Reflection Phase Research Articles

RCS reduction metasurface based on orbital angular momentum

A novel radar cross-section (RCS) reduction metasurface is designed, fabricated, and experimentally characterized to flexibility control wavefront and efficiency generated orbital angular momentum (OAM). The metasurface is composed of several square loops with different reflection phases. Utilizing the property of the OAM phase singularity, the metasurface presents a significant RCS reduction along the propagation axis. Simulation results show that RCS reduction over 40 dB for normal incident plane waves at 7.6 GHz. For further clarity the physical mechanism of the RCS reduction, the near-field and 3D far-field features of the metasurface are discussed in detail. Two prototypes are fabricated and experimented with different topological charges. Good agreement is achieved between full-wave simulations and measurements. The design methodology provides an alternative to low-RCS and wavefront modulation design.

Investigating Polarization-Sensitive Transmission and Reflection Metasurfaces for Advanced Wavefront Manipulation

This paper presents the design and optimization of a dual-band polarization-dependent metasurface capable of dynamically switching transmission and reflection characteristics. The metasurface is composed of three metallic patterns, with the bottom layer governing the reflection and transmission phase for both TE-polarization and TM-polarization states. The middle and top layers are strategically employed to ensure optimal transmission and reflection performance. The results confirm that the metasurface enables the transformation of the transmission band into a complete reflection band, and vice versa, through variations in the incident wave polarization. Remarkable transmission and reflection characteristics are achieved within the frequency ranges of 6.1–6.55 GHz and 8.9–9.3 GHz, respectively. The proposed metasurface offers promising applications in advanced communication systems and radar technology, enabling dynamic manipulation of electromagnetic waves.

Dual-mode switchable metasurface for multi-type OAM vortex beam generation and dual-band perfect absorption in terahertz band

As metasurface technology is developing rapidly in the past decades, multi-operating mode and tunability are evolving into hot spots in its development. In this paper, we present a dual-operating mode metasurface consisting of vanadium dioxide (VO2). At room temperature (25 °C), it operates as a reflection mode. Eight metasurface unit cells with different reflection phases are designed, which can achieve 2π phase coverage in the frequency band of 0.4 THz-0.5 THz. Furthermore, by bringing encoded convolution and superposition theorems into the design of metasurface arrays, vertically incident circularly polarized (CP) waves can be transformed into single-beam, multi-beam, deflected and superimposed orbital angular momentum (OAM) vortex beams, respectively. On the other hand, at high temperature (68 °C), it operates as a dual-band terahertz absorber. It achieves near-perfect absorption at 1.71 THz and 1.87 THz with 99.9% and 98.9%, and also has polarization insensitivity. Therefore, the metasurface designed in this paper has promising applications in future terahertz communications, high-resolution imaging, and electromagnetic stealth.

Improving NICU staff decision-making with parents in medical rounds: a pilot study of reflective group dialogue intervention.

The communication skills of healthcare professionals play a crucial role in successful shared decision-making with parents in neonatal intensive care. Improving communication skills can be achieved through practice and reflection on personal experiences after authentic interaction events with parents. The process of reflection typically involves three phases: description, reflection, and critical reflection. In this study, our aim was to explore the acceptability of the Reflective Group Dialogue intervention and its effectiveness in supporting the reflective process. This qualitative pilot study was conducted in the neonatal intensive care unit at Uppsala University Children's Hospital, Sweden. The sample consisted of nine medical rounds with seven families, five neonatologists, seven registered nurses, and five assistant nurses. Purposive sampling was used to collect the data. The intervention comprised four elements: (1) before the intervention, a recorded presentation on shared decision-making was given to the entire unit staff, (2) an observation of a normal medical round discussion with parents, (3) an interview with parents about their experience after the same round, and (4) a reflective discussion with the participating health care professionals after the round. The parent interviews and reflective discussions were audio-recorded and transcribed verbatim. They were analyzed using thematic analysis as a theoretical strategy. Both parents and staff widely accepted the intervention and found it beneficial. We identified four discussions that remained in the descriptive phase of the reflection process, four that reached the reflective phase, and one that reached the critical reflection phase. The descriptive discussions were characterized by using a single perspective to reflect, often based on personal opinions. The reflective discussions included analyzing interaction sequences from both staff and parent perspectives and were primarily based on actual observations of communication during medical rounds. The critical discussion led to a new awareness of current practices concerning parental involvement in decision-making. These discussions also utilized "what-if" thinking to evaluate potential new practices and their pros and cons. The intervention seems promising as it was perceived as beneficial by the recipients and facilitated reflection in most cases. However, to enhance the feasibility of the intervention, some improvements are discussed.

