Helical Array Research Articles

Designing a Compact Helical Slot Antenna for Multiple Circularly Polarized OAM Modes

In this letter, a helical slot antenna for generating multiple orbital angular momentum (OAM) modes is proposed. The proposed antenna consists of four concentric helical slot array antennas, which are excited by an annular microstrip line. The number of each helical slot, and length of microstrip feed are chosen to create circularly polarized OAM modes of 0, −1, −2, and −3 at 3.5 GHz frequency with more than 10% fractional bandwidth. The final multimode antenna has 89 mm in diameter and 19.1 mm in height. A prototype of the proposed compact antenna is fabricated. From the simulation and measurement results, prominent spiral phase planes are observed at all antenna ports. Both the measurement and simulation results show that the proposed compact antenna has valuable features to produce different vortex modes.

An only metal, compact, and circular polarizer designed with helical array rods

This paper presents a simple method to realize a circular polarizer by inserting rods arranged helically in a cylindrical waveguide. In the proposed polarizer, the rods are installed to excite the electric fields perpendicular to the input field. In addition, the rod locations create a 90° phase difference between two perpendicular axes to convert the polarization from linear to circular. In the proposed structure, the axial ratio is smaller than 0.4 dB, and the phase difference is approximately 90° at a frequency of 10 GHz. In addition, the reflection coefficients are better than −14 dB for both the E x ${E_x}$ and E y ${E_y}$ polarizations at the same frequency. Additionally, this structure is very compact compared to similar systems. Furthermore, this is made only of metal. Therefore, there is no dielectric loss. The validation results are in good agreement with the simulation.

Fast Phase Recognition of Mechanical Helical Phased Array Antenna Element Based on Line-Scan Machine Vision

Fast Phase Recognition of Mechanical Helical Phased Array Antenna Element Based on Line-Scan Machine Vision

Generation of Square Optical Vortex Array and Optical Helix Array by Periodic Orthogonal Binary Phase Plate

Generation of Square Optical Vortex Array and Optical Helix Array by Periodic Orthogonal Binary Phase Plate

A Novel 3D Helical Microelectrode Array for In Vitro Extracellular Action Potential Recording.

Recent advances in cell and tissue engineering have enabled long-term three-dimensional (3D) in vitro cultures of human-derived neuronal tissues. Analogous two-dimensional (2D) tissue cultures have been used for decades in combination with substrate integrated microelectrode arrays (MEA) for pharmacological and toxicological assessments. While the phenotypic and cytoarchitectural arguments for 3D culture are clear, 3D MEA technologies are presently inadequate. This is mostly due to the technical challenge of creating vertical electrical conduction paths (or ‘traces’) using standardized biocompatible materials and fabrication techniques. Here, we have circumvented that challenge by designing and fabricating a novel helical 3D MEA comprised of polyimide, amorphous silicon carbide (a-SiC), gold/titanium, and sputtered iridium oxide films (SIROF). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) testing confirmed fully-fabricated MEAs should be capable of recording extracellular action potentials (EAPs) with high signal-to-noise ratios (SNR). We then seeded induced pluripotent stems cell (iPSC) sensory neurons (SNs) in a 3D collagen-based hydrogel integrated with the helical MEAs and recorded EAPs for up to 28 days in vitro from across the MEA volume. Importantly, this highly adaptable design does not intrinsically limit cell/tissue type, channel count, height, or total volume.

Predictive gamma passing rate of 3D detector array-based volumetric modulated arc therapy quality assurance for prostate cancer via deep learning.

