Patent Publication Number: US-2019194086-A1

Title: Methodology for developing texture in simulants

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/608,940 entitled “Methodology for Developing Texture in Simulants,” filed on Dec. 21, 2017, incorporated herein by reference in its entirety. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The present invention was made by one or more employees of the United States Department of Homeland Security in the performance of official duties, and, thus the claimed invention may be manufactured, used, licensed by or for the United States without the payment of any royalties thereon. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of simulants, and more specifically to the field of simulants to serve as surrogates to hazardous threats and explosives for training and testing. 
     BACKGROUND OF THE INVENTION 
     Simulants are needed for both training and testing explosive detection systems (EDSs) and advanced imaging technology (AIT) portals, as well as for training and testing security personnel. The simulants are used in place of live explosives in locations where live explosives cannot be used due to safety concerns. Simulants are manufactured to produce the same detector response as live threats, but as technology improves, more measurable properties may be needed for a given simulant to match a specific threat. 
     For example, simulants have been designed for X-ray imaging explosive detection system (EDS) platforms where only the explosive&#39;s X-ray properties were matched, and only the averages of those properties. However, in recent years there has been a focus on developing simulants that better match the physical morphology of the threat. Characteristics such as flexibility, compressibility, and particle size have been studied in recent years with some success. 
     SUMMARY OF THE INVENTION 
     In an example embodiment, a simulant of a textured target threat includes a background material associated with a background attenuation; and a first texture component dispersed in the background material and associated with a first component attenuation and a first component characteristic. The first component characteristic prevents the first component attenuation of the first texture component from being homogeneously dispersed throughout the background attenuation of the background material, to cause the simulant to mimic a first aspect of an X-ray signature of the textured target threat. 
     In another example embodiment, a method of producing a simulant of a textured threat compound includes formulating a background material associated with a background attenuation; formulating a first texture component associated with a first component attenuation and a first component characteristic based on mechanically separating the first texture component according to the first component characteristic; and dispersing, in the background material, the first texture component. The first component characteristic enables dispersion of the first texture component in the background material of the simulant to mimic a first aspect of an X-ray signature of the textured target threat. 
     In yet another example embodiment, a method of producing a simulant of a textured threat compound includes quantitatively characterizing a threat texture of the textured threat compound; formulating a background material associated with a background attenuation; formulating a first texture component associated with a first component attenuation and a first component characteristic; dispersing, in the background material, the first texture component; quantitatively characterizing a simulant texture of the simulant; comparing the simulant texture to the threat texture; and iteratively adjusting the first texture component to cause the simulant texture to match the threat texture. 
     Other features and aspects of the invention will become apparent from the following detailed description, which taken in conjunction with the accompanying drawings illustrate, by way of example, the features in accordance with embodiments of the invention. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to limit the scope of the invention, which is defined solely by the claims attached hereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more example embodiments of the present invention are described in detail with reference to the following drawings. These drawings are provided to facilitate understanding of the present invention and should not be read as limiting the breadth, scope, or applicability thereof. For purposes of clarity and ease of illustration, these drawings are not necessarily made to scale. 
         FIG. 1  illustrates a simulant of a textured target threat according to an example embodiment. 
         FIG. 2  illustrates a two-dimensional slice of a textured target threat material to be simulated by a simulant produced according to an example embodiment. 
         FIG. 3  illustrates a three-dimensional image of a textured target threat material to be simulated by a simulant produced according to an example embodiment. 
         FIG. 4  illustrates a textured simulant according to an example embodiment. 
         FIG. 5  illustrates a textured simulant according to another example embodiment. 
         FIG. 6  illustrates a textured simulant according to yet another example embodiment. 
         FIG. 7  illustrates a textured simulant according to yet another example embodiment. 
         FIG. 8  illustrates a method of producing a simulant of a textured threat compound according to an example embodiment. 
         FIG. 9  illustrates another method of producing a simulant of a textured threat compound according to an example embodiment. 
     
