Theoretical Investigations On Behaviors Of Some Stealth Materials And Structures

As an important military application, the stealth technology has been taken into actual combat in United Sates and other developed countries. Meanwhile, our country is also actively developing the front technology. In addition to the basic preparation and manufacturing, establishing effective analysis method to characterize the stealth performance, and evaluating the effectiveness of the stealth materials are also the basis in stealth technology development. This doctoral thesis presented some theoretical analyses to the stealth performance of the core-shell absorbent, and the stealth, thermal and thermal stress properties of the gradient absorbing structures with multi-layer gradients materials in electromagnetic wave circumstance are also studied. In addition, the negative mass phenomenon of the membrane-mass metamaterial structure in acoustic wave is also investigated theoretically. The main research works and the results are as follows:Firstly, for the propagation characteristics of electromagnetic wave in the core-shell structure absorbent, some quantitative results of the scattering and absorption properties are achieved theoretically by Maxwell electromagnetic theory. On the basis of this, considering the effect of the particle shape, the discrete dipole approximation method is employed and compared to the Maxwell’s theory. The stealth performances for different core-shell shapes under different radios of particle size and wavelength are discussed, and the principles of selecting optimal core-shell absorbent are obtained, which is important for effectively selecting the stealth material in different electromagnetic wave environment. The study is the basis for further studying the stealth and mechanical behaviors.Secondly, some theoretical analyses of the stealth, thermal and thermal stress properties of the functionally graded wave-absorbing material in electromagnetic wave environment are presented. Since the material properties change continuously inside the absorbing plate, the EM wave propagation analysis is generally difficult to conduct. To treat with the inhomogeneity, the plate is approximated by subdividing it into thin homogeneous layers, and the electromagnetic wave propagation is solved. Based on this, considering the energy converting and the thermal deformation properties during wave absorption, some quantitative results of the stealth and mechanical performance are solved by numerical method with the effects of gradient parameter, plate thickness, wave incident angle and wave polarization mode. The results snow mat compared to the homogeneous plate, the stealth performance of graded absorbing plate is better, and has broad frequency band. The absorbing material with good performance on the high absorption and good mechanical properties is achieved by designing the parameter of the graded absorbing plate. In addition, the stealth performance can be evaluated by adding a metal substrate to the structure.Finally, for the negative mass phenomenon which in metamaterial stealth, this paper based on the vibration theory of membrane and treating the inertia forces of the ring mass as concentrated force, a theoretical model and analytical approach is presented to investigate the transmission loss of a circular membrane-ring structure of locally resonant acoustic metamaterials. The modes of membrane-ring system with free vibration are presented and the acoustic responses of the system are studied in the acoustic wave. The reasons of the locally resonant and negative mass phenomenon are explained theoretically. The model is good to predict the frequency of the system transmission loss where the negative mass occurred. As a degeneration of the ring inner radius being zero, the present model and approach is also suited for acoustic response analysis of the membrane-central mass structure. Good method is presented to show multi-peak transmission loss in the single locally resonant materials unit.