Beam Tilt Research Articles

A reconfigurable phase gradient metasurface antenna for beam steering

AbstractIn this article, a reconfigurable phase gradient metasurface (PGM) antenna for beam steering is presented. The antenna consists of a three‐layer transmitarray metasurface and a broadband patch antenna. The PIN diode is loaded onto the split ring resonator (SRR). The phase gradient principle is used to regulate the electromagnetic waves to achieve the function of the gain enhancement and beam tilt. By clever design, the antenna is quickly switched in beam tilt in the 8.9–9.9 GHz range and gain enhancement in the 7.9–9.4 GHz range without the need for additional circuits. The proposed PGM antenna can achieve beam tilt in a certain bandwidth range and gain enhancement simultaneously. Compared with the previous beam steering antenna, it has broader bandwidth and smaller volume. The experimental results are in good agreement with the simulated ones.

Universal and Non-Iterative Design Method for In-Phase Radiation of Microstrip Traveling-Wave Series-Fed Antenna Arrays

Microstrip traveling-wave series-fed antenna arrays (MTSAAs) have been popularly developed for radar systems in the millimeter-waveband. Because the antennas are connected and fed in series in MTSAA, in-phase radiation of the antenna elements with properly tapered amplitude for achieving a broadside beam with a low sidelobe level (SLL) is challenging. Although the reported series-fed patch and comb-line arrays accomplished the goal, design equations for the optimum distances between antenna elements in the series-fed array do not guarantee in-phase radiation due to the mutual coupling in array structures. Therefore, optimization of the distances in the array using full-wave simulations is inevitable. In this article, we propose the first universal and non-iterative design equation that compensates for the phase offset generated in patch and comb-line MTSAAs and successfully found optimum distances for broadside beams with low SLLs without optimization. Finally, we fabricated both MTSAAs with ten elements operating at 76.5 GHz and demonstrated almost 13 dB boresight gain and low SLLs near −18 dB without a beam tilt.

Virtual metasurfaces: reshaping electromagnetic waves in distance

Metasurface has provided unprecedented freedoms in manipulating electromagnetic (EM) waves, exhibiting fascinating functions. Conventionally, these functions are implemented right on metasurfaces, where spatial modulations on EM wave amplitudes or phases are achieved by meta-atoms. This study proposes the concept of virtual metasurface (VM), which is formed by arrays of foci away from the entity metasurface. Unlike conventional metasurfaces, spatial modulations on the amplitudes or phases of EM waves occur in the air, with a focal length distance from the entity metasurface. As a proof of concept, we demonstrated a transmissive VM. The entity metasurface consists of transmissive focusing metasurface tiles (TFMTs) with the same focal length. Two TFMTs were designed with phase difference π to enable the most typical checkerboard configuration. The TFMTs were assembled to form the entity metasurface, whereas their foci formed the VM. Due to the π phase difference among adjacent foci, EM propagation along the normal direction was cancelled, leading to four tilted far-field beams. The concept of VM can be readily extended to higher frequencies from terahertz to optical regimes and may find wide applications in communication, camouflage, and other fields.

Reusable and efficient energy-absorbing architected materials via synergy of snap-through instability and inter-locking mechanism

Reusable energy-absorbing materials of high energy dissipation capacity and low rebound force are highly desirable in engineering and daily life. In this work, we design a new type of architected materials consisting of elastic tilted beams and trapezoidal inter-locking structures (ILSs). The tilted beams buckle elastically and snap from undeformed state to a higher-energy state under compression. They are squeezed into the space between ILSs and locked at this configuration when the external load is removed. The energy applied to the structure turns into elastic strain energy of the beams and ILSs, as well as heat generated by friction and snapping motions. This strategy reconciles the conflict between loading bearing capacity and bistability of the structure. The tilted beams are tuned to increase the load they can sustain, and the ILSs are designed to lock the tilted beams. Compared to a counterpart without ILSs, our strategy expands the design space of energy-absorbing architected materials and improves the energy-absorbing capacity greatly. This work opens opportunities for designing reusable and efficient energy-absorbing materials for applications like sports protective equipment and packaging of delicate objects.

