JP2000162158A - Dielectric constant measuring method and apparatus - Google Patents

Abstract

(57) [Problem] To permit easy measurement of not only a sheet-shaped sample but also a dielectric constant of a sample such as a three-dimensional molded product or a liquid sample. SOLUTION: Under a constant condition in which a sample measurement surface of a dielectric resonator 20 is brought close to a standard sample having a known dielectric constant at a predetermined interval D, the dielectric constant and the thickness of the standard sample are appropriately changed. The change of the resonance frequency of the dielectric resonator 20 with respect to the dielectric constant and the thickness of the dielectric resonator 20 is measured, and a calibration curve of the change of the resonance frequency according to the dielectric constant and the thickness is obtained. Then, a change in the resonance frequency is measured by the dielectric resonator 20 under the same constant conditions as when the calibration curve was obtained from the measurement specimen having a known thickness, and the dielectric constant of the measurement specimen was measured from the measured value and the calibration curve. Ask for.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer sheet including a film, a sheet such as paper, a plastic,
A method and an apparatus for measuring the dielectric constant of a three-dimensional article such as a molded article such as a resin and a rubber by using a microwave, including a liquid such as an aqueous solution, an aqueous dispersion, an organic solvent liquid, and a liquid organic substance. It is about.

[0002]

2. Description of the Related Art The dielectric constant is a physical property value based on the polarization inside a substance, like the refractive index, and is considered to be an important physical property value because it has a close connection with electrical, optical and mechanical properties. ing. In a high-frequency region such as light, the refractive index and the dielectric constant have a relationship of (refractive index) ² = dielectric constant. Therefore, depending on the case, either of them can be substituted. For transparent materials, refractive index measurement by a refractometer is often used. For a flat sample, various methods such as a method of obtaining a dielectric constant from a capacitance of a flat capacitor, a method using a microwave cavity resonator or a dielectric resonator, have been used. The method using microwave resonance is based on the principle that the resonance frequency shifts according to the dielectric constant, and is applied to paper, film, plastic, ceramic, rubber, etc. Available regardless of

FIG. 1 is a diagram for explaining the principle of a conventional permittivity measurement using a microwave cavity resonator. The microwave resonator 6 is provided with a microwave introduction unit 2 at one end and a microwave detection unit 4 at the other end, and a waveguide between both ends is a waveguide having a fixed direction of electric field oscillation. The resonator 6 is provided with a slit 8 in the direction perpendicular to the axis of the resonator 6 at the position of the antinode of the standing wave. The sample 10 is arranged in the slit 8, a microwave is introduced from the microwave introduction unit 2, and the microwave intensity is detected by the microwave detection unit 4. The dielectric constant is measured from the difference between the resonance frequency when the sample 10 is arranged in the slit 8 and the resonance frequency when the sample is not arranged (Japanese Patent Publication No. 3-39632).
Reference).

FIG. 2 shows a method of measuring a dielectric constant using a microwave dielectric resonator. FIG. 2 is a sectional view showing a conventional orientation measuring device using a dielectric resonator. In the figure, a pair of dielectric resonators 12 opposed to each other with a sample 10 interposed therebetween is shown.
a, 12b, and a pair of antennas 14a, 14b arranged on opposite sides of one dielectric resonator 12a with the dielectric resonator 12a interposed therebetween.
An electric field vector having one direction parallel to the surface of the sample 10 is generated in 2b, and the dielectric constant is measured from its resonance characteristics (see Japanese Utility Model Laid-Open No. 3-70368). Here, antenna 1
4a and 14b are loop-shaped.

[0005]

In the measuring apparatus shown in FIG. 1 or FIG. 2, the cavity resonator or the dielectric resonator is
The sample 10 to be measured is limited to a sheet-like shape because the sample 10 is arranged so as to be opposed to both sides of the sample 10. However, in the field of plastic molding in recent years, there is an increasing need to measure the dielectric constant or anisotropy of plastic after molding. For example, in the case of resin molded products of electric products such as personal computers and television sets and plastic containers such as plastic bottles, the dielectric constant or its anisotropy may differ greatly from place to place due to fluidity distribution and pressure distribution during molding. Many are problematic. Therefore, it is required to measure the dielectric constant of a three-dimensional article or its anisotropy.

Further, the refractive index of a liquid is currently measured by an optical method, and the sugar content of fruit juice, the degree of fatigue of oil, the concentration of soy sauce and the like are sometimes controlled by this refractive index. However, this method has a problem that it is difficult to measure an opaque liquid such as heavy oil which is hard to transmit light. In addition, the optical method has a problem that the refractive index can be measured only up to a maximum of 1.52 from the critical angle in total reflection of light. An object of the present invention is to make it possible to measure the dielectric constant of not only a sheet-shaped sample but also a sample such as a three-dimensional molded product and a liquid sample.

