Estimation of the moisture regain of cotton fiber using the dielectric spectrum

A broad band dielectric spectrum measurement system and a newly presented measuring method were adopted to measure the dielectric spectrum of cotton fiber assemblies with different moisture regains in the measurement frequencies from 0.1 Hz to 20MHz. The experimental results showed that the permittivity of cotton fiber assembly increases with the increase in the moisture regain, and decreases with the increase in measurement frequency. For the cotton fiber assembly with the moisture regain less than 3%, its real part of permittivity is linear with respect to moisture regain from 0.1Hz to 20MHz. However, for the cotton fiber assembly with moisture regain greater than 3%, its real part of permittivity is linear with respect to moisture regain only in the frequency much higher than 100kHz. Moreover, the change rate of the real part permittivity per unit mass, which is independent of the weight but closely related to the moisture regain of the cotton fiber assembly, was presented to estimate the moisture regain of cotton fiber assembly with moisture regain greater than 3%.