RU2252426C2 - Very low frequency electromagnet field imitator and its versions - Google Patents

Abstract

FIELD: laboratory tests of operation of aerials and direction finders.

SUBSTANCE: separate uniform field formers are used for both kinds (E- and H-) of waves. Electric field (E) former is disposed inside magnetic field (H) former in such a way that uniform fields formed by both formers could coincide or cross each other in bigger area to create electromagnetic (EH) uniform field at that area. Tested aerial is mounted precisely into the area. Relation between intensities of electric and magnetic field is changed by means of matching dividers mounted at output of signal oscillator. Sonic frequency generator or pulse generators are used as signal oscillator. Any component of field can be changed without making changes in the others.

EFFECT: improved noise immunity; widened range of working frequencies.

3 cl, 3 dwg

Description

A simulator of an electromagnetic field of very low frequencies and its variant relate to devices for generation and measurement in the field of electromagnetic fields. It is designed for working out antenna patterns (BOTTOM) in the very low frequency (VLF) range, debugging in a set of instruments that include antennas of this range (e.g., lightning radars (GL), lightning direction finders - rangefinders (GPA), etc.) .

Lightning radars (GL), which determine the coordinates (bearing and range) of lightning discharges, operate on myriameter waves, i.e. on electromagnetic waves with a length of λ> 10 km (f <30 kHz). For example, in the GPO “Ochag-2P” ([1], p.23), magnetic frame ferrite antennas in the modes of direction finding and EH - ranging work in the frequency range f = 0.3 ... 7 kHz, direction finders of other known ground and airborne lightning radars (sometimes called lightning direction finders - rangefinders or stormoscopes) operate in the frequency range of 3 ... 7 kHz (λ = 100 ... 40 km), the Omega global navigation system operates at frequencies of f≅10 kHz, etc. The creation of an artificial electromagnetic (ЕН) field for debugging the DND in this wavelength range presents certain difficulties.

It is not necessary to create radiation fields corresponding to the Fraunhofer diffraction region in which the radiation has a flat wave front, the same amplitudes and polarization within the length of the receiving antenna (2 ], p. 259 ... 261). For such antennas, the phase ratios of the fields near individual antenna elements are almost equally independent of the rotation of the antenna with respect to the direction of wave arrival, and therefore the requirement of a plane wave front is removed. The requirement of field uniformity — the constancy of amplitudes and polarization — is maintained within the antenna extent. It was shown in ([5], p. 49) that the electrodynamic problem of the formation of an electromagnetic field (EH) can be reduced to the problem of the formation of two static fields (E-) and (H-) or quasistatic in the case when an alternating voltage is used.

Known electric field simulators for debugging E-antennas, which create an electric field using long open (load resistance Z _H = ∞) wire or flat lines, and magnetic field simulators for debugging H-antennas, which create magnetic fields using short-circuited (Z _H = 0) of wire or flat lines, as well as using the Helmholtz ring system ([2], p. 260, [4], p. 66 ... 68, [7], p. 93 ... 96, fig. .3.9). When using a flat line to form the E-field, the distance between the plates should be at least five times the dipole height of the antenna under study, and the width and length of the plates should be at least fifteen times the dipole height ([7], p. 96). When using a flat line to form an H-field, the magnetic field strength is proportional to the current and inversely proportional to the line width ([4], p. 66). When using a system of Helmholtz rings to form the reference H-field, the distance between the rings should be equal to the radius of the rings, and the radius of the rings should exceed twice the length of the ferrite core of the frame ([7], pp. 93, 94). The shape of the BOTTOM is determined by measuring the dependence of the voltage at the output of the antenna from its angle of rotation, measured by the relative position of the arrow associated with the antenna, and a fixed scale, graduated in degrees of rotation of the antenna in the EN field, or by some other method.

Since direction finders usually use the signal from the output of the E-antenna as a reference voltage ([3], p. 25, 517, Fig. 2.9), i.e. Since the receiving-and-direction finding device uses signals from two antennas simultaneously: the H-antenna frame and the vibrator of the open omnidirectional E-antenna, then working out the product complex requires simulating the joint ЕН-field simultaneously acting on both (E- and H-) antennas.

