Electrical Tapes Research Articles

Discrimination of electrical tapes using ATR-FTIR spectroscopy and chemometrics.

Electrical tapes are recovered during criminal investigations as physical evidence in cases of rape, kidnapping, and explosion incidents. The analysis of such evidence can provide an evidentiary link between the suspect, the victim, object, or the crime scene. In the present study, 25 brands of electrical tapes have been analyzed using ATR-FTIR (attenuated total reflectance Fourier transform infrared) spectroscopy. Samples (1cm2 ) were analyzed in the mid IR (Infrared) region from 4000-600cm-1 , and the functional groups of various components have been profiled. Chemometric methods-PCA (principal component analysis) and PCA-LDA (linear discriminant analysis) have been employed to interpret the data and classify the samples into its respective classes. Preliminary assessment of sample clustering due to similar chemical composition was visualized using PCA. PCA-LDA applied for classification purpose yielded classification accuracy (calibration) of 92.98% for the adhesive side and 88% for the backing side. The validation results showed classification accuracy of 89.47% for the adhesive side and 84% for the backing side. Blind validation study was carried out using 5 samples, and classification accuracy of 100% and 80% was obtained for the adhesive and the backing side, respectively. In the current study, a preliminary substrate study was carried out, and the results showed that the backing samples could be more accurately matched to their correct source of origin than the adhesive side.

Optimization and evaluation of spectral comparisons of electrical tape backings by X-ray fluorescence

This study describes the process of parameter optimization of an XRF method for casework use. The work expands upon previous discrimination studies by broadening the total sample set of characterized tapes and evaluating the use of spectral overlay, spectral contrast angle, and Quadratic Discriminant Analysis (QDA) for the comparison of XRF spectra. The expanded sample set consisted of 114 samples, 94 from different sources, of which 90 were previously analyzed, and 20 from the same roll. XRF provided superior discrimination to SEM-EDS on the expanded dataset and a more comprehensive elemental characterization (15 elements by XRF vs. 8 by SEM-EDS). While previous SEM-EDS analysis of the 90 electrical tapes resulted in 15 distinct groups and a discrimination power of 87.3%, current XRF analysis resulted in 61 distinct groups with further subgroups providing a discrimination power of 96.7%. Duplicate controls and tape fragments from the same roll were also analyzed to assess inter-day, intra-day, and intra-roll variability (n = 20). Parameter optimization included comparison of atmospheric conditions, collection times, and instrumental filters. A study of the effects of adhesive and backing thickness on spectrum collection revealed key implications to the method that required modification to the sample support material. Figures of merit and the performance of different methods for comparing and contrasting spectra are reported. The optimization of this method was part of an assessment to incorporate XRF to a forensic laboratory protocol for rapid, highly informative elemental analysis of electrical tape backings and to expand examiners’ casework capabilities.

Multi-element comparisons of tapes evidence using dimensionality reduction for calculating likelihood ratios

Computing the likelihood ratio (LR), as a measure of weight of evidence, has traditionally been difficult for multi-element evidence. A solution based on multivariate random effects models has been adopted by the forensic community but suffers from instability and has a tendency toward extreme values. This problem is magnified by increasing the number of variables. In this study, we consider reducing the dimensionality of the problem using principal component analysis (PCA) and a post-hoc calibration step suggested by van Es et al. [1] and evaluate the performance of this method using multi-element data collected from electrical tapes with up to 18 elements measured. A set of 90 tapes known to originate from different sources were analyzed by LA-ICP-MS. We used additive log-ratio transformation with respect to the signal of 208Pb to transform the 18-dimensional data. This transformation altered the scale of the signals and more importantly, the transformed signals exhibited characteristics similar to a normal distribution. We used scores of the first five principal components (PCs) as input to the LR formula given by Aitken and Lucy [2] where we assumed multivariate normal between-sources distribution (LR MVN) to compare the tapes.We observed that the calculated LRs were extremely positive and negative and did not conform with the definition of well-calibrated LRs. Thus, we used the post-hoc calibration method given by van Es et al. [1] to calibrate the likelihood ratios. The calibrated LRs were obtained within an appropriate range.Five scenarios, each related to the number of principal components used to compare the samples formed part of this study. The first scenario made the comparisons using only the first PC, the second scenario used the first two PCs together and so on. The last scenario, LR5, used 5 PCs for the comparisons. Comparing the results of these 5 scenarios provided an understanding around sensitivity of the method based on the percentage of information used for the comparisons.The lowest false exclusion (Type I) and false inclusion (Type II) error rates were obtained for LR5 scenario in comparison to all the other scenarios. False inclusion and false exclusion error rates of 3.7% and 2.2% were reported by using only 5 out of 17 PCs. False exclusion error rates of 2.2% indicated that only two same-source comparisons had LR<1.The proposed method overcomes the problem of using highly-dimensional data for the comparisons, while using a high percentage of information present in the original data.

