Antenna-contact method for detecting local objects in concealing environments.

Antenna-contact method for detecting local objects in sheltering environments.

A new method for detecting local objects in a semiconducting medium is proposed.

The essence of the method is to use the search object as a transmitting antenna.

The method allows, with a single contact with the search object, to determine its geometric dimensions and electrical properties, which significantly increases the objectivity of the information received and the speed of the search.

In recent years, the problem of searching for small man-made objects in sheltered environments has attracted the attention of an increasing number of specialists in various fields of activity: archeology, construction, humanitarian demining, etc.

It is known that the greatest objectivity of information is provided by the integrated use of contact and non-contact search methods.

The method of mechanical probing of the soil has been known to man since ancient times [1, 2] and is implemented using probes.

Currently, such probes are included in many metal detector kits.

They provide different depths of probing the covering environment.

Thus, Vladimirov's deep probe is designed to probe natural soils at a depth of up to 2 meters, and loosened soils more than 3.5 meters.

The sapper's drill will allow probing at a depth of up to 10 meters. The disadvantage of this method is the lack of the ability to recognize the heterogeneity detected by the contact method and, as a result, the low search speed.

Contact electrical methods of detecting objects in the ground have been widely used in electrical exploration of minerals since the beginning of the 20th century [3, 4].

The essence of these methods (resistance, charged body, etc.) is to record the distortions of the external electric or magnetic fields that occur when current flows around the search object located in the ground.

Despite the simplicity and relative cheapness of the technical implementation of this method, it is very labor-intensive. In addition, the ambiguity of the interpretation of the measurement results significantly complicates the recognition of the search object.

The fundamentally new, antenna-contact method of detecting local objects in concealing environments presented in this article allows, with a single contact with the search object, to determine its geometric dimensions and electrical properties, which significantly increases the objectivity of the information received and the speed of the search.

It combines to a certain extent the capabilities of contact and non-contact methods.

The physical basis of the method is to use the search object, during the contact period, as a transmitting antenna (Fig. 1).

The signal to the search object comes from the transmitting generator through a tip connected to its output.

The tip is electrically isolated and shielded from the rest of the structure, is located at the end of the probe and acts as a contact between the transmitting generator and the search object located in the ground.

The signal from the search object is sent through the receiving antenna and receiver to the indicator device.

The transmitting generator, receiving antenna, receiver and indicator device can be structurally located in the same housing.

One ​​of the important characteristics of the method is the ability to determine the geometric dimensions of the search object.

Fig. 1. Search for objects in sheltering environments using the antenna-contact method

The problem is difficult to calculate theoretically, since the passage of an electromagnetic wave in the near zone in two environments is considered: the sheltering environment, usually semiconducting, and the environment in which measurements are taken, in most cases dielectric.

Let us consider the solution of this problem for the particular case of finding the search object in a conducting medium, and the search equipment in a dielectric medium. The search object is approximated by a conducting sphere. The search equipment is located directly above the search object.

The search object connected to the transmitting generator can be represented as an elementary Hertzian emitter of the electric type. As is known [5 – 8], an electric vibrator, flown by a harmonic current, excites a quasi-spherical electromagnetic field in the surrounding space. Complex amplitudes of the components of the search object field, located in a semiconducting shelter medium, in a spherical coordinate system (Fig. 2.) can be represented as [5, 8, 9]:

(1)

(2)

, (3)

where:
Iэ – current amplitude in the search object, A;
l – reduced length of the search object, m;
R, q – spherical coordinates;
– complex permittivity of the semiconducting medium:

, (4)

g us – specific electrical conductivity of the covering medium, S/m;
e us – absolute permittivity of the covering medium, F/m;
w – angular frequency of the transmitting generator signal, Hz;
k – wave number in a medium with losses:

, (5)

m o – magnetic constant, H/m:
kо – wave number in a dielectric medium and in a lossless medium:

(6)

a – attenuation constant (absorption coefficient) of the covering medium:

, (7)

b – phase constant (phase coefficient) of the covering medium:

, (8)

Fig. 2. The search object connected to the transmitting generator, presented as an elementary Hertzian emitter in a spherical coordinate system

Boundary conditions on the interface of two semiconducting media [5]:

, (9)

, (10)

– normal and tangential complex components of the electric field of the search object in the measurement environment;

– normal and tangential complex components of the electric field of the search object in the sheltering medium.

