Beam Tilt Angle Research Articles

Tunable 3D printed composite metamaterials with negative stiffness

The paper proposes a class of tunable metamaterials that use inclined beams to achieve instability in a rigid system. Three different beam tilt angles, 25°, 45°, and 60°, are evaluated in the form of unit cells using quasi-static compression tests and numerical simulations. Snap-through behavirous are characterised by structural stiffness and buckling load. Periodic and gradient structures are assembled and analysed by arranging the unit cells in rows and columns. Size effect analyses and parametric studies are carried out on various unit-cell arrangements and different beam angles. The proposed metamaterials are manufactured through fused filament fabrication 3D printing technology with a composite material, onyx. The results from experiments, finite element analysis, and analytical models are compared and evaluated. The structural stiffness and buckling load are shown to be positively related to the inclination angle of the tilted beams. The number of rows of unit cells governs the nonlinear mechanical response (number of snap-throughs) of multiple-layered structures. By increasing the number of rows and columns of unit cells, which are less prone to manufacturing defects, the reliability and repeatability of the structural properties of periodic/gradient structures could be improved. A design plot is also provided to predict and tune the snap-through behaviour of multiple-layered structures via beam angles and unit-cell arrangements.

Design and Development of Parasitic Elements Loaded Quadband Frequency and Pattern Reconfigurable Antenna

Modern communication demands a low-profile, versatile antenna. In this paper, a low-profile antenna of size 38 × 40 × 0.787 m m 3 is proposed to reconfigure frequency and radiation pattern. The Rogers RT Duroid 5870 of dielectric constant 2.33 is used as a substrate. Frequency reconfiguration is achieved by connecting patches of different lengths corresponding to the resonant frequencies through three PIN diode switches. Switching on/off these three diodes results in frequency switching between four distinct frequency bands. The Yagi-Uda principle is utilized to alter the radiation pattern. Simple parasitic elements are loaded on either side of the radiating structure. Changing the electrical lengths of the parasitic elements using PIN diode switches facilitates pattern reconfiguration by making them behave as a reflector/director. The presented structure resonates at four distinct frequencies (5.3 GHz/3.82 GHz/2.77 GHz/2.2 GHz) with a maximum of three beam tilt angles for each resonating frequency. SMP1345-079LF PIN diode is used for switching operation. Biasing circuit has been designed to ensure RF and DC isolation. The proposed antenna offers acceptable radiation performance in all the switching states. The average measured gains are 2.43 dBi, 2.42 dBi, 3.5 dBi, and 3.29 dBi at 5.3 GHz, 3.82 GHz, 2.77 GHz, and 2.2 GHz, respectively. On an average, the proposed antenna exhibits the simulated efficiency of 81%. The proposed antenna is suitable for 5G communication as its bandwidth covers band 1, band 7, band 46, and band 77 of the 5G new radio (NR) standard. Fabrication and testing are done to validate the results.

Development of tilt-scan system for differential phase contrast scanning transmission electron microscopy.

Differential phase contrast (DPC) scanning transmission electron microscopy can directly visualize electromagnetic fields inside a specimen. However, their image contrast is not only sensitive to the electromagnetic fields in the sample, but also the changes in diffraction conditions such as sample bends or thickness changes. These additional contrasts are called diffraction contrasts, and sometimes make it difficult to extract pure electromagnetic field information from the experimental DPC images. In this study, we developed a beam scan system that can acquire many DPC images from the same sample region with arbitrarily varying incident beam tilt angles to the sample. Then, these images are precisely averaged to form tilt-scan averaged DPC images. It is shown that the diffraction contrast can be effectively reduced in the tilt-scan averaged DPC images.

A Low-Profile and Beam-tilted Continuous Transverse Stub Array Antenna at W-band

This paper presents a low-profile, high gain, beam-tilted continuous transverse stub (CTS) array antenna at W-band. The antenna compromises 32 radiating slots and is fed by a parallel plate waveguide (PPW) network with a linear source generator. To deflect the outgoing beam, the principle of linear array scanning is adopted to design inverted T-type structure in each stub to introduce wave path difference. PPW network allows the antenna to obtain lower profile compared to other transmission lines. The design procedure, and the antenna characterization are described. The main beam of the antenna is titled 12 degree in H-plane. The simulation and measured results show that this antenna achieves peak gain of 32.4 dB and a 12 degree beam tilt angle at 99GHz. S11 parameters of the antenna is less than -10 dB in a broadband from 96 GHz to 103 GHz. This antenna has an advantage of miniaturization over other high-gain antenna solutions. The promising performance of this proposed CTS antenna reveals the possible candidate for Millimeter wave (MMW) telecommunication applications.

