Spherical Helix Research Articles

Two Types of Bandwidth Evaluation of Crossed Spherical Helix Antennas Using Numerical Simulation

Two Types of Bandwidth Evaluation of Crossed Spherical Helix Antennas Using Numerical Simulation

Rapid construction of electrically small spherical and cylindrical antennas

Using three-dimensional (3D) printing technologies, two of the folded electrically small antennas (FESAs) are simulated, fabricated, and evaluated. A folded spherical helix and a cylindrical helix are chosen as a part of the verification of this fabrication process. FESAs are constructed on the polylactic acid (PLA) material-based 3D printed support and the effect of this extra support on antenna performances are discussed. The similarity index between measured and simulated performance parameters of both spherical helix and cylindrical helix shaped FESAs is high. The fabrication process is faster, dependable and provides the design flexibility of any complex-shaped spiral antenna.

Osculating mate of a Frenet curve in the Euclidean 3-space

A new kind of partner curves called osculating mate of a Frenet curve is introduced. Some characterizations for osculating mate are obtained and using the obtained results some special curves such as slant helix, spherical helix, C-slant helix and rectifying curve are constructed.

Closed-Form Expression of Radiation Characteristics for Electrically Small Spherical Helix Antennas

To understand the radiation mechanism of an electrically small spherical helix antenna, we develop a theory on the radiation characteristics of the antenna. An analytical model of the antenna presuming a current on the wire to be sinusoidally distributed is proposed and analyzed with the spherical wave expansion. The radiation efficiency, radiation resistance, and radiation patterns are obtained in closed-form expression. The radiation efficiency evidently varies with the surface area of the wire and the radiation resistance depends on the square of the length of the wire. The obtained result for the radiation pattern illustrates the tilt of the pattern caused by the modes asymmetric to the z-axis. The radiation efficiency formula indicates a good agreement between the simulation and measurement result. In addition, the radiation resistance of the theoretical and simulation results exhibits good agreement. Considering the effect of the feeding structure of the fabricated antenna, the radiation resistance of the analytical model can be treated as a reasonable result. The result of radiation pattern also shows good agreement between the simulation and measurement results excluding a small contribution from the feeding cable acting as a scatterer.

Research on design and fabrication of micro ball end milling tool with flat edge and conical flank

The microball end mills are widely used in the processing of micro parts in the fields of aerospace. These micro parts are often made of hard to machine materials with high hardness and strength, such as martensitic stainless steel. As the main processing tool of these parts, the micro cutting tools wear fast and have a short service life. At the same time, because of the small diameter and complex structure of the micro ball end milling tool, its preparation process is complex, and its quality is difficult to guarantee. In order to solve the above problems, a micro ball end milling tool with a flat edge and conical flank (FC-MBMT) made of cemented carbide is proposed, which reduces the difficulty of tool preparation through the design of the flat edge, and reduces the friction between the flank and the machined surface through the design of the conical flank. Firstly, based on the theory of the spherical helix, the mathematical model of FC-MBMT was established. Then, the motion expression of each axis of the machine tool in the grinding process of FC-MBMT is obtained by deriving the transformation matrix between the machine tool coordinate system and the tool coordinate system. The precision grinding of the FC-MBMT is realized, and its geometric parameter error is less than 8%. Finally, based on the above methods, two kinds of FC-MBMT with a flank width of 16 μm and a flank width of 24 μm were prepared, and their cutting performance was verified by micro groove milling experiments of martensitic steel. Ordinary equal guide cutting edge ball end milling tool participated in the machining as a comparison item. The milling experiment results show that the surface roughness of the FC-MBMT is less than 0.52 μm and the total cutting force is less than 7 N. The machining quality of the FC-MBMT with a conical flank width of 16 μm is better than the FC-MBMT with a flank width of 24 μm, and its cutting force is smaller than the FC-MBMT with a flank width of 24 μm, which indicates that it has better cutting performance with a conical flank width of 16 μm. The wear morphology shows that the wear forms of the FC-MBMT are chip adhesion on the conical flank and slight cutting edge wear. The anti-wear ability of the FC-MBMT with a conical flank width of 16 μm is obviously better than the FC-MBMT with a flank width of 24 μm. Compared with the ordinary micro ball end milling tool, the cutting performance and wear resistance of the FC-MBMT with a flank width of 16 μm are not significantly different. The experimental results verify the feasibility of the proposed tool structure.

