RU2451953C1 - Mine detector - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: mine detector has a power supply unit 1, a transmitting unit 2, a transmitting antenna 3, receiving antennae 4 and 5, a receiving unit 6, a thermal imager 7, an amplitude detector 8, a temperature measuring device 9, delay lines 10 and 11, subtracting units 12 and 13, integrating units 14 and 15, dividers 16 and 17, a reference voltage generating unit 18, a reference temperature generating unit 19, comparator units 20 and 21, switches 22, 23, 35 and 36, needle indicators 24 and 25, a strobe generator 26, a stroboscopic converter mixer 27, a correlator 28, a controlled delay unit 29, a multiplier 30, a low-pass filter 31, an optimal control 32, a range detector 33 and a flip-flop 34.

EFFECT: high reliability of detection and identification of subsurface objects, including mines, by excluding the interfering direct radiation of the transmitter and signals reflected from the air-ground boundary surface.

1 tbl, 1 dwg

Description

The proposed device relates to the field of instrumentation, in particular to devices designed to detect foreign bodies in the soil, and specifically mines, in particular anti-personnel.

The problem of searching and detecting mines is extremely relevant. The number of them in the soil is measured in hundreds of millions, annually 2.0-2.5 million new ones are added to them, and at best 100 thousand mines are neutralized. In minefields, not only military personnel are killed or injured during the hostilities, but also civilians visiting places of past battles. The world community in recent years raises the issue of banning mines as a type of weapon.

Modern means of detecting mines are not far from the level of World War II.

Known devices for detecting foreign formations in the soil, including mines (ed. Certificate of the USSR No. 336463, 380910, 411268, 417675, 734957, 930034, 932098, 941776, 947666, 1079946, 1208402, 1368685, 1462217, 1657988, 1781577 , 1800219; RF patents No. 1806390, 2011110, 2036372, 2047039, 2047815, 2053436, 2084757, 2206108; US patents No. 3045116, 3744289, 4091322, 4289019; UK patent No. 1349120; France patents No. 2374628, 2504651; German patent No. 3112829; Japan patents Nos. 46-11.795, 55-6.856, 63-22.531; Dikarev V.I., Koinash B.V., Salnikov V.P., Sandulov Yu.A. Explosive Hazardous Objects, Methods and Means of Search, Detection, Disinfection and utilization. - St. Petersburg, 2001 and others).

Of the known devices, the closest to the proposed one is the Mine Detector (RF patent No. 2206108, G01V 3/12, 2002), which is selected as a prototype.

The known device provides increased noise immunity, sensitivity and reliability of detection in the soil of mines, including non-metallic, such as plastic, in conditions of strong interference of natural and artificial origin.

However, reliable detection and identification of subsurface objects, including mines, at various depths is difficult in some cases due to interfering direct radiation from the transmitter and signals reflected from the air-ground interface.

An object of the invention is to increase the reliability of detection and identification of subsurface objects, including mines, by eliminating interfering direct radiation from the transmitter and signals reflected from the air-ground interface.

The problem is solved in that a mine detector, containing, in accordance with the closest analogue, a serially connected power supply unit, a transmitting unit and a transmitting antenna, a serially connected first receiving antenna and a receiving unit, serially connected a second receiving antenna and a thermal imager, serially connected amplitude detector, the first a delay line, a first subtraction unit, the second input of which is connected to the output of the amplitude detector, the first integration unit, the first division unit, the second input which of the second is connected to the output of the reference voltage generating unit, the first key, the second input of which is connected to the output of the amplitude detector, and the first dial indicator, a temperature meter in series, a second delay line, and a second block subtraction, the second input of which is connected to the output of the temperature meter, the second integration unit, the second division unit, the second input of which is connected to the output of the second subtraction unit, the second unit equalization, the second input of which is connected to the output of the reference temperature generating unit, the second key, the second input of which is connected to the output of the temperature meter, and the second dial indicator, while a multi-frequency microwave energy source is used as a transmitting unit, the antennas are made horn and combined into an antenna the block mounted on the rod differs from the closest analogue in that it is equipped with a strobe driver, a stroboscopic converter mixer, an adjustable delay unit, a multiplier, f low-frequency filter, extreme regulator, range indicator, trigger, third and fourth keys, and a mixer of a stroboscopic converter, the second input of which is connected to the output of the gate driver, is connected to the second output of the transmitting block, a trigger, the second input of which is connected to the second output of the adjustable delay unit , and a third key, the second input of which is connected to the output of the receiving unit, and the output is connected to the input of the amplitude detector, to the second output of the transmitting unit a multiplier is connected, the second input of which is connected through an adjustable delay unit to the output of the receiving unit, a low-pass filter, an extreme regulator and an adjustable delay unit, whose range indicator is connected to the second output, a fourth key is connected to the trigger output, the input of which is connected to the thermal imager output, and the output is connected to the input of the temperature meter.