Three dimensional vectorial imaging of surface phonon polaritons

Surface phonon polaritons (SPhPs) are coupled photon-phonon excitations that emerge at the surfaces of nanostructured materials. Although they strongly influence the optical and thermal behavior of nanomaterials, no technique has been able to reveal the complete three-dimensional (3D) vectorial picture of their electromagnetic density of states. Using a highly monochromated electron beam in a scanning transmission electron microscope, we could visualize varying SPhP signatures from nanoscale MgO cubes as a function of the beam position, energy loss, and tilt angle. The SPhPs' response was described in terms of eigenmodes and used to tomographically reconstruct the phononic surface electromagnetic fields of the object. Such 3D information promises insights in nanoscale physical phenomena and is invaluable to the design and optimization of nanostructures for fascinating new uses.

Betatron coupling measurement and optimization in Indus-2 storage ring.

Brightness is an important parameter for any synchrotron radiation source. Correcting the emittance coupling is one of the ways to increase photon beam brightness in the operational storage ring. The main source of this effect is betatron coupling, resulting from the skew quadrupolar errors. Tune split and Linear Optics from Closed Orbit (LOCO) techniques are used to measure the betatron coupling. We discuss the measurement result of betatron coupling and its correction in the Indus-2 storage ring using available four power supplies, as the knobs, driving the skew quadrupole windings located on sextupoles. The measured coupling ratio of ∼0.8% closely matches with the coupling ratio obtained from the LOCO fit model. Based on LOCO correction, the coupling ratio can be reduced to ∼0.4%, which is limited by the degrees of freedom and not by the field strengths. To achieve a smaller and controlled value of coupling, simulation studies based on the LOCO fit model and using the multi-objective differential evolution algorithm with more skew quadrupole power supplies are performed in Indus-2. With sixteen independent power supplies, the emittance ratio can be reduced to <0.04% and the brightness enhances by an order of magnitude. Besides, the optimization method used provides quantitative trade-offs between coupling related parameters such as beam tilt angle, emittance ratio, vertical emittance, and vertical beam size, and desired values can be chosen from the Pareto optimal front.

Flywheel calibration of a continuous-wave coherent Doppler wind lidar

Abstract. A rig for calibrating a continuous-wave coherent Doppler wind lidar has been constructed. The rig consists of a rotating flywheel on a frame together with an adjustable lidar telescope. The laser beam points toward the rim of the wheel in a plane perpendicular to the wheel's rotation axis, and it can be tilted up and down along the wheel's periphery and thereby measure different projections of the tangential speed. The angular speed of the wheel is measured using a high-precision measuring ring fitted to the periphery of the wheel and synchronously logged together with the lidar speed. A simple geometrical model shows that there is a linear relationship between the measured line-of-sight speed and the beam tilt angle, and this is utilised to extrapolate to the tangential speed as measured by the lidar. An analysis of the uncertainties based on the model shows that a standard uncertainty on the measurement of about 0.1 % can be achieved, but also that the main source of uncertainty is the width of the laser beam and its associated uncertainty. Measurements performed with different beam widths confirm this. Other measurements with a minimised beam radius show that the method in this case performs about equally well for all the tested reference speeds ranging from about 3 to 18 m s−1.