[0007]

One aspect of the dielectric constant measuring method according to the present invention includes the following steps. (Step 1) A sample measurement surface of one dielectric resonator arranged only on one surface side of a sample is arranged under constant conditions on a standard sample having a known dielectric constant, and the dielectric constant and thickness of the standard sample are measured. One or both (referred to as “dielectric constant and / or thickness”) are appropriately changed, and the change of the resonance frequency of the dielectric resonator with respect to each dielectric constant and / or thickness is measured. Obtaining a calibration curve of the change in the resonance frequency according to. (Step 2) a step of measuring a change in resonance frequency of the sample to be measured having a known thickness by the dielectric resonator under the predetermined condition. (Step 3) a step of obtaining a dielectric constant of the sample to be measured from the measured value and the calibration curve.

Another aspect of the dielectric constant measuring method according to the present invention is that the sample measuring surface of one dielectric resonator arranged only on one surface side of the sample is fixed to a sample to be measured having a known thickness. This is a dielectric constant measuring method in which the resonance frequency is measured, and the dielectric constant of the sample to be measured is determined according to the following equation (1). β _g L = π / 2 + Pπ + tan ⁻¹ (α ₂ / β _g ) · tanh [tanh ⁻¹ (α ₃ / α ₂ ) + α ₂ L ₂ ] (1) α ₂ = (k _c ² −ω ₀ ²⁾ ε ₀ μ ₀ ε _S ) ^1/2 α ₃ = (k _c ² −ω ₀ ² ε ₀ μ ₀ ) ^1/2 βg = (ω ₀ ² ε ₀ μ ₀ ε _r −k _c ² ) ^1/2 here Where ε _S is the dielectric constant of the sample, ε _r is the relative dielectric constant of the dielectric resonator, L is the thickness of the dielectric resonator, ε ₀ is the dielectric constant of the measurement atmosphere (air), and μ ₀ is the permeability of the measurement atmosphere. Magnetic susceptibility, ω ₀ is the microwave resonance angular frequency, L ₂ is the thickness of the sample to be measured, k _c is a constant (eigenvalue) determined by the shape of the dielectric resonator, the electromagnetic field mode, etc., and P is 0, 1, 2, 3 , ... (this number means an integral multiple of the axial direction λ _g / 2). here,
The certain condition is that the measurement is performed with the sample measurement surface of the dielectric resonator in contact with the sample, or the measurement is performed with the sample measurement surface of the dielectric resonator separated from the sample by a certain distance. Is shown.

In the dielectric constant measuring method of the present invention, the resonance mode of the dielectric resonator may be a mode in which an evanescent wave exudes from the inside of the dielectric resonator due to resonance on the sample measurement surface side of the dielectric resonator. preferable. In such a resonance mode, if the electric field vector of the evanescent wave is substantially parallel to one direction, the dielectric constant of the sample in the parallel direction can be measured.

In the dielectric constant measuring method of the present invention, a cylindrical resonator or a rectangular resonator can be used as the dielectric resonator. In the dielectric constant measuring method of the present invention, the excitation device of the dielectric resonator and the antenna of the detection device are rod-shaped rod antennas arranged in a direction perpendicular to the sample measurement surface approaching or in contact with the sample of the dielectric resonator. Certain configurations can be used preferably. In the dielectric constant measuring method as described above, a configuration in which the periphery of the dielectric resonator is covered with a shield container except for the sample measurement surface can be preferably used. In the above-described method for measuring the dielectric constant, the measurement can be performed even if the measurement sample is a liquid.

According to the dielectric constant measuring apparatus of the present invention, one dielectric resonator disposed only on one surface side of a sample, and the thickness of a standard sample having a known dielectric constant are changed, and the dielectric constant for each thickness is changed. A storage device that stores a calibration curve for a change in resonance frequency measured by a dielectric resonator, and a data processing device that calculates the dielectric constant of the sample to be measured from the measurement result of the change in resonance frequency of the sample to be measured and the calibration curve And

[Measurement Principle] FIG. 3 is a general schematic diagram when the sample 10 is brought into contact with the dielectric resonator 20. According to this figure, when the resonance state of the dielectric resonator is expressed by a mathematical expression, an electromagnetic field mode mainly used for measurement is taken as an example.
A brief description is given below. Assuming that the dielectric resonator and the sample dielectric have no loss, the resonance frequency f ₀ satisfies the following equation: ω ₀
= 2πf ₀ . β _g L = π / 2 + Pπ + tan ⁻¹ (α ₃ / β _g ) · tanh [{tanh ⁻¹ (α ₃ / α ₂ ) · coth α ₃ L ₃ } + α ₂ L ₂ ] …… (A)

Α ₂ , α ₃ , and βg are constants when each region is a waveguide, α ₂ and α ₃ are attenuation constants, and βg is a phase constant, and are expressed as follows. α ₂ = (k _c ² −ω ₀ ² ε ₀ μ ₀ ε _S ) ^1/2 α ₃ = (k _c ² −ω ₀ ² ε ₀ μ ₀ ) ^1/2 βg = (ω ₀ ² ε ₀ μ ₀ ε _r −k _c ² ) ^1/2

