Three kinds of rank coals were selected to prepare coal chars at temperatures ranging from8 00 ℃to 1 200 ℃.The coaxial probe method was applied to detect the dielectric properties parameters of the coal chars.The effects of measuring frequency

preparation temperature and coal type on the chars' dielectric property were investigated.The results show that

the real part

imaginary part of the complex permittivity and dielectric loss tangent of coal chars all decreased with the increasing frequency while increased with the elevated temperature.The measuring frequency and preparing temperature had great effect on the chars' dielectric properties at low frequencies

and the effect gradually weakened at high frequencies.The dielectric properties of chars prepared by different coals varied dramatically.The anthracite coal char had the maximum dielectric parameter while the bituminous coal char had the minimum.