Speckle Averaging in the Imaging Step in Sub-Channel Holography
TL;DR: In this article, the process of speckle averaging in the imaging step in sub-channel holography has been studied experimentally, and the calculated probability density functions and the values of specckle contrast have been presented.
Abstract: The process of speckle averaging in the imaging step in Sub-channel holography has been studied experimentally. First order statistics of the recorded speckle patterns have also been considered and the calculated probability density functions and the values of speckle contrast have been presented. Good agreement between the experimental speckle patterns and the first order statistics is found to exist. A model analysis of the integrated speckle pattern is given in which the randomness introduced by the photographic recording has been considered ia terms of a ‘screen’ function.
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TL;DR: In this article, a photoconductive coupling mechanism for negative index materials (NIM) in the GHz frequency range was proposed by using split ring resonator (SRR) structure and simulated using a high frequency structure simulator (HFSSTM) program.
Abstract: We introduce a modulation mechanism for negative index materials (NIM) in the GHz frequency range by means of photoconductive coupling. This leads the way to a monolithically integrated modulable NIM achieved by conventional microfabrication techniques. The photosensitive material is deposited in the gap of the split ring resonator (SRR) structure and the response in terms of S-parameters is simulated using a high frequency structure simulator (HFSSTM) program. Only a single SRR particle is simulated to demonstrate total suppression of resonance amplitude and without any loss of generality the concept is applicable to a NIM comprising of both negative permeability and negative permittivity. This simple modulation of refractive indices can lead to novel optical device developments with the potential to dramatically improve the performance of existing phased array antennas, optical beam-forming networks, antenna remoting and transportation of RF power through fiber.
20 citations
TL;DR: In this article, the spatiotemporal electric field distribution of coherent broadband THz pulses propagating through planar metamaterial arrays is measured with sub-wavelength precision within a volume that is several wavelengths in size.
Abstract: We present an experimental approach to record the spatiotemporal electric field distribution of coherent broadband THz pulses propagating through planar metamaterial arrays. The electric field can be measured with sub-wavelength precision within a volume that is several wavelengths in size, thus, having the potential to map the near-field to far-field transition of the resonant structures constituting the metamaterial. To demonstrate the potential we present measurements of THz pulses propagating through a planar array of double split-ring resonators and their inverse analogues.
6 citations
TL;DR: In this paper, the bianisotropic medium model was introduced into left-handed metamaterials (LHMs) and a method was proposed to calculate the constitutive parameters of LHMs.
Abstract: We introduce the bianisotropic medium model into left-handed metamaterials (LHMs). Based on the model, we propose a novel method, which differs from S-parameter retrieval method, to calculate the constitutive parameters of LHMs. Via the numerical calculation of permeability μ and permittivity e , the relation between resonance intensity and geometric parameters for arrays of hexagonal split-ring resonators (SRRs) is acquired. The dendritic structure allows for negative permeability μ in the frequency range of 7.6–9.4 GHz, which is in good agreement with experimental results. The permittivity spectra of arrays of continuous and cut wires reveal the plasmonic and ideal resonant responses, respectively. Moreover, the recovered permittivity e is free from antiresonance, which is consistent with physical laws.
6 citations
01 Jan 2019
TL;DR: A novel structure of hexagonal microstrip patch antennas is proposed which is based on the concept of zeroth-order resonator (ZOR) and it achieves gain of 4.374 dB with radiation pattern nearly half sphere, which is suitable for rooftop antenna of vehicles.
Abstract: In this paper, a novel structure of hexagonal microstrip patch antennas is proposed which is based on the concept of zeroth-order resonator (ZOR). The simulated result shows that the proposed antenna achieves return loss of \(-19.23\) dB and has bandwidth of 0.453 GHz centered at 6.92 GHz. It achieves gain of 4.374 dB with radiation pattern nearly half sphere, which is suitable for rooftop antenna of vehicles. The proposed antenna with dimension \(16\times 20 \times 1.6\,\text {mm}^3\) can be used for wireless and satellite communication. All the simulations have been done using commercially available finite element method (FEM) solver ANSYS-HFSS. Outmost precision has been taken by assigning \(\lambda \)/20 mm mesh size, and therefore the obtained results are much presized.
6 citations
01 Mar 2019-Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems
TL;DR: In this paper, an artificial magnetic conductor surface is introduced into the near field region of a vertical meander monopole antenna to improve its electromagnetic performances, where a split ring resonator-cell is selected as an Artificial magnetic conductor.