Here, ε _S is the dielectric constant of the sample, ε _r is the relative dielectric constant of the dielectric resonator, L is the thickness of the dielectric resonator, ε ₀ is the dielectric constant of the measurement atmosphere (air), and μ ₀ is The magnetic permeability of the measurement atmosphere, ω ₀ is the microwave resonance angular frequency, L ₂ is the thickness of the sample to be measured, k _c is a constant (eigenvalue) determined by the shape of the dielectric resonator, the electromagnetic field mode, etc., and P is 0, 1 2,3, ...
(This number means an integral multiple of the axial direction λ _g / 2). kc is determined by the shape of the dielectric resonator, the electromagnetic field mode, and the like.
In the case of b, k _cmn ² = (mπ / a) ² + (nπ / b) ² . m, n are 0, 1, 2, 3,... (this number means a mode that is an integral multiple of the sectional direction λ / 2)

[0015] In the above formula (A), the time of measurement, measurement atmosphere is usually in the air, because the electric wall of the right side in the drawing than the object to be measured may be considered to be at infinity, in the case of L ₃ → ∞, cothα ₃ L
₃ → 1, and Equation (1) is obtained from Equation (A). β _g L = π / 2 + Pπ + tan ⁻¹ (α ₂ / β _g ) · tanh [tanh ⁻¹ (α ₃ / α ₂ ) + α ₂ L ₂ ] (1)

From the above relationship, it is understood that if the dielectric constant ε _{S of the} sample or the thickness L _{2 of the} sample changes, the resonance frequency changes. In other words, the larger the dielectric constant ε _S , the larger the amount of shift of the resonance frequency as compared with the blank (when there is no measurement sample), and the larger the thickness L _{2, the} larger the shift amount. I do. However, since the evanescent wave is used, the intensity of the electric field vector is strongest on the surface of the dielectric resonator, and decreases exponentially as the distance from the surface increases.

When actually solving the equation (1), it can be easily obtained even with a personal computer by using mathematical software such as Mathemadeka. Also, by appropriately combining the solution of the above equation with the calibration curve data actually obtained, it is possible to obtain a measurement result with few errors. In the above formula, the case where the sample 10 is brought into contact with the dielectric resonator 20 has been described. However, when the sample is measured at a fixed interval from the sample measurement surface of the dielectric resonator 20, the same applies. An expression is obtained.

Therefore, for various dielectric constants, the relationship between the difference between the blank resonance frequency and the resonance frequency when the sample is placed (referred to as Δf) and the thickness of the sample is examined in advance to form a calibration curve. If you want to measure an unknown sample,
Only by measuring the thickness and Δf, the dielectric constant of the sample can be measured. Also, depending on the conditions, the above equation (1)
By solving, the dielectric constant of the sample can be obtained.

FIG. 4 is a block diagram of a measuring system according to one embodiment of the present invention. A dielectric resonator 20 having a flat surface approaching or in contact with the sample 10, and a shield container 26 substantially covering the dielectric resonator 20 except for a sample measurement surface thereof
And a microwave excitation device 15 for generating a frequency near the resonance frequency of the dielectric resonator 20 when a sample is present from the antenna 22a, and transmitting or reflecting energy from the dielectric resonator 20 through the antenna 22b. A detecting device 16 for detecting the resonance frequency, a resonance frequency detecting device 17 for obtaining a resonance frequency from a change in the output of the detecting device 16,
A computer 18 is provided as a data processing device for obtaining the dielectric constant of the sample 10 from the obtained resonance frequency. The computer 18 has a storage device 19 for storing calibration curve data obtained in advance.

Microwaves are sent to a dielectric resonator 20 from an excitation device 15 capable of continuously changing the microwave frequency over a certain frequency range near the resonance frequency,
The transmitted microwave intensity is detected by the detection device 16. This signal is sent to the resonance frequency detecting device 17, the resonance frequency is measured, and this is sent to the computer 18. The storage device 19 stores calibration curve data of various dielectric constants and sample thicknesses. The dielectric constant of the sample 10 is calculated from the calibration curve data and the measured resonance frequency by performing an extrapolation operation or the like. You.

In the above example, an example in which the calibration curve data is used has been described. However, the computer 18 can solve the equation (1) and calculate the dielectric constant of the sample by calculation. In this case, the dielectric constant of the sample can be obtained from the calibration curve data while reducing the error in the calculation process of equation (1).

The antennas of the microwave excitation device and the detection device can be loop-shaped or rod-shaped. However, when the dielectric resonator is rectangular, the antenna is more rod-shaped than loop-shaped. The rod-shaped one is preferable because the uniformity of the electric field vector in the plane inside the sample is excellent. At this time, the rod-shaped antenna is preferably arranged in a direction perpendicular to a plane approaching or in contact with the sample of the dielectric resonator.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] FIG. 5 shows a configuration diagram of a dielectric resonator according to one embodiment of the present invention. The dielectric resonator 20 is connected to the measurement system shown in FIG. When the transmitted energy is detected by the detection device, the excitation device and the detection device are connected to a pair of antennas 22a and 22b that are disposed to face each other with the dielectric resonator 20 interposed therebetween.

