and behind the apertures. The effects of the orientation and position of the transmitting antenna, the rotation, size, and form of the apertures and different cavities are explored. Additionally, the effect on the distance and the orientation angle of the outer antenna are studied. It is shown that the propagation of OAM waves through apertures is possible and that the resulting signal loss is similar to the loss of a plane wave or the field of a monopole. It is also shown that certain OAM waves penetrate the apertures better than others. [ABSTRACT FROM AUTHOR]

A wideband omnidirectional circularly polarized (CP) antenna using a conformal artificial anisotropic polarizer is proposed for millimeter-wave applications. The antenna consists of three parts: an omnidirectional linearly polarized (LP) radiator, an annular hyperbolic lens, and a conformal anisotropic polarizer. The annular hyperbolic lens regulates the spherical wavefront from the LP radiator into a cylindrical shape prior to propagating into the conformal artificial anisotropic polarizer. Each curved slab of the polarizer is conformally tilted 45° to the incident electric field. Therefore, the conformal polarizer is the three-dimensionalization of the 2-D planar artificial anisotropic polarizer. The polarizer designing methodology is the first of its kind to generate wideband CP wave omnidirectionally. The hyperbolic lens and the conformal polarizer are fabricated together using stereolithography (SLA) 3-D printing technology. The measurement results show that the antenna has a wide operating bandwidth of 45% (from 24 to 38 GHz), which completely covers potential 5G 28 GHz spectra. The proposed design has a low fabrication complexity and brings possibilities for high-speed wireless communications using circular polarization. [ABSTRACT FROM AUTHOR]

A planar folded dipole antenna that exhibits wideband characteristics is proposed. The antenna has simple planar construction without a ground plane and is easy to be assembled. Parameter values are adjusted in order to obtain wideband properties and compactness by using an electromagnetic simulator based on the method of moments. An experimental result centered at 1.7 GHz for 50 Ω impedance matching shows that the antenna has bandwidth over 55% (VSWR ⩽ 2). The gains of the antenna are almost constant (2 dBi) in this frequency band and the radiation patterns are very similar to those of a normal dipole antenna. It is also shown that the antenna has a self-balanced impedance property in this frequency band. [ABSTRACT FROM AUTHOR]

We utilize electrically detected magnetic resonance (EDMR) measurements to compare high-field stressed, and gamma irradiated Si/SiO2 metal–oxide–silicon (MOS) structures. We utilize spin-dependent recombination (SDR) EDMR detected using the Fitzgerald and Grove dc $I-V$ approach to compare the effects of high-field electrical stressing and gamma irradiation on defect formation at and near the Si/SiO2 interface. As anticipated, both greatly increase the concentration of $P_{b}$ centers (silicon dangling bonds at the interface) densities. The irradiation also generated a significant increase in the dc $I-V$ EDMR response of $E^{\prime }$ centers (oxygen vacancies in the SiO2 films), whereas the generation of an $E^{\prime }$ EDMR response in high-field stressing is much weaker than in the gamma irradiation case. These results likely suggest a difference in their physical distribution resulting from radiation damage and high electric field stressing. [ABSTRACT FROM AUTHOR]

Ideal dipole antennas are desirable for antenna calibration. However, real-world implementation issues introduce inevitable nonideal effects that can significantly affect the quality of calibration. In this communication, a 2 GHz standard dipole (SD) antenna is presented with an excellent overall performance. This result is achieved by an innovative design with an optimized element shape and an embedded (shielded) balun. The designed feeding structure is a balanced structure that transitions from parallel strip lines to coaxial lines. The feeding method avoids the impact of electromagnetic environment asymmetry while achieving an appropriate balance. The measured relative bandwidth of the dipole exceeds 15%, and the antenna gain is approximately 2 dBi. The cross-polarization ratio is greater than 27 dB in the horizontal plane, and the horizontal gain variation is less than 0.2 dB. The dipole has a symmetrical vertical plane pattern, and the maximum gain point does not deviate from the horizontal plane. The high performance of this SD makes it suitable for antenna calibration. [ABSTRACT FROM AUTHOR]

