RU2301432C2 - Mode of detection of objects concealed under cloth - Google Patents

Abstract

FIELD: the invention refers to systems of ensuring safety using electromagnetic radiation for sounding of the investigated space particularly to systems of remote detection of objects concealed under cloth of the people passing inspection.

SUBSTANCE: it is necessary to choose a working spectral diapason of sounding electromagnetic radiation depending on character thinness and dielectric penetrability of the sought object. The part of the surface of the body is scanned with electromagnetic radiation of the working diapason. A reflected signal is received and a phase and/or amplitude of the received signal measured. According to the results of comparison of data received from different parts of the scanned surface between themselves or availability or absence of a strange object on the body of the man is defined according to the result of comparison of received data with the standard.

EFFECT: increases reliability of detection.

6 dwg

Description

The invention relates to safety systems using electromagnetic radiation, and in particular to methods for remotely detecting objects hidden under the clothes of people undergoing screening.

Known systems of similar purpose, currently used in airports, guarded facilities, etc. The action of such systems is based on the perception and registration of an alternating electromagnetic field arising in the sensitive element of the system due to the presence of a metal object in the volume under investigation.

The mentioned devices have a significant limitation: they only respond to the presence of metal objects (see, for example, a device called Metor manufactured by the Finnish company Metorex).

Known technical solutions aimed at solving a similar problem, which use electromagnetic radiation of the microwave range as a means to obtain the necessary information, can be divided into two groups. One group combines US patents (No. 5073782 from 12.19.88, IPC G01S 13/18, No. 5760397 from 05.22.96, IPC G01S 13/89, No. 6777684 from 08.23.2000, IPC G01N 21/01), the authors of which are trying to use millimeter and submillimeter waves to obtain an image of a hidden object. In other words, they are trying to create an optical system similar to an optical system in the infrared range. Another group (US patent No. 4975968 from 10.27.89, IPC G06K 09/00 and No. 6057761 from 01/21/98, IPC G08B 021/00) combines inventions that essentially offer different variants of the tomographic system. The authors of these inventions offer methods and devices for obtaining the spatial distribution of dielectric constant near the surface of the human body.

All these inventions actually solve other, broader, but at the same time more complex tasks. For them, the discovery of objects hidden under clothing is just one of the possible uses. Because of this, from the standpoint of application for the detection of objects hidden under clothing, the considered solutions are unjustifiably technically complicated, expensive and require qualified personnel to service the proposed devices.

In the scientific justification of the proposed solutions in these patents, it is tacitly assumed that all the media through which electromagnetic radiation passes, except for the human body, do not have absorption. Indeed, the desired objects almost do not absorb electromagnetic radiation in the considered wavelength range. But the aforementioned statement, strictly speaking, does not apply to clothing. It’s enough to wet your clothes to get a strong absorption of microwave radiation. In this case, both the optical and tomographic approaches will be ineffective.

Therefore, when using the proposals discussed, there will always be a risk of not detecting the hidden movement of dangerous objects. At the same time, when searching for hidden objects such as explosives, I would like to have a method that provides the highest probability of detection.

The only way to provide a simple and reliable solution to the problem of detecting hidden objects is through personal searches of people. However, it takes too much time. The total time required for a personal search of a certain group of people could be reduced to an acceptable level if the personnel conducting the search had a simple and effective device that reliably records the presence of a foreign object under the clothing that is neither clothing nor a body. It was this isolated small group of people that would be subjected to personal search.

As a prototype of the invention, a method for remote detection of objects hidden under clothing of people is described, described in the patent of the Russian Federation No. 2133971, IPC G01V 03/11, G08B 13/18 from 07.27.99. This method allows you to detect both metallic and non-metallic objects and includes the following operations: exposure to an area of the human body by an electromagnetic field, scanning with an electromagnetic beam over a selected area, receiving electromagnetic radiation reflected from a surface area and recording its characteristics. The registration of characteristics in the known method consists in measuring the intensity of the received signal, displaying the intensity in the form of a glow of the display screen and analyzing the distribution of the glow intensity of the received image, which determines the presence or absence of an object hidden under clothing. This method has been tested in the millimeter wavelength range and is based on the analysis of the thermal radiation emitted by the surface of the human body and the temperature contrast between the object and the human body.

However, this method, like the previous ones, does not have a reliable guarantee of detecting a hidden object, because when applying this method indoors, the temperature contrast between the body and the environment is so small that the metal, plastic, human body become indistinguishable.

The objective of the present invention is to create a method that is devoid of this drawback and allows you to identify useful information, regardless of the influence of factors that reduce temperature contrast, and, thereby, leading to errors in the detection of hidden objects.

