RU2575468C1 - Device to define complex capacitivity of materials - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device comprises a section of metal waveguide transmission line, plate glass and additional second section of metal waveguide transmission line complete with flanges at both sides and having the same inner cross-section as the first section of metal waveguide transmission line, varactor diode; inner part of the second section of metal waveguide transmission line is filled with dielectric, the plate glass is made of metal and has a window of dimensions equal to dimensions of inner cross-section in the section of metal waveguide transmission line; metal outputs of the varactor diode and plate glass are separated by insulator, plate glass and flange of one end of the section of metal waveguide transmission line are interconnected mechanically, length of the second diction of metal waveguide transmission line is multiple to half length of electromagnetic wave in the second diction of metal waveguide transmission line.

EFFECT: increase in accuracy of complex capacitivity and simultaneous determination of actual and imaginary component of complex capacitivity is provided.

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Description

The invention relates to devices for determining the complex dielectric constant of materials using electromagnetic waves.

A device for determining the complex dielectric constant of materials, operating in the optical wavelength range, comprising means for regulating the current in the power supply circuit and for processing data, connected in series with a digital-to-analog converter, a semiconductor laser power supply, a temperature controller, a semiconductor laser radiation source and an optical tool [1].

The disadvantages of this device:

- a large error (20-30%) in determining the complex dielectric constant of the material,

- the need to use expensive laser and spectral equipment.

A device is known for determining the complex dielectric constant of materials, comprising a segment of a metal waveguide transmission line equipped with flanges at both ends with internal cross-sectional dimensions, in which an electromagnetic wave of a centimeter or millimeter wavelength range, a plane-parallel dielectric plate, propagates in a segment of a metal waveguide transmission line , which is located at one end of a segment of a metal waveguide line, with plane-parallel Ordering of a dielectric plate is in contact with the test material, the other end of the segment of the metal waveguide transmission line for connecting it to a source of electromagnetic waves and electromagnetic reflectance meter wave [2] - prototype.

This device

- improves the accuracy of measurements by matching the waveguide transmission line with the surface of the material using a matching plane-parallel dielectric plate,

- reduces the cost of research due to the use of widespread panoramic meters of the reflection coefficient of the electromagnetic wave of the centimeter or millimeter wavelength range.

The disadvantages of this device:

- to improve the matching of the incident electromagnetic wave with the surface of the materials, the matching dielectric plate must have a multiple of an odd number of a quarter of the length of the electromagnetic wave in the dielectric material of the plate, while the quality factor is reduced, therefore, the reflection coefficient of the electromagnetic wave in terms of power from the surface of the materials does not have a clearly defined minimum , which makes it difficult to determine the frequency corresponding to the minimum value of the electromagnetic reflection coefficient us power, and thereby reduces the accuracy of determination of the complex permittivity of materials

- the dielectric constant of the plate should be chosen so that the optimal matching conditions are met, however, this condition is practically not feasible, since the plate is made of dielectric material with a certain value of dielectric constant, which differs from the optimal value of dielectric constant, which reduces the accuracy of determining the complex dielectric permeability of materials

- the impossibility of determining both the real and imaginary parts of the complex dielectric constant of materials.

The technical result of the invention is

- increasing the accuracy of determining the complex dielectric constant of materials,

- determination of both the real and imaginary parts of the complex dielectric constant of materials,

- low cost of the used measuring equipment.

The specified technical result is achieved by the claimed device for determining the complex dielectric constant of materials containing

a section of a metal waveguide transmission line equipped with flanges at both ends, with dimensions of the internal cross section, in which an electromagnetic wave of a centimeter or millimeter wavelength range propagates in a section of a metal waveguide transmission line,

a plane-parallel plate located at one end of a segment of a metal waveguide line perpendicular to the direction of propagation of the electromagnetic wave in the metal waveguide transmission line,

the other end of the segment of the metal waveguide transmission line is designed to connect it to a source of electromagnetic waves and a meter for the reflection coefficient of the electromagnetic wave.