    
    
     These drawings are not intended to be exhaustive or to limit the invention to the precise form(s) disclosed. It should be understood that the present invention can be practiced with modification and alteration, and that the invention is limited only by the claims and the equivalents thereof. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Example embodiments described herein relate to developing and manufacturing explosive simulants having textured components. The simulants can be used as surrogates to explosive threats for training and testing on explosive detection systems (EDS) and advanced imaging technology (AIT) portals. Designing simulants can involve matching intrinsic properties of a threat as detected by a given technology. For X-ray EDS, these properties include mass density (ρ), effective atomic number (Z-effective), and electron density, which is highly correlated to computed tomography (CT) number. However, as EDS technology advances, higher spatial resolution images are being acquired, which provides the opportunity for performing a more rigorous characterization of the threat. The outcome of the analysis is that the texture of the threat as revealed in X-ray images can be quantitatively characterized, resulting in an additional aspect of the threat that can be incorporated into the development of a simulant. 
     With advances in EDS imaging technology, EDS are achieving the ability to distinguish and potentially detect texture within objects. For example, explosive detection systems can have varying degrees of image resolution, and as technology advances the spatial resolution of these systems is improving. Higher resolution EDS may be capable of identifying and detecting inhomogeneous texture within a given image or object. Furthermore, because some homemade explosives are known to contain significant texture that is visible to the human eye in X-ray images, simulants with such texture are needed to adequately train security personnel. 
     Some explosive threats are heterogeneous and contain texture or other identifiable components within the base material. If a given threat is known to contain texture that can be identified on an EDS or other type of scanner, then that component must be quantitatively characterized and reproduced in the simulant. Depending on the image resolution of the EDS, the acquired images may be used to identify the texture components. Positive identification of the texture in a threat may result in increased explosive detection performance, or may potentially decrease false positives. At the very least, the identification of texture within an object could initiate an alarm resolution procedure resulting in the object going through additional analysis. 
     If a threat contains identifiable texture then that characteristic should be reproduced in a simulant, otherwise the simulant doesn&#39;t accurately portray the identifiable feature set of the threat. Failure to fully represent the threat&#39;s characteristics in the simulant may result in detection failures by screeners or detection algorithms. 
     Example approaches can be used to measure, model, and reproduce the effects of a range of attenuating particles found in explosive threats that contribute to threat texture, e.g., by identifying and matching crystal or particle texture within the threat, and reproducing threat characteristics and/or textures that are spatially variant (e.g., non-homogeneously dispersed). Additionally, threat characteristics can be quantified based on average properties as measured by EDS or other type of scanner (such as a scanner to obtain micro-CT images), including average density, Z-effective, and X-ray attenuation properties. Example simulants also can be produced to match the threat morphology in terms of solid, semisolid, powder, or liquid. Thus, example approaches can characterize an explosive threat&#39;s internal identifiable texture and expanding the explosive-simulant development approach to include and match the texture components. Simulant formulations can be produced that contain attenuating particles similar to the threat, as verified using an X-ray micro-CT system. The simulant&#39;s texture component can be varied continuously such that the texture properties of the simulant spanned the range of texture properties measured from the threat material. Accordingly, a simulant developer or user can use the example approaches to combine different proportions of non-texture and texture components of the simulant to create a plurality of textures as needed to match a variety of threat(s) of interest. 
     Accordingly, the example approaches and embodiments described herein enable the development of a plurality of simulants that contain texture particles that can have a plurality of X-ray attenuation properties, using various methods described herein. The attenuation properties of the texture particles may be higher or lower than the background material, and the proportions may be varied continuously to match the texture properties of the threat. 
       FIG. 1  illustrates a simulant  100  of a textured target threat according to an example embodiment. The simulant  100  includes at least one background material  110  associated with a background attenuation  112  and morphology  114 . The simulant  100  also includes at least one texture component  120  associated with a component attenuation  122  and a component characteristic  124 . Example component characteristics  124  include particle size distribution  126 , particle shape distribution  128 , and other characteristics that, e.g., can prevent homogeneous dispersion of attenuation to mimic a textured aspect of an X-ray signature of a textured target threat. 
       FIG. 2  illustrates a two-dimensional slice of a textured target threat material  200  to be simulated by a simulant produced according to an example embodiment. The threat  200  includes a background material  210 , first texture component  220  associated with a first component attenuation, and a second texture component  230  associated with a second component attenuation. 