The problem is solved in that in the method for detecting objects hidden under clothing of people, which consists in exposure to an investigated field of a human body by scanning it, in receiving the reflected electromagnetic radiation and recording its characteristics, the wavelength of the used electromagnetic radiation is selected based on the condition

where ε _n is the dielectric constant of the desired sample;

- безразмерные координаты искомого образца, в направлении, перпендикулярном к поверхности тела человека, λ - длина волны, Z_n, Z_n-1 - размерные координаты образца, регистрируют фазу и/или амплитуду отраженного излучения в каждой из контролируемых точек исследуемого участка поверхности тела, о наличии постороннего предмета на теле человека судят по различиям полученных в разных точках данных или по результатам сравнения зарегистрированных фазы и/или амплитуды отраженного излучения с эталонными значениями, представляющими собой значения фазы и/или амплитуды отраженного излучения той же частоты, полученными при усреднении результатов измерения указанных характеристик отраженного человеческим телом излучения при отсутствии посторонних предметов.

- the dimensionless coordinates of the desired sample, in the direction perpendicular to the surface of the human body, λ is the wavelength, Z _n , Z _n-1 is the dimensional coordinates of the sample, record the phase and / or amplitude of the reflected radiation in each of the controlled points of the investigated section of the body surface, the presence of a foreign object on the human body is judged by the differences obtained at different points of the data or by comparing the recorded phase and / or amplitude of the reflected radiation with the reference values representing the values of zy and / or amplitudes of reflected radiation of the same frequency, obtained by averaging the results of measurements of the indicated characteristics of the radiation reflected by the human body in the absence of foreign objects.

The technical result of the proposed method is ensured by the fact that when electromagnetic radiation with an appropriate wavelength is selected on a layered medium, which, in essence, is clothing, skin and the fat layer of the human body and, possibly, a hidden object, the amplitude and phase of the reflected signal depend from the optical path traveled and the relationship between the permittivity at the boundaries between the layers. Therefore, the recorded values of the amplitude and phase will differ significantly in the case of the presence and absence of a foreign object under the clothing of a person. The wavelengths used to implement the method in this case lie in the centimeter range, i.e. correspond to the thicknesses of layers of different dielectric permittivity through which electromagnetic waves pass (frequency range 1-20 GHz).

The present invention is illustrated by specific examples, which, however, are not the only possible, but clearly demonstrate the ability to achieve the given set of essential features of the desired result.

Figure 1 shows a model of a plane-layered medium, illustrating the controlled area of the human body and used for calculations confirming the efficiency of the method. The example shows six layers: air, fabric, air, polyethylene, leather, and fat. The arrows indicate the incident electromagnetic wave and the reflected electromagnetic wave.

Figure 2 shows a block diagram of a device that implements the method. The device comprises a high-frequency generator 1, an OTDR 2, an antenna 3, a measuring unit 4, and a signal processing unit 5.

Figures 3a and 3b show the dependences of the reflection coefficient and phase of the reflected signal on the frequency of the emitter with a clothing thickness of 0.1 cm; on figa and 4b shows the same dependencies with a clothing thickness of 1 cm

On figa and 5b are photographs of oscillograms showing the phase value of the reflected electromagnetic wave in the frequency range 2.7-3 GHz for a person with a hidden object and without it.

On figa and 6b are photographs of oscillograms showing the value of the reflection coefficient of the electromagnetic wave for the same conditions.

The physical basis of the proposed invention is explained below.

When an electromagnetic wave is incident on a layered medium, the amplitude and phase of the reflected signal depend on the distance traveled and the relationship between the permittivities at the boundaries between the layers.

If the radii of curvature of the interregional boundaries are comparable or less than the wavelength of the incident radiation, then the layered medium can be approximately locally considered as flat-layered. For a plane-layered medium consisting of N + 1 layers, for the reflection coefficient R _n from the boundary between the layers n, n + 1, the following relation is valid (the case of normal incidence of an electromagnetic wave is considered):

- безразмерная координата границы между слоями n и n+1, ε_n - диэлектрическая проницаемость слоя с номером n; Z_n - размерная координата, отсчитываемая от верхнего слоя, λ=cν/2π - длина волны, с - скорость света в вакууме, ν - частота излучения.

is the dimensionless coordinate of the boundary between the layers n and n + 1, ε _n is the dielectric constant of the layer with number n; Z _n is the dimensional coordinate measured from the upper layer, λ = cν / 2π is the wavelength, s is the speed of light in vacuum, ν is the radiation frequency.

Expression (1) is a consequence of the boundary conditions — equality on the boundary surface of the tangential components of the electric and magnetic fields recorded for the boundary between the layers n and n + 1 [L.D. Landau, E.M. Livshits. Electrodynamics of continuous media. M .: Nauka, 1982. - 620 p.].

Obviously, the presence or absence of a layer with the number n will most clearly manifest itself when the relation

Since the range of possible values of the dielectric constant and the characteristic dimensions of an object in a direction perpendicular to the surface of the human body is known, it is always possible to choose a radiation wavelength that satisfies condition (2) and, therefore, provide the most optimal conditions for detecting an object.

