title: Invisible cloak design with controlled constitutive parameters and arbitrary shaped boundaries through Helmholtz's equation: comment.
abstract: In a recent paper, Chen et al. [Opt. Express 17, 3581 (2009)] develop an approach to design invisible cloaks with controllable constitutive parameters by adjusting the constant k in the Helmholtz's equation. In this comment, we discuss the limitation of the free parameter k in designing cloaks. It is found that the real constant k can be chosen only as limited values in order to avoid the singular material parameters.
authors.affiliation: School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081, PR China.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Chang
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Zhou
authors.forename: Jin
authors.initials: J
authors.lastname: Hu
authors.forename: Gengkai
authors.initials: G
authors.lastname: Hu
mesh_terms: D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008027:Light; D012031:Refractometry / Q000295:instrumentation* / Q000379:methods*; D012542:Scattering, Radiation