T-Type Vertical Wall for Decoupling and Pattern Correction of Patch Antenna

The requirements of 5G/6G promote progress in the miniaturization of the antenna array, which promotes the development of a closely spaced decoupling technique. However, the present techniques face the common problem of beam tilt if the spacing is close. Thus, a pattern-corrected, closely-spaced technique is proposed in this paper for the two patch antennas with the λ0/20 edge-to-edge distance of the H-plane. The corresponding structure, which is inserted at the center of the spacing, consists of a vertical wall with a single substrate and two symmetrical T-type metals, and a slot at the center is reserved to adequately accommodate the vertical wall. The vertical strip at the other end of the T-type metal is connected to the ground of the patch antenna, while the parallel strip is placed exactly above the patch substrate. After an exact analysis, a prototype was fabricated and measured, and the results showed that the measurements agreed well with those of the simulations, the decoupling coefficients in the 5.8 GHz band were below −20 dB, and the measured radiation pattern at 5.81 GHz was corrected to the broadside from 28° and the maximum realized gain was 5.30 dB.

Combining Azimuthal and Polar Angle Resolved Shadow Mask Deposition and Nanosphere Lithography to Uncover Unique Nano-Crystals.

In this article, we present a systematic investigation on a multistep nanosphere lithography technique to uncover its potential in fabricating a wide range of two- and three-dimensional nanostructures. A tilted (polar angle) electron beam shower on a nanosphere mask results in an angled shadow mask deposition. The shape of the shadow also depends on the azimuthal angle of the mask sitting on top of the substrate. We performed angled shadow mask depositions with systematic variation of these two angular parameters, giving rise to complex nanostructures (down to 50 nm), repeated over a large area without defect. In this article, nanosphere lithography with two- and four-fold azimuthal symmetry was studied at constant tilt angles followed by variations in tilt without azimuthal rotation of the substrate. Finally, both angular parameters were simultaneously varied. The structure of shadow crystals was explained using Matlab simulation. This work stretches the horizons of nanosphere lithography, opening up new scopes in plasmonic and magnonic research.

The effect of pelvic ring rotation and tilt on the radiographic teardrop distance: an important consideration in the assessment of dynamic displacement on stress radiographs.

The purpose of this study was to determine the effect of rotation and tilt on the radiographic teardrop distance (TD) on anteroposterior (AP) pelvis radiographs. Radiographic examination of a pelvis models was conducted utilizing increasing degrees of beam rotation and tilt on portable C-arm fluoroscopy. The TD, x-plane rotation (symphyseal-mid-sacrum distance (SMS)), and y-plane tilt (sacroiliac joint-symphysis distance (SIS)) were measured by four independent observers. Interobserver reliability was assessed using intraclass correlations. TD was altered by less than 2mm with up to 7.5° fluoroscopic rotation (SMS: 3cm) and up to 30° of inlet and 15° of outlet (SIS: ± 3.3cm). SMS distance effectively corresponded to the degree of rotation present (r = 1.00, CI: 0.97 to 1.00, p < 0.0001) and was strongly correlated to TD (r = -0.95, CI: -0.99 to -0.67, p = 0.001). SIS distance effectively corresponded to the degree of tilt present (r = -0.97, CI: -0.99 to -0.88, p < 0.0001) and was correlated to TD (r = 0.94, CI: 0.75 to 0.99, p = 0.0001). Linear regression models determined that, with every degree of rotation and tilt, TD was altered by 0.4mm and 0.09mm, respectively (p = 0.0004, r2 = 0.93 and p < 0.0001, r2 = 0.94, respectively). Interobserver reliability among observers was excellent (0.92). The TD has excellent interobserver reliability and is minimally impacted by up to 7.5° of rotation, 30° inlet tilt, and 15° of outlet tilt. Utilization of these thresholds may ensure reliability of TD measurements when assessing pelvis stress radiographs.

Reconfigurable monopole antenna with polarization and pattern diversity

A planar monopole antenna capable of reconfiguring both the polarization and radiation pattern is presented for MIMO systems. A star shape patch is used as the radiator. Four PIN diodes are inserted to control the polarization and radiation pattern. The antenna can operate over two frequency bands. A prototype antenna is designed and fabricated for radiation at 5.5 GHz and 8.4 GHz. The first switching state provides left-hand circular polarization (LHCP) in the first band with the main beam at ϕ = +60° and right-hand circular polarization (RHCP) at 8.4 GHz at ϕ = +140°. For the second switching state, the sense of polarizations changes with the main beam at ϕ = +120° and + 40°, respectively. Measured results show that overlapped bandwidths are obtained from 5.17 to 5.85 GHz at lower band and 8.35 to 8.49 GHz at upper band for both the first and second switching states. For the third switching state, it generates an omnidirectional radiation pattern with linear polarization (LP) over 3.78–5.87 GHz. The antenna possesses the measured peak gain values of 0.65 dBi at lower band and 1.15 dBi at upper band for first and second switching states and an average gain value of 1.1 dBi is obtained for the third switching state. The overall size of the prototype is 24 mm × 23.5 mm on a 1.6 mm thick FR4 substrate. The CP band positions, as well as beam tilt, are tunable. Design guidelines are provided. The demerit of the proposed antenna is that it has achieved lower gain values at dual bands.

