JPH05322736A - Plate wave ultrasonic device and viscosity sensor with it - Google Patents

Abstract

PURPOSE:To provide a plate wave ultrasonic device in which the velocity of a plate wave varies in compliance with the viscosity of liquid. CONSTITUTION:When rf pulses are fed to a reed-screen-shaped electrode 2, SH wave is energized in the direction of another reed-screen-shaped electrode 3. The SH wave is transmitted in a piezo ceramic 1 where a liquid is loaded on a metal thin film 4. Because the transmitted speed of the SH wave is related to the viscosity of liquid, the viscosity of a specimen to be measured can be calculated from the speed difference in the loaded state between the reference specimen and the specimen to be measured. Thereby a viscosity sensor can be achieved which presents measurability for specimen even through it is in a minute quantity, ensures simple handling and shortened measuring time, allows being constructed light and small, eliminates electric and mechanical affections on the specimen, and presents good sensitivity to permit sensing even fine change of viscosity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises at least two sets of interdigital electrodes provided on one plate surface of a piezoelectric substrate, and the piezoelectric substrate is adapted to correspond to the viscosity of a liquid in contact with the piezoelectric substrate. The present invention relates to a plate wave ultrasonic device in which the velocity of an SH (shear horizontal) wave of a zero-order symmetric mode (hereinafter referred to as So mode) of a propagating plate wave changes.

[0002]

2. Description of the Related Art Capillary viscometers, falling ball viscometers, rotational viscometers, and other viscometers are examples of conventional devices for measuring the viscosity of liquids. A capillary viscometer is a device for flowing a liquid into a capillary at a certain pressure to obtain the viscosity from the relationship between the pressure and the amount of effluent, and the Ostwald viscometer and the Canon-Fenske viscometer belong to this. The falling ball viscometer is one in which a ball is dropped into a liquid and the viscosity is calculated from the falling speed, and a Lawacheck viscometer, a Heppler viscometer and the like belong to this. The rotational viscometer is a method in which a liquid is placed in a double cylinder that rotates around an axis, the outer cylinder is rotated, and the force received by the inner cylinder due to the viscosity of the liquid is measured to calculate the viscosity. The Couette-Hachek viscometer and the MacMichel viscometer belong to this category. Other viscometers include parallel plate plastometers and penetrometers. The parallel plate plastometer sandwiches a sample between two plates and calculates the viscosity from the speed of crushing. The penetration meter calculates the viscosity from the penetration speed when a needle-shaped, conical or disk-shaped object is pushed into a sample. Since these conventional viscometers apply physical force directly to the liquid, such as flowing away the sample liquid or dropping a sphere into the liquid, the sample volume is relatively small, from several ml to several tens of ml. Requires a large amount. In addition, the device is generally large in size, and the measurement is troublesome and the measurement time is long. Above all, there is a big problem in measurement accuracy, and viscometers of ± 10% of the indicated value are also on the market, and it was almost impossible to catch a slight change in viscosity.

[0003]

Since the conventional viscometer applies a physical force directly to a liquid as a sample, the sample amount also requires a relatively large amount of several ml to several tens of ml. Not only that, the device is also generally large, and the measurement is troublesome and the measurement time is long. Besides, there is a big problem with the measurement accuracy, and there is a viscometer with ± 10% of the indicated value,
It was almost impossible to detect subtle changes in viscosity.

A delay line oscillator to which an ultrasonic device is applied is being studied for application to various sensors such as pressure sensors and biosensors. One of the conditions for an effective sensor is high sensitivity. That is, with respect to changes in the factors to be sensed (pressure, temperature, etc.),
It is desired that the amount of change in the delayed output signal with respect to the input is larger.

The object of the present invention is that it is possible to measure with a small amount of sample, the operation is simple, the measurement time is short, the size is small and the weight is small, and the electrical effect (dielectric property or conductivity) and mechanical effect on the sample are obtained. It is applied to a viscosity sensor (for example, a measurement system such as a plate wave delay line oscillator) that can eliminate (density, bulk modulus, etc.) and can detect subtle viscosity changes with high sensitivity. An object is to provide a plate wave ultrasonic device in which the speed of the plate wave changes.

