Super-high frequency method of measurement of dielectric permeability and thickness of dielectric plates

FIELD: MEASUREMENT TECHNOLOGY.

SUBSTANCE: electromagnet wave is induced by means of directed aerial. The wave is incident to dielectric plate. Brusterain angle of incident wave is defined from minimum value of reflected wave and value of dielectric permeability is calculated. Power of incident and reflected waves are measured and the value of reflectivity and specific conductivity are calculated as well as value of dielectric loss of dielectric plate. Then incident angle of electromagnet wave is increased till achieving value providing total internal reflection of electromagnet wave and attenuation of intensity is measured at normal plane relatively direction of wave propagation. Factors of normal attenuation and thickness of dielectric plate are calculated. Method allows to find complex dielectric permeability and thickness of dielectric plates free of dielectric substrates.

EFFECT: improved reliability.

1 dwg

 

The invention relates to a method of measuring the dielectric constant and thickness of the dielectric plates and can be used for control and regulation of the composition and properties of materials during their manufacture and operation.

The known method of determining the thickness of the coating of ferromagnetic material, on the basis of ponderomotive principle (see Instruments for non-destructive testing of materials and products. The guide below. edit VLA. - 2nd ed., revised and enlarged extra - M.: Mashinostroenie, 1986, p.58).

This method has the following disadvantages: does not allow for fast scanning of large surfaces and insensitive to changes in the dielectric constant.

There is a method of determining the thickness of a dielectric coating on a conductive base (refer to the 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), which consists in the creation of eddy currents in the conductive substrate and the subsequent registration of a comprehensive stressor resistanceeddy current probe as a function of the conductivity of the substrate and the gap between the transducer and the substrate.

Flaws on the frame of the method are the availability of the metal substrate that entails 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 dielectric permittivity of the cover or plate, high sensitivity to changes in parameters of the substrate (conductivity and permeability) and the low speed scanning of large surfaces.

Famous adopted for the prototype, the method of determining the dielectric constant dielectric materials or materials with small losses (see Brandt A.A. Investigation of dielectrics at microwave. - M.: YFML, 1963, s-294), based on the measurement of the Brewster angle. The ratio of the power detected by the receiver after reflection from the sample, to the power that is logged when replacing the sample ideally reflecting surface, allows you to find the reflection coefficient of the power. Measured this way, the reflection coefficient of the power at various angles of incidence allows you to calculate the real and imaginary parts of the dielectric constant.

The disadvantage of this method is the low accuracy of the measurement of the permittivity, the presence of the metal substrate and the inability to determine the thickness of the coating.

The technical result of the invention is to improve the accuracy of determination of the complex dielectric is eskay permeability and thickness of the dielectric plates in the absence of the metal substrate.

The essence of the invention lies in the fact that the microwave method for determining complex permittivity and thickness of the dielectric plates, including the location of the dielectric plate in a high-frequency electromagnetic field and the subsequent registration of changes of parameters characterizing high-frequency radiation through the device excitation, representing a directional antenna (horn), excite E-wave incident on a dielectric plate; no field of the reflected wave or at least determine the Brewster angle of the incident wavecalculate the value of dielectric permeability ε'

measuring the power of incident and reflected waves, determine the magnitude of the reflection coefficient

and I hope conductivity

and the value of the dielectric loss of the dielectric plate (imaginary part of the permittivity) ε"

increase the angle of incidence of the electromagnetic wave to a value that provides total internal reflection of electromagnetic waves to measure the attenuation of the field strength in the normal plane relative to the direction of wave propagation, R is schityvat the coefficients of the normal attenuation α Efrom the expression E(y)=E0exp[-α(y)·y] and the thickness of the dielectric plate

The essence of the proposed microwave method for determining the complex permittivity and thickness of the dielectric plates is illustrated in the following. Using the device of excitation of electromagnetic waves 1 (see drawing), which are external horn antenna, excite incident on the dielectric plate 2 electromagnetic wave with vertical polarization - S-wave where the electric field vector E lies in the plane of incidence of the electromagnetic wave.

Changing the angle of incidence of the electromagnetic wave mechanical swing emitter or e-change the position of maximum NAM, determine the Brewster angle of the incident wave. Indication of the Brewster angle is carried out by measuring the minimum power reflection or indication of change of the polarisation state 3. The definition of the Brewster angle is possible in two ways.

a) Indication of the absence of the field reflected wave if the coating is a dielectric, i.e. γ=0, or search for its minimum when the coating has losses (γ≠0) and the reflected wave does not disappear completely, and passes through a minimum at an angle of incidence of the electromagnetic wave, is equal to the Brewster angle.

