Effective Beam Width Research Articles

Statistical properties of circular and rectangular multi-sinc Schell-model beams propagating in uniaxial crystals

With the extended Huygens–Fresnel principle, we derive the expressions for the spectral intensity, coherence, and effective beam width of circular and rectangular multi-sinc Schell-model (MSSM) beams propagating through uniaxial crystals. Numerical simulations are employed to extensively explore how beam and crystal parameters modulate the optical field. The results reveal that the propagating field exhibits multiple ring-shaped and array-like intensity distributions, with adjustable features such as the number of concentric rings, central brightness, array dimensions, and the morphology and diversity of sub-beams. Additionally, the spectral coherence displays an oscillatory distribution that evolves into a Gaussian distribution as the transmission distance increases. The anisotropy of uniaxial crystals not only influences the morphology of intensity distribution but also affects the evolution rate of coherence and the expansion rate of effective beam width. Our work contributes to optimizing beam propagation through uniaxial crystals, potentially benefiting precision optical systems in laser technology.

The effects of laser cane cues on the freezing of gait of Parkinson's disease patients: can increasing the laser light beam width play a role?

Freezing of gait can be seen in a significant number of people with Parkinson's disease. Disappointingly, the classic standard treatment of Parkinson's disease with dopamine replacement has not shown promising results in improving the freezing of gait. Hence the approach have shifted towards using non-invasive methods to address this problem. To assess the effect of laser cane as a visual cue on the freezing of gait of people with Parkinson's disease and further determine the effect of laser light beam width and color on the freezing of gait. 7 known Parkinson's Disease patients were enrolled in this study, all of whom had at least one episode of freezing at at least one clinical visit. These patients underwent gait analysis in 4 stages: walking without a cane, walking with a thin red light laser cane, a thick red light laser cane, and a green light laser cane. Using laser canes effectively improved nearly all parameters of walking, including right and left stride length, step length, the velocity of movement, and rotation time, compared to walking without a stick. Using different colors of laser cane didn't make any significant difference in improving the freezing of gait of our patients. Nevertheless, increasing the laser light beam width significantly improved almost all walking parameters. This is the first study assessing the effect of laser light beam width on freezing of gait in Parkinson's disease patients and shows promising results in regards to increasing the thickness of laser lights in order to improve walking parameters in Parkinson's disease patients more effectively. Furthermore, this is the second study to evaluate the effect of laser light color, contradicting the previous results by showing no significant correlation between the color of laser light and improvements in walking parameters.

The accuracy of length measurements made using imaging SONAR is inversely proportional to the beamwidth

Abstract Multibeam imaging SONARs have been used for a range of measurement applications, such as measurements of fish lengths. This study aimed to quantify the accuracy of imaging SONAR systems, that varied in frequency and beam geometry, to measure the length of synthetic targets positioned perpendicularly. Blueprint Oculus imaging SONAR systems, with four different (centre) frequencies (750 kHz, 1.2 MHz, 2.1 MHz and 3 MHz), were used to measure the length of three targets of nominal lengths: 10 cm, 20 cm and at ranges between 1 and 15.5 m. The effect of beam geometry on measurement error was then examined using regression analysis. This study found that there was an overestimation of the actual length of the target for all measurements that was inversely proportional to the horizontal beamwidth. The measurement error can be reduced by normalising for beamwidth. However, the variation of measurements (i.e. the precision) was found to also increase with range, which was attributed to the increasing beam separation. It is important that the effect of beamwidth on the accuracy of target length measurements, by imaging SONARs is acknowledged in future studies. One approach to mitigating this problem, is to limit the range at which length measurements are made to a beamwidth that produces an estimated level of error that is acceptable for that study.

