Diffraction Losses Research Articles

Novel microwave apparatus for breast lesions detection: Preliminary clinical results

This paper presents preliminary results of an innovative microwave imaging apparatus for breast lesions detection. Specifically, a Huygens Principle based method is employed to process the microwave signals and to build the respective microwave images. The apparatus has been first tested on phantoms. Next, its performance has been verified through clinical examinations on 22 healthy breasts and on 29 breast having lesions, using as gold standard the output of the radiologist study review obtained using conventional techniques. Specifically, we introduce a metric, which is the ratio between maximum and average of the image intensity (MAX/AVG). We found that MAX/AVG of microwave images can be used for classifying breasts containing lesions. In addition, using MAX/AVG as classification parameter, receiver operating characteristic curves have been empirically determined. Furthermore, for one randomly selected breast having lesion, we have demonstrated that the localization of the inclusion acquired through microwave imaging is compatible with mammography images.

Interfacial Thermal Contact Conductance inside the Graphene–Bi2Te3 Heterostructure

AbstractGraphene–Bi2Te3, a graphene‐based compound with a metal/metalloid heterostructure, is recently discovered to be a potentially novel thermoelectric material, demonstrating unprecedently enhanced thermoelectric efficiencies. The interfacial thermal transport must play an important role in determining the thermoelectric performance of this heterostructure. In particular, the interfacial thermal contact conductance (Gc) must be known in order to correctly elaborate the thermoelectric performances of graphene–Bi2Te3. Furthermore, the large nonlinear optoelectric response of this heterostructure redefines both the graphene thermal conductivity (kg) and its optical absorbance (Ag). A significantly suppressed Ag is predicted as low as 0.86% from its nominal value of 2.72% when suspended, from the transfer matrix calculations based on the Fresnel principle. Both Gc and kg are simultaneously determined from the optothermal Raman thermometry by duplexing the Raman data sets using two different objective magnifications (20× and 100×), which allows for the matching of the number of unknowns (Gc and kg) with the corresponding two Raman data sets. The thermal properties of Gc and kg for the graphene–Bi2Te3 heterostructure are first determined as 3.455 ± 0.619 × 106 W m−2 K−1 and 440.124 ± 76.265 W m−1 K−1, respectively.

To the theory of gyrotrons with confocal resonators

In recent years, in addition to the development of traditional gyrotrons with an axially symmetric interaction space, there has been strong interest in developing gyrotrons, whose interaction space is not axially symmetric (e.g., gyrotrons with confocal resonators). The theory of such gyrotrons is presented in this paper. First, equations describing such gyrotrons in the cold-cavity approximation are formulated. Then, the linear theory is developed, which is followed by a simple, single-mode, nonlinear theory. After that, the theory describing the mode interaction in such gyrotrons is presented. Then, an alternative concept of gyrotrons with single and multicavity confocal resonators and sheet electron beams is proposed. This paper also includes the analysis of diffractive losses in confocal resonators and the estimates for curling of the ends of sheet beams of gyrating electrons caused by the space charge forces.

Propagation of multiple Bessel Gaussian beams through weak turbulence.

The average intensity of the multiple Bessel Gaussian beams (mBGBs), which comprise the summation of the Bessel function and a Gaussian function, are investigated based on the extended Huygens-Fresnel principle and the Rytov theory. The weak turbulence just leads the mBGBs diverge and has no influence on the angular distribution of both the mean field and the average intensity. Therefore, the angular distribution of the average intensity depends on the average in the free space. When the order difference between any two sub beams of the mBGBs is the integer multiple of the minimum order difference, there are the symmetric side lobes of the average intensity distribution and its angular frequency is equal to the minimum order difference. Moreover, for the mBGBs with two sub beams, the initial phase change of the different sub beams could make the average intensity distribution rotate in opposite direction. This paper provides the theoretical basis for the investigation of the mBGBs propagation and the application of the sub beam detection and the beam multiplexing.

On the Influence of Diffuse Scattering on Multiple-Plateau Diffraction Analysis at mm-Wave Frequencies

A study of the impact of the diffuse scattering phenomenon when calculating radio wave multiple-plateau diffraction losses at millimeter-wave (mm-wave) frequencies is hereby presented. In this sense, measurements of the total attenuation caused by a series of either rough or polished brick blocks are properly compared with the theoretical multiple-diffraction losses of an array of ideally smooth brick blocks predicted by a hybrid uniform theory of diffraction-physical optics (UTD-PO) formulation. The results show the influence of diffuse scattering phenomena when it comes to calculating radio wave multiple-plateau diffraction attenuation and can be applied to the obtaining of more realistic mm-wave propagation models when multiple diffraction over rectangular obstacles with irregular (rough) surfaces has to be considered.