[0006]

A plate wave ultrasonic device according to claim 1 is provided with at least two sets of interdigital electrodes on one plate surface of a piezoelectric substrate having two plate surfaces parallel to each other. In the plate wave ultrasonic device in which at least a part of at least one of the two plate surfaces is covered with a metal thin film, the interdigital transducer has an electrode period length substantially equal to the wavelength of the zero-order symmetric mode SH wave. And a portion of the piezoelectric substrate covered with the metal thin film is at least on the propagation path of the SH wave on the plate surface, and one or both of the two plate surfaces is in contact with a liquid. Characterize.

The plate wave ultrasonic device according to claim 2 is
The piezoelectric substrate is made of LiNbO ₃ , the plate surface of the piezoelectric substrate is a Z-cut surface of the LiNbO ₃ , and the SH wave is propagated in the X-axis direction of the Z-cut surface, or the X-axis ±
It is characterized in that the direction is 60 °.

The plate wave ultrasonic device according to claim 3 is
The piezoelectric substrate is made of piezoelectric ceramic, and the direction of the polarization axis of the piezoelectric substrate is parallel to the electrode fingers of the interdigital transducer.

A plate wave ultrasonic viscous sensor according to a fourth aspect comprises the plate wave ultrasonic device according to the first, second or third aspect, wherein the two sets of interdigital electrodes in the plate wave ultrasonic device are provided. A plate wave ultrasonic viscous sensor that detects a phase difference between electric signals input and output via the pair of electrodes and represents the velocity change of the SH wave propagating between the two sets of interdigital electrodes by the phase difference. It is characterized in that the viscosity of the liquid is calculated from the phase difference.

A plate wave ultrasonic viscous sensor according to a fifth aspect constitutes an oscillator using the plate wave ultrasonic device according to the first, second or third aspect as a delay element or a resonator, and
A plate-wave ultrasonic viscous sensor that expresses the velocity of the SH wave propagating between the pair of interdigital electrodes by the oscillation frequency of the oscillator, wherein the viscosity of the liquid is calculated from the oscillation frequency.

[0011]

The plate wave ultrasonic device of the present invention comprises a piezoelectric substrate and
It has a simple structure composed of at least two sets of interdigital electrodes, and further, in accordance with the viscosity of the liquid loaded on the propagation path of the So mode SH wave of the plate wave propagating in the piezoelectric substrate, The velocity of the plate wave SH wave propagating through the piezoelectric substrate can be changed. By coating a metal thin film between the piezoelectric substrate and the liquid in advance, the plate surface of the piezoelectric substrate loaded with the liquid can be electrically short-circuited. Therefore, it is possible to eliminate the electrical influence of the liquid (dielectricity, conductivity, etc.) that seems to affect the velocity of the SH wave. In addition, mechanical effects other than the viscosity that are considered to affect the velocity of SH waves (such as density and bulk modulus) are SH
It can be eliminated by using the So mode of waves. Since the So-mode SH wave has a small loss of ultrasonic waves into the liquid, the function as a viscous device can be further enhanced. In this way, by using the plate wave ultrasonic device of the present invention, a viscous sensor having excellent sensitivity can be constructed. For example, a liquid load plate wave delay line as a viscosity sensor can be constructed from the plate wave ultrasonic device of the present invention. When driving a plate wave delay line having a pair of input interdigital transducers and a pair of output interdigital transducers,
When the rf pulse signal is input to the input interdigital transducer, the pulse signal having the same frequency as the center frequency corresponding to the period of the input interdigital electrode is converted into a plate wave and propagates through the piezoelectric substrate to output the interdigital electrode. Leading to. At this time, if attention is paid to the SH wave of the plate waves and a liquid is loaded on the propagation path of the SH wave, a difference occurs in the propagation speed of the SH wave depending on the viscosity of the liquid. Moreover, the amount of change has a good correlation with the viscosity of the liquid. Therefore, the amount of change in velocity of the sample to be measured is calculated from the difference in propagation velocity between the reference sample serving as a reference and the sample to be measured, and the viscosity of the sample to be measured is detected from the amount of change in velocity.