The Effect of Poisson Ratio and Beam Width on the Fundamental Frequency of a Cantilever Beam

The Effect of Poisson Ratio and Beam Width on the Fundamental Frequency of a Cantilever Beam

The effect of beam width and crack-depth ratio on mode I fracture toughness of RCB: an experimental and numerical study

In the present work, the fracture performance of pre-cracked reinforced concrete beams was investigated numerically and experimentally. Experimental and numerical programs were designed to examine the effect of beam width, b, (120 and 250 mm) and crack-to-depth ratio, a/d, (0.1, 0.2 and 0.3) for concrete strength, fc, (40 MPa), on the behavior of stress intensity factor, K1C, and fracture energy, G, for reinforced concrete, RC, beams. The work utilized beams with three-point loading conditions experimentally. Through the use of the ANSYS program, a comprehensive 3-D finite element analysis was conducted with utmost precision to simulate and idealize all experimental specimens. It has been confirmed through numerical and experimental outcomes that the stress intensity factor for RC concrete beams experiences a significant increase as the a/d increases. Furthermore, the fracture toughness values in this study show a slight increase due to the utilization of RC concrete beams with wider width. The validity of the presented concept was demonstrated by comparing the experimentally measured load vs. deflection values to the predicted numerical values and finding them to be acceptable.

Finite Element Analyses of Cast-in-situ RC Flat Slab with an Equivalent Frame for Horizontal Loads

In structural construction practice, the use of reinforced concrete slabs is extremely common due to their structural and economic advantages. An important issue is the study of structural behavior given to horizontal effects. The significance of this is centered not only on the scales caused by wind and construction loads, which are considered to be “normal” i.e., the quasi-static, which is essentially one-way monotonically increasing but also the most researched seismic, i.e., cyclically varying, direction and magnitude effects. The most widespread methods for sizing flat plate slabs to unidirectional, quasi-static horizontal loads are the so-called Equivalent Frame Method and the Effective Beam Width Method. In addition to analytical and basically linear numerical theoretical methods, several laboratory experiments have been performed and published. In this paper, we investigate the behavior of column-supported flat plate slabs against unidirectional, monotonically increasing horizontal loads using an advanced nonlinear numerical modeling method. Numerical models constructed with different geometric dimensions were created with ATENA 3D three-dimensional nonlinear finite element software. In the numerical studies, in addition to the vertical loads in the global sense, the horizontal loads were also taken into account. In our studies, we analyzed the global behavior of the structure, crack propagation, and internal stresses. The results were illustrated on force - displacement diagrams and compared with the results of the laboratory experiments used, thus showing the accuracy and limitations of the numerical modeling procedure. The numerical results were also compared with the results determined on the basis of the equivalent framework models.

The effective beam width of a partially coherent rectangular mul-ti-Gaussian Schell-model vortex beam propagating in a turbulent plasma

Based on the derived analytical formulae for the optical intensity and effective beam width of a partially coherent rectangular multi-Gaussian Schell-model (RMGSM) vortex beam, we analyzed the evolution of the effective beam width of a partially coherent RMGSM vortex beam propagating in an anisotropic turbulent plasma using numerical examples. The numerical results demonstrated that the effective beam widths in the x and y directions were similar. In studies on the influences of the source parameters, one can see that an RMGSM vortex beam with a larger topological charge and beam waist or a smaller correlation coefficient σ evolves into a beam with a larger effective beam width. However, the influence of beam order was not evident. In addition, numerical examples proved that the effective beam width increases with increasing propagation distance and refractive index fluctuation variance or decreasing anisotropy parameter , outer scale , and inner scale . This study's results will be beneficial for applications in free-space optical communications.

Standalone-Intelligent Reflecting Surface Control Method Using Hierarchical Exploration by Beamwidth Expansion and Environment-Adaptive Codebook

Intelligent reflecting surfaces (IRS) have garnered attention for the high-capacity and reliable communication required by Beyond 5G. However, IRS control in existing studies assumes information sharing and control instructions from base stations (BSs), thus requiring a backhaul link to the core network and BSs. This requires the construction of a network system, ruining the advantages of IRS, such as its low cost and installation flexibility. Therefore, a standalone-IRS, which is completely independent of the core network and BSs, is expected to maximize the performance of the IRS. However, a standalone-IRS cannot obtain sufficient information for control decisions, such as channel state information, which is frequently used in existing studies; therefore, inefficient control methods, such as exploration, must be used. To this end, this study proposes a significant reduction in the overhead required for exploration by hierarchical exploration and a reduction in the exploration itself using codebooks to store the results of exploration. Furthermore, to prevent the degradation of communication quality due to the use of hierarchical exploration and codebooks, we propose an effective beamwidth expansion method for hierarchical exploration and an efficient codebook construction method based on user distribution as elemental methods. In this study, we evaluated the overhead reduction and communication quality of the standalone-IRS control by combining these methods through simulations.

