Walk-through millimeter wave imaging testbed based on double multistatic cross arrays.

A walk-through millimeter wave imaging testbed using double multistatic cross arrays is presented. The imaging testbed consists of a vector network analyzer, a power amplifier, a low-noise amplifier, 36 SP6T electrical switchers, and double homemade multistatic cross arrays placed on both sides of the imaging area. The imaging algorithm based on the range migration algorithm is deduced, and the imaging performance is analyzed. The metallic ball experimental results show that the imaging resolution is close to the theoretical value, and demonstrate the imaging feasibility of the testbed working in mutual mode.

Hydrogen Production from Ethanol Reforming by a Microwave Discharge Using Air as a Working Gas.

Hydrogen production from ethanol reforming using microwave plasmas has great potential. In this study, a microwave plasma torch is used as a plasma source. Air is used as a discharge gas to generate the plasma. Ethanol and air are mixed and injected directly into the plasma reaction zone in a vortex flow. The effects of the oxygen-to-ethanol molar ratio (O2/Et), ethanol flow rate, and absorbed microwave power on the reforming results are investigated. When the O2/Et exceeds 0.9, ethanol is completely converted. The hydrogen selectivity is the largest when the O2/Et is 1.1, which is about 66.5%. The maximum hydrogen production rate is 2.19 mol(H2)/mol(C2H5OH). The best carrier gas residence time is 0.64-0.81 s. An appropriate increase in the ethanol flow rate can improve the ethanol conversion rate and energy efficiency while reducing the hydrogen selectivity and hydrogen yield, so the ethanol flow rate should not exceed 42.1 mL/min. The cost of hydrogen production is minimum [$3.66/kg(H2)] when the ethanol flow rate is 42.1 mL/min. The positive effect of the absorbed microwave power on the reforming reaction is significant, but too much microwave power also reduces energy efficiency. The optimum experimental conditions are an O2/Et of 0.9, an ethanol flow rate of 42.1 mL/min, and an absorbed microwave power of 700 W. The maximum energy yield is 861.91 NL(H2)/kWh at an absorbed microwave power of 700 W. The main reforming products are H2, CO, CO2, CH4, C2H2, C2H4, C2H6, C3H6, C3H8, C4H10n, and C4H10i. The content of C2 or higher hydrocarbons is considerably low. Almost no deposited carbon is generated in the experiment, which means that the design of the reforming system is effective in suppressing carbon deposition.

Dimension-Factorized Range Migration Algorithm for Regularly Distributed Array Imaging.

The two-dimensional planar MIMO array is a popular approach for millimeter wave imaging applications. As a promising practical alternative, sparse MIMO arrays have been devised to reduce the number of antenna elements and transmitting/receiving channels with predictable and acceptable loss in image quality. In this paper, a high precision three-dimensional imaging algorithm is proposed for MIMO arrays of the regularly distributed type, especially the sparse varieties. Termed the Dimension-Factorized Range Migration Algorithm, the new imaging approach factorizes the conventional MIMO Range Migration Algorithm into multiple operations across the sparse dimensions. The thinner the sparse dimensions of the array, the more efficient the new algorithm will be. Advantages of the proposed approach are demonstrated by comparison with the conventional MIMO Range Migration Algorithm and its non-uniform fast Fourier transform based variant in terms of all the important characteristics of the approaches, especially the anti-noise capability. The computation cost is analyzed as well to evaluate the efficiency quantitatively.

A High Precision Terahertz Wave Image Reconstruction Algorithm.

With the development of terahertz (THz) technology, the applications of this spectrum have become increasingly wide-ranging, in areas such as non-destructive testing, security applications and medical scanning, in which one of the most important methods is imaging. Unlike remote sensing applications, THz imaging features sources of array elements that are almost always supposed to be spherical wave radiators, including single antennae. As such, well-developed methodologies such as Range-Doppler Algorithm (RDA) are not directly applicable in such near-range situations. The Back Projection Algorithm (BPA) can provide products of high precision at the the cost of a high computational burden, while the Range Migration Algorithm (RMA) sacrifices the quality of images for efficiency. The Phase-shift Migration Algorithm (PMA) is a good alternative, the features of which combine both of the classical algorithms mentioned above. In this research, it is used for mechanical scanning, and is extended to array imaging for the first time. In addition, the performances of PMA are studied in detail in contrast to BPA and RMA. It is demonstrated in our simulations and experiments described herein that the algorithm can reconstruct images with high precision.