With the increase in the demand for high-speed transmission communication, satellite communication is developing rapidly. Because of the bandwidth capacity, the K/Ka band is considered the mainstream frequency band of satellite communication. The performance of a power amplifier (PA) directly affects the power of the transmitter, so the application of a power amplifier in Ka-band satellite communication is very important. A review of the state-of-the-art PA in the Ka band is presented in this article. The structure of the PA introduced includes common source, cascode, stacked field-effect transistor (FET), power combining, and Doherty PA, highlighting the advantages and disadvantages. The main solid-state technologies are outlined, including Si, SiGe, GaAs, and GaN, emphasizing Si complementary metal–oxide–semiconductor (CMOS) due to low price and high integration.

As the practical applications in other fields, high-resolution images are usually expected to provide a more accurate assessment for the air-coupled ultrasonic (ACU) characterization of wooden materials. This paper investigated the feasibility of applying single image superresolution (SISR) methods to recover high-quality ACU images from the raw observations that were constructed directly by the on-the-shelf ACU scanners. Four state-of-the-art SISR methods were applied to the low-resolution ACU images of wood products. The reconstructed images were evaluated by visual assessment and objective image quality metrics, including peak signal-to-noise-ratio and structural similarity. Both qualitative and quantitative evaluations indicated that the substantial improvement of image quality can be yielded. The results of the experiments demonstrated the superior performance and high reproducibility of the method for generating high-quality ACU images. Sparse coding based super-resolution and super-resolution convolutional neural network (SRCNN) significantly outperformed other algorithms. SRCNN has the potential to act as an effective tool to generate higher resolution ACU images due to its flexibility.

针对锯材的节子缺陷,基于空气耦合式超声波的传输系数与待测样本密度之间的关系,探索了空气耦合式超声波的节子缺陷检测新方法,并采用自行研制的空气耦合式超声波检测仪对杉木锯材试样进行检测,结果表明,空气耦合式超声波技术不仅能检测出锯材表面可见的节子缺陷,也可以有效检测不可见的内部节子缺陷.

Wavelength selection is a challenging job for the detection of the bruises on pears using hyperspectral imaging. Most modern research used the feature wavelength set selected by a single selection method which is generally unable to handle the wide variability of the hyperspectral data. A novel framework was proposed in this work to increase the performance of the bruise detection, through combining three state-of-the-art variable selection methods and the concept of feature-level integration. Successive projection algorithm, competitive adaptive reweighted sampling, and RELIEF were first applied to the spectra of the Korla pear, respectively. Then, the corresponding feature wavelength subsets were integrated and an optimal feature wavelength set was constructed. An ELM-based classifier was employed for the pear bruise identification finally. Experimental results demonstrated that the feature wavelength integration resulted in lower detection errors. The proposed method is simple and promising for bruise detection of Korla pears, and it can be utilized for other types of defects on fruits.

利用声波的传播速度构建声学断层图像,已成为一种有效的木材无损检测方法.在实践中发现,树干横截面形状对林木声学断层成像的精度有显著影响.然而,现有研究都是假设树干为圆形的,导致生成的声学断层图像与实际情况不符.为了精确检测原木、活立木的树干横截面形状,研制了一种基于激光测距传感器的树干横截面轮廓检测仪器.采用滚珠丝杆在树干周围建立等边三角形,并利用步进电机驱动激光测距传感器沿滚珠丝杆移动,检测不同位置上树干表面的样本点与滚珠丝杆间的垂直距离,然后通过坐标平移、坐标旋转等坐标转换方法将样本点的测量数据转换到同一个坐标系,最后利用3次样条插值算法对所有样本点进行曲线拟合,可以方便地绘制出待测树干的轮廓.详细介绍了检测仪器的机械系统、电路系统、软件系统的设计方法,并分别采用近似圆形和不规则形状的原木样本进行了实验.实验结果表明,该仪器绘制的树干轮廓与真实情况基本一致,生成的轮廓曲线长度与树干周长之间的相对误差为0.83％.

为提高空气耦合式超声波木材无损检测的效率,提出木材空气耦合超声图像超分辨率重构方法.该方法首先用空气耦合式超声波木材成像仪对木板样本进行不同比例的下采样扫描成像,然后利用不同的计算机图像插值算法对下采样图像进行插值得到高分辨率重构图像,并分析实验结果.结果表明:利用图像插值算法能够对木材空气耦合下采样超声图像实现不同放大倍数的重构以提高木材无损检测的效率,而其重构质量则受到多方面因素影响.

Air-coupled ultrasonic (ACU) is a contactless ultrasonic measurement method which has become increasingly popular for material characterization. This is due to a growing number of advanced materials which cannot be contaminated during the testing processes by coupling agents utilized in conventional ultrasonic testing. This paper provides a review of the applications of ACU to wood and wood products. The ACU fundamentals, including principles, working modes and commercial transducers used for this purpose, is briefly described. The emphasis of this paper is on approaches of inspection and characterization. The applications of ACU to wood characterization with reference to wood quality aspects are summarized. Correlations between the ACU parameters (i. e. amplitude, velocity, and spectrum) and the wood properties (i.e. density, moisture content, strength, and stiffness) as well as the wood defects (i. e. knots, cracks, decay, insect damage, and delamination) are dealt with in detail. Finally, a discussion of apparent future research directions completes this review.

Air-coupled ultrasonic techniques, allowing contactless nondestructive testing u sing air as the cou-pling media instead of a liquid, have proven to be reliable and indispensable for nondestructive wood testing;however, instrumentation is still not widely available domestically. To help familiarize prospective users, the principle of the air-coupled ultrasonic was described first. Subsequently, a scanning imaging system was devel-oped and its structure comprising a pulser and receiver, a gantry scanner, and computer software, was described in detail. Two-dimensional scanning imaging was conducted with a single-spindle accuracy of 0.01 mm and a maximum scanning area of 500 mm × 300 mm. Scanning parameters, such as frequency, amplitude, and gain, were set conveniently according to the sample under testing. Metasequoia glyptostroboides board and Cunning-hamia lanceolata finger jointed board were utilized to test the designed scanning imaging system. Results showed that amplitude of the received signal was sensitive to cracks, knots, and density. The constructed im-ages provided information on knots, cracks, and finger joints, including location, shape, and size. Based on pre-liminary experimental results, the developed scanning imaging system could be used for non-destructive detec-tion of defects including knots and cracks and could be utilized to scan a wooden material for in-plane distri-bution of density.

Air-coupled ultrasound has shown excellent sensitivity and specificity for the nondestructive imaging of wood-based material. However, it is time-consuming, due to the high scanning density limited by the Nyquist law. This study investigated the feasibility of applying compressed sensing techniques to air-coupled ultrasound imaging, aiming to reduce the number of scanning lines and then accelerate the imaging. Firstly, an undersampled scanning strategy specified by a random binary matrix was proposed to address the limitation of the compressed sensing framework. The undersampled scanning can be easily implemented, while only minor modification was required for the existing imaging system. Then, discrete cosine transform was selected experimentally as the representation basis. Finally, orthogonal matching pursuit algorithm was utilized to reconstruct the wood images. Experiments on three real air-coupled ultrasound images indicated the potential of the present method to accelerate air-coupled ultrasound imaging of wood. The same quality of ACU images can be obtained with scanning time cut in half.

In light of the problem in applying the conventional solar water heater control system in the rural area,the paper proposes a solar water heater control system.The design thoughtways,methods of hardware and software are described in detail.A novel soft-based method to compensate the water quality effect on the water-level measurement is present.With lower cost,high security and strong practicability,the control system can meet the needs of rural area.