JP4826194B2 - Surface acoustic wave device and method of using the same - Google Patents

Description

The present invention relates to a surface acoustic wave element and an improvement of an electric signal processing method using the same.
In particular, the present invention is formed of a single crystal or a piezoelectric body such as LiNbO 3 or LiTaO 3 (hereinafter, these may be referred to as “piezoelectric crystals”), and is formed of at least a part of a spherical surface. A surface acoustic wave device having a base material having an annular surface that is continuous in an annular shape and exciting a surface acoustic wave (SAW) propagating along the annular surface (Hereinafter also referred to as SAW device)
The present invention relates to an improvement of a surface acoustic wave device suitable for testing body fluids in bio applications and the like, and detecting various physical properties such as elastic changes of liquids and a processing (use) method using the surface acoustic wave device.

  2. Description of the Related Art A surface acoustic wave element is well known as a device that generates a surface acoustic wave on a substrate and receives the generated surface acoustic wave.

In a SAW device, a pair of comb electrodes (Interdigital Transducer; IDT; hereinafter, also referred to as interdigital electrodes) is provided on a flat substrate.
The substrate is formed of a piezoelectric material, or a piezoelectric body is provided between the interdigital electrode and the substrate, and a high frequency voltage is supplied to one interdigital electrode, thereby arranging the electrodes in a line. To excite surface acoustic waves. The other interdigital electrode is disposed in the propagation direction of the surface acoustic wave and receives the surface acoustic wave.

A SAW device is an element that uses surface acoustic waves generated by the piezoelectric effect and has the following characteristics. Therefore, a delay line, an oscillation or resonance element for a transmitter, and a filter for selecting a frequency are used. , Chemical sensors, biosensors, remote tags, etc. have a wide range of applications.
1) The propagation speed is several thousand m / s, the wavelength is 1 GHz, the electromagnetic wave is 30 cm, whereas the surface acoustic wave is as short as 4 μm, so the device can be downsized (1 mm square or less).
2) Almost 90% of the energy is concentrated near the surface, so wave generation and detection from the surface and free access to light during propagation are possible.
3) Since it is an immobilization device, there is no adjustment and excellent reliability.
4) Mass production is easy because the same photolithography technology as LSI can be applied to the manufacturing technology.

International Publication WO 01/45255 discloses a spherical surface acoustic wave element (hereinafter also referred to as a ball SAW device or a spherical surface acoustic wave element).
The base of the ball SAW device has a spherical surface that can excite surface acoustic waves and can propagate the excited surface acoustic waves.
The electroacoustic transducer in the ball SAW device is arranged in a band having a predetermined width that is continuous in an annular shape on the spherical surface of the substrate, and the band is continuously generated by the surface acoustic wave excited on the surface. It is configured to propagate along the direction in which it is traveling and repeatedly circulate.

In the ball SAW device, the surface acoustic wave excited by the electroacoustic transducer in the surface acoustic wave propagation band that is continuous in an annular shape on the surface of the substrate is substantially not attenuated within the surface acoustic wave propagation band. The surface can be circulated repeatedly.
International Publication WO 01/45255

In ball SAW devices, when surface acoustic waves propagate with concentrated energy on a spherical surface, the energy does not leak from the surface of the sphere to the inside of the sphere or elsewhere, so the surface of the sphere propagates very many times. The phenomenon is used.
In the above device, since elastic waves are propagated repeatedly in a limited area, it is possible to measure very small changes in the propagation speed of surface acoustic waves or how to attenuate them. Its application is underway.

In exciting SAW in a SAW device using IDT,
A piezoelectric film is formed on the surface of a material such as glass or ceramic that constitutes a sphere (base material) that propagates a surface acoustic wave, and an interdigital electrode (IDT) disposed in contact with or close to the piezoelectric film is used. By applying an electric field, ultrasonic vibration (surface acoustic wave) can be generated based on the elastic deformation of the resulting piezoelectric film.
Alternatively, the substrate can be made of a piezoelectric crystal, and an electric field can be applied in contact with or close to the surface thereof to excite surface acoustic waves.
In the former case, the circulation path can be backed along an arbitrary maximum circumference on the sphere surface.
In the latter case, it is necessary to design a circular path in a path having a center line depending on the crystal axis of the crystal, but there is an advantage that the structure is simple and the attenuation due to the propagation of the surface acoustic wave is small.

In SAW, the propagation characteristics (velocity and amplitude) are perturbed due to changes in the characteristics of the medium in contact with the propagation plane and the adsorption and desorption of substances on the propagation plane. Therefore, a sensor can be realized by detecting these changes.
Propagation characteristics are the speed at which surface acoustic waves propagate on the device surface (even if the speed is required to circulate, absolute speed is not distinguished), or the frequency dependence of surface acoustic waves as a function of the speed, or propagation Indicates the amount of attenuation of surface acoustic waves.

