JPH07103917A - Measuring method for anisotropy of material - Google Patents

Abstract

PURPOSE:To obtain an accurate measured value from which an effect of thickness is removed, by a method wherein a half-width of a resonance curve is determined, a resonance frequency difference between maximum and minimum detection outputs is calculated reversely from the ratio between them and the resonance frequency difference between samples different in the thickness is calculated on the basis of that resonance frequency difference. CONSTITUTION:A half-width H0 of a resonance curve of a cavity resonator 1 and the thickness T of a sample S are stored 6 beforehand. This sample S is put in the resonator 1, the resonator 1 is excited with a resonance frequency f0 at the time of absence of the sample and an angular position A of the sample S at which a detection output of a detector 4 is maximum is searched for by rotating the sample S. The sample S being fixed at this position A, the resonance curve of the resonator 1 is measured and a half-width H is determined. Then, the excitation frequency of the resonator 1 is set at a frequency fm at the time when the sample S is present at the position A, and the frequency of the detector 4 is set at fm+H. While the sample S is rotated, a value R of a detection output Imax/ Imin is determined and a resonance frequency difference DELTAf is calculated reversely from the value R. Besides a half-width H1 and a difference DELTAf at the time of a thickness T1 are calculated from DELTAf and T1/T and the value R at the time when the thickness of the sample is T1 is computed by using the width H1 and the difference DELTAf1. Thereby an accurate measured value is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring material anisotropy using a high frequency electromagnetic field.

[0002]

2. Description of the Related Art There is a method of using a high frequency to measure anisotropy of a material such as a stretched polymer material whose permittivity varies depending on the direction. In this method, when the sample is rotated in the cavity resonator, the resonance frequency of the resonator shifts depending on the direction of the sample.Therefore, the anisotropy of the sample is obtained from the relationship between the direction of the sample and the deviation of the resonance frequency. is there. In the practice of this method, in the past, in order to detect the deviation of the resonance frequency with high sensitivity and accuracy, the detection frequency was fixed to the middle curve of the resonance curve, that is, the relationship curve between the frequency and the electric field strength in the cavity resonator. Then
The frequency shift is detected by the change in the electric field detection intensity at that frequency.

A conventional method for detecting a frequency shift is shown in FIG.
Will be described in detail. In FIG. 5, the horizontal axis is the frequency and the vertical axis is the detected value of the electric field strength at a certain frequency. The resonance curve is A,
Although three lines B and C are drawn, A is a resonance curve when the direction of the sample is the maximum resonance frequency, and B is a resonance curve when the sample is rotated 90 ° from that and the resonance frequency is the minimum. The resonance curve is C when the sample orientation is in the direction of 45 ° between A and B,
With this resonance curve of C, the frequency f half the height of the resonance peak
When the detection frequency is fixed to fs with s as the reference and the sample is rotated, the detection output fluctuates in the range of Ia and Ib with Ic at the center. Therefore, the deviation of the resonance frequency can be expressed by Ia / Ib = R.

The above-mentioned shift of the resonance frequency has a property of increasing even if the thickness of the sample is increased even in the case of the same type sample having the same anisotropy. This is because the deviation of the resonance frequency is determined by the anisotropy of the sample and the volume of the sample in the cavity resonator. Therefore, when measuring the anisotropy of the material by the shift of the resonance frequency, the thickness of the sample must be unified. However, in practice, it is difficult to make the thickness of the sample uniform, so the thickness of the sample should be measured separately, and the measured value for a certain fixed thickness should be obtained by proportional calculation from the measured value of Ia / Ib. ing.

[0005]

The above-mentioned conventional method gives a practicable result when the difference in sample thickness is not so large, but the maximum and minimum sample thickness differ by about 10 times. The error is large in such cases. In Fig. 5, the half-width of the resonance curve is considered as a straight line as long as the deviation of the frequency is small. However, if the deviation of the frequency becomes large, the position of the fixed detection frequency comes to the edge of the resonance curve. Because of the bending of the resonance curve, the frequency shift is observed to be smaller than it actually is. Further, as the sample becomes thicker, the half-value width of the resonance curve becomes wider, so that the apparent deviation of the resonance frequency also becomes small. The present invention is intended to correctly detect the deviation of the resonance curve over a wide range of the thickness of the sample and obtain an anisotropy measurement value excluding the influence of the thickness of the sample.

[0006]

In the method of measuring anisotropy as described above, a peak width, for example, a half width at a height of a predetermined ratio of the peak height of a resonance curve when a sample is inserted into a cavity resonator. By utilizing the fact that the relationship between the sample and the thickness of the sample is linear, the resonance curve when the sample is placed in the cavity resonator is actually measured, and the half value width H from the sample to the reference thickness Using the fact that the resonance curve is a function of the full width at half maximum, the full width at half maximum H ₁ is obtained, and the above H ₁ is substituted into the functional equation to obtain the resonance curve of the resonance curve when the sample of the reference thickness is inserted into the cavity resonator. Calculate the formula, find the difference in resonance frequency for the sample with the reference thickness proportionally from the resonance frequency difference between the maximum and minimum detection output for the actual sample, and substitute it into the formula for the resonance curve for the sample with the reference thickness. The maximum and minimum values of the detection output for the sample with the reference thickness Was calculated and the ratio R was calculated.