FIG. 5 shows a sectional view (a) and an upper view (b) of an example of a dielectric resonator including an antenna. In the figure, by arranging the microwave rod antennas (or loop antennas) 22a and 22b with respect to the dielectric resonator 20 in the positions and directions shown in the figure with respect to the dielectric resonator 20, the dielectric Resonate the body resonator 20,
In addition, a resonance mode in which an electric field vector seeping out of the dielectric resonator 20 exists can be created. The resonance mode includes a TM mode and a TE mode, and FIG. 5 shows the TM ₁₀₁ mode. Although the intensity of the electric field vector 24 decreases almost exponentially as the distance from the dielectric resonator 20 increases, the sample is placed at a small distance from the dielectric resonator 20 or in contact with the dielectric resonator 20. By placing, the resonance frequency shifts according to the dielectric constant of the sample due to electromagnetic coupling.

In the case of this resonance mode, the electric field vector becomes parallel on the dielectric surface and inside the sample, so that the dielectric constant in the direction of the vector can be measured. Therefore, by measuring the dielectric constant each time while rotating the dielectric resonator 20 by a certain angle around an axis perpendicular to the sample surface in some way, the anisotropy of the dielectric constant at that location can be obtained. Can be measured.

The microwave rod antenna (or loop antenna) 22 for the dielectric resonator 20 described above.
The arrangement, shape, and the like of the a and 22b are not limited to those described above.
Any arrangement and shape may be used as long as a resonance mode in which an electric field vector seeping from 0 to the outside exists can be created. In the embodiment of FIG. 5, a rectangular resonator is used as the dielectric resonator 20, and rod antennas 22a and 22b are used as antennas. By combining the rectangular resonator and the rod antenna in this manner, the most uniform electric field vector can be obtained. Except for the sample measurement surface, a shield container 26 is provided around the dielectric resonator 20.
Is preferable in terms of improving sensitivity and the like. Thereby, the Q value of the resonance curve can be increased. The shield container is usually made of a conductive material such as a metal.

[Second Embodiment] Unlike the example described in the first embodiment of the present invention, when it is not necessary to obtain information on the anisotropy of the dielectric constant, that is, when the average dielectric constant of the sample is determined. If measurement is desired, it is preferable to use a cylindrical dielectric resonator instead of a square one. By considering the position and the mounting direction of the antenna, for example, TE _01δ or H
By resonating in the EM _21δ mode or the like, the exuded evanescent wave becomes a loop-shaped or an electric field mode not biased in one direction as shown in FIG. 6 on the sample surface, and the average dielectric constant can be measured. FIG. 6 is a diagram showing the electric field distribution on the surface of the dielectric resonator in the HEM _21δ mode when the measurement of anisotropy is not required. In FIG. 6, the circle indicated by the solid line indicates the upper surface of the cylindrical dielectric resonator. Is shown. The present invention measures the dielectric constant using the evanescent wave that has leaked out of the dielectric resonator as described above.

[Third Embodiment] In order to further improve the sensitivity of a dielectric resonator, first, the sharpness of resonance (Q value)
It was considered effective to make the resonance curve sharper by further increasing. Then, the present inventors repeated various trials. As a result, it has been found that it is effective to appropriately set a distance between the surface other than the sample measurement surface and the shield container. We have also found the optimal value.

Specifically, the distance between the bottom surface of the dielectric resonator (the surface facing the sample measurement surface) and the shield container is 0.2 to 0.8 mm, preferably 0.3 to 0.6 mm. Met. Also, between the side of the dielectric resonator and the shield container,
When a rod antenna is used as an antenna, the side without the rod antenna has a width of 2 to 5 mm, preferably 1 mm.
３3 mm. The same was true for a side surface of the rod antenna. However, it was more preferable that the interval between the side surfaces of the rod antenna was smaller than the interval between the side surfaces having no rod antenna. The above values also depend on the operating frequency and the dimensions of the dielectric resonator, and it is considered that the above values are preferable for the current dimensions of the bottom surface (30 mm × 20 mm) and the height (20 mm). It is considered that it is preferable to make the interval shorter if the size becomes smaller or the operating frequency becomes higher than the currently used gigahertz. In any case, it is preferable that the dielectric resonator does not contact the shield container.

A polytetrafluoroethylene (PT) is provided between the bottom surface of the dielectric resonator facing the sample measurement surface (the surface facing the sample measurement surface) and the surface facing the shield container.
It was found that by inserting a substance having a small dielectric loss factor such as FE) or quartz as a spacer, the Q value was greatly improved, and accurate measurement of the resonance frequency was possible. The spacers may be kept as small as possible, and if possible, may be kept apart. In practice, a flat plate of several mm square or a disk of several mm in diameter was used.

Further, it has been found that the Q value is improved by optimizing the length of the rod antenna, the distance from the dielectric resonator, and the like. Furthermore, in order to prevent mixing of paper powder and liquid, a part or all of the gap between the dielectric resonator and the metal is filled with a substance having a small dielectric constant and a small dielectric loss rate (for example, polytetrafluoroethylene). As a result, it was found that foreign matter can be prevented from being mixed without substantially lowering the Q value. Alternatively, it was also found that the same object can be achieved by covering the entire detection unit with a thin sheet of a substance having a low dielectric constant and a low dielectric loss rate (for example, polytetrafluoroethylene).