Derivation of an in-plane amplitude equation and its paraxial approximation for elastic guided waves in plates

In addressing the construction of beam solutions for elastic guided waves in plates, we propose expressions of the amplitude function for the Lamb wave and the shear horizontal plate wave. The amplitude function is governed by an in-plane amplitude equation describing plate waves that has a same form as the two-dimensional Helmholtz equation. Therefore, beam solutions can be constructed within the same framework as this Helmholtz equation. The paraxial approximation is then applied to this in-plane amplitude equation. On the basis of this approximation, Gaussian beam solutions for both the Lamb and shear horizontal plate waves are derived. The effects of beam width, wavenumber, and guided-wave mode upon the wavefields are examined through several numerical examples.

The Evolution Characteristics of Twisted Hermite–Gaussian Schell-Model Beams Propagating in a Uniaxial Crystal

In this paper, we study the propagation properties of twisted Hermite–Gaussian Schell- model (THGSM) beams propagating in a uniaxial crystal orthogonal to the optical axis. We derive the concrete analytical expression of the cross-spectral density (CSD) function in the crystal and simulate the evolution characteristics of such beams, including normalized spectral intensity, the spectral degree of coherence (DOC), and effective beam width. We find that the spectral intensity distribution exhibits a non-circular symmetric self-splitting while rotating, and the distribution of the spectral DOC is non-circular symmetric rotationally distorted, which is quite different from that in an isotropic medium. The initial beam parameters and crystal parameters both affect the distribution of spectral intensity and DOC. Furthermore, increasing the twist factor and adjusting the ratio of the extraordinary light refractive index and the ordinary light refractive index ne/no of the uniaxial crystal can suppress the beam expansion as propagating in the crystal. Our results show that the uniaxial crystal can be used to determine whether light beams carry a twist phase or not, and to modulate the characteristics of light beams.

Antipodal Linearly Tapered Slot Antenna with Quasi-Hemispherical Pattern Using Subwavelength Elements

Antennas with quasi-hemispherical radiation patterns are preferred in many wide−area wireless communication systems which require the signals to uniformly cover a wide two−dimensional region. In this work, a simple but effective beamwidth broadening technique based on an antipodal linearly tapered slot antenna (ALTSA) is first proposed and then experimentally verified. Compared with most of the reported designs, the proposed antenna can significantly widen beamwidth and achieve a quasi-hemispherical radiation pattern without increasing the overall size and structural complexity. Only two rows of subwavelength metallic elements (eight elements in total) are simply and skillfully printed at specified positions on the dielectric substrate (relative permittivity εr = 2.94 and thickness h = 1.5 mm) of a general ALTSA whose peak gain is 11.7 dBi, approximately 200% half-power beamwidth (HPBW) enlargement can be obtained in all cut-planes containing the end-fire direction at the central frequency of 15 GHz, and the HPBW extensions in different cut-planes have good consistency. Thus, a quasi-hemispherical beam pattern can be acquired. Thanks to the simplicity of this method, the antenna size and structural complexity do not increase, resulting in the characteristics of easy fabrication and integration, being lightweight, and high reliability. This proposed method provides a good choice for wide−beam antenna design and will have a positive effect on the potential applications of wide-area wireless communication systems.

Linear and nonlinear optical properties surface plasmon polariton localization in plasmonic crystal metallic nanowires

Functionality and spatial concentration of light in periodic and disordered plasmonic crystal metallic nanowires are investigated under Kerr nonlinearity. The results show that nonlinear transverse localization of surface plasmon polaritons (SPP) in a periodic and disordered array of nanowires embedded in the Kerr medium changes with incident input wave amplitude (A). We study periodic and diagonal disordered nanowire arrays and study the propagation of SSPs under different inputs by solving nonlinear coupling relations. Finally, off-diagonal disordered nanowire arrays are studied. The results show that localization and effective beamwidth of the SPPs increases with an increase in their input amplitudes. Also, the SPPs become more localized with increase of diagonal (δr) and off-diagonal disorder (δd) into the nanowire arrays. Controlling SSPs' localization in the nanowire array using their input amplitude provides a high functional sub-wavelength device that can be utilized in future applications of nanophotonics functions.

