JP5567894B2 - Surface acoustic wave sensor device - Google Patents

Description

  The present invention relates to a surface acoustic wave sensor device having a surface acoustic wave component.

  In general, the surface acoustic wave device includes a piezoelectric substrate, and an input electrode and an output electrode made up of comb-like electrode fingers provided on the piezoelectric substrate. In the surface acoustic wave device, when an electric signal is input to the input electrode, an electric field is generated between the electrode fingers, and the surface acoustic wave is excited by the piezoelectric effect and propagates on the piezoelectric substrate. Among these surface acoustic waves, detection of various substances and physical property values using a surface acoustic wave device that uses a shear horizontal surface acoustic wave (SH-SAW) that is displaced in a direction orthogonal to the propagation direction. An elastic wave sensor for performing measurement has been studied (see Patent Document 1 and Non-Patent Document 1).

  The elastic wave sensor has a configuration composed of two surface acoustic wave sensor elements shown in FIG. 4, and a sensor region that is in contact with a liquid object to be measured placed on a piezoelectric substrate is electrically connected by an opening. In the case of being open (surface acoustic wave sensor element 100) and in the case of being short-circuited (surface acoustic wave sensor element 200), there is a difference in the characteristics of the output signal output from the output electrode. ing. That is, the output signal when the sensor region on the piezoelectric substrate is open is subjected to physical interaction (electrical interaction and mechanical interaction), and the sensor region on the piezoelectric substrate is short-circuited. The output signal of the case is only subjected to mechanical interaction. Therefore, the relative dielectric constant and the electrical conductivity of the object to be measured can be obtained by canceling the mechanical interaction from both output signals and extracting the electrical interaction.

Japanese Patent No. 3481298

Yasufumi Hatou et al., “Development of SAW Oscillator Integrated SAW Sensor System”, IEICE Technical Report, IEICE, February 2003

However, the temperature characteristics of the surface acoustic wave sensor element having the open propagation path that is electrically opened and the surface acoustic wave sensor element having the short propagation path that is not electrically opened, that is, short-circuited. Is different.
For example, FIG. 5 shows a surface acoustic wave propagation velocity (vertical axis) obtained by simulation in a surface acoustic wave element having an open propagation path and a surface acoustic wave element having a short-circuit propagation path when methanol is the measurement target. ) And temperature (horizontal axis).
FIG. 5 is a numerical value obtained in a state where the sensor surface is in contact with air. In FIG. 5, the change is measured with reference to the propagation velocity of the surface acoustic wave at 20 ° C.

FIG. 6 shows the propagation velocity of surface acoustic waves obtained from experiments in a surface acoustic wave sensor element having an open propagation path and a surface acoustic wave sensor element having a short-circuit propagation path when methanol is the measurement target. The correspondence relationship between (vertical axis) and temperature (horizontal axis) is shown.
In FIG. 6, □ indicates the theoretical value of the characteristic change due to the change in the relative dielectric constant of the propagation velocity of the surface acoustic wave sensor element having an open propagation path with respect to the water temperature, and ○ indicates the surface acoustic wave sensor element having an open propagation path Shows the experimental value of the temperature characteristics of the propagation speed of, △ shows the temperature characteristics of the propagation speed of the surface acoustic wave device having a short-circuit propagation path and the experimental value of the characteristic change due to the change of the relative dielectric constant with respect to the water temperature, × is open It is the difference between □ and ○ of the propagation velocity of a surface acoustic wave sensor element having a propagation path, and shows a change due to temperature characteristics.
FIG. 6 is a numerical value obtained when water is in contact with the sensor surface. In FIG. 6, the change is measured with reference to the propagation velocity of the surface acoustic wave at 20 ° C.

