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Copyright of Journal on Communication / Tongxin Xuebao is the property of Journal on Communications Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Synthetic aperture radar (SAR) uses microwave coherent imaging, so SAR images are complex in essence. Traditional SAR image target recognition methods based on neural networks usually only process the amplitude information of SAR images, but cannot effectively use the unique complex information of SAR images. This paper aims at the application of ship target recognition in SAR image. Starting from the essence of SAR image, the complex information representation of input data is implicitly provided by combining the real part, imaginary part and amplitude information of SAR image. Then the channel attention mechanism is introduced on the basis of the ResNet18 network and is structure, so that the network can adaptively learn the complex information contained in the three channels of real part, imaginary part and amplitude. Finally, label smoothing regularization is introduced to solve the over-fitting phenomenon due to the lack of samples in complex data sets. The experimental results based on the OpenSARShip data set show that the method proposed in this paper can make better use of the complex information of the SAR image itself, and to a certain extent improve the effect of ship target recognition based on neural network. [ABSTRACT FROM AUTHOR]

In this paper, we propose a detailed architectural design, principle of operation, and modeling analysis of a high-performance microwave computational imaging system based on information metamaterials. We use the excellent electromagnetic wave manipulation capabilities of information metamaterials, combined with compressive sampling theory, and elaborate the design approaches of stray beam generation and high-performance radiation. Furthermore, we develop a numeric model for describing this imaging system and propose a high-performance frequency-diverse information metamaterial element whose band stop characteristic can cover the X-band. Based on the element, a high-performance information metamaterial lens is designed, which achieved 75% radiation efficiency, which is three times compared with existing metamaterial apertures over the imaging region. Finally, on the basis of the proposed numeric model, we compute and reconstruct ideal scattering objects using the high-performance information metamaterial lens, validating the ability of image restoration. Study on the high-performance microwave computation imaging system in this work laid the foundation for solid theory and prospective exploration, which can be applied for imaging radar, security monitoring, and medical testing.

In recent, years, compared with the traditional phased array, the new metamaterial antenna has many advantages. However, the normal operation of the metamaterial antenna must be assisted by the frequency conversion signal, and the current super-resolution imaging algorithm does not compensate the error caused by the frequency variation, resulting in the serious decline of the imaging quality or even the inability of imaging. In addition, the frequency variation and different distances in the echo signal are coupled with each other, so the error phase can not be compensated directly. Therefore, an improved method of super-resolution correlation imaging algorithm based on compressed sensing is proposed. The super-resolution correlation imaging algorithm based on compressed sensing is combined with metamaterial antenna to realize microwave correlation imaging with low system complexity, low cost and high resolution. The correctness of the proposed method is verified by design simulation experiments, and it is verified that this method can process both two- dimensional and three-dimensional imaging. [ABSTRACT FROM AUTHOR]

This paper investigates the variation of lung tissue dielectric properties with tidal volume under in vivo conditions to provide reliable and valid a priori information for techniques such as microwave imaging. In this study, the dielectric properties of the lung tissue of 30 rabbits were measured in vivo using the open-end coaxial probe method in the frequency band of 100 MHz to 1 GHz, and 6 different sets of tidal volumes (30, 40, 50, 60, 70, 80 mL) were set up to study the trends of the dielectric properties, and the data at 2 specific frequency points (433 and 915 MHz) were analyzed statistically. It was found that the dielectric coefficient and conductivity of lung tissue tended to decrease with increasing tidal volume in the frequency range of 100 MHz to 1 GHz, and the differences in the dielectric properties of lung tissue for the 6 groups of tidal volumes at 2 specific frequency points were statistically significant. This paper showed that the dielectric properties of lung tissue tend to vary non-linearly with increasing tidal volume. Based on this, more accurate biological tissue parameters can be provided for bioelectromagnetic imaging techniques such as microwave imaging, which could provide a scientific basis and experimental data support for the improvement of diagnostic methods and equipment for lung diseases.

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Imaging technology plays an important role in the diagnosis, treatment and monitoring of diseases. As a new non-ionizing and non-invasive biomedical imaging technology, thermoacoustic imaging combines the advantages of microwave imaging high contrast and ultrasound imaging high resolution. Because of its ability to use endogenous contrast agents (such as water and ions) or multiple exogenous contrast agents (or both) to provide structure, function, and molecular information, it has been shown in pre-clinical and clinical applications. huge potential. In recent decades, due to the continuous development of microwave radiation sources and ultrasound hardware, thermoacoustic imaging technology has been widely used in the field of biomedical imaging. This article explains the basic principles and imaging characteristics of thermoacoustic imaging, introduces the application of thermoacoustic imaging technology in biomedicine in recent years, the current advantages and research status in solving corresponding clinical problems, and finally focuses on the current status of thermoacoustic imaging technology. There are challenges faced in biomedicine, and the technology is prospected. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The classical Frequency-Wavenumber (F-K) imaging algorithm can efficiently reconstruct the image for homogeneous medium; however, it cannot generate focused and properly-located images for layered medium. Considering the electrical properties of individual layer and the discontinuity between layers, the phase shift migration for layered medium is derived in this paper. The analysis on the backscattered transfer function shows that some assumptions and mathematical approximations are applied in the proposed method. The numerical and experimental results are presented to show the feasibility of the proposed method for real-time imaging of layered medium.

