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Due to the fields in the near-field area of an electric dipole source which is sharply and rapidly varying with distance, a novel approach to introduce an underwater low-frequency excited source is proposed in this paper. The approach is built up to combine the theoretical solution for an electric dipole in a conductive medium with the total-field scattered-field boundary to reduce the error in modeling the source. The spatial distributions of the magnetic field amplitude at a distance of 1 km above the sea surface are discussed. The numerical results verified the accuracy and validity of the approach by comparing with the results of the Sommerfeld numerical integration method.

Micromotion characteristics of conical-shaped high-speed moving targets are presented using the Lorentz finite-difference time-domain (Lorentz-FDTD) method. This research discusses the transformation formulas of the space and time increments, the incident wave, the field components between the moving system, and the laboratory system in case of a micromotion target. The validity and accuracy of the proposed transformation formulas are verified by presenting the results for a moving cone and a hemisphere–cylinder combination target.

Early Access; International audience; Acousto-electric tomography (AET) involves three steps to retrieve the distribution ofconductivity in a domain of interest (DOI): measure the potential on the DOI boundary (usually with alimited number of electrodes set there), compute the power density from this potential, use it to retrieve thedistribution sought after. Almost all developed algorithms for AET assume that the power density is known,so their focus is mostly on the last step. A complete framework for AET is proposed herein to connectthe three steps, the complete electrode model (CEM) being used to simulate the voltages measured onelectrodes. The potential on the whole DOI boundary is reconstructed from such voltages. Then, the powerdensity is computed, and the conductivity distribution in the DOI retrieved. A method based on singularvalue decomposition (SVD) is proposed. This method and the iterative Levenberg-Marquardt method areused for numerical illustration. The SVD-based method yields the potential on the whole DOI boundary,and a gross map of the conductivity distribution is also obtained, to serve as initial guess of the Levenberg-Marquardt method to yield the conductivity contribution with higher accuracy.

The stability and convergence performance of Levenberg&ndash, Marquardt method for acousto-electric tomography (AET) applied to different levels of conductivity contrast is studied in this paper. As a multi-physical imaging modality, acousto-electric tomography (AET) provides high spatial imaging resolution while also conserving the high contrast property of electrical impedance tomography. The Levenberg&ndash, Marquardt method is a well known iteration scheme which can be applied for the nonlinear problem of AET. However, the influence of the conductivity contrast on the stability and convergence performances of this conductivity reconstruction method is rarely discussed in the literature. In this paper, the performance of the Tikhonov regularization-based Levenberg&ndash, Marquardt method is applied to reconstruct conductivity map with different conductivity contrast between different regions of the domain of interest (DOI). Numerical investigations are carried out for phantoms with different conductivity contrast. Reconstructed results with different levels of noise are presented and discussed in detail.

To implement the Lorentz finite-difference time-domain (FDTD) method in a 3D case, this communication presents the transformation formulas of the spatial and time increments, the field components, and the incident plane wave between the moving system and the laboratory system. The radiated fields from a moving dipole source are shown to verify the accuracy and validity of the proposed transformation formulas. The relative errors are within an acceptable range. The scattered fields of a moving metallic sphere are also illustrated to verify the validity of the proposed method. And, the scattered fields from a complex pyramid-shaped target are discussed.

In this paper, a novel non-illuminated Graphical Electromagnetic Computing Method (NI-GRECO) based on GPU acceleration has been proposed. It has the advantages of high accuracy and efficiency compared to the traditional GRECO method, and does not suffer from the limitation in the illumination model anymore. In this NI-GRECO we also proposed a pixel subdivision technique, which can improve the display accuracy of the target model and then increase computing accuracy. In case of the data output, the method of data extraction by using the Frame Buffer Object (FBO) can also improve computing accuracy. In this way, the data output is no longer subject to color restriction. The extraction accuracy of the normal vector increased from 1/256 to 1/1000000. Additionally, the novel method has a significant speedup, which is up to 36 times than the original GRECO method for a sphere RCS simulation thanks to the parallel GPU processing.

An impulse plane wave is introduced in Lorentz finite-difference time domain for calculating the fields of high-speed moving dielectric. Applying the impulse plane wave and the fast Fourier transformation, we can directly read out the frequency shifts of the reflected and transmitted waves by one-time calculation. The proposed approach can greatly save run time and enhance the computation efficiency, especially in terms of considering a large number of incident frequencies. Two cases of moving canonical and noncanonical dielectric targets are considered to verify the accuracy and validity of the proposed method.

This paper extends the FDTD method to calculate the micro-motion characteristics of a moving cylinder by combining the Lorentz transformation and the central interpolation technique. The validity and accuracy of the proposed method are verified by the calculation results of the cylinder in a micro-motion state.

A voltage source is inserted into the surface of a metallic ship with the TSS-FDTD method to calculate the phase distribution of low-frequency surface current along the ship. The phase distribution of the surface current in f=10Hz is discussed with the proposed method. Numerical results show that the phase distribution is periodic round the voltage feed.