As can be seen from FIGS. 5 and 6, the surface acoustic wave sensor element having the short-circuit propagation path has a smaller speed change with respect to the temperature than the surface acoustic wave sensor element having the open propagation path.
For example, from the simulation result of FIG. 5, as the temperature changes by 1 ° C., a speed change of −41.2 ppm occurs in the open propagation path, and a speed change of −36.8 ppm occurs in the short-circuit propagation path. For this reason, a sensor sensitivity difference of 5 ppm occurs every time the temperature changes by 1 ° C., and an error in measurement of electrical characteristics (conductivity, relative permittivity) or mechanical characteristics (density, viscosity) due to temperature changes. Will occur.
In addition, even when the specific gravity of the measurement substance is high, the mechanical influences of the open propagation path and the short-circuit propagation path are different, and an error occurs in the measurement of electrical characteristics or mechanical characteristics due to temperature changes.

  The present invention has been made in consideration of the above problems, and suppresses the influence of disturbance elements such as the temperature change of the piezoelectric substrate forming the sensor and the high specific gravity or viscosity of the solution to be measured. It is another object of the present invention to provide a surface acoustic wave sensor device capable of measuring the electrical characteristics or mechanical characteristics of a solution to be measured with high accuracy.

The surface acoustic wave sensor device of the present invention receives a reference signal, and outputs a first measurement signal in which the reference signal is changed due to mechanical characteristics including specific gravity and viscosity in a solution in contact with the sensor surface. The surface acoustic wave sensor element 1 and the reference signal are input, and the sensor surface in contact with the solution is configured to be affected by the characteristics of the measurement target in the solution, and the mechanical characteristics and the measurement A second surface acoustic wave sensor element that outputs a second measurement signal in which the reference signal has changed according to the characteristics of an object, the first surface acoustic wave sensor element and the second surface acoustic wave sensor element the length in the direction of propagating a reference signal, the influence of temperature changes and mechanical properties due to the structure of the sensor surface in the said first surface acoustic wave sensor element and the second surface acoustic wave element and Formed differently length component corresponding to the difference of the measurement error due to the difference, characterized in that from the amplitude ratio and phase difference in the first measurement signal and said second measurement signal, detecting a characteristic of the measurement object And

Surface acoustic wave sensor apparatus of the present invention has the sensor surface in which the first surface acoustic Namise capacitors element is covered with the conductive film detection surface, the second surface acoustic Namise capacitors element detection surface A length of the reference signal in the propagation direction of each of the first surface acoustic wave sensor element and the second surface acoustic wave sensor element has an open sensor surface, and the reference signal depends on temperature characteristics. It is characterized in that it is formed so that the change in the propagation speed of the same is the same.

Surface acoustic wave sensor apparatus of the present invention, the first surface acoustic wave sensor element and the second surface acoustic wave sensor element is produced on a substrate of LiTa O _3, wherein the solution is covered with the conductive film The difference in the influence of the mechanical characteristics on both the sensor surface and the opened sensor surface is small with respect to the measurement error.

Surface acoustic wave sensor apparatus of the present invention has the sensor surface in which the first surface acoustic Namise capacitors element is covered with the conductive film detection surface, the second surface acoustic Namise capacitors element detection surface The sensor surface has an open sensor surface, and has a sensor surface in which rectangular conductive films are arranged in parallel on the detection unit so that the longitudinal direction is perpendicular to the direction in which the reference signal propagates. The surface acoustic wave sensor element and the second surface acoustic wave element have different lengths in the direction in which the reference signal propagates, the reference signal is input, and the reference characteristic is determined according to the mechanical characteristics and the characteristics of the measurement target. It further has a 3rd surface acoustic wave element which outputs the 3rd measurement signal in which the signal changed.

  The surface acoustic wave sensor device according to the present invention has an amplitude between the first measurement signal output from the first surface acoustic wave sensor element and the second measurement signal output from the second surface acoustic wave sensor element. From the ratio and phase difference, or in the first measurement signal output from the first surface acoustic wave sensor element and the third measurement signal output from the output from the third surface acoustic wave sensor element The characteristic of the measurement object is detected from the amplitude ratio and the phase difference.

