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Abstract
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 20 MHz. 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 0.1 Hz to 20 MHz. 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 100 kHz. 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%.
Keywords
cotton fiber assembly, dielectric spectrum, moisture regain, permittivity
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Dielectric phenomenon is one of the main electrical properties of the fiber assembly. The dielectric proper- ties have been exploited in textiles in a variety of appli- cations involving moisture content measurement,1 evenness measurement,2 impurities detection within fiber mass3 and other sensor-type applications.4 Further investigation of the dielectric phenomenon of fiber assembly and its measurement methods are desired to quantify the processing of the textile material.
Many authors have reported measurement methods of dielectric properties in many directions with various testing conditions. No standard method so far can be directly used for the dielectric properties measurement of the fiber assembly. Fiber assembly is usually known as a complex heterogeneous three-phase system of the fiber-moisture-air mixture.5
Some authors established the capacitance model of the air-fiber mixture and wanted to explain the experi- mental phenomena with an established model. Hearle6 tested the dielectric properties of various types of fibers at frequencies between 50 Hz and 200 kHz. He reviewed various models of the air-fiber mixture to interpret the observed capacitance in terms of the fibers. He com- pared the theoretical curves and pointed out that none...