Means for detecting controlled explosive devices.

Means of detection of controlled explosive devices.

SHCHERBAKOV Grigory Nikolaevich,
Doctor of Technical Sciences, Professor

MEANS FOR DETECTING CONTROLLED EXPLOSIVE DEVICES

More and more often, the media reports on explosions: on roads, train stations, underground passages, entrances to buildings, etc.

In this case, as a rule, terrorists use controlled explosive devices. Their detection has its own peculiarities.

CONTROLLED EXPLOSIVE DEVICES – AS A SEARCH OBJECT

Conventional engineering mines and unguided explosive devices (UD) have contact and non-contact fuses.

They are triggered by direct impact of the target.

Controlled explosive devices (CED), detonated by terrorists at the most optimal moment for them, are much more effective [1,2].

Explosions can be controlled:

• by radio;
• by wire;
• using a time delay.

The first option is used most often and in any conditions.

The second — as a rule, in field conditions, when carrying out sabotage on roads.

The third — is most typical when blowing up local objects (buildings, underground passages, passenger transport, etc.) in cities.

Photos 1 — 4 show the appearance of the most typical explosive devices confiscated from terrorists.

Photo 1. The executive device of the blast control radio line (the top cover is removed).

Photo 2. Non-industrial blast control radio line kit
(command and executive units).
The control range in field conditions is up to 400…500 m, in the city — up to 200…250 m.

Photo 3. A time fuse using an electromechanical alarm clock.

Photo 4. An explosive device using a 120 mm mortar mine.
Controlled by wires (200 m).

Typical control ranges of the explosive device by radio or wires range from 100…150 m to 300…400 m.

At distances less than 100 m, the explosion of the explosive device becomes dangerous for the terrorist-demolitionist himself.

At ranges greater than 300…400 m, the weight, size and cost characteristics of the control lines increase significantly.

In field conditions, the depth of installation of the explosive device in the ground lies within the range from 0.3…0.5 m to 1..1.5 m.

Sometimes the radio-controlled VU is camouflaged in the foliage of trees or inside engineering structures (bridge fences, road signs, etc.).

There are known cases of installing VU under asphalt or concrete road surfaces.

In this case, as a rule, the cable line is installed in the ground at a depth of 0.1 … 0.2 m only near the road at a distance of up to 20 … 30 m from it.

Then it is placed on its surface under a masking layer of vegetation or snow directly to the explosion control point.

In urban conditions, explosive devices are camouflaged in hand luggage, roadside urns, in piles of garbage, tree foliage and in bushes.

The mass of explosives contained in explosive devices usually ranges from tens of grams to several kilograms.

Sometimes, most often when mining roads, powerful controlled land mines with an explosive mass of several tens of kilograms are used.

In this case, the landmine usually includes unexploded ordnance (air bombs, artillery shells, etc.).

The landmine is installed directly on the road or near it at a distance of up to 5…10 m.

The unmasking signs of a landmine are due to a number of factors.

The main factors that are almost always present [3,4]:

• the presence of an explosive substance (ES);
• the presence of a locally located mass of metal, even if very small (the body of the detonator cap, individual metal parts of the detonator, etc.);
• the characteristic shape of the explosive device;
• heterogeneity of the host environment (disturbance of the soil surface, road surface, color of vegetation, etc.).

Controlled explosive devices have additional unmasking features:

• the presence of an antenna with a radio receiver;
• the presence of a cable (wire) control line;
• the presence of an electronic timer or clock mechanism.

The most important telltale signs of a controlled explosive device for our case are listed in Table 1.

Table 1. Telltale signs of controlled explosive devices.

+  — there is contrast
±  — contrast is not always present

The current state of possible methods for detecting explosive devices is characterized by diversity. Their analysis shows that each of them has limitations [4].

Of course, it is necessary to take into account both a priori information about the search object (dimensions, case material, etc.) and the properties of the concealing environment.

Currently, the following methods are most widely used in domestic and foreign portable developments:

• electromagnetic (induction, radio wave, magnetometric, nonlinear);
• X-ray introscopy;
• gas analytical;
• mechanical (mechanical probing, using probes).

They make it possible to create portable technical means for searching for all types of explosive devices (including controlled ones) for various conditions.

A description of these general-purpose means can be found in specialized literature [1,2,4,5,7,8, etc.].

The presence of a control channel in an explosive device dramatically increases its combat effectiveness. However, at the same time, its unmasking properties are somewhat increased.

The main detection methods that allow you to identify the control channels of the explosive device (i.e. implement these properties) are the following:

• nonlinear radar (reveals the electronic components of the detonator);
• induction harmonic and radio kip (reveal the control cable line);
• acoustic and electromagnetic passive (reveal the operation of the detonator's clock device). Let's consider them in more detail.

APPLICATION OF NONLINEAR RADAR FOR DETECTING EXPLOSIVE DEVICES

Most explosive devices contain electronic components in their design: diodes, transistors, thyristors, etc.

