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- 2017
- spectral reconstruction
- interference
- polarization
- transform
- imaging spectrometer
- Optoelectronic Information Science and Engineering
- BITTT
- Zhejiang University
- Guilin University of Aerospace Technology
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W-band Sparse Imaging System Using Frequency Diverse Cavity-Fed Metasurface Antennas
摘要： We experimentally demonstrate a frequency-diverse, computational imaging system at W-band frequencies utilizing an array of cavity-fed metasurface antennas. Each metasurface antenna consists of a cavity milled from aluminum stock, with an upper plate patterned with a set of radiating slots. As a function of frequency, the metasurface cavities produce a set of spatially diverse radiation patterns that probe the re?ectivity distribution of a scene. The antennas are designed to maximize the measurement diversity and hence imaging capacity of the system. The number and distribution of the radiating slots is optimized by balancing the cavity quality factor (Q) and Fourier space coverage. In the experimental realizations, the radiation patterns from each cavity-fed metasurface antenna is ?rst measured using near-?eld scanning techniques, propagated over the imaging domain, and then stored for use in the image reconstruction step. Comprehensive alignment procedure is implemented to align the measured radiation patterns with regard to the physical position of the cavities. Using a modeling platform, we ?nd excellent agreement between the simulation and experiment, indicating the validity of the calibration and alignment procedures. The scaling of the cavity-fed metasurface antenna represents a key step in the development of alternative high-frequency apertures for imaging and beam-forming applications.
关键词： Metasurface antennas,Resonant Cavity,W-Band,Millimeter waves,Frequency Diverse,Sparse Imaging
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - A Liquid with Tuneable Dielectric Properties for Wideband Microwave Sensing of Biological Targets
摘要： Biomedical microwave systems require antenna-to-body matching to transfer electromagnetic energy efficiently through the skin and inside the body. In this paper a paraffin oil and saline water based matching liquid is presented that can be modified in a straight-forward manner to match various dielectrics. The permittivity of this liquid may be varied between 10-52 by altering the proportions of paraffin oil to water. The conductivity can be varied between 0.3 and 1.0S/m (at 3GHz) by altering the salinity of the water, without significantly altering the permittivity. Dielectric measurements and one- and two-pole Debye parameters are given for a range of different mixtures at frequencies of 0.5-10GHz. The results highlight the flexibility of the matching liquid and mark it as a suitable antenna coupling medium as well as a biological phantom material in the low GHz range.
关键词： Biomedical signal processing,Dispersive media,Microwave imaging
更新于2025-09-04 15:30:14
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[IEEE 2018 20th International Conference on Transparent Optical Networks (ICTON) - Bucharest (2018.7.1-2018.7.5)] 2018 20th International Conference on Transparent Optical Networks (ICTON) - Recent Advances in Digital Holographic Microscopy
摘要： In digital holographic microscopy (DHM) a hologram is captured in the image space provided by a microscope. The transfer of the phase and amplitude structure in the original sample to the hologram is in fact strongly affected by the use of the imaging microscope. A big research effort has been devoted to correct these distortions both by numerical and optical compensation. In this contribution, we present several proposals to improve the performance of classical DHM architectures by an a priori approach to compensate physically these perturbations. Experimental results are also presented to validate the proposed techniques.
关键词： holography,digital holographic microscopy,quantitative phase imaging
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - The Design of High-Responsivity Millimeter Wave Imager using Vanadium Dioxide Microbolometers
摘要： A new class of millimeter wave (mmW) imaging sensor using a phase-change material (PCM) microbolometer is designed and presented. In this approach, non-linear and large change in electrical resistivity of antenna-coupled vanadium dioxide (VO2) bolometer are exploited to achieve high responsivity, fast response time, and low noise equivalent power (NEP). The sensor is biased near the phase transition cliff temperature of 68 ?C. Micro-electro-mechanical Systems (MEMS) microfabrication process is utilized to suspend the sensor in air to improve the thermal resistance and therefore overall performance of the sensor. Preliminary simulation studies, demonstrate results, approximately 30 times improvement in responsivity (9.4×103 V/W) and 60% reduction in NEP (5.5 pW/√Hz) as compared to the state-of-the-art sensor. The corresponding rise time and fall time of the device are 6 μs and 35 μs, respectively. In the near future, a pixilated array of the proposed sensor enables the realization of highly sensitive mmW camera for variety of sensing applications.