The device is additionally introduced

a second segment of a metal waveguide transmission line provided with flanges at both ends of the same internal cross section with a first segment of a metal waveguide transmission line,

varactor diode

the inside of the second segment of the metal waveguide transmission line is filled with a dielectric,

a plane-parallel plate is made of metal and is equipped with a window with dimensions equal to the dimensions of the internal cross section of a section of a metal waveguide transmission line,

a varactor diode is turned on in the middle of a wide window wall in a plane-parallel plate,

the metal leads of the varactor diode and the plane-parallel plate are separated by an insulator,

a flange of the other end of the segment of the metal waveguide transmission line, a plane-parallel plate and a flange of one end of the second segment of the metal waveguide transmission line are mechanically connected,

the other end of the second segment of the metal waveguide transmission line is intended for contact with the measured materials,

the length of the second segment of the metal waveguide transmission line is a multiple of half the length of the electromagnetic wave in the second segment of the metal waveguide transmission line with a dielectric.

SUMMARY OF THE INVENTION

The claimed device for determining the complex dielectric constant of materials, its essential features, namely

introducing an additional second segment of the metal waveguide transmission line and the varactor diode, filling the second segment of the waveguide transmission line with a dielectric, making a plane-parallel plate of metal and equipped with a window with dimensions equal to the dimensions of the inner cross section of the segment of the metal waveguide transmission line, turning on the varactor diode in the middle of the wide window wall in a plane-parallel plate, the implementation of the second segment of the waveguide transmission line with a length that is a multiple of half the length of the electric wave in the ferromagnetic metallic second segment of the waveguide transmission line with a dielectric,

each and in their entirety, as well as in conjunction with the known features, as well as in conjunction with the proposed connection of the elements of the device:

1. Due to the fact that

- the second segment of a metal waveguide transmission line filled with a dielectric, on one side of which there is a reflecting wall in the form of a plane-parallel plate made of metal with a varactor diode included in it, and on the other hand, the surface of the measured material is a resonator with reflective walls;

- the length of the second segment of the metal waveguide transmission line L is selected as a multiple of half the length of the electromagnetic wave in the segment of the metal waveguide transmission line with a dielectric (L = m × λv / 2, where λv is the length of the electromagnetic wave in a metal waveguide transmission line with a dielectric, m = 1, 2, 3, ...), therefore, standing waves are established in the resonator;

- electromagnetic processes occurring in the resonator lead to the fact that the resonator is a substantially narrow-band device, namely, at resonant frequencies, the reflection coefficient of the electromagnetic wave in power has a sharp minimum;

- the magnitude of the minimum reflection coefficient of an electromagnetic wave in power and the frequency at which it is achieved, is measured on a panoramic meter of reflection coefficient of electromagnetic waves with high accuracy,

Using narrow-band resonance phenomena, it will maximize the accuracy of determining the complex permittivity of materials.

2. Due to the fact that

- a varactor diode in working condition, that is, when a constant voltage is supplied to its metal terminals from a constant voltage source, is a frequency-dependent reactive conductivity included at the end of the second segment of the metal waveguide transmission line;

- the magnitude of this conductivity significantly affects the magnitude of the reflection coefficient of the electromagnetic wave in power;

- carry out a measurement on a panoramic meter of the reflection coefficient of electromagnetic waves of the three minimum values of the reflection coefficient of the electromagnetic wave in power and the corresponding three frequencies at three values of constant voltage on the varactor diode,

allows you to determine both the real and imaginary parts of the complex dielectric constant of materials.

3. At the same time, as in the prototype, the magnitude of the minimum reflection coefficient of the electromagnetic wave in power and the frequency at which it is achieved, is measured on a panoramic meter of the reflection coefficient of electromagnetic waves, which

ensures the low cost of the equipment used.

Thus, the claimed device will allow, in comparison with the prototype, using narrow-band resonance phenomena and triple measurements of the reflection coefficient of the electromagnetic wave in power and the corresponding resonant frequencies at three voltage values on the varactor diode, significantly increase the accuracy of determining the complex dielectric constant of materials and at the same time determine the real and imaginary parts of the complex dielectric constant of materials while maintaining low cost and used equipment.

The invention is illustrated by drawings.

In FIG. 1 is a drawing of the proposed device for determining the complex dielectric constant of materials in the context, where:

- the first and second segments of a metal waveguide transmission line - 1 and 2, respectively,

- plane-parallel plate of metal - 3, which is equipped

- by the window - 4,

- varactor diode - 5,

- insulator - 6,

- metal leads - 7,

- dielectric - 8,

- studied material - 9.