IMPLEMENTASI PBL (PROBLEM BASED LEARNING) BERBANTUAN MEDIA VIDEO SEBAGAI UPAYA MENINGKATKAN MOTIVASI DAN HASIL BELAJAR KOGNITIF SISWA PADA MATERI SISTEM KOORDINASI KELAS XI SMA

The teacher's ability to manage the class, specifically in the choice and use of learning models and media, is one of the causes of low motivation and poor learning results among students. Through the use of the problem-based learning approach and video media, this study seeks to improve the motivation and academic performance of class XI high school students. Class action research (PTK), which is conducted in two cycles with phases of planning, implementation, observation, and reflection, is this sort of study. The proportion of learning motivation was measured using the angket non-test method, and the results for cognitive learning were measured using the daily repetition test method with 35 students in high school's 11th grade. In the first cycle, the student participants' implementation of learning using the problem-based learning model and the motivational learning activity resulted in a score of 76.6% with sufficient good criteria, and in the second cycle, participants who experienced improvement received a rating of 90.3% with excellent criteria. The percentage of learning motivation as measured by four factors, attention, relevance, condifence, and satisfaction was rated at 58.49% in cycle I with a fairly high criterion and increased to 73.28% in cycle II. The cognitive learning outcomes of the students scored 65.71% in the first cycle of classical intensity and improved to 91.42% in the second cycle. The adoption of a learning model supported by video media can enhance the motivation and learning outcomes of students in grades XI high school, according to the research's findings.

Penerapan Pendekatan Supervisi Kolaboratif untuk Meningkatkan Kompetensi Profesional Guru Non PNS di MTs Negeri 1 Sintang

The teaching and learning process is a reciprocal relationship between teachers and students in order to achieve learning objectives. A teacher has a very important role in delivering learning so that it is well received by students. In addition, teachers also play a role in shaping the attitudes, behaviors, and thought processes of students. In the learning process, the teacher becomes one of the learning resources so that they must have the ability to master the subject matter. In order to carry out their duties properly, teachers must have one dimension of competence in accordance with the Regulation of the Minister of National Education of the Republic of Indonesia Number 16 of 2007 concerning Standards of Academic Qualifications and Teacher Competencies, namely professional competence. The study used the School Action Research (PTS) method with the Kemmis and Mc. Taggart models which are development models from the Kurt Lewin model. The model used consists of 2 cycles, each cycle consists of four components, namely: planning, action, observation and reflection. This research begins with an initial reflection phase to conduct preliminary studies as a basis for formulating research problems. Furthermore, followed by planning, action, observation, and reflection The implementation of collaborative supervision can increase the professional competence of non-civil servant teachers in MTsN 1 Sintang by 18.19%. The average professional competence in cycle 2 was 88.64 with a good category.

A multiband slot antenna with groundless EBG structure for wearable WLAN/WiMAX applications

ABSTRACT A multiband microstrip antenna integrated with an electromagnetic bandgap (EBG) structure operating at WLAN and WiMAX frequencies is proposed for wearable applications. The antenna consists of a circular patch surrounded by the ground plane, separated by a ring slot. The size of the integrated antenna has been significantly reduced to 0.28 λ ×0.28 λ and thickness of 0.024 λ . A single-layered planar groundless EBG structure has been designed to suppress the wideband of frequencies from 2.2 to 5.4 GHz. An equivalent circuit model is presented to explain the zero-degree reflection phase of the EBG. Integration of the antenna with the EBG structure and a simple resonator bestows operating bands at 2.45 and 5.2, 5.5 and 5.8 GHz with significantly low back radiation. The gain and directivity of the antenna have been increased to 5.41 dB and 6.2 dB, respectively. The Specific Absorption Rate (SAR) of the antenna has been reduced to 0.0859W/kg, which is significantly lower than the admissible SAR value recommended by the Federal Communications Commission (FCC). The antenna is fabricated on an FR4 substrate, and its measured radiation characteristics are well matched to the simulated one.