To predict the gamma passing rate (GPR) of the three-dimensional (3D) detector array-based volumetric modulated arc therapy (VMAT) quality assurance (QA) for prostate cancer using a convolutional neural network (CNN) with the 3D dose distribution. One hundred thirty-five VMAT plans for prostate cancer were selected: 110 plans were used for training and validation, and 25 plans were used for testing. Verification plans were measured using a helical 3D diode array (ArcCHECK). The dose distribution on the detector element plane of these verification plans was used as input data for the CNN model. The measured GPR (mGPR) values were used as the training data. The CNN model comprises eighteen layers and predicted GPR (pGPR) values. The mGPR and pGPR values were compared, and a cumulative frequency histogram of the prediction error was created to clarify the prediction error tendency. The correlation coefficients of pGPR and mGPR were 0.67, 0.69, 0.66, and 0.73 for 3%/3-mm, 3%/2-mm, 2%/3-mm, and 2%/2-mm gamma criteria, respectively. The respective mean±standard deviations of pGPR-mGPR were -0.87±2.18%, -0.65±2.93%, -0.44±2.53%, and -0.71±3.33%. The probabilities of false positive error cases (pGPR < mGPR) were 72%, 60%, 68%, and 56% for each gamma criterion. We developed a deep learning-based prediction model of the 3D detector array-based VMAT QA for prostate cancer, and evaluated the accuracy and tendency of prediction GPR. This model can provide a proactive estimation for the results of the patient-specific QA before the verification measurement.

Measurements of magnetic field fluctuations in TJ-II plasmas with new in-vessel helical arrays of magnetic coils.

This paper describes two new helical arrays of magnetic coils recently installed inside the TJ-II vacuum vessel. Their main objective is the precise measurement of the spatial periodicity of the magnetohydrodynamic perturbations usually found in the TJ-II plasmas. Given the high probability of coil failures due to the harsh plasma environment and in view of the extremely difficult access to the TJ-II vessel interior for maintenance, the coil system has been divided in two quasi-identical helical arrays. Both arrays consist of 32 triaxial sensors measuring orthogonal components of the local magnetic field along an ideal helical path whose trajectory runs close to the plasma edge. A description of the main characteristics of coils and arrays as well as their nominal positioning along an ideal helical path, inside the vessel, is given. A precise experimental determination of the real spatial orientation of the coils is performed by comparing the signals measured in current ramp-up and ramp-down experiments with calculations based on a filamentary model for the TJ-II magnetic coils. After this fine calibration procedure, it is possible to analyze the dependence of the amplitude of the measured magnetic field and its fluctuations as a function of the coil distance to the last closed flux surface. The study of the phase evolution of the parallel and perpendicular oscillatory components is also enabled. Finally, two examples of mode number determination are shown. One corresponds to a low frequency mode appearing in pure electron cyclotron resonance heating plasma, and the other one shows several modes observed during combined injection of both co and counter neutral beams and identified as shear Alfvén waves.

Activation of the myosin motors in fast-twitch muscle of the mouse is controlled by mechano-sensing in the myosin filaments.

Myosin motors in resting muscle are inactivated by folding against the backbone of the myosin filament in an ordered helical array and must be released from that conformation to engage in force generation. Time‐resolved X‐ray diffraction from single fibres of amphibian muscle showed that myosin filament activation could be inhibited by imposing unloaded shortening at the start of stimulation, suggesting that filaments were activated by mechanical stress. Here we improved the signal‐to‐noise ratio of that approach using whole extensor digitorum longus muscles of the mouse contracting tetanically at 28°C. Changes in X‐ray signals associated with myosin filament activation, including the decrease in the first‐order myosin layer line associated with the helical motor array, increase in the spacing of a myosin‐based reflection associated with packing of myosin tails in the filament backbone, and increase in the ratio of the 1,1 and 1,0 equatorial reflections associated with movement of motors away from the backbone, were delayed by imposing 10‐ms unloaded shortening at the start of stimulation. These results show that myosin filaments are predominantly activated by filament stress, as in amphibian muscle. However, a small component of filament activation at zero load was detected, implying an independent mechanism of partial filament activation. X‐ray interference measurements indicated a switch‐like change in myosin motor conformation at the start of force development, accompanied by transient disordering of motors in the regions of the myosin filament near its midpoint, suggesting that filament zonal dynamics also play a role in its activation. Key points Activation of myosin filaments in extensor digitorum longus muscles of the mouse is delayed by imposing rapid shortening from the start of stimulation.Stress is the major mechanism of myosin filament activation in these muscles, but there is a small component of filament activation during electrical stimulation at zero stress.Myosin motors switch rapidly from the folded inhibited conformation to the actin‐attached force‐generating conformation early in force development.

Supramolecular Ensembles Formed via Calix[5]arene-Fullerene Host-Guest Interactions.