Transcranial Neuromodulation Array With Imaging Aperture for Simultaneous Multifocus Stimulation in Nonhuman Primates.

Even simple behaviors arise from the simultaneous activation of multiple regions in the brain. Thus, the ability to simultaneously stimulate multiple regions within a brain circuit should allow for better modulation of function. However, performing simultaneous multifocus ultrasound neuromodulation introduces challenges to transducer design. Using 3-D Fullwave simulations, we have designed an ultrasound neuromodulation array for nonhuman primates that: 1) can simultaneously focus on multiple targets and 2) include an imaging aperture for additional functional imaging. This design is based on a spherical array, with 128 15-mm elements distributed in a spherical helix pattern. It is shown that clustering the elements tightly around the 65-mm imaging aperture located at the top of the array improves targeting at shallow depths, near the skull surface. Spherical arrays have good focusing capabilities through the skull at the center of the array, but focusing on off-center locations is more challenging due to the natural geometric configuration and the angle of incidence with the skull. In order to mitigate this, the 64 elements closest to the aperture were rotated toward and focusing on a shallow target, and the 64 elements farthest from the aperture were rotated toward and focusing on a deeper target. Data illustrated that this array produced focusing on the somatosensory cortex with a gain of 4.38 and to the thalamus with a gain of 3.82. To improve upon this, the array placement was optimized based on phase aberration simulations, allowing for the elements with the largest impact on the gain at each focal point to be found. This optimization resulted in an array design that can focus on the somatosensory cortex with a gain of 5.19 and the thalamus with a gain of 4.45. Simulations were also performed to evaluate the ability of the array to focus on 28 additional brain regions, showing that off-center target regions can be stimulated, but those closer to the skull will require corrective steps to deliver the same amount of energy to those locations. This simulation and design process can be adapted to an individual monkey or human skull morphologies and specific target locations within individuals by using orientable 3-D printing of the transducer case and by electronic phase aberration correction.

Design of a Highly Miniaturized, Inherently Matched, Spherical Folded Dipole Antenna and Evaluation of Its Quality Factor

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– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> 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.

Characterization of Rectifying Curves by Their Involutes and Evolutes

A rectifying curve is a twisted curve with the property that all of its rectifying planes pass through a fixed point. If this point is the origin of the Cartesian coordinate system, then the position vector of the rectifying curve always lies in the rectifying plane. A remarkable property of these curves is that the ratio between torsion and curvature is a nonconstant linear function of the arc-length parameter. In this paper, we give a new characterization of rectifying curves, namely, we prove that a curve is a rectifying curve if and only if it has a spherical involute. Consequently, rectifying curves can be constructed as evolutes of spherical twisted curves; we present an illustrative example of a rectifying curve obtained as the evolute of a spherical helix. We also express the curvature and the torsion of a rectifying spherical curve and give necessary and sufficient conditions for a curve and its involute to be both rectifying curves.

Exact trajectory solutions of a spherical microswimmer under flow and external fields

Exact trajectoires of microswimmers under flow are determined analytically exhibiting intriguing patterns such as a spherical helix.

Magnetoreception in multicellular magnetotactic prokaryotes: a new analysis of escape motility trajectories in different magnetic fields.

