JP3250849B2 - Surface acoustic wave device for measuring liquid properties. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device for measuring characteristics of a liquid, such as viscosity, conductivity, and dielectric constant, of the liquid using the surface acoustic wave.

[0002]

2. Description of the Related Art Conventionally, this type of device has a comb-shaped input electrode for forming first and second surface acoustic wave propagation paths 10a and 10b on a piezoelectric substrate 10, as shown in FIG. 11 and 12 and two sets of output electrodes 13 and 14 are provided so as to face each other, and the first and second surface acoustic wave propagation paths 10a and 10b, which are input electrodes 11 and 12 and output electrodes 13 and 14, respectively. A rectangular conductive thin film 15, which short-circuits the entirety thereof to each predetermined region on the piezoelectric substrate 10,
16 are provided. When measuring the characteristics of the liquid using this apparatus, a rectangular frame 17 made of synthetic resin is fixed on one conductive thin film 15 with silicon rubber or the like to form a pool therein. The pool is filled with a liquid to be measured, a high-frequency signal from an oscillator 18 is applied to the input electrodes 11 and 12, and a signal output from the output electrodes 13 and 14 is supplied to a vector volt meter 19, so that The difference in the propagation speed of the surface acoustic wave on the first and second surface acoustic wave propagation paths 10a and 10b due to the presence or absence is detected by the vector voltmeter 19 to measure the viscosity of the liquid.

[0003] Another conventional device of this kind is a comb-shaped input device for forming first and second surface acoustic wave propagation paths 20a and 20b on a piezoelectric substrate 20, for example, as shown in FIG. Two pairs of electrodes 21 and 22 and output electrodes 23 and 24 are provided to face each other, and a predetermined surface of the piezoelectric substrate 20 is provided between the input electrode 21 and the output electrode 23 in the first surface acoustic wave propagation path 20a. A rectangular conductive thin film 25 that short-circuits the entire surface is provided in the region, and a second surface acoustic wave propagation path 20 b is provided between the input electrode 22 and the output electrode 24 in a predetermined region on the piezoelectric substrate 20. A rectangular conductive thin film 26 that short-circuits only the conductive thin film 26 is provided. When measuring the characteristics of the liquid using this apparatus, a rectangular frame 27 made of synthetic resin is fixed on the conductive thin films 25 and 26 with silicon rubber or the like to form a pool therein. At the same time, the pool is filled with a liquid to be measured, a high-frequency signal from an oscillator 28 is applied to the input electrodes 21 and 22, and a signal output from the output electrodes 23 and 24 is supplied to a vector volt meter 29. The difference between the propagation speed and the propagation loss of the surface acoustic wave on the first and second surface acoustic wave propagation paths 10a and 10b due to the difference between the conductive thin films 25 and 26 is detected by the vector voltmeter 19, respectively, and The conductivity and the dielectric constant are respectively measured.

[0004]

However, when the viscosity, conductivity, and dielectric constant of a liquid are to be measured, it is necessary to use the above-mentioned conventional surface acoustic wave device for the viscosity of the liquid. With respect to the conductivity and permittivity of the liquid, it was necessary to use the latter conventional surface acoustic wave device. Therefore, in the conventional apparatus, it is difficult to measure the viscosity, conductivity, and dielectric constant of the liquid under the same condition, and the difference in the measurement conditions between the measured viscosity and the conductivity and dielectric constant is difficult. Error was included. In this case, the measurement of the viscosity of the liquid and the measurement of the conductivity and the dielectric constant of the liquid must be performed separately, and the measurement is troublesome. SUMMARY OF THE INVENTION The present invention has been made to address the above-described problems, and has as its object to reduce the viscosity, conductivity, and permittivity of a liquid without including errors due to differences in measurement conditions. An object of the present invention is to provide a surface acoustic wave device for measuring characteristics.