  Conventional ball SAW devices have been premised on driving (use) in a gas, but demand for driving (use) in a liquid is also increasing.

In the field of medical diagnosis, an analyte is handled as a solution, such as blood or a sample processed from it or a body tissue processed and dissolved in a solution.
This is because the biological material can exist more stably in the liquid state than in the dry state, and protein alteration occurs due to drying, and the work of reacting it with other substances is particularly difficult in the dry state. Obviously, it is easier to observe the results in solution without using a drying process.

As described above, not only the evaluation of biological materials but also the diagnosis or treatment is performed by inserting a catheter or the like directly into the body or performing posture control from the outside of the human body with electromagnetic waves or the like.
However, inserting a test chip into the body requires a great effort to insert a large sensor except for the case of the digestive organ, for example, the inner diameter of the defect is at most several millimeters.
For this reason, blood viscosity is measured by collecting blood, and it has been difficult to monitor it in daily life.
For example, the viscosity of blood is an important parameter in the evaluation of hyperlipidemia and the like, but a method such as examining the flow of a structure having resistance under a microscope has to be taken.
In measuring the viscosity of blood without using such a microscope, a method using a surface acoustic wave element has been implemented.

In the case of a ball SAW device in which the SAW propagation path is a part of a spherical surface or a cylindrical surface, particularly when a piezoelectric crystal is used as a ball base material, the base material is a crystal, and therefore the elastic physical properties of the propagation surface are continuous. It has changed.
In the piezoelectric crystal, the particle displacement direction on the surface of the substrate changes according to the location of the spherical surface on which the surface acoustic wave propagates.
For this reason, it has been considered that it is difficult to propagate SAW in the liquid because vertical particle displacement is unavoidable over the circumference.

The Rayleigh wave, which is the most famous surface acoustic wave, is a non-dispersive (sound speed does not depend on frequency) wave in which a transverse wave (SV wave) having a displacement not parallel to the surface and a longitudinal wave are combined.
The Rayleigh wave is 90 ° out of phase between the horizontal and vertical displacements, so as shown in FIG. 1, the motion of particles near the surface draws an elliptical orbit, and its amplitude decreases exponentially as it moves away from the surface. . Most of the energy is concentrated at a depth within one wavelength from the surface.
As described above, when an interdigital electrode (IDT) is provided on the surface of the piezoelectric body and a high frequency electric field is applied, a surface acoustic wave is excited through the piezoelectric effect.
In the non-piezoelectric material, there is no transverse wave (SH wave) surface wave having a displacement parallel to the surface and the propagation direction.
However, it is known that a specific piezoelectric body has a pure transverse surface acoustic wave that concentrates energy on its surface and propagates.
This surface wave is called a piezoelectric surface slip wave or BGS wave (Bleustein-Gulyaev-Shimizu wave), and exists on a substrate having a plane parallel to the c-axis or polarization axis of a hexagonal 6 mm piezoelectric crystal or piezoelectric ceramic. It is reported to be.

Various techniques have been clarified that make it possible to evaluate the viscosity of a liquid using a planar surface acoustic wave device.
The surface acoustic wave generated near the center is reflected by the reflectors formed on the ladder formed on the left and right by the conductive film. When a high frequency signal is input from the outside, a phenomenon that causes a resonance phenomenon at a specific frequency occurs. The propagation speed of the surface acoustic wave can be measured by measuring the frequency by utilizing it.
Alternatively, the attenuation amount of the surface acoustic wave can be obtained by obtaining the amount of high-frequency input energy necessary for maintaining a certain resonance phenomenon.
The surface acoustic wave is a propagation mode having a vibration component having a surface displacement only in the horizontal direction on the surface, and is called an SH wave. Since such a mode does not generate compressive stress with respect to the solution in contact therewith, it interacts with the solution by sliding stress via the viscosity of the liquid.
In the propagation process of the SH wave, when the viscosity of the solution increases, the propagation speed of the SH wave decreases and the attenuation rate also changes, and measurement is possible by observing them.

However, in the case of the above method, the reflector needs to reflect the surface acoustic wave that has traveled with sufficient reflectivity, so that a sufficient size is necessary and the device is inevitably large.
Therefore, it is difficult to use a planar SAW device because of its size to insert into a human body for use (inspection / measurement).
When using a flat surface acoustic wave device for body fluid inspection, etc., instead of inserting it into the human body, it is necessary to bring the sample solution into contact with the SAW propagation path of the device. However, there is a difficulty in dropping the liquid into a predetermined place, which has been a hurdle for realizing liquid evaluation using a surface acoustic wave element.

