Measuring trapped noise in metamaterials

Metamaterials constructed from conductive elements are lossy, and the structures act as sources of noise, whose spectrum is modified by the resonant nature of the medium itself. Furthermore, inside the medium, the noise is present as waves, which are standing waves for finite length samples. We present direct measurements of the noise spectra for a simple metamaterial comprising arrays of LC resonator elements, and compare them with the predictions of a circuit model incorporating Johnson noise. We find excellent agreement between the measured data and the model, reproducing both the resonant structure and the bandwidth of the noise spectrum, thus confirming the concept of noise waves in these metamaterials. These noise features match the frequency ranges where the metamaterial properties are useful, showing that noise is an inevitable companion to metamaterial performance in practical situations.