This Review introduces the research directions for the synthesis of supramolecular fullerene polymers. First, the discovery of host-guest complexes of pristine fullerenes is briefly outlined. We focus on progress in supramolecular fullerene polymers directed by the use of calix[5]arene-fullerene interactions, which comprise linear, networked, helical arrays of fullerenes in supramolecular ensembles. The unique self-sorting behavior of right-handed and left-handed helical supramolecular fullerene arrays is discussed. Thereafter, an extensive investigation of the calix[5]arene-fullerene interaction for control over the chain structures of covalent polymers is introduced.

Cooling intact and demembranated trabeculae from rat heart releases myosin motors from their inhibited conformation.

Myosin filament-based regulation supplements actin filament-based regulation to control the strength and speed of contraction in heart muscle. In diastole, myosin motors form a folded helical array that inhibits actin interaction; during contraction, they are released from that array. A similar structural transition has been observed in mammalian skeletal muscle, in which cooling below physiological temperature has been shown to reproduce some of the structural features of the activation of myosin filaments during active contraction. Here, we used small-angle x-ray diffraction to characterize the structural changes in the myosin filaments associated with cooling of resting and relaxed trabeculae from the right ventricle of rat hearts from 39°C to 7°C. In intact quiescent trabeculae, cooling disrupted the folded helical conformation of the myosin motors and induced extension of the filament backbone, as observed in the transition from diastole to peak systolic force at 27°C. Demembranation of trabeculae in relaxing conditions induced expansion of the filament lattice, but the structure of the myosin filaments was mostly preserved at 39°C. Cooling of relaxed demembranated trabeculae induced changes in motor conformation and filament structure similar to those observed in intact quiescent trabeculae. Osmotic compression of the filament lattice to restore its spacing to that of intact trabeculae at 39°C stabilized the helical folded state against disruption by cooling. The myosin filament structure and motor conformation of intact trabeculae at 39°C were largely preserved in demembranated trabeculae at 27°C or above in the presence of Dextran, allowing the physiological mechanisms of myosin filament-based regulation to be studied in those conditions.

The crystal structure of MreC provides insights into polymer formation.

MreC is a scaffold protein required for cell shape determination through interactions with proteins related to cell wall synthesis. Here, we determined the crystal structure of the major periplasmic part of MreC from Escherichia coli at 2.1 Å resolution. The periplasmic part of MreC contains a coiled‐coil domain and two six‐stranded barrel domains. The coiled‐coil domain is essential for dimer formation, and the two monomers are prone to relative motion that is related to the small interface of β‐barrel domains. In addition, MreC forms an antiparallel filament‐like structure along the coiled‐coil direction, which is different from the helical array structure in Pseudomonas aeruginosa. Our structure deepens our understanding of polymer formation of MreC.

Modulation Mechanism of Vortex Beam by Helical Microporous Array

Modulation Mechanism of Vortex Beam by Helical Microporous Array

Merging Supramolecular and Covalent Helical Polymers: Four Helices Within a Single Scaffold.

Supramolecular and covalent polymers share multiple structural effects such as chiral amplification, helical inversion, sergeants and soldiers, or majority rules, among others. These features are related to the axial helical structure found in both types of materials, which are responsible for their properties. Herein a novel material combining information and characteristics from both fields of helical polymers, supramolecular (oligo(p-phenyleneethynylene) (OPE)) and covalent (poly(acetylene) (PA)), is presented. To achieve this goal, the poly(acetylene) must adopt a dihedral angle between conjugated double bonds (ω1) higher than 165°. In such cases, the tilting degree (Θ) between the OPE units used as pendant groups is close to 11°, like that observed in supramolecular helical arrays of these molecules. Polymerization of oligo[(p-phenyleneethynylene)n]phenylacetylene monomers (n = 1, 2) bearing L-decyl alaninate as the pendant group yielded the desired scaffolds. These polymers adopt a stretched and almost planar polyene helix, where the OPE units are arranged describing a helical structure. As a result, a novel multihelix material was prepared, the ECD spectra of which are dominated by the OPE axial array.

