297 research outputs found
Model-driven CT reconstruction algorithm for nano-resolution X-ray phase contrast imaging
The low-density imaging performance of a zone plate based nano-resolution
hard X-ray computed tomography (CT) system can be significantly improved by
incorporating a grating-based Lau interferometer. Due to the diffraction,
however, the acquired nano-resolution phase signal may suffer splitting
problem, which impedes the direct reconstruction of phase contrast CT (nPCT)
images. To overcome, a new model-driven nPCT image reconstruction algorithm is
developed in this study. In it, the diffraction procedure is mathematically
modeled into a matrix B, from which the projections without signal splitting
can be generated invertedly. Furthermore, a penalized weighed least-square
model with total variation (PWLS-TV) is employed to denoise these projections,
from which nPCT images with high accuracy are directly reconstructed. Numerical
and physical experiments demonstrate that this new algorithm is able to work
with phase projections having any splitting distances. Results also reveal that
nPCT images with higher signal-to-noise-ratio (SNR) would be reconstructed from
projections with larger signal splittings. In conclusion, a novel model-driven
nPCT image reconstruction algorithm with high accuracy and robustness is
verified for the Lau interferometer based hard X-ray nano-resolution phase
contrast imaging
Nano-Resolution Visual Identifiers Enable Secure Monitoring in Next-Generation Cyber-Physical Systems
Today's supply chains heavily rely on cyber-physical systems such as
intelligent transportation, online shopping, and E-commerce. It is advantageous
to track goods in real-time by web-based registration and authentication of
products after any substantial change or relocation. Despite recent advantages
in technology-based tracking systems, most supply chains still rely on plainly
printed tags such as barcodes and Quick Response (QR) codes for tracking
purposes. Although affordable and efficient, these tags convey no security
against counterfeit and cloning attacks, raising privacy concerns. It is a
critical matter since a few security breaches in merchandise databases in
recent years has caused crucial social and economic impacts such as identity
loss, social panic, and loss of trust in the community. This paper considers an
end-to-end system using dendrites as nano-resolution visual identifiers to
secure supply chains. Dendrites are formed by generating fractal metallic
patterns on transparent substrates through an electrochemical process, which
can be used as secure identifiers due to their natural randomness, high
entropy, and unclonable features. The proposed framework compromises the
back-end program for identification and authentication, a web-based application
for mobile devices, and a cloud database. We review architectural design,
dendrite operational phases (personalization, registration, inspection), a
lightweight identification method based on 2D graph-matching, and a deep 3D
image authentication method based on Digital Holography (DH). A two-step search
is proposed to make the system scalable by limiting the search space to samples
with high similarity scores in a lower-dimensional space. We conclude by
presenting our solution to make dendrites secure against adversarial attacks
Direct Inversion of Digital 3D Fraunhofer Holography Maps
The Differential Fourier Holography (DFH) gives an exact mathematical
solution of the inverse problem of diffraction in the Fraunhofer regime. After
the first publication [1] the Differential Fourier Holography was successfully
applied in many experiments to obtain amplitude and phase information about
two-dimensional (2D) images. In this article we demonstrate numerically the
possibility to apply the DFH also for investigation of unknown 3D Objects. The
first simulation is made for a double-spiral structure plus a line as a
reference object
Determination of beam incidence conditions based on the analysis of laser interference patterns
Beam incidence conditions in the formation of two-, three- and four-beam laser interference patterns are presented and studied in this paper. In a laser interference lithography (LIL) process, it is of importance to determine and control beam incidence conditions based on the analysis of laser interference patterns for system calibration as any slight change of incident angles or intensities of beams will introduce significant variations of periods and contrasts of interference patterns. In this work, interference patterns were captured by a He-Ne laser interference system under different incidence conditions, the pattern period measurement was achieved by cross-correlation with, and the pattern contrast was calculated by image processing. Subsequently, the incident angles and intensities of beams were determined based on the analysis of spatial distributions of interfering beams. As a consequence, the relationship between the beam incidence conditions and interference patterns is revealed. The proposed method is useful for the calibration of LIL processes and for reverse engineering applications
Nanoscale resolution interrogation scheme for simultaneous static and dynamic fiber Bragg grating strain sensing
A combined interrogation and signal processing technique which facilitates high-speed simultaneous static and dynamic strain demodulation of multiplexed fiber Bragg grating sensors is described. The scheme integrates passive, interferometric wavelength-demodulation and fast optical switching between wavelength division multiplexer channels with signal extraction via a software lock-in amplifier and fast Fourier transform. Static and dynamic strain measurements with noise floors of 1 nanostrain and 10 nanostrain/sqrt(Hz), between 5 mHz and 2 kHz were obtained. An inverse analysis applied to a cantilever beam set up was used to characterise and verify strain measurements using finite element modeling. By providing distributed measurements of both ultahigh-resolution static and dynamic strain, the proposed scheme will facilitate advanced structural health monitoring
Complete light absorption in graphene-metamaterial corrugated structures
We show that surface-plasmon polaritons excited in negative permittivity
metamaterials having shallow periodic surface corrugation profiles can be
explored to push the absorption of single and continuous sheets of graphene up
to 100%. In the relaxation regime, the position of the plasmonic resonances of
the hybrid system is determined by the plasma frequency of the metamaterial,
allowing the frequency range for enhanced absorption to be set without the need
of engineering graphene.Comment: 6 pages, 4 figures; published version: text revised and references
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Robust control framework for piezoelectric actuation systems in micro/nano manipulation
Micro/nano manipulation has been identified as one of the key enabling technologies for many emerging challenges. Within this scope, piezoelectric actuators have played major roles in achieving the required nano-resolution motion. This paper proposes a robust control framework for piezoelectric actuation systems to follow specified motion trajectories. The basic concept associated with this methodology lies in the specification of a target performance and the robust control scheme formulation for piezoelectric actuation systems to ensure the convergence of the position tracking error to zero. This control methodology is attractive as its implementation requires only the knowledge of the estimated system parameters and their corresponding bounds, including bound of hysteresis and external disturbances. Feasibility study of the framework for piezoelectric actuation systems in micro/nano manipulation is described. Simulation results validated the suitability of the proposed control approach
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