RU173012U1 - DEVICE FOR DETECTING NON-METAL ITEMS HIDDEN UNDER CLOTHING OF PEOPLE - Google Patents

Abstract

The utility model relates to safety systems using electromagnetic radiation, and can be used to detect objects carried on the body, such as explosives, drugs, or other hidden objects that cannot be detected by metal detectors. The principle of the device is based on irradiating a person with low-intensity radio waves, receiving reflected signal and its processing. The proposed device consists of a broadband antenna operating in the frequency band 1-4 GHz, a dielectric plate attached to the antenna body, and a device for measuring the reflection coefficient module. In the operating mode, the plate is between the antenna and the irradiated object, as a result of which the frequency dependence of the reflection coefficient that appears on the screen of the device has a multi-resonance character. The values of the resonant frequencies make it possible to judge whether there is a hidden object or its absence. The technical result that can be obtained using the device is to increase the likelihood of detecting hidden objects and to simplify the equipment used. 3 s.p. f-ly, 4 ill.

Description

The utility model relates to safety systems using electromagnetic radiation, and can be used to detect objects carried on the body, such as explosives, drugs, or other hidden objects that cannot be detected by metal detectors.

Among the measures necessary to prevent terrorist acts, an important place is occupied by the screening of people when entering airports, train stations and other crowded places. Currently, there are effective methods for detecting metal objects hidden under clothing. A more difficult task is to detect hidden dielectric objects, which include, for example, a plastic explosive (plastid) in the form of a layer adjacent to the body, supplemented by damaging elements made of solid dielectric.

Known devices that solve this problem, which use the principle of obtaining images of hidden objects in the infrared or in the millimeter wave range due to the temperature contrast between the hidden object and the body (US patent No. 6777684, IPC G01N 21/01). However, electromagnetic waves of the indicated range are strongly absorbed in the substance, therefore, if the checked dense or wet clothes have a lower probability of detection. In addition, with a long stay in the room, the temperature contrast between the body and objects on the body practically disappears, which is also a disadvantage of this type of device.

Known devices that use tomography methods to detect hidden objects during the inspection (US patent No. 6057761, IPC G08B 21/00). However, devices of this type are technically complex, expensive stationary installations and require highly qualified personnel, which makes it unjustified to use them in cases where you need a mobile device for inspection in crowded places.

The closest in technical essence to the proposed utility model is a method for detecting objects hidden under clothing of people [RF patent No. 2301432, IPC G01V 3/12, publ. 06/20/2007, bull. No. 17]. The device consists of an antenna and a device for measuring the complex reflection coefficient with the output of information in numerical form or in the form of a graph on the screen. The principle of operation of this device is based on human exposure to decimeter-wave electromagnetic waves and analysis of the reflection coefficient at the antenna input. In the process of inspection, the antenna is moved over the surface of a person’s clothes, and the presence of objects hidden under the clothes is judged by the nature of the change in phase and reflection coefficient module or by comparing these data with reference values, that is, with average values obtained in advance when examining people with hidden items are missing.

The disadvantages of the known device are as follows.

Since the characteristics of the reflected wave depend on the thickness of the hidden object and its dielectric constant, in the specified invention choose the frequency of the electromagnetic wave corresponding to these parameters. Thus, it is assumed that the approximate value of the parameters of the hidden object is known in advance. This limits the effectiveness of the detection process, reduces the likelihood of reliable detection of a hidden object.

The proposed utility model solves the problem of increasing the efficiency of searching people when searching for items hidden under clothing. The technical result that can be obtained by using it is to increase the likelihood of detecting hidden objects and to simplify the equipment used.

To solve the problem with the achievement of the specified technical result in the proposed device, a dielectric plate 2 is attached to the antenna body so that the direction of the maximum radiation of the antenna 1 passes through the center of the plate 2 orthogonal to it, and a reflection coefficient modulus meter is used as a measuring device 3.

Description of illustrations.

FIG. 1. - Block diagram of the proposed device;

FIG. 2. - Block diagram of the proposed device with the irradiated object;

FIG. 3. - Experimental dependences of the reflection coefficient module in the frequency band: solid line - in the presence of a hidden object; dashed line - in its absence. Thin clothing (1 mm thick);

FIG. -four. Experimental dependences of the reflection coefficient modulus in the frequency band: solid line - in the presence of a hidden object; dashed line - in its absence. Thick clothes (thickness 10 mm).

The notation in FIG. 1-4:

1 - antenna;

2 - dielectric plate;

3 - a device for measuring the module of the reflection coefficient;

4 - clothes;

5 - hidden object;

6 - the human body.

The physical basis of the proposed device are as follows.

The electromagnetic wave emitted by the antenna 1 (Fig. 2) passes through the plate 2, through the air gap, through the clothes 4, through the hidden object 5 and spreads further in the human body 6, experiencing reflection and absorption. Thanks to the plate 2, a passage cavity with translucent walls is formed on the wave path. One wall of this resonator is plate 2, the other wall is the surface of the human body 6, and clothes 4 and a hidden object 5 can be considered as filling the resonator.

Pass-through resonators are used in the microwave technology as matching devices or band-pass filters. To create such a resonator, two inhomogeneities (for example, metal pins) spaced a certain distance [Sazonov DM, Gridin AN, Mishustin B.A. are added to the waveguide path connecting the generator to the load. Microwave Devices: Tutorial. M .: Higher school. 1981, p. 172]. The selection of the distance or parameters of inhomogeneities makes it possible to obtain the phenomenon of resonance between inhomogeneities at a given frequency. In this case, the reflection coefficient becomes equal to zero, and the wave completely passes into the load.

