scholarly journals Distance measurement using the spherical wave fact of astronomical objects

2020 ◽  
Vol 6 ◽  
Author(s):  
Yuanchuan Zou
Keyword(s):  
Electromagnetic Waves ◽  
Spherical Surface ◽  
Spherical Wave ◽  
Distance Measurement ◽  
Independent Method ◽  
Spherical Waves ◽  
Position Accuracy ◽  
Arduous Task ◽  
Measurable Distance

Distance measurement is very important for astrophysics, and it is also an arduous task. Here we propose an independent method to measure the distances directly. Considering that electromagnetic waves are actually spherical waves from the source, people can get the distance of the source by accurately measuring the curvature of the spherical surface. The farthest measurable distance is roughly b2/b, where d is the separation of telescopes, and b is the position accuracy of the telescopes.

RECIPROCITY RELATIONS FOR A CONDUCTIVE SCATTERER WITH A CHIRAL CORE IN QUASI-STATIC FORM

2018 ◽  
Vol 60 (1) ◽  
pp. 86-94
Author(s):  
C. E. ATHANASIADIS ◽  
E. S. ATHANASIADOU ◽  
S. DIMITROULA
Keyword(s):  
Electromagnetic Waves ◽  
Scattering Problem ◽  
Spherical Wave ◽  
Point Sources ◽  
Scattering Problems ◽  
Spherical Waves ◽  
Incident Plane ◽  
Reciprocity Relations ◽  
Static Form ◽  
Stationary Approximation

We analyse a scattering problem of electromagnetic waves by a bounded chiral conductive obstacle, which is surrounded by a dielectric, via the quasi-stationary approximation for the Maxwell equations. We prove the reciprocity relations for incident plane and spherical electric waves upon the scatterer. Mixed reciprocity relations have also been proved for a plane wave and a spherical wave. In the case of spherical waves, the point sources are located either inside or outside the scatterer. These relations are used to study the inverse scattering problems.

scholarly journals 3D Display System Based on Spherical Wave Field Synthesis

2019 ◽  
Vol 9 (18) ◽  
pp. 3862
Author(s):  
Claas Falldorf ◽  
Ping-Yen Chou ◽  
Daniel Prigge ◽  
Ralf Bergmann
Keyword(s):  
Liquid Crystal Display ◽  
Spherical Wave ◽  
Depth Information ◽  
Natural Scene ◽  
Display System ◽  
3D Display ◽  
Spherical Waves ◽  
New Type ◽  
Wave Field Synthesis ◽  
Novel Concept

We present a novel concept and first experimental results of a new type of 3D display, which is based on the synthesis of spherical waves. The setup comprises a lens array (LA) with apertures in the millimeter range and a liquid crystal display (LCD) panel. Each pixel of the LCD creates a spherical wave cutout that propagates towards the observer. During the displaying process, the curvature of the spherical waves is dynamically changed by either changing the distance between LA and LCD or by adapting the focal lengths of the lenses. Since the system, similar to holography, seeks to approximate the wavefront of a natural scene, it provides true depth information to the observer and therefore avoids any vergence–accommodation conflict (VAC).

Application of Fiber Point Diffraction in Measurement of Optical Surface

2011 ◽  
Vol 55-57 ◽  
pp. 1200-1205
Author(s):  
Liang Nie ◽  
Jun Han ◽  
Xu Jiang
Keyword(s):  
High Performance ◽  
Spherical Surface ◽  
Spherical Wave ◽  
Numerical Aperture ◽  
Single Mode ◽  
Single Mode Fiber ◽  
Optical Surface ◽  
Fiber System ◽  
Core Diameter ◽  
Fringe Contrast

The fiber point diffraction technology is applied in interferometer to measure optical surface with high precision. The wavefront diffracted from the single mode fiber with microns core diameter can be considered as ideal spherical wave and used as the referenced wave in interferometry. To estimate the quality of diffracted wavefront, the theoretical model of optical point diffraction is introduced at first. Based on the model, the influence of fiber core diameter, deformation and end-face shape on wavefront error is studied with numerical analysis. The analysis result shows that the single mode fiber used in experiment is available for instrument design and its influence over systematic error should be negligible within certain numerical aperture. Then a point diffraction interferometer with a single fiber is designed. Compared with the double fiber system, it has merit of noise immunity, high fringe contrast and high performance. Finally, the fiber point diffraction interferometer system is put up to measure spherical surface in experiment. The interference fringes are collected and analyzed with five-step shifting, least squares unwrapping and Zernike fitting method. The results show that the interferometer with optical fiber has achieved a worthy measurement precision and has great development potential.