X-Band Tile-Based Metal-Only Reconstructible Reflectarray With 3-D Printing Support

A tiled-based metal-only reflectarray (RA) using stainless steel unit cells (UCs) is proposed in this letter. The RA aims at providing a low-cost high-gain antenna solution with the agility for customers living in harsh environments such as in the wilderness or under military threatening. The metal-only UCs, each fabricated separately using the laser cutting process with a prescribed reflection phase, are treated as mosaic tiles on a panel supported with a low-loss 3-D printing frame. The reflection phase, and hence the main beam direction, of the RA can be re-constructible according to the arrangement of the UCs. For the proof of concept, an RA with a diameter of 16 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , consisting of 820 UCs, is demonstrated at X-band. The UC comprises four spiral slots whose lengths control the reflection phase. The focal-to-diameter radio is 0.625. By re-arranging the UCs on the panel similar to a jigsaw puzzle, four application scenarios are experimentally verified. The first case has the main beam point to the broadside direction (0°). The other two have an oblique beam of 30° or 45° from the zenith; the final case consists of two main beams pointing to broadside (0°) and 30° from the zenith simultaneously. In the broadside case, a peak gain of 29.1 dBi and an aperture efficiency of 35.7% are achieved at 10 GHz, while the 3-dB gain bandwidth is 10.1%. A comparison table is summarized to manifest the uniqueness of the proposed idea.

Design and Implementation of a Novel Radar Cross Section Reduction Metasurface Covering 12.5-17.4 GHz and 20.5-36.2 GHz

Based on the theory of polarization conversion, this paper designs and implements two electromagnetic units with a 180-degree reflection phase difference in the range of 10-40 GHz. By coding and optimizing the spatial arrangement of the two basic units to obtain a metasurface, which makes the incident electromagnetic waves reflect diffusely, the energy in a single beam direction is reduced to realize the reduction of the radar cross section (RCS). The full wave simulated and experimental results of the reduction of the RCS of the metasurface have been presented. The RCS of the proposed metasurface can be reduced by more than 10 dB in the two broadband bands of 12.5-17.4 GHz and 20.5-36.2 GHz, and the maximum reduction can reach 26 dB, compared with a metallic surface of the same size. In addition, the optimized metasurface can also maintain a good reduction effect under oblique incident wave directions of 30, 45, 60, and 70 degrees. A very good agreement between simulation and measurement results is observed.

Robust Design of IRS-Aided Multi-Group Multicast System With Imperfect CSI

In this paper, the robust design for the intelligent reflective surface (IRS) assisted wireless multi-group multicast system is considered, in which two optimization design problems under two different channel state information (CSI) error models are separately discussed, i.e., the fairness-based problems and the quality-of-service (QoS)-based problems for both the bounded CSI error model and the statistical CSI error model. In order to deal with the non-convex constraints of the considered problems, i.e., bounded CSI error based constraint and statistical CSI error based constraint, S-procedure is adopted to convert the non-convex SINR constraint with bounded CSI error into linear matrix inequalities (LMIs), and the Bernstein-type inequality is utilized to transform the outage probability constraint with statistical CSI error into a second-order cone (SOC) constraint and linear inequalities. Following that, two efficient algorithms based on alternate optimization (AO) are proposed to solve the fairness problems and QoS problems, wherein the semi-definite programming (SDP), penalty convex-concave procedure (CCP) and semi-definite relaxation (SDR) are utilized. Furthermore, we analyze the complexity of the proposed algorithms. Finally, some numerical simulation results are presented to verify the effectiveness of the proposed algorithms, and the impacts of the CSI error and the discrete precision of IRS reflection phase shift on the system performance are analyzed, which provides some insights for the IRS deployment and system robust design.

Characterization of a Split Circle Element for Microstrip Reflectarrays

A split circular element is proposed as a unit cell for reflectarray antennas. The unit cell is derived from a circle divided into four equal sectors. The radius of two oppositely located sectors is then scaled by a certain factor to form the proposed shape. The CST Microwave Studio Suite software simulator was used to investigate the performance of the proposed unit cell, which was evaluated using Floquet port excitation. The designed element's reflection phase range was compared to that of a conventional circular patch. Four scenarios of varied substrate characteristics are investigated for the antenna to establish the best performance parameters. The simulations showed that a basic substrate with a thickness of 0.16 mm and a dielectric constant of 3.2, backed by a 3 mm foam with a dielectric constant of 1.05 and a scaling factor of 0.72 offers a wide phase range of 601.3°. The obtained phase slope is 76.37°/mm or 134°/GHz.

Passive white light cavities with metal coatings.

White light cavities with broadband resonance are usually filled with negative dispersion medium, which inevitably leads to gain. In this article, pure passive white light cavities are designed, in which negative dispersion medium is no longer necessary. Theoretically, if the reflection phase of the cavity wall can exhibit a negative dispersion slope, then it can also satisfy white light cavities conditions without medium. In practice, the negative dispersion property of the cavity wall can be realized by two metal coatings with different reflection coefficients. Therefore, our white light cavities are composite cavities, in which the main cavity provides resonance while the auxiliary cavity forms the cavity wall, providing negative dispersion reflection phase. Further, atomic gas can be employed to improve the performance of the white light cavities. Atomic gas exploits effects such as Electromagnetic Induced Transparency (EIT), enabling the white light cavities to be controlled by coherent driving field. With the passive characters, our design can be realized and implemented much more easily.

