Central Aperture Research Articles

Plasmonic Color Filter Array with High Color Purity for CMOS Image Sensors.

We demonstrate the multiband color filtering of a standard RGB color and a complementary CMY color by a plasmonic color filter, composed of concentric corrugated metallic thin film rings. The surface plasmon resonance is excited by the periodic corrugation, and the coupled light is transmitted through the central subwavelength aperture. Color selectivity is achieved not only in the visible but also in the near-infrared (NIR) region. Therefore, simultaneous imaging with visible and NIR can be realized by the integration of plasmonic color filters with sensors. We investigate the angle of incidence dependence of the transmission color selectivity and the color purity of the fabricated plasmonic color filter array.

Changes in fundus reflectivity during myopia development in chickens.

Previous studies have shown that changes in functional activity in the retina can be visualized as changes in fundus reflectivity. When the image projected on the retina is low pass filtered or defocused by covering the eye with a frosted diffuser or a negative lens, it starts growing longer and develops myopia. We have tested the hypothesis that the resulting altered retinal activity may show up as changes in fundus reflectivity. Fundus reflectivity was measured in chickens in vivo, both in visible (400-800 nm, white) and near ultraviolet (UV) light (315-380 nm). Two CCD cameras were used; a RGB camera and a camera sensitive in near UV light (peak sensitivity at 360 nm). White and UV LEDs, respectively, placed in the center of the camera lens aperture, served as light sources. Software was written to flash the LEDs and record the average brightness of the pupil that was illuminated by light reflected from the fundus. The average pixel grey level (px) in the pupil was taken as a measure of the amount of reflected light while refractive errors were corrected by trial lenses after pupil brightness was corrected for pupil size. It was found that myopic eyes had brighter pupils in UV light, compared to eyes with normal vision, no matter whether myopia was induced by diffusers or negative lenses (48 ± 9 vs. 28 ± 3, p<0.001 and 47 ± 7 vs. 27 ± 2, respectively). Using SD-OCT in alert chickens it was found that the retinal nerve fiber layer (RNFL) and the retinal ganglion cell layer (RGCL) in the central retina became thinner already at early stages of myopia development, compared to controls (31.2 ± 5.8 µm vs. 43.9 ± 2.6 µm, p<0.001 and 36.9 ± 1.2 µm vs. 44 ± 0.5 µm, respectively). While the decrease in RNFL thickness occurred concomitantly with the increase in UV reflectivity, it remains unclear whether these changes were causally linked. Thinning of the RNFL could be due to reduced neural activity in retinal ganglion cells but also due to metabolic changes in the retina during myopia development.

Pinhole pupilloplasty: Small-aperture optics for higher-order corneal aberrations

This technique of performing pinhole pupilloplasty helps filter the straylight from the periphery of the cornea in cases with higher-order corneal aberrations. The pinhole effect blocks distorted and unfocused light rays and isolates more focused central and paracentral rays through the central aperture, thereby reducing aberrations of the optical system as a whole and enhancing visual acuity and its image quality.

Abstract B204: Collimator design and simulation for preclinical radiotherapy applications using a clinical cell irradiator