[0005]

In order to achieve the above-mentioned object, the present invention provides a first and a second method in which a first and a second layers are deposited in parallel on a piezoelectric substrate .
2 conductive thin films and one side of each of these conductive thin films
First and second input electrodes provided in a comb shape;
Provided on the plate in a comb shape on the other side of the conductive thin film, respectively.
A first output electrode and a second output electrode.
And the entire area of the second conductive thin film is covered by the first and second conductive films.
Short-circuit between the force electrode and the first and second output electrodes respectively
The first and second surface acoustic wave propagation paths
In both cases, in parallel with the second conductive thin film on the piezoelectric substrate
A third comb-like shape provided on one side of the deposited third conductive thin film
Provided in a comb shape on the other side of the third conductive thin film with the input electrode of
A third output electrode, the third conductive
Between the third input electrode and the output electrode around the thin film
A third surface acoustic wave propagation path configured to short-circuit
And the first surface acoustic wave propagation path and the second surface acoustic wave
Between the transport path and the second surface acoustic wave propagation path and the third bullet
A partition groove located between the conductive surface wave propagation paths and the piezoelectric substrate
The second conductive thin film and the third conductive thin film.
Form a pool on the membrane that is filled with the liquid to be measured
The frame is fixed and used
To measure liquid viscosity, conductivity, dielectric constant, etc.
And a surface acoustic wave device.

[0006]

According to the present invention, the first to third surface acoustic wave propagation paths are formed on the same piezoelectric substrate, and the first and second surface acoustic wave propagation paths have input electrodes. A conductive thin film whose entire area is short-circuited is provided between the first electrode and the output electrode, and the third surface acoustic wave propagation path has a conductive thin-film short-circuited only around the area between the input electrode and the output electrode. Since the thin film is provided, if a pool is formed with a frame on the conductive thin film of the second and third surface acoustic wave propagation paths and the pool is filled with the liquid to be measured, the first and second layers are formed. The viscosity of the liquid is measured by the difference in the propagation speed of the surface acoustic wave on the surface acoustic wave propagation path, and the difference between the propagation velocity and the propagation loss of the surface acoustic wave on the second and third surface acoustic wave propagation paths. Can measure the conductivity and permittivity of the liquid. Each partition between the first to third surface acoustic wave propagation paths prevents surface acoustic waves propagating on each surface acoustic wave propagation path from invading another propagation path.

[0007]

As can be understood from the above description of the operation, according to the present invention, the viscosity, conductivity and dielectric constant of a liquid can be measured simultaneously under the same conditions, so that errors due to differences in measurement conditions are not included, and The viscosity, conductivity, and dielectric constant of a liquid can be easily measured. Further, since each partition groove prevents entry of the surface acoustic wave into another propagation path, the accuracy of the measurement result is increased, and the width of each surface acoustic wave propagation path can be reduced. The device can be made compact.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view showing a surface acoustic wave device according to an embodiment of the present invention. This surface acoustic wave device is composed of LiNbO ₃ , LiTaO ₃ ,
Piezoelectric substrate 30 formed of a piezoelectric material such as quartz in a rectangular parallelepiped shape
(For example, the length of one side is about 20 mm and the thickness is about 0.5 to 1.0
mm). On the piezoelectric substrate 30, comb-shaped input electrodes 31, 32, 33 and output electrodes 34, 35, 36 which form first to third surface acoustic wave propagation paths 30a, 30b, 30c respectively face each other. It is provided. The first and second surface acoustic wave propagation paths 30a,
30b, input electrodes 31, 32 and output electrodes 34, 3
5, a thin gold film 3 deposited on the piezoelectric substrate 30 in a rectangular shape
7, 38 are provided. The gold thin films 37 and 38 function as conductive thin films, and are formed on the piezoelectric substrate 30 and the input electrodes 31 and 3 of the surface acoustic wave propagation paths 30a and 30b.
A predetermined area is entirely short-circuited between the second electrode 2 and the output electrodes 34 and 35. In the third surface acoustic wave propagation path 30c, a gold thin film 39 is provided between the input electrode 33 and the output electrode 36 and is deposited on the piezoelectric substrate 30 so as to surround the center in a rectangular shape.
The gold thin film 39 functions as a conductive thin film, and short-circuits only around a predetermined area on the piezoelectric substrate 30 between the input electrode 33 and the output electrode 36 of the surface acoustic wave propagation path 30c.

On the piezoelectric substrate 30, the first to third surface acoustic wave propagation paths 30a to 30
c may be provided repeatedly, or different types of surface acoustic wave propagation paths may be provided. Also, the piezoelectric substrate 30
On the top, the above-described first to third surface acoustic wave propagation paths 30a
It is not necessary to provide only the surface acoustic wave propagation path 30c and another surface acoustic wave propagation path.

[0010] Partition grooves 41a and 41 are provided between the first to third surface acoustic wave propagation paths 30a to 30c on the piezoelectric substrate 30.
are formed. This partition groove 41a,
The depth of 41b, 41c ... is about 0.2-0.3mm, and 50MHZ
This corresponds to 2 to 3 wavelengths of the surface acoustic wave of z.