Femtosecond pulsed laser ablation for paint removal at oblique illumination: Effect of the incidence angle

This research studies how the angle of incidence affects the ablation process when a pulsed femtosecond laser with a wavelength of 1040 nm and a high repetition rate is applied to spray paints used for graffiti. Flat test samples were painted using four different spray paints (red, blue, black and silver). All paints had an organic base but different physicochemical properties. For each paint, the ablation process was characterized using confocal microscopy, determining the threshold fluence and the penetration depth of the laser radiation at normal incidence. For different sample tilt angles in the range of 0°–60°, the effect of oblique incidence was analysed in terms of its effect on the ablation rate and the geometric properties (depth and width) of the ablation grooves on each paint. The results show a clear decrease in the ablation rate as the angle of incidence moves away from normal incidence. Moreover, it can also be observed that for a given angle, groove depth is the property most affected by beam tilt. These results represent a necessary step in addressing both cleaning and other laser ablation processes on non-flat surfaces in a controlled and reproducible manner.

Automating ALCHEMI at the nano-scale using software compatible with PC-controlled transmission electron microscopy.

Atom location by channeling-enhanced microanalysis (ALCHEMI) is a technique to obtain atom-site-specific information on constituent elements in a crystalline sample by acquiring a set of core electron transition spectra while tilting the incident beam. This methodology has been extended to a more quantitative technique called high-angular-resolution electron-channeled X-ray/electron spectroscopy (HARECXS/HARECES). There is a growing demand for analyzing smaller areas, such as small particles and multilayers. However, the minimum size of a region of interest probed by the present hardware-assisted automated HARECXS/HARECES scheme is limited to no smaller than 1 µm, not only by the size of the electron probe and its convergence angle but also by the movement of the probe position associated with the beam tilt due to aberrations of the hardware system. Herein, QED (quantitative electron diffraction), a commercial plug-in working on an integrated software platform, Gatan Microscopy Suite, was modified to enable the calibration and control of the probe to resolve the aforementioned limitation. In addition, a more sophisticated scheme for QED was developed to realize the ALCHEMI method for energy-dispersive X-ray spectroscopy, electron energy-loss spectroscopy or both concurrently. This allows access to ALCHEMI and its derivative methods, automatically executed with any type of current PC-controlled commercial microscope on an area as small as 30 nm, without modifying the hardware system.

Three-dimensional particle size and position measurement by linear complex amplitude Wiener filtering.

Digital in-line holography (DIH) combined with a Wiener filter has been applied to measure particle size and position in the flow inside a capillary model, seeded with magnetic particles (3µm) and with solid opaque particles that simulated red and white cells. The proposed filtering process takes advantage of the linearity implicit in the numerical reconstruction of the object complex amplitude. A modified DIH set-up, with a tilted illumination beam, was used as it presents two main advantages: it solves the twin image issue associated to in-line holography and increases the out-of-plane resolution. Experiments show that the proposed method discriminates particles within a range from 3 to 30µm with a sensitivity of 0.5µm.

Phase‐shifted circularly polarised ring microstrip antenna and application in phased array antennas

A phase-shifted circularly polarised ring microstrip antenna (PS-CP-RMSA), which can switch between three different phases, is proposed. The phase of a circularly polarised antenna can be shifted by changing the angle of rotation. Taking advantage of this property, the proposed PS-CP-RMSA comprises a circularly polarised ring microstrip antenna (CP-RMSA) with three groups of feed lines and perturbation elements; phase shift can be achieved by switching their groups. Thus, the phase of a circularly polarised antenna can be electronically shifted without phase shifters, which has been difficult in the past. Therefore, the PS-CP-RMSA array can perform beam tilt electronically. In this study, PS-CP-RMSA and its four-element array were designed, fabricated, and measured. The maximum circular polarisation gain of the prototype PS-CP-RMSA was 6.3 dBic with an axial ratio of 1.1 dB at 5.7 GHz. The maximum gain of the boresight directional beam of the four-element array was 11.3 dBic with an axial ratio of 0.4 dB at 5.67 GHz. The proposed antenna can be a candidate for a new beam-control method for array antennas.

