Study On Porosity Of Porous Composites Using Terahertz Spectroscopy

The internal structure parameters and defects of composite materials have a significant impact on mechanics or chemical properties of composite materials.The composite porosity is one of the most difficult defects to be detected,and few researches regarding detections of composite porosity based on terahertz spectroscopy have been reported so far.In this paper,the research on measuring porosity of composites using terahertz spectroscopy has been studied.First,we have built the model of calculating porosity of mixed tablets composed by microcrystalline cellulose(MCC)and indomethacin(API).Based on this model,this paper has furtherly analyzed the terahertz spectroscopy and porosity of mixed tablets and polymethacrylimide foam.Meanwhile,simulation has been made to verify the process of scattering effect of polymethacrylimide foam caused by its internal microstructure.The main contents of this paper are as follows:1.The definition,classification,main applications and common material defects of composites has been reviewed.Specially,we focus on the influence of porosity on properties of composite materials.Besides,this paper illustrates the common methods to detect composite material porosity and then the advantages of nondestructive testing by terahertz are discussed in detail.2.Based on Fresnel equations,we have deduced the method to calculate material dielectric parameters within the terahertz band,such as absorption coefficient and refractive index.To reduce the error during data analyses,the effect of multi-reflections has been analyzed,and the method of intercept and zero padding is used to correct the reflection peak.Based on the linear relationship between porosity,refractive index and indomethacin mass fraction,the model of porosity calculation of two-phase tablet has been built.3.A composite material measurement system is established based on terahertz time domain spectroscopy.The porosity of mixed tablet composed by microcrystalline cellulose and indomethacin using terahertz spectroscopy has been studied,and the corresponding formula and parameters are given.The measurement result has been compared to the theoretical value calculated by density method.Thus,this model has been proved to be suitable for the measurement of the mixed tablets composed by microcrystalline cellulose and indomethacin.4.This paper has furtherly studied the dielectric parameters and porosity of PMI foam within terahertz band.With Mie scattering simulation theory,the scattering effect caused by aperture size of PMI foam has been verified to influence THz waves greatly.