RU2343430C2 - Explosives detection system based on spectroscopy method of multibroken total internal reflection (mbtir) within biometric identification procedure - Google Patents

Abstract

FIELD: physics, measurement.

SUBSTANCE: invention refers to measurement technology. The system consists of personal identification system representing system of biometric information comparison including optical scanner with MBTIR element mounted on its working surface, and systems of explosives (E) detecting and identification including analyser with IR source. Besides the system comprises signal processing unit and alarm indicator. MBTIR element represents parallel-sided plate with bevel side faces made of optical material with refraction index exceeding that of the material used for optical scanner prism. The plate material transmits radiation within the range corresponding to absorption spectra of identified substances, as well as radiation with which the biometric scanner operates.

EFFECT: higher reliability and downsizing of system.

3 cl, 4 dwg

Description

The invention relates to means for ensuring human security and can be used in various places of controlled access, such as transport terminals, airports, as well as in other closed guarded objects, for example, military institutions.

There are many different systems and methods for obtaining information about a person’s personality, for example photographs that are scanned at the input, biometric identification systems that compare biometric information with information stored in the system’s memory. Identification using biometric technologies is currently one of the most promising, rapidly developing areas, among which methods and tools using fingerprints occupy one of the leading places. In addition, there are also many systems and methods for detecting and identifying explosives (BB) used to restrict access in the same situations and at the same facilities as biometric access control systems.

One of the pressing problems that have received widespread in recent years throughout the world is the fight against terrorism using explosives. Conventional methods for detecting explosives require either exposure to ionizing radiation, which is unsafe for human health, or air sampling or flushing the sample from the surface, that is, additional operator work and time required to prepare the sample for research.

Currently, work is underway on the development and implementation of biometric certification. At airports, in banks, at the border, etc. widely used methods of biometric identification of the person, based on the analysis of the structure of papillary lines of fingers by scanning and comparing human fingerprints with the database. In this regard, it is very promising to include in the biometric identification procedure an analysis of the surface of the skin, for example, fingerprints, for the presence of traces of explosives. This is due to the fact that with the fingerprint control method, fingerprints are analyzed, which are parts of the human body, most likely as a carrier of residual quantities of substances with which he dealt the day before. It should also be noted that most explosives are poorly soluble in water and have strong adhesive properties, so the likelihood of retaining trace amounts of explosives in the skin folds for a long time after contact and even after washing hands is high. Thus, the study of the spectrum of the surface of the skin can provide information on the contact of a person with explosives.

There are many methods for detecting and identifying explosives and modern devices that implement them, among which are spectroscopic methods for detecting explosives. In this case, both non-optical methods are used, such as gas chromatography, ion mobility spectrometry and mass spectrometry, and optical. When implementing non-optical methods, an air sample is taken by a hand-held remote sampler, its concentration and analysis are carried out in the device chamber.

From the point of view of manufacturing commercial detectors of vapor and explosive particles, the first two directions have advanced most successfully. Due to the high sensitivity, selectivity and speed recently, for monitoring the micro-concentrations of impurities of organic and inorganic substances in gases and, in particular, in atmospheric air, devices based on the method of detection by ion mobility are increasingly used.

An example is the ion mobility spectrometer known from the patent literature (see RF patent No. 2216817, IPC 7 H01J 49/40, G01N 27/62, op. 2003.11.20). The invention relates to the field of gas analysis and can be used to determine the trace amounts of various substances in gases or used in gas chromatography as a sensitive detector. The known ion mobility spectrometer consists of an ionization chamber and a drift chamber. The ionization chamber made of a dielectric has an opening for introducing the analyte mixed with the carrier gas into the ionization region, an opening for discharging drift gas and a mixture of the analyte with the carrier gas. In addition, in the chamber there is a pushing electrode, which is a plate of nickel or stainless steel, and a disk, on the surface of which a radioactive preparation is applied. The disk has an opening in which a mesh shutter is fixed. The drift chamber is made of dielectric and has a hole for introducing drift gas. An aperture grid and an ion collector are placed in the drift chamber. A uniform electric field in the drift region is created by guard rings, which are insulated from each other by dielectric bushings.