关键词： Micobolometer,millimeter wave (mmW) imaging,phase-change material (PCM)
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - 3D Printed Compressive Horn Antenna for High-Sensing-Capacity Millimeter-Wave Imaging
摘要： This paper presents a new millimeter-wave sensing system used for near-field imaging applications. The presented system is composed of a parabolic reflector which is fed by an array of compressive antennas. A Compressive Horn Antenna (CHA) is manufactured by inserting a dielectric piece with a pseudo-random geometric pattern inside a Pyramidal Horn Antenna (PHA). The presented CHA is capable of performing spectral coding, which is of special interest for high-sensing-capacity applications. The antenna is fabricated using additive manufacturing (3D printing) techniques and then spray coated with silver. Near-field measurements are carried out in the near-field region of the antenna. The measured fields are then compared with those of the full-wave simulations to validate the performance of the fabricated antenna. Using the surface equivalence principle, the electric and magnetic fields at the aperture of the horn antennas are used to calculate the equivalent radiating electric and magnetic currents. These currents are then integrated to an in-house physical optics-based solver to feed a parabolic reflector and image metallic scatterers in the near-field region of the system. Numerical simulations show that the imaging performance of the reflector fed by the CHAs outperforms those of the reflector fed by PHAs.
关键词： millimeter-wave imaging,3D printed antenna,compressive antenna,sensing capacity
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Suppressing Ghost Images for Synthetic Aperture THz Imaging with Large Sampling Spacing
摘要： This paper presents our study on the ghost images suppression for THz imaging system with large sampling spacing which are achieved by both sparse antenna array (SPA) of large element spacing (>8λ) and mechanical scanning. The ghost images in synthetic aperture imaging algorithm is due to the grating lobes of the array radiation pattern, so we propose a ghost image suppression method based on a weighting function in the traditional imaging algorithm. Therefore, the large sampling spacing between array elements for synthetic aperture THz imaging becomes possible, which can further reduce the cost and data acquisition time. And this study will help to guide the scheme design of SPA for THz imaging system.
关键词： THz imaging,ghost images suppression,sparse antenna array
更新于2025-09-04 15:30:14
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Using Schlieren imaging to estimate the geometry of a shock wave radiated by a trumpet bell
摘要： The Schlieren method has been used before to visualize weak shock waves radiated from the open ends of brass instruments, but no attempt has previously been undertaken, however, to measure the geometry of the radiated wavefronts using the Schlieren images. In this paper Schlieren visualization is used to estimate the geometry of the two-dimensional shock wavefronts radiated from the bell of a trumpet at different frequencies. It is observed that the geometry of the shocks does change with frequency, in the expected manner. The propagation speeds of these shocks are also calculated, and they too exhibit the anticipated behavior.