A novel planar dielectric polarizer made of a low-profile high-dielectric-constant material is proposed. Two anisotropic antireflection layers are used on both sides to provide impedance transformation and anisotropy simultaneously. The proposed design uses a high-dielectric-constant material to reduce the overall thickness without severe reflections. The unit cells of the middle layer and the antireflection layer use separate periods for better adapting to the fabrication limitation. A polarizer prototype centered at 24 GHz is designed, fabricated, and measured. The prototype is 3-D-printed by commercial fused-deposition-modeling (FDM) technology using a material with a dielectric constant of 10. Experiments show that the prototype has a 25% operating bandwidth and a thickness of $0.52\lambda _{0}$ ($\lambda _{0}$ is the wavelength in the free space). The design methodology widens the choice for material selection and reduces the dimensions of the dielectric polarizer. [ABSTRACT FROM AUTHOR]

A highly miniaturized 3-D spherical folded dipole antenna has been reported, for which inherent impedance matching is achieved with respect to a practical source impedance by employing a simple series– $LC$ loading combination, thereby engineering its input impedance. In order to maximize its bandwidth, the miniaturized antenna employs a spherical helix structure as the folded arm that occupies the full volume of the corresponding Chu sphere. A bifilar (two folded arms) and a quadrifilar (four folded arms) helix loaded folded dipole antenna are designed, and full-wave simulations show that both the resulting antennas demonstrate excellent impedance matching when miniaturized by 85% in comparison to a resonant dipole operating at the same frequency. Despite the high degree of miniaturization, the resulting radiation efficiencies for the bifilar and quadrifilar antennas are found to be 87.1% and 90.6%, respectively. Furthermore, various quality-factor definitions are explored for the quadrifilar antenna, and it is observed that the resulting quality factor is around 1.83 (1.22) times that predicted by the Chu (Thal) lower bound. [ABSTRACT FROM AUTHOR]

In this communication, we present a miniaturized multiband metamaterial (MTM)-based antenna for array applications, operating with good radiation performance over the long term evolution (LTE) and Universal Mobile Telecommunications System (UMTS) uplinks within the 800–3000 MHz range. Each antenna element consists of a radiator and an MTM reflector. The former is a miniaturized Archimedean spiral antenna with an integrated matching line. The latter is placed 39 mm below the radiator and is shared among the multiple elements in the array application. The radiator is very compact, a square of 75 mm per side, equivalent to only 0.2 (0.75) times the free-space wavelength at 800 MHz (3000 MHz). The reflector is incorporated to achieve half-space radiation and is implemented with a novel multilayered MTM structure to improve the radiation efficiency. The MTM, moreover, is used in a nonconventional way. In fact, we take advantage of its complete phase-response function, behaving, thus, as a magnetic or electric conductor in different parts of the band. In this way, the in-phase reflection is not limited by the typical narrow bandwidth of artificial magnetic conductors. The measured $S_{11}$ parameter is less than −8 dB and the simulated gain is greater than 4.2 dBi in a range exceeding the one covered by the UMTS and LTE uplinks. Furthermore, a $2\times 2$ antenna array was also built. The reflections of each element are similar to those obtained in the single-element antenna. [ABSTRACT FROM AUTHOR]

The major axis of the elliptically polarized wave generated by a linearly polarized (LP) radiating source and an artificial anisotropic polarizer has been analyzed in this communication. Both theoretical and experimental results show that the major axis of the elliptically polarized wave generated by such a combination has an angle of 0° or 90° to the E-plane of the LP radiator. The angle between the major axis and the E-plane depends on the phase difference of the two orthogonal electric components after propagating through the polarizer. Measurement has been conducted for verification which covered the entire V-band (50–75 GHz). The result in this communication provides instructions for the usage of artificial anisotropic polarizers in detection and measurement, such as the calculation of the polarization efficiency during transmission. [ABSTRACT FROM AUTHOR]

An omnidirectional wireless local area network (WLAN) loop-slot antenna with common-mode current (CMC) suppression is proposed in this communication. First, based on the analysis of the equivalent model of odd–even mode, the feeding coaxial line is led out at the voltage-zero point of the loop-slot element, which suppresses the CMC over the full band. Second, through the theory of array, three loop-slot elements form an array to obtain omnidirectional radiation. Finally, the physical size is reduced by loading Stubs T in the slot. The roundness of the radiation pattern is modified by the Stubs T and the chamfering edge of the antenna. A prototype of the proposed antenna was fabricated and measured. The measured results show that the antenna achieves $\vert \text{S}_{11}\vert < -10$ dB in bands of 2.15–2.65 and 4.85–5.92 GHz. In addition, the roundness is 0.95 dB at 2.4 GHz, 1.84 dB at 5.2 GHz, and 2.43 dB at 5.8 GHz. The antenna effectively suppresses the CMC to keep a favorable roundness over a wide band, showing its potential in WLAN communication systems. [ABSTRACT FROM AUTHOR]