The advantages of the known spectrometer include high resolution and high sensitivity of the device, due to the geometric arrangement of the elements in the ionization chamber (ejection electrode, grid gate and disk with a radioactive preparation).

However, a disadvantage of the known device is the low selectivity of detection. The device is often not able to distinguish explosives from their counterparts, and also detects only a limited part of the types of explosives. In addition, this device cannot be used to detect and identify explosives contained in fingerprints.

Optical methods are distinguished by distance and automation, and therefore have two fundamental advantages: invisibility to a terrorist and the absence of a manual sampling phase.

Optical methods for detecting explosives can be divided into the following main groups:

- absorption spectroscopy;

- Raman spectroscopy.

However, due to the technical complexity and high cost of these methods, only some of them were able to be brought to commercial implementation. For example, multipass absorption spectroscopy for the detection of explosives was proposed in the work (see MWTodd, RAProvencal, TGOwano, BAPaldus, A. Kachanov, VIVodopyanov, M.Hunter, S. Coy, JISteinfeld, and JTArnold “The use of a medium infrared Cavity Ringdown Spectroscopy using a widely tunable optical parametric oscillator to detect trace amounts of explosives”, Applied Physics B75, 367, 2002).

A detector for detecting explosives is known from the patent literature (see RF patent No. 2188825, IPC 7 G01N 33/22, G01N 25/54, G01N 21/65, op. 2000.05.10). The invention relates to devices for detecting explosive material in a sample. The essence of the invention lies in the fact that the presence of a plastic explosive substance Semtex in a sample, such as a fingerprint on an object, is detected using Raman spectroscopy. The active chemical ingredients of Semtex have stable Raman peaks at 885 and 874 cm ^-1, respectively. With this in mind, these peaks can be detected by the Raman spectroscopic system using a filter having a narrow transmission width centered at 880 cm ^-1 and transmitting light to the detector in a narrow band that overlaps 874 and 885 cm ^-1 . Such a filter is used in the Raman system used to scan aircraft boarding passes, or in the Raman microscope, which reproduces the image of fingerprints. A device for detecting explosive material in a sample comprises a light source for illuminating the sample in order to cause Raman scattered light, and a detector for detecting Raman scattered light received from the sample. A narrow-band filter, the middle of the passband of which is tuned to a value of about 880 cm ^-1 , is placed between the sample and the detector. The optical scheme contains a diffraction grating and a charge-coupled device and allows detecting the most commonly used explosives in a relatively short period of time and in the presence of contaminants in the sample.

A significant disadvantage of the known technical solution is the ability of the device to work only with samples that are secondary carriers of traces, which reduces the amount of analyte. Moreover, the device is designed to operate only in conditions where there is qualified personnel who collects samples with prints (tickets, documents). Very cumbersome and complex is also the optical design of the device, equipped with a laser light source, as well as a large number of mirrors, dichroic filters and lens systems.

In the patent literature (see US patent No. 6420708, IPC 7 G01N 21/27, G01N 21/35, op. 16.07.2002) describes a device for spectrum analysis by the method of repeatedly impaired total internal reflection (MNIPO). The known device includes an extended light source, a device for decomposing light into a spectrum, a sample stand, which is a crystal of total internal reflection, and a line of photosensitive elements for detecting the spectrum and creating an output data array in the form of a dependence of intensity on wavelength. The sample stand is located between the light source and the device for the decomposition of light into the spectrum. Light propagates along the sample stand from the source to the spectral arrangement. The crystal of the stand has two surfaces, on one of which a sample of the material subjected to INLT analysis is placed, and two faces, beveled at an angle to the above surfaces. Infrared radiation from the above light source may be continuous, electronically modulated or modulated by a mechanical modulator. In the described device there is no need to use focusing optics, its optical system is simple and compact, which is an undoubted advantage of the device. However, a significant drawback of the known technical solution is the lack of responsiveness due to the large time spent on preparing the sample for research. For spectral analysis of samples of material, for example, fingerprints taken at the crime scene, they must be delivered to a special laboratory and installed on a stand from the above MNPVO crystal.

