Symmetric Aperture Research Articles

Diffraction of ultrashort Gaussian pulses within the framework of boundary diffraction wave theory

We study the diffraction of Gaussian pulses and beams within the framework of boundary diffraction wave theory. For the first time the boundary diffraction wave theory is applied to pulsed Gaussian beams, and it is shown that the diffracted field of a pulsed Gaussian beam on a circularly symmetric aperture can be evaluated by a single 1D integration along the diffracting aperture at every point of interest. We compare theoretical simulations to experimental measurements of ultrashort pulses diffracted off a circular aperture, an opaque disc, an annular aperture, and a system of four concentric annular apertures. Using the recently developed SEA TADPOLE measurement technique, we obtain micron spatial and femtosecond temporal resolutions in the spatio-temporal measurements of the diffracted fields.

Approximate synthesis formulas for microstrip line with aperture in ground plane

Approximate closed-form expressions for the propagation characteristics of a microstrip line with a symmetrical aperture in its ground plane are reported in this article. Well-known expressions for the characteristic impedance of a regular microstrip line have been modified to incorporate the effect of this aperture. The accuracy of these expressions for various values of substrate thickness, permittivity and line width has been studied in detail by fullwave simulations. This has been further verified by measurements. These expressions are easier to compute and find immense use in the design of broadband filters, tight couplers, power dividers, transformers, delay lines, and matching circuits. A broadband filter with aperture in ground plane is demonstrated in this article. (c) 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

Symmetric-Aperture Antenna for Broadband Circular Polarization

A novel symmetric-aperture antenna is proposed for broadband circularly polarized (CP) radiation using a coplanar waveguide (CPW) feed. The proposed antenna consists of a CPW-feed and a wide symmetric aperture along the diagonal axis. A symmetric-aperture consists of two diamond-shaped sections. The symmetric-aperture and CPW-feeding structure are fabricated on the same plane of a dielectric substrate. Wideband CP radiation is achieved by changing the arms of symmetric-aperture and stripline length. The measured bandwidths of 3-dB axial ratio (AR) and 10-dB return loss are around 68% (2.4-4.85 GHz) and 107% (1.6-5.25 GHz), respectively. The measured boresight gain is more than 3.0 dBic over the CP bandwidth. Overall antenna size is around 0.7λo × 0.7λo × 0.019λo at 3.5 GHz.

Simulation of high order short range wakefields for particle tracking codes

We consider the effects of short range (intra bunch) wakefields in axially symmetric apertures for bunches of arbitrary shape, and show how they can be included in particle tracking codes in a computationally efficient way, including modes of any angular order. The MERLIN simulation code is given as an example. Results from these simulations strongly indicate that such higher order mode wakefield effects are not significant even for the unprecedentedly small-dimension collimation system proposed for the ILC.

Power-law flow statistics in anisometric (wedge) hoppers

We find the probability for N particles to exit an anisometric (having unequal dimensions) hopper before jamming to have a broad power-law decay with exponent α = -2, in marked contrast to the exponential decay seen in hoppers with symmetric apertures. The transition from exponential to power law is explained by amodel that assumes particle motion is correlated over a distinct length scale. Hoppers with lengths larger than this length are modeled as a series of adjacent, statistically independent "cells." Experiments with apertures 27-37 particle diameters D long are well fit by a three-cell model, implying that the correlation length is ≈ 9-12D.

Spatio-temporal characterization of ultrashort pulses diffracted by circularly symmetric hard-edge apertures: theory and experiment

We carry out a complete spatio-temporal characterization of the electric field of an ultrashort laser pulse after passing through a diffractive optical element composed of several binary amplitude concentric rings. Analytical expressions for the total diffraction field in the time and spectral domain are provided, using the Rayleigh-Sommerfeld formulation of the diffraction. These expressions are experimentally validated. The spatio-temporal amplitude and phase structure of the pulse are measured at different planes beyond the diffractive optical element using spatially-resolved spectral interferometry assisted by an optical fiber coupler (STARFISH). Our results allow corroborating theoretical predictions on the presence of multiple pulses or complex spectral distributions due to the diffraction-induced effects by the hard-edge ring apertures.

