Cylindrical Aperture Research Articles

Cylindrical aperture Three-dimensional synthetic aperture imaging with pulsed terahertz waves

Cylindrical aperture Three-dimensional synthetic aperture imaging with pulsed terahertz waves

Amplitude and Phase Synthesis at Cylindrical Apertures of Omnidirectional Dual-Reflector Antennas for Uniform Coverage

Amplitude and Phase Synthesis at Cylindrical Apertures of Omnidirectional Dual-Reflector Antennas for Uniform Coverage

Sub-Diffraction Photon Trapping: The Possible Optical Energy Eigenstates within a Tiny Circular Aperture with a Finite Depth

One of the challenging riddles that is set by light is: do photons have wavefunctions like other elementary particles do? Wave–particle duality has been a prevailing fact since the beginning of quantum theory thought; in electromagnetism, light is already a kind of undulation, so what about the waves of probability then? Well, Quantum Field Theory (QFT) has a rigorous explanation and supports the idea when they are considered as fields of particles via second quantization; they do have wavefunctions of probability, and it does not have anything to do with the regular oscillations. They can be related to the energy and momentum signatures of harmonic oscillations, resembling an imitation of the behavior of a classical harmonic oscillator, which then has a wavefunction to solve the corresponding time-independent Schrödinger equation. For the last half century, electrical engineering has owned the best out of these implications of Quantum Electrodynamics (QED) and QFT by engineering better semiconductor techniques with finely miniaturized transistors and composite devices for digital electronics and optoelectronics fields. More importantly, these engineering applications have also greatly evolved into combined fields like quantum computing that have introduced a completely new and extraordinary world to electronics applications. The study takes advantage of the power of QFT to mathematically reveal the bosonic modes (Laguerre–Gaussian) that appear in a sub-diffraction cylindrical aperture. In this way, this may lead to the construction of the techniques and characteristics of room-temperature photonic quantum gates which can isolate photon modes under a diffraction limit.

3D THz-TDS SAR Imaging by an Inverse Synthetic Cylindrical Aperture

Terahertz time-domain spectroscopy (THz-TDS) is a promising tool for high-resolution 3D imaging of objects due to the high center frequency and bandwidth compared to microwave systems. In addition, terahertz waves have a higher penetration depth than visible or near-infrared radiation. Typically, optics are used to focus the terahertz radiation onto an object under test. This limits the imaging capability in the axial dimension to the depth of field and limits simple imaging of complex surfaces. In this work, we adapt a backpropagation algorithm from synthetic aperture radar (SAR) imaging to reconstruct high-resolution 3D images from time-domain traces acquired with a lensless THz-TDS system. For this purpose, an inverse cylindrical aperture is used and an equation that describes the maximum achievable resolution as a function of the beam pattern, the bandwidth, and the length of the synthetic aperture is derived. The calculated resolution is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$960 \mu \text{m}$ </tex-math></inline-formula> for the linear dimension of the aperture and 75 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> for the rotationally symmetric dimension of the cylindrical aperture for a bandwidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\,\text {THz}$ </tex-math></inline-formula> . The resolving power is verified by measurements on metallic and dielectric objects. In the future, this method can be used for non-destructive testing of objects with complex shaped surfaces and internal structures.

Efficient Wavenumber Domain Processing for Near-Field Imaging With Polyline Arrays

We propose an efficient wavenumber domain approach for polyline array-based millimeter-wave imaging. The polyline multiple-input–multiple-output (MIMO) array provides more uniform illumination of the target than the planar MIMO array while enjoying the planar array’s easy manufacturing. However, no existing efficient imaging algorithms deal with such an array topology. This article presents an approach that first implements a polyline-to-arc transformation on the polyline array, accompanied by a phase calibration method to maintain the transformation precision. The wavenumber domain technique is then employed to perform image reconstruction. This processing enables the transformation of the polyline array scheme into a monostatic cylindrical aperture, for which efficient imaging algorithms exist. The imaging performance and computational efficiency of the proposed approach are demonstrated with both simulations and experiments.

