RU2338179C1 - Uhf method for defining surface moisture of dielectric coatings on metal, and device for implementation of method - Google Patents

Abstract

FIELD: physics, measurement.

SUBSTANCE: method involves placement of examined material in high frequency electromagnetic field and further registration of changing parametres characterising high frequency emission. Expectation function, dispersion and average standard deviation of linear field damping factor by the set of measured linear field damping factors for each discrete surface point, average standard deviation of field damping factor for all scanned surface points is defined and compared to limit deviation values of linear field damping factor. Fractal dimension and surface 'non-reflection' factor are defined. Combined transceiver antenna is mounted in the centre of scanned area, and UHF generator is adjusted at given wavelength. Actual and virtual parts of complex inductive capacity of surface layer are defined by the minimum reflected power and UHF generator wavelength corresponding to that minimum, and surface layer moisture is determined.

EFFECT: enhanced sensitivity and accuracy of measurement.

2 cl; 1 dwg

Description

The present invention relates to methods for determining the moisture content of dielectric coatings on a metal surface, taking into account electrophysical and geometric inhomogeneities of the surface, and can be used to control the composition and properties of hard coatings on metal in the development and operation of radar absorbing materials and coatings, as well as in chemical, paint and varnish and other industries industry.

Known microwave method for determining the moisture content of solid materials / Non-destructive testing and diagnostics: Reference / Under. ed. V.V. Klyueva. - M .: Mashinostroenie, 1995. - 488 pp. /, Based on the principle of measuring the wave characteristics of the reflected electromagnetic wave when measuring material moisture.

The method and the device that implements it have such disadvantages as the lack of an integrated moisture estimate for materials of large thickness; when measuring humidity, it is necessary to take into account multiple reflections from the back surface of the sample, the state and nature of the reflecting surfaces, the large spurious radiation of the microwave signal power, and the complexity the implementation of the method.

Known microwave method for determining the moisture content of solid materials by the Brewster angle / Berliner MA Moisture measurement. - M .: Energy, 1973 /, which consists in finding the angle of incidence, which corresponds to the minimum reflected horizontal-polarized electromagnetic wave from the flat surface of the sample.

The disadvantages of the method and the device that implements it are the dependence of the measurement accuracy on the thickness of the test sample, on the state and nature of the reflecting surfaces, the low accuracy of measurements of large humidity values, the high dispersion of microwave energy and the low accuracy of determining the Brewster angle, the inability to determine inhomogeneities of electrophysical and geometric parameters.

Known microwave method for localizing inhomogeneities in dielectric and magnetodielectric coatings on metal and assessing their relative magnitude / RF Patent No. 2256165, IPC ⁷ G01R 29/08, G01N 15/08; Publ. 07/10/05, Bull. No. 19 /, which consists in creating an electromagnetic field in the volume of a controlled dielectric coating on an electrically conductive substrate and then recording changes in its parameters using a system of receiving vibrators in a normal plane relative to the direction of propagation of the electromagnetic wave within the boundaries of the scanned coating.

The disadvantages of the method are the ability to determine only the properties of the inhomogeneities of the coating, low sensitivity and low accuracy of localization and evaluation of the geometric and electrophysical parameters of the inhomogeneities, the impossibility of determining moisture.

For the prototype, a non-destructive microwave method for controlling the humidity of solid materials and a device for its implementation were selected / RF Patent No. 2269763, IPC ⁷ G01N 9/36, 22/04; Publ. 04/10/06, Bull. No. 4 /, which consists in finding the angle of incidence of the electromagnetic wave, at which the minimum power of the reflected wave from the surface of the studied wet material is observed, and the calculation of the moisture content of the surface layer W _n according to known formulas, by changing the temperature of the local volume of the studied wet material when it absorbes a fixed dose energy of incident EMW, determine the value of humidity W in the volume of the material.

The disadvantages of the method are: low accuracy of measurements of surface humidity W _n due to the imaginary part of the complex dielectric constant of the material, stochastic roughness and electrophysical inhomogeneities of the coating (material) not taken into account, the width of the radiation pattern (BH) of the emitter and the area of the area essential for reflection are not taken into account, as well as the presence of microwave heating and contact with the studied material, low accuracy of measurements of large humidity values, the dependence of the accuracy of measurements of the Brewster angle on nine tion tube frequency microwave generator hardware implementation complexity of the method.

The technical result of the invention is to increase the sensitivity and improve the accuracy of measuring the moisture content of the surface layer W _{n of the} dielectric coating by taking into account the imaginary part of the complex dielectric constant of the surface layer, the emitter bottom width, the electrophysical inhomogeneities of the coating and its surface roughness.