  According to the present invention, the influence of disturbance elements such as the temperature change of the piezoelectric substrate forming the sensor and the specific gravity or viscosity of the solution to be measured is high. By controlling the length of the propagation direction of each sensor, the change in the velocity change of the propagating elastic wave due to the change in the disturbance of each sensor is controlled in the same way, and the change in the velocity due to the change in the characteristics of the measured object The difference between the sensors can be detected with high accuracy, and the electrical property or mechanical property of the solution to be measured can be measured with high accuracy.

It is a conceptual diagram which shows the structural example of the surface acoustic wave sensor apparatus by the 1st Embodiment of this invention. It is a conceptual diagram which shows the structural example of the surface acoustic wave sensor apparatus of the other form in the 1st Embodiment of this invention. It is a conceptual diagram which shows the structural example of the surface acoustic wave sensor apparatus by the 2nd Embodiment of this invention. It is a figure explaining the 1st surface acoustic wave sensor element (with a short circuit propagation path) and the 2nd surface acoustic wave sensor element (with an open propagation path) in the conventional surface acoustic wave sensor device. The LiTaO ₃ in the case of the substrate material is a diagram showing the correspondence between the temperature and the velocity change in the first surface acoustic wave sensor element and the second surface acoustic wave sensor device obtained from the simulation. The LiTaO ₃ in the case of the substrate material is a diagram showing the correspondence between the temperature and the velocity change in the first surface acoustic wave sensor element and the second surface acoustic wave sensor device obtained by actual measurement.

According to the surface acoustic wave sensor device of the present invention, in the surface acoustic wave sensor elements provided in plurality, the length of the acoustic wave propagation direction is determined for each surface acoustic wave sensor element by the propagation speed of the elastic wave due to the influence of disturbance. These changes are adjusted so as to be the same between the surface acoustic wave sensor elements.
For example, in two surface acoustic wave sensor elements, a surface acoustic wave sensor element (a short-circuit propagation path is used) that has a sensor surface in which the surface of the detection unit, which is a region (propagation path) where the acoustic wave propagates, is covered with a conductor. Sensor surface having the first surface acoustic wave sensor element, and the upper surface of the detection portion of the conductive film on the surface of the detection portion which is a region (propagation path) where the acoustic wave propagates, and the detection portion is exposed The present invention relates to a surface acoustic wave sensor device including a second surface acoustic wave sensor element that is a surface acoustic wave sensor element (a sensor element having an open propagation path).

<First Embodiment>
Hereinafter, with reference to the drawings, two surface elasticity measures the electrical properties (conductivity, relative permittivity, etc.) and mechanical properties (density, viscosity, etc.) of a solution according to the first embodiment of the present invention. A surface acoustic wave sensor device including a wave sensor element will be described. FIG. 1 is a conceptual diagram showing a configuration example of the surface acoustic wave sensor device according to this embodiment. In particular, in the surface acoustic wave sensor device of the first embodiment, the solution to be measured is an alcohol (a substance in which a hydrocarbon hydrogen atom is replaced with a hydroxy group (—OH), for example, methanol (methanol in this embodiment)). : CH ₃ OH)), and the relative dielectric constant of the solution is obtained, and the alcohol concentration is detected from the relative dielectric constant.

The surface acoustic wave sensor device of the present embodiment includes a first surface acoustic wave sensor element 1, a second surface acoustic wave sensor element 2, an oscillator 51, a distributor 52, an amplitude ratio / phase difference detector 53, and a characteristic value calculation. Part 54 and RF (Radio Frequency) switches 55 and 56. The first surface acoustic wave sensor element 1 and the second surface acoustic wave sensor element 2 are formed on a piezoelectric substrate (not shown), which is LiTaO ₃ in this embodiment.

The first surface acoustic wave sensor element 1 includes a first propagation path 13 in which the surface of the detection unit (substrate surface on which acoustic waves propagate) is covered with a conductive film, for example, a metal film, between the input electrode 11 and the output electrode 12. The length of the first propagation path 13 (detection unit) in the direction x in which the elastic wave propagates is set to L2.
Moreover, in the 1st surface acoustic wave sensor element 1, the surface of this 1st propagation path 13 becomes a sensor surface which touches the solution of the object which detects a characteristic.

