Study On The Inspection Of Electrical Tapes By Optical Coherence Tomography

Electrical tape is found as one type of important trace evidence in forensic science.The inspection of the type and source of electrical tapes can not only indicate clues and directions for investigators,but also provide evidence for litigation.Most of the traditional methods require the pretreatment of the sample,which is unfavorable to ensure the integrity of the evidence and the preservation of litigation evidence.Optical Coherence Tomography(OCT)is an optical inspection method that appeared in the 1990 s,which has the characteristics of in-situ,nondestruction,high resolution and cross-sectional imaging.This paper proposed the imaging inspection of electrical tapes by OCT for the first time,it can make a better distinction between electrical tapes and meet the requirements of forensic science.In this study,a fiber-based spectral-domain OCT(SD-OCT)system with ~5?m resolution was employed,aimed to obtain the image of 73 kinds of electrical tapes from different manufacturers and brands.A broadband SLED with a wavelength of 832 nm is selected as the system light source.2D OCT cross-sectional imaging and A-scan signal of samples were obtained,from which can obtain the optical characteristic parameters such as the number of signal peaks,the optical path,the scattering intensity ratio,and the attenuation coefficient,etc.Statistically significance differences of the parameters are compared in those different samples by an independent t-test.Meanwhile,three-dimensional(3D)OCT image reconstruction of the electrical tape samples is also implemented to create transverse sectional images beneath the surface,which provided a new method for the morphological inspection of electrical tapes.Based on OCT 3D imaging capabilities,this paper obtained the image of fingerprint sandwiched between two opaque electrical tapes without any pre-processing procedure like peeling-off.Three-dimensional(3D)OCT reconstruction was performed and the subsurface image was produced to visualize the latent fingerprints.The results demonstrate that OCT achieves distinguish of 99.60% and 90.55% respectively in red and white electrical tapes,which shows a better effect.Through the 3D imaging capabilities,OCT can visualize the latent fingerprints beneath opaque electrical tapes.OCT can realize the in-situ,non-destructive and real-time inspection of the physical evidence samples,and it is easy to operate and has high resolution,which will provide a new method for electrical tape physical evidence examination in forensic science.