In addition, there is a method called QCM as a liquid evaluation using a surface type surface acoustic wave element. In this method, electrodes are formed on the front and back of a section called an AT-cut crystal and immersed in a solution. is there.
The AT-cut quartz has a surface equilibrium in the direction of particle vibration on its surface, and can detect the response to the shear displacement with the solution with very high accuracy.
In the measurement using the above method, an antibody that binds to a specific protein is immobilized on the surface, and a technique for detecting a specific protein by measuring the resonance frequency associated with the surface mass load based on the binding with the protein in solution is also used. Applied.
In the case of an element using an AT cut crystal, the diameter is about 8 mm and it is difficult to reduce the size. Further, the sensitivity can be increased by increasing the resonance frequency of the AT cut crystal, but there is a limit to making it thin. There was also a difficulty in increasing sensitivity.

  An object of the present invention is to provide a ball SAW device capable of exciting to propagating a mode SAW capable of propagating through a solid-liquid interface.

The ball SAW device according to the present invention comprises:
A substrate having an annular surface formed of a part of a spherical surface or a cylindrical surface and continuous in an annular shape;
A surface acoustic wave excitation means for exciting a surface acoustic wave propagating along the annular surface,
The annular surface has a propagation path made of a convex curved surface through which surface acoustic waves can propagate, and the base material constituting the annular surface is LiNbO3 or LiTaO3,
The surface acoustic wave excitation means includes an interdigital electrode provided along the annular surface and connected to a high-frequency power source,
According to the application of an electric field to the interdigital electrode, a surface acoustic wave of a mode having at least a portion not displaced in the normal direction of the annular surface that propagates is excited.
In addition, using the surface acoustic wave element,
The surface acoustic wave propagation state is measured by exciting the surface acoustic wave with the surface acoustic wave excitation means and propagating it with at least a part of the annular surface in contact with the solution, and detecting the circulation of the surface acoustic wave. A method of using a surface acoustic wave device is proposed.

  By using a device capable of exciting and propagating a SAW in a mode that can propagate through a solid-liquid interface, the mechanical properties (viscosity, elastic modulus, density, etc.) and electrical properties (conductivity, dielectric constant) of the liquid are used. Etc.) can be applied to the measurement of the ball SAW device.

<Embodiment 1>
FIG. 2 shows a configuration example of a ball SAW device, an example of a main part in a state where measurement is performed using the ball SAW device, and an example of an observed surface acoustic wave circulation path.

Ball SAW device
A base material formed of a part of a spherical surface and having an annular surface continuous in an annular shape;
A surface acoustic wave excitation means for exciting a surface acoustic wave propagating along the annular surface, and
The annular surface has a propagation path composed of a curved surface through which surface acoustic waves can propagate,
The surface acoustic wave excitation means includes an interdigital electrode provided along the annular surface and connected to a high frequency power source.

In the present embodiment, LiNbO3 or LiTaO3 is employed as the base material made of piezoelectric crystals.
Using the above device,
The surface acoustic wave propagation state is measured by exciting the surface acoustic wave with the surface acoustic wave excitation means and propagating it with at least a part of the annular surface in contact with the solution, and detecting the circulation of the surface acoustic wave. To do.
In the figure, the annular surface and the solution are in contact with each other at a portion that is a “contact portion”.

Alternatively, a substrate having interdigital electrodes formed on the concave wall surface is immersed in pure water, and a piezoelectric crystal material shaped to fit into the concave wall surface is disposed, and generated when an electric field is applied to the interdigital electrode. As a result of observing SAW, it was possible to observe surface acoustic waves that circulate in water.
As described above, the method of exciting the elastic wave in the piezoelectric crystal material by indirectly acting the electromagnetic field generates an electric field corresponding to the interdigital electrode pattern with sufficient strength on the surface of the material to generate the elastic wave. Needless to say, it is necessary to be sufficiently close to the interval of the interdigital electrode pattern so as to be excited.

  When measuring in air (including in vacuum), the SAW propagation speed (sound speed) that could be measured most efficiently was 3600 to 4000 m / s and 3800 to 5000 m / s.

  The vibration excited at the former frequency is a mode called a Rayleigh wave or a vibration having a similar displacement, and the latter is a mode having a displacement horizontally on the surface.

It was also possible to change the mode of the excited surface acoustic wave by changing the frequency of the input high-frequency signal.
The method of influence with the solution due to the mode difference can be performed by selecting the mode.