[0007]

The resonance curve is expressed by the Lorentz function, for example, I (f) = I ₀ / {1 + {(f-fc) / H} ₂ } (1). Here, f is an arbitrary frequency, fc is a resonance frequency when the sample is in the reference orientation, H is a half value width, and I ₀ is an electric field detection value at the resonance point. The frequency of the electric field strength in the resonance curve becomes half of that in the resonance point and to say the frequency of the half-value width, which upon the fs, in fs is _{I (f) = I 0/} 2. Measurement frequency fs
The detected value I ₁ of the electric field strength at fs when the resonance frequency is deviated by Δf is expressed by the equation (1) and the value of f is fc +
Because it is I (f) when placing a Delta] f + H, with _{I 1 = I 0 / {1} + {(H + Δf) / H} 2} I in the reference orientation of the sample being measured (fs) Toko of I ₁ since I (fs) is I _0/2, a reference orientation of the sample and when the dielectric constant maximum direction of the sample is the direction of the electric field within the cavity resonator, I ₁ is the minimum value of I (f) When, because _{R = (I 0/2)} / I 1 = {1+ {H + Δf) / H} 2} in ... (2) R is been obtained from actual measurement of the calculation of the Delta] f from the above equation, Delta] f = H √ (2R-1) -H (3) Even if the frequency shift is large in the equation (3), the frequency shift can be accurately obtained from the detected value of the electric field strength when the frequency is fixed.

Next, consider the problem of sample thickness. For samples of the same material with the same anisotropy, the frequency shift is proportional to the thickness, so if the full width at half maximum of the resonance curve does not change with the thickness of the sample, directly measure the thickness of the sample. Although the deviation of the resonance frequency when the thickness of the sample has a constant value can be calculated by the equation (3), the half-width changes, so that the correction is necessary. As a result of experiments, it was found that there is a linear relationship between the half width and the sample thickness. FIG. 6 shows an example of this relationship. Since the thickness of the sample can be directly measured by T, the resonance curve is actually measured by changing the frequency of the sample, and the half-value width H is actually obtained. Using this H, the measurement frequency is determined and Δf is calculated by the above equation (3). When actually measuring the resonance curve of the cavity resonator seeking half-width which is referred to as H ₀ when not put the other samples, the half-width H ₁ when the specimen thickness is T ₁ refers to FIG. 6 H ₁ = H ₀ + (H−H ₀ ) T ₁ / T (4) The thickness T ₁ of the resonant frequency of the sample shift Delta] f ₁
Is a proportional calculation Δf ₁ = Δf · T ₁ / T (5) These H ₁ and Δf ₁ are put into the equation (2) to obtain the thickness T ₁
It is possible to obtain R for each sample. In this way, from the measured value of the sample of arbitrary thickness, the constant thickness T
R in ₁ can be obtained, and anisotropy can be compared even in samples having different thicknesses.

[0009]

1 shows an example of an apparatus for carrying out the method of the present invention. Reference numeral 1 is a cavity resonator, which is provided with a slit 2 so as to cross the center thereof, and the sample S is inserted into this slit. The sample S has a sheet shape and can be rotated around the axis of the cavity resonator. The cavity resonator has partitions 11 near both ends thereof, a resonance space is provided between the partitions, and a slit at the center of the cavity serves as an antinode of the electric field. Each partition 11 has a small hole h, and an antenna 12 is inserted between one end of the cavity resonator and the partition, and the antenna 12 is connected to the exciting high frequency power source 3. An antenna 13 is inserted between the other end of the cavity resonator and the partition, and this antenna is connected to the detector 4. The sample S is rotated by the motor 5, the angular position of the sample and the detection output of the detector 4 at that time are taken into the control device 6, and data processing is performed.