Abstract The use of preclinical studies with animal models in biomedical research provides a critical step in the assessment of novel therapeutic approaches. In vivo studies using small animals play a pivotal role in generating and improving methods for therapeutic treatment of cancer including radiotherapy (RT). Rodents, and in particular mice, have led to extensive development in cancer research. Currently, there are two commercially available radiation devices for small animal irradiation: The Small Animal Radiation Research Platform. Both deliver targeted radiation to preclinical animal models with an accuracy equivalent to clinical RT using a rotating gantry and implement high-resolution cone beam-CT and 3D bioluminescent tomographic imaging. However, the complexity of these systems makes them rather expensive, which is often a hindering factor for hospitals or research institutions to acquire them. The Gammacell 40 Exactor is a low-dose research irradiator widely available, commonly used for radioimmunology studies and is suitable to treat murine models. The device implements two 137Cs sources; each one has a nominal activity of 55.5 TBq and together they can produce a central dose rate of 1.0 Gy/minute. In this study two collimators were designed capable of precisely collimating a 1 cm radiation beam for focal irradiation, accommodated within a Gammacell 40 Exactor irradiator. This machine allows to insert in the main chamber collimator designs with a maximum dimension of 312 mm in diameter and 106 mm in height. The one-chamber collimator was designed cylindrical with an internal space for the mouse of 100 mm in diameter and a height of 50 mm. This chamber was surrounded on its sides by a cylindrical wall of steel and lead, and two 25mm-thick lead lids at the top and bottom with central apertures of 10mm in diameter. This geometry conforms the beam of the two Cs137 sources to a 10mm beam. In the wall that surrounds the inner chamber, four ventilation apertures were designed, which allow the mice to breath while they are been irradiated, in an anesthetized state. The four-chamber collimator was designed to be capable of irradiating up to 8 mice at a time. For this collimator the apertures were angled to 13 degrees to cope with the divergence of the two sources of Cs137. They conform an angled 10mm beam. The dimensions of the inner chambers were 25mm thick lead for the lids and internal height 50mm, also with breathing apertures for the mice. Monte Carlo (MC) simulations were executed as a verification method. These simulations were implemented using EGSnrc in particular DOSxyznrc and BEAMnrc to simulate the sources, collimators and phantom. Two simulations were run in DOSXYZnrc for the two radiation sources of the Gammacell exactor at 0 and 180 degrees, and the results were added to find the total radiation at mid-point of the internal chamber. These simulations were run in a phase-space option, which allows to modify the angle of the sources, to 0 and 180 degrees in the source type option. For dosimetric verification, radiochromic films and gel dosimetry are projected to be used. Radiochromic films are composed of layers that experience coloration upon receiving radiation, with no need of further chemical, optical or thermal development. One of the main advantages of gel dosimeters is the possibility of storing 3D distribution of the radiation dose, as they are made of radiosentitive chemicals that polymerize upon radiation. The simulations showed that the design of the collimators was able to correctly create well-collimated beams with a diameter of 1cm and to reduce out-of-field dose in both collimator designs. In the four-chamber collimator the simulations proved that the angled hole copes with the divergence of the two radiation sources. The results will also be verified against dosimetric measurements with Gafchromic films and dosimetric gels. Citation Format: Jessica Benitez, Davide Fontanarosa, Robert Mazzieri, Davide Moi. Collimator design and simulation for preclinical radiotherapy applications using a clinical cell irradiator [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B204.

Design of a Cascaded Black – Linear Distribution (CBLD) in Circular Aperture and Its Application on Confocal Laser Scanning Microscope (CLSM)

A new model of Cascaded Black – Linear Distribution (CBLD) in circular aperture is suggested. Four different models of CBLD are studied. In the 1st model, ten strips are considered where half of them are black and the other half has linear distribution, starting with black strip from the center of the circular aperture. In the 2nd model, twenty strips are considered of equal black and linear zones. In the 3rd model, a ratio of 2:1 is given for the twenty strips of the CBLD. In the 4th model, annular aperture of linear distribution is considered. We have computed the Point Spread Function (PSF) corresponding to all arrangements and compared with the corresponding PSF for different apertures of circular, annular, and black and white (B/W) transparent circular apertures. The cut-off spatial frequency which is the indication of resolution is investigated in all the described apertures. The Coherent Transfer Function (CTF) using the CBLD apertures is computed. Application of the CBLD arrangement corresponding to the objective and collector lenses in the CLSM using microscopic input images is shown. The reconstructed images using the described models in the CLSM are investigated. A Mat-Lab code is used for the computation of all images.

Antenna for Ultra-Wideband Applications With Non-Uniform Defected Ground Plane and Offset Aperture-Coupled Cylindrical Dielectric Resonators

A new compact Cylindrical Dielectric Resonator Antenna (CDRA) with a defected ground for ultra-wideband applications is presented. The structure is based on two cylindrical dielectric resonators asymmetrically located with respect to the center of an offset rectangular coupling aperture, with consideration of three and four Dielectric Resonators (DR). The resonant modes generated by the defected ground are studied and investigated. A parametric optimization study of the antenna design has been carried out to determine the optimal dimensions of the defected ground plane, resulting in an impedance bandwidth of over 133% that covers the frequency band from 3.6 GHz to 18.0 GHz. A power gain of about 7.9 dBi has been achieved. Design details and measured and simulated results are presented and discussed.

Ion Optics’ Thermally-Induced Gap and Aperture Misalignment Reduction by Selective Laser Melting

High operation temperatures in ion thrusters with metallic ion optics lead to unequal thermal expansion of screen and accelerator grids. Larger normal and tangential displacements of the screen grid result in grid-to-grid gap change and aperture misalignment, which affects the perveance of the optics and modifies ion trajectories. To mitigate this problem, a solution that consists of more uniform thermal expansion of the optics is proposed. By rendering accelerator grid more elastic (i.e., reducing the elastic modulus) to make it easier to expand and increasing the coefficient of thermal expansion (CTE), grid-to-grid gap change and aperture center misalignment are not as pronounced as when both optics have the same properties. Selective laser melting with different fabrication parameters was used to produce molybdenum and titanium samples with different CTE and Young moduli, which were introduced in a thermoelastic model applied to a set of 50 cm domed ion optics. It has been showed that a 20% CTE increase and 25% elastic modulus reduction of the accelerator grid with respect to screen grid produced a 65% grid-to-grid gap change reduction and a 38% aperture misalignment reduction, compared with typical optics’ sets. However, the selective laser melting fabrication and testing of grids with feature control have not been accomplished yet.