[0032]

EXAMPLES The present invention will be described more specifically based on examples. (Embodiment 1) FIG. 7 shows an embodiment of the present invention, and is a cross-sectional view in the case where a sample is brought into contact with a dielectric resonator and measurement is performed. The dielectric resonator itself has the same configuration as that shown in FIG. A rectangular dielectric resonator 20 having a dielectric constant of 20.84 is mounted in a rectangular shield container 26 made of brass with an open top, with the bottom surface in the horizontal direction. The upper surface of the dielectric resonator 20 is set to be substantially the same height as the opening edge of the shield container 26, and the sample 10 is placed so as to cover the opening of the shield container 26. The excitation antenna 22a and the detection antenna 22b are rod antennas, and are installed between the shield container 26 and the dielectric resonator 20.

The dielectric resonator 20 is brought into contact with three 100 mm × 100 mm, 2 mm thick polyethylene (PE) boards as the sample 10. The antennas 22a and 22b of the dielectric resonator 20 were connected to a measurement system having the configuration shown in FIG. 4 for measurement.

FIG. 8 shows, as a part of the raw data obtained by the measurement, a change in the transmission intensity when the frequency is changed from 2 GHz to 6 GHz, measured by a network analyzer. FIG. 8 shows a resonance spectrum when one polyethylene board is mounted on the dielectric resonator 20. The horizontal axis indicates frequency (2 GHz to 6 GHz), and the vertical axis indicates microwave transmission intensity. Each resonance peak corresponds to each resonance mode. In this case, a peak having a relatively large change width of the resonance frequency is shown in FIG. , The peaks of the resonance frequency in the blank are indicated by 1A, 2A, 3A, and 4A, and the peaks of the resonance frequency when one of the polyethylene boards is brought into contact are indicated by 1B, 2B, 3B, and 4B. Indicated.
When the peak was used from among the peaks, the best detection sensitivity was shown in relation to the frequency shift amount (the difference between the frequency of the peak 1A and the peak 1B), the dielectric constant of the sample, and the thickness of the sample. At this peak, FIG. 9 shows the result of measuring the resonance frequency at the time of blanking and the resonance frequency at the time of contacting one of the polyethylene boards on the same coordinates.
FIG. 9 is an enlarged view of the peak in FIG. 8, and shows the resonance curve when the right resonance curve is blank and one polyethylene board is mounted on the left.

Size 100 mm × 100 mm, thickness 2 m
m, a polyethylene board and an acrylic (PMMA) board are prepared, and when one board is placed horizontally on the dielectric resonator, the shift amount with respect to the number of sheets at the peak (resonance frequency at blank−sample placed) FIG. 10 shows the change in the resonance frequency at the time. FIG. 10 shows, using the peaks of FIG.
FIG. 9 is a diagram illustrating a result of measuring a relationship between a resonance frequency shift amount and the number of sheets (thickness). The difference between the curves of PMMA and PE is due to the difference in the dielectric constant of each material. That is, the shift amount is larger in PMMA having a larger dielectric constant.

Therefore, if a plurality of sheets having a known permittivity and a known thickness are measured in advance and a plurality of calibration curves as shown in FIG. It can be seen that the dielectric constant of the unknown measurement sample can be measured only by measuring the thickness and measuring the amount of resonance frequency shift.
That is, for example, in FIG. 10, if calibration curves are obtained for various materials having a dielectric constant between PE and PMMA, for example, the resonance frequency shift amount of an unknown sample having a thickness of four sheets is 120 MHz. In order to calculate the permittivity by looking at which material has a medium permittivity on the calibration curve, or if there is no calibration curve with the measured value, extrapolate from a calibration curve close to the measured value Can be.

If the calibration curve is previously obtained in a state where the sample is arranged at a position close to the surface of the dielectric resonator 20 with a predetermined interval, the sample measurement of the sample 10 and the dielectric resonator 20 can be performed. Measurement can be performed even when the surface is not in contact.
FIG. 11 shows that the sample 10 and the dielectric resonator 20 are arranged at a fixed distance D.
FIG. 1 is a cross-sectional view of an example of a measuring device that measures by approaching with a gap. Thus, by providing the sample support member 27 so that the distance D between the sample 10 and the dielectric resonator 20 is always constant, non-contact and non-destructive measurement becomes possible.

When the measurement surface of the measurement sample is a simple curved surface or the like, each minute portion of the measurement sample is applied to each of the minute resonators up to the dielectric resonator 20 by using the above-described equation (1). By calculating the amount of resonance frequency shift for the distance of, finally comparing the sum of the sum with that of the plane, and correcting based on the result, it can be applied to the case of a curved surface sample. Become. Of course, in this case as well, in various cases, a method in which actual measurement is performed on each curved surface in advance to obtain a calibration curve is also possible.

The non-contact measurement as described above can be performed even when the sample is a liquid. In the case of measuring a liquid, the sample measurement surface is preferably separated from the liquid surface because the dielectric loss factor is large. At this time, a case may be considered in which a liquid case or a sample measurement surface cover is interposed between the liquid surface and the sample measurement surface. It is preferable to select a material for the case and the cover having a dielectric constant close to 1, such as air. It is also conceivable to install the sample measurement surface at a fixed interval from above the liquid surface via air.However, fluctuations such as fluctuations in the liquid surface affect the measurement, and measures to reduce it are necessary. Becomes Further, in order to reduce the influence on the measurement, it is more preferable to increase the capacity of the case for containing the liquid. In addition, since it is sufficient that the resonance frequency can be measured as described above, there is no need for the liquid sample to have transparency as in the case of an optical measurement method, and the critical angle limits the range of dielectric constant (refractive index) measurement. There is no limitation.