     Image texture can be portrayed as any feature within the image that is identifiably different from the background in the image. For example, air gaps within an object that are evident in an X-ray image is a form of texture. In addition, aggregates or crystals within a powdered material can result in image texture. Although there are many ways to calculate features derived from images that are defined as texture, the concept of texture is that there are irregularities within the sample with sufficient size and preponderance that it can be identified and used in explosive detection. Therefore, it is necessary to accurately identify and characterize texture within threat materials, and reproduce the same effect in a simulant. 
     A particular type of improvised threat was scanned for characterization, e.g., with a dual-energy microCT system (which can have much higher resolution than current and near-future EDS), providing excellent images for texture analysis. The reconstructed tomographic slices, such as the slice illustrated in  FIG. 2 , were found to contain bright pixels and objects  220 ,  230  that were distinguishable from the background material  210 . Example particles range from approximately 200 microns (0.2 millimeter) up to approximately 5 mm, and depending on the type of threat, particles can potentially exceed 1 cm or higher. 
     MicroCT texture analysis revealed that this particular threat material contained two distinct types of particles  220 ,  230 , associated with significantly different attenuation, identified by the brightness of texture in the images. These first and second texture components  220 ,  230  can be referred to as “low” and “high” attenuation texture for convenience, but the attenuation was still higher than the background  210  in the images in both cases. Low attenuation texture particles  230  were only slightly brighter than the background  210  of the material, whereas the high attenuating particles  220  were much brighter than the background  210 . Both low and high texture components  220 ,  230  are identified in  FIG. 2 . The grayscale value of each texture piece was characterized on an eight bit scale with pixel values ranging from 0 to 255, or black to white, respectively. 
       FIG. 3  illustrates a three-dimensional image of a textured target threat material  300  to be simulated by a simulant produced according to an example embodiment. The image of  FIG. 3  is representative of a stack of two-dimensional images, such as the image shown in  FIG. 2 . 
     The three-dimensional image is helpful for characterizing and/or quantifying the contrast of texture particles, as well as other component characteristics such as the size, number, shape, and distribution of component particles in the samples to be used for producing simulants. Two dimensional image slices were stacked together and reconstructed into a 3-dimensional image. Background pixels were removed from the image using thresholding (e.g., by setting the threshold to remove those pixels with a pixel value less than the lowest value of any texture component), resulting in a 3D image of the texture particles, as illustrated in  FIG. 3 . The texture was analyzed using 2D slice images (to obtain a cross-sectional size/shape/number distribution of texture particles), and the 3D image stack (to obtain texture particle distribution information for all three dimensions). The component characteristic features of interest included the average pixel contrast distribution and the particle size distribution, but also included features related to particle shape distribution and pixel contrast distribution, as well as corresponding values for such characteristics, separate from their distributions. The results of the analysis confirmed that the illustrated threat contained two distinctly different types of texture, differentiated by their average contrast. One group, referred to as low attenuating, had image grayscale values in the range of 145-165, while the second group, referred to as high attenuating, had grayscale values greater than 200. Using a set of images from twelve different specimens, it was evident that the size and shape of particles was somewhat random. While there was no particular particle shape that was preferentially evident, the particle size distribution was regarded as an important feature to adequately characterize and then match in the simulant, in addition to matching the attenuation properties of the low and high attenuation particles. 
       FIG. 4  illustrates a textured simulant  400  according to an example embodiment. More specifically, the simulant  400  includes a plurality of first texture components  420 , to provide high attenuating properties compared to the background material  410 . To develop the simulant  400  that accurately represented the threat, the base morphology, average X-ray properties, and texture of the threat  400 , had to be reproduced. First, a formulation was developed matching the morphology and X-ray properties of the threat&#39;s background  410 . Table 1 provides the X-ray signature data for the threat and the simulant background material, detected using both the micro-CT and the commercial EDS. The difference between the simulant and threat was less than 3% for all features, serving as a confirmation of the validity of the formulated background material. As shown in Table 1 below, X-ray properties are shown, as derived from an example EDS system. CTN High and CTN Low represent high and low energy CT number from the EDS, respectively. Ze and Pe represent effective atomic number and electron density, respectively, derived from the EDS data. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Grayscale 
                   