This study proposes a novel Multiple Input Multiple Output (MIMO) microwave imaging mode based on arc antenna array, which is mounted on the belly of platform. In this mode, an arc aperture is quickly synthesized using an MIMO. Consequently, high space and time resolution images of the illuminated scene around the platform are acquired. First, an imaging principle model based on arc antenna array is described, and its signal model is developed. Then, an imaging algorithm based on confocal projection is discussed and the performance of the mode is analyzed. Finally, the feasibility of the imaging mode and the validity of the proposed algorithm are demonstrated with a numerical simulation.

Sparse microwave imaging requires nonlinear algorithm that is expensive for large scene imaging. Therefore, the sub-block imaging method is studied, in which the measured data and the relative imaging region is divided into sub-blocks, and then sparse microwave imaging algorithm based on Least absolute shrinkage and selection operator (Lasso) is performed on each sub-block, finally the sub-blocks are combined to obtain the whole image of the large scene. Compared to the overall reconstruction of the sparse scene, sub-block algorithm can control data amount involved in each reconstruction, so as to avoid the signal processor frequently accessing the disk, which will cost huge time. Indeed, the theoretical analysis illustrates that the sub-block sparse imaging method is also accurate and stable, and the associated reconstruction error is no more than two times of that of the overall reconstruction. The result proved by simulation and real data processing supports the validity of our method.

Microwave staring imaging as a new radar imaging mode, depends on antenna sensor radiating random signal respectively and spatial-temporal two-dimension random radiation field is formed. The received echo signal and pre-stored random radiation field are processed and the image is obtained. Due to the problem of strong correlation for electromagnetic signal, the scatterer point sidelobe is very high after directly correlated processing. To solve the proposed problem, this paper proposes a new method, which is based on Schmidt and Bjorck-Schmidt orthogonalization of the pre-stored random radiation field. The correlation of random radiation field between different scatterers is reduced by these two methods and the sidelobe of scatterer is suppressed. The ratio of signal-to-noise for processed image is enhanced. Finally, the fine focused image is obtained. The comparison between signals orthogonlized by Schmidt and Bjorck-Schmidt is shown in this paper and the characteristic of the pre-stored random radiation field is analyzed. Simulation experiments show that the proposed approach is feasible. [ABSTRACT FROM AUTHOR]

Objective: To investigate the sensing volume of open-ended coaxial probe technique for measurement of dielectric characteristics., Methods: A measurement model combining macro- measurement device with a layer model of dielectric properties parameters was established for evaluating the sensing volume of open-ended coaxial probe technique. We defined sensing depth and sensing diameter to describe the distance that could be detected in vertical and horizontal direction. Using a variety of materials with different dielectric properties (Teflon, deionized water, ethanol, and gradient concentration sodium chloride solution), a layered model of dielectric properties differentiation was established. The total combined uncertainties (TCU) were calculated for different output power, and the output power was controlled to increase from -50 dBm to 15 dBm to calibrate the error range of the dielectric properties measurement system. The optimal output power range was determined based on the results of TCU test. In sensing volume measurement experiment, we set the control groups based on measurement parameters that potentially affect the sensing volume including output power (-10, -5, 0, 3, 6, and 9 dBm), frequency (1-500 MHz), Teflon, deionized water, and ethanol to form a dielectric constant difference between high and low contrast groups. Different concentrations of sodium chloride solution and Teflon were used to generate a conductivity difference between high and low contrast groups. These groups were tested in the sensing depth and sensing diameter measurement experiments., Results: The result of TCU test indicated that accurate and stable measurement results could be obtained when the output power was greater or equal to-10 dBm (TCU < 2%). Sensing volume measurement experiment revealed a positive correlation between the sensing depth and output power ( P < 0.05). As the measured power increased, the sensing depth gradually increased in deionized water and ethanol, and the difference reached 70 μm. The sensing depth was negatively correlated frequency ( P < 0.05). As the concentration of sodium chloride solution increased, the corresponding sensing depth gradually decreased, with a difference reaching 270 μm. The sensing depth of high dielectric materials was greater than that pf low dielectric materials. The results of sensing diameter measurement were not obviously affected by the measurement parameters, and the sensing diameter was stable in a fixed range (1.0 to 1.8 mm) between the diameter of the inner conductor and the diameter of the insulation layer, and was less than the diameter of the probe., Conclusions: The sensing volume of open-ended coaxial probe technique is affected by measurement parameters and dielectric properties of materials, which significantly affect the sensing depth.