By loading the liquid on the propagation path of the plate wave, that is, between two sets of interdigital electrodes on the piezoelectric substrate, the characteristic of the liquid itself propagates between the two sets of interdigital electrodes. Effectively reflected in the velocity of the plate wave. Therefore,
Since the rate of change of the speed with respect to the difference in the viscosity of the liquid can be increased, the sensitivity as a device can be improved. The same effect can be obtained by loading the liquid on the back side of the piezoelectric substrate corresponding to the space between the interdigital electrodes. Furthermore, the sensitivity of the device can be further improved by applying the liquid to portions of the plate surfaces of the piezoelectric substrate corresponding to the space between the interdigital electrodes and between the interdigital electrodes.

Since the piezoelectric substrate is made of LiNbO ₃ propagating in the Z-cut X-axis direction or propagating in the X-axis ± 60 ° direction, the rate of change of the velocity with respect to the difference in the viscosity of the liquid can be increased, so that the sensitivity as a device is increased. Can be improved. Further, plate waves SH of various modes propagating through the piezoelectric substrate
The sensitivity of the device can be further improved by targeting the SH wave of the So mode among the waves.
This is because the velocity change amount of the SH wave in the So mode (the velocity change amount of the measured sample with respect to the reference sample) is proportional to the square root of the viscosity of the measured sample over a wide range.

Since the piezoelectric substrate is made of piezoelectric ceramic and the direction of the polarization axis of the piezoelectric substrate is parallel to the electrode fingers of the interdigital transducer, the rate of change of the velocity of the plate wave with respect to the difference in the viscosity of the liquid is high. Can be increased,
The sensitivity of the device can be improved. Further, the sensitivity of the device can be further improved by selecting the So mode SH wave among the plate wave SH waves of various modes propagating through the piezoelectric substrate.
This is because the velocity change amount of the SH wave in the So mode is proportional to the square root of the viscosity of the sample to be measured over a wide range.

[0015]

FIG. 1 is a perspective view showing an embodiment of a plate wave ultrasonic device of the present invention. In this embodiment, the piezoelectric ceramic 1
, The interdigital electrode 2, the interdigital electrode 3, and the metal thin film 4
It consists of and. The piezoelectric ceramic 1 has a length of 35 mm and a width of 1.
5mm, 150 μm thick Tokin NEPEC-1
0, and the direction of the polarization axis of the piezoelectric ceramic 1 is parallel to the electrode fingers of the interdigital electrodes 2 and 3. Interdigital electrode 2
And 3 are aluminum thin films. The metal thin film 4 is made of aluminum and has a length L of 10 mm and a width of 10 mm.
And is provided on the propagation path of the plate wave.

FIG. 2 is a plan view showing a first embodiment of a liquid load plate wave delay line formed by using the plate wave ultrasonic device of the present invention. In this embodiment, the piezoelectric ceramic 11, the interdigital electrode 12, the interdigital electrode 13, and the interdigital electrode 1 are provided.
4, metal thin film 15, metal thin film 16, and signal generator 1
7, vector voltmeter 18, computer 19
It consists of and. The piezoelectric ceramic 11 has a length of 60 mm, a width of 15 mm and a thickness of 150 μm made by Tokin NEPEC-.
10 and the direction of the polarization axis of the piezoelectric ceramic 11 is parallel to the electrode fingers of the interdigital electrodes 12, 13, 14. The interdigital electrodes 12, 13, 14 are made of aluminum thin film. The metal thin films 15 and 16 are made of aluminum, have a length L of 15 mm and a width of 5 mm, and are provided on the propagation path of the plate wave. Interdigital electrodes 12, 13, 1
Reference numeral 4 is a normal type having the same shape and 10 pairs of electrode fingers, the electrode period length is 480 μm, and the center frequency is 4 MHz. The interdigital electrodes 13 are used for input, and the interdigital electrodes 12 and 14 are used for output. The distance between the interdigital electrodes 12 and 13 and the interdigital electrodes 13 and 14 is 20 mm. When the present embodiment is used, the liquids serving as the reference sample and the sample to be measured are loaded on the metal thin films 15 and 16, respectively. The metal thin films 15 and 16 are provided to electrically short-circuit the surface of the piezoelectric ceramic 11 loaded with the liquid. The reference sample and the sample to be measured are loaded to a thickness of 5 mm.

