1,026 research outputs found
Ultrasound Matrix Imaging. I. The focused reflection matrix and the F-factor
This is the first article in a series of two dealing with a matrix approach
\alex{for} aberration quantification and correction in ultrasound imaging.
Advanced synthetic beamforming relies on a double focusing operation at
transmission and reception on each point of the medium. Ultrasound matrix
imaging (UMI) consists in decoupling the location of these transmitted and
received focal spots. The response between those virtual transducers form the
so-called focused reflection matrix that actually contains much more
information than a raw ultrasound image. In this paper, a time-frequency
analysis of this matrix is performed, which highlights the single and multiple
scattering contributions as well as the impact of aberrations in the
monochromatic and broadband regimes. Interestingly, this analysis enables the
measurement of the incoherent input-output point spread function at any pixel
of this image. A focusing criterion can then be built, and its evolution used
to quantify the amount of aberration throughout the ultrasound image. In
contrast to the standard coherence factor used in the literature, this new
indicator is robust to multiple scattering and electronic noise, thereby
providing a highly contrasted map of the focusing quality. As a
proof-of-concept, UMI is applied here to the in-vivo study of a human calf, but
it can be extended to any kind of ultrasound diagnosis or non-destructive
evaluation.Comment: 14 pages, 3 figure
Ultrasound Matrix Imaging. II. The distortion matrix for aberration correction over multiple isoplanatic patches
This is the second article in a series of two which report on a matrix
approach for ultrasound imaging in heterogeneous media. This article describes
the quantification and correction of aberration, i.e. the distortion of an
image caused by spatial variations in the medium speed-of-sound. Adaptive
focusing can compensate for aberration, but is only effective over a restricted
area called the isoplanatic patch. Here, we use an experimentally-recorded
matrix of reflected acoustic signals to synthesize a set of virtual
transducers. We then examine wave propagation between these virtual transducers
and an arbitrary correction plane. Such wave-fronts consist of two components:
(i) An ideal geometric wave-front linked to diffraction and the input focusing
point, and; (ii) Phase distortions induced by the speed-of-sound variations.
These distortions are stored in a so-called distortion matrix, the singular
value decomposition of which gives access to an optimized focusing law at any
point. We show that, by decoupling the aberrations undergone by the outgoing
and incoming waves and applying an iterative strategy, compensation for even
high-order and spatially-distributed aberrations can be achieved. As a
proof-of-concept, ultrasound matrix imaging (UMI) is applied to the in-vivo
imaging of a human calf. A map of isoplanatic patches is retrieved and is shown
to be strongly correlated with the arrangement of tissues constituting the
medium. The corresponding focusing laws yield an ultrasound image with an
optimal contrast and a transverse resolution close to the ideal value predicted
by diffraction theory. UMI thus provides a flexible and powerful route towards
computational ultrasound.Comment: 17 pages, 8 figure
Reflection matrix approach for quantitative imaging of scattering media
We present a physically intuitive matrix approach for wave imaging and
characterization in scattering media. The experimental proof-of-concept is
performed with ultrasonic waves, but this approach can be applied to any field
of wave physics for which multi-element technology is available. The concept is
that focused beamforming enables the synthesis, in transmit and receive, of an
array of virtual transducers which map the entire medium to be imaged. The
inter-element responses of this virtual array form a focused reflection matrix
from which spatial maps of various characteristics of the propagating wave can
be retrieved. Here we demonstrate: (i) a local focusing criterion that enables
the image quality and the wave velocity to be evaluated everywhere inside the
medium, including in random speckle, and (ii) an highly resolved spatial
mapping of the prevalence of multiple scattering, which constitutes a new and
unique contrast for ultrasonic imaging. The approach is demonstrated for a
controllable phantom system, and for in vivo imaging of the human abdomen. More
generally, this matrix approach opens an original and powerful route for
quantitative imaging in wave physics.Comment: 18 pages, 6 figure
Super-Resolution of License Plate Images Using Attention Modules and Sub-Pixel Convolution Layers
Recent years have seen significant developments in the field of License Plate
Recognition (LPR) through the integration of deep learning techniques and the
increasing availability of training data. Nevertheless, reconstructing license
plates (LPs) from low-resolution (LR) surveillance footage remains challenging.
To address this issue, we introduce a Single-Image Super-Resolution (SISR)
approach that integrates attention and transformer modules to enhance the
detection of structural and textural features in LR images. Our approach
incorporates sub-pixel convolution layers (also known as PixelShuffle) and a
loss function that uses an Optical Character Recognition (OCR) model for
feature extraction. We trained the proposed architecture on synthetic images
created by applying heavy Gaussian noise to high-resolution LP images from two
public datasets, followed by bicubic downsampling. As a result, the generated
images have a Structural Similarity Index Measure (SSIM) of less than 0.10. Our
results show that our approach for reconstructing these low-resolution
synthesized images outperforms existing ones in both quantitative and
qualitative measures. Our code is publicly available at
https://github.com/valfride/lpr-rsr-ext
Quantum capacitance and charge sensing of a superconducting double dot
We acknowledge the support from Hitachi Cambridge Laboratory and EPSRC Grant No. EP/K027018/1. A.J.F. is supported by a Hitachi Research fellowship.We study the energetics of a superconducting double dot, by measuring both the quantum capacitance of the device and the response of a nearby charge sensor. We observe different behaviour for odd and even charge states and describe this with a model based on the competition between the charging energy and the superconducting gap. We also find that, at finite temperatures, thermodynamic considerations have a significant effect on the charge stability diagram.PostprintPeer reviewe
Antenna Near-Field Probe Station Scanner
A miniaturized antenna system is characterized non-destructively through the use of a scanner that measures its near-field radiated power performance. When taking measurements, the scanner can be moved linearly along the x, y and z axis, as well as rotationally relative to the antenna. The data obtained from the characterization are processed to determine the far-field properties of the system and to optimize the system. Each antenna is excited using a probe station system while a scanning probe scans the space above the antenna to measure the near field signals. Upon completion of the scan, the near-field patterns are transformed into far-field patterns. Along with taking data, this system also allows for extensive graphing and analysis of both the near-field and far-field data. The details of the probe station as well as the procedures for setting up a test, conducting a test, and analyzing the resulting data are also described
Probe Station and Near-Field Scanner for Testing Antennas
A facility that includes a probe station and a scanning open-ended waveguide probe for measuring near electromagnetic fields has been added to Glenn Research Center's suite of antenna-testing facilities, at a small fraction of the cost of the other facilities. This facility is designed specifically for nondestructive characterization of the radiation patterns of miniaturized microwave antennas fabricated on semiconductor and dielectric wafer substrates, including active antennas that are difficult to test in traditional antenna-testing ranges because of fragility, smallness, or severity of DC-bias or test-fixture requirements. By virtue of the simple fact that a greater fraction of radiated power can be captured in a near-field measurement than in a conventional far-field measurement, this near-field facility is convenient for testing miniaturized antennas with low gains
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