JP3109065B2 - Electrode for dielectric relaxation measurement - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

This invention relates to electrodes used to measure dielectric relaxation. More specifically, the present invention relates to an electrode useful for measuring the dielectric relaxation of the skin surface layer for the purpose of obtaining information on the amount of water present in the skin surface layer and the state of the water.

[0002]

2. Description of the Related Art The measurement of the water content of the skin surface layer is useful for evaluating the properties of the skin itself and for evaluating cosmetics or pharmaceuticals applied to the skin.

Conventionally, a high-frequency impedance method has been generally used as a method for measuring the moisture in the surface layer of the skin. However, since the high-frequency impedance method does not directly observe the behavior of water on the surface of the skin, there are many factors other than the moisture on the surface of the skin that affect measured values, and there is a problem in reproducibility. There is also a problem that information obtained by the high-frequency impedance method is ambiguous at what depth from the skin surface. Furthermore, this method does not provide information on the state of the water, whether it is free water or bound water.

[0004] On the other hand, a method of measuring the dielectric relaxation of water present on the skin surface layer is considered. There are two methods for measuring dielectric relaxation: a frequency domain measurement method and a time domain reflection method (hereinafter abbreviated as TDR method). In recent years, research on the latter measurement technique and its application has been actively conducted. Is being advanced.

In the TDR method, an excitation signal (for example, a step pulse) having a specific waveform is applied to a sample to observe a reflected wave, and the complex permittivity of the sample is determined from changes in the phase and intensity of each frequency component of the reflected wave. , And the physical properties of the sample are known based on it. According to this method, free water and bound water in a sample can be measured nondestructively and quantitatively. For example, Japanese Patent Application Laid-Open No. 2-110357 discloses that T
As an apparatus for the DR method, an apparatus for applying a step pulse to a sample as an excitation signal has been proposed, and an application example relating to the measurement of water content in a living body using this apparatus is described (top right column on page 4 of the publication). Line 10 to page 7, lower right column, line 17).

FIG. 9 shows an electrode (probe) 1 used in an apparatus for the TDR method disclosed in Japanese Patent Application Laid-Open No. Hei 2-110357.
FIG. This electrode 1 has a coaxial internal electrode 1a.
And the external electrode 1b. The internal electrode 1a is connected to the internal conductor 2a of the coaxial cable 2, and the external electrode 1b is connected to the external conductor 2b of the coaxial cable 2. The inner electrode 1a and the outer electrode 1b have the same diameter as the inner conductor 2a and the outer conductor 2b of the coaxial cable 2, respectively, and their end faces in contact with the sample to be measured are flat. Until now, the size of the electrode as shown in FIG. 9 used for the measurement of the TDR method is such that the inner electrode has a diameter of 320 μm or more, the outer electrode has an inner diameter of 1.05 mm or more, and the electric length is 1
It exceeds 15 μm.

[0007]

By the way, on the skin,
An epidermis having a thickness of 100 to 300 μm is present on the surface, and the outermost layer is called the stratum corneum (10 to 20 μm in thickness). The dermis is located below the epidermis, and the subcutaneous tissue is located below the dermis. For this reason, in order to examine the effect of cosmetics and pharmaceuticals on the surface moisture of the skin, it is preferable to measure the moisture at a desired depth of the skin, and to measure the moisture from at least the outermost layer or the skin surface to about 100 μm. It is necessary to be able to do. However, the conventional moisture measuring device of the TDR method does not clarify at what depth of the skin the moisture is measured when it is used for measuring the moisture of the skin.

Therefore, the present inventor estimated the measurement depth in the case where the TDR method was performed using the electrodes as shown in FIG. As a result, the inner electrode had a diameter of 0.51 mm and the outer electrode had an inner diameter of 1.7.
When using an electrode of mm, it is almost equal to the electrical length of the electrode,
It was found that moisture was measured over a wide range of depths of about 180 μm from the outermost layer of the skin. Therefore, it was found that the effect of cosmetics and pharmaceuticals on the moisture of the skin surface layer cannot be sufficiently investigated by the conventional method.