Research on separation mechanism of waste palladium catalyst in a structure-optimized compound dry separator based on DEM-CFD

Recovery of precious metals from waste catalysts is necessary. The compound dry separator provides a new method for the recycling of waste catalysts with special morphology. The bed surface structure was modified in consideration of the unique properties of spent palladium catalyst in petrochemical industry. The solid-fluid coupling method (DEM-CFD) was used to study the distribution of airflow on the bed surface and the motion characteristics of particle swarm with different combinations of properties. The results showed that the best size of the apertures of bed surface was 2 mm and the optimum installation angle (β) of the lattice bars on bed surface was 50°. The velocity of air flow was small in the backplane region, but relatively large in the region far away from the backplane. And so was the case with dynamic pressure. The dynamic pressure was the largest in the central wind apertures and decreased gradually along the upward direction. The key factor influencing the distribution and movement of the aggregate on the bed surface was the shape of particles, while the effect of density was relatively weak. The separation efficiency (Ef) in numerical simulation was 99.83%, which coincided with the actual experimental result (99.57%).

Plasmonic Interferometer Array Biochip as a New Mobile Medical Device for Cancer Detection.

We report a plasmonic interferometer array (PIA) sensor and demonstrate its ability to detect circulating exosomal proteins in real-time with high sensitivity and low cost to enable the early detection of cancer. Specifically, a surface plasmon wave launched by the nano-groove rings interferes with the free-space light at the output of central nano-aperture and results in an intensity interference pattern. Under the single-wavelength illumination, when the target exosomal proteins are captured by antibodies bound on the surface, the biomediated change in the refractive index between the central aperture and groove rings causes the intensity change in transmitted light. By recording the intensity changes in real-time, one can effectively screen biomolecular binding events and analyze the binding kinetics. By integrating signals from multiple sensor pairs to enhance the signal-to-noise ratio, superior sensing resolutions of 1.63×10-6 refractive index unit (RIU) in refractive index change and 3.86×108 exosomes/mL in exosome detection were realized, respectively. Importantly, this PIA sensor can be imaged by a miniaturized microscope system coupled with a smart phone to realize a portable and highly sensitive healthcare device. The sensing resolution of 9.72×109 exosomes/mL in exosome detection was realized using the portable sensing system building upon a commercial smartphone.

Microbial uniqueness of architecture modified loofah sponge as biological filler for efficient nitrogen removal

By shrinking the major central apertures in the natural loofah sponge, it is easy to establish inner-DO-reduced-zones within the biofiller. The study compared the performances of two sequencing batch biofilm reactors (SBBR), which were packed with the natural and the major-central-pores-shrunk (the architecture modified) biofillers, respectively. The modified biofillers inhabited higher abundance of anaerobic bacteria, including Lentimicrobiaceae and Anaerolinea Chloroflexi (the acetogenic bacteria). These bacteria were found to closely related to some types of denitrifying bacteria (Rhodobacteraceae). The relative abundance of narG and nosZ genes in the attached-growth biomass of the architecture modified biofillers were 5% and 10% higher, respectively. The potential nitrogen removal pathways are discussed. This study demonstrated the advances and insight of using the internal closed porous biofiller in Sequencing Batch Biofilm Reactor (SBBR) without deliberately controlling the DO level in the reactor.

Using Aperture Impedance for Shielding Effectiveness Estimation of a Metallic Enclosure With Multiple Apertures on Different Walls Considering Higher Order Modes

In this paper, our previously published analytical method for calculation of shielding effectiveness ( SE ) of a metallic enclosure with a centered aperture is extended to generalize the method for a much wider range of applications. The new extended analytic formulation considers an enclosure with centered and off-centered apertures on different enclosure walls and the monitoring point can be anywhere inside the enclosure. In addition, the incident field angle and the polarization angle are arbitrary and higher order modes are considered. An analytic discussion and an experimental setup are proposed for the validation of the new method. The proposed measurement setup can lead to a new SE measurement method for enclosures with arbitrary position apertures. In this measurement method, there is no need for antennas, reverberation chambers, etc. Another advantage of the proposed method is introducing a new figure of merit for shield evaluation. This new figure of merit is S11 of a two port microstrip line which is placed over the apertures.