The orbital angular momentum (OAM) based communication is a promising technology in the wireless communication system for its improving spectrum efficiency. However, for the OAM demultiplexing, it requires a very large aperture size in the receiving end due to the OAM beam divergence and the amplitude null in the beam center, which restricts the full development of OAM based communication. In this paper, we propose a novel partial arc sampling receiving (PASR) scheme based on the augmented dynamic mode decomposition (ADMD) to solve this issue. We explore the use of the phase delay coordinates in the conventional DMD to sort the arbitrary OAM modes with arc sampling receiving. Simulation results demonstrate the accuracy and robustness of the proposed approach in sorting both integral and fractional OAM modes with the PASR scheme. Our work offers a practical approach for demultiplexing OAM beams in radio communication systems with fewer receiving devices, especially for the long-distance transmission case. [ABSTRACT FROM AUTHOR]

The performance of piezoelectric ultrasonic transducer (PUT) is obviously affected by its matching layer. An intelligent optimization method for matching layer of PUT is proposed to fabricate PUT with high performance. The original data, including matching layer and performance parameters of PUT, is obtained by PiezoCAD software. Then the neural network models are established to mathematically characterize the effect of matching layer on the performance of PUT. The optimization criteria for PUT is constructed according to its performance requirements, such as center frequency (CF), bandwidth (BW) and pulse width (PW). In order to decrease the material cost, the thicknesses of matching layers are also considered in the optimization criteria. The modified particle swarm optimization algorithm is used to optimize the thicknesses of matching layers (Ag-epoxy and Parylene C). According to the designed performance, the optimized thicknesses of Ag-epoxy and Parylene C are about 54 μm and 21 μm, respectively. Based on the optimized thicknesses of matching layers, the simulated and experimental performances of PUT well agree with the designed ones. In addition, compared to the traditional quarter-wavelength theory, the proposed method can effectively decrease the materials cost. The −6dB BW and PW of PUT fabricated according to the optimized parameters are about 68.5% and 0.123 μs, which are better than that fabricated according to the quarter-wavelength theory (about 50% and 0.147 μs). [ABSTRACT FROM AUTHOR]

An optimization design strategy is developed for ultrasonic transducer (UT) with multimatching layer to improve its performance. The piezoelectric equivalent circuit model is used to determine the optimization interval of matching layer, and the PiezoCAD software is used to simulate the performance of UT with multimatching layer. The neural network (NN) models are trained by the simulation data to characterize the relationship between the thickness of matching layer and performance of UT. Then, the multiobjective optimality criteria for UT is established based on its performance parameters, including center frequency (CF), −6 dB bandwidth (BW) and pulsewidth (PW). The thickness of matching layer is optimized by particle swarm optimization (PSO) algorithm. According to the designed performance, the optimized copper thickness and parylene thickness are about 17.76 and 23.05 μm, respectively. The simulation results of UT with the optimized multimatching layer well agree with the designed targets. Also, CF, −6 dB BW, and PW of the fabricated UT with the optimized multimatching layer are 5.672 MHz, 50.08%, and 0.295 μs, respectively, which nearly achieve the designed performance. In addition, the performance of UT with the optimized multimatching layer is much better than that of UT without matching layer. Moreover, compared with UT with single or double matching layers determined by the quarter wavelength theory, the UT with the optimized multimatching layer has better comprehensive performance. Finally, the fabricated UT with the optimized multimatching layer is used to measure the thickness of testing block, and the relative errors are all less than 1.0%, which implies that the optimized UT has excellent performance. [ABSTRACT FROM AUTHOR]