In order to measure the viscosity of the liquid to be measured (strictly speaking, the value obtained by multiplying the viscosity by the density), the conductivity and the dielectric constant using the surface acoustic wave device configured as described above,
Prior to the measurement, a rectangular frame 42 having a height of 1 to several mm formed of a synthetic resin is fixed to the upper surfaces of the gold thin films 38 and 39 using silicon rubber or the like. A pool capable of containing a liquid is formed on 38 and 39. In this case, two frames having a size approximately half the size of the frame 42 may be provided on the upper surfaces of the gold thin films 38 and 39, respectively.

At the time of measurement, first, the high-frequency oscillator 4 is shared by the input electrodes 31 to 33 in a state where the liquid to be measured is not filled in the pool formed by the frame 42.
3, and the vector electrodes 44 to 36 are commonly connected to the output electrodes 34 to 36, and the input electrodes 31 to 33 are connected.
And supplies the high-frequency signal received by the output electrodes 34 to 36 to the vector voltmeter 44.
In the vector voltmeter 44, the output electrodes 34,
The difference between the propagation velocities of the surface acoustic waves respectively input from 35 is measured and the difference is stored as a reference value. Further, the propagation velocity difference and the propagation loss difference of each of the surface acoustic waves input from the output electrodes 35 and 36 are measured, and each difference is stored as a reference value.

Next, the pool is filled with a liquid to be measured (solution), and the propagation velocity difference of each surface acoustic wave input from the output electrodes 34 and 35 to the vector voltmeter 44 is determined in the same manner as described above. Measure and output electrode 3
The propagation velocity difference and the propagation loss difference of each of the surface acoustic waves input from 5 and 36 are measured. The viscosity, conductivity, and dielectric constant of the liquid are calculated by subtracting each of the reference values from these measurement results. The reason why the viscosity, conductivity, and dielectric constant of the liquid are measured in this manner will be briefly described below.

Regarding Viscosity If the liquid is not filled in the pool, the difference in propagation speed between the elastic surfaces propagating through the first and second surface acoustic wave propagation paths 30a and 30b is essentially "0". On the other hand, when the pool is filled with the liquid, the second surface acoustic wave propagation path 30b becomes the gold thin film 38.
Is not affected by the electrical properties (conductivity and permittivity) of the liquid because it is electrically short-circuited, but is affected by the mechanical properties (viscosity and density) of the liquid and its acoustic impedance is Varies depending on the mechanical properties (viscosity and density). Thereby, the second elastic surface propagation path 3
The propagation velocity of the surface acoustic wave on the first surface acoustic wave propagation path 30a varies according to the mechanical properties (viscosity and density) of the liquid. The change occurs as shown. Then, the viscosity of the liquid (a value strictly multiplied by the density) is derived from the map based on the measurement result and Equation 1.

[0015]

(Equation 1)

Here, ΔV is the difference between the propagation speeds of the detected surface acoustic waves, V is the surface acoustic wave propagation speed (constant) determined by the material of the piezoelectric substrate 30, and ω is the angle of the high-frequency signal generated from the oscillator 43. Frequency (constant), P is input electrode 3
1, 32, ρ is the density of the liquid to be measured, η is the viscosity of the liquid to be measured, and υ is the piezoelectric substrate 30.
Is the particle displacement velocity determined by the material of

Unless the pool is filled with the liquid, the difference in the propagation velocity and the difference in the propagation loss of the surface acoustic waves propagating through the second and third surface acoustic wave propagation paths 30b and 30c are essentially different from each other. It is "0". Even when the pool is filled with the liquid, since the liquid exists evenly on the second and third surface acoustic wave propagation paths 30b and 30c, the mechanical properties (viscosity of the liquid) for both propagation paths 30b and 30c And density) are offset. On the other hand, in this case, since the gold thin film 39 on the third surface acoustic wave propagation path 30c is short-circuited only at the periphery and is open at the center, the electric field due to the particle displacement in the piezoelectric substrate 30 is generated in the liquid. Leak. Therefore, the third surface acoustic wave propagation path 30
c is affected by the electrical properties (conductivity and dielectric constant) of the liquid, and the acoustic impedance of the propagation path 30c changes depending on the electrical properties (conductivity and dielectric constant) of the liquid. Accordingly, the propagation speed and propagation loss of the surface acoustic wave on the third surface acoustic wave path 30c change depending on the electrical properties (conductivity and dielectric constant) of the liquid, and the second surface acoustic wave path 30b
A change as shown in the following Expressions 2 and 3 occurs between the propagation speed and the propagation loss of the above surface acoustic wave. Then, the conductivity and the dielectric constant of the liquid are derived with reference to the measurement result and a map based on these Equations 2 and 3.