Millimeter wave beam‐tilted antenna using 1D‐phase gradient metasurface

In this article, radiation beam deflection of a mm-Wave antenna is presented using a metasurface (MTS). The beam tilting MTS consists of phase gradient resonators to transform an incoming wavefront to a tilted planar wavefront. The MTS is fed via gain enhanced dipole antenna having a tilted radiation beam. The gain of the dipole antenna is enhanced by printing a high refractive index surface in front of the radiator. The MTS is then loaded vertically in front of the gain enhanced dipole antenna using a 3D printed stand. The prototype antenna covers 27–30 GHz band with a tilted radiation beam. A beam tilt of 20° is achieved using the MTS with a peak gain of 10 dB over the frequency band.

A semi-automated procedure for the emitter–receiver geometry characterization of motor-controlled lidars

Abstract. To correctly understand and interpret lidar-acquired signals and to provide high-quality data, the characterization of the lidar transmitter–receiver geometry is required. For example, being fundamental to correctly align lidar systems, this characterization is useful to improve the efficiency of the alignment procedure. In addition, some applications (e.g. air quality monitoring) need to quantitatively interpret the observations even in the range where the overlap between the telescope field of view and the laser beam is incomplete. This is generally accomplished by correcting for the overlap function. Within the frame of lidar-based networks (e.g. ACTRIS/EARLINET, the Aerosol, Clouds and Trace Gases Research Infrastructure/European Aerosol Research Lidar Network), there is a need to define standardized approaches to deal with lidar geometry issues. The multi-wavelength multi-telescope Rayleigh–Mie–Raman “9-eyes” system in Rome Tor Vergata, part of ACTRIS/EARLINET, has the capability, through computer-controlled servomotors, to change the orientation of the laser beams and the 3D position of the diaphragm of the receiving optical system around the focal point of the telescopes. Taking advantage of these instrumental design characteristics an original approach to characterize the dependency of the acquired signal from the system relative transmitter–receiver geometry (the mapping procedure) was developed. The procedure consists in a set of programs controlling both the signal acquisition as well as the motor movements. The approach includes solutions to account for atmospheric and laser power variability likely to occur during the mapping sessions. The paper describes in detail the developed procedure and applications such as the optimization of the telescope/beam alignment and the estimation of the overlap function. The results of the mapping applied to a single combination of telescope-laser beam are shown and discussed. The effectiveness of the mapping-based alignment was successfully verified by comparing the whole signal profile and the outcome of the telecover test, adopted in EARLINET, for a manual and a mapping-based alignment. A significant signal increase and lowering of the full overlap height (from 1500 m to less than 1000 m) was found. The overlap function was estimated down to 200 m and compared against the one obtained from a geometric model. The developed procedure also allowed estimating the absolute and relative tilt of the laser beam. The mapping approach, even in simplified versions, can be adapted to other lidars to characterize and align systems with non-motorized receiving geometry.

Synergistic Energy Absorption Mechanisms of Architected Liquid Crystal Elastomers.

A unique rate-dependent energy absorption behavior of liquid crystal elastomer (LCE)-based architected materials is reported. The architected materials consist of repeating unit cells of bistable tilted LCE beams sandwiched between stiff supports. The viscoelastic behavior of the LCE causes the energy absorption to increase with strain rate according to a power-law relationship, which can be modulated by changing the degree of mesogen alignment and the loading direction relative to the director. For a strain rate of 600 s-1 , the unit cell exhibits up to a 5MJ m-3 energy absorption density, which is two orders of magnitude higher than the same structure fabricated from poly(dimethylsiloxane) elastomer and is comparable to the dissipation from irreversible plastic deformation exhibited by denser metals. For a multilayered structure of unit cells, nonuniform buckling of the different layers produces additional viscoelastic dissipation. This synergistic interaction between viscoelastic dissipation and snap-through buckling causes the energy absorption density to increase with the number of layers. The sequence of cell collapse can be controlled by grading the beam thickness to further promote viscous dissipation and enhance the energy absorption density. It is envisioned that the study can contribute to the development of lightweight extreme energy-absorbing metamaterials.