There are scientific works, for example, A. Grant, TJ Wilkinson, D.R. Holman, M.C. Martin, “Identification of trace substances by analysis of latent fingerprints using infrared microspectroscopy”, Appl. Spectrosc. 59: 1182-7, 2005. In this work, the method of MNVPO is used to identify substances contained in fingerprints found at the crime scene. The fingerprint is taken from the place of detection and sent to the laboratory, where it is pressed to the element MNPVO and get the spectrum.

Also known is a personal identification and security system (see US patent No. 6914668, IPC 7 G01J 3/30, op. 2004.11.18), which is in its technical essence closest to the claimed invention. This technical solution is selected as a prototype. The known system includes a personal identification system and a detection and identification system for controlled (explosive) substances. The indicated systems used: a document reader to read information from a document and a spectroscopic analyzer to analyze the aforementioned document in order to determine the presence or absence of controlled (explosive) substances on it. The system also includes a system that processes signals from a personal identification system and a detection and identification system for controlled (explosive) substances, and an alarm indicator that generates an alarm signal from at least one of the above signals.

The personal identification system may be a system for comparing biometric information. In accordance with one embodiment of the invention, a transparent base is mounted on the surface of the biometric image reader on which a part of the body, such as a palm, is placed. Preferably, the transparent base is made of a material that does not create a second harmonic of Raman (Raman) scattering and luminescence at the parameters determined for the identification of the controlled substances. Even more preferably, the transparent base is coated with a thin layer of material that creates a surface-enhanced Raman spectrum (SERS), for example silver, gold or rough-surface copper. With such a surface, molecules of controlled substances can give SERS, which increases the visibility of the Raman spectrum by 10 or more times.

The above spectroscopic analyzer for analyzing the aforementioned document in order to determine the presence or absence of explosives on it may be a spectroscopic analyzer using a laser as a radiation source.

A feature of the identity and safety identification system is that the identity verification system and the explosive detection and identification system carry out identity identification and the detection and identification of explosives at the same time. This is an undoubted advantage of the known system, distinguishing it from the analogues described above.

Another important feature of the well-known personal identification and security system is that the person whose identity is verified by the personal identification system does not realize that the system can detect and identify explosives. This fact is also an important advantage of the system selected as a prototype, in comparison with the analogues described above.

However, despite these advantages, the described system has drawbacks due to the high cost of the technical means necessary for its implementation. As mentioned above, in a spectroscopic analyzer that determines the presence or absence of explosives on a document, a laser is used as a light source, as well as scanning elements, such as mirrors rotated by motors. This complicates and increases the cost of the system design, makes it less reliable, and also increases its size.

The task of the invention is to increase reliability, simplify the design and reduce the size of the system while maintaining the reliability of the results, as well as reducing material costs for its manufacture.

To solve the tasks, a system is proposed for detecting explosives in fingerprints by the method of spectroscopy of repeatedly impaired total internal reflection (INLM) in the process of biometric identification, which, like the system closest to it, chosen as a prototype, consists of a personal identification system, which is a system for comparing biometric information, including a biometric scanner with a transparent base mounted on its working surface, and detection systems Bani and identification of explosives, comprising a spectroscopic analyzer with an emission source. The system for detecting explosives in fingerprints also includes a device for processing signals from an identification system and a system for detecting and identifying explosives, and an alarm indicator that generates an alarm signal from at least one of the aforementioned signals.

A feature of the present invention, which distinguishes it from the well-known system adopted as a prototype, is that an optical biometric scanner is used in the personality identification system, moreover, the transparent base mounted on its working surface is made in the form of an INME element. The INMIS element is a plane-parallel plate with beveled side faces: inlet and outlet, made of optical material having a refractive index greater than that of the material from which the prism of the optical scanner is made. The plate material transmits radiation in the range corresponding to the absorption spectra of the identified substances, as well as the radiation on which the biometric scanner operates. The radiation source is configured to be installed in front of the input beveled side face of the MNVO element, while it emits radiation in the range corresponding to the absorption spectra of the identified substances. The spectroscopic analyzer of the system for detecting explosives in fingerprints by the MNPVO spectroscopy method can be made in the form of a diffraction polychromator with a multi-channel infrared receiver, or in the form of a tunable opto-acoustic filter with a single-channel infrared receiver.