                   
                   
                 Pe 
               
               
                 Sample 
                 Morphology 
                 (micro-CT) 
                 CTN High 
                 CTN Low 
                 Ze 
                 (mol e−/cc) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Threat 
                 Powder 
                 122 
                 4152 
                 4060 
                 6.754 
                 0.207 
               
               
                 Simulant 
                 Powder 
                 119 
                 4191 
                 4140 
                 6.764 
                 0.211 
               
               
                 Background 
               
               
                 Difference 
                 — 
                 3.00 
                 39 
                 80 
                 0.010 
                 0.004 
               
               
                 % 
                 — 
                 2.52% 
                 0.93% 
                 1.93% 
                 0.15% 
                 1.90% 
               
               
                   
               
            
           
         
       
     
     Next, to create the high attenuation texture particles  420 , a wax formulation was developed, melted, and cast into a solid block. The block was then broken apart, ground down, and sieved into various sizes of particles. A sample was prepared combining the background material  410  with the high attenuation particles  420  and scanned on the microCT for analysis.  FIG. 4  illustrates this example of the resulting slice images containing high attenuating texture particles  420 . 
       FIG. 5  illustrates a textured simulant  500  according to another example embodiment. The simulant  500  represents the results of one example method, and see  FIG. 6  below, illustrating the results of another example method. To develop low attenuating texture particles  530 , two methods were explored. The first method of  FIG. 5  used a high amount of wax binder (&gt;80% by weight), mixed with a material having very low attenuation compared to the high attenuation components  420  of  FIG. 4 . The same melt-cast process, as described above and used to produce the high attenuating particles  420  in  FIG. 4 , was then applied on the low attenuation material to produce the low attenuation particle  530  in  FIG. 5 . The resulting particles  530  had an average grayscale value in the range of 180, which was too high to be used as a low attenuation particle when attempting to match this particular threat to be simulated. Furthermore, unlike that of the threat&#39;s low attenuating particles having relative and uniform particle characteristics, the simulant&#39;s low attenuating texture was irregular as illustrated in  FIG. 5 . A different approach was then used for simulating the low attenuation particles, as described below with reference to  FIG. 6 . 
       FIG. 6  illustrates a textured simulant  600  according to yet another example embodiment. An alternative method was used for creating the illustrated low attenuating texture particles  630 , which involved combining ground wax with the powdered background formulation  610  previously developed, in a 1:1 ratio by weight. The powders were then mixed together and aggregated by compression, which was achieved through vacuum suction. Once fused, the semi-solidified object was broken apart and sieved into varying mesh sizes. A sample was then prepared combining the background material  610  with these new particles and scanned on the microCT for analysis. The resulting low attenuating texture particles  630  had a grayscale in the range of 140-150, with an example slice as shown in  FIG. 6 . These results were then combined to mimic the texture of the threat as described below with reference to  FIG. 7 . 
       FIG. 7  illustrates a textured simulant  700  according to yet another example embodiment. To create the simulant  700  that contains both the high and low attenuation texture components  720 ,  730 , a formulation was developed that used the background material  710  (such as the previously-described background materials  410 ,  510 , or  610 ) mixed with a proportion of high attenuating melt cast particles  720  (such as the previously-described particles  420 ) and low attenuating vacuum-fused aggregates  730  (such as the previously-described particles  630 ). The simulant  710  was scanned on the microCT for analysis and verification.  FIG. 7  illustrates a cross-sectional slice of the combined texture simulant  700 . The amount and size of each texture type  720 ,  730  was then adjusted as needed to match the internal texture makeup of the various threat specimens, e.g., based on characterizing various above-described component characteristics and/or distributions for the threat and sample, to ensure that they match within a desirable range corresponding to being generally visually indistinguishable when viewing scanning results. Characteristics of the simulant should match the threat at the appropriate spatial resolution level, e.g., as available on a given scanning machine and available state-of-the-art for scanning machines. 
       FIG. 8  illustrates a method  800  of producing a simulant of a textured threat compound according to an example embodiment. The method starts at block  805 . In block  810 , a background material associated with a background attenuation is formulated. For example, a background formulation was developed by producing a powder matching the morphology and X-ray properties of the threat&#39;s background. 
     In block  820  a first texture component associated with a first component attenuation and a first component characteristic is formulated based on mechanically separating the first texture component according to the first component characteristic. For example, the first texture component can be melted and cast, then broken up into various particle sizes, and separated into discrete size ranges by corresponding stages of sieves of varying mesh size, then combined in various proportions to achieve a desired size distribution. Other approaches include use specific techniques (sieve mesh shapes) for achieving particle shape distributions, or alternatives for casting the component ingredient before breaking it into particles (forming the ingredient into a sheet instead of a block, to achieve flake-shaped particles). For example, mechanical compression can be used to form granular texture, or to form a solid block that is then broken up in a manner similar to that used on a wax-based melt-cast block as described above. The texture component may or may not have a binder added. Such approaches can be different than a vacuum-based compression approach, in terms of how the compression is achieved. 