In FIG. Figure 2 gives a general view of an experimental setup for measuring the complex permittivity of materials:

- panoramic meter of reflection coefficient PNA-LN5230C - 1,

- coaxial cable - 2,

- coaxial waveguide transition - 3,

- the proposed device is 4,

- the studied material - 5.

In FIG. Figure 3 shows the resonance dependences of the reflection coefficient for the device power on the frequency for three voltage values on a varactor diode (curve 1 at U ₁ = 6 V, curve 2 at U ₂ = 8 V, curve 3 at U ₃ = 10 V).

The claimed device (Fig. 1) contains a second segment of a metal waveguide transmission line 2, filled with a dielectric 8, with an internal cross section with the dimensions of the wide side of the wall equal to a, and narrow equal to b, length L, a multiple of half the wavelength in the segment of the metal waveguide lines with a dielectric, and a plane-parallel plate of metal 3, located at the end of the second segment of the metal waveguide line 2.

In a plane-parallel plate of metal 3, a window 4 is made of width a and height b with a varactor diode 5, the metal terminals of which 7 are separated from the metal plate 3 by an insulator 6.

A piece of metal waveguide transmission line 1 at one end is connected via a flange to the waveguide transmission line from an electromagnetic wave source of the centimeter or millimeter wavelength range.

The second segment of the metal waveguide transmission line 2 at one end is brought into contact with the surface of the investigated material 9.

The other ends of the first and second segments of the metal waveguide transmission line and a plane-parallel plate of metal 3 are mechanically interconnected.

The device operates as follows.

A voltage U _k is supplied to the varactor diode from a constant voltage source, which brings the varactor diode to a working state at which its capacitance is

C _k = C ₀ (1 + U _k / φ) ^-0.5 ,

Where

С ₀ - capacitance of a varactor diode at U _k = 0

φ is the contact potential difference of the semiconductor material from which the varactor diode is made (for gallium arsenide φ = 0.7 V) [3].

The reactive relative conductivity of a varactor diode is

Y _k = jb _k (f),

Where

j = (- 1) ^0.5 - imaginary unit,

b _k (f) = 2 πfC _k / Y _B ,

Where

f is the frequency of the electromagnetic wave.

Y _B is the wave conductivity of the segment of the waveguide transmission line 1,

Y _B = {1- [λ / (2 a)] ² } ^0.5 (120 π) ^-1 ,

Where

λ = s / f is the length of the electromagnetic wave,

C is the speed of light in vacuum,

π = 3.1415 ...

When taking measurements on the measuring apparatus shown in FIG. 2, the electromagnetic wave from the panoramic reflection coefficient meter 1 through the coaxial cable 2 and the coaxial waveguide transition 3 enters the claimed device 4, where it interacts with the test material 5.

The electromagnetic wave reflected from the device returns to the panoramic meter, on the screen of which the resonance dependence of the reflection coefficient in power R _k (f) of the device on the frequency f is displayed.

When applying three values of a constant voltage U ₁ , U ₂ , U ₃ to the varactor diode in series, the relative conductivity of the varactor diode will be equal to b ₁ , b ₂ , b _3, respectively, and the reflection coefficient of the device power at the resonant frequency will be equal to R ₁ (f ₁ ), R ₂ (f ₂ ), R ₃ (f ₃ ).

In this case, the active and reactive parts of the relative value of the complex conductivity of the studied material y = g + j b are determined from the expressions

g = 0.25 (b ₂₂ -b ₃₃ ) / (a ₁₂ -a ₁₃ ),

b = 0.5 [a ₁₃ (b ₁ + b ₂ ) -a ₁₂ (b ₁ + b ₃ )] / (a ₁₂ -a ₁₃ ),

Where

a _1k = [R ₁ (f ₁ ) -R _k (f _k )] / {[1-R ₁ (f ₁ )] [1-R _k (f _k )] [b ₁₁ -b _kk ]},

b ₁₁ = b ₁ (f ₁ ),

b _kk = b _k (f _k ),

k = 2, 3.

f ₁ , f ₂ , f ₃ - resonant frequencies at which the dependence of the power reflection coefficient R ₁ (f), R ₂ (f), R ₃ (f) reaches a minimum, respectively.

