Speedup of minimum discontinuity phase unwrapping algorithm with a reference phase distribution

In this work, the fishnet metamaterial is applied to several converging metalenses by combining the zoning, reference phase, and phase reversal techniques. First, the zoning and reference phase techniques are implemented in several metalenses at 55 GHz (λ0=5.45 mm) with a short focal length of 1.5 λ0. Then, the phase reversal technique is applied to these metalenses by switching from a concave to a convex profile in order to change the phase distribution inside of them. The designs are evaluated both numerically and experimentally demonstrating that chromatic dispersion (the shift of the position of the focus at different frequencies) is reduced when using the phase-reversed profiles. It is shown how the position of the focus remains at the same location within a relatively broadband frequency range of ~4% around the design frequency without affecting the overall behaviour of the metalenses. The best performance is achieved with the design that combines both reference phase and phase reversal techniques, with an experimental position of the focus of 1.75 λ0, reduced side lobes, and a power enhancement of 6.5 dB. The metalenses designed here may find applications in situations where a wideband response and low side lobes are required because of the reduced chromatic aberrations of the focus.

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A Range Resolution Enhancement Algorithm for Active Millimeter Wave Based on Phase Unwrapping Mechanism

Electronics ◽

10.3390/electronics10141689 ◽

2021 ◽

Vol 10 (14) ◽

pp. 1689

Author(s):

He Zhang ◽

Hua Zong ◽

Jinghui Qiu

Keyword(s):

Millimeter Wave ◽

Phase Distribution ◽

Resolution Enhancement ◽

Continuous Phase ◽

Target Object ◽

Phase Unwrapping ◽

Practical Applications ◽

Range Resolution ◽

Security Inspection ◽

Security Check

Traditional security check technology is mainly based on metal detection by manual inspection. This method is simple and convenient, can detect a few different kinds of contrabands, and also takes into account the safety of inspectors. Because of its strong penetration characteristics, millimeter waves make up for the deficiency of existing security check technologies. Therefore, it is urgent to research and develop millimeter wave holographic imaging technology for human security inspection. In traditional imaging methods, the azimuthal resolution can be improved through various methods of image processing, but the traditional way to improve the range direction resolution is to increase the system bandwidth. However, improvements of the system bandwidth will greatly increase the cost. The bandwidth improvement space is also limited, so it cannot be expanded indefinitely in practical applications. In this study, the interferometric synthetic aperture theory was used to improve the range direction resolution of 3D millimeter wave holographic images without improving the system bandwidth. Phase unwrapping was used to reconstruct the phase information of complex images and restore the continuous phase distribution of the target object so as to achieve improvement of the range direction resolution without increasing the system bandwidth. This work has theoretical guiding significance to improve the range resolution of millimeter wave imaging.

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Digital phase analysis in interference electron microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100106272 ◽

1988 ◽

Vol 46 ◽

pp. 842-843

Author(s):

S. Hasegawa ◽

T. Kawasaki ◽

J. Endo ◽

M. Futamoto ◽

A. Tonomura

Keyword(s):

Magnetic Field ◽

Electron Microscopy ◽

Phase Distribution ◽

Magnetic Recording Media ◽

Electron Wave ◽

Vector Potentials ◽

Weak Magnetic Fields ◽

Leakage Magnetic Field ◽

Optical Reconstruction ◽

Processing Techniques

Interference electron microscopy enables us to record the phase distribution of an electron wave on a hologram. The distribution is visualized as a fringe pattern in a micrograph by optical reconstruction. The phase is affected by electromagnetic potentials; scalar and vector potentials. Therefore, the electric and magnetic field can be reduced from the recorded phase. This study analyzes a leakage magnetic field from CoCr perpendicular magnetic recording media. Since one contour fringe interval corresponds to a magnetic flux of Φo(=h/e=4x10-15Wb), we can quantitatively measure the field by counting the number of finges. Moreover, by using phase-difference amplification techniques, the sensitivity for magnetic field detection can be improved by a factor of 30, which allows the drawing of a Φo/30 fringe. This sensitivity, however, is insufficient for quantitative analysis of very weak magnetic fields such as high-density magnetic recordings. For this reason we have adopted “fringe scanning interferometry” using digital image processing techniques at the optical reconstruction stage. This method enables us to obtain subfringe information recorded in the interference pattern.

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Application of electron holography to material science studies on magnetic domain states of small particles

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100150976 ◽

1993 ◽

Vol 51 ◽

pp. 1028-1029

Author(s):

T. Hirayama ◽

Q. Ru ◽

T. Tanji ◽

A. Tonomura

Keyword(s):

Magnetic Field ◽

Material Science ◽

Science Studies ◽

Phase Distribution ◽

Carbon Film ◽

Objective Lens ◽

Electron Holography ◽

Transform Method ◽

Transmission Electron ◽

Thin Carbon

The observation of small magnetic materials is one of the most important applications of electron holography to material science, because interferometry by means of electron holography can directly visualize magnetic flux lines in a very small area. To observe magnetic structures by transmission electron microscopy it is important to control the magnetic field applied to the specimen in order to prevent it from changing its magnetic state. The easiest method is tuming off the objective lens current and focusing with the first intermediate lens. The other method is using a low magnetic-field lens, where the specimen is set above the lens gap.Figure 1 shows an interference micrograph of an isolated particle of barium ferrite on a thin carbon film observed from approximately [111]. A hologram of this particle was recorded by the transmission electron microscope, Hitachi HF-2000, equipped with an electron biprism. The phase distribution of the object electron wave was reconstructed digitally by the Fourier transform method and converted to the interference micrograph Fig 1.

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Microstructure and microanalysis of sintered Fe-Nd-B permanent magnets

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100178082 ◽

1990 ◽

Vol 48 (4) ◽

pp. 990-991

Author(s):

Mahesh Chandramouli

Keyword(s):

Electron Microscope ◽

Liquid Phase ◽

Permanent Magnets ◽

Phase Distribution ◽

Energy Dispersive Spectrometer ◽

Nucleation And Growth ◽

Liquid Phase Sintering ◽

Domain Wall Energy ◽

Oxide Phases ◽

Scanning Electron

Magnetization reversal in sintered Fe-Nd-B, a complex, multiphase material, occurs by nucleation and growth of reverse domains making the isolation of the ferromagnetic Fe14Nd2B grains by other nonmagnetic phases crucial. The magnets used in this study were slightly rich in Nd (in comparison to Fe14Nd2B) to promote the formation of Nd-oxides at multigrain junctions and incorporated Dy80Al20 as a liquid phase sintering addition. Dy has been shown to increase the domain wall energy thus making nucleation more difficult while Al is thought to improve the wettability of the Nd-oxide phases.Bulk polished samples were examined in a JEOL 35CF scanning electron microscope (SEM) operated at 30keV equipped with a Be window energy dispersive spectrometer (EDS) detector in order to determine the phase distribution.

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