A simulator of an electromagnetic (ЕН) field of very low frequencies is known ([3], pp. 520 ... 522, Fig. 9.2) using a single-wire traveling wave line, i.e. line loaded on wave impedance (ρ)

where d is the distance of the line from the conducting plane;

r is the radius of the line wire.

However, this simulator does not ensure the formation of a uniform field in the space region commensurate with the geometric dimensions of the antenna; does not allow to establish the desired E / H tension ratios; generates completely different from the real ratios of the induced EMF in the E- and H-antennas, to eliminate which the E-antenna of the test product is replaced with a special piece of straight-line conductor located parallel to the test line; requires to eliminate the influence of external interference in the shielded camera.

Of the known technical solutions, the closest (prototype) is an electromagnetic field simulator using a flat line of wide metal, for example, aluminum plates ([4], p. 66, [6], p. 50, [7], p. 96) . The ratio of electric and magnetic fields created by such a flat line loaded on the resistance Z _n is determined by the expression (2) ([5], p. 50):

where Z _H is the load resistance of the flat line;

W is the wave impedance of a flat line.

At Z _H = 0, there is only a magnetic field, at Z _H = ∞ there is only an electric field. To simulate the EN field in the wave zone, the load value is determined by the formula (3), providing a traveling wave mode:

To select the desired nature of the load, providing a field ratio in a flat line close to the field ratio from a real source, a two-terminal device consisting of LCR elements is recommended.

However, the prototype has several disadvantages:

- the strength of both the electric and magnetic components of the total electromagnetic field is significantly less than in the case of the formation of a field of only one type (E-field at Z _H = ∞ or H-field at Z _H = 0),

- excluded the possibility of varying the ratio of the intensities E / N with a constant value of the intensity of one of the field components (E or H),

- the presence of reactive elements L and C in the load reduces the frequency band formed by the device,

- low field uniformity in the vertical plane ([4], p. 67),

- the volume of the region of uniformity of the EN field when changing the E / H ratio is not defined,

- nearby objects and external interference affect the formation of the electromagnetic field ([6], p. 70, [3], p. 520), causing measurement errors.

The task of the invention is to develop a device that eliminates the disadvantages of the prototype, namely:

- provides an EN field of higher intensity corresponding to the formation conditions of the field of only one kind,

- forms a region of space with a uniform EN field that exceeds the geometric dimensions of the antenna,

- provides a wider range of working very low frequencies (VLF),

- increases noise immunity from external fields, reduces the influence of nearby objects,

- provides the ability to change one of the components of the field at a constant value of the other components of the electromagnetic field.

It is possible to form a homogeneous electromagnetic (EH) field in a certain region of space as areas of coinciding or intersecting for the most part homogeneous electric (E) and magnetic (H) fields created by the corresponding separate, but structurally defined way, combined electric (E) and magnetic ( H) fields. The solution to this problem is achieved with two options for constructing a simulator of the electromagnetic (EH) field of the VLF, connected by a single inventive concept.

1. In the first embodiment, in a simulator of an electromagnetic (ЕН) field containing a flat line consisting of upper and lower metal plates and a signal generator, another flat line is introduced so that the lower plates of the flat lines are aligned, the upper plates of the flat lines are separated by an electrically insulating with a gasket, the upper plate of the outer line is short-circuited with the lower common plate from the side opposite to the entrance of the flat lines, the inner flat line is open, the input of the inner flat line forming the electric (E) field connected to the output of the matching E-divider, the input of an external flat line forming a magnetic (H) field, connected to the output of the matching H-divider, the inputs of the matching dividers are connected to the output of the signal generator, the inputs and outputs of all elements of the circuit with zero potential connected.

2. In the second embodiment, a Helmholtz ring system is introduced in such a way that an open flat line is placed inside the Helmholtz ring system, an open flat line input is introduced into the electromagnetic (ЕН) field simulator containing a flat line consisting of upper and lower metal plates and a signal generator forming an electric (E) field is connected to the output of the matching E-divider, the input of the Helmholtz ring system forming a magnetic (H) field is connected to the output of the matching H-divider, the inputs of the matching dividers are connected with the output of the signal generator, the inputs and outputs of all elements of the circuit with zero potential are connected.