We apply the parallel TSS-FDTD method to obtain the spatial distributions of fields in air radiated from an underwater magnetic dipole source. The equivalent principle is used to calculate the far fields in a far zone by recording the tangential electromagnetic fields on a virtual surface above the air-sea surface. Numerical results show that the presence of sea surface affects the spatial distributions of electric field along the propagation direction.

In order to improve the computation efficiency for analyzing the underwater electromagnetic propagation at low frequency, a novel parallel total-field scattered-field source finite-difference time-domain (FDTD) method is presented in this letter. The accuracy and validity were verified by comparison to the analytical solution. Numerical results show that the parallel speedup of 13.68 and efficiency of 68.4% are obtained with 20 processors.

In order to precisely calculating the fields in air from an underwater magnetic dipole source, a novel method to introduce a low-frequency source is proposed. This method is built up by combining the analytical solution of the magnetic dipole source in the conductive medium with the total-field scattered-field boundary condition. Numerical results verified the validity and accuracy of the proposed method.

The scattered properties in the far-field region of an ellipsoid target., moving at high speed., are presented by a three-dimensional Lorentz Finite-Difference Time-Domain (FDTD) method. When the target is rest., the results are in good agreement with those by the MoM method and the conventional FDTD method. Numerical results show that the radar cross section (RCS) in the far-field region from the moving target is modulated by the moving speed.

The scattered properties of a cone-sphere target, moving at high speed, are presented by a three-dimensional Lorentz-FDTD method. Numerical results show that the amplitudes of the scattered wave are modulated by the movement of target. Moreover, different operating frequencies cause different amplitudes of scattered wave for the same moving speed of target.

A lossy Drude dispersive medium is used to analyze the propagation properties of the low-frequency electromagnetic wave under the rough sea surface. Numerical results in f=150Hz are illustrated for two different rough sea surfaces. It is noted that the rough sea surface affects the phase and amplitude distributions of the low-frequency electromagnetic wave.

Calibration is important to service robot, but the process of calibration is time consuming and laborious. With the popularity of service robot, an automatic and universal calibration system is urgent to be developed, therefore we propose a general batch-calibration framework, Motion Capture System is adopt as an external measurement device in virtual of it can provide realtime, accurate movement data of measured objects. We will show that the system is effective and promising with a case study of odometry calibration.

Nowadays there are a lot of kinds of cleaning robots which producted by different manufacturers come into people’s lives. But it is still a problem that how to evaluate each robot’s performance to check whether the quality is acceptable. In this paper, we make the first trial to evaluate the complete coverage path planning algorithm which is the core algorithm of a cleaning robot with Mocap system, and three simple metrics were proposed to evaluate overall performance of the algorithm. Lastly, the comparisons between different kinds of robots are presented.

In this paper, the coefficients of reflection and transmission of high-speed dielectric target is discussed by Lorentz-FDTD method. In this method, two coordinate systems are defined, one is the laboratory coordinate system, marked by K; another is the moving coordinate system, marked by K'. The Lorentz transformation and interpolation are used to connect the laboratory coordinate system and the moving coordinate system. The electromagnetic reflection and transmission coefficients of high-speed dielectric target are calculated. By comparing the simulation result and the analytical result, it is shown that there are a good agreement between the simulation results and the analytical results.

In order to further detect underwater targets, such as oil, gas, and shipboard equipment and so on, we discuss the underwater radiation fields of a magnetic dipole array with 3×3 elements in the TSS-FDTD method. Numerical results show that the H z and E z amplitude and phase snapshots are symmetrical related to the z axis in the yoz plane in the working frequency f=180Hz. By analyzing the radiated fields, it is more readily to distinguish if there is an abnormal underwater target or not.

This paper presents a novel shared-aperture dual-band dual-polarized high-gain antenna for potential applications in synthetic aperture radars (SAR). To reduce the complexity of SAR antennas, a dual-band dual-polarized high gain antenna based on the concept of Fabry-Perot resonant cavity is designed. This antenna operates in both C and X bands with a frequency ratio of 1:1.8. To form two separate resonant cavities, two frequency selective surface (FSS) layers are employed, leading to high flexibility in choosing desired frequencies for each band. The beam scanning capability of this proposed antenna is also investigated, where a beam scanning angle range of ±15o is achieved in two orthogonal polarizations. To verify this design concept, three passive antenna prototypes were designed, fabricated and measured. One prototype has broadside radiation patterns whilst the other two prototypes have frozen beam scanned to +15o. The measured results agree well with the simulated ones, showing that high gain, high port isolation, and low cross cross-polarization levels are obtained in both bands. Compared to the conventional high gain dual-band dual-polarized SAR antennas, the proposed antenna has achieved a significant reduction in the complexity, mass, size, loss and cost of the feed network.