They are contained in the actuator of the radio control line, the quartz clock generator, the output circuit of the explosion control cable line, etc.

All these components have nonlinear electrical characteristics, which allows them to be detected using nonlinear radar methods.

Detection is carried out by irradiating the search objects with a probing microwave field of the decimeter range with the registration of harmonics in the spectrum of the reflected signal.

The irradiation mode can be continuous or pulsed.

The first mode provides more opportunities for recognizing the detected “nonlinear object”, and the second – a greater detection range, which is especially important for field conditions.

It is possible to detect UVU through covering (opaque) media: soil, vegetation, snow, ice, building structures, as well as in hand luggage and baggage. The physical principles of nonlinear radar are described in more detail in a number of sources [4, 9, etc.].

Characteristic technical parameters of pulsed foreign and domestic portable NLRs:

• duration of probing pulses of units of μs;
• pulse repetition rate – hundreds of Hz … tens of kHz;
• pulse power – tens … hundreds of W;
• Received harmonic signals – only the 2nd or the 2nd and 3rd;
• Receiver sensitivity (at harmonic frequencies) – 10-11…10-12 W;
• Antennas – with rotating polarization (spiral or strip with a gain of 5 to 15);
• Weight (without packaging) – from 1.5…2 kg to 8…9 kg.

For continuous-wave radars, the radiated power is tenths…of a unit of W, and the sensitivity reaches a very high value – 10-14…10-16 W.

An experienced operator, comparing the levels of the 2nd and 3rd received harmonics, can recognize an explosive device with electronic components against the background of interference from contacting oxidized metal objects (shell fragments, rusty wire, etc.).

The latter, as is known, also have nonlinear properties.

It has been experimentally established that the nonlinear EPR (NEPR) of explosive devices with electronic components at a power flux density of the irradiating microwave field Ppod = 1 W/m2 is, as a rule: 10-7 … 10-12 m2 at the second harmonic and 10-10 … 10-13 m2 at the third.

Moreover, the backscattering diagram has a “multi-petal” structure.

Dependencies are known that determine the range of the NRS in various conditions [4,9]. Using them, taking into account the above technical parameters of existing portable NRS, we obtain that the detection range of the URS with electronic components lies within the range from fractions of a meter to tens of meters.

The first values ​​are typical for detecting miniature time delay devices, the second — for searching for homemade radio-controlled explosive devices of the HF range, camouflaged on trees.

Of the known portable NRS, as applied to the task being solved, the NR series devices have the most optimal characteristics.

The tests of the NR-900EM (pulse radiation) and NR-m (continuous radiation) devices showed that they detect explosive devices with electronic components at ranges from 0.2 m to 13.5 m, which is acceptable for practice in urban conditions.

During the experiments, 26 search objects were used, including those shown in photos 1 — 4.

It is very important that no unauthorized activation of search objects under the influence of the probing microwave field was noted in this case.

However, in principle, the use of the nonlinear radar method, like any other active method (induction, X-ray introscopy, etc.) can cause the fuse to operate.

This requires the use of a number of measures: increasing the range of the NRS, using protective equipment for the operator, installing the NRS on a reconnaissance robot, etc.

It should be noted that the range of the NR-900EM device is greater than that of the non-contact mine detector in service with the Russian Army.

In addition, unlike the non-contact mine detector, the NR-900EM device ensures recognition of electronic devices against the background of strong interference from rusty metal objects.

This is explained by the reception of not only the 2nd but also the 3rd harmonic, as well as the large dynamic range of the NR-900EM receiver.

Experience in combat operations in local conflicts shows that it is advisable to use a radio interference generator together with a portable NLR to block the detonation of radio-controlled explosive devices by terrorists.

However, the interference generator should not suppress the operation of the NLR receiver, i.e. it should be matched to it in spectrum.

In the future, it is advisable to use the nonlinear-parametric effect of excitation of electronic circuits to recognize the detected search object [4,6]. In this case, the NRS will include an additional source of the excitation field.

The ability to recognize the detected object will increase the safety of mine clearance operations.

DETECTION OF CONTROL CABLE LINES OF EXPLOSIVE DEVICES

To search for de-energized cable lines, the location of which on the ground is unknown, portable devices are used that operate on electromagnetic methods:

• radiokip method;
• harmonic induction method.

The radiokip method is based on recording spatial distortions of the magnetic component of the electromagnetic field of a remote radio station of the LW and MW ranges over an elongated conductor, the length of which is commensurate with the wavelength of the field or longer.

In a first approximation, an extended conductor (cable, pipe, etc.) can be represented as a passive re-radiating metallic electric vibrator located in a medium with losses.

The alternating magnetic field of the induced currents is superimposed in space on the primary field, distorting it and thereby creating stable anomalous effects.

The strongest secondary currents will be induced when the length of the desired conductor is determined by the expression:

,
where l is the wavelength of the probing electromagnetic field (remote radio station); is the complex permittivity of the host medium (soil), and the conductor itself is oriented perpendicular to the surface of the radio wave propagation front (i.e. parallel to the anomalous horizontal component of the vector E).