The present invention has been made to solve the above-mentioned problems of the prior art, and when measuring the water content of the skin surface layer by measuring the dielectric relaxation such as the TDR method, the present invention is not limited to the case where the outermost layer of the skin is within 100 μm. It is an object of the present invention to be able to measure moisture in a range, and to measure moisture in the skin at a desired depth, and to measure moisture in the stratum corneum.

[0010]

Means for Solving the Problems The present inventors have made it possible to reduce the electric length of the electrode to 100 μm or less by reducing the size of the tip of the electrode used for measurement. It has been found that the depth of the lines of electric force passing through the skin can be controlled and the above object can be achieved, and the present invention has been completed.

That is, the present invention comprises a core-shaped internal electrode and an external electrode coaxially arranged on the internal electrode with an insulator interposed therebetween, and the tip surface of the internal electrode and the tip surface of the external electrode are measured. Provided is an electrode for measuring dielectric relaxation, which serves as a contact surface with a sample, wherein the electrode has an electrical length of 100 μm or less.

Hereinafter, the present invention will be described in detail with reference to the drawings. In each of the drawings, the same reference numerals represent the same or equivalent components.

The present invention is useful for measuring the dielectric relaxation of the skin surface from the skin surface to a depth of about 100 μm for the purpose of obtaining information on the amount of water present in the skin surface and the state of the water. Electrode. Its structure is basically composed of a core-shaped internal electrode and an external electrode coaxially arranged on the internal electrode via an insulator, as in the conventional electrode shown in FIG. The electrical length of the electrode is 100
μm or less.

Here, the electrical length of the electrode means that a load having a complex permittivity ε ^* (ω) is provided at one end of a transmission line such as a coaxial cable, and an electromagnetic wave V (ω) having an angular frequency ω is applied from the other end. Equation (1), which is a relational expression between the electromagnetic wave V (ω), the reflected wave R (ω), and the complex permittivity ε ^* (ω) of the load,
, Is included as a parameter γd.

[0015]

(Equation 1) The electric length γd can be obtained by measuring a reflected wave of a known standard sample whose complex permittivity ε ^* (ω) is known.

The electrical length is a physical quantity unique to the electrode determined by the shape and size of the electrode, and does not depend on the measuring method. Therefore, the electrical length of the electrode is constant in any of the dielectric relaxation measurement methods such as the frequency domain measurement method and the time domain reflection method (TDR method).

On the other hand, the present inventor has found that the electrical length is closely related to the measurement depth of the sample to be measured during the dielectric relaxation measurement, and that the electrical length is a measure of the measurement depth. For example, as shown in Examples described later, when measuring dielectric relaxation for a sample composed of a surface layer and a lower layer, and the thickness of the surface layer is equal to the electrical length of the electrode used for measurement, the electrode is 63% (1-e ^-1 ) of the total information obtained is information from the surface layer, and 86% is information from a measurement depth up to twice the electrical length.

Therefore, the electrode of the present invention is useful for measuring the surface layer from the surface to a depth of about 100 μm in any of the frequency domain measurement method and the time domain reflection method for measuring the dielectric relaxation. Become.

In the present invention, specific examples for setting the electrical length of the electrode to 100 μm or less, which is shorter than the conventional one, include, for example, (1) reducing the area of the electrode tip surface where the internal electrode contacts the sample, or (2) An embodiment in which the distance between the inner electrode and the outer electrode at the tip end surface is narrowed or the like can be given. Note that the inner diameter of the external electrode is related to the distance from the internal electrode, but other shapes and sizes can be arbitrarily set.

In order to minimize multiple reflections at the time of dielectric relaxation measurement and to perform the measurement accurately, the impedance of the electrode and the coaxial cable connected to the electrode must be determined.
In addition, it is preferable to make the impedance inside the electrode constant, and therefore, it is preferable to make the ratio between the diameter of the internal electrode and the inside diameter of the external electrode constant at an arbitrary position of the electrode. Therefore, as a preferable mode for reducing the area of the tip surface of the internal electrode in (1), for example, FIG.
As shown in the electrode 10a shown in FIG. 2, the internal electrode 1a and the external electrode 1b connected to the coaxial cable have the cross-sectional area continuously reduced toward the tip, and the electrode 10b shown in FIG. Like the electrode 10c shown in FIG. 10C or the electrode 10d shown in FIG.
And the cross-sectional area of the external electrode 1b gradually reduced toward the tip.