The second surface acoustic wave sensor element 2 is between the input electrode 21 and the output electrode 22, has a second propagation path 23 whose detection portion surface is covered with a conductive film, and an opening 24 is provided in the conductive film. The detection unit is exposed, and the length of the second propagation path 23 (detection unit) in the direction x in which the elastic wave propagates is set to L1.
In the second surface acoustic wave sensor element 2, the surface of the second propagation path 23 (that is, the surface of the detection unit) is a sensor surface that comes into contact with the solution whose characteristics are to be detected.
The first surface acoustic wave sensor element 1 and the second surface acoustic wave sensor element 2 are arranged in parallel so that the propagation direction of the surface acoustic wave is parallel to x.
In the present embodiment, the first surface acoustic wave sensor element 1 and the second surface acoustic wave sensor element 2 will be described as being arranged in parallel. As another configuration, the first surface acoustic wave sensor element 1 and the first surface acoustic wave sensor element 1 The two surface acoustic wave sensor elements 2 may be arranged in series so that the propagation direction is parallel to the x direction.

In the input electrode 11 and the input electrode 21, in order to excite the surface acoustic wave by the reference signal input from the oscillator 51 via the distributor 52, the interval between the combs is a high-frequency wavelength λ, and the width of the comb is λ. It is comprised by the comb-shaped electrode formed by / 8. As the width of the comb, various values such as λ / 4, λ / 8, and λ / 12 are used, but in this embodiment, λ / 8 is used.
Similarly, the output electrode 12 and the output electrode 22 receive the surface acoustic wave excited and propagated by the input electrode 11 and the input electrode 21, and the interval between the combs is a high-frequency wavelength λ, and the width of the comb is λ. It is comprised by the comb-shaped electrode formed by / 8.

The oscillator 51 generates a reference signal that is a high-frequency electrical signal.
The distributor 52 distributes the reference signal output from the oscillator 51 to the RF switch 55 and the amplitude ratio / phase difference detector 53.

The amplitude ratio / phase difference detector 53 detects the amplitude ratio and phase difference between the reference signal and the first measurement signal output from the first surface acoustic wave sensor element 1, and the detected amplitude ratio and phase difference are detected in the first order. 1 is output to the characteristic value calculator 54 as a detection signal.
The amplitude ratio / phase difference detector 53 detects the amplitude ratio and phase difference between the reference signal and the second measurement signal output from the second surface acoustic wave sensor element 2, and the detected amplitude ratio and phase difference are detected. Is output to the characteristic value calculator 54 as a second detection signal.

  The characteristic value calculation unit 54 calculates the ratio of the solution based on the amplitude ratio and phase difference in the first detection signal and the amplitude ratio and phase difference in the second detection signal output from the amplitude ratio / phase difference detection unit 53. The dielectric constant and conductivity are calculated (details will be described later).

The RF switch 55 is a switch that connects the output terminal of the distributor 52 to either the input electrode 11 of the first surface acoustic wave sensor element 1 or the input electrode 21 of the second surface acoustic wave sensor element 2. .
That is, the RF switch 55 transmits the reference signal supplied from the distributor 52 to the input electrode 11 of the first surface acoustic wave sensor element 1 or to the input electrode 21 of the second surface acoustic wave sensor element 2. This is a switch for switching the operation.

The RF switch 56 is one of the output electrode 12 of the first surface acoustic wave sensor element 1 and the output electrode 22 of the second surface acoustic wave sensor element 2 with respect to the input terminal of the amplitude ratio / phase difference detector 53. It is a switch to connect.
That is, the RF switch 56 outputs the first measurement signal output from the output electrode 12 of the first surface acoustic wave sensor element 1 or the second measurement output from the output electrode 22 of the second surface acoustic wave sensor element 2. This is a switch for switching which signal is transmitted to the amplitude ratio / phase difference detector 53.