The structural diagram of the mine detector is shown in the drawing. The penetration depth of microwave energy depending on the wavelength in various soils is presented in the table. An analysis of this table indicates that it is advisable to use a multi-frequency microwave energy source for irradiating the soil.

The mine detector includes serially connected power supply unit 1, transmitting unit 2 and transmitting antenna 3, serially connected first receiving antenna 4, receiving unit 6, third key 35, amplitude detector 8, first delay line 10, first subtraction unit 12, the second input of which is connected to the output of the amplitude detector 8, the first integration unit 14, the first division unit 16, the second input of which is connected to the output of the first subtraction unit 12, the first comparison unit 20, the second input of which is connected to the output of the reference generating unit 18 voltage, the first key 22, the second input of which is connected to the output of the amplitude detector 8, and the first dial indicator 24, sequentially connected to the second receiving antenna 5, the thermal imager 7, the fourth key 36, the second input of which is connected to the output of the trigger 34, temperature meter 9, the second a delay line 11, a second subtraction unit 13, the second input of which is connected to the output of the temperature meter 9, a second integration unit 15, a second division unit 17, the second input of which is connected to the output of the subtraction unit 13, the second comparison unit 21, the second the input of which is connected to the output of the reference temperature generating unit 19, the second key 23, the second input of which is connected to the output of the temperature meter 9, and the second dial indicator 25 connected in series to the second output of the transmitting unit 2, the mixer 27 of the stroboscopic converter, the second input of which is connected to the output a gate former 26, a trigger 34, the second input of which is connected to the second output of the adjustable delay unit 29, and the output is connected to the second input of the third key 35, connected in series e to the second output of the transmitting unit 2, a multiplier 30, the second input of which through the adjustable delay unit 29 is connected to the output of the receiving unit 6, a low-pass filter 31, an extreme regulator 32, an adjustable delay unit 29 and a range indicator 33. Antennas 3, 4 and 5 are made horn, combined into an antenna unit and mounted on a rod.

The mine detector works as follows.

The main mode of the mine detector is the "Search" mode. This mode is set automatically when the device is turned on and is used when searching and detecting subsurface objects, including mines.

When applying voltage to the mine detector, the transmitting unit 2 generates a probing microwave signal emitted by the transmitting antenna 3 in the direction of the Earth's surface.

Detection of subsurface objects, including mines, in the "Search" mode is carried out by a sapper by moving an antenna block containing antennas 3-5 and mounted on a rod (not shown in the drawing) in front of it to the right and left, and moving it forward in a given direction. In this case, it is necessary to ensure that the antenna unit moves parallel to the surface being examined at a fixed distance (no more than 5 cm from it). The speed of movement of the antenna unit is selected depending on the search conditions and should be within 0.1 ... 1.0 m / s. In the search process, it is necessary to alternate the transverse and longitudinal displacements of the antenna unit so that after each swing from right to left or left to right, the antenna unit moves forward up to 20 cm (by the size of its linear size). In this case, it is necessary to ensure that the entire checked area is examined.

An electromagnetic wave reflected from a subsurface object (mine) acts on the receiving antenna 4. The same antenna is affected by interfering direct radiation from the transmitter 2 and the signal reflected from the air-ground interface.

Part of the energy of the probe signal from the second output of the transmitting unit 2 is supplied to the first input of the mixer 27 of the stroboscopic converter, the second input of which is supplied with a short strobe pulse from the output of the gate former 26. The pulse generated in the mixer 27, which is the instantaneous value of the probing periodic signal, is supplied to the installation input of the trigger 34. The trigger 34 is transferred to the first (zero) state, in which a negative voltage is generated at its output.