Self-organization of rectangular bipyramidal helical columns by supramolecular orientational memory epitaxially nucleated from a Frank-Kasper σ phase

Programming living and soft complex matter via primary structure and self-organization represents the key methodology employed to design functions in biological and synthetic nanoscience. Memory effects have been used to create commercial technologies including liquid crystal displays and biomedical applications based on shape memory polymers. Supramolecular orientational memory (SOM), induced by an epitaxial nucleation mediated by the close contact spheres of cubic phases, emerged as a pathway to engineer complex nanoscale soft matter of helical columnar hexagonal arrays. SOM preserves the crystallographic directions of close contact supramolecular spheres from the 3D phase upon cooling to the columnar hexagonal periodic array. Despite the diversity of 3D periodic and quasiperiodic nanoarrays of supramolecular dendrimers, including Frank-Kasper and quasicrystal, all examples of SOM to date were mediated by Im3¯m (body-centered cubic, BCC) and Pm3¯n (Frank-Kasper A15) cubic phases. Expanding the scope of SOM to non-cubic arrays is expected to generate additional morphologies that were not yet available by any other methods. Here we demonstrate the SOM of a dendronized triphenylene that self-organizes into helical columnar hexagonal and tetragonal P42/mnm (Frank-Kasper σ) phases. Structural analysis of oriented fibers by X-ray diffraction reveals that helical columnar hexagonal domains self-organize an unusual rectangular bipyramidal morphology upon cooling from the σ phase. The discovery of SOM in a non-cubic Frank-Kasper phase indicates that this methodology may be expanded to other periodic and quasiperiodic nanoarrays organized from self-assembling dendrimers and, most probably, to other soft and living complex matter.

Control of phase, polarization, and amplitude based on geometric phase in a racemic helix array

The Pancharatnam–Berry geometric phase has attracted great interest due to the elegant phase control strategy via geometric transformation of optical elements. The commonly used geometric phase is associated with circular polarization states. Here, we show that by exploiting the geometric phase associated with the two elliptical eigen-polarization states in a racemic metallic helix array, exotic features including full range phase modulation for linear polarization states, diverse polarization conversion, and full complex amplitude modulation can be obtained with rotation of the helices. As a proof of concept, several devices for implementing polarization conversion, vortex beam generating, and lateral dual focusing are built with a racemic helix array in the microwave regime. The calculated and experimental results validate our proposals, which can stimulate various advanced metadevices.

Three-Dimensional Transition Metal Dichalcogenide Helical Nanorod Arrays for High-Performance Aluminum-Ion Batteries

The rechargeable aluminum-ion battery (AIB) is a promising candidate for next-generation high-performance batteries, but its cathode materials require more development to improve their capacity and cycling life. We have demonstrated the growth of MoSe2 three-dimensional helical nanorod arrays on a polyimide substrate by the deposition of Mo helical nanorod arrays followed by a low-temperature plasma-assisted selenization process to form novel cathodes for AIBs. The growth MoSe2 HNRAs on PI substrates as the cathode in AIBs with extremely high performance was realized by glancing angle deposition followed by a low-temperature plasma-assisted selenization process. These binder-free MoSe2 HNRA-based AIBs showed a specific capacity of 753 mAh g–1 at a current density of 0.3 A g–1 and an ultralong cycling life of at least 1000 cycles even at a higher current density. Ex situ Raman, XPS, and TEM techniques were applied to the MoSe2 HNRA cathode at the different discharge–charge statuses and confirmed the reversible conversion–intercalation hybrid reactions. Furthermore, plane-interdigital flexible and stretchable MoSe2 HNRA-based AIBs were produced, revealing excellent flexibility and stretchability. The AIBs with MoSe2 HNRAs as cathodes exhibited a high capacity and cycle life, making it possible for these AIBs used in future applications of energy-storage devices in flexible and wearable electronics.