  It was also confirmed that both measurement in air and measurement in solution were possible using the same element.

  By applying a predetermined high-frequency signal to the spherical surface acoustic wave element, it is possible to propagate the surface acoustic wave propagating in the solution. It is clear that even when a sensor using a SAW device is installed or inserted into the body, the possibility of damaging the tissue is small and effective.

<Embodiment 2>
FIG. 3 is an explanatory view showing an element having a shape different from that of the above device (a cylindrical shape whose center is a Z axis).
The diameter is slightly over 1 mm to 3 mm, and the SAW can be circulated along the side surface of the cylinder.
The piezoelectric crystal substrate used in the present embodiment is lithium niobate, and can be easily manufactured by cutting a linearly processed crystal material.
The advantage of the cylindrical shape is that it can be easily inserted into a blood vessel or the like and can be handled easily.

<Embodiment 3>
In applications where the element surface is in contact with a limited amount of sample outside the body, the solution is introduced into a container having a spherical inner surface using surface tension to excite the surface acoustic wave and It is obvious that the solution can be evaluated by measuring the propagation state, and that only a very small amount of sample is required.

<Embodiment 4>
It is also possible to use (measure) in a form in which a burst signal is input to a cylindrical element and the output is detected.
In the above case, when contact occurs in the body, the transmission of the surface acoustic wave is hindered depending on the degree of contact, and the output is reduced because energy is deprived.
Furthermore, the position of the region in contact with the tissue in the body on the circular path can be obtained from the output time of the reflected wave on the path that occurs at the contact portion, and the state of contact with the tissue can be recognized from the outside during catheter insertion. In addition to being considered effective, it is possible to identify elastically characteristic parts such as the hardness of cancerous tissue if the contact state changes as the element is pressed against the body tissue. Is possible.

<Embodiment 5>
FIG. 4 is an explanatory view showing another usage pattern of the ball SAW device, and relates to a type that drives a surface acoustic wave element in a non-contact manner.
In other words, the interdigital electrode is not formed on the ball surface, but is used in a case where the interdigital transducers are arranged very close (at least one-fourth or less of the electrode period of the interdigital electrode).
When a large number of ball SAW devices are used and various measurements and inspections need to be performed many times, it is not necessary to form interdigital electrodes on all the balls made of the piezoelectric crystal base material, which is consumed. This is effective in reducing the cost required for devices and measurement.
When the interdigital electrode is in contact with the electrolyte, it is difficult to apply an electric field to the piezoelectric surface with a sufficient voltage. Therefore, the intensity of the surface acoustic wave that can be generated and the intensity of the propagated surface acoustic wave that can be detected are reduced.

For this reason, the interdigital electrode is devised so as not to contact the solution.
In the figure, since there is an annular void region, the solution supplied from the lower part due to capillary action does not rise from this part to the upper part, preventing the interdigital electrode from contacting the solution (especially electrolyte solution). I can do it.

<Embodiment 6>
FIG. 5 is an explanatory view showing another embodiment, which is an example of a spherical shell type surface acoustic wave element.
In this type of device, it was mainly used for gas piping, and it was considered to be applied to a gas leak sensor by detecting the inflow of liquid or forming a gas sensitive film in the circulation path. Can be used to measure the viscosity and temperature of liquids.
it can.

<Embodiment 7>
FIG. 6 is an explanatory view showing another embodiment, and is an explanatory view relating to a case where the circulation path of the spherical surface acoustic wave element is immersed in the solution to be analyzed.
High-frequency generating means for generating a high-frequency signal to be applied to the spherical surface acoustic wave element;
A signal analyzer for analyzing the output is provided.

  The high-frequency generating means is a burst signal generator of several hundred MHz, and the signal analyzing means has means for analyzing the frequency from the digitizer and its time waveform information or analyzing the attenuation rate from the change in the intensity of the surface acoustic wave that circulates. May be.

FIG. 7 is an explanatory diagram showing another embodiment, and is an explanatory diagram related to a case where it is used for measuring an ultra-high pressure.
As described above, the spherical surface acoustic wave device according to the present invention can infer the elastic property of a solution from the propagation state of the surface acoustic wave propagating in contact with the solution.
If the container is sealed in a container filled with liquid (pressure resistance such as metal), even if the pressure on the outside of the container becomes extremely high, the container will not change its shape and the pressure will be changed to the liquid inside. Can be affected.
Liquids are known to change elastic constants under ultra-high pressure, and pressure changes can be measured from these changes.
When used in a gas environment like a conventional element, there is a problem that the container is deformed because the internal pressure changes as the external pressure changes. In order to protect it, a filter was also necessary.
When filled with a solution, the volume change with respect to the pressure of the solution is limited, and even if a shielding film that protects the element from the external environment is made of metal, the volume change of the solution is small and the element that functions as a pressure measurement application is calibrated It becomes possible to do.
The use form as this embodiment is effective when the pressure is several hundred atmospheres or more, and it is possible to measure pressures with different characteristics by selecting solutions with different elastic changes due to the pressure as the solution sealed inside. To.