A Coaxial Feeder with Two Pairs of Parasitic Pins for Realizing Rotationally Symmetric Aperture Illumination in Spiral Array Radial Line Slot Antennas

A spiral array radial line slot antenna (SA-RLSA) is designed in 22GHz band. A SA-RLSA excited with a coaxial feeder suffers from aperture illumination fluctuation in amplitude and phase in the circumferential (φ-) direction while in the radial direction, reasonably uniform distribution is observed. Rotational symmetry of radiation patterns is degraded and especially the sidelobe levels are unbalanced. This fluctuation is associated with the generation of the higher order modes in the φ-direction and is the unique defect of SA-RLSA which uses oversized waveguide. In this paper, a novel feeding structure with two pairs of parasitic pins around a coaxial feeder is proposed and designed so as to compensate the rotational asymmetry of aperture illumination. A measurement using the model antenna designed in 22GHz band demonstrates the enhancement of the rotational symmetry; the circumferential fluctuation is reduced from 5.1dB and 33 degrees to 1.8dB and 12 degrees, while the fluctuation in the first sidelobe level suppressed from 10.7dB to 1.2dB.

Complex Resonances of a Hard Rectangular Cavity Coupled to a Half-Space Through a Narrow Aperture

Electromagnetic coupling through a small slot into a two-dimensional rectangular cavity is computed via a simple Ritz-Galerkin expansion of the aperture field for the case of transverse electric (TE) polarization. One term expansions for each of the symmetric and antisymmetric dynamic aperture fields use the exact solutions for harmonic potentials that solve the related Neumann problem of a slot in a hard plane. Source-free solutions exist at discrete, complex-values of the frequency variable. These eigenfunctions of the negative Laplacian are improper modes and several of the low-order, complex resonances are found from zeros of the variational expression that relates the aperture field to the excitation. The complex resonances are perturbations of the real, closed-cavity resonances and their presence is unmistakable in the net stored energy in the cavity under plane-wave excitation from the exterior half-space.

Pattern of morphological variety of angeospermous pollen aperture distribution and natural ordering of biological variety, or – what is a variety (problems of description and interpretation)

Beside typical pollen forms with symmetrical aperture arrangement, various deviant forms with less symmetrical arrangements have been observed in remote Angiospermous taxa. The pollen forms may be arranged in the continuous, geometrically regular and taxonomically unspecific transformational series. Continuous and regular pattern of the variety obtained can not be described by any way of the classification without complete destroying of the unity of this pattern due to the typological procedures (discretization). The paradox is considered: the variety described consists of discrete pollen grains (as the biological variety consists of mortal living bodies) i.e. has the discrete pattern, but the variety of pollen morphological characteristics have the continuous pattern. Problems of description of the pattern of the biological variety and ways of interpretation are discussed.

Optical filters with fractal transmission spectra based on diffractive optics

The duality between the axial irradiance distribution originated by any circularly symmetric diffracting aperture under monochromatic illumination and its diffracted spectral intensity at a fixed on-axis point under broadband illumination is highlighted and experimentally investigated. Two applications are derived from this basic result. On the one hand, we suggest the use of a broadband source and a spectrometer for a single-shot measurement of the axial response of pupil filters. Second, we implement a spectral filter having a transmission spectrum with a fractal structure of frequencies. Experimental results and potential applications in synthetic spectra designs are provided.

Optimal Synthesis of Directivity Constrained Pencil Beams by Means of Circularly Symmetric Aperture Fields

The problem of the optimal synthesis of circularly symmetric aperture distributions able to radiate pencil beams fulfilling well-defined requirements on the far-field and/or the directivity is addressed and solved. In particular, constraints concerning both the sidelobe level (SLL) and the directivity within a coverage zone are dealt with while being careful not to incur into the so called super-directive sources or into aperture fields actually difficult to be realized. The case wherein a constraint is enforced on the dynamics of the excitations is also considered. Numerical examples concerning cases of practical relevance are also shown in support to the given theory.