This result is achieved by the fact that in the microwave method for determining the surface humidity of dielectric coatings on metal, which consists in placing the test material in a high-frequency electromagnetic field with subsequent recording of changes in the parameters characterizing the high-frequency radiation, based on a set of measured values of the normal field attenuation coefficients at each discrete point on the surface calculate the mean, variance and standard deviation of the coefficient of normal attenuation I field, determine the average standard deviation value field attenuation coefficient at all points of scanning the surface σ _αcp and compared with threshold ratio deviations of the normal field attenuation Δα _por.i where i∈ [1, ..., N] - number of predefined discrete values Δα _then :

Δα _cpi = | σ _αavg -Δα _por.i |;

determine the fractal dimension:

D _f = tgα,

where α is the slope of the dependence Δα _cpi = f (Δα _por.i )

and the coefficient of non-mirroring of the surface:

K _NC = 3-D _f ;

и мнимую

части комплексной диэлектрической проницаемости поверхностного слоя из уравнений:install the combined receiving-emitting antenna in the center of the scanning area and rebuild the microwave generator at a wavelength of λ _g = 0.45 cm, the minimum reflected power P _{ex min} and the wavelength of the microwave generator λ _{g min} corresponding to this minimum, calculate the actual

and imaginary

parts of the complex dielectric constant of the surface layer from the equations:

where C is the coefficient of proportionality;

determine the average humidity of the surface layer W _n by solving the system of equations:

- дисперсионно-температурная зависимость действительной части диэлектрической проницаемости свободной воды:Where

- the dispersion-temperature dependence of the real part of the dielectric constant of free water:

- дисперсионно-температурная зависимость мнимой части диэлектрической проницаемости свободной воды:

- dispersion-temperature dependence of the imaginary part of the dielectric constant of free water:

ε _in - dielectric constant of the "dry" material:

₀ where ε - dielectric constant of dehydrated building material, ε _{communication} - the permittivity of bound water (4,5-5,8) is invariant under change in wavelength λ of the generator _g and the temperature t ° C, t - temperature of the material or environment material, ° C , W _{St. in} = 0.05 - a constant volumetric moisture content of bound water.

A device that implements this method includes a microwave semiconductor generator with a control device, a diode switch controlled by a microprocessor device (MPU), to the first output of the diode switch, through Y - circulator with matched load, the horn receiving-emitting part of the combined antenna with a feed current absorber is connected and an aperture angle providing satisfactory coordination with free space to the second output of the diode switch, through the second Y - a circulator with combined load, the second part of the antenna is connected in the form of a spiral waveguide-slot antenna with absorbing (matched) load, a receiving vibrator unit with a switching and magnetizing unit controlled by MPU, a receiving probe for measuring the power of the reflected wave and a device for measuring the ambient temperature, the AFC unit the search for the minimum power of the reflected wave associated with the MPU and the control device of the microwave generator.

The implementation of the method is illustrated using the device depicted in the drawing, containing a microwave diode generator - 1, a control unit; MPU - 3, AFC unit for finding the minimum power of the reflected wave - 4, switching and magnetizing unit 5 of the receiving vibrator line of the receiving vibrator unit 6, combined receiving and emitting antenna - 7, two Y - circulators 8 and 9, diode switch - 10, receiving a probe for measuring the power of the reflected wave P _omp - 11, a device for measuring the ambient temperature (for example, a thermocouple, thermistor, thermometer) - 12.

The combined receiving and emitting antenna 7 consists of a circular in-phase receiving and transmitting horn antenna 13 with an aperture angle that provides satisfactory coordination with free space, the feed current absorber 14, the spiral waveguide-slot antenna 15 with the absorbing (matched) load 16.

The device operates in two modes, the first mode is the mode of determining, evaluating the electrophysical and geometric (topological) inhomogeneities of the dielectric coating and determining the coefficient of non- _{mirroring of the} surface. The second mode of operation is the determination of material moisture on a metal surface, taking into account fractal heterogeneity.

Transfer the device to the first mode of operation. Using a circular in-phase receiving and transmitting horn antenna 13, fed by the UHF through a diode switch 10 and a waveguide Y-circulator 9, a slow surface E-wave with a wavelength of λ _g = 2 ÷ 3 cm is excited along the magnetodielectric coating 17 with unknown electrophysical parameters and thickness coatings b. Using the receiving vibrators of block 6, controlled by the MPU 3 through the switching and magnetizing unit 5, the surface of the coating is scanned at the given boundaries ΔS and the set of values of the normal field attenuation coefficient α _j is determined at each measurement point, where j∈ [1, ..., n-1] is the number of measurements along the normal to the surface (along the Y axis) / RF Patent No. 2256165, IPC ⁷ G01R 29/08, G01N 15/08; Publ. 07/10/05, Bull. No. 19 /. In MPU 3, the coordinates of the scanning points and the corresponding values of α _j at each point are stored.