Unequally‐excited linear totally random antenna arrays for multi‐beam patterns

Linear random antenna arrays are usually studied in conjunction with uniform excitations with, at most, a linear phase shift in order to steer the main beam. This offers some advantages in terms of the feeding network but puts limitations on the array factor that can be obtained. The authors introduce unequally excited random arrays whose excitation currents are obtained by suitable transformations of the random variables related to the element positions. Besides, the first- and second-order statistic characterisation, the uniform norm (i.e. the supremum) of difference between the mean (the desired one) and the actual array factors is estimated. In particular, while in the general case, this is achieved only via a Monte Carlo study, for the case of symmetric arrays (where the elements are randomly deployed symmetrically with respect to the array aperture centre) that norm is analytically estimated using the up-crossing theory for random processes. It is shown that the proposed unequally excited random arrays, unlike some other previous approaches, allow shaping the mean radiation pattern. However, the procedure in general yields reduced achievable performance. Therefore, the theoretical findings are checked through some numerical examples only for the important class of multi-beam array factors.

Focused ultrasound transducer spatial peak intensity estimation: a comparison of methods

Characterisation of the spatial peak intensity at the focus of high intensity focused ultrasound transducers is difficult because of the risk of damage to hydrophone sensors at the high focal pressures generated. Hill et al (1994 Ultrasound Med. Biol. 20 259–69) provided a simple equation for estimating spatial-peak intensity for solid spherical bowl transducers using measured acoustic power and focal beamwidth. This paper demonstrates theoretically and experimentally that this expression is only strictly valid for spherical bowl transducers without a central (imaging) aperture. A hole in the centre of the transducer results in over-estimation of the peak intensity. Improved strategies for determining focal peak intensity from a measurement of total acoustic power are proposed. Four methods are compared: (i) a solid spherical bowl approximation (after Hill et al 1994 Ultrasound Med. Biol. 20 259–69), (ii) a numerical method derived from theory, (iii) a method using measured sidelobe to focal peak pressure ratio, and (iv) a method for measuring the focal power fraction (FPF) experimentally. Spatial-peak intensities were estimated for 8 transducers at three drive powers levels: low (approximately 1 W), moderate (~10 W) and high (20–70 W). The calculated intensities were compared with those derived from focal peak pressure measurements made using a calibrated hydrophone. The FPF measurement method was found to provide focal peak intensity estimates that agreed most closely (within 15%) with the hydrophone measurements, followed by the pressure ratio method (within 20%). The numerical method was found to consistently over-estimate focal peak intensity (+40% on average), however, for transducers with a central hole it was more accurate than using the solid bowl assumption (+70% over-estimation). In conclusion, the ability to make use of an automated beam plotting system, and a hydrophone with good spatial resolution, greatly facilitates characterisation of the FPF, and consequently gives improved confidence in estimating spatial peak intensity from measurement of acoustic power.

Cornea and anterior eye assessment with placido-disc keratoscopy, slit scanning evaluation topography and scheimpflug imaging tomography.

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple and several devices and technologies allow to explore and to manage patients. The purpose of this special issue is to present and also to update in the evaluation of cornea and ocular surface and this second part, reviews a description of the corneal topography and tomography techniques, providing updated information of the clinical recommendations of these techniques in eye care practice. Placido-based topographers started an exciting anterior corneal surface analysis that allows the development of current corneal tomographers that provide a full three-dimensional reconstruction of the cornea including elevation, curvature, and pachymetry data of anterior and posterior corneal surfaces. Although, there is not an accepted reference standard technology for corneal topography description and it is not possible to determine which device produces the most accurate topographic measurements, placido-based topographers are a valuable technology to be used in primary eye care and corneal tomograhers expanding the possibilities to explore cornea and anterior eye facilitating diagnosis and follow-up in several situations, raising patient follow-up, and improving the knowledge regarding to the corneal anatomy. Main disadvantages of placido-based topographers include the absence of information about the posterior corneal surface and limited corneal surface coverage without data from the para-central and/or peripheral corneal surface. However, corneal tomographers show repeatable anterior and posterior corneal surfaces measurements, providing full corneal thickness data improving cornea, and anterior surface assessment. However, differences between devices suggest that they are not interchangeable in clinical practice.

Polarization Multiplexing of Fluorescent Emission Using Multiresonant Plasmonic Antennas.