When the liquid load delay line of FIG. 2 is driven, when an rf pulse is input to the interdigital transducer 13 from the signal generator 17, the interdigital electrode 13 is interleaved with the interdigital electrodes 12 and 1.
The SH wave is excited in both directions of 4. Pure water as a reference sample is loaded on the metal thin film 15, and liquid of the sample to be measured is loaded on the metal thin film 16. Since the amount of change in the propagation velocity of the SH wave differs between pure water and the sample to be measured, and since the amount of change correlates with the viscosity of the liquid, it is possible to detect the difference in delay phase between the pure water and the sample to be measured. The viscosity of the sample to be measured can be measured. In the liquid load delay line of FIG. 2, this velocity difference is detected by the vector voltmeter 18 in the form of the phase difference of the delayed output signals at the interdigital electrodes 12 and 14 and analyzed by the computer 19. Since the propagation speed of the SH wave correlates with temperature, information about the correlation between the propagation speed and the temperature when a reference sample is loaded is input to the computer 19 in advance, so that the temperature with respect to the viscosity of the liquid The influence can be eliminated. In this way, since the viscosity is corrected by the temperature change, the viscosity of the sample to be measured can be accurately measured.

FIG. 3 shows SH propagating through the piezoelectric ceramic 11.
It is a characteristic diagram showing a velocity dispersion curve of a wave, and is a diagram showing a phase velocity of each mode with respect to a product of a frequency f of an SH wave and a thickness d of the piezoelectric ceramic 11. However, piezoelectric ceramic 1
In No. 1, both plate surfaces were electrically short-circuited. That is, a metal thin film is also provided on the plate surface of the piezoelectric ceramic 11 that does not have the interdigital electrode to electrically short the plate surface. In the figure, "short" indicates a short circuit state. SH as a plate wave
The wave has a plurality of modes, and the modes other than the So mode have large velocity dispersion. The So mode has a characteristic that the fd value exists from zero and the dispersibility is low as compared with other modes.

FIG. 4 is a characteristic diagram showing the relationship between the electromechanical coupling coefficient k ² calculated from the velocity difference of the So mode SH wave and the fd value under two different electrical boundary conditions of the piezoelectric ceramic 11. In the figure, "open" indicates that it is in an electrically open state. As is clear from this figure, the electromechanical coupling coefficient is larger when the plate surface that does not include the interdigital transducer (IDT) is in an electrically open state. When the fd value is 1 MHz · mm, the k ² value is about 46.
%, Fd value is 8 MHz · mm, k ² value is 20%
That is all. In this way, it can be seen that a large electromechanical coupling coefficient is exhibited over a wide range of fd values. A large electromechanical coupling coefficient increases the signal-to-noise ratio and, therefore, not only can the measurement accuracy be improved, but a stable liquid load delay line can be constructed.

FIG. 5 shows the velocity variation ΔV of the So-mode SH wave under four types of electrical boundary conditions when one plate surface of the piezoelectric ceramic 11 is loaded with a liquid of known viscosity.
It is a characteristic view which shows the relationship between / V and the square root of viscosity alpha.
However, the velocity change amount ΔV / V is based on the velocity V of pure water having a viscosity of 0 mPa · s, and ΔV is the velocity V _{L when the} liquid is loaded minus the velocity V when the pure water is loaded. It is a thing. The amount of change in speed greatly depends on whether the plate surface of the piezoelectric ceramic 11 is short-circuited or open. In this figure, S / O indicates that the plate surface on the liquid load side is short-circuited and the other plate surface is open. Similarly, S / S indicates that both plate surfaces are short-circuited, O / S indicates that the liquid load side is open, and O / O indicates that both plate surfaces are open. When the plate surface on the liquid load side is in a short circuit state, that is, in the case of S / O and S / S, the amount of change in speed is proportional to the square root of viscosity. In this way, S
By configuring a device such as / O and S / S, it is possible to eliminate the electrical influence of the liquid, thus enabling a precise measurement of the viscosity of the liquid.