Assessment of the utility of X-ray Fluorescence for the chemical characterization and comparison of black electrical tape backings

Elemental analysis of electrical tapes is typically conducted by Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), although Laser Ablation-Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) recently showed to enhance the sensitivity of the determinations. In this study, the utility of X-ray Fluorescence (XRF) is compared to previously published SEM-EDS and LA-ICP-MS data. Three XRF systems were used to evaluate a range of configurations commonly available at crime laboratories. A set of 40 electrical tape backings known to originate from difference sources was used to assess the inter-roll variability, discrimination and classification capabilities of the method. The discrimination for this tape set increased from 78.8% achieved by SEM-EDS to 81.5–91.0% by XRF, depending on the instrumental configuration. In comparison, LA-ICP-MS achieved 84.6% discrimination on these tapes. The overall characterization, classification, and discrimination capabilities for this set improved as follows: SEM-EDS < iXRF < small spot size benchtop XRF with SDD, LA-ICP-MS < large spot size XRF. A set of 20 pieces of tapes collected from the same roll were analyzed for intra-roll variability. Duplicate control same-source samples were used to evaluate inter-day and intra-day instrument variability. No false exclusions were observed in the data set, demonstrating the within-sample variability and instrumental variability are relatively lower than the inter-sample variability. One concern of the method is the penetration depth of the X-ray beam beyond the target backing, requiring careful sample preparation to avoid interference from the adhesive or sample holder. XRF is a viable analytical tool for the forensic examination of electrical tapes, with advantages of speed of analysis, minimal destruction of the tape, and high informing power.

Interlaboratory evaluations of the performance of elemental analytical methods for the forensic analysis and comparisons of electrical tapes

Adhesive tapes are an important type of evidence related to violent crimes such as the construction of improvised explosive devices and kidnappings as well as involved in other types of common evidence such as drug packaging. The methods of comparison of tape evidence consist of physical and microscopic examination followed by chemical analysis of the organic and inorganic components inherent to the tapes as part of their formulations.This work evaluates the performance of the conventional methods used in forensic analysis of adhesive tapes (physical and microscopic examination, FTIR, Py-GC-MS, and SEM-EDS) and the more recently developed elemental methods, LIBS and LA-ICP-MS, for the comparison of tape samples in different laboratories.Two interlaboratory exercises were designed to study the performance of the different analytical methods for the forensic analysis of electrical tapes. The exercises were developed with the objective to imitate forensic case scenarios where known and question tapes are compared following the laboratory’s analytical protocol. The participants were asked to compare the tape samples as in a regular forensic case. Seven (7) laboratories participated in the two interlaboratory exercises.All the laboratories performing SEM-EDS in both interlaboratory exercises (#1 and #2) were able to correctly associate the pairs of tapes originating from the same rolls, therefore the rate of false negatives was zero. Two of the laboratories performing SEM-EDS for the first interlaboratory exercise incorrectly associated two pairs of tapes belonging to different rolls, resulting in a 17% false positive rate. One of the laboratories performing SEM-EDS for interlaboratory exercise #2 incorrectly associated two pairs of tapes belonging to different rolls, resulting in a 13% false positive rate. Up to 7 and 8 elements were detected by SEM-EDS for interlaboratory exercise #1 and #2, respectively.The increased sensitivity and selectivity of LIBS and LA-ICP-MS methods allowed to distinguish all the pairs of tapes originating from different sources and for correctly associate the tapes originating from the same rolls, resulting in no false positives or false negatives. In addition, increased characterization of the samples was obtained by detecting up to 14 elements by LIBS and 27 elements by LA-ICP-MS for interlaboratory exercise #1, and 17 elements by LIBS and 32 elements by LA-ICP-MS for interlaboratory exercise #2. A match criterion of ±5 s allowed to numerically compare LIBS ratios and LA-ICP-MS signal areas for a more objective assessment of the differences between the tape samples.