As described above, in the present embodiment, the lengths of the first propagation path 13 and the second propagation path 23 are formed different from L2 and L1, respectively.
The substrate has temperature characteristics. For example, in the case of the substrate made of LiTaO ₃ used in the present embodiment, when the propagation speed of the surface acoustic wave propagating as the temperature rises, the rate of decrease is the first propagation path. Compared to 13, the second propagation path 23 is 5 ppm smaller in the change in propagation speed every 1 ° C.
That is, the first surface acoustic wave sensor element 1 and the second surface acoustic wave sensor element 2 are connected to the first surface acoustic wave sensor having a short-circuit propagation path, and the propagation speed changes by −36.8 ppm every 1 ° C. in the element. In the second surface acoustic wave sensor element 2 having the propagation path, the propagation speed per 1 ° C. changes by −41.2 ppm.
Accordingly, even when the temperature of the 1 ° C. changes, even if the solution characteristics do not change, a difference of 5 ppm in the propagation speed is measured, and the phase difference between the first propagation path 13 and the second propagation path 23 differs depending on this difference. As a result, a measurement error occurs when measuring the characteristics of the solution.

For example, when the propagation path lengths L2 and L1 are formed to be the same 50λ, the obtained phase change is expressed by the following formula for calculating the amount of phase change per 1 ° C. (every time) every time the temperature changes by 1 ° C. (Short) = 41.2 × 10 ⁻⁶ (speed change) × 360 × 50 (propagation path length) = 0.7416
Δφ1 (open) = 36.8 × 10 ⁻⁶ (speed change) × 360 × 50 (propagation path length) = 0.6624
It becomes.
Here, Δφ 2 (short) is a phase change per 1 ° C. in the first propagation path 13, and Δφ 1 (open) is a phase change per 1 ° C. in the second propagation path 23. As a result, due to the difference in temperature change in the propagation speed of the surface acoustic wave between the first propagation path 13 and the second propagation path 23, the temperature of 1 ° C. is reduced between the first propagation path 13 and the second propagation path 23. A phase change of 0.0792 degrees is generated for each temperature change.
In methanol targeted for measurement by the surface acoustic wave sensor device of the present embodiment, when the target is to measure a concentration change of 0.1%, the detection accuracy of the phase difference Δφ needs to be 0.0096 degrees, The phase change 0.0792 due to the temperature change described above cannot be allowed.

Therefore, in this embodiment, from 0.7416 / 0.6624 = 1.1196, the propagation path length L2 of the first propagation path 13 and the propagation path length L1 of the second propagation path length 23 are 1.196 times. By setting 55.98λ,
Δφ1 (open) = 36.8 × 10 ⁻⁶ (speed change) × 360 × 55.98 (propagation path length) = 0.7416
Thus, the phase change amount per 1 ° C. in the second propagation path 23 can be matched with the first propagation path 13.
At this time, the propagation path length L2 of the first propagation path 13 may be 1 / 1.196 times the propagation path length L1 of the second propagation path 23, but the phase change amount due to the actual concentration change of methanol. Therefore, as described above, it is better to adjust the length of the propagation path with the smaller speed change.

Next, calculation of the relative dielectric constant and conductivity of the solution in the characteristic value calculation unit 54 will be described.
In the following description, the phase change amount of the first propagation path 13 is Δφ2 (degree), the attenuation amount of the signal level of the reference signal is ΔA2, the phase change amount of the second propagation path 23 is Δφ1 (degree), and the reference signal The amount of signal level attenuation is ΔA1, temp is added as a subscript to the change due to temperature, vis is added as a subscript to the change accompanying the change in density-viscosity product, and the physical change of the solution (solution and sensor) Phys is added as a subscript to the amount of change due to mechanical interaction and electrical interaction with the surface, and elec is added as a subscript to the amount of change associated with the electrical interaction between the solution and the sensor surface.