:The obtained values of α _j at each discrete point on the surface determine the mathematical expectation

:

как функцию геометрических и электрофизических параметров неоднородностей:and attenuation coefficient dispersion

as a function of geometric and electrophysical parameters of inhomogeneities:

и определяется его среднее значение по всей площади сканирования. Сравнивают получившееся значение σ_αср с пороговыми значениями отклонения коэффициента затухания поля Δα_пор.i, где i∈[1,..., N] - количество предварительно заданных дискретных значений Δα_пор:The standard deviation of the field attenuation coefficient is calculated

and its average value over the entire scanning area is determined. Compare the resulting value of σ _αav with threshold values of the deviation of the field attenuation coefficient Δα _por.i , where i∈ [1, ..., N] is the number of predefined discrete values of Δα _pore :

Δα _cpi = | σ _αcp -Δα _por.i |.

Is determined by least squares dependence Δα _cpi = f (Δα _por.i) as a linear function y = k · x + b, wherein a tangent angle of inclination is the fractal dimension:

D _f = tgα.

Next, determine the coefficient of non-mirroring of the scanned surface:

K _ns = 3-D _f .

Transfer the measuring device to the second mode of operation. Install the combined receiving-emitting antenna in the center of the scanning area. The microwave generator 1 is tuned to a wavelength of λ _g = 0.45 cm. The electromagnetic wave through a MPU 3 diode switch 10 and the second waveguide Y-circulator 8 is fed to a spiral alternating-phase multi-slot antenna 15, the angle of inclination of the maximum of the beam θ _{gl of} which depends on the length waves λ _{g of} exciting microwave oscillations.

Changing the wavelength λ _{g of} the microwave diode generator using the control unit of the UHF 2 associated with the MPU 3 and the AFC unit 4, the angle of inclination of the radiation emitting antenna / antenna and the microwave device is changed. Calculation and design of antenna arrays and their radiating elements. Ed. D.I. Voskresensky. - M .: Owls. Radio, 1972 / and achieve the minimum power of the reflected wave in the receiving part 13 of the complex antenna 7. The angle of inclination of the maximum of the beam θ _T (λ _g ) of the emitting antenna, at which the effect of maximum absorption of the incident electromagnetic wave is observed, will be equal to the Brewster angle θ _Br .

The minimum power of the reflected wave P _{omp min is} proportional to the minimum of the Q _min criterion for the field strength of the reflected wave in the angular spectrum of the radiation path, that is, in the zone essential when reflecting along the maximum of the radiation path. The expression for the criterion Q _min for 2≤ε'≤10, 0≤ε''≤1 has the form:

where C is the coefficient of proportionality, A = R (Δθ, ε ', ε' ') is the reflection coefficient:

B = F (λ _g , Δθ) is the type of bottom hole emitter:

θ _T (λ _g ) is the current angle of inclination of the beam, is determined by the expression

Δθ - integration variable across the width of the beam, varies within

θ _T (λ _{g min} ) -Δθ _0.5 (λ _{g min} ) ≤Δθ≤θ _t (λ _{g min} ) + Δθ _0.5 (λ _{g min} ),

численно он равен 50,82,θ ₀ is the initial angle of inclination of the beam

numerically it is 50.82,

и

- действительная и мнимая части комплексной диэлектрической проницаемости поверхностного слоя,

and

- the real and imaginary parts of the complex dielectric constant of the surface layer,

Δθ _0.5 (λ _g ) - beam width:

где

Where

a = 0.00355 [m] is the size of the wide wall of the waveguide, d = 0.003 [m] is the length of the radiating slit, N = 7 is the number of slots in the antenna, λ _g = 0.0045 ... 0.0065 [m] - tuning range of the wavelength of the generator, λ _gn = 0.0045 [m] is the initial wavelength of the generator.