Magnetotactic microorganisms can be found as unicellular prokaryotes, as cocci, vibrions, spirilla and rods, and as multicellular organisms. Multicellular magnetotactic prokaryotes are magnetotactic microorganisms composed by several magnetotactic bacteria organized almost in a spherical helix, and one of the most studied is Candidatus Magnetoglobus multicellularis. Several studies have shown that Ca. M. multicellularis displays forms of behavior not well explained by magnetotaxis. One of these is escape motility, also known as "ping-pong" motion. Studies done in the past associated the "ping-pong" motion to some magnetoreceptive behavior, but those studies were never replicated. In the present manuscript a characterization of escape motility trajectories of Ca. M. multicellularis was done for several magnetic fields, considering that this microorganism swims in cylindrical helical trajectories. It was observed that the escape motility can be separated into three phases: (I) when the microorganism jumps from the drop border, (II) where the microorganism moves almost perpendicular to the magnetic field and (III) when the microorganism returns to the drop border. The total time of the whole escape motility, the time spent in phase II and the displacement distance in phase I decreases when the magnetic field increases. Our results show that the escape motility has several characteristics that depend on the magnetic field and cannot be understood by magnetotaxis, with a magnetoreceptive mechanism being the best explanation.

Investigation of spherical helix inflatable mechanism for capture of space debris

Investigation of spherical helix inflatable mechanism for capture of space debris

Metal Additive Manufactured Freeform Antenna

In this letter, we introduce a metal additive manufactured (AM) freeform antenna using thin, overhanging wires. For most AM processes, overhanging features generally require support structures when building at angles of 45° or greater to the build direction. The need for support structures in an AM antenna fabrication limits the minimum wire diameter possible. The design presented here is a three-dimensional (3-D) spherical helix folded dipole antenna, which has been shown to approach the theoretical limit for the size of antennas called Chu's limit in past research. Electron beam melting enables the creation of this type of antenna geometry in one process using thin, overhanging wires without the need for supports. This demonstrates one of the advantages of AM via complex 3-D space filling geometries. In addition, the impact of the rough AM surface on gain is discussed.

Airflow-Assisted 3D Bioprinting of Human Heterogeneous Microspheroidal Organoids with Microfluidic Nozzle.

Hydrogel microspheroids are widely used in tissue engineering, such as injection therapy and 3D cell culture, and among which, heterogeneous microspheroids are drawing much attention as a promising tool to carry multiple cell types in separated phases. However, it is still a big challenge to fabricate heterogeneous microspheroids that can reconstruct built-up tissues' microarchitecture with excellent resolution and spatial organization in limited sizes. Here, a novel airflow-assisted 3D bioprinting method is reported, which can print versatile spiral microarchitectures inside the microspheroids, permitting one-step bioprinting of fascinating hydrogel structures, such as the spherical helix, rose, and saddle. A microfluidic nozzle is developed to improve the capability of intricate cell encapsulation with heterotypic contact. Complex structures, such as a rose, Tai chi pattern, and single cell line can be easily printed in spheroids. The theoretical model during printing is established and process parameters are systematically investigated. As a demonstration, a human multicellular organoid of spirally vascularized ossification is reconstructed with this method, which shows that it is a powerful tool to build mini tissues on microspheroids.

Characterizations of slant and spherical helices due to pseudo-Sabban frame

In this paper, we investigate that under which conditions of the geodesic curvature of unit speed curve $\gamma$ that lies on $S_1^2$ or $H^2,$ the curve $\alpha$ which is obtained by using $\gamma$, is a spherical helix or slant helix in Minkowski 3-space.

Stationary acceleration of Frenet curves

In this paper, the stationary acceleration of the spherical general helix in a 3-dimensional Lie group is studied by using a bi-invariant metric. The relationship between the Frenet elements of the stationary acceleration curve in 4-dimensional Euclidean space and the intrinsic Frenet elements of the Lie group is outlined. As a consequence, the corresponding curvature and torsion of these curves are computed. In Minkowski space, for the curves on a timelike surface to have a stationary acceleration, a necessary and sufficient condition is refined.