  The following expression (1) is an expression for obtaining the attenuation change amount Δα / k. α is the propagation attenuation of the surface acoustic wave, Δα is the amount of change in attenuation of the surface acoustic wave in the solution (for example, methanol) with respect to the standard solution (for example, pure water), k is the wave number, and Δamp is the reference signal and the surface It is the amplitude ratio with the measurement signal from the acoustic wave sensor element, ΔA is the amount of change in the signal level of the reference signal, λ is the wavelength, and L is the propagation path length.

  In this equation (1), since the unit of attenuation change amount Δα / k (unit is Neper) and change amount ΔA (unit is dB) is different, unit conversion using the following equation (2) is performed. ing.

  Since the wave number k is k = (2π / λ), the equation (1) is transformed into the following equation (3).

  Similarly, the relational expression between the phase change and the speed change is expressed by the following expression (4).

  Also in this equation (4), the phase is output in units of degree. However, since the calculation is performed in units of radians (rad), X [degree] is expressed as Y [rad] by the following equation (5). Is converted to In the equation (4), the wave number k and the function of conversion by radians are canceled out in the numerator / denominator and simplified.

Next, calculation for obtaining the conductivity and relative dielectric constant performed in the characteristic value calculation unit 54 will be described.
The characteristic value calculator 54 receives the first detection signal corresponding to the first surface acoustic wave sensor element 1 input from the amplitude ratio / phase difference detector 53 and the second detection signal corresponding to the second surface acoustic wave sensor element 2. The following calculation is performed based on the detected signal.
The characteristic value calculator 54 generates the following equation (6) using the equation (1) based on the attenuation amount ΔA2 [dB] as the loss as the amplitude ratio in the first detection signal.

  The attenuation change amount Δα / k is expressed by the following equation (7) using the density-viscosity product of the solution. In equation (7), ν2 is the particle velocity along the propagation direction, P is the average value of power flow per unit width along the propagation direction, and ω is 2πf (f is the frequency of the reference signal). .

  The equations (6) and (7) are converted, and the density viscosity product ρ′η ′ of the solution is obtained by the following equation (8) as a mechanical interaction. In this equation (8), the amount of attenuation change due to the density viscosity product is Δαvis / k. Here, those with 'are those of the solution to be measured, and those without, for example, the density viscosity product ρη is a characteristic value of 20 ° C. water as a measurement standard, and the density ρ = 0.998. The viscosity η = 1.002, the conductivity σ = 0, and the relative dielectric constant er = 80.37.

  Next, the speed change of the signal level due to the temperature change is obtained by the following processing. From the mechanical interaction calculated as described above, a phase change amount due to the mechanical interaction in the first surface acoustic wave sensor element 1 is calculated by the following equation (9). The speed change due to the density viscosity product is ΔVvis / V. V represents the speed of the reference signal, and ΔVvis represents the speed difference between the reference signal and the first measurement signal propagated through the first propagation path 13.

  In the change of only the density-viscosity product, since the formulas (7) and (9) are reciprocals, the speed change ΔVvis / V obtained from the formula (9) is a negative (minus) value. Therefore, the formula (9) is substituted into the following formula (10).

  The phase change amount Δφ 2 in the first propagation path 13 of the first surface acoustic wave sensor element 1 is a combined amount of an element caused by a speed change in temperature characteristics and an element caused by a mechanical interaction. . For this reason, by using the following equation (11), the phase change amount Δφcal2 due to the mechanical interaction obtained by calculation is subtracted from the phase change amount Δφ2 as the measurement result, whereby the phase change amount due to the temperature change is obtained. Find Δφtemp.

  As a result, by using the first surface acoustic wave sensor element 1, the density-viscosity product of the mechanical interaction and the phase change amount due to the temperature change can be calculated separately from the measured phase change amount Δφ2. Can do.