Sensitivity evaluation of miniature microstrip line‐based sensors using multiple sensing parameters for non‐invasive blood glucose monitoring

AbstractA number of high‐sensitivity microwave sensors with compact resonators are designed, fabricated, and tested for non‐invasive blood glucose monitoring. In the first step, a split ring resonator (SRR)‐based sensor is designed, and then it’s sensing parameters, viz. the reflection coefficient magnitude and phase coupled with its input impedance, are extracted and calibrated by different glucose solutions. The results of this structure are subsequently saved as a reference sensor. During the second step, the swastika‐shaped and electric‐LC (ELC) geometries are substituted for the SRR to enhance the sensitivity of the reference sensor, and the sensing parameters of these structures, which are sensitive to the glucose solutions, are obtained. In the third step, the sensitivity of the three proposed designs is calculated and compared, using the reflection coefficient amplitude, phase, and input impedance. The comparisons typically demonstrate that the sensitivity of the swastika‐shaped structure is equal to 148.367 (Ω/mgmL−1) if the sensitivity is acquired from the imaginary part of the input impedance, which is better than the SRR and ELC geometries. On the contrary, the sensitivity of the SRR geometry is at a maximum and equal to 16.79 (deg/mgmL−1) if the sensitivity is calculated in terms of the reflection coefficient phase.

Substrate Comparison on Multiband Reflector Performance for Intelligent Reflecting Surfaces (IRSs)

This paper presents the substrate comparison on the multiband reflector performance at X-band frequency for an Intelligent Reflecting Surface (IRS). Functioning as a multiband reflector, the proposed reflector is using a circular multi-ring resonator on several substrates such as RO5880, F4BMX220, RO4003C, and FR4, with slightly different substrate thicknesses based on the available market, that can be operated at X-band frequency. The simulated results have shown in the graph of S-parameters and reflection phase among the substrates. In addition, the bandwidth of the proposed reflector is calculated based on the simulation results. Also, the incident wave angle effect against the proposed reflector is shifted along the horizontal axis. For the overall simulation results, the reflector that uses a RO5880 substrate has slightly better results and a wider bandwidth than the F4BMX220 substrate.

Does the Hartman effect exist in triangular barriers

We study the phase, Larmor and dwell times of a particle scattered off triangular barriers (TBs). It is interesting that the dependences of dwell, reflective phase and Larmor times on the wave number, barrier width and height for a pair of mirror-symmetric (MS) exact triangular barriers (ETBs) are quite different, as the two ETBs have quite distinct scattering surfaces. In comparison, the dependence of the transmitted phase or Larmor times is exactly the same, since the transmitted amplitudes are the same for a pair of MS TBs. We further study the Hartman effect by defining the phase and Larmor velocities associated with the phase and Larmor times. We find no barrier width saturation effect for the transmitted and reflected times. This is indicated by the fact that all the velocities approach finite constants that are much smaller than the speed of light in vacuum for TBs with positive-slope impact faces. As for ETBs with vertical left edges, the naive velocities seem to also indicate the absence of the Hartman effect. These are quite distinct from rectangular barriers and may shed new light on the clarification of the tunneling time issues.

Channel reconfiguration for intelligent reflecting surface‐aided vehicular networks

AbstractIntelligent reflecting surface (IRS) has been recognized as one of the core technologies in the sixth generation (6G). Nevertheless, the character of channel state rapid change is a major problem in vehicular networks due to the dynamic vehicle movement and electromagnetic wave random scattering. In order to address the above problem, a strategy that joint phase shifts and channel alignment (PS‐CA) is proposed to reduce Doppler shift impact and improve communication performance in IRS‐aided vehicular networks. In this article, the channels can be divided into two types: the one type is the cascaded channel from the base station (BS) to the IRS and then to the vehicle; the other one is the direct channel from the BS to the vehicle. Thus, the proposed PS‐CA strategy can be divided into two stages. In the first stage, the cascaded channel fast fading state is reduced by designing IRS reflection phase shifts. In the second stage, considering the phase difference between the direct channel and the cascaded channel, we designed a correction function to align the direct channel with the cascaded channel. Then, we combined the designed correction function with IRS reflection phase shifts to reduce the impact of the direct channel fast fading state on overall performance. Simulation results demonstrate that compared to the RPS strategy, the PS‐CA strategy achieves higher spectral efficiency by 31.5.

