# Method of measuring length, thickness and dielectric constant of dielectric coating on metal surface

FIELD: measurement technology.

SUBSTANCE: microwave electromagnetic fields of running surface slow E-waves and E1 and E2 at two wavelengths λ_{osc1} and λ_{osc2} of oscillator being close in value above dielectric-metal surface at single-mode regime. Damping factors α_{e1} and α_{e2} of electric field strength are measured at normal plane relatively direction of propagation of slow surface of wave. Real value of dielectric constant and thickness of coating are calculated. Taking measured values of damping factors into account, values of deceleration are calculated for those wavelengths by relation of Directional pattern maximum angle of inclination θ_{dp max(fz)}=θ_{e1(e2)} is measured at far zone by means of vertically oriented receiving vibrator. Length of dielectric coating l_{e1} and l_{e2} is determined from relation of l_{e1(e2)}=0.552·λ_{osc e1(e2)}/(ν_{df e1(e2)}-cosθ_{e1(e2)} and its value l=(l_{e1}+l_{e2})/2 is subject to averaging.

EFFECT: improved precision of measurement of longitudinal sizes of dielectric coating.

1 dwg

The present invention relates to methods of measurement of electro-physical and geometric parameters of the dielectric coating on the metal substrate and can be used to control the structure and properties of liquid and solid coatings in chemical and other industries.

The known method of determining the thickness of the dielectric coating of ferromagnetic material, on the basis of ponderomotive principle (see, for example, Devices for non-destructive testing of materials and products. The guide below. edit VLA. - 2nd ed., revised and enlarged extra - M.: Mashinostroenie, 1986/.

This method has the following disadvantages: low speed scanning of large surfaces, low sensitivity to the change of permittivity and permeability, as well as the inability to determine the length of the cover.

There is a method of determining the thickness of a dielectric coating on a conductive based /see Devices for non-destructive testing of materials and products. The guide below. edit VLA. - 2nd ed., revised and enlarged extra - M.: Mashinostroenie, 1986. S-125/, consisting in the creation of eddy currents in the conductive substrate and the subsequent registration of a comprehensive stressor resistanceeddy current pre is brazaletes as a function of the conductivity of the substrate and the gap between the transducer and the substrate.

The disadvantages of this method are: the dependence of the accuracy of measurement of the thickness of the coating from the gap between the transducer and the substrate, the inability to measure the permittivity and permeability of the coating, as well as its length, a high sensitivity to changes in the parameters of the substrate (conductivity and permeability) and the low speed scanning of large surfaces.

Famous adopted for the prototype microwave method for determination of dielectric constant and thickness of the dielectric coatings on metal /see Suslin M.A. Dmitriev, D.A. and others, "a microwave method for determining the dielectric constant and thickness of coatings on metal". Patent No. 2193184, CL G 01 N 15/00, from 20.11.02, Bulletin No. 32/introducing microwave electromagnetic field running surface slow S waves at two close-largest lengths λ_{G1}that λ_{T2}excited generator, waves over the surface of the insulator-metal single-mode, measurement of attenuation coefficients of the electric field strength α_{E1}that α_{E2}in a normal plane relative to the distribution of slow surface waves and calculating the dielectric constant ε and the thickness of the coating b by the formulas:

N the prosperity of this method is the impossibility of determining the longitudinal dimensions of the dielectric coating.

The technical result of the invention is to improve the accuracy of determining the longitudinal dimensions of the dielectric coating.

The essence of the invention lies in the fact that the microwave method for measuring length, thickness and dielectric constant of the dielectric coating on the metal surface, which consists in the successive creation of microwave electromagnetic fields of the running surface of the slow S-waves E1 and E2 on two close-largest wavelengths generator λ_{G1}that λ_{T2}above the surface of the insulator-metal single-mode regime, the dimension in the normal plane relative to the distribution of the slow surface wave attenuation coefficients α_{E1}and α_{E2}the strength of the electric field and the calculation of the actual dielectric constant and the thickness of the coating; on the measured values of attenuation coefficients calculated values of the coefficients slow for these wavelengths by the formula;

measure the far field using a vertically oriented receiving vibrator angle of maximum beam θ_{Mahdi(DZ)}=θ_{E1(E2)}; define the length of the dielectric coating l_{E1}and l_{E2}by the formula

and its average l=(l_{
E1}+l_{E2})/2.

Microwave method for measuring length, thickness and dielectric constant of the dielectric coating on the metal is illustrated is as follows (see drawing).

The device slow excitation of surface waves (mouthpiece) 1 along the dielectric coating 3 (μ=1) on a conductive metal substrate 2 sequentially excite the slow surface E-wave single mode on a different, but similar wavelengths λ_{G1}that λ_{T2}so that the product of the coefficient of the phase wave β_{E}the thickness of the coating b to satisfy the condition: β_{E1}b≪π/2.

