Several solutions have been recently investigated for the design of passive tags over metals, mainly based on the use of high permittivity slabs and of metallic shields, integrated in the antennas as ground planes. Typical antennas are the patch-like family comprising PIFA and IFA layouts, [7] (maximum gain up
to 6 dB using the parasistic constructive effect of the surrounding objects), [8] (gain max: 2 dB) [9]
(gain max: 6.4 dB).