Measuring the near-target neutron field of a D–D fusion facility with the novel NCT-WES spectrometer

A new directional neutron spectrometer called NCT-WES (Neutron Capture Therapy Wide Energy Spectrometer) was recently developed within the INFN ENTER_BNCT project. This device constitutes a more compact and portable alternative to state-of-the-art directional neutron spectrometers. The device was used for the first time to characterise the near-target field produced by an accelerator-driven D–D fusion neutron source. NCT-WES operates as a “parallelised” Bonner spheres spectrometer, embedding six semiconductor-based thermal neutron detectors in a cylindrical moderator. Owing on a cylindrical collimating aperture, the device exhibits sharply directional response. To account for the non-uniform irradiation condition experienced in the near-target field, a dedicated NCT-WES response matrix was developed. The neutron spectrum at 0^{circ } from the D–D neutron target, determined by means of the FRUIT unfolding code, is coherent with that previously derived with Bonner spheres. NCT-WES proved to be a promising device for angular spectrometric characterisation of neutron-emitting targets.

Generalized Moore‐Gibson‐Thompson thermoelastic fractional derivative model without singular kernels for an infinite orthotropic thermoelastic body with temperature‐dependent properties

AbstractMany challenges in different applied fields of research, such as materials science, viscoelasticity, biological sciences, physics, and mechanical engineering, require the study of derivative operators using single singular or nonsingular kernels. Atangana and Baleanu (AB) constructed a novel fractional derivative without a singular kernel based on the extended Mittag–Leffler function to overcome the singular kernel problem seen in previous definitions of fractional‐order derivatives. In this article, we provide a novel mathematical thermoelastic heat conduction model that includes the fractional AB derivative operators. In addition, the Moore–Gibson–Thompson (MGT) equation has been incorporated into the proposed heat transport model. The proposed model has been applied to study an infinite orthotropic material with a cylindrical aperture, and the thermal conductivity coefficient of the body depends on the temperature change. The Laplace transform approach has been used to solve the system of governing partial differential equations (PDEs). To assess the validity of the proposed model and for the purposes of comparison, the numerical results have been depicted in figures as well as in tables.

Terahertz Measurements on Subwavelength-Size Samples Down to the Tunneling Limit

For terahertz spectroscopy on single crystals, the wavelength lambda often is comparable to the size of the studied samples, emphasizing diffraction effects. Using a continuous-wave terahertz spectrometer in transmission geometry, we address the effect of the sample size on the achievable accuracy of the optical properties, focusing in particular on the phase data. We employ alpha-lactose monohydrate as a paradigmatic example and compare data that were measured using apertures with diameters D in the range from 10 to 0.2 mm. For small D, strong diffraction typically invalidates a quantitative analysis of the transmitted amplitude at low frequencies. The phase data, however, can be evaluated to lower frequency and show a more systematic dependence on D. For a quantitative analysis, we employ a waveguide picture for the description of small apertures with a cylindrical bore. For D as small as 0.2 mm, corresponding to 1/D = 50 cm^{-1}, a circular waveguide does not support propagating waves below its cut-off frequency 1/lambda _c = omega _c/2pi c approx 29 cm^{-1}. Experimentally, we confirm this cut-off for cylindrical apertures with a thickness d_{text {ap}} = 1 mm. Close to omega _c, the measured phase velocity is an order of magnitude larger than c, the speed of light in vacuum. The cut-off is washed out if a sample is mounted on a thin aperture with a conical bore. In this case, the phase data of alpha-lactose monohydrate for D = 0.2 mm can quantitatively be described down to about 10 cm^{-1} if the waveguide-like properties of the aperture are taken into account in the analysis.

Optimization of the cylindrical sieves for separating threshed rice mixture using EDEM

