Design and Implementation of a FPGA and DSP Based MIMO Radar Imaging System

The work presented in this paper is aimed at the implementation of a real-time multiple-input multiple-output (MIMO) imaging radar used for area surveillance. In this radar, the equivalent virtual array method and time-division technique are applied to make 16 virtual elements synthesized from the MIMO antenna array. The chirp signal generater is based on a combination of direct digital synthesizer (DDS) and phase locked loop (PLL). A signal conditioning circuit is used to deal with the coupling effect within the array. The signal processing platform is based on an efficient field programmable gates array (FPGA) and digital signal processor (DSP) pipeline where a robust beamforming imaging algorithm is running on. The radar system was evaluated through a real field experiment. Imaging capability and real-time performance shown in the results demonstrate the practical feasibility of the implementation

Polarization modes of gravitational waves in general modified gravity: General metric theory and general scalar-tensor theory

In this paper, we establish a unified parameterized framework for analyzing the polarization modes of gravitational waves in the general metric theory (gravity is only described by the metric) and the general scalar-tensor theory (gravity is described by the metric and an additional scalar field). Specifically, we study the polarization modes of gravitational waves in the most general metric theory and general scalar-tensor theory that satisfy the following conditions: (1) Spacetime is four-dimensional; (2) The theory satisfies the principle of least action; (3) The theory is generally covariant; (4) The action describing a free particle is $\int ds$. We find that the polarization modes of gravitational waves in the theory satisfying the above conditions depends on the selection of parameters in the framework, and the theory allows for up to all six polarization modes. Once we have established our framework, the analysis of the polarization modes of gravitational waves in specific theories will depend on determining the corresponding parameters within our framework. In our analysis, we also find that the polarization modes of gravitational waves in the general metric theory and the general scalar-tensor theory that satisfy the conditions also have some interesting universal properties.Comment: v3: 38 pages, 1 figure, 2 tables, typos correcte

Polarization modes of gravitational waves in generalized Proca theory

In this paper, we study polarization modes of gravitational waves in generalized Proca theory in the homogeneous and isotropic Minkowski background. The results show that the polarizations of gravitational waves depend on the parameter space of this gravity theory and can be divided into quite rich cases by parameters. In some parameter space, it only allows two tensor modes, i.e., the $+$ and $\times$ modes. In some parameter space, besides tensor modes, it also allows one scalar mode, or two vector (vector-$x$ and vector-$y$) modes, or both one scalar mode and two vector modes. The scalar mode is a mixture mode of a breathing mode and a longitudinal mode, or just a pure breathing mode. Interestingly, it is found that the amplitude of the vector modes is related to the speed of the tensor modes. This allows us to give the upper bound of the amplitude of the vector modes by detecting the speed of the tensor modes. Specifically, if the speed of tensor modes is strictly equal to the speed of light, then the amplitude of vector modes is zero.Comment: v2: 28 pages, 1 figure, 2 tables, improved versio

Constraining Palatini-Horndeski theory with gravitational waves after GW170817

In this paper, we investigate the possible parameter space of Palatini-Horndeski theory with gravitational waves in a spatially flat Universe. We find that if the theory satisfies the following condition: in any spatially flat cosmological background, the tensor gravitational wave speed is the speed of light $c$, then only $S = \int d^4x \sqrt{-g} \big[K(\phi,X)-G_{3}(\phi,X){\tilde{\Box}}\phi+G_{4}(\phi)\tilde{R}\big]$ is left as the possible action in Palatini-Horndeski theory.Comment: 23 pages, no figur

MEGA: An Energy Aware Algorithm for Self-Powered Wireless Sensor Networks in Sustainable Smart Infrastructure

Smart infrastructure is attractive for possessing many desirable features, such as uninterrupted monitoring of health conditions, timely response to damages, and human-infrastructure interactions. Embedded sensors that collectinformation are critical for decision making. However, the lifetime of electronic sensors is a constraint to infrastructure lifetime if sensors are physically embedded in the infrastructure at construction time. In this paper, we studied a self-powered wireless sensor network that harvests energy from mechan-ical vibration in the environment. A dynamic, hierarchical algorithm called MEGA is proposed that constructs clusters and elects the cluster head based on residue energy and energy harvest rate. Taking a smart bridge as an application example, the simulation study has verified the effectiveness of the proposed protocol