[0018]

(Equation 2)

[0019]

(Equation 3)

Here, ΔV is the difference in the propagation velocity of the detected surface acoustic wave, Δα is the difference in the propagation loss of the detected surface acoustic wave,
V is the surface acoustic wave propagation velocity (constant) determined by the material of the piezoelectric substrate 30, (ΔV / V ₀ ) _LSC is the ratio of the propagation velocity difference to the surface acoustic wave propagation velocity V when water is selected as the liquid Ω is the angular frequency (constant) of the high-frequency signal generated from the oscillator 43, ε
_L is the dielectric constant of the liquid to be measured, ε _W is the dielectric constant (constant) of water, ε _P is the dielectric constant (constant) of the substrate 30 determined by the material of the piezoelectric substrate 30, and σ is the dielectric constant of the liquid to be measured. Conductivity.

As can be understood from the above description of the measuring method, according to the above-described embodiment, the measuring object is measured by using the first to third surface acoustic wave propagation paths 30a to 30c provided on the same piezoelectric substrate 30. Since the viscosity, conductivity, and dielectric constant of the liquid can be measured, the viscosity, conductivity, and dielectric constant of the liquid can be measured simultaneously under the same conditions. Therefore, the viscosity, conductivity, and dielectric constant of the liquid can be easily measured without including an error due to a difference in measurement conditions. During the measurement, most of the energy of the surface acoustic wave is concentrated within about two wavelengths from the upper surface of the piezoelectric substrate 30. Therefore, each of the surface acoustic wave propagation paths 30a is formed by the partition grooves 41a to 41c.
The surface acoustic waves propagating on a to 30c do not enter other propagation paths, and the accuracy of the measurement result is increased.
The width of each surface acoustic wave propagation path can be reduced, and the size of the piezoelectric substrate 30 can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a surface acoustic wave device according to one embodiment of the present invention.

FIG. 2 is a schematic plan view of a conventional surface acoustic wave device.

FIG. 3 is a schematic plan view of another conventional surface acoustic wave device.

[Explanation of symbols]

30: piezoelectric substrate, 30a to 30c: surface acoustic wave propagation path,
31 to 33 ... input electrodes, 34 to 36 ... output electrodes, 37 to
39: gold thin film, 41a to 41c: partition groove, 42: frame.

Continuation of the front page (56) References JP-A-2-227661 (JP, A) JP-A-62-190905 (JP, A) JP-A-61-128138 (JP, A) JP-A-5-275653 (JP, A) JP-A-5-322736 (JP, A) JP-A-3-209157 (JP, A) JP-A-3-140838 (JP, A) Shoko Shiokawa, Solution-based sensor using SH-SAW device, IEICE bibliography, Japan, The Institute of Electronics, Information and Communication Engineers, May 25, 1992, Vol. 75, No. 5, Page. 224-234 (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 29/00-29/28 G01N 5/02 G01N 11/00-11/16 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A first and a second vapor deposition method, which are deposited in parallel on a piezoelectric substrate .
2 conductive thin films and one side of each of these conductive thin films
First and second input electrodes provided in a comb shape;
Provided on the plate in a comb shape on the other side of the conductive thin film, respectively.
A first output electrode and a second output electrode.
And the entire area of the second conductive thin film is covered by the first and second conductive films.
Short-circuit between the force electrode and the first and second output electrodes respectively
The first and second surface acoustic wave propagation paths
In both cases, in parallel with the second conductive thin film on the piezoelectric substrate
A third comb-like shape provided on one side of the deposited third conductive thin film
Provided in a comb shape on the other side of the third conductive thin film with the input electrode of
A third output electrode, the third conductive
Between the third input electrode and the output electrode around the thin film
A third surface acoustic wave propagation path configured to short-circuit
And the first surface acoustic wave propagation path and the second surface acoustic wave
Between the transport path and the second surface acoustic wave propagation path and the third bullet
A partition groove located between the conductive surface wave propagation paths and the piezoelectric substrate
The second conductive thin film and the third conductive thin film.
Form a pool on the membrane that is filled with the liquid to be measured
Surface acoustic wave device for measuring characteristics such as viscosity, conductivity, and dielectric constant of a liquid, wherein the surface of the frame is fixed and used .