  We exploit here the dramatic field enhancement caused by energy squeezing and
tunneling (i.e., 'supercoupling') in metamaterial-inspired ultranarrow
waveguide channels with near zero effective permittivity in order to sense
small permittivity variations in a tiny object. The supercoupling effect is
accurately modeled analytically and closed form expressions are derived to
describe the presence of defects or permittivity perturbations along the
channel. Applications for tailoring its pass-band frequency and for high-Q
sensing are proposed at microwave frequencies.
