Constraints on effective constitutive parameters of certain   bianisotropic laminated composite materials
  When the electrically thin unit cell of a laminated composite material is made of two bianisotropic sheets whose constitutive properties in the thickness direction are decoupled from the constitutive properties in the interfacial planes, the laminated composite material can be homogenized into a material not all of whose constitutive parameters are independent of each other. This non-independence of the constitutive dyadics of the constituent materials and the homogenized composite material is captured by two simple constraints, which may not hold if even one of the two constituent materials has more complicated constitutive properties than stated above. 
A. Lakhtakia