FIG. 6 shows the So mode S when the liquid is loaded on one plate surface or both plate surfaces of the piezoelectric ceramic 11.
It is a characteristic view which shows the relationship between the amount VV of velocity changes of H wave, and the square root of viscosity alpha. However, the piezoelectric ceramic 11 is S /
It is in the S state. Eight types of glycerin aqueous solutions were used as the samples to be measured. In this figure, the open circles indicate measured values, and the solid lines indicate calculated values. It can be seen that the amount of change in velocity is proportional to the square root of the viscosity, and the measured and calculated values are in good agreement. Further, it can be seen that the detection sensitivity is almost doubled by loading the liquid on both plate surfaces of the piezoelectric ceramic 11.

FIG. 7 is a side view showing a second embodiment of the liquid load delay line formed by using the plate wave ultrasonic device of the present invention. In this embodiment, the piezoelectric substrate 21 and the interdigital transducer 2 are provided.
2, the interdigital transducer 23, and the computer 24. In this figure, the X, Y, and Z axes correspond to the coordinate system of the device. The piezoelectric substrate 21 has a length of 35 mm and a width of 15
The Z-cut X-propagation LiNbO ₃ having a thickness of 200 μm and the interdigital electrodes 22 and 23 are made of aluminum. The interdigital electrodes 22 and 23 have the same shape and are regular types each having 10 pairs of electrode fingers, and have an electrode cycle length of 480 μm and a center frequency of about 8.4 MHz. The interdigital electrode 22 is used for input, and the interdigital electrode 23 is used for output. The distance between the interdigital electrodes 22 and 23 is 20 mm. When using the present embodiment, a liquid as a reference sample or a sample to be measured is loaded on the propagation path of the plate wave. The reference sample and the sample to be measured are loaded to a thickness of 5 mm, and the length L on the propagation path thereof is 15 mm,
The width is 10 mm.

When an rf pulse is input to the interdigital transducer 22 when driving the liquid load delay line shown in FIG.
SH waves are excited in the direction of the interdigital transducer 23. S
The H wave propagates through the piezoelectric substrate 21 loaded with the liquid. SH
Pure water as the reference sample or the liquid of the sample to be measured is loaded on the wave propagation path. The amount of change in the propagation velocity of the SH wave differs between pure water and the sample to be measured, and since the amount of change correlates with the viscosity of the liquid, it is possible to detect the difference in the velocity of propagation between the pure water and the sample to be measured. The viscosity of the sample to be measured can be measured. At the time of measurement, since the SH wave propagation velocity correlates with temperature, information relating to the correlation between the propagation velocity and temperature when a reference sample is loaded is input to the computer 24 (not shown in the figure) in advance. By doing so, the influence of temperature on the viscosity of the liquid can be eliminated.

FIG. 8 is a characteristic diagram showing a velocity dispersion curve of SH waves propagating through the piezoelectric substrate 21. Pure water having a viscosity of 0 and 945 are shown.
The glycerin aqueous solution of mPa · s is applied to each piezoelectric substrate 21.
It is a figure which shows the propagation velocity of each mode of SH wave with respect to a frequency when it loads on the board surface which has a comb-shaped electrode.
However, the piezoelectric substrate 21 used had both plate surfaces electrically short-circuited. That is, by providing a metal thin film between the liquid and the piezoelectric substrate 21 on both plate surfaces of the piezoelectric substrate 21 with and without the interdigital electrodes, the plate surfaces are electrically short-circuited. .. The SH wave as a plate wave has a plurality of modes, and other modes except the So mode have large velocity dispersion. In this case, the So mode has a feature that the frequency value exists from zero and the dispersibility is lower than that of the other modes.

FIG. 9 shows a comb-shaped electrode (ID
T), when only the plate surface having no T is metal-coated and in a short circuit state, the product of the wave number k of the SH wave propagating in the piezoelectric substrate 21 and the thickness d of the piezoelectric substrate 21 and each mode of the SH wave. FIG. 6 is a characteristic diagram showing the relationship with the electromechanical coupling coefficient k ² . In this figure, both the case where the liquid is loaded and the case where the liquid is not loaded are shown. In the So mode, the maximum value is 5.0% when kd = 1.5. In Ao mode, kd = 4.0-
A value exceeding 4% is shown in the region of 9.0. Thus, it can be seen that the electromechanical coupling coefficient is large in the vicinity of kd = 1.5 in the So mode and kd = 4.0 to 9.0 in the Ao mode.