The design of the cylindrical sieve equipment used for the screening and separation of agricultural granular materials is mainly through the experimental method, which has the disadvantages of a long development cycle and high cost. To solve this problem, the discrete element method (DEM) was utilized to accurately build the particle models of threshed rice components (grains, shriveled grains, and short stalks), and simulated the separation of grains from the mixture in a cylindrical sieve. The influences of rotational speed (A), cylindrical sieve diameter (B), cylindrical sieve aperture (C), and inclinational angle (D) on screening cleaning rate, screening loss rate, and screening efficiency were investigated. Meanwhile, the optimal parameters of the cylindrical sieve were obtained using a central composite design (CCD) under response surface methodology (RSM). The results of CCD showed that the quadratic multinomial model is credible and revealed that the cylindrical sieve aperture has a significant impact on the screening characteristics. It is predicted that the optimal values for screening cleaning rate, loss rate, and efficiency were 97.84%, 0.27%, and 85.38%, respectively, while A, B, C, and D were 23.6 r/min, 297 mm, 8.7 mm, and 2°, respectively. The experimental results using a real threshed rice mixture were found to be in good agreement with the optimal simulation results. This study proved a reliable research method and provides a design reference for the cylinder sieving systems for threshed rice or separation of other bulk material. Keywords: cylindrical sieve, threshed rice mixture, discrete element method, separation, rice, optimization DOI: 10.25165/j.ijabe.20221502.5150 Citation: Yuan J B, Wang J F, Li H, Qi X D, Wang Y J, Li C. Optimization of the cylindrical sieves for separating threshed rice mixture using EDEM. Int J Agric & Biol Eng, 2022; 15(2): 236–247.

Fast and Robust Capacitive Imaging of Cylindrical Non-Metallic Media

In this paper, a unique approach to the imaging of non-metallic media using capacitive sensing is presented. By using customized sensor plates in single-ended and differential configurations, responses to hidden objects can be captured over a cylindrical aperture surrounding the inspected medium. Then, by processing the acquired data using a novel imaging technique based on the convolution theory, Fourier and inverse Fourier transforms, and exact low resolution electromagnetic tomography (eLORETA), images are reconstructed over multiple radial depths using the acquired sensor data. Imaging hidden objects over multiple depths has wide range of applications, from biomedical imaging to nondestructive testing of the materials. Performance of the proposed imaging technique is demonstrated via experimental results.

Artifact expression of polyetheretherketone in cone beam computed tomography: An in vitro study

Statement of problemDental prosthetic materials can cause artifacts in cone beam computed tomography (CBCT) images, adversely affecting diagnostic quality, although the problem may be less with polyetheretherketone (PEEK). Studies evaluating the artifacts caused by frequently used prosthetic materials are lacking. PurposeThe purpose of this in vitro study was to compare the artifacts in CBCT images caused by PEEK, zirconia, cobalt-chromium (Co-Cr) alloy, and titanium (Ti). Material and methodsA polymethylmethacrylate phantom (Ø4.0×4.0 cm) with a central cylindrical aperture (Ø0.5×0.5 cm) was produced. Co-Cr, Ti, zirconia, and PEEK cylinders (0.5×0.5 cm) were manufactured, and CBCT images of the empty phantom (control group) with the test cylinders inside were made 3 times. In all images, the axial sections passing through the middle of the materials were evaluated. Eight regions of interest (ROI) area were determined around the materials (0.5×0.5 cm). The presence of artifacts was evaluated by making gray value standard deviation (SD) calculations in these ROI areas. The average SD values of 8 ROI fields from the 3 CBCT scans were made, and the materials were compared with each other in terms of the presence of artifacts by using 1-way analysis of variance (α=.05). ResultsThe difference between the SD values of the control and the PEEK cylinder was not statistically significant (P>.05). The SD values of both the control and PEEK groups were significantly lower than those of the zirconia, Co-Cr, and Ti groups (P<.05). ConclusionsZirconia, Ti, and Co-Cr caused artifacts in CBCT images, but the artifacts with PEEK were similar to those in the control group, suggesting it was the optimal choice in terms of achieving diagnostic quality.

