RU2497155C1 - Method and device to detect antipersonnel explosive devices with contact-wire target sensors - Google Patents

Abstract

FIELD: blasting.

SUBSTANCE: method to detect antipersonnel explosive devices with contact-wire target sensors consists in the fact that excitation of a conductor is carried out by an electromagnetic field retuned by frequency with frequency ratio of at least two and registered speed of reflected signal amplitude variation. The device to detect antipersonnel explosive devices with contact-wire target sensors comprises a generator, a transmitting magnet antenna, a receiver, a receiving magnetic antenna, an indicator device. Besides, the device additionally includes a block of retuning of generator bearing frequency and a differentiating chain connected between the output of the receiving amplifier and the input of the indicator device.

EFFECT: increased speed of searching, increased safety during mine clearing.

3 cl, 1 dwg

Description

The invention relates to safety and can be used to create technical means for identifying explosive devices having short contact-wire target sensors with electrical contactors, the fight against terrorism, humanitarian clearance, as well as when searching for underground cable communication and control lines.

Known georadars designed to identify various objects in the ground [1].

The disadvantage of such devices is a strong susceptibility to the interference effect of various inhomogeneities of the soil and foreign objects (stones, tree branches, etc.), which sharply reduces the search speed and its safety.

Known cable line detector "Zond-I" [2, 3], which implements a detection method that includes excitation of the cable with a probing electromagnetic field from a transmitting ferrite antenna, which is the source of the detector’s own electromagnetic field, the axis of which is perpendicular to the axis of the receiving ferrite antenna, which ensures their minimum magnetic coupling, and registration of a secondary electromagnetic field re-emitted by a cable line. This device operates at a fixed frequency in the region of resonant frequencies of the detected cable. He is able to detect underground wires longer than 20 meters [3].

The disadvantage of this device is the difficulty in detecting de-energized insulated conductors located in the ground and a length of not more than a few meters. But it is precisely such short, thin, insulated wires that are used in the target sensors of modern terrorist explosive devices mounted on foot troop routes.

The complexity of the detection is due to the high level of interference from the surface of the soil and its inhomogeneities at high frequencies. But it is precisely such frequencies that must be used to ensure resonant re-emission from short search objects several meters long. The wavelength of the probe field should also be units of meters. This drawback limits the speed of the search for this device in a real field environment and reduces the safety of clearance.

The technical result of the invention is to increase the speed of search and increase safety during clearance.

The technical result is achieved by exciting the desired underground conductor with a probing electromagnetic field with a variable carrier frequency. The presence of resonant properties of an insulated metal wire causes a pronounced response of the signal reflected from it when the resonant frequency of the wire coincides with the frequency of the exciting signal. At the same time, the amplitude of the interference signal from the semiconducting soil has a smooth character of change when the frequency of the probe electromagnetic field is tuned. Moreover, the overlap coefficient of the expected range of resonant frequencies of the search object is taken at least two, which provides at least one resonant response from the desired insulated conductor. Registration of the rate of change in the amplitude of the reflected signal, and not its amplitude value, allows you to select the signal against the background of noise from inhomogeneities of the soil, which does not have resonance properties.

To reduce the intrinsic resonances of the search device, magnetic antennas from a coaxial wire are used as its emitting and receiving antennas with a minimum magnetic coupling between them and resistors included at their input with active resistance equal to the wave impedance of the coaxial wire. To reduce the capacitive effect of the soil, the external conductor of the coaxial wire (its braid) is used as a grounded electrostatic shield. An open gap is made at the input of each loop antenna in the shielding braid.

Figure 1 shows a block diagram of a device for detecting anti-personnel explosive devices with contact-wire target sensors.

The detection device includes a transmitting broadband loop antenna 1, a matching resistor 2, a generator 3, a frequency tuner 4, a broadband receiving loop antenna 5, a matching resistor 6, a receiver 7, a differentiating circuit 8 and an indicator device 9.

Moreover, the transmitting and receiving antennas are located coplanar with a partial antiphase "overlap" on each other, which ensures minimal magnetic coupling between them.

A device for detecting anti-personnel explosive devices with contact-wire target sensors works as follows. The contact-wire target sensor, falling into the irradiation zone of the transmitting antenna 1, connected through the resistor 2 to the generator 3, re-emits the induced high-frequency energy into the broadband receiving frame antenna 5. The frequency tuning unit 4 provides a smooth change in the carrier frequency of the generator 3 with an overlap factor of at least two . From the output of the broadband loop antenna 5 through the terminating resistor 6 to the input of the receiver 7, where it is amplified. From the output of the receiver 7, the signal is fed to the input of the differentiating circuit 8, where the response of the reflected signal from the resonant search object is extracted. From the output of the differentiating circuit, the signal is fed to the input of the indicator device 9.

The testing of the method was carried out in the field on a large (more than 30) short thin insulated wires with a length of two to five meters. The depth of the wires was 3 ... 10 cm. The tests were carried out in various soils (sand, loam, etc.). Small stones, pieces of wood, fragments of brick served as interferences. The antenna system of the detection device consisted of two coplanar single-turn loop antennas with a diameter of 20 cm from a RK-50 coaxial cable. In order to reduce mutual magnetic coupling, the loop antennas were located on a fiberglass antenna board with a partial overlap on each other. The design of both coaxial antennas included 50 Ohm resistors connected in series to the central core. As the generator used a high-frequency generator G4-119A in the frequency range from 50 to 100 MHz. The output power was 0.1 watts. To increase the overall sensitivity of the measuring setup, internal amplitude modulation with a frequency of 1 kHz was used. The receiving loop antenna was connected to an amplitude detector on a D2E diode. A selective low-frequency voltmeter B6-9 tuned to a frequency of 1 kHz was connected to its output. When moving the search element over the wires hidden in the ground, a characteristic response of the reflected signal was observed, the amplitude of which exceeded the background noise by 7 ... 12 dB in moist soil and 10 ... 12 dB in dry soil.

Information sources:

1. Izyumov S.V. and others. Theory and methods of georadar. - Moscow. The Mountain Book, 2008, p.178 ... 183.

2. Scherbakov G.N. and others. Detector of cable lines. RF patent for utility model RU 45195, 04/27/2005

3. Scherbakov G.N., Antselevich M.A. New methods for detecting hidden objects. Moscow. "Ella IPR", 2011, from 68-72.

Claims (3)

1. A method for detecting anti-personnel explosive devices with contact-wire target sensors, characterized in that the conductor is excited by a frequency-tunable electromagnetic field with an overlap coefficient of the frequency range of at least two and a recorded rate of change in the amplitude of the reflected signal. 2. A device for detecting anti-personnel explosive devices with contact-wire target sensors, comprising a generator, a transmitting magnetic antenna, a receiver, a receiving magnetic antenna, an indicator device, characterized in that a tuner for the carrier frequency of the generator and a differentiating circuit connected between the output of the receiving amplifier and input indicator device. 3. The device according to claim 2, characterized in that as the emitting and receiving magnetic antennas are used single-turn loop antennas from a coaxial wire with a minimum of magnetic coupling with each other included at their input resistors with an active impedance equal to the wave impedance of the coaxial wire, the outer conductor of the coaxial wire is a grounded electrostatic shield.