The cold cathode flat-panel X-ray source is a new type of X-ray source with advantage of smaller footprint and lower-dose imaging than current sources. In this study, we optimized the thickness of the anode target of a flat-panel X-ray source to maximize the photon fluence of X-rays generated from the device. Utilizing EGSnrc-based Monte Carlo code, X-ray fluence was calculate from the simulated photons deposited in the virtual detector. These results revealed an optimal target thickness at a specific anode voltage to maximize the output of X-ray intensity. For experimental validation, tungsten thin film anodes with different thicknesses were prepared, and a flat-panel X-ray source was fabricated using a ZnO nanowire cold cathode. A figure of merit was introduced to characterize the output efficiency of the X-rays. The experimental results agree well with the simulation results, showing an optimal tungsten-target thickness of 1200 nm at an anode voltage of 40 kV. Using a flat-panel X-ray source with the optimized anode thickness, we took X-ray absorption images of both biological and non-biological subjects, and high-resolution images were demonstrated.

In order to study the feasibility of co-time co-frequency full-duplex (CCFD) relay, it is crucial to characterize the self-interference (SI) in practical deployment scenarios. However, modeling the SI channels is still an open issue. In this paper, a measurement campaign on the SI channels for relay communications in a dense urban scenario is presented. The transmitting and receiving antennas were installed next to each other and raised up to different heights. At each height the transmitting antenna was rotated to change the angle between their orientations. The channels were sounded at 2.6 GHz with the bandwidth of 32 MHz. The loop-back propagation and direct coupling were measured. Multiple clusters were observed in the power delay profiles (PDPs) which were reflected by the nearby buildings. The delay spreads of the loop-back channels had a decreasing tendency with the increase of the angular gap between the antenna orientations, because the second cluster was attenuated more severely than the first one. The loop-back power and the coupling power both decreased too, and the ratio between them remained consistent. The antenna isolation by angular gap is also evaluated. The measurement results in this work illustrate the behavior of loop-back propagation in an dense urban area and can help to design and evaluate the SI cancellation algorithms for the in-band full-duplex relay.

Acoustic microimaging (AMI), a technology for high-resolution imaging of materials using a scanning acoustic microscope, has been widely used for non-destructive testing and evaluation of electronic packages. Recently, the internal features and defects of electronic packages have reached the resolution limits of conventional time domain or frequency domain AMI methods with the miniaturization of electronic packages. Various time-frequency domain AMI methods have been developed to achieve super-resolution. In this paper, the sparse representation of AMI signals is studied, and a constraint dictionary-based sparse representation (CD-SR) method is proposed. First, the time-frequency parameters of the atom dictionary are constrained according to the AMI signal to constitute a constraint dictionary. Then, the AMI signal is sparsely decomposed using the matching pursuit algorithm, and echoes selection and echoes reconstruction are performed. The performance of CD-SR was quantitatively evaluated by simulated and experimental ultrasonic A-scan signals. The results demonstrated that CD-SR has superior longitudinal resolution and robustness.