Fundamental Limits on Detection of UAVs by Existing Terrestrial RF Networks

Detection of drones carries critical importance for safely and effectively managing unmanned aerial system traffic in the future. Given the ubiquitous presence of the drones across all kinds of environments in the near future, wide area drone detection and surveillance capability are highly desirable, which require careful planning and design of drone sensing networks. In this paper, we seek to meet this need by using the existing terrestrial radio frequency (RF) networks for passive sensing of drones. To this end we develop an analytical framework that provides the fundamental limits on the network-wide drone detection probability. In particular, we characterize the joint impact of the salient features of the terrestrial RF networks, such as the spatial randomness of the node locations, the directional 3D antenna patterns, and the mixed line of sight/non line of sight (LoS/NLoS) propagation characteristics of the air-to-ground (A2G) channels. Since the strength of the drone signal and the aggregate interference in a sensing network are fundamentally limited by the 3D network geometry and the inherent spatial randomness, we use tools from stochastic geometry to derive the closed-form expressions for the probabilities of detection, false alarm and coverage. This, in turn, demonstrates the impact of the sensor density, beam tilt angle, half power beam width (HPBW) and different degrees of LoS dominance, on the projected detection performance. Our analysis reveals optimal beam tilt angles, and sensor density that maximize the network-wide detection of the drones.

Low-Profile Circularly Polarized Transmitarray for Wide-Angle Beam Control With a Third-Order Meta-FSS

In this article, we develop a low-profile high-gain transmitarray antenna (TA) with a meta-frequency-selective surface (FSS) operating in the X-band. The employed metaFSS element is designed to realize a third-order bandpass filter, which has a high transmission and wide angular stability. A phase difference of 180° can be introduced between the two orthogonal directions with optimized parameters. Based on element rotation theory, the meta-FSS elements are arranged with the desired rotation angles to convert the incident quasi-spherical wave to the outgoing plane wave with the reverse polarization, e.g., a left-hand circularly polarized (LHCP) wave to a right-hand circularly polarized (RHCP) wave. To experimentally validate the focusing ability and wide-angle beam control ability of the proposed structure, principle prototypes are designed, fabricated, and measured. The experimental results show that the full transmitarray can achieve a 1 dB gain bandwidth of 13.0%, an aperture efficiency of 40.2%, and a 3 dB axial ratio bandwidth of 24.0% in the broadside direction. In addition, good circular polarization radiation performance can be successfully realized with the proposed structure at beam tilt angles from θ = 0° to 600°.

Multifunctional optofluidic lens with beam steering.

In this paper, we demonstrate a multifunctional optofluidic (MO) lens with beam steering, which is actuated by electrowetting effect. A liquid lens chamber and a liquid prism chamber are stacked to form the MO lens. When the liquid lens chamber is actuated with voltage, the curvature of liquid-liquid interface changes accordingly and the focal length of the liquid lens can be varied. In the liquid prism chamber, a navigation sheet is just placed on the position of the liquid-liquid interface. When the liquid prism chamber is applied with voltage, the navigation sheet can be tilted to different angles in order to adjust the beam steering angle and keep high beam quality. Thereby, the MO lens has the zoom lens and the beam steering functions. The experiments show that the focal length can be tuned from -180 mm to -∞ and +∞ to 161 mm and the maximum beam tilt angle can be adjusted from 0° to 22.8° when the voltage is applied on one side of the electrode. The proposed MO lens can be applied in zoom imaging system, laser detecting system, and lighting system.

Design Procedure for Compact Dual-Circularly Polarized Slotted Substrate Integrated Waveguide Antenna Arrays

In this paper, a complete design procedure of low-profile dual-circularly polarized slotted substrate integrated waveguide antennas is developed at the Ku-band frequencies. The design method includes a recipe for controlling the beam squint angle, determining the optimum slot aperture distribution, and tapering slots coupling and excitation to increase the gain/efficiency and reduce the array sidelobe levels. The structure is designed in such a way to provide dual circular polarization and improve the radiation characteristics including reduced sidelobe levels using optimized symmetric nonuniform coupling factors and tapering the lengths of the slots. The radiation performance of the fabricated 64×12 slot antenna array has been tested using a planar near-field range measurement. The beam tilt angles in elevation, peak gain, cross polarization component, and sidelobe levels have been measured and compared to previously designed 32 × 13 and 16 × 12 slot arrays.

