Coiling-Up Space Metasurface for High-Efficient and Wide-angle Acoustic Wavefront Steering

The recent advent of acoustic metasurface displays tremendous potential with their unique and flexible capabilities of wavefront manipulations. In this paper, we propose an acoustic metagrating made of binary coiling-up space structures to coherently control the acoustic wavefront steering. The acoustic wave steering is based on the in-plane coherent modulation of waves in different diffraction channels. The acoustic metagrating structure with a subwavelength thickness is realized with 3D printed two coiling-up space metaunits. By adjusting structural parameters of the metaunits, the −1st-order diffraction mode can be retained, and the rest of the diffraction orders are eliminated as much as possible through destructive interference, forming a high-efficiency anomalous reflection in the scattering field. The anomalous reflection performance of the designed metagrating is achieved over a wide range of incident angles with high efficiency.

Modeling of the Scattering Field of an FGM-148 Javelin Anti-Tank Missile in Altair Feko

Introduction. Computer-aided design systems for microwave devices are an effective tool for assessing the backscattering characteristics of complex-shaped objects. However, these calculations are often associated with significant computational costs, especially at large values of the ratio of the characteristic dimensions of the object to the wavelength. The use of asymptotic methods in combination with the mesh coarsening of object partition can significantly reduce these costs. However, in each practical case, this leads to a deterioration in the accuracy of the estimates obtained, which is hard to predict.Aim. Comparative assessment of the results of modeling the scattering field in the CAD of microwave devices using various methods for calculating and detailing the object model in the decimeter and centimeter wavelength ranges.Materials and methods. The research object was an anti-tank guided missile FGM-148 Javelin. The scattering field of Altair FEKO microwave devices was modeled in CAD using the methods of moments and physical optics in the frequency range from 1 to 10 GHz and angles from 0 to 180°. A comparison of one-dimensional backscatter diagrams and radar images obtained using these methods was carried out.Results. For the class of objects under consideration, the method of physical optics provides acceptable accuracy at frequencies of 5 GHz and higher with a step of partitioning the model surface of the order of one centimeter and a total calculation duration of the order of several minutes (Intel Core i5-4460 PC / 3.2 GHz / 8 MB RAM). At lower frequencies, acceptable accuracy and a similar calculation duration are achieved when calculating by the method of moments and a partitioning step of about 20 cm. The possibility of using the Altair FEKO CAD system for modeling radar images of objects with a resolution of at least 20 cm is demonstrated.Conclusion. The results obtained complement the well-known studies in the field of comparative assessment of the time and accuracy characteristics of various methods for calculating the scattering field of objects in the CAD of microwave devices.

Numerical approximation of the scattering amplitude in elasticity

We propose a numerical method to approximate the scattering amplitudes for the elasticity system with a non-constant matrix potential in dimensions $$d=2$$ d = 2 and 3. This requires to approximate first the scattering field, for some incident waves, which can be written as the solution of a suitable Lippmann-Schwinger equation. In this work we adapt the method introduced by Vainikko (Res Rep A 387:3–18, 1997) to solve such equations when considering the Lamé operator. Convergence is proved for sufficiently smooth potentials. Implementation details and numerical examples are also given.

Modelling of the anti-tank guided missile scattering field and radar performance evaluation in terms of missile detection

The study presents the results achieved in an analysis of the variation of the level of an echo signal generated by the FGM-148 Javelin anti-tank missile, received by the active protection system radar with consideration given to the target attack flight profile. For our study, we use the results of modelling of the missile’s scattering field at frequencies of 1, 3, 6, and 10 GHz using the Altair FEKO CAD suite. According to estimated data, a radar using the frequency-modulated signal and operating at a medium radiation power of up to 1 W is able to detect a missile at a distance of at least 1,000 m. The results show that a combination of low power and a continuous broadband signal (100…150 MHz) along with coherent integration to units of seconds ensures concealed operations of the active protection system radar (estimated range of its radiation detection by a reconnaissance radar is not greater than 10 km).

The Mono/Bistatic SAR Imaging Simulation of Sea Surface with Breaking Waves Based on a Refined Facet Scattering Field Model

In order to analyze the scattering characteristics of sea surface under high sea state, a complete scattering model of sea surface considering breaking wave is established in this study based on the refined facet scattering field model (RFSFM) and the scattering theory of breaking wave. On the basis of this model, the influence of breaking waves on the mono/bistatic SAR imaging of sea surface at HH and VV polarization is studied. The results show that with the increase in wind speed, the coverage of breaking wave increases obviously and the consideration of breaking wave has a good correction for the scattering coefficient at HH polarization under grazing incidence; however, for VV polarization, the effect of breaking wave is very small.

Influence of Geometry and Boundary Conditions in Area of Cohesion between Materials on the Reflection of an Ultrasonic Beam. Part 1. Theoretical research

The improvement of efficiency, reliability and productivity of ultrasonic testing of objects with cohesion between materials connected by welding, soldering, gluing, etc. is 'an important problem of the modern production technologies. The purpose of the paper is to determine in 3D space the conditions for increasing the sensitivity and reliability of the flaw detection in the cohesion zone between materials when the form of defect interface can be different.In the first part of the theoretical study the features of the formation of the acoustic fields of ultrasonic waves scattered from solid's interface when spot of an acoustic beam crosses the boundary of the defective region in the shape of an ellipse or a long strip have been investigated. In this case, the boundary conditions in the defect area change discretely or linearly.It was suggested to use a phase shift between reflected waves from the defect and defect-free interfaces as the more informative parameter depending on the cohesion between materials. There is shown that there are conditions to achieve sufficiently high sensitivity detection of interface defects when the scattered waves receiving are to be at angles outside the main directivity lobe of the scattering field pattern. The evolution features of the scattering field structure which are needed for the development of the method of evaluation the cohesion of materials has been got.