Microwave hologram reconstruction for cylindrical geometry

Microwave imaging is a technique for evaluation of hidden or embedded objects in an optically opaque structure (or media) using electromagnetic waves in microwave regime. The result of the study is a microwave image of the internal structure of the investigated object, which is built by reconstructing the electromagnetic field scattered by the object (microwave hologram), recorded using some radar system at some aperture. Along with the widespread flat aperture, a cylindrical aperture is often used in personnel screening systems, microwave system for automated body measurement for apparel fitting, and medical tomographic scanners. Cylindrical geometry requires special holograms reconstruction methods. The work is dedicated to comparison of three hologram reconstruction methods: №1 – back projection, №2 – back propagation and №3 – Gauss–Newton, and identifying the advantages and disadvantages of each method. All methods were adopted to cylindrical geometry, software implemented using Python programming language and compared. Comparison was performed by reconstruction of microwave holograms of the same objects. Microwave holograms for comparison were calculated in accordance with the principles of physical optics for point scatterers and using the computational electromagnetics software product FEKO for solid objects. Comparison criteria were: speed of calculations, quality of obtained microwave images, required random access memory (RAM) of the computer. Based on the results of numerical experiments, the following conclusions can be made. For both point and solid objects, all methods have showed a similar quality of the obtained microwave images, the difference turned out to be minimal both in visual and numerical estimation. The advantage of method №1 is the simplicity of its software implementation. In addition, using the first method, you can easily do reconstruction for any area (line, surface, volume), the position of which can be arbitrary in relation to the positions of the samples of the radar signal. Method №2 is the fastest method. With the parameters considered in the article, it is two orders of magnitude faster than method №1, and its performance can be easily increased by parallelizing calculations for different radii. Among the shortcomings, one can note the complexity of its software implementation and the dependence of the position and size of the reconstructed area on the location and number of samples of the radar signal. A significant drawback of method №3 is its high requirements to the RAM of the computer, as well as low speed of calculations. When processing microwave holograms with a large number of samples, calculations may require more memory than is installed in the computer, and the calculation time will increase many times due to the continuous exchange of data with the hard disk, or it will be impossible to do the calculations at all.

Sound transmission through annular cylindrical apertures using rapidly converging expansion series.

The problem of sound transmission through an annular aperture with perfectly rigid walls and located in a hard infinite baffle was solved analytically. The three separated regions with suitable boundary conditions were considered. There are two regions for the upper and the lower half spaces and one for the aperture. The solutions to the Helmholtz equation in each region and the continuity conditions were satisfied. The rigorous formulations describing the acoustic pressure and the transmitted and scattered acoustic powers were obtained. The obtained solutions resulted in the derivation of the modal coupling coefficients in the form of infinite integrals. The spectral mapping technique based on the Zernike circle polynomials was adopted for the annular geometry. The modal coupling impedances were presented in the form of a rapidly convergent expansion series. Finally, high accuracy and time efficiency were achieved. The problem of sound scattering and transmission through a circular aperture could be generalized for the annular aperture.

Magnetoelastic Coupled Wave Diffraction and Dynamic Stress Intensity Factor in Graded Piezomagnetic Composites with a Cylindrical Aperture.

A theoretical method is developed to study the magnetoelastic coupled wave and dynamic stress intensity around a cylindrical aperture in exponential graded piezomagnetic materials. By employing the decoupling technique, the coupled magnetoelastic governing equations are decomposed. Then the analytic solutions of elastic wave fields and magnetic fields are presented by using the wave function expansion method. By satisfying the boundary conditions of the aperture, the mode coefficients, and the analytic solutions of dynamic stress intensity factors are determined. The numerical examples of the dynamic stress intensity factor near the aperture are presented. The numerical results indicate that the incident wave number, the piezomagnetic properties, and the nonhomogeneous parameter of materials highly influence the dynamic stress around the aperture.

Study on Method of Extracting Circle of Complex Objects Based on 3D Scanning

This paper proposes a method for extracting information about circular holes for complex objects with cylindrical apertures which base on special 3D scanning platform. After scanning the object, the point cloud is sliced after fitting the plane using the eigenvalue method. Aiming at the slice data, a point cloud segmentation extraction algorithm is proposed. The experimental results show that the system can effectively control the aperture extraction error and broaden the types of detectable parameters.

Point Cloud and 3-D Surface Reconstruction Using Cylindrical Millimeter-Wave Holography

Different from conventional millimeter-wave (MMW) holographic 3-D imaging, a new technique that can produce accurate point cloud and the 3-D surface model of the target based on a cylindrical MMW holography system is proposed. The precision of the obtained model is much higher than the resolution of the 3-D image since the phase information in the echoes is utilized more sufficiently. Compared with some optic-based point cloud and 3-D surface reconstruction methods, the proposed method is independent of the ambient light conditions and is capable to penetrate clothes and wrappers. An overall processing framework is first presented. Subapertures and the cylindrical-to-planar wave transformation technique are used to split the whole cylindrical aperture into several equivalent planar subapertures. Then, an enhanced frequency interferometry method is proposed to reconstruct the depth maps of the target from different views. Finally, the integrated point cloud and 3-D surface model is obtained by merging all the subaperture results. A series of numerical simulations and a proof-of-concept experiment are carried out. Both the simulation and experimental results validate the effectiveness and show the superiority of the proposed method.