In any of the above-described embodiments, various methods have been proposed for analyzing the output, and any method is not particularly excluded in the present invention.
When a general QCM or surface acoustic wave device is used as a sensor, its resonance frequency can be changed by a frequency called a counter and a circuit that searches for the maximum intensity is used. Obviously, a method similar to this may be used.

Explanatory drawing which shows the energy distribution in the behavior and depth direction of Rayleigh wave. FIG. 3 is an explanatory diagram showing a configuration example of a ball SAW device, an example of a main part in a state where measurement is performed using the ball SAW device, and an example of an observed circulation path of a surface acoustic wave. Explanatory drawing which concerns on other embodiment of this invention. Explanatory drawing which concerns on other embodiment of this invention. Explanatory drawing which concerns on other embodiment of this invention. Explanatory drawing which concerns on other embodiment of this invention. Explanatory drawing which concerns on other embodiment of this invention.

Claims (11)

A substrate having an annular surface formed of a part of a spherical surface or a cylindrical surface and continuous in an annular shape;
A surface acoustic wave excitation means for exciting a surface acoustic wave propagating along the annular surface, and
The annular surface has a propagation path made of a curved surface through which surface acoustic waves can propagate, and the base material constituting the annular surface is LiNbO3 or LiTaO3,
The surface acoustic wave excitation means includes an interdigital electrode provided along the annular surface and connected to a high-frequency power source,
A surface acoustic wave element that excites a surface acoustic wave in a mode having at least a portion that has no displacement in the normal direction of the annular surface that propagates in response to application of an electric field to the interdigital electrode.

The surface acoustic wave excited by the surface acoustic wave excitation means and propagating through the annular surface is
2. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave element is at least one selected from an SH wave, a piezoelectric surface slip wave, and a BGS wave (Bleustein-Gulyaev-Shimizu wave). The base material constituting the annular surface is made of a single crystal,
3. The surface acoustic wave device according to claim 1, wherein the annular surface is formed along a predetermined path determined by a crystal orientation of a single crystal forming the base material. 4. Propagation velocity of elastic surface waves, surface acoustic wave element according to claim 1 or 2, characterized in that a 3600~5000m / s.

The surface acoustic wave excited by the surface acoustic wave excitation means and propagating through the annular surface is
3. The surface acoustic wave device according to claim 2, wherein the surface acoustic wave is a transverse surface acoustic wave whose displacement is a mode parallel to the propagation surface.   The surface acoustic wave element according to claim 1, wherein the annular surface has a liquid flow path formed of a concave surface capable of propagating surface acoustic waves. The width of the propagation path through which the surface acoustic wave propagates on the annular surface has an apparent angle of 60 degrees or less as viewed from the center of the spherical surface of the propagation path,
Collimation angle from the center of the sphere surface obtained from the radius of curvature R of the spherical surface of the propagation path and the mean wavelength λ obtained from the circulation time and circumference of the surface acoustic wave excited there and the frequency of the surface acoustic wave excited. The surface acoustic wave element according to claim 1, wherein the surface acoustic wave element is larger than 0.5 times. Using the surface acoustic wave device according to claim 1,
The surface acoustic wave propagation state is measured by exciting the surface acoustic wave with the surface acoustic wave excitation means and propagating it with at least a part of the annular surface in contact with the solution, and detecting the circulation of the surface acoustic wave. A method of using a surface acoustic wave device.   The surface state of the propagation path of the element or the elastic change of the surrounding liquid is detected by measuring the propagation state of the surface acoustic wave using the surface acoustic wave element according to claim 1. A method of using the surface acoustic wave device as a feature. The surface acoustic wave element according to any one of claims 1 to 7 is disposed in a container in which a liquid is sealed, with at least a part of the annular surface in contact with the solution,
A method of using a surface acoustic wave element, wherein the pressure is measured by detecting a change in a propagation state of the surface acoustic wave according to the pressure outside the enclosure.   8. A surface acoustic wave device, wherein the surface acoustic wave device according to claim 1 is inserted into a body and used as an internal body environment evaluation device for evaluating the internal environment from a propagation state of the surface acoustic wave. How to use.

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