In order to effectively and flexibly control acoustic pattern, an efficient optimization design method of acoustic liquid lens (ALL) is developed by the frame of particle swarm optimization (PSO) algorithm. The ALL is composed of ethanol and dimethicone, and its parameters include ethanol concentration (EC), volume fraction of dimethicone (VFD), and total volume (TV). Based on the established finite element model and orthogonal design method, the data of acoustic pattern and ALL can be obtained by using COMSOL Multiphysics. Based on the simulation data, the neural network models are constructed to characterize the relationship between the parameters of ALL and the performance of acoustic pattern. The optimization design criteria of ALL are constructed based on the performance parameters of acoustic pattern, including focal distance (FD), transverse resolution (TR), and longitudinal resolution (LR). Based on the optimization criteria, the modified PSO algorithm is utilized to optimize the design parameters of ALL in the developed method. According to the desired FD, TR, and LR of acoustic pattern (20, 1, and 17 mm), the optimized EC, VFD, and TV of ALL are about 0.838, 0.165, and 164.4 μL. The performance parameters of acoustic pattern verified by simulation and experiments agree with the desired ones. In addition, using 6 MHz ultrasonic transducer with the optimized ALL, the ultrasonic imaging of tungsten wires and porcine eyeball further demonstrates the effectiveness and feasibility of the developed method. [ABSTRACT FROM AUTHOR]

In this letter, we present a dual-polarized orbital angular momentum multiple-input.multiple-output (OAM-MIMO) with uniform circular arrays (UCAs) that achieves a transmission rate of over 200 Gb/s. We design and evaluate the properties of microstrip antennas on 28 GHz band and then fabricate the antennas and implement them on a transmitter and receiver with four UCAs disposed concentrically. Each UCA consists of 16 microstrip antenna elements and is connected to a Butler matrix that can generate and separate five OAM modes (±2, ±1, and 0). There is also a center antenna capable of transmitting mode 0, so the total number of antenna elements is 65 and 21 streams can be transmitted simultaneously. In order to maximize the transmission capacity, we use polarization multiplexing. We conduct two data transmission experiments at a distance of 10 m. In the experiment of virtual dual-polarized OAM-MIMO transmission, we achieved approximately 110 Gb/s transmission for both polarizations. In the experiment of 21 streams, simultaneous transmission of dual-polarized OAM-MIMO, the result of 201.5 Gb/s was achieved. [ABSTRACT FROM AUTHOR]

Due to the low efficiency of traditional design method, an efficient optimization design method is developed to design and fabricate high-performance ultrasonic transmitting transducer (UTT) based on PiezoCAD software and particle swarm optimization (PSO) algorithm. Based on the data of design and performance parameters of UTT obtained by PiezoCAD software, the genetic algorithm-based back-propagation neural networks (GA-BPNNs) are established to describe their mapping relationship. The optimality criterions are established based on the performance parameters including center frequency (CF) and maximum echo amplitude (MEA). Then, based on the established GA-BPNNs and optimality criterions, the optimization design method of UTT is developed under the framework of PSO algorithm. According to the desired performance, the design parameters of UTT, including the thickness and diameter of PZT-4 (Pb(ZrxTi1-x)O3), the acoustic impedance of backing, are optimized by the developed method, and they are 2 mm, 30 mm and 3 MRayl, respectively. Based on the optimized design parameters, the CF and MEA simulated by PiezoCAD are 1.05 MHz and -45.1 dB, which are in good agreement with the designed ones (1 MHz and -45 dB). In addition, the CF of the fabricated UTT is 1.07 MHz, and its insertion loss is -7.2 dB at 1.075MHz, which implies that the fabricated UTT has excellent performance. Therefore, the developed optimization design method is effective to fabricate high-performance UTT. [ABSTRACT FROM AUTHOR]

Radio waves carrying orbital angular momentum (OAM) have been intensively studied in recent years with respect to generation, propagation, and communication. In this article, the effect of an infinite ground on OAM wave propagation and communication is investigated numerically using the method of moments (MoM). A circular array of half-wavelength dipoles is taken as a uniform circular array, for the generation and reception of OAM waves. First, electromagnetic image theory is adopted for analysis and numerical investigation of image OAM arrays and their influence of reflections from the ground plane. Employing MoM and mixed-mode scattering parameters, the impact of the ground plane on wireless communication is further explored by varying the communication distances between the transmitting and receiving arrays, heights of OAM arrays above the ground, and array orientations. Compared to OAM-based communication in free space, the effect of the ground plane turns out to be considerable. Specifically, it was found that OAM-based communication not only suffers from destructive influence due to reflections from the ground but also from reduced mode isolation. The results obtained in this article will be fundamental for optimizing OAM-based communication in a realistic environment. [ABSTRACT FROM AUTHOR]