Two Elastodynamic Incremental Models: The Incremental Theory of Diffraction and a Huygens Method.

The elastodynamic geometrical theory of diffraction (GTD) has proved to be useful in ultrasonic nondestructive testing (NDT) and utilizes the so-called diffraction coefficients obtained by solving canonical problems, such as diffraction from a half-plane or an infinite wedge. Consequently, applying GTD as a ray method leads to several limitations notably when the scatterer contour cannot be locally approximated by a straight infinite line: when the contour has a singularity (for instance, at a corner of a rectangular scatterer), the GTD field is, therefore, spatially nonuniform. In particular, defects encountered in ultrasonic NDT have contours of complex shape and finite length. Incremental models represent an alternative to standard GTD in the view of overcoming its limitations. Two elastodynamic incremental models have been developed to better take into consideration the finite length and shape of the defect contour and provide a more physical representation of the edge diffracted field: the first one is an extension to elastodynamics of the incremental theory of diffraction (ITD) previously developed in electromagnetism, while the second one relies on the Huygens principle. These two methods have been tested numerically, showing that they predict a spatially continuous scattered field and their experimental validation is presented in a 3-D configuration.

Accurate Monte Carlo simulation of frequency-domain optical coherence tomography.

Optical coherence tomography (OCT) relies on optical interferometry to provide noninvasive imaging of living tissues. In addition to its 3D imaging capacity for medical diagnosis, its potential use for recovering optical parameters of biological tissues for biological and pathological analyses has also been explored by researchers, as pathological changes in tissue alter the microstructure of the tissue and therefore its optical properties. We aim to develop a new approach to OCT data analysis by estimating optical properties of tissues from OCT scans, which are invisible in the scans. This is an inverse problem. Solving an inverse problem involves a forward modeling step to simulate OCT scans of the tissues with hypothesized optical parameter values and an inverse step to estimate the real optical par1meters values by matching the simulated scans to real scans. In this paper, we present a Monte Carlo (MC)–based approach for simulating the frequency‐domain OCT. We incorporated a focusing Gaussian light beam rather than an infinitesimally thin light beam for accurate simulations. A new and more accurate photon detection scheme is also implemented. We compare our MC model to an analytical OCT model based on the extended Huygens‐Fresnel principle (EHF) to demonstrate the consistency between the two models. We show that the two models are in good agreement for tissues with high scattering and high anisotropy factors.

Directional fracturing by slotting-blasting-caused stress wave form changes

Slotting blasting is widely used for directional fracture in geotechnical engineering. Due to limited research methods, the basic propagation theory of stress waves has not yet been applied in the literature to explain directional fracturing mechanism. In this work, the stress wave propagation during slotting blasting has been analyzed, and through the dynamic caustics blasting experiments, the blastings in circular-holed, square-holed and slotting-holed specimens have been contrast-analyzed, the propagation of stress waves and the explosion cracks have been observed. The theoretical and experimental results show that ① As the shock wave reached the slotting tip, based on “Huygens principle”, it separated into two independent waves symmetric to the median axis of the slotting tips and transmitted in different directions, due to directional stress concentration in materials. The directional fracture zone and directional damage zone were formed as the stress wave is attenuated during propagation; ② Observed in the experiment. The stress waves, which propagated outward in concentric circles, in circular-holed specimens did not change in form. Whereas those of square-holed and slotting-holed specimens changed significantly. The presence of the blasting hole tip changed the stress wave propagation form in the specimen, and the tip propagation angle of stress wave measured was in good agreement with the theoretical calculation; ③ The explosion cracks of the experiment specimens have been analyzed statistically. The blasting holes with tip overcame the static field stress, since the directional damage zone have been formed, leading to directional initiating and propagation of the cracks. In circular-holed specimens, the distribution of crack initiation was random, and in square-holed and slotting-holed specimens, the cracks were initiating at the tip. Crack deflected at twice blasting hole diameter and at six times blasting hole diameter in circular-holed and square-holed specimens, respectively. In contrast, cracks didn't deflect in slotting-holed specimens. The research results can provide theoretical support for selecting the shape and arrangement of the blasting holes for directional fracturing in geotechnical engineering.

Starting Currents for Eigenmodes of a Gyrotron Cavity With Mode Conversion

In the fixed-field (cold) approximation, a generalized formula is derived for the starting currents of eigenmodes excited by an electron beam in a gyrotron cavity with the mode conversion. Tapered gyrotron cavities with gradual and abrupt transitions are considered as examples. It is shown that the effect of the mode conversion on the starting current consists mainly in the change of the diffractive quality factor and, therefore, is small for cavities with low diffractive losses. For such cavities, our formula is in good agreement with single-mode, self-consistent (hot) calculations of the electron beam–wave interaction. The agreement degrades for high-order axial modes having clear-cut distinctions of cold and hot fields. The derived formula is used to test the validity of the single-mode approximation for a complex gyrotron cavity with the abrupt change in radius.

