Conductivity in the two-dimensional-site percolation problem

Measurements of the electrical conductivity of a 137 ×{} 137-site simple-square screen mesh versus concentration of removed sites are reported. The new critical exponent is reported to be t=1.38±0.12 within an estimated critical region Δx~0.1 about a critical percolation concentration xc=0.413±0.005. A new effective medium theory, which includes overlap effects of adjacent removed sites, is derived, which gives σ(x)σ(0)=1-πx+πx²2, in agreement with the experiment, except within the critical region.