It is obvious that anomalous effects are easier to detect when the primary field is uniform. This can be achieved by observing the field of a radio station that is removed from the research site at a sufficiently large distance compared to its linear dimensions (practically at a distance of no less than 10-20 km).

At the observation point at the ground surface, directly above the extended conductor, an anomalous vertical magnetic component appears, which is absent under normal conditions.

In practice, it is recorded by a portable transistor radio receiver with a vertically located ferrite antenna.

The antenna must be free from the capacitive effect, which is achieved by its additional electrical shielding, symmetrization, etc.

When the operator passes over the underground conductor, the magnitude of the received signal is described by a double-humped curve.

Moreover, the “gap” between the two maxima is located directly above the center of the conductor, and the distance between these maxima on the route of movement is equal to twice the depth of the extended conductor.

The actual speed of the operator on the ground is no more than 0.5-1 km/h. Such a low speed is due to the need for the operator to hold the search radio receiver strictly on a plumb line so that the axis of its ferrite antenna is always perpendicular to the ground surface.

The radio key method is used in the portable compact cable control line detector R-299, which has been in service with the Russian army since the 1970s.

The harmonic induction method is used in portable metal pipe detectors from Fisher (USA) and others.

The device contains an emitter and receiver of an alternating magnetic field, located at the ends of a detachable support rod.

The operating frequency of such devices is tens of kHz.

They provide detection of large metal objects in the ground, as well as power cables (including de-energized ones) at a depth of up to 1..1.5 m.

However, these devices are not always effective for detecting very thin conductors, such as control cable lines. This is explained, first of all, by their low operating frequency.

Currently, a portable electromagnetic device is being developed that enables detection of control cable lines of the VU when moving at a fairly high speed — up to 2.5 … 3 km/h.

DETECTION OF CLOCK DELAYERS

Clock delayers of the VU are the source of various unmasking physical fields.

For example, mechanical clock devices create acoustic and seismic fields around themselves.

Electromechanical clocks and electronic timers, which always contain a power source, are emitters of quasi-stationary electric and magnetic fields.

All this is used, for example, in the explosive device detector “Anker-2”.

The “Anker-2” product is designed for express, contactless detection of explosive devices with active time delays, as well as radio explosive devices.

The product can detect mechanical, electromechanical and electronic (including wristwatches) clocks and other electronic devices for remote control of explosive devices.

The product, being a passive detector, does not create conditions for unauthorized activation of explosive devices.

The Anker-2 product is intended for use by law enforcement and security personnel when examining suspicious objects, buildings, vehicles, etc. for the possible presence of explosive devices in them in situations where calling a special bomb squad is impossible for some reason.

The product is shaped like a police baton and can be conveniently placed on a belt.

The Anker-2 product includes:

• electromagnetic field detector;
• microphone;
• contact microphone;
• headphones;
• charger.

Technical specifications.

Detection range (depending on the amount of interference):

• mechanical clock devices 20…100 cm;
• electromechanical clock devices 15…40 cm;
• electronic clock devices 1…5 cm;
• electronic control units 3…10 cm.

Supply voltage (two AA batteries) 2.4…3.2 V.
Current consumption, no more than 6 mA.
Overall dimensions:

• length 570 mm;
• diameter 40/60 mm.

In conclusion, it should be noted that currently the means of searching for explosive devices do not fully meet modern requirements. The sharp increase in “explosive” terrorism throughout the world requires the rapid creation of new, more effective means of detecting explosive devices.

BIBLIOGRAPHY

1. Ivliev S.A., Shcherbakov G.N. et al. Search and neutralization of explosive devices. (Reference manual). Publ. Academy of Energy and Information Sciences. Moscow, 1996.
2. Shamshurov V.K. Engineering support of combat. Textbook. Publ. VIA. Moscow, 1998.
3. Mikolaychuk M.A., Shcherbakov G.N. et al. Detection, neutralization and destruction of explosive objects. Foundation «For Economic Literacy», M., 1999.
4. Shcherbakov G.N. Detection of objects in concealing environments (for forensics, archeology, construction and the fight against terrorism). Moscow Academy of Comprehensive Security of Entrepreneurship, 1998.
5. Shcherbakov G.N. Means of detecting caches of weapons and ammunition in the soil. Special equipment, M., 2000, No. 2, pp. 18-23.
6. Shcherbakov G.N. et al. Use of the excitation effect of electronic circuits for identification of remotely controlled special technical means. Information security issues. M. 1999, No. 3 (46), pp. 60-62.
7. R. Ronin. Our Own Intelligence. Minsk. Harvest”, 1998.
8. Kovalev A.V. Search Technical Means Based on Introscopy Methods. Special Equipment. M., 1999, No. 6, pp. 13-21.
9. Shcherbakov G.N. Application of Nonlinear Radar for Remote Detection of Small Objects. Special Equipment. M., 1999, No. 6, pp. 34-39.