     In block  830 , the first texture component is dispersed in the background material. For example, the texture component can be dispersed according to a component characteristic, to cause dispersion of the first texture component in the background material of the simulant to mimic a first aspect of an X-ray signature of the textured target threat, e.g., a variant/non-homogeneous distribution of the texture variations. 
       FIG. 9  illustrates another method  900  of producing a simulant of a textured threat compound according to an example embodiment. The method starts at block  905 . In block  910 , a threat texture of the textured threat compound is quantitatively characterized. For example, the textured threat compound can be scanned to acquire at least one threat image; the background and texture components of the image are identified; the grayscale values of the background and texture components are characterized; and component characteristic(s) of the texture components are identified. Example approaches include 1) thresholding, followed by segmentation to identify particles, and 2) gray level co-occurrence matrices. 
     In block  920 , a background material associated with a background attenuation is formulated. For example, a formulation is developed by matching a morphology property and an X-ray property of a background of the textured threat compound. 
     In block  930 , a texture component(s) associated with component attenuation(s) and component characteristic(s) is formulated. For example, a wax formulation exhibiting the component attenuation can be developed to match a high-attenuation characteristic of a textured component of the textured threat compound; the wax formulation can be melted and cast into a solid block that is then mechanically separated into particles; and the particles can be sieved according to a plurality of particle size bins spanning a range of particle sizes of the high-attenuation characteristic of the textured component of the textured threat compound. In an alternate example, an aggregate formulation exhibiting component attenuation to match a low-attenuation characteristic of a textured component of the textured threat compound is developed; the aggregate formulation is fused by compression via vacuum suction fusion to achieve a semi-solid morphology of the aggregate formulation; the solid block is mechanically separated into particles; and the particles are sieved according to a plurality of particle size bins spanning a range of particle sizes of the low-attenuation characteristic of the second textured component of the textured threat compound. 
     In block  940 , the texture component(s) is dispersed in the background material, e.g., by mixing, stirring, or otherwise mechanically combining the texture component(s) with the background material. A desired dispersion (e.g., a dispersion consistent with a target characteristic/distribution) can be accomplished by controlling an intensity and/or duration of the process of combining the ingredients. 
     In block  950 , a simulant texture of the simulant is quantitatively characterized, e.g., using scanning and analytical analysis with an image processing algorithm or tool. 
     In block  960 , the simulant texture is compared to the threat texture, e.g., by quantifying various characteristics of the simulant and threat, such as morphology, grayscale (micro-CT), CTN high, CTN low, Ze, Pe, or other characteristics that can include distributions or other characterizations of non-homogenous aspects 
     In block  970 , the texture component(s) is iteratively adjusted to cause the simulant texture to match the threat texture. For example, a relative contribution by weight of a given texture component can be adjusted to vary its overall percent by weight of the resulting simulant compared to the background material(s) or other component(s). The distribution characteristics of a given texture component can be varied, e.g., by adjusting how the component is achieved by using different approaches to breaking into pieces, or sieving, or various other adjustments to the component. Furthermore, it is possible to adjust the duration or intensity of the mixing to vary the distribution characteristics of the component in the overall mixture producing the simulant. 
     While a number of example embodiments of the present invention have been described, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of ways. The example embodiments discussed herein are merely illustrative of ways to make and use the invention and are not intended to limit the scope of the invention. Rather, as will be appreciated by one of skill in the art, the teachings and disclosures herein can be combined or rearranged with other portions of this disclosure and the knowledge of one of ordinary skill in the art. 
     Terms and phrases used in this document, unless otherwise expressly stated, should be construed as open ended as opposed to closed—e.g., the term “including” should be read as meaning “including, without limitation” or the like; the term “example” is used to provide example instances of the item in discussion, not an exhaustive or limiting list thereof; the terms “a” or should be read as meaning “at least one,” “one or more” or the like; and adjectives such as “conventional,” “traditional,” “normal,” “standard,” “known” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Furthermore, the presence of broadening words and phrases such as “one or more,” “at least,” “but not limited to,” or other similar phrases, should not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent. Any headers used are for convenience and should not be taken as limiting or restricting. Additionally, where this document refers to technologies that would be apparent or known to one of ordinary skill in the art, such technologies encompass those apparent or known to the skilled artisan now or at any time in the future.