Study on Axially Symmetric Aperture Lenses with Extension of an Inhomogeneous Electric Field

Study on Axially Symmetric Aperture Lenses with Extension of an Inhomogeneous Electric Field

Laser fabricated microchannels inside photostructurable glass-ceramic

Microchannels have been fabricated by laser direct-write in photostructurable glass-ceramic (Foturan) for their application in 3D-microfluidic systems. A Nd:YAG laser delivering 10 ns pulses at 355 nm wavelength has been used for irradiation. Afterwards, thermal treatment and chemical etching have been required for channel formation. The kinetics of channel formation and the channel morphology have been studied by optical and electron microscopy. A minimum accumulated energy (pulse energy multiplied by the number of pulses in a same site) is required to induce channel formation. Channels with symmetric round apertures at both ends can be obtained when using low pulse energies. On the contrary, irradiation with too high energetic pulses produces direct material damage in Foturan and provokes the formation of non-symmetric channels. One millimetre long channels with a minimum radius of 15 μm can be opened through Foturan slides after 15 min of chemical etching.

Isolated Upper Eyelid Retraction: A Sign of Idiopathic Inflammatory Orbital Disease

A 41-year-old woman was examined for left upper eyelid retraction. Remaining ocular and systemic examination was unremarkable. Orbital CT demonstrated an ill-defined, extraconal, superior orbital soft-tissue mass involving the levator palpebrae superioris muscle. Incisional biopsy with histopathology demonstrated idiopathic orbital inflammation. The patient was started on a gradually tapering dose of oral steroids, for 6 weeks. On follow-up, the eyelid retraction had resolved. We report this case to demonstrate that idiopathic inflammatory orbital disease, localized to the superior orbit, may cause isolated upper eyelid retraction without associated proptosis. This condition resolves with medical therapy, leading to symmetrical palpebral apertures.

Sudoriferous cyst of the orbit of adult origin after trauma

A rare case of sudoriferous cyst of the orbit occurring in an adult, who had facial trauma, is reported. Several factors suggest its adult onset. The only other case reported in an adult is of presumed childhood origin. Very few congenital cases have been reported. A 65-year-old lady presented with recent onset of left-sided ptosis and a painless mass below the left supraorbital margin. The patient had traumatic ptosis after a road traffic accident 13 years ago. The ptosis was surgically repaired, which resulted in symmetrical palpebral apertures. Computed tomographic scan revealed a well-defined cystic mass in the anterior orbit. The mass was removed in toto by anterior orbitotomy. Histopathological examination revealed a single cyst lined by double-layered cuboidal epithelium in some areas and transitional epithelium at others. A periodic acid Schiff (PAS) positive, diastase-resistant glycocalyx lined the inner epithelium. Apical snouting suggested an apocrine nature. This confirmed a diagnosis of sudoriferous cyst.

Focusing and spectral characteristics of periodic diffractive optical elements with circular symmetry under femtosecond pulsed illumination

The analytical solution is derived, within the Rayleigh-Sommerfeld formulation of diffraction, for the on-axis spectral irradiance of a broadband source after diffracting through a circular symmetric hard aperture. By using this solution, and within the paraxial approximation, we investigate several diffraction-induced effects originated by binary diffractive optical elements made up of a set of annular apertures with equal areas and periodic in the squared radial coordinate. In particular, the ability to focus femtosecond pulses is investigated. In addition, the analysis of the spectral modifier function associated with these elements allows us to simulate spectral shifts at focus positions. Finally, we introduce a relatively simple and low-cost technique to slice the spectrum of a broadband source in order to generate narrow bands or wavelength channels.