Forensic comparison of PVC tape backings using time resolved LA-ICP-MS analysis

Adhesive tapes are common tools for criminal acts such as the construction of improvised explosive devices. Hence, tape samples can be used as evidence to link a suspect to a scene of crime or different crime scenes to each other.A set of 87 black electrical tapes was the subject of a study evaluating a LA-ICP-MS method for the characterization of tape backings regarding their elemental composition in a forensic context. LA-ICP-MS is a powerful tool in forensic investigations due to fast, quasi nondestructive analysis of small samples and detection or determination of elements up to the ultra-trace range. In this study, the development of a semiquantitative LA-ICP-MS method for forensic tape examination using doped polymethacrylate as an “in-house” external calibration standard is presented. Semiquantitative data of Al, B, Ba, Bi, Ca, Co, Cr, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Nb, Nd, Ni, Pb, Pr, Rb, Sb, Sr, Ti, Tl, W, Y, Zn and Zr were obtained. These data were used to assess different match criteria with respect to their performance for the discrimination of tape samples originating from different rolls and association of tape samples from the same roll. A dataset of 87 PVC electrical tape samples from different rolls and a dataset of 24 samples (3 fragments from 8 sections) from each of three different rolls were analyzed to assess the discrimination and association potential of the method.The best compromises were found to be at 99.3% (100%) correct associations and 98.5% (97.5%) discrimination for symmetrical 5 (6) sigma match criteria using fixed relative standard deviations, which considered inter-day variations.

Prototyping of petalets for the Phase-II upgrade of the silicon strip tracking detector of the ATLAS experiment

In the high luminosity era of the Large Hadron Collider, the instantaneous luminosity is expected to reach unprecedented values, resulting in about 200 proton-proton interactions in a typical bunch crossing. To cope with the resultant increase in occupancy, bandwidth and radiation damage, the ATLAS Inner Detector will be replaced by an all-silicon system, the Inner Tracker (ITk). The ITk consists of a silicon pixel and a strip detector and exploits the concept of modularity. Prototyping and testing of various strip detector components has been carried out. This paper presents the developments and results obtained with reduced-size structures equivalent to those foreseen to be used in the forward region of the silicon strip detector. Referred to as petalets, these structures are built around a composite sandwich with embedded cooling pipes and electrical tapes for routing the signals and power. Detector modules built using electronic flex boards and silicon strip sensors are glued on both the front and back side surfaces of the carbon structure. Details are given on the assembly, testing and evaluation of several petalets. Measurement results of both mechanical and electrical quantities are shown. Moreover, an outlook is given for improved prototyping plans for large structures.

基于光学相干层析技术的电工胶带检验方法

基于光学相干层析技术的电工胶带检验方法

Acetone facilitated DNA sampling from electrical tapes improves DNA recovery and enables latent fingerprints development

Electrical tapes (ETs) are a common component of improvised explosive devices (IEDs) used by terrorists or criminal organizations and represent a valuable forensic resource for DNA and latent fingerprints recovery. However, DNA recovery rates are typically low and usually below the minimal amount required for amplification. In addition, most DNA extraction methods are destructive and do not allow further latent fingerprints development. In the present study a cell culture based touch DNA model was used to demonstrate a two-step acetone–water DNA recovery protocol from ETs. This protocol involves only the adhesive side of the ET and increases DNA recovery rates by up to 70%. In addition, we demonstrated partially successful latent fingerprints development from the non-sticky side of the ETs. Taken together, this protocol maximizes the forensic examination of ETs and is recommended for routine casework processing.