Next, in the surface acoustic wave sensor device in which the propagation path length L2 of the first propagation path 13 is made longer than the propagation path length L1 of the second propagation path 23 in correspondence with the speed change due to the temperature characteristics in the present embodiment, A process in which the characteristic value calculation unit 54 determines the relative dielectric constant εr ′ and the conductivity σ ′ of the solution will be described.
When pure water is added as a solution, for each temperature change of 1 ° C., when the speed change in the first propagation path 13 is 49 ppm and the temperature change in the second propagation path 23 is 40 ppm, as already described, The propagation path length L2 of one propagation path 13 is formed to be 1.225 times the propagation path length L1 of the second propagation path 23 so as to have a propagation path length difference corresponding to the temperature change difference.

  Thus, by adopting a configuration in which the speed change caused by the temperature change is adjusted, Δφtemp is directly subtracted from the phase difference Δφ1 in the second propagation path 23 as shown in the following equation (12), The phase difference Δφphys due to the interaction (both the electric interaction and the mechanical interaction) is calculated. The difference is directly calculated by adjusting the lengths of the propagation path length L2 of the first propagation path 13 and the propagation path length L1 of the second propagation path 23 so that there is a speed change due to a temperature change. It is because it is doing.

Next, the conductivity and relative dielectric constant are calculated from the electrical interaction using the phase change Δφpyhs calculated by the equation (12).
In order to calculate the electrical interaction in the physical interaction, a process for canceling the mechanical interaction from the physical interaction is performed. The speed change ΔVvis / V or the attenuation change amount Δαvis / k (that is, −ΔVvis / V) due to the density-viscosity product, which is a mechanical interaction of the first surface acoustic wave sensor element 1.
Here, in this embodiment, since the propagation path lengths of the first propagation path 13 and the second propagation path 23 are different, the phase change is not used, and the speed change per unit length of the second propagation path 23 is not used. Each of ΔV1 / V and attenuation change amount Δαvis / k is converted using the following equations (13) and (14).

  The difference between the speed change ΔV1 / V in the second propagation path 23 and the speed change ΔVvis / V due to the density-viscosity product obtained from the first propagation path 13 is obtained by the following equation (15). Since each is a speed change per unit length, a difference can be directly obtained as shown in equation (15).

  Similarly, the difference between the attenuation change amount Δα1 / k in the second propagation path 23 and the attenuation change amount Δαvis / k due to the density-viscosity product obtained from the first propagation path 13 is obtained by the following equation (16). Since each is a change in speed per unit length, a difference can be directly obtained as in equation (16).

The relative dielectric constant εr ′ of the solution is calculated by the following equation (17) from the velocity change ΔVelec / V and the attenuation change amount Δφelec / k obtained by the equation (15), and (18) The conductivity σ ′ of the solution is calculated from the equation. (17) In the formula, and (18), .epsilon.0 is the dielectric constant of vacuum, Ks is the electromechanical coupling coefficient, the epsilon _P ^T is performed permittivity.

The methanol concentration corresponds to the obtained relative dielectric constant εr ′. Therefore, the characteristic value calculation unit 54 stores therein a table or an expression indicating the correspondence between the relative dielectric constant εr ′ and the methanol concentration, and calculates and obtains the methanol concentration from the obtained relative dielectric constant εr ′. .
The electrical conductivity σ ′ is related to the concentration of formic acid generated by oxidation due to consumption of methanol. A change in the concentration of methanol does not affect the change in the conductivity σ ′, and a change in the concentration of formic acid does not affect the change in the relative dielectric constant εr ′.
For this reason, the surface acoustic wave sensor device of the embodiment of the present application can accurately determine the methanol concentration by accurately measuring the relative dielectric constant εr ′.

As shown in FIG. 1, the surface acoustic wave sensor device of the present embodiment obtains a change in methanol concentration periodically (for example, every second). A control unit (not shown) periodically operates the oscillator to generate a high-frequency reference signal having a wavelength λ (which varies depending on the measurement target).
Next, the control unit controls the RF switches 55 and 56 to transmit the reference signal output from the distributor 52 to the input electrode 11 of the first surface acoustic wave sensor element 1 and output from the output electrode 12. The first measurement signal is output to the amplitude / phase difference detector 53.
The control unit controls the RF switches 55 and 56 to transmit the reference signal output from the distributor 52 to the input electrode 21 of the second surface acoustic wave sensor element 2 and output from the output electrode 22. The second measurement signal is output to the amplitude / phase difference detector 53.