However, there is no practical problem even if impedance matching is not taken into consideration at the electrode tip within 10 mm, particularly within 1 mm from the electrode tip. Therefore,
Like the electrode 10e shown in FIG. 2, as the electrode of the present invention, only the tip of the internal conductor of the commercially available coaxial cable is processed so that only the tip of the internal electrode 1a becomes thinner toward the tip surface. In this manner, the inner and outer diameters of the external electrode 1b may be constant.

Although the tip surface of the internal electrode of the electrode of the present invention is circular, the shape of the tip of the internal electrode is not limited to a circle in the present invention. As shown in FIG. 3, by processing only the tip of the inner conductor of a commercially available coaxial cable, a cylindrical recess (FIG. 3A) or a conical recess (FIG. 2B) is formed in the internal electrode 1a. May be formed so that the front end surface is annular, thereby reducing the area of the front end surface.

Further, as long as the electrical length of the electrode of the present invention is 100 μm or less, it can be used directly without specially processing the inner conductor of the coaxial cable. As such a coaxial cable, a small-diameter cable having an inner conductor having a diameter of 10 μm to 270 μm can be used. When the electrode of the present invention is formed from a small-diameter coaxial cable, the electrode of the present invention requires a connector portion that can be connected to the tip of a normal coaxial cable having a larger diameter than the electrode. In this case, as the connector part, one that changes the diameter of the internal electrode continuously or stepwise is used, similarly to the electrode shown in FIG.

In the present invention, when reducing the area of the tip surface of the internal electrode, its specific value can be determined according to the depth of the skin surface layer to be measured, the electrode shape of the electrode, and the like. it is preferable that the 78μm ² ~5.7 × 10 ⁴ μm ² corresponding to the area of a circle having a diameter 10Myuemu～270myuemu. Therefore, when the end face of the internal electrode is circular, the diameter is preferably 10 μm to 270 μm.

With this, 100 μm from the outermost layer of the skin
It is possible to perform a moisture measurement at a depth within the range. Further, the electric length is 1 μm to 100 μm, more preferably 5 μm to
By setting it to 25 μm, it becomes possible to measure the water content of the stratum corneum.

The distance between the internal electrode and the external electrode on the tip surface of the electrode is preferably 10 μm to 310 μm from the viewpoint of impedance matching between the coaxial cable and the electrode.

The material of the electrode is not particularly limited, but is preferably a corrosion-resistant metal, for example, gold, platinum, copper or the like.

Also, as shown in FIGS. 3A and 3B, between the internal electrode 1a and the external electrode 1b, and as shown in FIGS.
It is preferable to fill the concave portion formed at the front end portion a with an insulating material such as Teflon resin or epoxy resin. This makes it possible to measure a liquid sample as a standard sample, and to prevent unnecessary foreign substances from adhering to the concave portions.

The method for producing the electrode of the present invention is not particularly limited.

When dielectric relaxation measurement such as TDR method is performed using the electrode of the present invention, the coaxial cable connected to the electrode of the present invention is not particularly limited as long as it has the impedance matching as described above. Commercially available ones can be used. From the viewpoint of operability when bringing the electrode into contact with the measurement sample, it is preferable to use a flexible cable. The measurement itself by the TDR method is disclosed in
A known method described in, for example, Japanese Patent No. 0357 can be used.

[0031]

When measuring moisture in the skin by performing dielectric relaxation measurement such as the TDR method, the electrical length of the electrode corresponds to the depth of a signal oozing from the electrode into the skin, that is, the measurement depth. According to the present invention, since the electrical length of the electrode is 100 μm or less, the measurement depth can be reduced. In addition, 100
By appropriately setting the electrode length to not more than μm, it becomes possible to measure the water content of the skin surface layer at a desired depth within 100 μm from the skin surface, and it is also possible to measure the water content of the stratum corneum.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments.