Low-profile closed cavity backed spiral antennas with circular AMC reflector for V/UHF bands

In this study, two low-profile wideband spiral antennas that are backed by Circular Artificial Magnetic Conductors (C-AMC) are proposed for V/UHF bands. Rather than using a C-AMC design that has single resonance frequency, different C-AMC structures that have different resonance frequencies are used beneath corresponding active regions of spiral antenna, such that frequency independent radiation characteristics are achieved. The C-AMC surface is designed to aim of covering the entire frequency band of antenna so that frequency regions where reflection phase of C-AMC rings are between +90° and −90° will follow each other. It is observed that using frequency-independent C-AMC and a thin absorber between C-AMC and outer region of spiral antenna element provides wideband antenna characteristics and improves axial ratio of antennas. Proposed Antenna 1 in this paper has low-profile (0.47λ0×0.47λ0×0.055λ0) at 300 MHz and high gain at frequencies between 300 MHz and 950 MHz. An absorbing material is used at the inner wall of the closed cavity to improve performance of Proposed Antenna 2 at lower frequencies. In this manner, 0 dBi realized gain transition point is achieved at 235 MHz. Proposed Antenna 2 has also low-profile (0.37λ0×0.37λ0×0.043λ0) at 235 MHz.

Modulation of antenna beam in both elevation and azimuth planes by reflective phase gradient metasurface

ABSTRACT A broadband low profile magneto-electric dipole (ME-dipole) antenna is proposed which can control the steering of the antenna beam in the elevation plane and azimuth plane. A reflective phase gradient metasurface (RPGMS) is designed to act as the partially reflecting surface of the antenna and provides two different phase shifts for it. By rotating and translating RPGMS around the center of the antenna can reshape the wavefront shape, realize beam steering with directions (, )= (±40°, 0°), (±30°, 0°), (±20°, 0°), (±20°, 90°). The results of full wave simulation are in good agreement with the measured results, the beam tilted range of ± 40° in E-plane and ± 20° in H-plane are obtained at 8 GHz. The bandwidth is between 42.5% and 48.4%, with a maximum gain of 6.29dBi.

An Optofluidic Reflective Phase Modulator Based on Electrowetting

This work presents an electrowetting-based optofluidic reflective phase modulator. The modulator mainly consists of two functional cavities and one storage cavity filled with two immiscible liquids. Two transparent sheets are fixed between the liquid-liquid interfaces in the functional cavities to get planar interfaces. The flat interfaces in the two working chambers move up and down when different voltages are applied, changing the optical path length. With the aid of two vertical top reflectors, the incident beam passes through one working chamber and then enters the other chamber in the opposite direction, leading to enlarging the variation range of optical path length. To verify the feasibility and correctness of this design, a prototype of the phase modulator is fabricated and detected in an experiment. Our reflective modulator realizes continuous adjustment in optical phase up to 11.732π when the voltage is increased to 95 V.

ENHANCING COMPREHENSION AND MOTIVATION IN LOWER LEVEL ECUADOR EFL STUDENTS: AN ACTION RESEARCH STUDY OF THREE READING STRATEGIES AT UNAE

It has been observed that EFL students at the National University of Education (UNAE) struggle with acquiring basic vocabulary, reading comprehension skills, and intrinsic motivation to promote reading in English. To address this issue, a qualitative exploratory action research was conducted aimed at improving these areas through the use of three reading strategies—extensive reading, language experience approach (LEA), and literacy circles—on the reading and motivation of 89 lower-level EFL students in UNAE within three different courses which were conducted over a six-month period. Qualitative and quantitative tools such as diagnostic and summative exams, questionnaires, observations, and reflective journals were used to understand and identify students' improvement and progress throughout the exploratory, intervention, and reflection phases of the study. Throughout this period the teachers regularly observed the strategies being utilized in the classes and reflected on their experiences. The findings from these tools suggest that the implementation of the different reading strategies together had a positive impact on students' reading abilities, writing abilities, vocabulary, comprehension, engagement, and motivation. Additionally, students were more motivated to read not only in class but also for pleasure, which promoted increased reading in English. The study provides insights into the potential benefits of using these strategies to facilitate autonomous reading, improve overall language competencies and may support EFL teachers in the development of reading programs that foster autonomous learning, increase motivation, and promote language development among EFL learners.&lt;p&gt; &lt;/p&gt;&lt;p&gt;&lt;strong&gt; Article visualizations:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;img src="/-counters-/soc/0056/a.php" alt="Hit counter" /&gt;&lt;/p&gt;