Elemental analysis and characterization of electrical tape backings by LA-ICP-MS

Adhesive tapes are commonly found as physical evidence in cases involving violent crimes and national security threats. This research evaluated the utility of Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) for the characterization of chemical signatures of electrical tapes for forensic comparison and provenance purposes. The backings of 90 black electrical tapes, previously characterized by microscopical examination, Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR) and Pyrolysis–Gas Chromatography–Mass Spectrometry (Py–GC–MS), were analyzed by LA-ICP-MS to evaluate the ability of the technique to discriminate samples originating from different sources and to associate pieces of tapes originating from the same roll. The results showed that LA-ICP-MS is a useful tool that complements current protocols for the organic and inorganic characterization and comparison of electrical tapes and results in improved discrimination and superior characterization. The developed LA-ICP-MS method alone provided 94% correct discrimination of the tapes known to originate from different rolls and 100% correct association of the tapes known to originate from the same roll. Moreover, LA-ICP-MS captured a large amount of compositional information, as the use of elemental profiles alone provide similar discrimination and classification capabilities as all the conventional methods together. The analytical sensitivity of LA-ICP-MS provides a means for the classification of tapes to support investigations as well as the potential for database searching capabilities in the future.

Forensic examination of electrical tapes using high resolution magic angle spinning 1H NMR spectroscopy

The application of high resolution magic angle spinning (HR-MAS) (1)H NMR spectroscopy is ideally suited for the differentiation of plastics. In addition to the actual material composition, the different types of polymer architectures and tacticity provide characteristic signals in the fingerprint of the (1)H NMR spectra. The method facilitates forensic comparison, as even small amounts of insoluble but swellable plastic particles are utilized. The performance of HR-MAS NMR can be verified against other methods that were recently addressed in various articles about forensic tape comparison. In this study samples of the 90 electrical tapes already referenced by the FBI laboratory were used. The discrimination power of HR-MAS is demonstrated by the fact that more tape groups can be distinguished by NMR spectroscopy than by using the combined evaluation of several commonly used analytical techniques. An additional advantage of this robust and quick method is the very simple sample preparation.

The Pabst's method: An effective and low-budget tool for the forensic comparison of opaque thermoplastics - Part 1: Additional discrimination of black electrical tapes

For many years now, Pabst's micro-press has been used in German forensic science laboratories as a valuable addition to methods of comparative analysis of plastic trace evidence. However, it is as yet hardly known in laboratories outside of Germany. The principal reproducibility is demonstrated by a homogeneity check of a raw backing material of defined origin. The illustrated results of a proficiency test emphasise the applicability of the Pabst method for forensic comparisons. The discrimination power of the Pabst method was tested by taking 90 black PVC-backings provided by the FBI Laboratory, i.e. those that could not be discriminated by standard methods. In this way further discriminations could be achieved. In the following, the Pabst method is therefore introduced as a straightforward, inexpensive and useful tool.

Elemental analysis of white electrical tapes by wavelength dispersive X-ray fluorescence spectrometry

The aim of this study was to analyze and discriminate electrical tapes using the wavelength dispersive X-ray fluorescence (XRF) spectrometry and statistical techniques. The backings of 46 white electrical tapes were analyzed. A discrimination of 90.4% was performed only by quantitative analysis of major elements (relative ratio of Cl to Ca). Ten distinct groups with a discrimination of 78.9% were yielded only by qualitative analysis of trace elements. Ninety-nine electrical tape pairs which could not be discriminated by major elements were further compared with the characteristics of trace elements. The overall discriminating power of 96.1% was obtained by the combination of quantitative and qualitative analysis. The ability of XRF technique to discriminate different electrical tapes was similar to several well-known methods combined.