<> b) the Second method is based on the phenomenon of polarization of the reflected wave is observed at an angle of Brewster. If the incident wave has a rotating polarization (elliptical in the General case), the indication of the Brewster angle occurs at the time when the reflected wave will have parallel linear polarization. Full polarization of the reflected wave is absent for waves with H-polarization, where the vector E is perpendicular to the plane of incidence of the electromagnetic wave.

According to Markov G.T., Petrov BM, Gruzinskoi G.P. (Electrodynamics and wave propagation. - M.: Owls. Radio, 1979, s-240) full angle of refraction for E-will - Brewster angle in a first approximation for environments lossless (γ=0) is determined by the

This allows (see Brandt A.A. Investigation of dielectrics at microwave. - M.: YFML, 1963, s-294) measured the Brewster angle to determine the value of the dielectric constant ε' by the formula

The value of permeability is determined from (2) for the dielectric plates with losses corresponding to the tgδ≤0,2, has an error of not more than 2%.

A measure of the magnitude of the losses of the dielectric layer, i.e. the values ε″, is the minimum value of the reflection coefficient at an angle of incidence of the electromagnetic wave θ0that is aunoma the Brewster angle. The reflection coefficient at γ>0 is not equal to zero and greater, the greater the value of γ or ε″ (see Markov G.T., Petrov BM, Grodinsky G.P. Electrodynamics and wave propagation. - M.: Owls. Radio, 1979, s-240).

Measuring with 3 power reflected wave RRefand knowing the power of the incident wave, Rpaddefined value εor γ. In the first approximation

or

Let the measured value=αthen

where k1, k2, k3, k4the coefficients of proportionality.

From the second law of Snell's law, given thatand μ’=1, it follows

where

When the value of the magnetic permeability

The module of the reflection coefficient (its minimum value)

Considering the fact that

whereand

get the

Despite the loss, the dielectric parameters satisfy oraut condition

then

Given that,;andby some mathematical transformations finally get theWhere the resulting formulas conductivity

where λG- wavelength generator

and value of the dielectric loss of the dielectric plate (imaginary part of the permittivity) ε"

Thus, values γ or ε" are calculated at a known wavelength generator λGthe measured reflection coefficientand the previously calculated value of the Brewster angle size ε’.

This inside layer is absent slow surface wave, i.e. θCRis always smaller than the angle of total internal reflection, i.e

sinθCR=sinθPoort-1/2.

According to the obtained values ε' and ε″ counti.e. the module

and the argument

Increase the angle θ0dailychina, knowingly providing total internal reflection, i.e. whenIt has been recorded on top of the wave, in contrast to the slow wave, the resulting “fast” waves at small values of gradient dielectric constant or the thickness of the dielectric plate, and when the radius of curvature of the plate is much greater than the length of the wave generator.

With the help of the device measuring the coefficient of the normal attenuation αE- 4 measure the attenuation of the field strength of an electromagnetic wave in the normal plane relative to the direction of wave propagation and calculate the coefficients of the normal attenuation αEfrom the expression

E(y)=E0exp[-α(y)·y]

where E(y) - field intensity of the wave at a distance y from the dielectric plate in a normal plane relative to the direction of propagation of surface waves (see drawing);

E0the field strength of the wave, measured foster vibrator at distance0from the dielectric plate in the normal plane (see drawing);

α(y)=αEthe normal coefficient of attenuation of the wave field on the distance from the dielectric plate;

the distance from the surface of the dielectric plate to the receiving vibrator.

In a microprocessor-based device 5 count t is Lino dielectric plate from the formula

Thus, the proposed microwave method for determining complex permittivity and thickness of the dielectric plates allows to determine the complex dielectric permittivity of the dielectric plates and their thickness, and to determine the conductivity.

Because in this way there is no metal backing and there is a mode of traveling waves, and measuring the relative and does not depend on the distance of the vibrators to the surface that does not require special measures the detuning from the gap, increases the accuracy of measurements and there is the ability to quickly scan the surface without moving the pathogen surface waves.

Microwave method for determining complex permittivity and thickness of the dielectric plates, including the location of the dielectric plate in a high-frequency electromagnetic field and the subsequent registration of changes of parameters characterizing high-frequency radiation, characterized in that the device excitation, representing a directional antenna (horn), excite E-wave incident on a dielectric plate, in the absence of the field reflected wave or at least determine the Brewster angle of the incident wavecalculate the value of IER is ectrically permeability ε ':

measuring the power of incident and reflected waves, determine the magnitude of the reflection coefficientand I hope conductivity

and the value of the dielectric loss of the dielectric plate (imaginary part of the permittivity) ε"

increase the angle of incidence of the electromagnetic wave to a value that provides total internal reflection of electromagnetic waves to measure the attenuation of the field strength in the normal plane relative to the direction of wave propagation, calculate the coefficients of the normal attenuation αEand the thickness of the dielectric plate:



 

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