Abstract: In this paper, a new metamaterial-inspired high frequency surface wave antenna is designed. An artificial magnetic conductor surface is introduced into the near field region of a vertical meander monopole antenna to improve its electromagnetic performances, where a split ring resonator-cell is selected as an artificial magnetic conductor. The return loss, the radiation pattern, the electric field distribution and efficiency are evaluated through the finite element method (FEM simulations). The designed antenna has advantages of low cost, small size, and light weight.
5 citations
References
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01 Jan 1975
TL;DR: Dainty et al. as mentioned in this paper described statistical properties of laser speckle patterns and proposed a method to reduce the number of sparseness of the laser beam in Partially Coherent Light (PCL).
Abstract: Contents: Dainty, J. C.: Introduction. - Goodman, J. W.: Statistical Properties of Laser Speckle Patterns. - Parry, G.: Speckle Patterns in Partially Coherent Light. - McKechnie, T. S.: Speckle Reduction. - Francon, M.: Information Processing Using Speckle Patterns. - Ennos, A. E.: Speckle Interferometry. - Dainty, J. C.: Stellar Speckle Interferometry. - Dainty, J. C.: Recent Developments. - Subject Index.
1,254 citations
TL;DR: The power spectrum of the intensity fluctuations in a random speckle pattern is derived in a simplified manner for coherent illumination in this article, and the effect of the power spectrum on the measured signal-to-noise ratio is discussed.
Abstract: The power spectrum of the intensity fluctuations in a random speckle pattern is derived in a simplified manner for coherent illumination. The effect of the power spectrum on the measured signal-to-noise ratio is discussed, and some preliminary measurements of the power spectrum are presented. The power spectrum of the intensity fluctuations for partially coherent illumination is derived for the special case of an aberration-free system, using quadratic filter theory.
154 citations
TL;DR: This paper described a multibeam recording technique that produces redundant holograms that yield speckle free images of transparencies and shows that, in order to obtain an acceptably high signal-to-noise ratio, the area of this type hologram must be more than 100 times the area needed to achieve a desired image resolution.
Abstract: Holograms made of diffusely reflecting or diffusely illuminated objects can be scratched, spotted with dirt, and even broken into pieces without serious loss of information. This remarkable property is due to the redundancy introduced by diffuse illumination which, in effect, spreads information all over the hologram. Unfortunately, an unwanted by-product of diffuse illumination is speckle noise. This noise becomes more severe as hologram size is reduced. We show that, in order to obtain an acceptably high signal-to-noise ratio, the area of this type hologram must be more than 100 times the area needed to achieve a desired image resolution, making it prohibitively large for most data storage applications. In this paper we described a multibeam recording technique that produces redundant holograms that yield speckle free images of transparencies. We show that (1) achievable redundancy is equal to the ratio of actual hologram area to that area which just satisfies resolution requirements, (2) a two-dimensional phase grating provides a simple, efficient means for generating multiple beams, an optimized grating producing nine equally intense beams with 81% efficiency, (3) an optimized phase grating having a spatial period just equal to desired image resolution yields fourfold redundancy in holograms that are just large enough to encompass both side bands of the central (or zero order) beam, and (4) holograms having fourfold redundancy give reasonably good immunity to dust and scratches.
98 citations
TL;DR: In this article, high resolution reconstructions without granulation can be obtained by superimposing reconstructions of a large number of differently illuminated holograms of the same object without granulating them.
51 citations
TL;DR: Analysis of a technique for improving image quality by using a spatially phase-modulated wavefront to illuminate the object shows that the resulting image should be free from Fresnel diffraction patterns and should have a negligible amount of residual granularity.
Abstract: When coherent light is used for imaging transparent objects, the images may be inferior because of Fresnel diffraction patterns from scattered light or may be degraded by granularity from diffuse illumination. This paper proposes a technique for improving image quality by using a spatially phase-modulated wavefront to illuminate the object. Analysis shows that the resulting image should be free from Fresnel diffraction patterns and should have a negligible amount of residual granularity. Experimental results verify these conclusions. Requirements of the imaging system and the wavefront are discussed. The technique is applicable to any nondiffuse, two-dimensional object and can be used in holography or with any other coherent imaging system.
38 citations