Table 1.

Measured antenna parameters at 13.56 MHz at different conditions.

Parameter	Free Space	at 0.5 mm Metal	with Ferrite Sheet and Metal
Number of turns N	5	5	5
Dimmensions	30 mm × 30 mm	30 mm × 30 mm	30 mm × 30 mm
Width	0.5 mm	0.5 mm	0.5 mm
Gap	0.5 mm	0.5 mm	0.5 mm
Inductance $L_a$	1.26 $\mathsf{\mu }$H	0.55 $\mathsf{\mu }$H	2.47 $\mathsf{\mu }$H
Quality factor $Q_a$	90.7	33.6	35.7
Resonance frequency $f_r$	85 MHz	121 MHz	48 MHz