Since in the overwhelming majority of cases the receiving antenna will be located near the interface between the media, then

, (11)

where is the value of the field strength created by the search object at the location of the receiving antenna.

The sheltering medium can be considered as quasi-conducting if the following condition is met:

. (12)

The frequency range at which condition (12) is satisfied for different types of sheltering media is presented in Table 1.

Table 1. Electromagnetic characteristics and frequency range satisfying the quasi-conductivity condition of the main covering media

Equations (1) – (3) for a conductive medium, when the search equipment is located directly above the search object (q = 900) and when registering only the electrical component can be represented as a single equation:

, (13)

where nq is the function of decreasing field amplitude in a conductive medium:

, (14)

where x is the numerical distance from the observation point to the emitter in units of field penetration depth:

, (15)

where d is the field penetration depth in the conducting medium, m:

, (16)

The boundary conditions for the conditions described above and at will take the form:

. (17)

Fig. 3 shows the dependences of the relative increase in the signal on the receiving antenna from the search object of different reduced lengths at a frequency of 1 MHz. The theoretical dependence is obtained from expressions (13 — 17). The experimental values ​​​​were obtained using search objects with different reduced lengths (photo 1).

Fig. 3. Relative increase in the signal on the receiving antenna from the search object of different reduced lengths, where
1 — theoretical dependence;
2 — experimental values;
3 – curve extrapolating the results of experimental studies

Analysis of these dependencies shows that the received signal has a stable tendency to increase with an increase in the geometric dimensions of the search object.

Photo 1. Search objects (balls and metal plates)

It should be noted that when placing measuring equipment in the environment where the search objects are located (for example, when a diver probes the bottom of a reservoir), only equations (13) – (16) are solved.

The conducted experimental studies also showed that at significantly higher frequencies it is possible to search for objects of artificial origin made of dielectric materials.

The analysis of theoretical and experimental studies allows us to draw the following conclusions:

• The antenna-contact method can be used to detect local objects in concealing environments.
• The method allows one to determine the geometric dimensions and electrical properties of the search object with a single contact.

This method is patented [10].

Currently, this idea has been implemented in a prototype of an electronic contact probe designed to search for metal objects in a concealing environment (photo 2). Field tests have shown the potential of this method for humanitarian demining. Although, according to the authors, the applicability of this method is much wider: archeology, construction, search for underground utilities, etc.

Photo 2. A prototype of an electronic contact probe,
designed to search for metal objects in a concealing environment

The authors express their gratitude to Stanislav Ivanovich Mironov for his assistance in creating the experimental setup and prototype.

References:
1. Shcherbakov G.N. Detection of objects in concealing environments. For forensics, archeology, construction and the fight against terrorism. Moscow: Arbat-Inform, 1998.
2. Shcherbakov G.N. Detection of hidden objects for humanitarian demining, forensics, archeology, construction and the fight against terrorism. Moscow: Arbat-Inform, 2004.
3. Zhdanov M.S. Electrical prospecting. Moscow: Nedra, 1986.
4. Yakubovsky Yu.V., Lyakhov L.L. Electrical prospecting. Moscow: Nedra, 1982.
5. Bessonov L.A. Theoretical foundations of electrical engineering. Moscow: Vysshaya shkola, 1973.
6. Dolukhanov M.P. Propagation of radio waves. Moscow: Gosizdat, 1960.
7. Belotserkovsky G.B. Fundamentals of radio engineering and antennas. Part II. Antennas. M.: Sovetskoe Radio, 1969.
8. Ogorodneychuk I.F., Zhuravlem I.Ya., Yatsishin V.I. Low-frequency wireless communication in mines. M.: Nedra, 1975.
9. Radio communication in conducting media./Korchagin Yu.A., Salomatov V.P., Chernov A.A. Novosibirsk: Nauka. Sib. Branch, 1990, 148 p.
10. Metal-detecting probe. Patent RU 37843 U1. Priority February 6, 2004.

SHCHERBAKOV Grigory Nikolaevich, Professor, Doctor of Technical Sciences
ANTSELEVICH Mikhail Aleksandrovich, Doctor of Technical Sciences
UDINTSEV Dmitry Nikolaevich, Candidate of Technical Sciences
MERKUSHIN Yuri Maksimovich,
VOSTRIKOV Dmitry Vladimirovich.