  We have measured the relative permeability of split-ring resonator (SRR)
arrays used in metamaterials designed to have $\mu^\prime< 0$ over a narrow
range of microwave frequencies. The SRR arrays were loaded into the bore of a
loop-gap resonator (LGR) and reflection coefficient measurements were used to
determine both the real and imaginary parts of the array's effective
permeability. Data were collected as a function of array size and SRR spacing.
The results were compared to those obtained from continuous extended split-ring
resonators (ESRRs). The arrays of planar SRRs exhibited enhanced damping and a
narrower range of frequencies with $\mu^\prime<0$ when compared to the ESRRs.
The observed differences in damping, however, were diminished considerably when
the array size was expanded from a one-dimensional array of $N$ SRRs to a
$2\times 2\times N$ array. Our method can also be used to experimentally
determine the effective permeability of other metamaterial designs.
