More Like this

1. Holey-Cavity-Based Compressive Sensing for Ultrasound Imaging

   https://doi.org/doi.org/10.3390/s18061674  

   Ashkan Ghanbarzadeh-Dagheyan, Chang Liu (May 2018, Sensors)

   The use of solid cavities around electromagnetic sources has been recently reported as a mechanism to provide enhanced images at microwave frequencies. These cavities are used as measurement randomizers; and they compress the wave fields at the physical layer. As a result of this compression, the amount of information collected by the sensing array through the different excited modes inside the resonant cavity is increased when compared to that obtained by no-cavity approaches. In this work, a two-dimensional cavity, having multiple openings, is used to perform such a compression for ultrasound imaging. Moreover, compressive sensing techniques are used for sparse signal retrieval with a limited number of operating transceivers. As a proof-of-concept of this theoretical investigation, two point-like targets located in a uniform background medium are imaged in the presence and the absence of the cavity. In addition, an analysis of the sensing capacity and the shape of the point spread function is also carried out for the aforementioned cases. The cavity is designed to have the maximum sensing capacity given different materials and opening sizes. It is demonstrated that the use of a cavity, whether it is made of plastic or metal, can significantly enhance the sensing capacity and the point spread function of a focused beam. The imaging performance is also improved in terms cross-range resolution when compared to the no-cavity case. 

   more » « less
2. High Capacity and Efficiency Optimization of Compressive Antennas for Imaging Applications

   https://doi.org/10.1049/cp.2018.0835  

   Obermeier, R.; Martinez-Lorenzo, J.A. (January 2018, 12th European Conference on Antennas and Propagation (EuCAP 2018))

   Compressive Reflector Antennas (CRA )have been shown to provide enhanced imaging capabillities over Traditional Reflector Antennas (TRA) when compressed sensing (CS) techniques are employed. This paper presents a novel method for designing dielectric CRA’s for high sensing capacity imaging applications.In the design procedure, the dielectric constants of scatterers added to a TRA are optimized in order to maximize the capacity and efficiency of the imaging system’s sensing matrix. Numerical results are presented that demonstrate the method’s ability to enhance the CS reconstruction capabilities of the CRA. 

   more » « less
3. Imaging-based cavity optomechanics

   https://doi.org/10.1117/12.2676081  

   Pluchar, Christian M; Agrawal, Aman R; Wilson, Dalziel J (October 2023, SPIE)

   Dholakia, Kishan; Spalding, Gabriel C (Ed.)

   Cavity optomechanics has led to advances in quantum sensing, optical manipulation of mechanical systems, and macroscopic quantum physics. However, previous studies have typically focused on cavity optomechanical coupling to translational degrees of freedom, such as the drum mode of a membrane, which modifies the amplitude and phase of the light field. Here, we discuss recent advances in “imaging-based” cavity optomechanics – where information about the mechanical resonator’s motion is imprinted onto the spatial mode of the optical field. Torsion modes are naturally measured with this coupling and are interesting for applications such as precision torque sensing, tests of gravity, and measurements of angular displacement at and beyond the standard quantum limit. In our experiment, the high-Q torsion mode of a Si3N4 nanoribbon modulates the spatial mode of an optical cavity with degenerate transverse modes. We demonstrate an enhancement of angular sensitivity read out with a split photodetector, and differentiate the “spatial” optomechanical coupling found in our system from traditional dispersive coupling. We discuss the potential for imaging-based quantum optomechanics experiments, including pondermotive squeezing and quantum back-action evasion in an angular displacement measurement. 

   more » « less
4. Coded aperture optimization in compressive X-ray tomography: a gradient descent approach

   Cuadros, Angela; Arce, Gonzalo (October 2017, Optics express)

   Abstract: Coded aperture X-ray computed tomography (CT) has the potential to revolutionize X-ray tomography systems in medical imaging and air and rail transit security - both areas of global importance. It allows either a reduced set of measurements in X-ray CT without degrada- tion in image reconstruction, or measure multiplexed X-rays to simplify the sensing geometry. Measurement reduction is of particular interest in medical imaging to reduce radiation, and airport security often imposes practical constraints leading to limited angle geometries. Coded aperture compressive X-ray CT places a coded aperture pattern in front of the X-ray source in order to obtain patterned projections onto a detector. Compressive sensing (CS) reconstruction algorithms are then used to recover the image. To date, the coded illumination patterns used in conventional CT systems have been random. This paper addresses the code optimization prob- lem for general tomography imaging based on the point spread function (PSF) of the system, which is used as a measure of the sensing matrix quality which connects to the restricted isom- etry property (RIP) and coherence of the sensing matrix. The methods presented are general, simple to use, and can be easily extended to other imaging systems. Simulations are presented where the peak signal to noise ratios (PSNR) of the reconstructed images using optimized coded apertures exhibit significant gain over those attained by random coded apertures. Additionally, results using real X-ray tomography projections are presented. 

   more » « less
5. Coded aperture optimization in compressive X-ray tomography: a gradient descent approach

   Cuadros, Angela; Arce, Gonzalo (October 2017, Optics express)

   Abstract: Coded aperture X-ray computed tomography (CT) has the potential to revolutionize X-ray tomography systems in medical imaging and air and rail transit security - both areas of global importance. It allows either a reduced set of measurements in X-ray CT without degrada- tion in image reconstruction, or measure multiplexed X-rays to simplify the sensing geometry. Measurement reduction is of particular interest in medical imaging to reduce radiation, and airport security often imposes practical constraints leading to limited angle geometries. Coded aperture compressive X-ray CT places a coded aperture pattern in front of the X-ray source in order to obtain patterned projections onto a detector. Compressive sensing (CS) reconstruction algorithms are then used to recover the image. To date, the coded illumination patterns used in conventional CT systems have been random. This paper addresses the code optimization prob- lem for general tomography imaging based on the point spread function (PSF) of the system, which is used as a measure of the sensing matrix quality which connects to the restricted isom- etry property (RIP) and coherence of the sensing matrix. The methods presented are general, simple to use, and can be easily extended to other imaging systems. Simulations are presented where the peak signal to noise ratios (PSNR) of the reconstructed images using optimized coded apertures exhibit significant gain over those attained by random coded apertures. Additionally, results using real X-ray tomography projections are presented. 

   more » « less