Embodiment 2 In order to improve the Q value (sharpness of resonance) of the dielectric resonator, a spacer 30 is provided between the bottom surface of the dielectric resonator 20 and the shield container 30 as shown in FIG. Intervened. In FIG. 12, (A) is a plan view, (B)
1 is a vertical sectional view of FIG. Thickness of spacer 30 and Q
The relationship with the value changed as shown in FIG. 13 when the TM ₂₀₁ mode resonance was caused at 4 GHz. 13A shows a case where the spacer 30 is a metal sheet, and FIG.
0 is the case of a PET (polyethylene terephthalate) film. From this result, the thickness of the spacer 30 is set to 0.
It can be seen that around 5 mm is optimal for improving the Q value.

FIG. 14 shows the result of measuring the difference in the Q value depending on the presence or absence of the spacer 30. The horizontal axis indicates frequency, and the vertical axis indicates microwave transmission intensity. (A) shows the case where the spacer 30 is interposed, and (B) shows the case where the bottom surface of the dielectric resonator 20 is brought into direct contact with the shield container 30 without the spacer. In each figure, the lower spectra (A-2) and (B-2) show the peaks at the same frequency position in the respective spectra (A-1) and (B-1), and the horizontal axis is 100 times. This is shown enlarged.
Comparing (A) and (B), the Q value is increased from 360 to 1050 by attaching the spacer 30. As a result, the accuracy of peak detection, that is, the measurement of the resonance frequency, has been greatly improved.

Examples of the material used for the spacer include a metal and a polymer film, and a quartz plate having a small dielectric loss is preferable. The spacers 30 can be provided at a plurality of locations on the bottom surface of the dielectric resonator 20, for example, when the dielectric resonator 20 is rectangular, can be divided and provided at four corners of the bottom surface. Fig. 1
It was also found that placing one sheet in the center, as in 2, increased the Q value. After all, the spacer is preferably as small as possible. As a result of the trial, the inventors have used a flat plate having a square shape of several mm or a disk-shaped spacer having a diameter of several mm.

The rod antennas 22a and 22b are shown in FIG.
As shown in the figure, it is preferable that the dielectric resonator 20 and the shield container 26 be disposed substantially at the center of the metal wall. When the length is increased, the received microwave intensity increases, but the Q value tends to decrease. 1/2 to 2 of the height of the resonator 20
It is preferably set to about / 3. The thinner the Q, the thinner
Although the value is high, it is 0.1 mm to 0.5 mm from the relation with the strength.
The degree is preferred.

A spacer 30 is interposed between the central portion of the bottom surface of the dielectric resonator 20 and the shield container 30, and a gap between the dielectric resonator 20 and the shield container 26 is appropriately opened, for example, as shown in FIG. As described above, the dielectric resonator 20
Electric field vector at the surface can make the resonant mode (TM ₂₀₁₎ to be parallel in all the axial direction. (A) shows the electric field vector on the surface of the dielectric resonator 20 in the plan view, and (B) shows the electric field vector inside the dielectric resonator 20 at a position cut in the vertical direction so as to pass through the spacer 30. It is a thing. Although illustration of the rod antennas 22a and 22b is omitted in FIG. 15, they are arranged in the same manner as in FIG. Such a resonance mode can be used to measure the dielectric anisotropy of the sample 10.

By filling the gap between the dielectric resonator 20 and the shield container 26 with a substance 40 having a low dielectric constant and a low dielectric loss rate such as polytetrafluoroethylene as shown in FIG. Foreign matter can be prevented from being mixed without dropping. Also, as shown in FIG. 17, by lowering the height of the shield container 26 and attaching a substance 42 having the same characteristics as the shield container 26 instead, foreign matter can be prevented from being mixed without substantially lowering the Q value. . 17A is a plan view and FIG. 17B is a vertical sectional view.

As shown in FIG. 18, the upper surface of the dielectric resonator 20 is set to be substantially equal to the height of the opening edge of the shield container 26. Also, by covering the entire sensor including the gap between the dielectric resonator 20 and the shield container 26 with a sheet 44 of polytetrafluoroethylene, foreign substances can be prevented from being mixed.

In the measurement system as shown in FIGS. 16, 17, and 18, the example in which the measurement surface is directed upward has been described, but the measurement surface may be used so as to be vertical or oblique.
Also, in the measurement system as shown in FIGS. 16, 17, and 18, the members 40, 4 having a low dielectric constant and a low dielectric loss ratio are used.
If the dielectric resonator 20 is sandwiched between 2 and 44 or the dielectric resonator 20 is mechanically held by using an adhesive, the bottom surface of the dielectric resonator 20 and the shield container 2
It is not necessary to use the spacer 30 between 6 and the Q value can be further improved.