A Microstrip Yagi Antenna With an Enlarged Beam Tilt Angle via a Slot-Loaded Patch Reflector and Pin-Loaded Patch Directors

In this letter, a microstrip Yagi antenna with a resonating patch driver, one slot-loaded patch reflector, and two pin-loaded patch directors is proposed. Different from all the reported counterpart antennas, the lengths and widths of all the patch elements involved herein are set to be the same, and a parasitic patch reflector and patch directors are realized by loading the slot and shorting pins on the patches, respectively. For a square patch, its resonance frequency can be reduced by etching out a slot, acquiring a reflective function. However, its resonance frequency can be increased by adding a pair of shorting pins underneath the patch, thus acquiring a directive function. By placing these two types of parasitic patches in the two sides of the driving patch radiator, an alternative microstrip Yagi antenna can be constructed to achieve a quasi-endfire radiation pattern with an enlarged beam tilt angle. A prototype operating at 5 GHz is finally fabricated and tested. The measured results achieve an impedance bandwidth of 8%. In addition, the maximum deviation angle reaches approximately 56° from the broad side, and its 3 dB beamwidth in the xoy plane exceeds 62°.

Space-time characteristics of aero-optical effect around conformal turrets

This study simulated the aero-optical effect of beams with different projection directions around conformal turrets with different radii(400 mm and 2 000 mm). The Mach number was fixed, and the Reynolds number remained similar in all cases. The space-time characteristic of beam quality factor and beam tilt angle caused by the aero-optical effect was comprehensively studied. The aero-optical effect was mainly determined based on the mean flow effect, and the characteristic frequency of the mean flow effect was determined based on that of the flow around the turret. The spatial characteristic of the aero-optical effect was accurately reproduced in the reduced-scale experiments; however, the temporal characteristic was poorly simulated. It is pointed out that the wavefront distortion statistics and fluctuation values caused by aero-optical effect aero-optical effect appear to be minimized at a projection direction of 40° zenith in the forward direction, and the increase of projection radius can result in fast increaseing of the mean flow effect while maintaining the turbulent effect almost constant.

Millimeter-Wave Beam-Tilting Vivaldi Antenna With Gain Enhancement Using Multilayer FSS

This letter presents a new design of tilted-beam antenna with gain enhancement based on the multilayer frequency selective surfaces (FSSs) for fifth-generation applications. A dual-sided printed FSS element with two C-shaped resonators at the top layer and a slotted circular patch at the bottom side, is proposed. The FSS element holds a size of 0.46λ × 0.46λ (at 28 GHz). A wideband Vivaldi antenna with an end-fire radiation is used to excite the elements of the FSS layers. The effects of different sizes, number, and the angular rotation of the FSS layers are employed to achieve the best antenna performance in terms of beam-tilting, realized gain, and reducing the sidelobe level (SLL). The best antenna performance is achieved when two unequal-sized FSS layers rotated to 45° and fixed under the Vivaldi. The proposed antenna is fabricated and measured. The obtained measured results show a maximum beam tilt angle of 38°, realized gain of 9 dBi, and SLL at –8 dB. The beam tilt angles are validated with the results obtained using the Snell's law in a multilayer environment and found a good agreement.

Increased beam tilt angle from a patch antenna with three inhomogeneous loop‐based plates

An antenna system composed of an activated patch backed by a ground plane and three square parasitic plates with inhomogeneous loops is analysed using the finite-difference time-domain method. Analysis of an antenna with an infinite ground plane reveals that a tilted beam of ~60° from the broadside direction is obtained with a gain of ~18 dBi. For confirmation, an antenna system with a finite-sized ground plane that approximates the antenna characteristics for the infinite ground plane is fabricated and measured. The measured results are in good agreement with the analysis results.

Adjustable Tilt Angle of Liquid Microlens With Four Coplanar Electrodes

We present a novel method to adjust the beam tilt angle and tune the axial focus of an electrowetting on dielectric liquid microlens encapsulated by parylene film. The lens system consists of four control electrodes with two immiscible spherical liquid lenses of different refractive indexes encapsulated by a flexible polymer. To tilt the incident beam, the lateral position and curvature of the inner lens were modulated by ac voltage applied to the electrodes. The measured lateral position and curvature of the inner lens allowed us to estimate the position of the focal point. The tunability of the tilt angle was increased by ±2.13° at an applied voltage of $45.3~V_{\mathrm {rms}}$ when using thin dielectric layers. The resolvable image was 80% and 68% of the aperture diameter for 20 and 50 L&S/mm, respectively, assuming that the critical modulation transfer function value was 50% for quality imaging.