Experimental proof on the effect of beam width and spatial coherence on Goos-Hänchen shift

We have experimentally investigated the effect of beam width and spatial coherence on Goos-Hänchen (GH) shift of light in a double-prism structure. The beam width and spatial coherence of the incident light are well controlled and measured. The experimental results show that the GH shift is affected by both the beam width and spatial coherence of light, and this is qualitatively consistent with the prediction of coherence theory of light. The result can promote the application of controlling GH shifts of partially coherent finite beams in optical devices and sensors.

Investigation of the disordered optical fiber with wavelength-scale feature size mediated by transverse Anderson localization.

A narrow beam propagating through the disordered optical fiber first undergoes diffusive broadening, until its width becomes comparable to the localization length. The study of numerical algorithms and statistical methods in the simulation analysis process of disordered optical fibers demonstrates that the influence of polarization characteristics and transverse grids on calculation errors is critical for statistical numerical simulation in disordered systems. We performed a detailed numerical analysis of the effect of different design parameters in disordered fibers on the localization effect-that is, the localization length, including the refractive index contrast, feature size, and fill-fraction. The results show that the optimal fill-fraction is 50%, and that higher refractive index contrast and larger feature size relative to the wavelength both result in a smaller effective beam width. Finally, numerical evidence is also provided that optical images can be transported via transverse Anderson localization.

Characteristics of an Airy beam at a dielectric interface

A full analytical theory for the reflection and transmission of an Airy beam impinging on a dielectric surface is presented. Based on the plane-wave angular spectrum expansion, the analytical expressions for the reflected and transmitted fields comprising beam modes are derived. To improve the calculation accuracy, the actual beam field retains up to the second-order terms. The influences of decay factor and beam width on the intensity distributions of the incident, reflected, and transmitted beams are studied. In addition, we investigate the effects of decay factor and beam width on the beam shift of the reflected beam near the Brewster angle. There is a giant negative lateral shift near the Brewster angle. Results show that the beam shift decreases and increases with increasing decay factor and beam width, respectively. A comparison with the beam shifts of Airy beams incident on the interface and dielectric slab at the Brewster angle is also discussed. The beam shift of the dielectric slab exists an abrupt increase. Finally, an Airy beam incident from air to the left-handed material (LHM) is considered. Results indicate that the imaging position of the incident Airy beam in the LHM is affected by the incident angle and negative refractive index. Our results may provide some theoretical support for the applications of Airy beams in detection and imaging.

Eigenvalue Buckling Analysis of Beams with Different Width and Square Cutout

In this study, effect of square cutout and beam widths on eigenvalue buckling analysis of beams is evaluated using finite element and Taguchi methods. ANSYS software is used to perform the finite element analyses and the analyses were conducted Taguchi L9 orthogonal array with three control factors. Each control factor has three levels. The first control factor is considered as position of square cutout whereas the second control factor was assumed as beam widths. The influence of levels of the beam widths and square cutouts on responses is determined using analysis of signal-to-noise ratio whereas variance analysis was operated to notice the effect of each control factor on the buckling behavior of the beams. According to results obtained from the study, the buckling value of the beams increase as the square cutout get closer to the free edge. Increase of the beam widths leads to an increase on buckling result of the beams. The effect of beam width on the buckling analysis is higher than square cutout.