In order to have an idea of the behavior of the quantities describing the scattered radiation, to evaluate the possible range of their variation, to select the wavelength interval where the expected effect will be the greatest, calculations were performed in which the human body (with and without an object) was modeled by a plane-layered medium and the case was considered normal incidence of electromagnetic waves.

In the calculation, six layers were used: air, fabric, air, polyethylene, leather, fat (Fig. 1).

To prove the operability of the proposal under consideration, it is enough to show that the recorded signal in the case of the presence of an object on the human body is noticeably different from the signal when there is no object.

The calculation results are presented in figure 2 a, b and 3 a, b. The gaps in the phase graphs are due to the fact that, by definition, the phase values must belong to the interval [-π, π].

From the results presented in the figures, it follows that in the frequency range from about 1.5 to 3.5 GHz, the reflected signal in the case when an object is on the body is significantly different from the signal without an object. It was in this frequency range that experimental studies were conducted that confirmed the theoretical results.

In an experiment simulating a hidden carry on a plastic explosive body, a rectangular block of polyethylene (ε = 2.3) with a thickness of 2.3 centimeters with a characteristic transverse size of about 10 centimeters was used.

A series of experiments was carried out with a half-open cavity when registering the reflection coefficient and phase in the frequency region of about 3 GHz. Significant qualitative and quantitative differences of the reflected signals were observed in the case of the presence and absence of a sample simulating plastic explosives. Figure 5a shows the measurement data of the phase of the reflected signal from a person under whose clothes there is a sample simulating plastic explosives, and figure 5b without a sample. The results of measuring the reflection coefficient of an electromagnetic wave from a person with a sample are presented in Fig.6a and without it in Fig.6b. The change in the phase of the reflected signal is almost π radians, and the modulus of the reflection coefficient is tens of percent.

амплитуды - более чем на 10%).Similar experiments were carried out for a microstrip antenna in the range from 2 to 2.2 GHz. As in the previous case, a significant change in the amplitude and phase of the reflected signal was observed (phase change by more than

amplitudes - more than 10%).

Thus, the possibility of detecting objects hidden under clothing by registering the phase and amplitude of reflected microwave radiation has been proved theoretically and experimentally. The operating frequency range is determined by expression (2) and extends from 1 GHz to about 10-20 GHz. The extension of the frequency range towards higher values is due to the fact that the thickness of the transferred objects can be significantly less than those used in the experiment.

The implementation of the method is as follows.

Testing using an antenna 3, made, for example, in the form of a half-open resonator, examines a portion of the human body in direct contact with his outer clothing. In this case, the electromagnetic radiation of the generator 1 in the selected frequency range irradiates all layers, up to the fat layer. The reflected radiation is received by the same antenna 3 and enters the OTDR 2 and from it to the measurement unit 4, which determines the amplitudes and phases of the incident and reflected electromagnetic fields and supplies the measurement results to the analog and / or digital signal processing unit 5 to extract the necessary information from it .

The recorded phases and amplitudes of the reflected radiation are compared:

1) with phase and amplitude values obtained in the process of scanning the human body at previous points in time;

2) with reference values representing the phase and amplitude values of the reflected radiation of the same frequency obtained experimentally after averaging the measurement results of the indicated characteristics of the radiation reflected by the human body in the absence of foreign objects.

If during the scanning process there are significant changes in the amplitude (by tens of percent) and the phase of the reflected signal (by more than π / 4 radians) and / or they fall into the range of values corresponding to the appearance of a potentially dangerous object, the sound signal will trigger and / or indicator light showing the need for personal search.

Thus, the implementation of the method is quite feasible by known technical means and does not require highly professional training from the inspector. The device, created on the basis of the proposed method, will be quite effective in detecting the presence of a foreign object under the clothing of the person being checked, which is neither clothing nor the body. With the allocation of such a small group, the time for personal examination of suspicious persons is significantly reduced, which is the most reliable solution to the problem.

Claims (1)

A method for detecting objects hidden under people's clothes, which consists in exposure to an investigated area of a person’s body by scanning it, in receiving reflected electromagnetic radiation and recording its characteristics, characterized in that the wavelength of the used electromagnetic radiation is selected based on the condition

where ε _n is the dielectric constant of the desired sample;

- the dimensionless coordinates of the desired sample, in a direction perpendicular to the surface of the human body; λ is the wavelength; Z _n , Z _n-1 - the dimensional coordinates of the sample, record the phase and / or amplitude of the reflected radiation at each of the controlled points of the investigated area of the body surface, the presence of a foreign object on the human body is judged by the differences obtained at different points of the data or by the results of comparison of the registered phase and / or amplitude of the reflected radiation with reference values representing the values of the phase and / or amplitude of the reflected radiation of the same frequency obtained by averaging the measurement results of these characteristics characteristics of the radiation reflected by the human body in the absence of foreign objects.

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