Application of magnetic tomography in walk-through metal detectors..
Application of magnetic tomography in walk-through metal detectors
Grigory Nikolaevich Shcherbakov, Professor, Doctor of Technical Sciences,
Antselevich Mikhail Aleksandrovich, professor, doctor of technical sciences,
Udintsev Dmitry Nikolaevich, doctor of technical sciences,
Shlykov Yuri Aleksandrovich, candidate of technical sciences,
Brovin Andrey Vitilievich, candidate of technical sciences
Source: magazine «Special Equipment» No. 6 2007.
Currently, in the context of criminal and radical groups, increased terrorist activity in the Russian Federation, the relevance of identifying firearms, grenades, bladed weapons, disguised under clothing or in luggage is determined by the need to solve the problem of ensuring the safety of the population, organizations and enterprises. More and more often we see a picture of security officers inspecting citizens and their belongings in order to find items that are a source of increased danger to the population. Various technical devices are used to conduct inspections. One of the most common, designed to conduct inspections in crowded places, are walk-through metal detectors.
The objects of search in the fight against terrorism are in most cases ferromagnets: firearms; grenades; bladed weapons disguised under clothing or in luggage; «shahid belts» containing ready-made fragments; batteries in an electronic detonation circuit, mechanical, electronic and radio fuses from various explosive devices. At the same time, signals from products made of diamagnetic metals (watches, jewelry, confectionery foil, etc.) in this case are interference, reducing throughput
When it is necessary to inspect a large number of people, for example, during mass events, a low search speed makes it impossible to carry out high-quality control.
Most modern walk-through metal detectors operate on the eddy current principle and have a number of disadvantages, the main ones being:
- a large number of false positives due to the reaction to any metal objects, including those made of diamagnetic materials (watches, jewelry, etc.), which significantly reduces the search speed;
- the unresolved problem of mutual compensation of several metal objects with opposite magnetic properties (for example, a pre-selected part made of a non-ferrous metal composition can be placed next to a pistol, which makes detection of the weapon difficult);
- the lack of effective methods for recognizing a useful signal against a background of interference (correlation analysis, etc.).
In addition, such metal detectors are active, i.e. possessing their own probing fields, search devices, and can lead to the detonation of an explosive device, for example, a suicide belt with a duplicate radio detonator. The medical aspect is also important in this case [8]. For many years, it was believed that electromagnetic fields have only a thermal effect on the body, and the existing man-made sources, especially in the area of ultra-low frequencies (less than 100 Hz, primarily industrial frequencies of 50 and 60 Hz), have too little energy to have a noticeable effect on human tissue. However, by now a fairly stable correlation has been established between the time personnel spend in the area of electromagnetic radiation and a number of neurological disorders of the body (headache, irritability, increased fatigue), as well as disorders of the cardiovascular and digestive systems. Now it is considered an established fact that even low-intensity electromagnetic radiation has an effect on the human body. The nervous system of the embryo is very sensitive to the effects of electromagnetic radiation. In addition, there are requirements of various international institutions regarding the impact of electromagnetic radiation on implanted pacemakers. Even short-term small external magnetic fields with an induction of 0.1-0.3 μT lead to noticeable changes in sections of electrocardiograms. The observed changes increase with increasing magnetic field strength. It is necessary to take into account that in existing induction walk-through metal detectors (both harmonic and pulsed) the induction of the low-frequency magnetic field reaches units of μT, and sometimes more.
Thus, walk-through «anti-terrorist» metal detectors designed to detect firearms, grenades, bladed weapons, disguised under clothing or in luggage must meet the following requirements:
- Detect only products made of ferrous metals (ferromagnetic materials).
- Do not have their own probing fields. Be passive.
- Indicate the area of the search object on the human body.
The use of the magnetometric search method as a physical basis for the development of walk-through metal detectors [1,2,3,6,7] will allow the first and second requirements to be met. The possibility of using the magnetometric method as an inspection tool is considered in the works [5,6,7]. This idea is implemented in the form of a portable magnetometric search device for detecting covertly worn ferromagnetic objects (weapons, mines and explosive objects) in an unfavorable interference environment.
To quickly determine the search object location area on the object of inspection (the human body), it is advisable to use several sensors connected into a single system. As the conducted studies have shown, it is most advisable to use the principle of magnetic tomography for these purposes.
The basis of tomography (in the broad sense) is the possibility of mathematically reconstructing the spatial distribution of a particular characteristic of a substance inside an object based on the effect of this substance on the physical field or radiation penetrating the object and recorded by external sensors.