Method for optimising the performance of PML in anchor‐loss limited model via COMSOL

Perfectly matched layer has been used for solving anchor-loss limited quality factor in the Micro electromechanical systems. However, setting up a well-behaved perfectly matched layer requires users to change the parameters of a perfectly matched layer to give correct results, while the current existing methods for choosing the right parameters are vague and lack theoretical support. Based on the mathematical theory of perfectly matched layer and simulation results of a beam structure's quality factor, this paper proposes a method for choosing the parameter to optimise the performance of perfectly matched layer in COMSOL. The accuracy of the proposed method is proved by matching the effect of substrate height on beam's quality factor with theory prediction. The author also studies the effect of beam height and beam width on the quality factor of the beam. The results demonstrate that simulated quality factors are in agreement with analytical values when the ratio of height over length is small but will show great divergence when height equals the length. This trend can be observed for the beam width as well. Especially for larger ratio of beam width over beam length, instead of decreasing monotonously as analytical equitation would expect, the simulated quality factor will converge into a stable value of 1700, which matches the result of two-dimensional model for the same beam structure. This means that a three-dimensional model has to be used for estimating the quality factor of a beam structure.

Beam width and arm position but not cognitive task affect walking balance in older adults

Detection of changes in dynamic balance could help identify older adults at fall risk. Walking on a narrow beam with its width, cognitive load, and arm position manipulated could be an alternative to current tests. Therefore, we examined additive and interactive effects of beam width, cognitive task (CT), and arm position on dynamic balance during beam walking in older adults. Twenty older adults (69 ± 4y) walked on 6, 8, and 10-cm wide beams (2-cm high, 4-m-long), with and without CT, with three arm positions (free, crossed, akimbo). We determined cognitive errors, distance walked, step speed, root mean square (RMS) of center of mass (COM) displacement and trunk acceleration in the frontal plane. Beam width decrease progressively reduced distance walked and increased trunk acceleration RMS. Step speed decreased on the narrowest beam and with CT. Arm crossing decreased distance walked and step speed. COM displacement RMS and cognitive errors were not affected by any manipulation. In conclusion, distance walked indicated that beam width and arm position, but less so CT, affected dynamic balance, implying that beam walking has the potential to become a test of fall risk. Stability measurements suggested effective trunk adjustments to control COM position and keep dynamic balance during the task.

Finite Element Analysis of Heavy Duty Riveted Steel Grating Bridge Deck

Heavy duty riveted gratings are a good alternative for applications that often employ other deck systems, if they are carefully analyzed under static and fatigue loads. Understanding the static behavior of a riveted steel deck under tire patch loads will aid in establishing a design model based on an effective beam width. In addition, use of a riveted system avoids welded details that may lead to fatigue cracking, thereby improving design life. In this study, analysis of a typical riveted steel deck under a standard AASHTO fatigue truck with a 15% impact factor was conducted. Hand calculations were compared with the results of a finite element model using SAP2000 v19.2.1. Bending moments and stresses were evaluated and compared. Stresses at the rivet hole for the most highly loaded bearing bar were evaluated. A model for fatigue cracking around a rivet hole is discussed.

Analysis of multi-pulse position modulation free space optical communication system employing wavelength and time diversity over Malaga turbulence channel

Free space optics (FSO) communication has proved to be a useful technology both in the scientific and commercial domains in response to exponential growth in demand for ultrahigh bandwidth for applications such as urban broadband services, cellular backhaul and earth to satellite links among others. However, atmospheric turbulence, prevailing adverse weather conditions and pointing errors between the transmitter and receiver affect significantly this technology. To mitigate these challenges, different approaches have been considered in literature such as error control coding, spatial diversity, the use of relays and so on alongside different modulation techniques. Therefore in this paper, we have considered the use of multipulse position modulation (MPPM) modulation technique first with wavelength diversity and then with time diversity techniques over the Malaga (M) distribution as a way of mitigating against turbulence fading and pointing error effects. Closed form expressions for the average bit error rate (BER) and outage probability have been derived and later on used to analyze the system performance. The effect of diversity order, normalized jitter and beam width has been scrutinized, all as functions of the transmitted power. Beside the fact that the increase in diversity order improves both the BER and outage probability, it has been noted that the system performance is highly degraded when the normalized jitter is increased beyond 4 for any given diversity order. The BER decreases while the receiver beam width, Wz increases for all diversity orders, reaching to an optimum value of 0.5 m and 1.2 m for normalized jitter of 2 and 5 respectively. Ultimately, the conclusion drawn from the analytical results of this paper support the application of wavelength as well as time diversity as means of enhancing the FSO communication system performance