Using system vertically oriented receiving vibrators B1 and B2 at the starting point (X_{0},Z_{0}on the middle of the cover (tape) along the line of maximum NAM near dielectric coatings measured attenuation coefficients α_{E1}and α_{E2}the electric field intensity E(X_{0},Z_{0}in a normal plane relative to the direction of propagation of the slow surface S-wave.

Condition for the neglect of the influence of geometrical and electrical gradients investigated layer is the measurement with a small base d between the receiving vibrators (see drawing) and at low altitude y_{0}.

Decide transcendent equation:

Provided

and β_{E}b≪π/2

the solution of the transcendent equation (1) and (2) is written as a system of arithmetic equations:

Thus, the measured values of the attenuation coefficients of the field surface slow E-waves determine the dielectric constant (real part) and the thickness of the dielectric coating (tape) on its middle.

On the measured values of attenuation coefficients and wavelengths of the generator, which is excited by a slow surface E-wave, determine the coefficients of a slowdown for these wavelengths generator:

The angle of inclination of the maximum beam θ_{Mahdi(DZ)}=θ_{E1(E2)}excitation of the horn in the far zone (l_{RS}=const≫λ_{G1(G2)}), indicated by the maximum value of current (the maximum of the electric field) vertically oriented receiving vibrator B3 (see the drawing), is determined by the formula:

where_{mage,E2}- the maximum distance from the receiving vibrator B3 normal to the horizontal plane of the surface of the dielectric pok is itia.

As part of the admissions instead of vertically oriented vibrator you can use the horn aperture - receiving mouthpiece 4 (see drawing). In this case, the angle of the maximum of DN will correspond to the angle of the receiving horn 4, recorded at the maximum of the electric field in it.

The expression for DN in RS for the antenna system of surface waves, provided l=varia and b=varia, is:

and ν=f_{1}(b,ε), and θ_{Mahdi(DZ)}=θ=f_{2}(ν_{C},l) / see, for example, Lavrov A.S., Reznikov GV Antenna-feeder devices - Kiev: QUIAPO air force, 1969, s/.

When the search condition of the maximum of the first petal DN,

and,

then the maximum angle of inclination of the NAM θ_{Mahdi(DZ)}=θcorresponding to the position of the maximum of DN, is determined from the conditions [F(θ)]'=0, where

Approximately we can assume that

and solving equation (8) subject to (9) with respect to cosθget:

since 0≤cosθ≤1 a ν_{3}always greater than one, then:

Consider two cases: quasi-optical and quasi-stationary.

a) Quasi - . In this case, the expression (10) takes the formor

on the basis of which the measured and calculated values ν_{3}and θ(cosθ) determining the magnitude of the l - length of the dielectric coating (tape). Note that when increasing the length of the dielectric tape l and deceleration rate ν_{C}value θ decreases. In this case, the angle θ close to zero.

b) Quasi-steady -

In this case, considering the fact that

,

where

expression (10) takes the form

where found:

From the expression (12) shows that when increasing the length of the dielectric coating (tape) l and deceleration rate ν_{C}value θ decreases. In this case, the angle θ seeks π/2, which confirms the adequacy of the considered method.

Of the two cases from the point of view of feasibility of the measurement of the parameters of the coating is applied quasi-optical case in which l≫λ_{G}.

On the measured values θ_{1(2)}and ν_{SE(E2)}determine the length of the dielectric coating (tape) l_{E1}and l_{E2}by the formula (11)and average the value l=(l_{
E1}+l_{E2})/2.

Thus, the proposed microwave method for measuring length, thickness and dielectric constant of the dielectric coating on the metal surface improves the accuracy of determining the longitudinal dimensions of the dielectric coating.

Microwave method for measuring length, thickness and dielectric constant of the dielectric coating on the metal surface, which consists in the successive creation of microwave electromagnetic fields of the running surface of the slow S-waves and E1 and E2 two close-largest wavelengths generator λ_{G1}that λ_{T2}above the surface of the insulator - metal single-mode regime, the dimension in the normal plane relative to the distribution of the slow surface wave attenuation coefficients α_{E1}and α_{E2}the strength of the electric field and the calculation of the actual dielectric constant and the thickness of the coating, characterized in that the measured values of attenuation coefficients calculated values of the coefficients slow for these wavelengths by the formula

measure the far field using a vertically oriented receiving vibrator angle of maximum beam θ_{Mahdi(DZ)}=θ_{E1(E)}
; define the length of the dielectric coating l_{E1}and l_{E2}by the formula

and his average is l=(l_{E1}+l_{E2})/2.

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