The signals reflected from the interface and from the subsurface object are received from the output of the receiving unit 6 through the adjustable delay unit 29 to the first input of the multiplier 30, the second input of which is supplied with a sounding signal from the second output of the transmitting unit 2. The adjustable delay unit 29, the multiplier 30 , the low-pass filter 31 and the extreme controller 32 form a correlator 28. At the output of the multiplier 30, a low-frequency voltage is generated proportional to the correlation function R (τ), which is highlighted by the low-pass filter 31 from. Extreme controller 32 maintains the correlation function R (τ) at the maximum level, providing a delay value τ equal to τ _s

,

,

where h is the distance from the transmitting antenna 3 to the subsurface object (mines),

h = h ₁ + h ₂ ;

h ₁ is the distance from the transmitting antenna 3 to the Earth;

h ₂ - the depth of the subsurface object (mines) in the ground;

C is the propagation velocity of radio waves.

A voltage proportional to h is supplied to the input of the range indicator 33 and to the second input of the trigger 34 from the second output of the adjustable delay unit 29. The trigger 34 is translated into the second (single) state, in which a positive voltage is generated at its output. This voltage is supplied to the control inputs of the keys 35 and 36, opening them. Keys 22, 23, 35 and 36 in the initial state are always closed. The adjustable delay unit 29 is necessary for the most complete control of the influence of reflections from the media interface on the operation of the amplitude detector 8, temperature meter 9, and subsequent blocks. The adjustable delay unit 29 provides a variable delay, which eliminates the influence of direct radiation of the transmitting antenna 3 and signals reflected from the air-ground interface and from layers of different depths, i.e. carries out "vertical gating", which provides sequential viewing of the subsurface space from the air - soil interface to layers of various depths and determining h = h ₁ + h ₂ , which is fixed by the range indicator 33.

“Horizontal gating” allows against the background of electromagnetic field variations not related to the electromagnetic wave reflected from the subsurface object (mines), it is possible to reliably select subsurface objects (mines) in the subsurface layers. To exclude the influence of periodic and quasi-stationary variations of the Earth’s electromagnetic field, periodic measurements of the field strength and the operation of normalizing the difference signal of two successive measurements are carried out, i.e. integrate the difference signal, divide the difference signal into the integrated difference signal. The operation of comparing a normalized signal with a given threshold value allows you to make a decision about the presence or absence of a subsurface object (mine).

To do this, the voltage from the output of the receiving unit 6 through the open key 35 is supplied to the input of the electromagnetic field strength meter, which can be used as an amplitude detector 8.

At each observation point, at least two consecutive measurements of the intensity of the reflected electromagnetic field are made. Then, the operation of subtracting two consecutive measurements is performed. For this, the signal corresponding to the previous measurement is delayed by the delay line 10 until it is compared with the subsequent signal in the subtraction unit 12. The operations of integrating the difference signal and dividing the difference signal by the integrated difference signal are performed in blocks 14 and 16. In block 20, the normalized signal is compared with the threshold value of the signal specified by block 18.

The operation of comparing a normalized signal with a given threshold value allows you to make a decision about the presence or absence of a subsurface object (mine). If the normalized signal exceeds a threshold value, then a constant voltage is generated in the comparison unit 20, which is supplied to the control input of the key 22, opening it. In the initial state, key 22 is always closed. In this case, the voltage from the output of the amplitude detector 8 through the public key 22 is supplied to the dial indicator 24.

A multi-frequency source of 2 microwave energy provides irradiation of the soil and objects located in it, including mines. In this case, depending on the type of soil, the appropriate wavelength of microwave radiation is selected (table). With the complex nature of the soil, two or more wavelengths can be used simultaneously or sequentially.

The resulting temperature field of the surface as a result of heating the soil layer in the irradiated area is perceived by the receiving antenna 5, the thermal imager 7 and is measured by the temperature meter 9 through the key 36. At the same time, at least two consecutive measurements of the temperature field are made at each observation point. Then, the operation of subtracting two consecutive measurements is performed. For this, the thermal signal corresponding to the previous measurement is delayed until it is compared with the subsequent thermal signal (temperature) in the subtraction unit 13. The operations of integrating the temperature difference and dividing the temperature difference by the integrated temperature difference are performed in blocks 15 and 17. In block 21, the normalized temperature is compared with the temperature threshold value set by block 19. If the specified threshold value is exceeded, a constant voltage is generated in block 19, which is supplied to the control input of the key 23, opening it. In this case, temperature measurements from the output of the meter 9 through the public key 23 are received on the dial indicator 25.