Propagation of a radial phase-locked partially coherent elegant Laguerre–Gaussian beam array in non-Kolmogorov medium

A model of a radial phase-locked partially coherent elegant Laguerre–Gaussian (PCELG) beam array has first been introduced in theory. The analytical propagation equation for the cross-spectral density function of a radial phase-locked PCELG beam array in non-Kolmogorov medium has been derived using the extended Huygens–Fresnel principle. The average intensity and spectral degree of coherence properties of a radial phase-locked PCELG beam array propagating in non-Kolmogorov medium have been studied in details using the numerical examples. One can find that the evolution properties of a radial phase-locked PCELG beam array propagating in non-Kolmogorov medium are affected by the initial beam parameters and the non-Kolmogorov medium, and the beam array propagating in non-Kolmogorov medium will evolve into a solid beam with Gaussian-like distribution in the far field.

Statistical properties of partially coherent radially and azimuthally polarized rotating elliptical Gaussian beams in oceanic turbulence with anisotropy.

A new class of partially coherent radially and azimuthally polarized rotating elliptical Gaussian (PCRPREG and PCAPREG) beams is introduced. The analytical expressions of the PCRPREG and PCAPREG beams propagating through anisotropy oceanic turbulence are derived based on the extended Huygens-Fresnel principle and the spatial power spectrum of oceanic turbulence. The effects of beam waist size w0, coherence width σ0, propagation distance z and oceanic turbulence parameters on the evolution statistics properties of PCRPREG and PCAPREG beams are studied in detail by numerical simulation. Our results indicate that with the increase of the propagation distance in the far field region, the normalized initial profile with a doughnut-like distribution of PCRPREG and PCAPREG beams gradually converts into a flat-topped one, and finally evolves into a Gaussian-like beam profile. We also find that the salinity-induced turbulence fluctuation makes a greater contribution to the decrease of beam quality compared with the temperature-induced turbulence fluctuation. Furthermore, the full width at half maximum becomes wider for the larger propagation distance z and wavelength λ or the smaller dissipation rate ε. Our work will pave the way for the development of underwater optical communication and underwater laser radar in oceanic environment.

Generation of aerosol-particle light-scattering patterns from digital holograms.

The similarity between the light-scattering pattern of a particle in the near-forward direction and diffraction from the particle's silhouette is investigated. Images of irregularly shaped free-flowing aerosol particles are obtained from digital hologram measurements, which are then binarized to yield a silhouette. Application of Huygens's principle to the silhouette generates an approximate scattering pattern, which when compared to the true measured pattern shows good agreement for particles much larger than the wavelength of light.

Practical Design Considerations for Compact Array-Fed Huygens' Dielectric Lens Antennas.

This paper presents a practical design consideration for the dielectric lens based on Huygens’ principle (HP) at a short distance (=λ0/2) from a feed antenna to overcome the limitation of the conventional design method. It is suggested that certain ranges of dielectric thickness values are not considered to exclude undesired resonant effects that hamper the effectiveness of Huygens’ lens which relies on phase shifting elements. In the proposed HP-based design method, phase distributions are captured at the target distance away from the feed array for the two cases of 2 × 2 and 1 × 4 array antennas and based on these, the proposed lens topology is designed to compensate the phase distributions for gain enhancement. A case study shows that the proposed HP-based design approach considering the actual phase information and undesired dielectric resonant phenomenology can achieve a gain enhancement of up to 5.34 dB compared to the conventional dielectric lens, depending on the feed array arrangement that can render circular or elliptic shapes of phase distributions for radiated fields.

Huygens principle: exact and approximate wavefronts propagated through conic lenses.

Exact and approximate formulae for refracted wavefronts through singlet lenses are obtained by considering an incident plane wavefront propagating along the optical axis. We provide two different approaches for the wavefronts approximated at the second order based on the Huygens principle and the Malus-Dupin theorem. We have in the first method found a way to use iterative wavelets instead of the usual evaluated integral to arrive at these formulae, showing a physical and mathematical correspondence between both methods. Finally, we introduce a parabolic wavefront into the irradiance transport equation in order to provide an analytical solution for the distribution of illumination.

Estimation of concentration of DNA and protein through PARD and modified analysis: A realization of an accurate biomedical device using photonic structure

The concentration of DNA and protein is estimated in this paper using a 2D photonic structure with the inclusion of propagation, absorption, reflection, and diffraction (PARD) losses along with the modified equation at the signal of 400 nm. Simulation studies with the help of the plane wave expansion method disclosed to compute the reflection characteristics, where other sorts of losses such as propagation, absorption, and diffraction are divulged by means of numerical computation. Final output in terms of transmitted power is an excellently fitted with linear trend line with respect to the concentration of DNA which varies from 0 to 0.025 gm/mL and protein from 0 to 0.01 gm/mL, which leads to an accurate investigation of aforementioned of biomaterials.