Analysis and Discrimination of Electrical Tapes: Part II. Backings*,†

The backings of 90 black electrical tapes were analyzed to evaluate the chemical components of these films, the ability of individual techniques to discriminate samples, and the ability of the techniques combined to distinguish samples. The techniques utilized and their respective discrimination results were stereomicroscopy and physical measurements, to include observation of surface features of the backing, width, and thickness measurements (c. 64%); Fourier transform infrared spectroscopy (FTIR) using a microscope accessory (c. 83%); pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS; c. 81%); and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS; c. 87%). Ninety-four percent of the backings were discriminated through this combination of analytical methods. Finally, evaluating these results in conjunction with previously published data on the analysis of the adhesives from the same set of electrical tapes provided an overall discrimination of nearly 96%.

Forensic utility of carbon isotope ratio variations in PVC tape backings

Forensic interest in adhesive tapes with polyvinyl chloride (PVC) backings (electrical tape) derives from their use in a variety of illicit activities. Due to the range of physical characteristics, chemical compositions, and homogeneity within a single roll of tape, traditional microscopic and chemical analyses can offer a high degree of discrimination between tapes, permitting the assessment of potential associations between evidentiary tape samples. The carbon isotope ratios of tapes could provide additional discrimination among tape samples. To evaluate whether carbon isotope ratios may be able to increase discrimination of electrical tapes, particularly with regards to different rolls of tape of the same product, we assessed the δ(13)C values of backings from 87 rolls of PVC-based black electrical tape (~20 brands, >60 products) Prior to analysis, adhesives were removed to prevent contamination by adhering debris, and plasticizers were extracted because of concern over their potential mobility. This result is consistent with each of these tapes having approximately the same plasticizer δ(13)C value and proportion of carbon in these plasticizers. The δ(13)C values of the 87 PVC tape backings ranged between -23.5 and -41.3 (‰, V-PDB), with negligible carbon isotopic variation within single rolls of tape, yet large variations among tape brands and tape products. Within this tape population, carbon isotope ratios permitted an average exclusion power of 93.7%, using a window of +/-0.3‰; the combination of carbon isotope ratio measurement with additional chemical and physical analyses raises the discrimination power to over 98.9%, with only 41 out of a possible 3741 pairs of tape samples being indistinguishable. There was a linear relationship between the δ(13)C value of tape backings and the change in δ(13)C value with the extraction of plasticizers. Analyses of pre- and post-blast tape sample pairs show that carbon isotope signatures are within 0.3‰ of pre-blast values, indicating that carbon isotope values are largely preserved during an explosion.

Atomic force microscopic investigation of commercial pressure sensitive adhesives for forensic analysis

Pressure sensitive adhesive (PSA), such as those used in packaging and adhesive tapes, are very often encountered in forensic investigations. In criminal activities, packaging tapes may be used for sealing packets containing drugs, explosive devices, or questioned documents, while adhesive and electrical tapes are used occasionally in kidnapping cases. In this work, the potential of using atomic force microscopy (AFM) in both imaging and force mapping (FM) modes to derive additional analytical information from PSAs is demonstrated. AFM has been used to illustrate differences in the ultrastructural and nanomechanical properties of three visually distinguishable commercial PSAs to first test the feasibility of using this technique. Subsequently, AFM was used to detect nanoscopic differences between three visually indistinguishable PSAs.

Identification and Comparison of Electrical Tapes Using Instrumental and Statistical Techniques: II. Organic Composition of the Tape Backing and Adhesive*

The microtexture and elemental composition of the backing of electrical tapes have been shown to be highly discriminating. In this study, the organic composition of electrical tape was evaluated as a complementary means of distinguishing tape brands. The backing and adhesive of 72 rolls of electrical tape were analyzed via Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR FTIR) and discriminant analysis was used to classify all samples by brand. Generally, the accuracy for FTIR data (88-99%) was higher than that for elemental data (86-94%). FTIR spectra from the adhesive layer were the most discriminating. In separate studies, two fragments of blast-damaged tape were correctly assigned to their brand of origin and discriminant analysis was used to quantitatively associate or exclude tape samples from two bombing cases.