The proposed mine detector must have the following parameters:

1. The frequency of the soil warming microwave radiation

The wavelength should be comparable with the depth of radiation penetration into the soil and with the size of the desired object (mine), which has thermophysical properties other than the soil. In this case, one should take into account the nonlinear nature of the absorption of microwave energy in materials, which increases with increasing frequency (table).

Thus, the maximum frequency should be chosen so that the wave does not "flow around" the mine, i.e. the wavelength should not significantly exceed the size of the desired item. It follows that it is advisable to take the maximum wavelength no more than 50 ... 60 cm, and the minimum radiation frequency, respectively, of the order of 500 MHz. When using multiple lengths, they can be applied in series or in parallel.

2. The power of microwave radiation

This power can be estimated from the condition of the need to warm the soil layer to a predetermined level, determined by the ability to indicate a subsurface object, while the dimensions of the soil layer are determined by the tactical and technical requirements of the min search. Thus, the following data can be used to estimate power:

1 - the thickness of the heated layer of the order of 5 cm (laying depth of anti-personnel mines);

S is the irradiated surface of 0.5 · 0.5 m ² (more than the size of the mine, but less than the step size of the sapper);

c - soil heat capacity 0.75 ± 0.9 kJ / kg · ° C;

ρ - soil density 900 ... 1600 kg / m ³ ;

Δt — irradiation time (time between steps of a sapper along a mined field) not more than 2 min;

ΔT is the temperature increase recorded by the sensor, which for modern monitoring means (a thermal imager with a temperature meter, arrays of highly sensitive thermocouples, etc.) is ~ 0.1 ° C; however, for reliable detection, this value must be increased by a factor of five.

Considering that at a radiation wavelength of ~ 12 m, the power P of microwave radiation decays in the soil 2 ... 3 times, we get:

,

,

those. radiated power should be hundreds of watts.

3. Mine detector sensitivity

The proposed device does not record the absolute temperature of the irradiated surface, but its growth, cutting off the constant electromagnetic and thermal backgrounds that are not informative for the task. This is easy to do by dividing the irradiation time equal to the temperature measurement time into separate intervals, the value and number of which can be set arbitrarily. In addition, to exclude uninformative electromagnetic and thermal backgrounds, periodic measurements of the electromagnetic and temperature fields of the surface and the normalization of the difference between the intensities and temperatures of two consecutive measurements are carried out. The operations of comparing normalized temperature and signal differences with predetermined threshold values make it possible to increase the reliability of deciding on the presence or absence of a mine.

Using in the proposed device it is the increase in temperature and electromagnetic field intensity as registered parameters allows you to:

- use methods and devices known from radio engineering for the isolation and analysis of variable signals against a background of constant components;

- to increase the information content of the identification of mines, because only the dimensions of the mines and various thermophysical properties of mines and soil are reflected in the distortion of the heat flux, manifesting itself in the contour of the object distorting the heat flux. As a rule, mines have some correct configurations (circle, rectangle, ring), due to the technology of making mines. The interference (cobblestones, plant roots, fragments of bricks, etc.) have irregular shapes. The higher the discrimination sensitivity ΔТ, the sharper the contours of the object distorting the heat flux appear.

Modern medical thermal imagers and temperature meters can distinguish between temperature increases ΔT up to 0.1 ° C. Naturally, the higher the sensitivity ΔT of the recording device, the lower the power level required for irradiating the soil.

4. Mass and size characteristics of the mine detector

The overall dimensions of the mine detector are also determined by the tactical and technical requirements of its operation: the mine detector must be autonomous and serviced by personnel of 1-2 people.