The approximated expression of the minimum criterion of reflected power will have the form:

и

имеет вид:The approximated dependence of λ _{g min} on

and

has the form:

показывает инвариантность λ_{г мин}

от вариации

и для приблизительных расчетов можно использовать формулу:Mathematical modeling of the dependence of λ _{g min}

shows the invariance of λ _{g min}

from variation

and for approximate calculations, you can use the formula:

The moisture value of the surface layer is determined through the imaginary parts of the dielectric constant of the surface layer and free water:

- дисперсионно-температурная зависимость мнимой части диэлектрической проницаемости свободной воды:Where

- dispersion-temperature dependence of the imaginary part of the dielectric constant of free water:

In addition, the moisture of the surface layer can also be determined through the real parts of the dielectric permittivities of the surface layer and free water / microwave thermal moisture measurement. / P.A. Fedyunin, D.A. Dmitriev, A.A. Vorobyov, V.N. Chernyshev. - M.: Mechanical Engineering - 1, 2004. - p.230 /:

- дисперсионно-температурная зависимость действительной части диэлектрической проницаемости свободной воды:Where

- the dispersion-temperature dependence of the real part of the dielectric constant of free water:

ε _in - the dielectric constant of the "dry" (with bound moisture) material, determined by the generalized Reynolds and Hugh formula:

₀ where ε - dielectric constant of dehydrated building material, ε _{communication} - the permittivity of bound water (4,5-5,8) is invariant under change in wavelength λ of the generator _g and the temperature t ° C, t - temperature of the material or environment material, ° C , W _{St. in} = 0.05 - a constant volumetric moisture content of bound water.

и мнимую

части комплексной диэлектрической проницаемости поверхностного слоя из уравнений (1) и (2) и, решая (3) и (4), определяют среднее значение влажности поверхностного слоя W_n:Calculate Valid

and imaginary

parts of the complex dielectric constant of the surface layer from equations (1) and (2) and, solving (3) and (4), determine the average humidity of the surface layer W _n :

The technical and economic effect of the invention is to increase the sensitivity and improve the accuracy of measuring the moisture content of the surface layer W _{n of the} dielectric coating by taking into account the imaginary part of the complex dielectric constant of the surface layer, the emitter bottom width, the electrophysical inhomogeneities of the coating, and its surface roughness.

As a result, the error in measuring surface humidity decreases no less than 2.5 times on the basis of experimental studies on samples with known humidity (from 10% in the prototype to 4% in the proposed method).

Claims (2)

1. The microwave method for determining the surface humidity of dielectric coatings on metal, which consists in placing the material under study in a high-frequency electromagnetic field, followed by recording changes in the parameters characterizing the high-frequency radiation, characterized in that the set of measured values of the normal field attenuation coefficients at each discrete point on the surface is calculated expectation, variance and standard deviation of the normal field attenuation coefficient, determine t average value of the standard deviation of the field attenuation coefficient σ _αav over all points of the scanning surface and compare with threshold deviations of the normal field attenuation coefficient Δα _por.i , where i∈ [1, ..., N] is the number of predefined discrete values Δα _pore : Δα _cp.i = | σ _αavg -Δα _nop.i |; determine the fractal dimension: D _f = tgα, where α is the angle of inclination of the dependence Δα _cp.i = f (Δα _por.i ), and the coefficient of non-mirroring of the surface: K _ns = 3-D _f ; install a combined receiving-emitting antenna in the center of the scanning area and rebuild the microwave generator at a wavelength of λ _g = 0.45 cm, the reflected power P _neg at the minimum _{. min} and the wavelength of the microwave generator λ _{g min} corresponding to this minimum, calculate the actual

and imaginary

parts of the complex dielectric constant of the surface layer from the equations:

where C is the coefficient of proportionality; determine the average humidity of the surface layer W _n by solving the system of equations:

and

Where

- the dispersion-temperature dependence of the real part of the dielectric constant of free water:

- dispersion-temperature dependence of the imaginary part of the dielectric constant of free water:

ε _in - dielectric constant of the "dry" material: ε _in = ε ₀ + ε ₀ W _{St. in} (ε _St. -ε ₀ ) [ε ₀ +0.33 (ε _St.- ε ₀ )] ^-1 , where ε ₀ is the dielectric constant of the dehydrated building material, ε _sv - dielectric constant of bound water (4.5-5.8) is invariant to a change in the wavelength of the generator λ _g and temperature t ° C, t is the temperature of the material or the environment surrounding the material, ° C, W _{St. in} = 0.05 - a constant volumetric moisture content of bound water. 2. The device that implements the method according to claim 1, containing a semiconductor microwave generator with a control device, characterized in that it contains a diode switch controlled by a microprocessor device, a horn receiving-emitting part of the combined connected to the first output of the diode switch through a Y-circulator with matched load antennas with a leakage current absorber and an aperture angle that provides satisfactory coordination with free space to the second output of the diode switch through The second Y - circulator with matched load connects the second part of the antenna in the form of a spiral waveguide-slot antenna with absorbing (matched) load, a block of receiving vibrators with a switching and magnetizing unit controlled by a microprocessor device, a receiving probe for measuring the power of the reflected wave and a device for measuring ambient temperature medium, AFC unit for finding the minimum power of the reflected wave, coupled with a microprocessor device and a control device of the microwave generator.