Examples 1 to 5 and Comparative Examples 1 to 3 As shown in FIG.
An electrode composed of c and the external electrode 1b was formed in three types of shapes A, B, and C. In this case, the radius (or width) L of the tip surface of the internal electrode 1a and the area S of the tip surface of the internal electrode 1a
1, the area S2 of the end face of the combined internal electrode 1a and insulating material 1c, and the inner diameter D of the end face of the external electrode were as shown in Table 1. The electrode material is copper for both the internal electrode 1a and the external electrode 1b, and the internal electrode 1a is used as the insulating material 1c.
Teflon was filled between the electrode and the external electrode 1b.

(Evaluation) (1) Measurement of Electric Length of Electrode Dielectric relaxation measurement was performed using acetone, whose dielectric spectrum was already known, as a standard sample, and the electric length of the electrode was obtained. That is, the tip of the electrode is immersed in acetone, the reflected wave is measured by the TDR method using a step pulse as an excitation signal, and the electrical length γd is calculated using the excitation signal and the measured reflected wave.
Was used as a parameter to calculate the dielectric spectrum from equation (1). In this case, the dielectric spectrum was calculated while changing the value of the electrical length γd, and the electrical length γd when the calculated value of the dielectric spectrum most closely matched the known dielectric spectrum of acetone was defined as the electrical length γd of the electrode. The results are shown in Table 1. FIG. 8 shows the relationship between the obtained electrical length γd and the radius L of the internal electrode for the electrodes of shapes A and B.

(2) Measurement of electrode measurement depth In order to examine the measurement depth when each electrode is used for measuring skin moisture by the TDR method, two layers of water (surface layer) and Teflon (lower layer) are used. The dielectric constant at 100 MHz was measured as follows by changing the thickness of the surface water with respect to the sample.

First, as shown in FIG.
A Teflon tape (dielectric constant of Teflon 2) 12 was put in a water bath (dielectric constant 78 of water) 13, and the electrode 10 was set in the bath so as to face the Teflon tape 12. The water bath 13 was placed on a Z stage 14, and a film thickness gauge 15 was attached to the Z stage 14. By moving the Z stage 14 up and down, the electrode 10
The distance x between the tape and the Teflon tape 12 was changed, and the dielectric constant at that time was measured. In this case, a TDR method using a step pulse as an excitation signal was used as a method of measuring the dielectric constant.

The dielectric constant thus obtained is shown in FIG. 6 for Experimental Example 3 and Comparative Examples 1 to 3. In the figure, the permittivity change rate is such that the permittivity of Teflon is 0 and the permittivity of water is 1
00 shows a standardized value. In the same figure, the lower diagram is an enlarged view of the range of L = −100 to 400 μm in the upper diagram. Further, for Example 3 and Comparative Examples 1 to 3, FIG. 7 shows the relationship between -ln (1-dielectric constant change rate) and a reading of a film thickness meter. In FIGS. 6 and 7, the region where the reading of the film thickness meter (that is, the distance x between the electrode 10 and the Teflon tape 12) is a negative value is a region where the electrode 10 is the Teflon tape 1.
2 is moving upward while contacting with No. 2.

In such a measurement of the dielectric constant, when the electrode 10 is in contact with the Teflon tape 12, the exudation of the excitation signal from the electrode 10 is performed only on the Teflon tape 12, so that it is shown in FIG. As shown, the observed permittivity shows a constant value. On the other hand, when the electrode 10 is moved away from the Teflon tape 12 and the distance x between them is increased, the exudation of the excitation signal from the electrode 10 reaches both the water and the Teflon tape 12, so that the observed dielectric constant Is increased, and as the distance x is further increased, the dielectric constant gradually approaches the standardized value of water of 100.

Here, in FIG. 7, in a region where the distance x is positive, since the plot shows a linear relationship,
It can be seen that the measured permittivity changes exponentially with distance x. That is, assuming that the permittivity of the surface layer (water) is ε ₁ , the permittivity of the lower layer (Teflon) is ε ₂ , and the observed permittivity is ε _obs , the observed permittivity ε _obs is given by the following equation (2). It can be seen that it is represented.