In the measurement system as shown in FIG. 12, the side face of the cylindrical or prismatic dielectric resonator 20 may be arranged so as to be supported by being sandwiched from both sides by the spacer, instead of the spacer 30 on the bottom face. it can. In this case, since it is necessary to support the dielectric resonator by the spacer, it is necessary to use an adhesive or to support the spacer with elasticity. Further, as a special example in such a case, when the dielectric resonator is arranged so that the measurement surface is substantially vertical, it is only necessary to support the spacer from below, and it is not necessary to sandwich the dielectric resonator. In any case, in the case of a prismatic dielectric resonator, when the dielectric resonator is supported by the spacer from the side, it is more preferable that the antenna is not disposed on the side supported by the spacer.

FIG. 19A shows the same peak in the microwave transmission intensity spectrum when the polytetrafluoroethylene sheet having a thickness of 50 μm is covered (left) and when it is not covered (right). Although the resonance frequency shifts due to the change in the dielectric constant, the shape of the peak hardly changes, and the Q value hardly decreases in this case as well.

FIG. 19B shows a state in which the whole sensor is covered with a polytetrafluoroethylene sheet 44, and a PET film (188510) as a sample is placed on the polytetrafluoroethylene sheet 44 to shift the resonance frequency. 5 shows the results of the measurement. The peak on the right is the case where no sample is mounted, and the peak on the left is the case where the sample is mounted. Thus, while preventing foreign substances from entering the gap between the dielectric resonator 20 and the shield container 26, the peak of the sample is measured. The dielectric constant can be measured.

[0051]

According to the present invention, the dielectric constant of a sample can be easily measured simply by measuring the resonance frequency when the sample approaches or contacts the dielectric resonator. Further, since this method is a detection method from one side, it is not necessary to limit the measurement sample to a sheet shape as in the conventional method, and it is possible to measure even a thick block-shaped sample or a liquid sample. Thus, the present invention is a three-dimensional article such as a molded article such as a polymer sheet or paper, plastic, resin, rubber, etc.
The dielectric constant of a liquid including an aqueous dispersion, an organic solvent, and a liquid organic substance can be easily measured by microwave.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a conventional orientation measuring device using a microwave cavity resonator.

FIG. 2 is a cross-sectional view showing a conventional orientation measuring device using a dielectric resonator.

FIG. 3 is a general schematic diagram when a sample is brought into contact with a dielectric resonator.

FIG. 4 is a block diagram showing a measurement system according to an embodiment of the present invention.

FIG. 5 is a configuration diagram of a dielectric resonator according to an embodiment of the present invention, which is a cross-sectional view (a) and a top view (b) of an example of a dielectric resonator including an antenna.

FIG. 6: HEM _21δ without anisotropic measurement
FIG. 4 is a diagram illustrating an electric field distribution on a dielectric resonator surface in a mode.

FIG. 7 is a cross-sectional view when a sample is brought into contact with a dielectric resonator including an antenna according to an embodiment of the present invention for measurement.

8 is a waveform diagram showing a resonance spectrum when one polyethylene board is mounted on the dielectric resonator shown in FIG.

9 is an enlarged view of the peak in FIG. 8, where the right resonance curve is blank and the left one shows the resonance curve when one polyethylene board is placed.

FIG. 10 shows the results of PMM using the peaks in FIG.
FIG. 11 is a diagram illustrating a result of measuring a relationship between a shift amount and the number of sheets for each of boards A and PE.

FIG. 11 is a cross-sectional view showing an example of a measuring apparatus for measuring a sample and a dielectric resonator by approaching them at regular intervals.

FIGS. 12A and 12B are diagrams showing an embodiment in which a spacer is interposed between the bottom surface of the dielectric resonator and the shield container, wherein FIG. 12A is a plan view and FIG. 12B is a vertical sectional view of FIG.

FIGS. 13A and 13B are diagrams showing the relationship between the thickness of the spacer and the Q value in the same example, where FIG. 13A shows the case where the spacer is a metal sheet, and FIG. 13B shows the case where the spacer is a PET film.

FIG. 14 is a graph showing Q based on the presence or absence of a spacer in the embodiment.
FIG. 7A is a diagram showing a difference in value, (A) shows a case where a spacer is interposed, and (B) shows a case where no spacer is interposed.

FIG. 15 shows an example of a resonance mode (TM) in the embodiment.
_201A ), (A) is a diagram showing an electric field vector on the surface of the dielectric resonator in a plan view, and (B) is an electric field inside the dielectric resonator at a position cut in a vertical direction so as to pass through a spacer. It is a figure showing a vector.

16A and 16B are diagrams showing an embodiment in which a gap between a dielectric resonator and a shield container is filled, in which FIG. 16A is a plan view and FIG. 16B is a vertical sectional view.

17A and 17B are diagrams showing an embodiment in which a gap between a dielectric resonator and a shield container is sealed, wherein FIG. 17A is a plan view and FIG.
Is a vertical sectional view.

FIG. 18 is a view showing another embodiment in which the gap between the dielectric resonator and the shield container is sealed, wherein FIG.
(B) is a vertical sectional view.