The overall dimensions of the mine detector are composed of four parts:

a) multi-frequency transmitting unit of microwave radiation. In the case of using low-power magnetrons, the mass and dimensions of the transmitting unit are 4 ... 6 kg and 7 ... 10 dm ^3, respectively;

b) power source. In the case of using a battery (for example, from a KamAZ car), the mass is 25 kg, and the dimensions are 5 dm ³ ;

c) temperature field meter. In the case of using a thermal imager and a temperature meter, the mass is 2 ... 3 kg and dimensions 3 dm ³ ;

d) a device to protect the sapper from microwave radiation. In principle, it is possible to use just overalls.

The protection problem is the topic of a separate technical solution, and for the proposed mine detector it is important that the mass of protective devices should not exceed 2 ... 3 kg.

Therefore, even when using a combination of known devices, we obtain the dimensions of the mine detector at the level of 20 dm ³ , and the mass is about 35 kg. Such characteristics are already acceptable for autonomous servicing by personnel of 1 ... 3 people, although it is possible that they can be reduced (for example, by increasing the sensitivity of the temperature meter, reducing the mass of the battery, etc.).

The proposed mine detector allows you to increase the noise immunity, sensitivity and reliability of detection in the soil of mines, including non-metallic, such as plastic, in conditions of strong interference of natural and artificial origin. This is achieved by eliminating variations in the electromagnetic and temperature fields that are not related to the reflected electromagnetic field and the thermophysical parameters of mines: thermal interference of natural (Sun) and artificial (industrial installations, pipelines with hot water, heat pipes, etc.) origin, using a multi-frequency microwave energy source and using horn antennas.

Thus, the proposed mine detector in comparison with the prototype and other technical solutions of a similar purpose can improve the reliability of detection and identification of subsurface objects, including mines, as well as determine the distance h from the transmitting antenna 3 to the subsurface object (mines) and its depth h ₂ occurrence in the ground. This is achieved by eliminating the interfering direct radiation of the transmitter 2 and the signals reflected from the air-ground interface.

Characteristics of penetration of radio waves into the soil Soil type Wavelength, cm Attenuation coefficient, dB / m Depth of penetration when attenuating 100 times, m 1. Frozen soil 300 4.2 4,5 2. Dry soil 500 0.8 25 3. Quartz sand 3.0 2.0 10 4. Sandy soil with moisture: 3% 3 300 0,07 12% 60 3 6.7 5. Clay soil with moisture: 3% 3 1100 0.02 12% 60 12 1,6

Claims (1)

Mine detector containing a serially connected power supply unit, a transmitting unit and a transmitting antenna, a serially connected first receiving antenna and a receiving unit, serially connected a second receiving antenna and a thermal imager, serially connected amplitude detector, a first delay line, a first subtraction unit, the second input of which is connected to the output amplitude detector, the first integration unit, the first division unit, the second input of which is connected to the output of the subtraction unit, the first comparison unit, the second input to connected to the output of the reference voltage generating unit, the first key, the second input of which is connected to the output of the amplitude detector, and the first dial indicator, a temperature meter connected in series, a second delay line, a second subtraction unit, the second input of which is connected to the output of the temperature meter, the second block integration, the second division unit, the second input of which is connected to the output of the second subtraction unit, the second comparison unit, the second input of which is connected to the output of the standard formation unit temperature, the second key, the second input of which is connected to the output of the temperature meter, and the second dial indicator, while a multi-frequency microwave energy source is used as a transmitting unit, the antennas are made horn and combined into an antenna unit mounted on a rod, characterized in that it is equipped with a strobe driver, a stroboscopic converter mixer, an adjustable delay unit, a multiplier, a low-pass filter, an extreme regulator, a range indicator, a trigger, a third and a h with fourth keys, and a mixer of a stroboscopic converter, the second input of which is connected to the output of the gate driver, a trigger, the second input of which is connected to the second output of the adjustable delay unit, and a third key, the second input of which is connected to the output of the receiving unit, connected to the second output of the transmitting block, and the output is connected to the input of the amplitude detector, a multiplier is connected in series to the second output of the transmitting unit, the second input of which is through the adjustable delay unit connected to the output of the receiving unit, a low-pass filter, an extreme controller and an adjustable delay unit, the range indicator is connected to the second output of the trigger, a fourth key is connected to the trigger output, the input of which is connected to the output of the thermal imager, and the output is connected to the input of the temperature meter.