Asymptotic behavior of solutions to the Helmholtz equations with sign changing coefficients

This paper is devoted to the study of the behavior of the unique solution $u_δ\in H^{1}_{0}(Ω)$, as $δ\to 0$, to the equation \begin{equation*} \dive(\epss_δA \nabla u_δ) + k^2 \epss_0 Σu_δ = \epss_0 f \mbox{in} Ω, \end{equation*} where $Ω$ is a smooth connected bounded open subset of $\mR^d$ with $d=2$ or 3, $f \in L^2(Ω)$, $k$ is a non-negative constant, $A$ is a uniformly elliptic matrix-valued function, $Σ$ is a real function bounded above and below by positive constants, and $\epss_δ$ is a complex function whose {\bf the real part takes the value 1 and -1}, and the imaginary part is positive and converges to 0 as $δ$ goes to 0. This is motivated from a result in \cite{NicoroviciMcPhedranMilton94} and the concept of complementary suggested in \cite{LaiChenZhangChanComplementary, PendryNegative, PendryRamakrishna}. After introducing the reflecting complementary media, complementary media generated by reflections, we characterize $f$ for which $\|u_δ\|_{H^1(Ω)}$ remains bounded as $δ$ goes to 0. For such an $f$, we also show that $u_δ$ converges weakly in $H^1(Ω)$ and provide a formula to compute the limit.

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