FIG. 2 is a flow chart showing the procedure of the measuring operation when the present invention is carried out using the above apparatus. The resonance curve of the cavity resonator 1 is actually measured in advance, the half value width H ₀ of the resonance curve of the cavity resonator itself is obtained, and stored in the control device 6 (a). In the actual measurement of the sample, first, the thickness T of the sample is measured with a micrometer or the like and stored in the control device 6 (b). Next, the sample is put in a cavity resonator, the cavity resonator is excited at a resonance frequency f ₀ when there is no sample, the detection frequency of the detector 4 is set to f ′ higher than f _0, and the sample S is set. Turn to find the angular position A of the sample that maximizes the detection output (C). The angular position of this sample is such that the direction of the maximum dielectric constant along the sample surface of the sample becomes the same as the direction of the electric field at the sample position in the cavity resonator. Next, the sample is fixed at the angular position A and the resonance curve of the cavity resonator is measured (d). The resonator curve may be measured by keeping the excitation frequency and the detection frequency the same while measuring the output of the detector 4 while changing the frequencies. From this result, the full width at half maximum H of the resonance curve when the sample is inserted is obtained (e). The excitation frequency of the cavity resonator is set to the resonance frequency fm when the orientation of the sample is A, and the detection frequency of the detector 4 is set to fm + H, and the sample is started from the angular position A and then pointed once. Then, the detection output reaches a minimum value Imin at a position 90 degrees from A after passing from the maximum value Imax to the intermediate value I, and while changing between Imax and Imin, two cycles are performed up and down during one point. While returning to the maximum value. This change is shown by polar coordinates in FIG.
The data of FIG. 3 is collected in the step (f). From this data, R = Imax / Imin is obtained. (G).
From the measured value of R, Δf is calculated (4) by the equation (3). Further, the full width at half maximum H ₁ of the resonance curve when the sample thickness is T ₁ is calculated by the equation (4) (i). Further, the frequency deviation Δf ₁ when the sample thickness is T ₁ is calculated by the above equation (5) (nu). Using the values H ₁ and Δf ₁ obtained in this way, R when the sample thickness is T ₁ is calculated (L) by the equation (2), and the measurement operation ends.

FIG. 4 is a result of obtaining R by changing the number of stacked samples of the same kind having a thickness of 100 μm from one to eight.
R is calculated in the case of a thickness of 400 μm. The dotted line shows R obtained at a thickness of 400 μm by simple proportional calculation from the ratio of Imax and Imin actually measured, and it can be seen that R becomes apparently smaller as the thickness increases. On the other hand, in the result of application of the present invention shown by the solid line, R shows a substantially constant value regardless of the number of stacked sheets.

In the above description, when the detection output is maximum at the frequency at the position of the half-value width position of the resonance curve in the direction of the sample in which the deviation of the frequency from the resonance frequency of the cavity resonator itself is the maximum. However, the present invention is not limited to such a form. Based on the frequency corresponding to the half-value width of the resonance curve in the sample direction in which the frequency shift takes an intermediate value between the maximum and the minimum (direction rotated by 45 ° from the sample direction when the frequency shift is maximum), The maximum deviation Δfma from the reference frequency to the high frequency from the intermediate value, the maximum value, and the minimum value of the detection output at that frequency.
The minimum deviation Δfmin from x may be calculated. In this case, in principle, Δfmax and Δfmin have the same absolute value and opposite signs, so Δfmax−Δ
It is sufficient to set fmin to Δf described above. In the above description, the frequency corresponding to the full width at half maximum of the resonance curve is used, but this is not limited to the full width at half maximum.
It is also possible to use a frequency corresponding to the peak width at a height of some predetermined percentage of the peak height of the resonance curve.

[0013]

EFFECTS OF THE INVENTION According to the present invention, even samples having different thicknesses can be compared with each other by accurately converting the values of R in the case of the same thickness. This makes it possible to easily and accurately measure the anisotropy of samples having different thicknesses such as the measurement of the relationship with the directionality.

[Brief description of drawings]

FIG. 1 is a block diagram of an example of an apparatus for carrying out the method of the present invention.

FIG. 2 is a flowchart of a measurement operation by the above device.

FIG. 3 is a graph showing an example of the relationship between detector output and sample angular position.

FIG. 4 is a graph showing the relationship between the number of stacked samples and R.

FIG. 5 is a graph illustrating the principle of the present invention.

FIG. 6 is a graph showing the relationship between the thickness of the sample and the full width at half maximum H of the resonance curve.

[Explanation of symbols]

 1 cavity resonator 2 slit S sample 3 high frequency power source 4 detector 5 motor 6 controller

Claims (1)

[Claims] 1. A change in the resonance frequency when the orientation of a sample is changed in a cavity resonator is detected as a change in the detection output of a detector having a constant detection frequency, and the maximum and minimum of the detection output are detected. In the anisotropy measuring method that expresses the anisotropy of the sample by the ratio of, the resonance curve of the cavity resonator is measured in advance with the sample inserted in the cavity resonator, and the peak height of the resonance curve is determined. The peak width H at the height of the ratio is obtained, and since the resonance curve is a function of this peak width, the difference Δf in the resonance frequency between the maximum and the minimum of the above detection output is calculated backward, and the sample thickness is the reference thickness. The resonance frequency difference Δf ₁ with respect to the maximum and the minimum of the above detection output is calculated from the proportional relationship with Δf from the sample thickness, and the relationship between the peak width of the resonance curve and the sample thickness is linear. For samples of the above standard thickness The peak width H ₀ of the curve were calculated, the peak width function formula of the resonance curve H ₀ and the Delta] f ₁
By calculating the ratio of the maximum and the minimum of the detection output to the sample of the reference thickness by substituting for the ratio R of the detection output of the sample of the reference thickness from the measured value for the actual sample. Method for measuring material anisotropy.