A simple and affordable experiment to determine Reynolds number

In this work, we present a simple and affordable experiment to determine the Reynolds number for water flowing through a cylindrical aperture. Commercially available equipment exists but often at high cost. Instead, the use of simple laboratory equipment (stopwatches, measuring cylinders and plastic bottles) allows an entire class to complete the experiment simultaneously. By measuring the mean bulk flow rates and calculating a value for the mean bulk speed of the fluid the Reynolds number (Re) can be determined. Using this experimental equipment we observed both laminar and turbulent flow, as confirmed through our calculated values of Re = 1100 300 and Re = 9400 700 respectively. Finally, we offer practical advice for carrying out these experiments as well as suggesting suitable further activities to make this activity accessible to various levels of study.

A Low-Cost and Compact Three-Dimensional Microwave Holographic Imaging System

With the significant growth in the use of non-metallic composite materials, the demands for new and robust non-destructive testing methodologies is high. Microwave imaging has attracted a lot of attention recently for such applications. This is in addition to the biomedical imaging applications of microwave that are also being pursued actively. Among these efforts, in this paper, we propose a compact and cost-effective three-dimensional microwave imaging system based on a fast and robust holographic technique. For this purpose, we employ narrow-band microwave data, instead of wideband data used in previous three-dimensional cylindrical holographic imaging systems. Three-dimensional imaging is accomplished by using an array of receiver antennas surrounding the object and scanning that along with a transmitter antenna over a cylindrical aperture. To achieve low cost and compact size, we employ off-the-shelf components to build a data acquisition system replacing the costly and bulky vector network analyzers. The simulation and experimental results demonstrate the satisfactory performance of the proposed imaging system. We also show the effect of number of frequencies and size of the objects on the quality of reconstructed images.

Bistatic cylindrical millimeter-wave imaging for accurate reconstruction of high-contrast concave objects.

A high-contrast target with complex shape, especially concave surfaces, often exhibits strong high-order scattering during forward propagation, which is often misinterpreted as artifacts or phantom targets during imaging. In this work, a bistatic imaging method for reducing artifacts caused by high-order scattering from concave objects under cylindrical millimeter-wave scanning geometry is proposed. The effects of multiple reflections within concave structures are firstly analyzed by using ray-tracing techniques. It is observed that these troublesome multiple reflection echoes are often confined in limited scattering angles. Under this specific requirement for transceiver setup, a bistatic cylindrical aperture synthesis technique is proposed to obtain accurate images of concave object despite strong high-order scattering. To verify this method, simulated imaging results in bistatic near-field cylindrical imaging geometry are presented. Finally, the effectiveness of artifact reduction is confirmed by experimental results of complex metallic targets with concave outlines.

A Cylindrical Lens Antenna With Extremely Flat Beams

This paper presents an extremely flat-beam cylindrical lens antenna with a 180 mm ($36~\lambda$ ) diameter lens at 60 GHz. The parameters of lens antennas in the horizontal plane i.e. dielectric constants, radii, and focal length are optimized to widen beams in the vertical plane while obtaining pencil beams in the horizontal plane. The optimization procedure consists of a theoretical method and differential evolution (DE) algorithm. This beam-widening idea is analyzed and proved to be feasible owing to cylindrical apertures, which is quite different from the results of antennas with planar apertures. Then, the permittivity distribution which results in an extremely flat beam is investigated and shows a novel S-shape rather than following either the law of modified Luneberg lens or the Luneberg's Law. Finally, the proposed lens antenna is fabricated and measured. At the design frequency of 60 GHz, the measured 3-dB E- and H-plane beamwidths separately are 100.4° and 2.3°. As compared to the gain peak, the measured and simulated gain drop at ±60° in the E-plane are less than 4 dB and 5 dB, respectively. Measured results show good agreements with the simulated results, thus validating the extremely flat beam of the proposed lens antenna and the effectiveness of the optimization procedure.