Thus, in both versions, the electric (E) field shaper, consisting of two parallel metal sheets, is structurally placed inside the magnetic (H) field shaper. Metal sheets of an open flat line, having a screening effect, can weaken the magnetic field strength. However, in the VLF range, the effect of shielding the magnetic field with a thin metal sheet is negligible. To evaluate it, let us consider in more detail the mechanism and amount of shielding ([8], p. 152 ... 168). According to field theory, shielding efficiency depends on three factors: loss due to reflection from the outer surface of the screen (R), loss of absorption by the material of the screen (A), and loss due to reflection inside the screen (B). The shape of the solid screen does not matter. In the near zone (induction zone r≤λ / 6) the components of the E- and H-fields are taken into account separately.

Losses due to reflection inside the screen (B) are relatively small compared to the absorption losses (A), which are proportional to the product:

where d [mm] is the thickness of the screen;

f [MHz] is the frequency;

μ is the magnetic permeability of the material;

G is the permeability of the material relative to copper.

For a non-magnetic material having μ = 1, G = 0.1, at frequencies f = 1 ... 10 kHz (VLF range) with a screen thickness d = 0.8 mm, the absorption loss for all types of fields is 1 ... 10 dB, and the reflection loss of the magnetic field is 30 ... 60 dB. It can be noted that the dependences of the magnitude of the reflection loss (R) of the magnetic field on the frequency in the frequency range of 1.0 ... 100 kHz and the magnetic permeability of the screen in the range μ = 1 ... 1000 are rather uncertain and reliably rely on experimental data.

In (9, p. 150), on the basis of experimental studies, it was shown that with full screening of magnetic ferrite antennas with metal (duralumin sheets 0.8 ... 1.0 mm thick) at a frequency of 7 kHz, the output voltage of the antennas decreases by 1, 4 times (3 dB). In accordance with formula (4), the effect of screening at lower frequencies will decrease. Such losses can be easily compensated (if necessary) by a corresponding increase in the current in the magnetic field driver, since it is known that the magnetic field is proportional to the current.

Figure 1 shows a diagram of a very low frequency EH field simulator in embodiment (1) containing two flat lines, the outer flat line being short-circuited and forming a magnetic (H) field, and the inner flat line open and forming an electric (E) field; figure 2 shows a diagram of a simulator of the EN field of very low frequencies in option (2), including an open flat line that forms an electric (E) field, and a system of 3 Helmholtz rings, which forms a magnetic (H) field; figure 3 shows a block diagram of a simulator of an electromagnetic (EH) field of very low frequencies.

In FIG. 1 ... 3 are indicated:

1 - bottom plate common for flat lines forming an electric (E) field and a magnetic (H) field;

2 - the upper plate of the inner flat line forming the electric (E) field;

3 - the upper plate of the outer flat line forming a magnetic (H) field;

4 - electrical insulating gasket (textolite, plastic or plywood);

5 - short circuit wires of the plates of an external flat line forming a magnetic (H) field;

6 - electrical connection (contact);

7 - signal generator;

8 - block mating E - and H-dividers;

9, 10, 11 - three identical Helmholtz rings;

12 - shaper of the electric (E) field (open internal flat line forming the electric (E) field);

13 - shaper of magnetic (H) field (short-circuited external flat line or Helmholtz ring system).

In the first embodiment, the output of the mating E-divider (8E) is connected to the upper plate (2) of the flat line of the electric (E) field former (12), the output of the mating H-divider (8H) is connected to the upper plate (3) of the magnetic (H) former fields (13), inputs of matching dividers (8E) and (8H) are connected to the “0” output of the signal generator (7 “0”), a common plate (1) of flat lines is connected to the outputs “0” of the signal generator (7 “0” ) and matching divisors (8 “0”).

In the second embodiment, the output of the mating E-divider (8E) is connected to the upper plate (2) of the flat line of the electric (E) field driver (12), the output of the mating H-divider (8H) is connected to the input (13) of the Helmholtz ring system (9, 10, 11), the inputs of the matching dividers (8E) and (8H) are connected to the output of the signal generator (7), the lower plate (1) of the flat line of the electric (E) field driver (12 “0”) is connected to the outputs “0” of the rings (9, 10, 11) Helmholtz (13 “0”), with the output “0” of the signal generator (7 “0”) and matching dividers (8 “0”).