It is known that the phenomenon of resonance in a closed one-dimensional resonator occurs when its size is a multiple of an integer number of half-waves [AD Grigoriev Electrodynamics and microwave technology. SPb .: Publishing house "Doe". 2007, p. 405]. The resonator formed in the proposed device is open, therefore, for it, the resonance condition has the form:

where d is the distance between the walls of the resonator shown in FIG. 2; λ is the wavelength in vacuum; n = 1,2,3 ...; ε _eff - effective dielectric constant, taking into account the properties of objects 4 and 5 located in the resonator; A is a constant that takes into account the properties of the cavity walls. From (1), the expressions for the resonance frequencies corresponding to resonances with numbers n and n + 1 follow:

where c is the speed of light in vacuum.

The difference of expressions (2) gives the interval between two adjacent resonant frequencies:

Obviously, the presence of the object under clothing value ε _eff is greater than in its absence, while according to formula (3), Δƒ value will be less. Thus, the value of the interval Δƒ between adjacent resonant frequencies can serve as a criterion that determines the presence or absence of a hidden dielectric object.

Given the possible parameter values:

we obtain from formula (3) the range of possible values of the interval Δƒ between adjacent resonant frequencies:

Inequality (5) allows you to approximately determine the requirements for the operating frequency band of the antenna and the measuring device included in the proposed device.

The proposed device operates as follows (Fig. 2).

The inspector directs the antenna 1 with the plate 2 fixed on it to the studied area of the human body so that the distance from the plate 2 to the surface of the person’s clothes is within 30-80 mm. The device 3 generates microwave oscillations, and the antenna 1 emits electromagnetic waves that are reflected from the irradiated object, are received by the antenna 1 and enter the device 3, on the screen of which there is an image of the frequency dependence of the wave reflection coefficient module. Due to the presence in the device of the plate 2, the indicated frequency dependence has a resonant character, that is, it has sharply expressed minima at the resonant frequencies. The values of the resonant frequencies are easily determined visually on a scale on the device screen. If the difference Δƒ between adjacent resonant frequencies is less than some critical value Δƒ _cr , this indicates the possible presence of an object under clothing. The value Δƒ _{cr is} determined in advance when calibrating the device, since it depends on the type of elements used in the device and on the selected distance between the plate 2 and the surface of the garment 4.

In the prototype of the device as the antenna 1 was used horn antenna P6-23A with a frequency band including the range of 1-4 GHz; as instrument 3, a P2M-04 reflection coefficient module meter was used, which provides data output to a laptop screen; as plate 2, a ceramic plate with a thickness of 5 mm (a plate with a thickness of 4-8 mm can be used) with transverse dimensions of 200 × 300 mm and a dielectric constant of ε = 2.5 (dielectric constant can be in the range of 1.5-3) . Plate 2 was fixed with an adhesive tape in the aperture of antenna 1. In order to fix the distance from plate 2 to the surface of clothes 4, a block was attached to the center of plate 2 orthogonally, which in working mode touched the clothes of the person being checked. The bar is made of medium hard polyethylene, has a length of 70 mm and a square section of 15 × 15 mm.

The experiments simulating the search of a person were carried out with people with different physiques and different types of clothing. In this case, various options for hidden objects were used. The measurements showed that the curves are resonant in nature, and if there is an object under clothing, the interval between adjacent resonant frequencies does not exceed 1000 MHz, and in its absence the indicated interval is greater than 1000 MHz. Thus, for this variant of the device, the value Δƒ _{cr of} 1000 MHz can serve as a criterion for recognizing objects hidden under clothing.

As an example in FIG. 3-4 show the results obtained for a person under whose clothing was a belt of dense fabric with an analogue of an explosive device (analogue of plastid with pieces of ceramics). For thin clothes (Fig. 3), the interval between adjacent resonant frequencies in the presence of a hidden object Δƒ = 900 MHz, and in its absence Δƒ> 1500 MHz. For thick clothes (Fig. 4) in the presence of a hidden object Δƒ = 800 MHz, and in its absence Δƒ = 1400 MHz.

Compare these curves with the curves obtained in the absence of an additional plate 2. For this, refer to the prototype [RF patent No. 2301432] FIG. 3a-4a, which show that it is impossible to detect a hidden object using information about the reflection coefficient modulus, since the nature of the curves strongly depends on the thickness of the clothes.

Thus, the presence of a plate 2 in the device is an essential feature, which allows for the use of a simple quantitative criterion when searching people, based on determining only two numbers - the values of neighboring resonant frequencies. This increases the likelihood of recognizing objects hidden under clothing. In addition, there is no need to measure the phase of the reflection coefficient, therefore, you can use a simpler and cheaper than in the prototype device, a device that measures only the module of the reflection coefficient.

Claims (4)

1. A device for detecting non-metallic objects hidden under people's clothing, consisting of an antenna connected to a measuring device, characterized in that a dielectric plate is attached to the antenna body so that the direction of the maximum radiation of the antenna passes through the center of the plate orthogonal to it, and as a measuring The instrument uses a reflectance modulus meter. 2. The device according to p. 1, characterized in that the antenna uses a broadband horn antenna with a frequency band including the range of 1-4 GHz, and the dielectric plate is fixed in the aperture plane of the specified horn antenna. 3. The device according to p. 1, characterized in that the plate is made of ceramic, the dielectric constant of which is in the range of 1.5-3, and the thickness of the plate is in the range of 4-8 mm. 4. The device according to claim 1, characterized in that in the operating mode, the distance from the plate to the clothes surface of the irradiated object is in the range of 30-80 mm.

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