The main tasks set during the creation of the invention are:

- increased reliability;

- simplification of the design;

- reducing the size of the system;

- maintaining the reliability of the results;

- reduction of material costs for the manufacture of the system.

The implementation of these tasks was made possible thanks to the following.

The basis of the inventive system for detecting explosives in fingerprints is the phenomenon of impaired total internal reflection (ATR). This phenomenon is associated with the propagation of light into a second medium adjacent to the boundary at which internal reflection occurs in the first, optically denser medium. Internal reflection is called full (AA) if the entire luminous flux is reflected from the border without loss. Total internal reflection is impaired if the reflected flux is smaller than the incident one, either due to absorption or due to the propagation of part of the flux into the second medium. The ATR element is a transparent optical part, with the help of which the conditions are created for obtaining the ATR spectra of materials at a single reflection. The method of obtaining the optical spectrum of a sample in contact with an optically denser medium is based on measuring the light reflected by the surface and returned back to a denser medium. The obtained spectra are characteristic for this sample. To enhance the intensity of the spectrum, elements with a large number of reflections from the boundary — elements of repeatedly disturbed total internal reflection (INRM) —are used.

The principle of the MNE method is shown schematically in FIG. The most widely used MNE method is in the infrared.

The claimed invention proposes to use an optical biometric scanner in a personality identification system, and the transparent base mounted on its working surface is made in the form of an INME element, which is a plane-parallel plate with beveled side faces (see figure 1). Other important components of the system are the radiation source and spectroscopic analyzer, which allows to obtain the spectrum of radiation passing through the element MNIPO (see figure 2). In the interaction of radiation propagating inside the MNEO element with an object adjacent to the surface, for example, a terrorist’s finger with traces of explosives, spectra are recorded that allow the substance to be identified according to its molecular composition. Each elementary group of the molecule has a spectrum of natural vibrations that interact with electromagnetic radiation through dipole absorption. As a result, absorption bands are formed in the radiation of a broadband source of electromagnetic radiation, creating a “signature” unique to each molecule. EXPLOSIVES are relatively simple organic compounds with characteristic elemental groups, such as a nitro group, a benzene ring, unsaturated bonds, etc. In addition, as mentioned above, the likelihood of traces of explosives remaining on the fingers of a person who has been involved in the manufacture or packaging of explosives is very high strength of high adhesion and poor solubility in water.

The time of recording the optical spectrum by the method of MNPVO spectroscopy does not exceed 1 s, and the spectrum itself is a unique numerical information for each sample, reliably processed by software. Thus, the use of the MNVO method allows solving the problem of speed, reliability of identification and automation of explosive detection.

Another significant feature that distinguishes the invention from the closest analogue is the presence in the system of a radiation source installed in front of the input face of the element MNVO. In the inventive system, there is no need for a laser source, due to which it was possible to significantly simplify the design of the system, and therefore, increase its reliability, reduce overall dimensions, and reduce material costs.

The MNE method is very promising because it has great potential for optimization due to changes in the material, size and geometry of the MNE element, as well as the variety of sources and receivers of optical radiation. The number of penetrations of radiation into the sample is governed by the thickness of the INME element and the angle of reflection of the scanning radiation. The penetration depth of the radiation depends on the angle of reflection, on the material of the element MNPVO and the state of its surface. By increasing the number of reflections and increasing the sensitivity of the radiation receiver, it is possible to increase the sensitivity of the method to small amounts of the analyte. These capabilities are implemented in the presented specific example of the optical design of the inventive system for detecting explosives in fingerprints (see figure 3).

The essential features related to the geometry of the element of the MNIPO, as well as the requirements for the material from which it is made, provide the creation of optimal conditions for the effective implementation of the MNIPO method in the system design proposed by the authors.

The signs set forth in paragraphs 2 and 3 of the formula relate to the various possibilities of implementing a spectroscopic analyzer, which is part of the system for detecting explosives in fingerprints using the MNVPO spectroscopy.

Thus, the combination of the above features allows us to solve the tasks.

The invention is illustrated by drawings.