Fulfilment of all three requirements imposed on walk-through metal detectors is achieved by using a line of solid-state semiconductor magnetic field sensors as sensors, which perform dynamic “layer-by-layer” scanning, as well as by introducing into the walk-through metal detector a controller, a receiving and transmitting device and an autonomous indicator device, including a receiving and transmitting device and a computer interface unit.
Fig. 1 shows the structural diagram of a promising magnetic tomograph — a walk-through metal detector that meets all three of the above requirements.
The magnetic tomograph contains a data collection and transmission unit and an autonomous indicator device. The data collection and transmission unit includes sensors for distortion of the Earth's magnetic field in the form of a line of solid-state semiconductor magnetic field sensors[4] fixed on one axis, a controller, a receiving and transmitting device, and a housing made of non-magnetic material. The autonomous indicator device includes a housing made of non-magnetic material, a receiving and transmitting device, and a unit for interfacing with a special computer.
The magnetic tomograph operates as follows.
Fig. 1. Magnetic tomograph — passive walk-through metal detector:
1- contains a data collection and transmission unit;
2- autonomous indicator device;
3- Earth's magnetic field distortion sensors in the form of a line of magnetometric sensors fixed on one axis;
4- backup unit;
5- controller;
6- receiving and transmitting device;
7- non-magnetic housing;
8- housing of the autonomous indicator device made of non-magnetic material;
9- receiving and transmitting device of the autonomous indicator device;
10-computer interface unit;
11-computer with flexible interface.
A ferromagnetic search object, entering the detection zone, distorts the lines of force of the Earth's magnetic field. This distortion is recorded by magnetic field sensors (solid or film structure), the signals from which are processed by a microcontroller using a special algorithm that eliminates interference. Then the information is sent to the computer via wires or a radio channel. It is very important that the device interface is not a static picture based on the «yes» — «no» principle, but a dynamic «breathing» layer-by-layer scanned picture of changes in the magnetic field.
Currently, almost all known multi-zone walk-through metal detectors use the induction (eddy current) operating principle. Of the known multi-zone walk-through metal detectors with software signal processing, only the Zond-P product is passive, i.e. does not irradiate people passing through them (Fig. 2).
Its technical characteristics:
Dimensions — 190x4x2 cm;
Weight of the set — (placed in two stacks) — 12 kg;
Operating voltage — 220V, 50 Hz;
Power consumption — 60 W;
The assembly time of the kit and commissioning into the operating mode is no more than 10 minutes;
Operating temperature range from 0 to +500C;
Passage width up to 1 m.
Fig. 2. External appearance of the metal detector «Zond-P»
Main advantages over existing metal detectors:
1. Two levels of intelligent object recognition: its own built-in microprocessor and special software on a personal computer.
2. Higher detection speed due to the search for only ferromagnetic products and electronic devices that are in an active state. Pibor does not react to products made of non-ferrous metals (foil from confectionery and tobacco products, jewelry, coins, etc.)
3. High security of searching for explosive devices due to the absence of its own probing fields, causing accidental activation of fuses with electronic components.
4. There is no electromagnetic radiation that affects human health. In particular, it does not affect implanted pacemakers.
The small dimensions of the product ensure its mobility, does not require preparation, and, if necessary, provide concealment of installation.
Literature:
1. Shcherbakov G.N. Detection of objects in concealing environments. For forensic science, archeology, construction and the fight against terrorism. — M .: Arbat-Inform, 1998.
2. Shcherbakov G.N. Detection of hidden objects — for humanitarian demining, forensics, archeology, construction and the fight against terrorism. — M .: Arbat-Inform, 2004.
3. Udintsev D.N., Shcherbakov G.N., Antselevich M.A. Selection of an electromagnetic method for probing concealment environments. Special equipment, 2005.- No. 1.- pp. 21-25.
4. Baranochnikov M.L. Micromagnetoelectronics. T. 1.- M .: DMK Press, 2001.
5. Detector of ferromagnetic objects./Shcherbakov G.N., Antselevich M.A., Udintsev D.N., Mironov S.I. Patent No. 38962 dated 6.02.2004.
6. Detector of ferromagnetic objects./Shcherbakov G.N., Antselevich M.A., Udintsev D.N., Mironov S.I., Glushchak B.P., Filin V.G. Patent No. 42329 dated 8.09.2004.
7. Ways to improve noise immunity of magnetometric search equipment and their practical implementation//Shcherbakov G.N., Antselevich M.A., Udintsev D.N. et al. Special equipment-.№3, 2005.- pp. 19-24.
8. Gordienko V.A. Physical fields and life safety.-M.: AST, 2006.-316 p.