Correlation Between Detector Array Measurements and a Computer Algorithm for Enhanced Dynamic Wedge Profiles

Verification of dosimetric data computed by a treatment planning system is necessary in the commissioning process for any clinical software, just as it is necessary for any annual quality assurance testing. Direct verification of the dosimetric data is achievable when calculating the enhanced dynamic wedge (EDW) off-axis ratio at each point of interest. As mathematical models for hand-calculating such factors are still evolving, measurement of these external beam arrangements has proven significantly more accurate. This research presents a correlation for measured and planned data, specific for 6- and 18-MV photon beams on a Varian 21EX linear accelerator, using the EDW mode. Field generation was created using the Varian Eclipse treatment planning system. On treatment field delivery, the Sun Nuclear MapCHECK diode array was used to plot each beam profile in 2 dimensions. Wedge angles of 10°, 15°, 20°, 25°, 30°, 45° and 60° were studied here, under isocentric geometry, at a fixed water equivalent depth of 15 cm. Field size dependence was considered with each wedge and energy combination, where symmetric apertures of 5 × 5 cm 2, 10 × 10 cm 2, 15 × 15 cm 2 and 20 × 20 cm 2 were used. Accurate dosimetric results were found to be achievable when using this treatment planning system to within 2.8% maximum deviation, and to within 1% deviation averaged over all. The diode array also proved to be simple and ideally suited for EDW measurements.

On-axis diffraction of an ultrashort light pulse by circularly symmetric hard apertures

The analytical solution of the Rayleigh-Sommerfeld on-axis diffraction integral for an ultrashort light pulse diffracted by circularly symmetric hard apertures is derived. The particular case of a circular aperture is treated in detail. The time changes of the instantaneous intensity along the axial direction are predicted. An analysis of the standard deviation width shows a pulse broadening about the axial positions where the instantaneous intensity reaches a zero value. We show that the temporal shape of the instantaneous intensity depends on the number of oscillation cycles at the central frequency of the real electric field.

Beamforming using spatial matched filtering with annular arrays

A linear array beamforming method for ultrasonic B-mode imaging using spatial matched filtering (SMF) and a rectangular aperture geometry was recently proposed Kim et al., [J. Acoust. Soc. Am. 120, 852-861 (2006)]. This letter extends those results to include circularly symmetric apertures. SMF applied to annular arrays can improve the lateral resolution and echo signal-to-noise ratio as compared with conventional dynamic-receive delay-sum beamforming. At high frequencies, where delay and sum beamforming is problematic, SMF showed greatly improved target contrast over an extended field of view.

The stability of mechanical calibration for a kV cone beam computed tomography system integrated with linear acceleratora)

The geometric accuracy and precision of an image-guided treatment system were assessed. Image guidance is performed using an x-ray volume imaging (XVI) system integrated with a linear accelerator and treatment planning system. Using an amorphous silicon detector and x-ray tube, volumetric computed tomography images are reconstructed from kilovoltage radiographs by filtered backprojection. Image fusion and assessment of geometric targeting are supported by the treatment planning system. To assess the limiting accuracy and precision of image-guided treatment delivery, a rigid spherical target embedded in an opaque phantom was subjected to 21 treatment sessions over a three-month period. For each session, a volumetric data set was acquired and loaded directly into an active treatment planning session. Image fusion was used to ascertain the couch correction required to position the target at the prescribed iso-center. Corrections were validated independently using megavoltage electronic portal imaging to record the target position with respect to symmetric treatment beam apertures. An initial calibration cycle followed by repeated image-guidance sessions demonstrated the XVI system could be used to relocate an unambiguous object to within less than 1 mm of the prescribed location. Treatment could then proceed within the mechanical accuracy and precision of the delivery system. The calibration procedure maintained excellent spatial resolution and delivery precision over the duration of this study, while the linear accelerator was in routine clinical use. Based on these results, the mechanical accuracy and precision of the system are ideal for supporting high-precision localization and treatment of soft-tissue targets.