Flexible Three-Dimensional Helical Molybdenum Diselenide Nanorod Arrays for High-Performance Magnesium Rechargeable Batteries

Rechargeable magnesium (Mg) batteries have received considerable attention as a promising candidate for next-generation high-performance batteries with the theoretic advantages of lower cost, better safety, and even higher energy density than lithium-ion batteries. In this work, we have created three-dimensional helical nanorod arrays of MoSe2 derived from Mo arrays grown by glancing angle deposition (GLAD) on a polyimide substrate, through a low-temperature plasma-assisted selenization process to form novel cathodes for magnesium ion batteries (MIB). The advanced 3D MoSe2 based MIB cathode shows a specific capacity of 179 mAh g–1 at a current density of 0.1 A g–1 , and maintains 123 mAh g–1 at a current density of 0.1 A g–1 after 200 cycles. A detail investigation of the chemical bonding in MoSe2 cathode during charge and discharge has been taken by Raman, XPS and TEM. Furthermore, we also demonstrated exploratory works on interdigital flexible MIBs and stretchable MIBs, exhibiting a stable output performance under various bending and stretching states. To such selenide nanostructure-based MIBs, this method proves a huge potential for future applications of energy-storage devices in flexible and wearable electronics.

Computational Modeling of Chromatin Fiber to Characterize Its Organization Using Angle-Resolved Scattering of Circularly Polarized Light.

Understanding the structural organization of chromatin is essential to comprehend the gene functions. The chromatin organization changes in the cell cycle, and it conforms to various compaction levels. We investigated a chromatin solenoid model with nucleosomes shaped as cylindrical units arranged in a helical array. The solenoid with spherical-shaped nucleosomes was also modeled. The changes in chiral structural parameters of solenoid induced different compaction levels of chromatin fiber. We calculated the angle-resolved scattering of circularly polarized light to probe the changes in the organization of chromatin fiber in response to the changes in its chiral parameters. The electromagnetic scattering calculations were performed using discrete dipole approximation (DDA). In the chromatin structure, nucleosomes have internal interactions that affect chromatin compaction. The merit of performing computations with DDA is that it takes into account the internal interactions. We demonstrated sensitivity of the scattering signal’s angular behavior to the changes in these chiral parameters: pitch, radius, the handedness of solenoid, number of solenoid turns, the orientation of solenoid, the orientation of nucleosomes, number of nucleosomes, and shape of nucleosomes. These scattering calculations can potentially benefit applying a label-free polarized-light-based approach to characterize chromatin DNA and chiral polymers at the nanoscale level.

The sperm structure and the spermiogenesis of the drugstore beetle Stegobium paniceum (L.) (Coleoptera-Ptinidae-Anobinae)

We describe in this paper the morphology of the male reproductive system, the spermiogenesis and the sperm ultrastructure of the drugstore beetle S. paniceum (L) (Coleoptera, Ptinidae). The male reproductive apparatus has a pair of long testes with six follicles, filled with cysts, each containing 128 germ cells. The sperm is about 480 μm long and is endowed of an apical spiral cylindrical acrosome, 1.7 μm long. The nucleus, 25 μm long, is also cylindrical at maturity. During spermiogenesis the nuclear envelope gives rise to two ovoid membranous structures flanking the nucleus for its whole length. The centriole adjunct material is configurated as concentric electron-dense rings. The flagellar components have a helical array; the axoneme has the typical 9 + 9+2 pattern for most of its length, but in the posterior flagellar region it modifies greatly its ultrastructure and is embedded in an electron-dense material. The two accessory bodies have a crescent-moon shape in the mature sperm, but at the beginning of spermiogenesis they are small structures lateral to the axoneme, later assuming a crescent-moon structure. A flattened cistern located between the axoneme and the plasma membrane is present in the early spermatids, but soon it fuses with the plasma membrane. Two symmetrical, largely crystallized mitochondrial derivatives are present for most of the flagellar length. S. paniceum and Lasioderma serricorne share several sperm structures. Ultrastructural results and molecular data confirm a close relationship between these two species and support their positioning within Ptinidae.

Transmission of electromagnetic wave through an in-plane square array of small helices overlying a dielectric slab

Transmission of a linear polarized electromagnetic wave through an infinite square array of small helices overlying a dielectric layer has been investigated by using semi-analytical method. The possibility of an abrupt change of polarization characteristics of the transmitted wave at varying of wavelengths in the vicinity of the waveguide resonance in a dielectric slab has been demonstrated. The phenomenon can prove useful for creation of switching devices, for light polarization control, for fine tuning of laser emission frequency, for precise measurement of the refraction index of dielectric media and for solving some other spectroscopy problems.