FIG. 10 shows a comb-shaped electrode (I
The wave number k of the SH wave propagating through the piezoelectric substrate 21 when only the plate surface having no DT) is metal-coated and in a short-circuited state.
FIG. 6 is a characteristic diagram showing a relationship between a product of the thickness d of the piezoelectric substrate 21 and a reduction rate of each mode of SH waves (a loss amount of ultrasonic waves in a liquid). In the So mode, it is almost zero when kd = 3.0 or less. On the other hand, in the Ao mode, the reduction rate is 13% of the maximum value when kd = 3.4, indicating that the loss of ultrasonic waves into the liquid is large. Thus, considering the characteristics in FIG. 9 as well, in the vicinity of kd = 1.5 in the So mode, the electromechanical coupling coefficient is large and the loss of ultrasonic waves in the liquid is small. Not only can the accuracy be improved, but also a stable liquid load delay line can be constructed.

FIG. 11 shows the velocity change amount ΔV / V of the So mode SH wave under four kinds of electrical boundary conditions when a liquid having a known viscosity is loaded on one plate surface of the piezoelectric substrate 21.
FIG. 3 is a characteristic diagram showing a relationship between a loss (amount of decrease) and a square root of viscosity α. However, the velocity change amount ΔV / V is 0
It is based on the speed V under a pure water load of mPa · s, and ΔV is a value obtained by subtracting the speed V under a pure water load from the speed V _L under the liquid load. Piezoelectric substrate 2
Although the plate surface of No. 1 hardly depends on whether the plate surface of the piezoelectric substrate 21 is short-circuited or open, the amount of change in speed greatly depends on the state of the plate surface of the piezoelectric substrate 21 being short-circuited or open. When the plate surface on the liquid load side is in a short circuit state, the amount of change in speed is proportional to the square root of viscosity.
In this way, by constructing a device in which one or both plate surfaces of the piezoelectric substrate 21 are short-circuited, the electrical influence of the liquid can be eliminated, so that the viscosity of the liquid can be precisely measured. ..

FIG. 12 shows the So mode SH when one surface of the piezoelectric substrate 21 is loaded with a liquid of known viscosity.
FIG. 6 is a characteristic diagram showing the relationship between the wave velocity change amount ΔV / V and the loss (reduction amount), and the square root of the viscosity α. Frequency is 15
It can be seen that the velocity change amount is proportional to the square root of the viscosity below MHz, and the viscosity can be detected from the velocity difference.

FIG. 13 shows the So mode SH when liquid is loaded on one plate surface or both plate surfaces of the piezoelectric substrate 21.
FIG. 6 is a characteristic diagram showing the relationship between the wave velocity change amount ΔV / V and the loss (reduction amount), and the square root of the viscosity α. However, the piezoelectric substrate 21 is in the S / S state. It can be seen that by loading the liquid on both plate surfaces of the piezoelectric substrate 21, the detection sensitivity due to the amount of change in speed is almost doubled. In this way, by utilizing the plate wave, both plate surfaces of the piezoelectric substrate can be used, so that the detection sensitivity can be improved.

FIG. 14 shows So of fd = 1.0 MHz · mm.
Phase velocities under four kinds of electrical boundary conditions of modes, and Z
FIG. 6 is a characteristic diagram showing a relationship with an in-plane propagation direction φ. However, f shows the frequency of the phase velocity. The phase velocities with respect to the propagation direction show similar tendencies in four types of electrical boundary conditions, and are 30 °, 90 ° (corresponding to the X-axis direction), 1
The maximum value is shown at 50 °, and the same change is repeated every 60 °.