True amplitude recovery in reverse time extrapolation of plane and spherical waves

Geophysics ◽  
2018 ◽  
Vol 83 (3) ◽  
pp. T103-T122 ◽  
Author(s):  
Yulang Wu ◽  
George A. McMechan
Keyword(s):  
Incident Wave ◽  
Horizontal Well ◽  
Spherical Wave ◽  
Reverse Time ◽  
Multiple Reflections ◽  
Reflection And Transmission ◽  
Spherical Waves ◽  
Reflection Data ◽  
Time Propagation ◽  
Time Extrapolation

A challenging outstanding problem in reverse time extrapolation is recovering accurate amplitudes at reflectors from the receiver wavefield. Various migrations have been developed to produce accurate image locations rather than correct amplitude information because of inadequate compensation of attenuation, dispersion, and transmission losses. We have evaluated the requirements, and determined the theoretical feasibility, of true amplitude recovery of 2D acoustic and elastic seismic data by using the analytic Zoeppritz equations for plane-wave reflection and transmission coefficients. Then, we used synthetic acoustic and elastic wavefield data generated by elastodynamic finite differences to verify the recovery, in the reverse time propagation, of spherical waves and illustrated the salient differences between the incident wavefields reconstructed from reflection data only and from the combination of reflection and transmission data. These examples quantitatively verify that recovering an incident plane or a spherical wave requires the reverse time propagation of all reflections and transmissions in a model with the correct velocity and density. Accurate reconstruction of an incident wave is not possible by backward propagation of only reflections. As an application, we removed downgoing internal multiple reflections generated by upgoing waves incident at reflectors shallower than a horizontal well, in which geophones are deployed. The subtraction of the downgoing reflection involves wavefield reconstruction at depths shallower than the horizontal well and separation of upgoing and downgoing wavefields. This approach assumes that the correct acoustic (or elastic) velocity and density models are available in, and shallower than, the layer where the horizontal well is located. Incident-wave reconstruction works equally well for smooth models, as for models with sharp boundaries. Uncertainties in the model used for reconstruction, and incompleteness of the data aperture are propagated into the equivalent uncertainties, and incompleteness of the reconstruction.

On: “DIFFRACTION OF ELECTROMAGNETIC WAVES BY AN INHOMOGENEOUS SPHERE” BY. J. G. NEGI (GEOPHYSICS, AUGUST 1962, PP. 480–492)

Geophysics ◽  
1963 ◽  
Vol 28 (4) ◽  
pp. 665-665
Author(s):  
Ari Ben‐Menahem ◽  
Armando Cisternas
Keyword(s):  
Electromagnetic Waves ◽  
Spherical Wave ◽  
Wave Functions ◽  
Inhomogeneous Sphere

In the section of the paper by Dr. Negi dealing with “The Influence of the Air‐Earth Boundary,” the author is using results given in a paper by B. P. Dyakonov (1959). Formula (28) in Dyakonov’s paper is incorrect because the spherical wave functions should be given differently.