Beam Tilt-Angle Estimation for Monopole End-Fire Array Mounted on a Finite Ground Plane

A modified method for the beam tilt-angle estimation of monopole end-fire array mounted on finite ground plane is proposed. In the simplified model, the monopole array and ground plane are approximated to two line sources of transverse and longitudinal electric current, respectively. It is deduced that the beam tilt angle is a function about the length of ground plane in front of arrayLg, the length of monopole arrayLa, and the phase constantβα. After verifying the optimizing principle of monopole end-fire array, a 10-element monopole Yagi-Uda antenna satisfying Hansen-Woodyard condition is designed and measured for the analysis. By comparison and analysis, the value ofβαis demonstrated to be the key point of the proposed method. And a slow wave monopole array is proved to be able to achieve a low beam tilt angle from end-fire with only a short-length ground plane.

3D grain orientation mapping of nanocrystalline materials in the TEM

Nanocrystalline materials (i.e. polycrystalline aggregates where the individual crystallites/grains or particles have sizes below 100 nm) are formed through various processes ranging from mechanical treatments of bulk materials, to electrodeposition of thin films and coatings to aggregation of nanoparticles. The materials constitute one of the most rapidly growing new classes of materials and exhibit enhanced properties, see e.g. [1,2], ranging from high strength and wear resistance, to unique functional characteristics, which open up a large spectrum of applications e.g. for micro- and nano-electro-mechanical systems (MEMS and NEMS). Consequently, materials models tend to be based only on simple observables such as a 2D crystalline projection or an average grain/particle size. Motivated by this, a new and non-destructive technique called "3D-Orientation Mapping in TEM" (3D-OMiTEM) was developed and it was demonstrated that both orientation and 3D morphology of ~1000 individual nanograins could be measured with spatial and angular resolutions of 1 nm and 1 degree [3]. Notably, the foil may have five or more grains stacked on top of each other in the thickness direction. Technically speaking, 3D-OMiTEM is based on conical-scanning dark-field imaging. By recording images at a series of different beam and sample tilt angles it is possible to reconstruct the complete 3D orientation map of nanograins or nanoparticles. With the availability of 3D-OMiTEM crystallographic orientation relationships, interface curvatures, 3D connectivity between nanograins or nanoparticles as well as evolution of 3D structures e.g. during heat treatments or deformation steps, can be addressed for the first time in nanocrystalline materials. An overview of the methodology and latest results is given.

Addition of energy dispersion characteristics to the diagram of axis intercept for aberration analysis of core-lens

The diagram of axis intercept (Nishi and Takaoka [1]) is extended to consider the energy dispersion characteristic. The operating condition of core-lenses can be optimized by taking into account not only the aperture aberration but also the chromatic aberration. The diagram is applied to a typical core-lens system configured with three point charges of different polarities and is plotted as a function of the electron energy in addition to the starting angle. Near the stigmatic condition, the diagram fits the quadratic dependence on both the energy dispersion and the beam tilt angle. Then, the coefficients of aperture aberration, energy dispersion and chromatic aberration are obtained.

A Method for Gyrotron Beam Coupling into a Corrugated Waveguide

In the radio-frequency (rf) power transmission system of an electron cyclotron heating and current drive (EC H&CD) system, the gyrotron power should couple with the fundamental mode of the corrugated waveguide (HE11 mode) because unwanted higher-order modes affect the beam radiation characteristics, which is a problem in the quasi-optical launcher design. To achieve high HE11 mode purity, a beam coupling method that measures the transmission mode in the waveguide was examined using a 170-GHz high-power gyrotron for the first time. In beam coupling, the offset and tilt angle of the input beam at the waveguide inlet were minimized by controlling the angles of the mirrors in the matching optical unit (MOU) to minimize unwanted LP11 modes in the waveguide. The rf field profile in free space after 1.3 m of the waveguide from the MOU was measured, and the transmission mode content was analyzed. According to the analyzed mode content, the HE11 mode content was optimized by remote adjustment of the mirror angles with a digital controller. The optimization procedure of beam coupling achieved 95% of HE11 mode purity at the entrance of transmission line, which is the first demonstration that meets the criteria of the ITER EC H&CD system.