19A and 19B are diagrams showing characteristics of the embodiment in FIG.
Shows the peaks of the microwave transmission intensity spectrum when the polytetrafluoroethylene sheet was covered (left) and when it was not covered (right), and (B) shows the results of the measurement with the sample placed thereon. (Left side).

[Explanation of symbols]

 2 Microwave introduction part 4 Microwave detection part 6 Cavity resonator 8 Slit 10 Sample 12a Dielectric resonator 12b Dielectric resonator 14a Loop antenna 14b Loop antenna 15 Excitation device 16 Detection device 17 Resonance frequency detection device 18 Computer 19 Storage device (Calibration curve) 20 Dielectric resonator 22a Rod antenna 22b Rod antenna 24 Electric field vector 26 Shield container 30 Spacer

Claims (12)

[Claims] 1. A dielectric constant measuring method for determining a dielectric constant of a sample to be measured, comprising the following steps. (Step 1) A sample measurement surface of one dielectric resonator arranged only on one surface side of a sample is arranged under a constant condition on a standard sample having a known dielectric constant, and the dielectric constant of the standard sample and / or Measuring the change in the resonance frequency of the dielectric resonator with respect to each dielectric constant and / or thickness by appropriately changing the thickness, and obtaining a calibration curve of the change in the resonance frequency according to the dielectric constant and / or the thickness; . (Step 2) a step of measuring a change in resonance frequency of the sample to be measured having a known thickness by the dielectric resonator under the predetermined condition. (Step 3) a step of obtaining a dielectric constant of the sample to be measured from the measured value and the calibration curve. 2. A sample measurement surface of one dielectric resonator arranged only on one surface side of a sample is arranged on a sample having a known thickness under a predetermined condition, and a resonance frequency is measured. A dielectric constant measurement method for determining the dielectric constant of a sample to be measured according to (1). β _g L = π / 2 + Pπ + tan ⁻¹ (α ₂ / β _g ) · tanh [tanh ⁻¹ (α ₃ / α ₂ ) + α ₂ L ₂ ] (1) α ₂ = (k _c ² −ω ₀ ²⁾ ε ₀ μ ₀ ε _S ) ^1/2 α ₃ = (k _c ² −ω ₀ ² ε ₀ μ ₀ ) ^1/2 βg = (ω ₀ ² ε ₀ μ ₀ ε _r −k _c ² ) ^1/2 here Where ε _S is the dielectric constant of the sample, ε _r is the relative dielectric constant of the dielectric resonator, L is the thickness of the dielectric resonator, ε ₀ is the dielectric constant of the measurement atmosphere (air), and μ ₀ is the permeability of the measurement atmosphere. Magnetic susceptibility, ω ₀ is the microwave resonance angular frequency, L ₂ is the thickness of the sample to be measured, k _c is a constant (eigenvalue) determined by the shape of the dielectric resonator, the electromagnetic field mode, etc., and P is 0, 1, 2, 3, , ... (this number means an integral multiple of the axial direction λ _g / 2). 3. The dielectric constant measurement method according to claim 1, wherein the predetermined condition is that the measurement is performed by bringing a sample measurement surface of the dielectric resonator into contact with a sample. 4. The dielectric constant measurement method according to claim 1, wherein the predetermined condition is that the measurement is performed with a sample measurement surface of the dielectric resonator separated from the sample by a predetermined distance. 5. The measurement of the resonance frequency is performed in a mode in which the resonance mode of the dielectric resonator is such that an evanescent wave exudes from the inside of the dielectric resonator due to resonance on the sample measurement surface side of the dielectric resonator. The dielectric constant measurement method according to claim 1. 6. The dielectric resonator excitation device and the detection device antenna are rod-shaped rod antennas arranged in a direction perpendicular to a plane of the dielectric resonator approaching or in contact with a sample. The dielectric constant measurement method according to any one of Items 1 to 5, 7. A dielectric resonator disposed only on one surface side of a sample, a shield container substantially covering the dielectric resonator except for a sample measurement surface, a standard having a known dielectric constant. A storage device for changing the thickness of the sample and storing a calibration curve for a change in resonance frequency measured by the dielectric resonator for each thickness; a measurement result of the change in resonance frequency of the sample to be measured and the calibration A data processing device for calculating the dielectric constant of the sample to be measured from the line. 8. The dielectric resonator according to claim 7, wherein the dielectric resonator has a prismatic or cylindrical shape, and a bottom surface on one side of the pillar is a sample measurement surface.
The dielectric constant measuring device according to the above. 9. The dielectric constant measuring apparatus according to claim 7, wherein a gap is provided between a surface of the dielectric resonator other than the sample measurement surface and the shield container. 10. The dielectric constant measurement apparatus according to claim 9, wherein a spacer is provided between the bottom surface facing the sample measurement surface and the shield container. 11. The dielectric constant measuring apparatus according to claim 9, wherein a spacer is provided between a side surface of the dielectric resonator and the shield container. 12. A substance having a small dielectric constant and a low dielectric loss factor such that at least a part of a gap between the surface of the dielectric resonator other than the sample measurement surface and the shield container includes all outer edges of the sample measurement surface. 13. The orientation measuring device according to claim 7, wherein the orientation measuring device is filled or sealed so as to have substantially the same height as the sample measurement surface.