Prospect for measuring two-dimensional van der Waals magnets by electron magnetic chiral dichroism

Two-dimensional (2D) van der Waals magnets have drawn considerable attention in recent years triggered by the huge interest in novel magnetism and spintronic devices. Magnetic measurement of 2D van der Waals (vdW) magnets is crucial to understand the physical origin of magnetism in 2D limits. Therefore, advanced magnetic characterization techniques are highly required. However, only a limited number of such techniques are available due to the extremely small volume of 2D vdW magnets. Here, we introduce the electron magnetic chiral dichroism (EMCD) technique in transmission electron microscope (TEM) to measure 2D vdW crystals. In comparison with some other already-employed techniques in 2D magnets, EMCD is able to quantitatively measure magnetic parameters in three orthogonal directions at nanometer or even at atomic scale. We then perform EMCD simulations on several typical 2D vdW magnets with respect to the accelerating voltage, the number of atomic layers and beam tilt under zone axial orientation. The intensity and distribution of EMCD signals in three orthogonal directions are given in the diffraction plane, thereby providing an optimized design to achieve EMCD measurements. Finally, we discuss the signal-to-noise-ratio and required electron dose in order to obtain a measurable EMCD signal for 2D vdW magnets. Our results provide a feasibility analysis and guideline to measure 2D vdW magnets in future experiments.

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.

Differential-Fed, Dual-Aperture Based, Quasi-End-Fire 5G mmWave Antenna-in-Package Design

A low-profile, wideband antenna-in-package (AiP) design is proposed for 5G mmWave mobile applications. The aperture-coupled feeding incorporated with the microstrip feed line through the slots in the ground is used to excite the patch antenna. Firstly, a thin quarter-wave shorted patch antenna (QW-SPA) with the dominant <i>TM</i>^<i>z</i>_1/2,0,0 mode is realized. To broaden the operating band, the QW-SPA is extended along its resonant length so that the <i>TM</i>^<i>z</i>_1,0,0 mode can also be excited. The offset introduced into the two slots together with the additional shorting via wall are applied to enhance the beam tilt toward the end-fire direction. The proposed single-patch design shows a wide fractional bandwidth, covering the 5G mmWave band n257 (26.5&#x2013;29.5 GHz). Furthermore, to increase more beam tilt, the differential-fed, two-patch sub-array formed by two QW-SPAs spaced a half-wavelength at 28 GHz apart is also presented. Compared with the single-patch design, the beam-tilt enhancement of around 10&#x2013;27 degrees is obtained over the desired frequency band with the peak gain of around 8.2 dBi for the sub-array AiP design.

High-Gain Single-Feed Overmoded Cavity Antenna With Closely Spaced Phased Patch Surface

High-gain single-feed antennas are desired for current and future wireless systems. Slot-based highly overmoded cavity antennas are one solution, but the fact that they can only radiate broadside beams limits their applications. An innovative phase-control technique is developed for slot-based resonant cavity antennas that utilizes a planar array of closely-spaced, appropriately-sized metallic patches integrated into the very near field of their slot arrays. It facilitates the design and realization of the phase distribution over their radiating aperture that is required for them to generate single and/or multiple tilted beams pointed at specified directions. A TE(10)(11)(0)-mode slot-based cavity antenna is selected as the pathfinder system. A TE110-mode single-slot cavity antenna that is equivalent to the half-wavelength subsection of that cavity is introduced initially to monitor the phase radiated from each slot. The phase control surface is then carefully engineered to facilitate tilted output beams from the base design. The approach is validated with two subsequent tilted-beam systems. The first system achieves a single beam tilted to 30° with respect to the broadside direction. The second system is extended to produce two independently-directed titled beams pointing at –10° and 20°, respectively. All of the measured results agree well with their simulated values.

Generation of Beam Tilt through Three-Dimensional Printed Surface

In this paper, 3D printed surfaces are presented to study this technology’s application in generating beam tilt for the electromagnetic waves in the Ku-band. Additionally, the input source is maintained by a feed horn that is additively manufactured and is coated with copper spray paint to add conductivity, which is fed by a WR-75 waveguide. The proposed beam tilt generating surface is also referred to as a Beam Deviating Surface (BDS). There is no relative gap between the BDS and the aperture of the horn, which eventually decreased the overall antenna height. The BDS layer is able to deviate the beam for a fixed elevation angle of 22.5∘ and could be consequently rotated along with the rotation of the BDS prototype. The voltage standing wave ratio value is less than two over the operating frequency range, which depicts the wideband behavior. The measured and simulated radiation patterns show that we can tilt the electromagnetic waves in ranges of up to +/−22.5∘ with a minimum side lobe level of −5 dB at frequencies from 10 to 15 GHz. This signifies the wideband characteristic of the proposed prototype, which is achieved by Vero material from Multijet Printing that is a low-cost and rapid manufacturing 3D printing technology.