Figure 1 shows a schematic diagram of the method MNVO, laid the basis of the claimed invention;

figure 2 presents a block diagram proposed as one of the specific embodiments of the inventive system;

figure 3 presents one of specific examples of the optical design of the inventive detection system of explosives in fingerprints (main view);

figure 4 shows the spectra of tetranitropentaerythritol (TENA), a clean finger and traces of TENA of different intensities.

The system for detecting explosives in fingerprints by the MNIPO spectroscopy installed, for example, at the airport in the area for checking baggage or personal belongings of passengers, consists of an identity system 1 and an explosive detection and identification system 2 (see FIG. 2). System 1 is a system for comparing biometric information and contains an optical biometric scanner 3, on the working surface of which an element MNIPO is fixed (see figure 3). As a biometric scanner 3 can be used, for example, one of the variants of a device for recording a fingerprint patented by the applicant (see RF patent for utility model No. 46914, IPC 7 A61B 5/053, A61B 5/117, publ. 10.08.2005 ) The system 2 for detecting and identifying an explosive consists of an infrared radiation source 5, an MNE element 4, a spectroscopic analyzer 6 (see FIG. 2), made in the form of a polychromator with a multi-channel uncooled infrared receiver 7 (see FIG. 3). The BB detection system also includes a device 8 for processing signals from the personality identification system 1 and the BB detection and identification system 2, as well as an alarm indicator 9 that generates an alarm based on signals from the signal processing device 8. The signal processing device 8, which is, for example, a personal computer, contains a database of 10 fingerprints and spectra of explosives, as well as software 11 for identifying and detecting explosives.

Below is considered in more detail the design of one of the specific examples of the optical design of the inventive detection system of explosives in fingerprints by the method of spectroscopy MNPVO (see figure 3).

The main element of the optical scheme of the claimed system is element 4 single-pass MNIPO, made in the form of a plane-parallel plate with beveled side faces: input "A" and output "B". In the context of the element 4 MNPVO is a regular trapezoid with angles at the base equal to 45 °. Such angles provide the most complete filling of the element with radiation. The upper and lower faces of the element 4 MNPVO, as well as the side beveled edges “A” and “B” are polished according to the optical class. Element 4 is made of an optical material with a refractive index greater than that of the material from which the prism 12 of the optical fingerprint scanner 3 is made (see FIG. 3). This is necessary for full internal reflection on the lower edge of the element 4 MNIPO. The element MNIPO installed on the working surface of the prism 12 and secured with glue, the spectrum of which does not contain strong absorption lines in the infrared region (for example, IR-1M). This is necessary so that the spectrum of glue formed as a result of the INLO on the lower face of the INLO element 4 does not obscure the spectrum of the substance analyzed on the upper face. In front of the input face “A” of the element 4 MNPVO installed source 5 of infrared radiation. Source 5 of IR radiation is a heated body with a pulsed nature of radiation, for example, an infrared radiation source manufactured by Patinor Coatings Limited, Moscow.

The radiation from the source 5 enters the input face “A”, propagates in element 4 of the MNEPA by multiple internal reflections from the upper and lower faces, and exits through the output face “B”. The astigmatic beam formed at the exit is converted by the lens 13 into a collimated beam and is directed to a plane diffraction grating 14. The diffraction grating 14 reflects radiation of different wavelengths at different angles, that is, decomposes it into a spectrum. The radiation reflected from the diffraction grating 14 is incident on the lens 15, which constructs an infrared image in the plane of the infrared receiver 7. Moreover, as a result of the fact that the focal points for different wavelengths are arranged sequentially in space, with the multichannel infrared detector 7 extended, each part of it receives radiation of the same wavelength.

As the receiver 7 of infrared radiation can be used a line of pyroelectric elements sensitive to radiation in the range of 7-11 microns, for example Microray64, a Swiss company IRmicrosystems with a window that blocks radiation with wavelengths less than 6.5 microns. The parameters of the lens 15 are designed so that the distance between the focal regions for radiation with wavelengths of 7 and 11 μm is equal to the length of the multi-channel infrared receiver 7. As a result, an energy spectrum of the required spectral range is formed at the infrared radiation receiver 7. The IR receiver 7 and the IR source 5 are controlled from a single pulse generator (not shown). To increase the efficiency, it is desirable to select a phase shift so that the infrared radiation receiver 7 is turned on with a slight delay, which compensates for the heating time of the infrared radiation source 5.