The real ε ′ and imaginary ε ′ ′ components of the complex dielectric constant of the measured material are calculated by the formulas

, $$\epsilon \text{'}\text{'}=\left(n_{\mathrm{one}}^2-{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="00000004.png"\; state="\{\{state\}\}">n</figure-callout>}}_2^2\right)$$

,

ε ′ ′ = 2 n ₁ n ₂ ,

Where

n ₁ = g {1- [λ / (2a)] ² } ^0.5 ,

n ₂ = b {1- [λ (2a)] ² } ^0.5 .

Example.

The device was implemented in the millimeter wavelength range.

The first 1 and second 2 segments of the metal waveguide transmission line are made of copper of the same rectangular internal cross section with a wide side a = 7.11 mm and a narrow side b = 3.56 mm. In a plane-parallel plate of metal 3, a rectangular window 4 is made with dimensions equal to the dimensions of the internal cross section of a waveguide line segment and a plate thickness of 1 mm. The length of the second segment of the waveguide transmission line 2 is 3.1 mm. The inner part of this segment was filled with a dielectric - fluoroplastic with a relative permittivity of 2.04.

Paragraph type open-circuit varactor diode 5 is included in a plane-parallel plate made of metal 3 with a maximum capacitance value C ₀ = 0.5 pF, a minimum capacitance value of 0.05 pF and a capacitance overlap - the ratio of the maximum capacitance to the minimum value - equal to 10.

To measure small changes in the complex dielectric constant of the material, they work in the range of power reflection coefficient modules (on a logarithmic scale) from minus 30 to minus 45 dB. In this case, the measurement error of the panoramic power reflection coefficient meter does not exceed 1%, and the resonance frequency is 0.01%.

We studied the material - water - at a temperature of 21 ° C in the frequency range 30 GHz.

On the fabricated sample of the device for three values of the constant voltage on the varactor diode, equal to 6 V, 8 V and 10 V, the resonance dependences of the power reflection coefficients on frequency were measured, which are shown in FIG. 3. The minimum values of the power reflection coefficients and the corresponding resonant frequencies for each voltage, determined from FIG. 3 are presented in table

Based on these measured data, the real and imaginary components of the complex dielectric constant of water, which are equal to

ε ′ = 23.96,

ε ′ ′ = 31.89.

Thus, the proposed device will allow you to measure the power reflection coefficient with high accuracy - 1%, which is about 5 times more than the accuracy of the prototype and, as a result, 5 times increase the accuracy of determining the complex dielectric constant of the material.

Information sources

1. US patent. US Patent # 5,243,983. Sept. 14, 1993.

2. US patent. Patent US # 2006/0025664 A1, Published Feb. 2, 2006. - prototype.

3. Copyright certificate No. 475051. Priority December 20, 1971.

Claims (1)

A device for determining the complex dielectric constant of materials containing
a section of a metal waveguide transmission line equipped with flanges at both ends, with dimensions of the internal cross section, in which an electromagnetic wave of a centimeter or millimeter wavelength range propagates in a section of a metal waveguide transmission line,
a plane-parallel plate located at one end of a segment of a metal waveguide line perpendicular to the direction of propagation of the electromagnetic wave in the metal waveguide transmission line,
while the other end of the metal waveguide transmission line is designed to connect it to a source of electromagnetic waves and a meter of the reflection coefficient of the electromagnetic wave, characterized in that
additionally introduced into the device
a second segment of a metal waveguide transmission line provided with flanges at both ends of the same internal cross section with a first segment of a metal waveguide transmission line,
varactor diode
the inside of the second segment of the metal waveguide transmission line is filled with a dielectric,
a plane-parallel plate is made of metal and is equipped with a window with dimensions equal to the dimensions of the internal cross section of a section of a metal waveguide transmission line,
a varactor diode is turned on in the middle of a wide window wall in a plane-parallel plate,
the metal leads of the varactor diode and the plane-parallel plate are separated by an insulator,
a flange of the other end of the segment of the metal waveguide transmission line, a plane-parallel plate and a flange of one end of the second segment of the metal waveguide transmission line are mechanically connected,
the other end of the second segment of the metal waveguide transmission line is intended for contact with the measured materials,
the length of the second segment of the metal waveguide transmission line is a multiple of half the length of the electromagnetic wave in the second segment of the metal waveguide transmission line with a dielectric.

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