Propagation properties of a partially coherent anomalous hollow vortex beam in underwater oceanic turbulence

Based on the extended Huygens–Fresnel principle, the cross-spectral density function of a partially coherent anomalous hollow vortex beam (AHVB) propagating in underwater oceanic turbulence has been derived, and the influences of the beam parameters and underwater oceanic turbulence on the average intensity and coherence properties are investigated by using numerical examples. Our results show that the partially coherent AHVB with smaller coherence length and smaller M will evolve into the flat-topped faster as the propagation distance increases, and the partially coherent AHVB propagating in stronger underwater oceanic turbulence (the larger χT and ς or the smaller ε) will lose the initial dark hollow center and evolve into the Gaussian beam more rapidly. In the influences of oceanic turbulence on the spreading of partially coherent AHVB, it is found that the parameters χT and ς will cause the larger spreading than the parameter ε at the same propagation distance. This research is useful to the practical application of the partially coherent AHVB beam in underwater oceanic turbulence.

Propagation factor and beam wander of electromagnetic Gaussian Schell-model array beams in non-Kolmogorov turbulence

The propagation formulae for the propagation factor (known as M2-factor) and beam wander of electromagnetic Gaussian Schell-model (EGSM) array beams in non-Kolmogorov turbulence are derived by using the extended Huygens-Fresnel principle and the second-order moments of the Wigner distribution function. The results indicate that the M2-factor and beam wander depend on the beam parameters and turbulence parameters, and the relative M2-factor has a maximum when the generalized exponent parameter α is equal to 3.1. Otherwise, the changes of the separation distances (x0, y0) have great influence on the relative M2-factor. The relative beam wander increases rapidly when 3<α<3.2; however, it increases slowly when 3.2<α<4. It is also shown that the beam spreading of EGSM array beams is more affected by turbulence than the root mean square beam wander.

Influence of anisotropic turbulence on the Second-order statistics of a general-type partially coherent beam in the ocean

We investigate detailedly evolution properties of the angular spread and propagation factor (M2-factor) of a general-type partially coherent beam with Schell-model correlator in anisotropic oceanic turbulence. According to the extended Huygens–Fresnel principle, analytical expressions for the second-order moments of Wigner distribution function (WDF) in anisotropic oceanic turbulence are derived. In order to measure the resistance of a general partially coherent beam to effects of anisotropic oceanic turbulence, we introduce deviation percentage of the normalized angular spread and M2-factor respectively between the general-type partially coherent beam and conventional Gaussian Schell-model (GSM) beam. Numerical results show that influence of anisotropy on the angular spread and M2-factor is less for a general-type partially coherent beam than a conventional GSM beam in oceanic turbulence. Besides, the initial beam parameters have a significant effect on the angular spread and M2-factor of a general-type partially coherent beam. Our results may be useful for underwater communication.

Massive Spin Zero Fields in Cosmology and the Tail-Free Property

Fields of spin s ≥ 1 / 2 satisfying wave equations in a curved space obey the Huygens principle under certain conditions clarified by a known theorem. Here, this theorem is generalized to spin zero and applied to an inflaton field in de Sitter-like space, showing that tails of scalar radiation are an unavoidable physical feature. Requiring the absence of tails, on the contrary, necessarily implies an unnatural tuning between cosmological constant, scalar field mass, and coupling constant to the curvature.

ПРОСТРАНСТВЕННО-ВРЕМЕННОЙ АНАЛИЗ СЕЙСМИЧЕСКОГО ВОЛНОВОГО ПОЛЯ ОТ РАСПРЕДЕЛЕННОГО КАРЬЕРНОГО ВЗРЫВА

The article presents a space-time analysis of the seismic wave from a distributed career explosion. The method of direct measurement based on the dynamic model of the wave field is used to form an image of the seismic wave field in the field of quarry explosions. The efficiency of the proposed method is shown by the example of experimental seismic recording processing. The program "Nelumbo" is used to visualize the seismic field, which on the basis of experimental seismic records allows to form an image of the wave field in the space of the hemisphere, the center of which corresponds to the position of the seismometer (registration point). The algorithm of the program "Nelumbo" is based on the Huygens – Fresnel principle and Kirchhoff's theorem. The algorithm of the program allows to allocate from record of a seismic signal frames of a certain duration and to form the image of a wave field in space of a solid angle dimension π. This approach can be used as a tool to analyze the nature of the development of disturbances in the environment and the analysis of environmental risks in the production of blasting.