The system operates as follows.

The analyzed finger is pressed to the working face of the element 4 MNPVO. In the places of contact of the protrusions on the skin of the finger with the working face of the element 4 MNIPO there is a violation of the total internal reflection, therefore, the intensity of the light reflected in these places is significantly lower than with full reflection. The biometric information scanner 3 reads the image of papillary lines, which is supplied to the signal processing device 8, is converted by mathematical processing into the biometric information necessary for identifying a person, and is compared with fingerprints available in the database 10.

At the same time, dips corresponding to the absorption lines of substances contained on the surface of the finger appear in the emission spectrum from the source 5 of IR radiation propagating along the MNEHI element 4 to the output face “B” and detected by the IR radiation receiver 7. The signal from the receiver 7 of infrared radiation enters the device 8 signal processing, in which it is processed for the presence of absorption lines located at frequencies corresponding to the explosive. If there are several lines of a given substance in the spectrum, their relative intensities should be compared. Different substances can be assigned a different degree of reliability of detection. Depending on the result of the comparison and the degree of reliability of the detection of a substance, a conclusion about the level of anxiety may be formed. At any level of anxiety, the program gives a negative conclusion about the passage of control, however, verification actions can be differentiated according to the level of anxiety.

As an illustration, Fig. 4 shows the spectra of a heating element, a clean finger, a finger with small traces of a heating element and a finger washed with water after contact with a heating element. The spectra were calculated as the ratio of the intensity of the radiation transmitted through the MNE element 4 to the intensity of the radiation entering it through face “A” (in Fig. 4, it corresponds to a transmission level of 100% for all wavelengths).

The spectra were obtained from fingers in contact with the surface of the working face of the element 4 MNPVO for 2 seconds. From figure 4 it is seen that the absorption lines of the heating element fall on the area of the smooth behavior of the spectrum of a clean finger and therefore are clearly distinguished. The degree of reliability of TEN detection for a case called a “finger with small traces” is significantly higher than for a case of a finger washed after a TEN. In the first case, 5 TENA absorption lines can be distinguished, and in the second, only two of the strongest. Nevertheless, two lines in the spectrum of the washed finger are enough for software 11 to conclude that there is an explosive and generate a positive signal for alarm indicator 9. The minimum detectable mass for a heating element in this case is estimated to be ≈ 2 μg.

Thus, the present invention, which is based on the method of spectroscopy MNPVO, compared with the prototype can significantly increase reliability, simplify the design, reduce the size of the system and reduce material costs while maintaining high reliability of the results of detection of explosives in fingerprints.

Claims (3)

1. The system for the detection of explosives by the method of spectroscopy of multiple impaired total internal reflection (INLM) in the process of biometric identification, consisting of a personality identification system, which is a system for comparing biometric information, including a biometric scanner with a transparent base mounted on its working surface, a detection and identification system explosives containing a spectroscopic analyzer with a radiation source, signal processing devices, coming from the personal identification system and the detection and identification system of explosives, an alarm indicator generating an alarm signal from at least one of the above signals, characterized in that an optical biometric scanner is used in the identification system, with a transparent base mounted on its working surface, made in the form of an element MNPVO, which is a plane-parallel plate with beveled side faces, the input and output, made of optical material having a refractive index greater than that of the material from which the prism of the optical scanner is made, and transmitting radiation in the range corresponding to the absorption spectra of identifiable substances, and radiation on which the biometric scanner operates, while the radiation source is configured to be installed in front of the input beveled lateral face of the element MNPVO and emits radiation in the range corresponding to the absorption spectra of identified substances. 2. The system according to claim 1, characterized in that the spectroscopic analyzer is made in the form of a diffraction polychromator with a multi-channel infrared receiver. 3. The system according to claim 1, characterized in that the spectroscopic analyzer is made in the form of a tunable optoacoustic filter with a single-channel infrared radiation receiver.

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