[0040]

(Equation 2) In the equation, do is the reciprocal of the slope of the straight line in the region where x is positive in the plot of FIG. Table 1 shows the values of do thus obtained. From Table 1, this value of do is equal to the above γ
It turns out that it matches d.

Thus, it can be seen that equation (2) can be expressed as equation (3).

[0042]

(Equation 3) Thus, the observed permittivity ε _obs weighs 63% of the information in the range of the electrical length γd of the electrode, and thus the electrical length γ as a measure of the measured depth of the electrode.
It turns out that it is appropriate to use d.

Further, from Table 1, it can be seen that the electrical length γd can be reduced by reducing the area of the tip surface of the internal electrode or by reducing the distance between the internal electrode and the external electrode. Therefore, it can be seen that by reducing the area of the tip surface of the internal electrode, the measurement depth when performing the moisture measurement by the TDR method can be reduced. In addition, since the measurement depth can be set to several tens μm or less,
It can be seen that the water content of the skin surface layer such as the stratum corneum can be measured.

[0044]

[Table 1]

[0045]

When the electrode of the present invention is used to measure the moisture of the skin surface by measuring the dielectric relaxation such as the TDR method, the moisture of a desired depth is measured within 100 μm from the outermost surface of the skin. This makes it possible to measure the water content of the stratum corneum.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electrode of the present invention.

FIG. 2 is a sectional view of the electrode of the present invention.

FIG. 3 is a perspective view of an internal electrode of the electrode of the present invention.

FIG. 4 is a cross-sectional view of electrodes of an example and a comparative example.

FIG. 5 is an explanatory diagram of a method of measuring a measurement depth of an electrode.

FIG. 6 is a diagram showing the relationship between the reading of a film thickness meter and the rate of change in dielectric constant.

FIG. 7 is a diagram showing a relationship between a reading of a film thickness meter and a dielectric constant change rate.

FIG. 8 is a diagram illustrating a relationship between a radius of an internal electrode and an electrical length.

FIG. 9 is a sectional view of a conventional electrode.

[Explanation of symbols]

 Reference Signs List 1 electrode 1a internal electrode 1b external electrode 1c insulating material 2 coaxial cable 2a internal conductor 2b external conductor 10, 10a to 10e electrode 11 glass plate 12 Teflon tape 13 water bath 14 Z stage 15 thickness gauge

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI G01N 22/04 G01N 22/04 Z (56) References JP-A-2-110357 (JP, A) JP-A-60-63039 ( JP, A) JP 57-46852 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 5/00 A61B 5/05 A61B 10/00 G01N 22/00 G01N 22 / 04

Claims (7)

(57) [Claims] 1. An internal electrode having a core wire and an external electrode coaxially disposed on the internal electrode via an insulator, wherein the tip surface of the internal electrode and the tip surface of the external electrode are in contact with the sample to be measured. An electrode for measuring dielectric relaxation, which is a surface, wherein the electrode has an electric length of 100 μm or less. 2. The electrode for dielectric relaxation measurement according to claim 1, wherein the electric length of the electrode is 1 μm to 100 μm. 3. The electrode for dielectric relaxation measurement according to claim 1, wherein the diameter of the internal electrode is reduced continuously or stepwise toward the tip of the electrode. 4. The electrode for dielectric relaxation measurement according to claim 1, wherein the tip surface of the internal electrode is circular or the tip surface is annular by forming a concave portion at the tip portion. . 5. The area of the tip surface of the internal electrode is 78 μm ²
5. The electrode for dielectric relaxation measurement according to claim ^{4, wherein the} thickness is from about 5.7 × 10 ⁴ μm ² . 6. A circular tip surface of an internal electrode having a diameter of 10
The electrode for dielectric relaxation measurement according to claim 4, wherein the thickness is from μm to 270 μm. 7. The dielectric relaxation measurement electrode according to claim 1, wherein a distance between the internal electrode and the external electrode on the distal end surface is 10 μm to 310 μm.