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Register a new userA surface-scattering model satisfying energy conservation and reciprocity
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Added by
Karthik Sasihithlu Dr
Publication date
2015
fields
Physics
and research's language is
English
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In order for surface scattering models to be accurate they must necessarily satisfy energy conservation and reciprocity principles. Roughness scattering models based on Kirchoffs approximation or perturbation theory do not satisfy these criteria in all frequency ranges. Here we present a surface scattering model based on analysis of scattering from a layer of particles on top of a substrate in the dipole approximation which satisfies both energy conservation and reciprocity and is thus accurate in all frequency ranges. The model takes into account the absorption in the substrate induced by the particles but does not take into account the near-field interactions between the particles.
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We introduce a method for breaking Lorentz reciprocity based upon the non-commutation of frequency conversion and delay. The method requires no magnetic materials or resonant physics, allowing for the design of scalable and broadband non-reciprocal circuits. With this approach, two types of gyrators --- universal building blocks for linear, non-reciprocal circuits --- are constructed. Using one of these gyrators, we create a circulator with > 15 dB of isolation across the 5 -- 9 GHz band. Our designs may be readily extended to any platform with suitable frequency conversion elements, including semiconducting devices for telecommunication or an on-chip superconducting implementation for quantum information processing.
Reciprocity is a fundamental principle governing various physical systems, which ensures that the transfer function between any two points in space is identical, regardless of geometrical or material asymmetries. Breaking this transmission symmetry offers enhanced control over signal transport, isolation and source protection. So far, devices that break reciprocity have been mostly considered in dynamic systems, for electromagnetic, acoustic and mechanical wave propagation associated with spatio-temporal variations. Here we show that it is possible to strongly break reciprocity in static systems, realizing mechanical metamaterials that, by combining large nonlinearities with suitable geometrical asymmetries, and possibly topological features, exhibit vastly different output displacements under excitation from different sides, as well as one-way displacement amplification. In addition to extending non-reciprocity and isolation to statics, our work sheds new light on the understanding of energy propagation in non-linear materials with asymmetric crystalline structures and topological properties, opening avenues for energy absorption, conversion and harvesting, soft robotics, prosthetics and optomechanics.
Under certain conditions usually fulfilled in classical mechanics, the principle of conservation of linear momentum and Newtons third law are equivalent. However, the demonstration of this fact is usually incomplete in textbooks. We shall show here that to demonstrate the equivalence, we require the explicit use of the principle of superposition contained in Newtons second law. On the other hand, under some additional conditions the combined laws of conservation of linear and angular momentum, are equivalent to Newtons third law with central forces. The conditions for such equivalence apply in many scenarios of classical mechanics; once again the principle of superposition contained in Newtons second law is the clue.
An unconstrained, non-linearly elastic, semi-infinite solid is maintained in a state of large static plane strain. A power-law relation between the pre-stretches is assumed and it is shown that this assumption is well-motivated physically and is likely to describe the state of pre-stretch for a wide class of materials. A general class of strain-energy functions consistent with this assumption is derived. For this class of materials, the secular equation for incremental surface waves and the bifurcation condition for surface instability are shown to reduce to an equation involving only ordinary derivatives of the strain-energy equation. A compressible neo-Hookean material is considered as an example and it is found that finite compressibility has little quantitative effect on the speed of a surface wave and on the critical ratio of compression for surface instability.
Electromagnetic (EM) scattering systems widely exist in EM engineering domain. For a certain objective scattering system, all of its working modes constitute a linear space, i.e. modal space. Characteristic mode theory (CMT) can effectively construct a basis of the space, i.e. characteristic modes (CMs), and the CMs only depend on the inherent physical properties of the objective system, such as the topological structure and the material parameter of the objective system. Thus, CMT is very valuable for analyzing and designing the inherent EM scattering characters of the objective system. This work finds out that integral equation (IE) is not the best framework for carrying CMT. This dissertation proposes a completely new framework for carrying CMT, i.e. work-energy principle (WEP) framework, and at the same time proposes a completely new method for constructing CMs, i.e. orthogonalizing driving power operator (DPO) method. In new WEP framework and based on new orthogonalizing DPO method, this work resolves 5 pairs of important unsolved problems existing in CMT domain.
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