Chemical Fingerprinting of Adhesive Tapes by GCMS Detection of Petroleum Hydrocarbon Products

Pressure-sensitive adhesive tapes often represent key evidence of crimes such as assault, rape or homicide; thus, the development of analytical techniques able to contribute to a detailed characterization of these materials is of forensic importance. The gas chromatography-mass spectrometry (GCMS) analysis of the solvent extractable fractions of a suite of electrical and gaffer adhesive tapes spanning a range of colors and manufacturers identified a number of petroleum-derived hydrocarbons. Molecular and isotopic analyses of hydrocarbon constituents of complex materials have found wide analytical utility including the forensic investigation of oil spills and arson. Here, we investigate the utility of these techniques for characterizing the hydrocarbon composition of pressure-sensitive adhesive tapes for forensic correlation purposes. Subtle distinction of tape samples was evident in the GCMS distribution of several hydrocarbon groups including alkyl-naphthalenes, hopane and sterane biomarkers. Linear discriminant analysis of the abundances of these products provided high level differentiation of tape manufacturer. The distinction of different adhesive tape samples was further extended by measurement of their stable carbon isotopic values. The molecular and isotopic differences of the petroleum content of tapes are consistent with the use of different petroleum materials used in the manufacturing process and demonstrate the benefits of the combined use of complementary oil hydrocarbon characterization approaches. This study reveals the forensic potential of using established petroleum characterization methods for characterizing materials with a petroleum-derived hydrocarbon element.

Identification and Comparison of Electrical Tapes Using Instrumental and Statistical Techniques: I. Microscopic Surface Texture and Elemental Composition*

Comparisons of polyvinyl chloride electrical tape typically rely upon evaluating class characteristics such as physical dimensions, surface texture, and chemical composition. Given the various techniques that are available for this purpose, a comprehensive study has been undertaken to establish an optimal analytical scheme for electrical tape comparisons. Of equal importance is the development of a quantitative means for sample discrimination. In this study, 67 rolls of black electrical tape representing 34 different nominal brands were analyzed via scanning electron microscopy and energy dispersive spectroscopy. Differences in surface roughness, calendering marks, and filler particle size were readily apparent, including between some rolls of the same nominal brand. The relative amounts of magnesium, aluminum, silicon, sulfur, lead, chlorine, antimony, calcium, titanium, and zinc varied greatly between brands and, in some cases, could be linked to the year of manufacture. For the first time, quantitative differentiation of electrical tapes was achieved through multivariate statistical techniques, with 36 classes identified within the sample population. A single-blind study was also completed where questioned tape samples were correctly associated with known exemplars. Finally, two case studies are presented where tape recovered from an improvised explosive device is compared with tape recovered from a suspect.

High electrical performance Ag-sheathed Bi-2223 multifilamentary tapes prepared by an optimised PIT processing route

An optimised PIT processing route is introduced and discussed, using results from experiments investigating the effect of processing on microstructure, and subsequently on J/sub c/ in PIT tapes. At 77 K and self-field, the highest J/sub c/ performance of 51000A/cm/sup 2/ has been obtained for 69-filament tapes. High critical current samples with I/sub c/=108A and J/sub c/=36000A/cm/sup 2/ have been measured at 77 K and self-field for 361-filament tapes. Our results indicated that J/sub c/ is influenced by the Pb distribution of Pb-2212, phase composition for the precursor powder, the deformation reduction rate, and the core thickness. Intermediate processing (cooling, deformation and heating) between thermal-mechanical cycles and finally cooling procedures also play an important role on Bi-2223 phase purity and achievement of such high electrical performance in the tapes.