전기적 소형 Folded Slot Spherical Helix 자기 다이폴 안테나에 관한 연구

In this paper, we propose an FSSH(Folded Slot Spherical Helix) magnetic dipole antenna with a form factor easy to build and study its radiation properties. The number of folded arms, the gap between them and the metal thickness are tuned to achieve relatively simple structure to realize whereas maintaining high radiation efficiency at an electrically small size. The proposed design shows wide radiation efficiency bandwidth and it is confirmed by circuit simulation that the non-Foster impedance matching techniques could be utilized for its practical use. The prototype of the proposed antenna is built with the aid of an SLS(Selective Laser Sintering) 3D printing technology. The measured result shows lower Q impedance characteristic due to high resistive loss of the copper tape joints.

Non‐foster impedance matching sensitivity of electrically small electric and magnetic spherical dipole antennas

The impedance bandwidth (BW) improvement property of a self-resonant folded spherical helix electric dipole and a spherical split ring (SSR) magnetic dipole is compared when a negative reactance element is loaded on the parasitic resonator of the antennas. They have the same electrical size of ka = 0.38 and both approach each lower Q -bound. It is found that the impedance characteristic reacts more sensitively to the loaded element for the SSR antenna due to the inherent two-times higher Q of the magnetic antenna. It is also found that a conventional non-Foster circuit composed of a series negative inductor and a capacitor cannot be used for wide impedance matching of the SSR antenna due to the high sensitivity. Subsequently, a circuit topology that enables more precise matching of the reactive values for widened impedance matching in the high- Q SSR antenna and satisfies the stable operating condition is proposed. It is observed that the improvement ratio of the BW is limited in practical situation. Nevertheless, the measured reflection coefficient of the 3D-printed SSR antenna loaded with the designed active matching circuit shows two-times wider impedance BW than passive matching, verifying the simulated result from the circuit and electromagnetic (EM) simulations.

Electrically small folded spherical helix antennas using copper strips and 3D printing technology

Folded spherical helix (FSH) antennas using thin and wide copper strips instead of thick wires as a means of reducing the electrical size of ka is designed. It is found that FSH antennas made of copper strips show comparable radiation properties to FSH antennas made of thick wires. Furthermore, such designs can achieve even smaller size down to ka of 0.11 while keeping the radiation quality factors approaching the lower physical bound. An FSH antenna made of copper strips with ka of 0.21 is fabricated as a prototype using 3D printing technology. The measured resonance occurs at 307 MHz with the radiation efficiency of about 90%, verifying the simulated results and the proposed method of utilising copper strips in designing extremely small yet highly efficient volumetric folded helix antennas.

INTRODUCING NOVEL GENERATION OF HIGH ACCURACY CAMERA OPTICAL-TESTING AND CALIBRATION TEST-STANDS FEASIBLE FOR SERIES PRODUCTION OF CAMERAS

Abstract. The recent advances in the field of computer-vision have opened the doors of many opportunities for taking advantage of these techniques and technologies in many fields and applications. Having a high demand for these systems in today and future vehicles implies a high production volume of video cameras. The above criterions imply that it is critical to design test systems which deliver fast and accurate calibration and optical-testing capabilities. In this paper we introduce new generation of test-stands delivering high calibration quality in single-shot calibration of fisheye surround-view cameras. This incorporates important geometric features from bundle-block calibration, delivers very high (sub-pixel) calibration accuracy, makes possible a very fast calibration procedure (few seconds), and realizes autonomous calibration via machines. We have used the geometrical shape of a Spherical Helix (Type: 3D Spherical Spiral) with special geometrical characteristics, having a uniform radius which corresponds to the uniform motion. This geometrical feature was mechanically realized using three dimensional truncated icosahedrons which practically allow the implementation of a spherical helix on multiple surfaces. Furthermore the test-stand enables us to perform many other important optical tests such as stray-light testing, enabling us to evaluate the certain qualities of the camera optical module.

SOME CHARACTERIZATIONS OF SLANT AND SPHERICAL HELICES DUE TO SABBAN FRAME

In this paper, we are investigating that under which conditions of the geodesic curvature of unit speed curve that lies on the unit sphere, the curve c which is obtained by using , is a spherical helix or slant helix.