Combining the ability to localize electromagnetic fields at the nanoscale with a directional response, plasmonic antennas offer an effective strategy to shape the far-field pattern of coupled emitters. Here, we introduce a family of directional multiresonant antennas that allows for polarization-resolved spectral identification of fluorescent emission. The geometry consists of a central aperture surrounded by concentric polygonal corrugations. By varying the periodicity of each axis of the polygon individually, this structure can support multiple resonances that provide independent control over emission directionality for multiple wavelengths. Moreover, since each resonant wavelength is directly mapped to a specific polarization orientation, spectral information can be encoded in the polarization state of the out-scattered beam. To demonstrate the potential of such structures in enabling simplified detection schemes and additional functionalities in sensing and imaging applications, we use the central subwavelength aperture as a built-in nanocuvette and manipulate the fluorescent response of colloidal-quantum-dot emitters coupled to the multiresonant antenna.

Offset Aperture-Coupled Double-Cylinder Dielectric Resonator Antenna With Extended Wideband

A compact dielectric resonator antenna for ultrawideband vehicular communication applications is proposed. Two cylindrical dielectric resonators are asymmetrically located with respect to the center of an offset rectangular coupling aperture, through which they are fed. Optimizing the design parameters results in an impedance bandwidth of 21%, covering the range from 5.9 to 7.32 GHz in the lower band and a 53% relative bandwidth from 8.72 to 15 GHz in the upper band. The maximum achieved gain is 12 dBi. Design details of the proposed antenna and the results of both simulations and experiment are presented and discussed.

Folded monocentric imager with deformable mirror focus.

We describe a catadioptric monocentric imager using an elastic central element focused by deformation of a fold mirror. We show the design of 6 mm and 12 mm focal length F/2.8 achromats and compare design performance when focusing by translating the sensor, translating the fold mirror, and by spherically deforming the fold mirror. We tested the 12 mm focal length design using a diamond turned polystyrene element as the outer meniscus lens (and mechanical mount), filled with an optical gel in contact with the central aperture and fold mirror, and demonstrate focusing by mechanical deformation of the fold mirror. The resolution at the spherical image surface was inspected by optical relay imaging, yielding a best focus MTF50 of 52.6 lp/mm.

Congenital Duodenal Obstruction, Situs Inversus Totalis, and Gastric Perforation in a Neonate.

We report a rare case of incomplete congenital duodenal obstruction (Type 1 duodenal atresia) in association with situs inversus totalis presenting with gastric perforation in a neonate. The infantogram was suggestive of perforation with air under diaphragm along with dextrocardia. On exploration, a pin point perforation at fundus near lesser curvature along with situs inversus was noted. Primary closure of gastric perforation was done. Patient was then discharged on full breast feeds but was readmitted with intolerance to feeds and recurrent bilious vomiting. Further, upper GI contrast study revealed partial duodenal obstruction. On re-exploration, duodenal web with central aperture was seen and duodeno-duodenostomy was done.

Optical characteristics of Alvarez variable-power spectacles.

To establish the optical performance of currently available Alvarez variable-power spectacles in relation to their possible utility for ametropes and presbyopes. Two commercial designs of variable-power (variable-focus) spectacles were studied: FocusSpecs and Adlens Adjustables. Using focimetry, power and prism at three different power settings were measured across the aperture of the lenses of each design and local optical quality was explored in more detail using interferometry. In general, equivalent-sphere powers at all lens settings were adequately stable across the central aperture (about 20 mm diameter) of the lenses, with prism changes following the Prentice rule. Some astigmatism (generally ≤0.5 DC over the central area) and higher-order aberration (comparable to the normal wavefront aberration of the eye) were found, the latter increasing towards the edge of the useable lens area. Within their designed power ranges, optical performance of currently-available Alvarez variable-power spectacles appears to be adequate to correct the distance and near vision of spherical ametropes.

Study on the Fatigue Crack Growth of the 3D Surface of the Curved Steel Plate

In the present study, the author researched on the fatigue crack growth of the 3D surface of the curved steel plate. The new conceptual design of the fatigue crack arrest device provides the user with flexible operating. The proposed device design consists of a handle, body, closed-circuit monitoring system assembly, nozzle, material flow nozzle, material tanks and piston assembly. The component can be repaired by laser; the laser flows to the nozzle central aperture. The curved steel plate channel outlets are around the nozzle aperture, material aligned at working focal point follow the laser beam. Presence and detection of a flaw by proximity sensor enable the repairing process. The temperature sensor enables the material flow once achieved the required set temperature. Piston assembly may follow the material flow process. These all processes are accomplished by a compact design. This novel conceptual design provides high degree of freedom to arrest the fatigue crack with simple mechanism. It demonstrates that the proposed technique alters the fatigue crack behaviour of the 3D surface of the curved steel plate with the proposed method.