This paper presents the design and simulation results of a novel 200 GHz sub-harmonic mixer. The device is based on an anti-parallel pair of GaAs Schottky diodes. The circuits are integrated with the IF filter and fabricated on a suspended quartz-based substrate. A best double sideband mixer conversion loss of 10.5 dB was achieved with 6 mW of LO power. Over an RF band of 183-220 GHz, the double sideband mixer conversion loss is below 15 dB.
Tomographic approaches in confined space require advanced imaging algorithms that can properly consider the refractive distortion as the imaging rays pass through the optical wall. Our previous work established an algorithm (cross-interfaces computed tomography, CICT) and practically solved tomographic problems in confined space. However, critical restriction was found in CICT, which is that images simulated at small azimuth angles are contaminated with noticeable signal loss and become unusable. Based on this recognition, this work has developed an improved tomography approach, namely, full-field cross-interfaces computed tomography (FCICT), to extend the available view angles to all perspectives. The key to this approach involves the 3D domain discretization using voxel parallelepipeds instead of traditional voxel layers to establish the ray-tracing relationship between imaging planes and the measurement domain. The imaging process of FCICT is first validated by quantitatively comparing the grid imaging locations in measured and simulated projections of a calibration plate. By evenly distributing the view angles in the whole azimuth angle range, the FCICT reconstruction is then numerically validated by reconstructing a simulated double-cone flame phantom. The reconstruction presents a high correlation coefficient of ∼98% with the original phantom. Finally, the FCICT is employed to reconstruct an ethylene-air premixed flame. Comparisons show that re-projections generated by the FCICT reconstruction are in accordance with measured flame images, with the mean correlation coefficients of more than 95%.
Preparation of ultrafine highly dispersed VO2(M) nanoparticles that are essential materials to fabricate thermochromic flexible films remains a challenge, preventing effective use of their promising properties. Here, we report an original hydrothermal approach by controlling oxidizing atmosphere of reaction with hydrogen peroxide to prepare ultrafine VO2(M) nanoparticles free from annealing. Hydrogen peroxide is separated from precursor solution in a reactor, which creates a moderate oxygenation environment, enabling the formation of stoichiometric VO2(M) nanoparticles. The obtained VO2(M) nanoparticles are well-dispersed, highly uniform, and single-phase, with an average particle size ∼30 nm. The flexible thermochromic films fabricated with the VO2(M) nanoparticles exhibit excellent thermochromic performance with a solar modulation efficiency of 12.34% and luminous transmittance of 54.26%. While the films prepared with annealed nanoparticles show reduced transmittance due to light scattering of the large size particles resulting from agglomeration and growth during annealing. This work demonstrates a promising technique to realize moderate oxidizing atmosphere by hydrothermal process for preparing well-dispersed stoichiometric nano-oxides.
Abstract Practical applications of computed tomography (CT) in optical engines require an advanced algorithm that can correct the light refraction via optical windows and reconstruct the 3D signal field partially blocked by structural obstacles. In this work, an advanced CT algorithm is designed for optical engines to simultaneously eliminate the imaging distortion by refraction and diminish the reconstruction errors using partial signal blocking. By combining the pinhole model and Snell’s law, the ray tracings from discretized 3D voxels in the measurement domain to 2D pixels in the imaging planes are accurately calculated, thus restoring the distortion in recorded projections. Besides, by deciding the locations and numbers of voxels that actually participate in iterative CT calculation, the iterative update process of voxel intensity becomes independent of the blocked rays, reducing the reconstruction errors. The algorithm is then numerically validated by reconstructing a simulated signal phantom inside an optical cylinder with a lightproof obstacle between the phantom and a recording camera, which imitates the refraction and blocking conditions in practical optical engines. Moreover, experimental demonstration is performed by reconstructing practical premixed flames inside optical engines. Both the simulation and the experiment present significantly enhanced flame chemiluminescence reconstruction by applying the optimized CT algorithm compared to the original algorithm utilized in open space applications.
The smart radiator device (SRD) with low solar absorption (αs) and large infrared emittance modulation (Δɛ) is desirable to a spacecraft thermal control system. In this work, the SRD was fabricated through depositing the Ag/Al2O3/VO2 triple-layer film on the Si substrate by magnetron sputtering. The properties of the SRD devices were optimized by tuning the thickness of the VO2 layer, and a fantastic SRD device was acquired, which showed low αs, high Δɛ, and intense high-temperature infrared emittance (ɛHT). For the device with a VO2 layer of 50 nm thickness, αs was as low as 29.7% and Δɛ reached 0.53 with ɛHT up to 0.87. The triple-layer film device shows great potential for applications in the spacecraft thermal control system.
Coherent radio emission mechanism of solar radio bursts is one of the most complicated and controversial topics in solar physics. To clarify the mechanism(s) of different types of solar radio bursts, (radio) wave excitation by energetic electrons in homogeneous plasmas has been widely studied via particle-in-cell (PIC) code numerical simulations. The solar corona is, however, inhomogeneous over almost all spatial scales. Inhomogeneities of the plasma could influence the emission properties of solar radio bursts. In this paper, we, hence, investigate effects of inhomogeneity (in the magnetic field, plasma density and temperature) of plasmas in the solar corona on radio wave emission by ring-beam distributed energetic electrons utilizing 2.5-dimensional PIC simulations. Both the beam and electron cyclotron maser (ECM) instabilities could be triggered with the presence of the energetic ring-beam electrons. The resultant spectrum of the excited electromagnetic waves presents a zebra-stripe pattern in the frequency space. The inhomogeneous density or temperature in plasmas influences the frequency bandwidth and location of these excited waves. Our results can, hence, help to diagnose the plasma properties at the emission sites of solar radio bursts. Applications of our results to the solar radio bursts with zebra-stripe pattern are discussed.
Abstract Three-dimensional (3D) tomographic reconstruction in confined-space requires a mapping relationship which considers the refraction distortion caused by optical walls. In this work, a tomography method, namely full-field cross-interface computed tomography (FCICT), is proposed to solve confine-space problems. The FCICT method utilizes Snell’s law and reverse ray-tracing to analytically correct imaging distortion and establishes the mapping relationship from 3D measurement domain to 2D images. Numerical phantom study is first employed to validate the FCICT method. Afterwards, the FCICT is applied on the experimental reconstruction of an illuminated two-phase jet flow which is initially generated inside an optical cylinder and then gradually moves outside. The comparison between accurately reconstructed vapor by FCICT and coarse result by traditional open space tomography algorithm provides a practical validation of FCICT. Based on the 3D vapor reconstructions at different time sequences, the distributions of surface velocity and 3D curvatures are calculated, and their correspondences are systematically analyzed. It is found that the velocity of a surface point is positively correlated with the mean curvature at the same point, which indicates the concavity/convexity of vapor surface is possibly in accordance with the surface velocity. Moreover, the surface velocity presents monotonical increasing trend with larger Gaussian curvature for elliptic surface points only, due to the dominated Brownian motion as the vapor develops.
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