Reflection and Transmission of Elastic-Plastic Spherical Waves at a Spherical Interface

1975 ◽  
Vol 42 (4) ◽  
pp. 837-841 ◽  
Author(s):  
M. G. Srinivasan
Keyword(s):  
Shock Wave ◽  
Spherical Wave ◽  
Acceleration Wave ◽  
Wave Fronts ◽  
Reflection And Transmission ◽  
Elastic Plastic ◽  
Spherical Waves ◽  
The Many ◽  
Discontinuity Conditions ◽  
Spherical Interface

When a spherical wave is incident on a spherical interface of two different elastic-plastic, rate-independent materials, which of the many different admissible cases of reflection and transmission will actually occur must be determined in order to extend any numerical solution for subsequent times. An analytical method for this determination in terms of the known solution for times just prior to the incidence of the wave is outlined. The wave considered may be either an acceleration wave or a shock wave. The discontinuity conditions across the wave fronts and the continuity of displacement at the interface form the basis of this method and examples are given for illustration.

Heterogeneous integration of a miniaturized W-band radar module

2015 ◽  
Vol 2015 (1) ◽  
pp. 000766-000770 ◽  
Author(s):  
K.-F. Becker ◽  
L. Georgi ◽  
R. Kahle ◽  
S. Voges ◽  
F. Brandenburger ◽  
...  
Keyword(s):  
Electromagnetic Waves ◽  
High Performance ◽  
Continuous Wave ◽  
Low Cost ◽  
Distance Measurement ◽  
Heterogeneous Integration ◽  
Frequency Range ◽  
Band Frequency ◽  
Technological Basis ◽  
W Band

For radar applications, the W-band frequency range (75 – 110 GHz) is a good candidate for high-resolution distance measurement and remote detection of small or hidden objects in distances of 10 cm to ≫ 20 m. As electromagnetic waves in this frequency range can easily penetrate rough atmosphere like fog, smoke or dust, W-band radars are perfectly suited for automotive, aviation, industrial and security applications. Additional benefit is that atmosphere has an absorption minimum at 94 GHz, so relative small output power is sufficient to achieve long range coverage. By combining and enhancing knowledge from the disciplines of heterogeneous integration technology and compound semiconductor-technology, the Fraunhofer Institutes IAF, IPA and IZM developed a miniaturized and low cost 94 GHz radar module. Result of this approach is a highly miniaturized radar module built using a modular approach. The radar components are mounted on a dedicated RF-NF-hybrid PCB while the signal processing is done on a separate board stacked below. This hybrid RF-module is combined with highly integrated digital processing PCB via micro connectors in a way that the radar system and an adapted conical HDPE-lens fit into an aluminum housing of 42×80×27 mm3 with a weight of only 160 grams for the whole module. The paper will describe the technological basis for such a frequency modulated continuous wave [FMCW] W-band radar module and describe in detail the technological features that enabled the assembly of such a miniaturized but high-performance system. The module yields an evaluated distance measurement accuracy of 5 ppm (5 μm deviation per meter target distance) while its low weight and small dimensions pave the way for a variety of new applications, including mobile operation.

scholarly journals Planar ESPAR Array Design with Nonsymmetrical Pattern by Means of Finite-Element Method, Domain Decomposition, and Spherical Wave Expansion

2012 ◽  
Vol 2012 ◽  
pp. 1-8
Author(s):  
Jesús García ◽  
Juan F. Izquierdo ◽  
Jesús Rubio ◽  
Miguel A. González ◽  
Juan Zapata
Keyword(s):  
Finite Element ◽  
Domain Decomposition ◽  
Mutual Coupling ◽  
Ground Plane ◽  
Spherical Wave ◽  
Scattering Matrix ◽  
Mode Expansion ◽  
Spherical Waves ◽  
Spherical Wave Expansion ◽  
Generalized Scattering Matrix

The application of a 3D domain decomposition finite-element and spherical mode expansion for the design of planar ESPAR (electronically steerable passive array radiator) made with probe-fed circular microstrip patches is presented in this work. A global generalized scattering matrix (GSM) in terms of spherical modes is obtained analytically from the GSM of the isolated patches by using rotation and translation properties of spherical waves. The whole behaviour of the array is characterized including all the mutual coupling effects between its elements. This procedure has been firstly validated by analyzing an array of monopoles on a ground plane, and then it has been applied to synthesize a prescribed radiation pattern optimizing the reactive loads connected to the feeding ports of the array of circular patches by means of a genetic algorithm.

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