FIG. 15 shows So of fd = 1.0 MHz · mm
And the electromechanical coupling coefficient k ² and reduction rate C in four electrical boundary conditions mode, which is a characteristic diagram showing the relationship between the propagation direction phi. The electromechanical coupling coefficient and the reduction rate with respect to the propagation direction show the same tendency in four kinds of electrical boundary conditions, showing the maximum values at 30, 90, and 150 °, and repeating the same change every 60 °. ing. Also,
The reduction rate is as small as 0.02% or less even at the maximum value, so that it is almost negligible as a viscosity sensor. In this way, when the use as a viscosity sensor is considered, the piezoelectric substrate 21 has a propagation direction of 90% in the LiNbO ₃ Z plate.
It can be seen that it is preferable to use so that the propagation direction of the SH wave is the X-axis direction or the propagation directions are 30 ° and 150 °.

[0032]

By using the plate wave ultrasonic wave device of the present invention, a viscous sensor having excellent sensitivity can be constructed.
In other words, configure a measurement system (for example, a sensor such as a plate wave delay line oscillator) that can measure even a small amount of sample, is easy to operate, has a short measurement time, is small and lightweight, and can detect subtle changes in viscosity. Is possible. When the liquid of the sample to be measured is loaded on the propagation path of the plate wave SH wave propagating through the piezoelectric substrate, the propagation speed of the plate wave SH wave changes according to the viscosity of the liquid. The viscosity of the sample to be measured can be calculated from the amount of change in velocity of the sample to be measured with reference to the reference sample under the liquid load.
At this time, since the propagation velocity of the SH wave correlates with temperature,
The influence of temperature on the viscosity of the liquid can be eliminated by previously inputting information on the correlation between the propagation velocity and the temperature when the reference sample is loaded into the computer. In this way, since the viscosity is corrected by the temperature change, the viscosity of the sample to be measured can be accurately measured.

By adopting the structure in which the metal film is coated between the piezoelectric substrate and the liquid, it is possible to eliminate the electrical influence on the viscosity. Further, by using the So mode SH wave, it is possible to eliminate the influence of mechanical constants on the viscosity.

When a liquid is loaded on the piezoelectric substrate, by adopting a structure of loading both plate surfaces of the piezoelectric substrate,
The sensitivity of the device can be improved almost twice as much as that of a single-sided load.

By adopting LiNbO ₃ that propagates in the Z-cut X-axis direction or propagates in the X-axis ± 60 ° direction as the piezoelectric substrate, the rate of change in velocity with respect to the difference in the viscosity of the liquid can be increased, so the sensitivity as a device is improved. it can. Furthermore, by using the SH wave of the So mode among the plate wave SH waves of various modes propagating in LiNbO ₃ , the sensitivity of the device can be further improved. This is because the velocity change amount of the SH wave in the So mode is proportional to the square root of the viscosity of the sample to be measured over a wide range.

By adopting a piezoelectric ceramic in which the direction of the polarization axis is parallel to the electrode fingers of the interdigital transducer as the piezoelectric substrate, the rate of change in speed with respect to the difference in the viscosity of the liquid can be increased, and therefore the sensitivity as a device. Can be improved. Furthermore, plate waves S of various modes propagating through the piezoelectric substrate
By targeting the SH wave of the So mode among the H waves, the sensitivity of the device can be further improved.
This is because the velocity change amount of the SH wave in the So mode is proportional to the square root of the viscosity of the sample to be measured over a wide range.

In general, it is known that solutes having a higher molecular weight have a larger increase in viscosity when comparing solutions having the same weight concentration. Therefore, a liquid load plate wave delay line constructed by using the plate wave ultrasonic device of the present invention is known. By using, it is possible to obtain an approximate molecular weight based on an empirical relational expression. Further, since the viscosity varies depending on the size and structure of the solute organic molecule, it is possible to obtain a clue about the structure of the solute organic molecule. In this way it is also possible to obtain information about organic compounds.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a plate wave ultrasonic device of the present invention.

FIG. 2 is a plan view showing a first embodiment of a liquid load delay line formed using the plate wave ultrasonic device of the present invention.

FIG. 3 is a characteristic diagram showing a velocity dispersion curve of SH waves propagating in the piezoelectric ceramic 11.

FIG. 4 is a characteristic diagram showing a relationship between an electromechanical coupling coefficient k ² and an fd value of the piezoelectric ceramic 11 under two different electrical boundary conditions.