For operation, the studied antenna is placed in the center of the space between the common plate and the upper plate of the internal flat line forming an electric (E) field. By changing the controlled angle of the studied antenna and measuring the voltage at its output at each fixed angle, determine the radiation pattern. The angle of the position of the antenna under study is controlled by any available method, for example, mechanically using an arrow fixed to the antenna and a scale fixed to a flat line plate, or optical.

To perform the inventive device can be used devices, materials manufactured by domestic industry.

содержится 90% всей энергии сигнала прямоугольной формы ([10], стр.57). Для согласующих делителей можно использовать как омические, так и емкостные сопротивления. Плоские линии будут жесткими и легкими, если для них использовать дюралевые листы толщиной 0,5...1 мм. Кольца Гельмгольца лучше изготовить не из металлического прутка или трубки, а из радиочастотного кабеля [6], так как это исключит влияние на результаты измерения окружающих предметов и внешних помех.As a signal generator, an audio frequency generator, for example, type G3-35, can be used. If necessary, when working on the spectrum of signals, you can use a pulse generator, the pulse duration τ must be consistent with the desired spectrum, given that in the band

contains 90% of the total energy of a square wave signal ([10], p. 57). For matching dividers, you can use both ohmic and capacitive resistances. Flat lines will be hard and light if you use duralumin sheets with a thickness of 0.5 ... 1 mm for them. Helmholtz rings are best made not from a metal rod or tube, but from a radio-frequency cable [6], as this will exclude the influence of surrounding objects and external noise on the measurement results.

The use of the proposed simulator of an electromagnetic (EH) field of very low frequencies or a variant thereof in laboratory or factory conditions during the development, research, testing, industrial production of devices operating using electromagnetic fields in the very low frequency range will allow homogeneous regions to be formed artificially quasistatic electromagnetic fields increase the accuracy and quality of such devices.

List of references

1. Halperin S.M. and others (total 9 names). Lightning direction finder - rangefinder “Hearth-2P”. L .: Gidrometeoizdat, 1988.

2. Fradin A.Z., Ryzhkov E.V. Measurement of the parameters of antenna-feeder devices. M .: Communication, 1972.

3. Kukes I.S. and other Fundamentals of direction finding. M .: Sov. Radio, 1964.

4. Baru N.V., Kononov I.I., Solomonik M.E. Radio direction finders - rangefinders of near thunderstorms. L .: Gidrometeoizdat, 1976.

5. Pashchenko EG On the measurement of loop antennas. - Questions of radio electronics, 1963, ser.XII, issue 10, p. 47-53.

6. Khomich V.I. Ferrite antennas. Measurements in a standard field. M .: Energy, 1969.

7. Gein E.E., Kurgan L.S. Technique for measuring the field strength of radio waves. M .: Communication, 1967.

8. Knyazev A.D. Elements of the theory and practice of ensuring the compatibility of electronic equipment. M .: Radio and communications, 1984.

9. Stepanenko V.D., Halperin S.M. Radio engineering methods for the study of thunderstorms. L .: Gidrometeoizdat, 1983.

10. Gonorovsky I.S. Radio circuits and signals. M .: Sov. Radio, 1971.

Claims (2)

1. A simulator of an electromagnetic field of very low frequencies, containing a flat line consisting of upper and lower metal plates, and a signal generator, characterized in that it is additionally introduced another flat line so that the lower plates of the flat lines are aligned, the upper plates of the flat lines are divided electrically insulating gasket, the upper plate of the outer flat line is short-circuited with the lower common plate from the side opposite to the entrance of the flat lines, the inner flat line is open, the input of the inner The line that forms the electric (E) field is connected to the output of the matching E-divider, the input of the external flat line that forms the magnetic (H) field is connected to the output of the matching H-divider, the inputs of the matching dividers are connected to the output of the signal generator, and the inputs and outputs of circuit elements with zero potential are connected. 2. A simulator of an electromagnetic field of very low frequencies, containing a flat line consisting of upper and lower metal plates, and a signal generator, characterized in that an additional Helmholtz ring system is introduced in such a way that an open flat line is placed inside the Helmholtz ring system, the input is open flat the line forming the electric (E) field is connected to the output of the matching E-divider, the input of the Helmholtz ring system forming the magnetic (H) field is connected to the output of the matching H-divider, the inputs are reads dividers connected to the output of the signal generator and input and output elements with zero potential circuit connected.

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