JPH10142170A - Probe for dielectric relaxation measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a probe by which the property of a measuring part in a sample is confirmed and by which the concentration of moisture in the surface layer of the sample can be measured precisely when the concentration of the moisture in the sample is measured nondestructively according to a dielectric relaxation measurement by a time domain reflection(TDR) method or the like. SOLUTION: A probe is composed of a core-shaped internal electrode 21 and of an external electrode 23 which is arranged coaxially on the internal electrode 21 via an insulator 22. Then, an electrode 2, for dielectric relaxation measurement, in which the tip face of the internal electrode 21 and the tip face of the external electrode 23 are used as a contact face with a sample and an imaging means which images the enlarged image of a measuring part S0 at the sample by the electrode 2 for dielectric relaxation measurement are installed at the probe for dielectric relaxation measurement. A borescope 30 is preferably used as the imaging means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe for measuring dielectric relaxation, which makes it possible to determine the moisture concentration in a sample by measuring the dielectric constant of the sample. In particular, the present invention relates to a probe for measuring dielectric relaxation, which is capable of measuring a dielectric constant while confirming a measurement site in a sample with an enlarged image and obtaining a moisture concentration in the sample.

[0002]

2. Description of the Related Art In general, the properties of a sample containing water, such as skin and food, are greatly affected by its water content. Therefore, measurement of the water content of these samples is useful for grasping the properties and states of the samples, and also useful for evaluating the performance of chemicals, cosmetics, and the like applied to the samples.

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

On the other hand, as a method for measuring the moisture content of a sample surface layer, there has been proposed a method of measuring the dielectric constant of the sample surface layer and measuring the dielectric relaxation of water existing there. As a method of measuring dielectric relaxation, a frequency domain measurement method and a time domain reflection method (hereinafter, TDR method (Time Domain Reflectometry method))
In recent years, research on the latter measurement technique and its application has been actively pursued.

In the TDR method, an excitation signal (for example, a step pulse) having a specific waveform is applied to a sample, the reflected wave is observed, 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. For example, JP-A-2-110357 describes an example of measuring the moisture content of a living body by the TDR method (page 4, upper right column, line 10 to page 7, lower right column, line 17). According to this method, the water content in the sample can be measured nondestructively and quantitatively, and information on the state of water such as free water or bound water can be obtained. preferable.

FIG. 3 is a schematic diagram of a probe and a system used for measuring the dielectric relaxation. As shown in the figure, as the probe 1 used for measuring dielectric relaxation, a probe provided with a single electrode 2 in a cylindrical probe case 3 is used. One end of the electrode 2 of the probe 1 is open so that it can be in close contact with the sample S, and the other end is connected to the oscillation / reception device 6 via the cable 4 and the connector 5. The oscillation / reception device 6 has a built-in oscillator for generating an excitation signal and a receiver for receiving a reflected wave from the sample S, and is further connected to an oscilloscope for displaying respective waveforms. The oscillation / reception device 6 is connected to a computer 7 for obtaining a complex dielectric constant from an observed waveform and calculating a water concentration.

FIG. 4 is a sectional view of the electrode 2 used for the probe 1. As shown in the figure, the electrode 2 is composed of a core-shaped internal electrode 21 and an external electrode 23 disposed coaxially therearound via an insulator 22. The tip surface forms a contact surface with the measurement sample.

FIG. 5 is also a sectional view of a modification 2x of the electrode used in the probe 1. Similarly to the electrode 2 of FIG. 4, the electrode 2x has a core-shaped internal electrode 21 and an insulator 2
2 comprises external electrodes 23 arranged coaxially through
The diameters of the internal electrodes 21 and the external electrodes 23 are reduced while the ratio of the inner diameters of the inner electrodes 21 and the outer electrodes 23 is kept constant from the center of the electrode 2x toward the tip end surface. In this way, the electrical length of the electrode can be shortened by reducing the diameter of the tip surface of the internal electrode 21 that comes into contact with the sample and reducing the area of the tip surface. Further, when the diameter of the tip end surface of the internal electrode 21 is reduced, the impedance in the electrode is kept constant by keeping the ratio between the internal electrode 21 and the inner diameter of the external electrode 23 at an arbitrary position of the electrode. Is preferred. This makes it possible to prevent multiple reflections during dielectric relaxation measurement.

[0009]

However, in the conventional moisture measurement by the TDR method, is the measurement site of the sample to which the probe is closely attached a suitable measurement site for measuring the moisture content of the surface layer of the sample? Without confirming whether
The probe is simply brought into close contact with the surface of the sample, and the permittivity is measured. For this reason, even if the surface of the sample looks uniform by visual observation, it may be microscopically different, and the water content of the sample surface layer may not be accurately obtained.

For example, although the surface of the skin appears to be a flat plane when observed with the naked eye, microscopically, as shown in FIG. 2, there are skin grooves S1, skin ridges S2, sweat glands S3, and hairs S4. Therefore, when measuring the moisture content of the skin surface layer, the probe 1
4 If it is located above, it does not mean that the water content in the keratinocytes or epidermal cells in the skin surface layer is accurately measured.