FIG. 5 is a characteristic diagram showing the relationship between the velocity change amount ΔV / V of the So mode SH wave and the square root of the viscosity α of the piezoelectric ceramic 11 under four types of electrical boundary conditions.

FIG. 6 is a characteristic diagram showing the relationship between the velocity change amount ΔV / V of the So mode SH wave of the piezoelectric ceramic 11 and the square root of the viscosity α.

FIG. 7 is a side view showing a second embodiment of a liquid load delay line formed using the plate wave ultrasonic device of the present invention.

8 is a characteristic diagram showing a velocity dispersion curve of SH waves propagating in the piezoelectric substrate 21. FIG.

9 is a characteristic diagram showing the relationship between the product of the wave number k of SH waves propagating in the piezoelectric substrate 21 and the thickness d of the piezoelectric substrate 21 and the electromechanical coupling coefficient k ^2. FIG.

FIG. 10 is a characteristic diagram showing the relationship between the product of the wave number k of SH waves propagating in the piezoelectric substrate 21 and the thickness d of the piezoelectric substrate 21 and the reduction rate.

FIG. 11 is a characteristic diagram showing the relationship between the velocity change amount ΔV / V and loss of SH waves under four types of electrical boundary conditions and the square root of the viscosity α.

FIG. 12 shows SH wave velocity variation ΔV / V and loss,
The characteristic view which shows the relationship with the square root of viscosity (alpha).

FIG. 13 is an SH wave velocity change amount ΔV / V and loss;
The characteristic view which shows the relationship with the square root of viscosity (alpha).

FIG. 14 shows phase velocities under four kinds of electrical boundary conditions,
The characteristic view which shows the relationship with the propagation direction (phi).

FIG. 15 is a characteristic diagram showing the relationship between the electromechanical coupling coefficient k ² and the reduction rate C and the propagation direction φ under four kinds of electrical boundary conditions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 piezoelectric ceramic 2 interdigital electrode 3 interdigital electrode 4 metal thin film 11 piezoelectric thin film 12 interdigital electrode 13 interdigital electrode 14 interdigital electrode 15 metal thin film 16 metal thin film 17 signal generator 18 vector voltmeter 19 computer 21 piezoelectric substrate 22 interdigital Electrode 23 Interdigital electrode 24 Computer

Claims (5)

[Claims] 1. A piezoelectric substrate having two plate surfaces parallel to each other, wherein at least two sets of interdigital electrodes are provided on one plate surface, and at least a part of at least one of the two plate surfaces is made of metal. In the plate wave ultrasonic device covered with a thin film, the interdigital electrode has an electrode period length substantially equal to a wavelength of a zero-order symmetric mode SH wave, and a portion of the piezoelectric substrate covered with the metal thin film is ,
A plate wave ultrasonic device, wherein the liquid is in contact with at least one of the two plate surfaces and is on at least the propagation path of the SH wave on the plate surface. 2. The piezoelectric substrate is made of LiNbO ₃ , the plate surface of the piezoelectric substrate is a Z-cut surface of the LiNbO ₃ , and the propagation direction of the SH wave is the X-axis direction of the Z-cut surface, or The plate wave ultrasonic device according to claim 1, wherein the X-axis is in the direction of ± 60 °. 3. The piezoelectric substrate is made of piezoelectric ceramic,
The plate wave ultrasonic device according to claim 1, wherein a direction of a polarization axis of the piezoelectric substrate is parallel to an electrode finger of the interdigital transducer. 4. The plate wave ultrasonic device according to claim 1, 2 or 3, wherein a phase difference between electric signals input and output via the two sets of interdigital electrodes in the plate wave ultrasonic device is provided. A plate-wave ultrasonic viscous sensor for detecting and changing the velocity change of the SH wave propagating between the two sets of interdigital electrodes, wherein the viscosity of the liquid is calculated from the phase difference. Plate wave ultrasonic viscous sensor. 5. An oscillator using the plate wave ultrasonic device according to claim 1, 2 or 3 as a delay element or a resonator, wherein the velocity of the SH wave propagating between the two sets of interdigital electrodes is set. A plate wave ultrasonic viscous sensor represented by an oscillation frequency of the oscillator, wherein the viscosity of the liquid is calculated from the oscillation frequency.