The orbital angular momentum (OAM) in radio frequency is expected to provide a new dimension to the OAM mode and benefit the degree of freedom of the electromagnetic wave. However, a central energy hollow exists in the OAM-carrying beam, and its radius varies with the OAM mode values, which is the main bottleneck in the radio frequency OAM applications. This article proposes a solution to eliminate the central hollow, by fundamentally changing the transmitted signal of the uniform circular array (UCA). To generate the unidirectional beam pattern, defined as the beaming OAM (BOAM), the orthogonal waveforms are radiated by UCA with an equidifferent initial phase. The BOAM wave can be received by one single antenna, and the separate OAM mode demodulation is then achieved based on the waveform diversity. This article studies the theoretical model of the BOAM field distribution and shows that the waveform diversity among distributed units can not only alter the doughnut-like shape into the closed beam, but also maintain the intact vortex characteristic. On this basis, the extended OAM mode multiplexing system is designed with one single UCA. A 16-element UCA is shown to be capable of generating 15 OAM modes simultaneously, with all modes superposing on the same direction. Furthermore, it is verified by the simulation that the vortex phase of each single mode can be precisely extracted from the OAM-mode-multiplexing signal. [ABSTRACT FROM AUTHOR]

The emerging orbital angular momentum (OAM) based wireless communication is expected to be a high spectrum-efficiency communication paradigm to solve the growing transmission data rate and limited bandwidth problem. Academic researchers mainly concentrate on the OAM-based line-of-sight (LoS) communications. However, there exist some surroundings around the transceiver in most practical wireless communication scenarios, thus forming multipath transmission. In this paper, a hybrid orthogonal division multiplexing (HODM) scheme by using OAM multiplexing and orthogonal frequency division multiplexing (OFDM) in conjunction is proposed to achieve high-capacity wireless communications in sparse multipath environments, where the scatterers are sparse. We first build the OAM-based wireless channel in a LoS path and several reflection paths combined sparse multipath environments. We concentrate on less than or equal to three-time reflection paths because of the severe energy attenuation. The phase difference among the channel amplitude gains of the LoS and reflection paths, which is caused by the reflection paths, makes it difficult to decompose the OAM signals. We propose the phase difference compensation to handle this problem and then calculate the corresponding capacity in radio vortex wireless communications. Numerical results illustrate that the capacity of wireless communications by using our proposed HODM scheme can be drastically increased in sparse multipath environments. [ABSTRACT FROM AUTHOR]

Implantable device miniaturization is a cornerstone in modern medicine and the key to unlock new and exciting applications for both monitoring and treatment of diseases. Such miniaturization can be facilitated resorting to miniaturized antennas that will support wireless communications, wireless power transfer (WPT), and energy-harvesting applications. The development of such new miniaturized devices is being supported by innovative fabrication and integration technologies that will lead to challenges in antenna design and characterization. In this article, a miniaturized microantenna produced with a self-folding technique is presented, as well as its characterization challenges. The microcube antenna’s geometry ($500\times 500\times 500\,\,\mu \text{m}^{3}$) is optimized for operation inside biological tissue, and an interface board that allows interfacing the antenna with characterization equipment is presented. The antenna’s radiation pattern is obtained both experimentally and numerically, where a good agreement between both the results was achieved. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the method of autonomous hovering control for the biomimetic underwater robot named RobCutt-II. First, a modular configuration for mimicry of undulatory propulsion is presented, followed by a coordinated control of dual fins for enhancing the maneuverability and stability of the RobCutt-II. Then the vision-based hovering problem is formulated. A dual-loop hovering control framework integrating an image processing module, a tracking differentiator, a hovering controller, a velocity controller, and a fuzzy-based control allocation module is proposed to govern the locomotion of the RobCutt-II. Finally, simulations and experimental results demonstrate the effectiveness of the proposed mechanical design and control methods. [ABSTRACT FROM AUTHOR]