In addition, when the skin surface is actually repeatedly measured a plurality of times at random, there is a problem that the obtained measured value of the amount of water greatly varies.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a dielectric relaxation measurement method capable of accurately measuring the water concentration of the surface layer of a sample while confirming the properties of the measurement site in the sample. The purpose is to obtain a probe.

[0013]

Means for Solving the Problems The present inventor has found that the above object can be achieved by incorporating imaging means for taking an enlarged image of a measurement site of a sample in one probe for measuring dielectric relaxation, 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 front end surface of the internal electrode and the front end surface of the external electrode are formed. Provided is a probe for dielectric relaxation measurement, comprising: a dielectric relaxation measurement electrode serving as a contact surface with a sample; and an imaging means for taking an enlarged image of a measurement site of the sample by the dielectric relaxation measurement electrode.

According to the present invention, since the electrode for dielectric relaxation measurement and the imaging means for taking an enlarged image are provided in one probe, an enlarged image of a portion where the electrode for dielectric relaxation measurement is in close contact with the sample is provided. Observation can be easily performed. For this reason, it is possible to determine the moisture concentration by measuring the dielectric constant of the measurement site with the dielectric relaxation measurement electrode while microscopically checking the properties of the measurement site in the sample.

Therefore, for example, when the skin is used as a measurement sample, the probe is brought into close contact with the hairless portion of the skin surface while confirming the hair on the skin surface by the image pickup means, whereby accurate moisture measurement of the skin surface layer can be performed. Make it possible.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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.

FIG. 1 shows a probe 1A according to an embodiment of the present invention.
FIG. The probe 1A has an electrode 2 having a predetermined electric length in a probe case 3,
Has a front perspective borescope 30 as an imaging means for taking an enlarged image of the site S0 where the sample is measured.

The borescope 30 comprises a small illuminator 31 for obliquely illuminating a measurement site S0 of the electrode 2, that is, a site where the electrode 2 is in close contact with the sample, an objective lens 32, and a cylindrical relay lens 33. The measurement site S0 is illuminated by the illumination device 31 to form an image of the measurement site S0. Further, a CCD camera 34 and a monitor 35 are sequentially connected to the borescope 30 so that an image formed by the borescope 30 can be observed on a screen of the monitor 35 as an enlarged image.

As such a borescope 30, a commercially available industrial endoscope or medical endoscope can be used. For example, a borescope FBtype or SLtype manufactured by Machida Manufacturing Co., Ltd. can be used. Can be used.

As the borescope, a direct-view type and a side-view type are known in addition to the above-mentioned front perspective type.
Since it is possible to take an image of the measurement site S0 of the electrode 2 without moving the lens, it is preferable to use a front perspective borescope.

The small illuminator 31 attached to the borescope 30 shown in FIG. 1 is provided as needed in the present invention. As the small illuminator 31, for example, a halogen lamp is used as a light source. Use a light guide that guides the light and illuminates any part.

On the other hand, the electrode 2 is composed of a core-shaped internal electrode and an external electrode coaxially arranged on the internal electrode via an insulator, and the front end surface of the internal electrode and the front end surface of the external electrode are formed. There is no particular limitation as long as it is an open-type electrode for measuring dielectric relaxation, which is a contact surface with the sample. For example, the same electrode as the conventional dielectric relaxation measurement electrode shown in FIG. 4 or 5 can be used.

When measuring the dielectric constant of a sample using an open-type electrode having an electrical length of γd, the present inventors have calculated the dielectric constant ε _obs (γd) by the following equation (1). , Electrical length γ
It has been found that by using an open-type electrode d, it is possible to measure the average water content in the range of approximately γd from the sample surface (Japanese Patent Application No. 7-150910).

[0025]

(Equation 1) In the formula, ε (z) represents a dielectric constant at a depth of z from the surface. This dielectric constant is obtained by comparing the dielectric constant ε _∞ and the water relaxation intensity Δ in a region sufficiently faster than the water relaxation time in the dielectric constant measurement.
The relaxation strength Δ 水 の of water is proportional to the water content of the sample.

The electric length γd of the electrode is such 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 (2), which is a relational expression between the electromagnetic wave V (ω) in the case, the reflected wave R (ω), and the complex permittivity ε ^* (ω) of the load.
, Is included as a parameter γd.

[0027]

(Equation 2) This electrical length γd can be obtained without covering the side surface of the electrode with an insulator.
The electrode can be determined by immersing the electrode tip in a known standard sample having a known complex permittivity ε ^* (ω) of 1 cm or more from the tip face and measuring the reflected wave.

The electrical length γd 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).