关键词： wavefront geometry,trumpet bell,propagation speed,shock waves,Schlieren imaging
更新于2025-09-04 15:30:14
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Reliability and Determinants of Retinal Vessel Oximetry Measurements in Healthy Eyes
摘要： PURPOSE. To assess the reliability and determinants of retinal vessel oximetry measurements with the Oxymap T1 Retinal Oximeter in normal Asian eyes. METHODS. Subjects older than 40 years without a history of stroke and heart disease were recruited from a community-based clinic. Subjects underwent standardized systemic and ocular examinations. Normal eyes were de?ned as eyes without major eye diseases such as age-related macular degeneration, glaucoma, or retinopathy. Retinal vessel oximetry levels were measured by using the Oxymap T1 Retinal Oximeter. Intra- and intergrader reliability of retinal vessel oximetry measurements were assessed by using 50 images. Intravisit repeatability of retinal vessel oximetry measurements was assessed by using 20 paired images. Univariable linear regression was performed to examine the associations between retinal vessel oximetry measurements and systemic determinants. RESULTS. A total of 118 retinal oximetry images were included in the ?nal analysis. Intra- (intraclass correlation coef?cient [ICC] values: 0.89–0.99) and intergrader (ICC values: 0.77–0.94) reliability, and intravisit (ICC values: 0.85–0.96) repeatability were both high. In the linear regression analysis, older age was associated with reduced overall retinal venular oximetry levels (b: (cid:2)2.61%; 95% con?dence interval [CI]: (cid:2)4.92 to (cid:2)0.29) and reduced inferior–nasal retinal venular oximetry levels (b: (cid:2)3.53%; 95% CI: (cid:2)6.07 to (cid:2)0.99). CONCLUSIONS. The Oxymap Retinal Oximeter allows reliable and repeatable retinal vessel oximetry measurements. Age is the main factor that in?uences retinal venular oximetry levels and should be taken into account when retinal oximetry measurements are interpreted.
关键词： retinal oximetry,functional imaging,retinal oxygen saturation
更新于2025-09-04 15:30:14
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Passive ultrasound aided acoustic resolution photoacoustic microscopy imaging for layered heterogeneous media
摘要： Photoacoustic imaging reconstructions usually assume a known speed-of-sound (SOS) distribution; however, in most cases, the SOS distribution is not revealed and is dif?cult to estimate from photoacoustic signals. In this paper, we propose passive ultrasound aided acoustic resolution photoacoustic microscopy which simultaneously reconstructs SOS distributions and photoacoustic images for layered heterogeneous media. The passive ultrasound is a kind of laser-induced acoustic wave generated by a transducer absorbing the backscattered light. It can be used to measure the layer thicknesses due to its sensitivity to structural information and broad bandwidth and further determine the SOS distributions. After estimating the SOS distributions, a phase shift plus interpo- lation is employed to reconstruct the photoacoustic image for heterogeneous media. Without intro- ducing additional hardware, this method can be conveniently incorporated into a conventional photoacoustic imaging system. A curved shell immersed in water is adopted as a layered heteroge- neous phantom, and the proposed method reconstructs the targets (carbon rods) under this shell. Under the test of a 5 MHz focused transducer (NA 0.25), the maximum reconstruction deviation of 1.2 mm carbon rods is only 0.15 mm.
关键词： passive ultrasound,speed-of-sound distribution,acoustic resolution photoacoustic microscopy,layered heterogeneous media,photoacoustic imaging
更新于2025-09-04 15:30:14
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Development of a radiative transfer model for the determination of toxic gases by Fourier transform–infrared spectroscopy with a support vector machine algorithm
摘要： This report describes a radiative transfer model for Fourier transform-infrared (FT-IR) spectroscopy to create close-to-reality toxic gas spectra by reflecting the unique spectral responses of detectors and using the atmospheric radiative transfer code, MODTRAN. This system can be highly useful in overcoming the limitations for measuring toxic gases in open environments. The emulated gas spectra can be used to train support vector machine (SVM) for chemical gas detection. Its detection performance is evaluated with nerve agents (tabun, sarin, soman, and cyclosarin) and a simulant gas (sulfur hexafluoride) for indoor and outdoor experiments by using two off-the-shelf FT-IR gas detectors. The experimental results show that the proposed SVM algorithm successfully detected and classified targeted gases while reducing false negative and false positive detection rates.
关键词： support vector machine gas detection,Fourier transform infrared remote sensing,support vector machine,hyperspectral imaging,Fourier transform – infrared spectroscopy,stand-off detection
更新于2025-09-04 15:30:14