Therefore, in the present invention, the quantity of electricity of the electrode 2 to be used is appropriately set according to the depth at which the moisture concentration of the sample is measured, the expected mode of the concentration distribution in the depth direction, and the like. However, usually, the electric length is preferably in the range of 1 to 2000 μm, more preferably 10 to 500 μm.
m. If the electrical length is less than 1 μm, the change in the waveform of the reflected wave is too small, making accurate measurement difficult. On the other hand, when the electrical length exceeds 2000 μm, the attenuation of the signal in the GHz range increases, and the measurement accuracy decreases.

As a specific method for setting the electrical length of the electrode 2 to a desired value, for example, the area of the tip surface of the electrode where the internal electrode contacts the sample may be appropriately changed.
The distance between the inner electrode and the outer electrode at the tip surface may be changed as appropriate. For example, the tip surface of the internal electrode has a diameter of 10 μm to 2 μm.
70 μm circle, and the distance between the internal and external electrodes is 1
When the length is 0 μm to 310 μm, the electrical length is 100 μm.
An electrode of m or less can be obtained with good impedance matching with a coaxial cable to be connected to the electrode when measuring the dielectric constant.

The method of determining the dielectric relaxation at the electrode 2 using the probe 1A of the present invention may be either a frequency domain measurement method or a time domain reflection method (TDR method). it can.

Although the present invention has been described in detail with respect to the probe 1A shown in FIG. 1, the present invention can take various other forms. For example, although an example is shown in which one electrode 2 is provided in one probe case 3 in the probe 1A of FIG. 1, a plurality of electrodes may be incorporated as needed. In this case, the electrical lengths of the plurality of electrodes may be different from each other, or may be the same. When obtaining the water concentration distribution in the depth direction of the sample, even if it is necessary to obtain the permittivity of a plurality of electrodes having different electrical lengths, it is necessary to incorporate a plurality of electrodes with different electrical lengths into one probe. By doing so, measurement can be easily performed by a single dielectric constant measurement operation using this probe. Also, even when it is necessary to repeatedly measure the dielectric constant of an electrode having a specific electrical length a plurality of times in order to improve the measurement accuracy of the moisture concentration at a specific depth, the electrical length can be measured by one probe. By incorporating a plurality of equal electrodes, the dielectric constant measurement at a predetermined electrical length is simultaneously performed a plurality of times by a single dielectric constant measurement operation using this probe. Therefore, the total measurement time can be reduced, and the complexity of adjusting the electrodes to the same measurement site of the sample for each measurement can be eliminated.

The probe of the present invention has a guide for bringing the electrode into close contact with the sample, if necessary, a pressing means such as a spring for pressing the electrode against the surface of the sample with a predetermined pressure,
Sensors for simultaneously acquiring information other than moisture, such as a temperature sensor, a pH sensor, a Doppler blood flow meter, a color tone meter, a pressure sensor, a viscoelasticity measuring transducer, an ultrasonic probe for tomography, a microphone, an optical fiber,
An electromagnetic wave reception device of 1 kHz to 100 MHz or the like can be provided.

The sample to be measured by the probe of the present invention is not particularly limited. Although those having a water concentration near the sample surface can be widely measured, in particular,
It is useful for microscopically uneven surfaces such as skin, food, agricultural and marine products, wood, concrete and the like.

[0035]

According to the probe for dielectric relaxation measurement of the present invention, it is possible to accurately measure the water concentration in the surface layer of a sample while confirming the properties of the measurement site in the sample.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a probe for measuring dielectric relaxation of the present invention and a system for measuring a water concentration by dielectric relaxation measurement using the probe.

FIG. 2 is an explanatory diagram illustrating a state in which a probe is brought into close contact with the skin surface and dielectric relaxation measurement is being performed.

FIG. 3 is a schematic diagram of a conventional probe for measuring dielectric relaxation and a system for measuring a water concentration by dielectric relaxation measurement using the probe.

FIG. 4 is a sectional view of an electrode for dielectric relaxation measurement.

FIG. 5 is a sectional view of an electrode for dielectric relaxation measurement.

[Explanation of symbols]

 1, 1A probe 2 Dielectric relaxation measurement electrode 3 Probe case 4 Coaxial cable 5 Connector 6 Oscillator / receiver 7 Computer 21 Internal electrode 22 Insulator 23 External electrode 30 Borescope 31 Small illumination device 32 Objective lens 33 Relay lens 34 CCD camera 35 Monitor S0 Measurement site

Claims (3)

[Claims] 1. An internal electrode having a core wire shape and an external electrode coaxially disposed on the internal electrode via an insulator, wherein a tip surface of the internal electrode and a tip surface of the external electrode are in contact with a sample. A dielectric relaxation measurement probe, comprising: a dielectric relaxation measurement electrode to be used; and an imaging means for taking an enlarged image of a measurement site of a sample by the dielectric relaxation measurement electrode. 2. An imaging device according to claim 1, wherein said imaging means is a borescope.
The probe for measuring dielectric relaxation according to the above. 3. The borescope according to claim 2, wherein the borescope has a small illumination device for illuminating a measurement site of the sample by the dielectric relaxation measurement electrode, and is a front oblique borescope for obliquely imaging the measurement site of the sample. Probe for dielectric relaxation measurement.