Then, the amplitude ratio / phase difference detector 53 obtains an attenuation change ΔA2 and a phase change Δφ2 of the first measurement signal with respect to the reference signal based on the input reference signal, the first measurement signal, and the second measurement signal, As the first detection signal, the attenuation change ΔA1 and the phase change Δφ1 of the second measurement signal with respect to the reference signal are obtained and output to the characteristic value calculation unit 54 as the second detection signal.
The characteristic value calculation unit 54 uses the above-described equations (6) to (18) to change the attenuation change ΔA2 and phase change Δφ2 of the first measurement signal and the attenuation change ΔA1 and phase change Δφ1 of the second measurement signal. Thus, the relative dielectric constant εr ′ and the electrical conductivity σ ′ of methanol that is the solution to be measured are calculated.

With the configuration described above, according to the present embodiment, the surface acoustic wave sensor element (second surface acoustic wave sensor element 2) having the larger speed change per 1 ° C. is used to correct the difference in speed change due to temperature change. The surface elasticity of the surface acoustic wave sensor element with the smaller speed change so that the speed change with the surface acoustic wave sensor element with the smaller speed change per 1 ° C. (first surface acoustic wave sensor element 1) matches. The propagation distance of the wave is increased by the distance corresponding to the speed change per 1 ° C. with respect to the surface acoustic wave sensor element having the larger speed change.
As a result, the speed change due to the temperature characteristics between the first surface acoustic wave sensor element 1 and the second surface acoustic wave sensor element 2 can be made substantially the same.
Therefore, according to the present embodiment, the temperature-dependent speed change can be obtained from the first measurement signal with high accuracy, the phase change due to the physical interaction can be calculated, and finally the methanol The relative dielectric constant can be obtained with high accuracy, and the concentration of methanol can be easily and accurately obtained from the relative dielectric constant.

FIG. 2 shows a configuration of a surface acoustic wave sensor device having a different form from that of FIG. The difference from FIG. 1 is that the RF switches 55 and 56 are eliminated, and the outputs distributed to the two distributors 52 are the input electrode 11 of the first surface acoustic wave sensor element 1 and the second surface acoustic wave sensor element 2, respectively. The output electrode 12 of the first surface acoustic wave sensor element 1 and the output electrode 22 of the second surface acoustic wave sensor element 2 are connected to an amplitude ratio / phase difference detector 53. is there.
With this configuration, since the speed change due to the temperature change is adjusted for the propagation path length between the first propagation path 13 and the second propagation path 23, the amplitude ratio / phase difference detector 53 A difference in signal level from the second measurement signal is obtained and output to the characteristic value calculation unit 54 as an attenuation change ΔA. Further, the amplitude ratio / phase difference detector 53 obtains the phase difference between the first measurement signal and the second measurement signal, and outputs it to the characteristic value calculation unit 54 as Δφ.

  The characteristic value calculation unit 54 uses the attenuation change ΔA and the phase difference Δφ input from the amplitude ratio / phase difference detector 53 and calculates the attenuation change amount Δα / k according to the following equations (19) and (20). Each of the speed change amounts ΔV / V is calculated. The propagation length used in the equations (19) and (20) is L1 of the first propagation path 13 in the second surface acoustic wave sensor element 1.

  Then, the characteristic value calculation unit 54 calculates the relative permittivity εr ′ and the conductivity σ ′ according to the equations (21) and (22) using the calculated attenuation change amount Δα / k and the speed change amount ΔV / V. calculate.

In the present embodiment, the sensor surface is opened to the second surface acoustic wave sensor element 2, and the change due to the electrical interaction of the solution is measured to obtain the concentration of the solution. Both the acoustic wave sensor element 1 and the second surface acoustic wave sensor element 2 may have a configuration having a sensor surface in which the detection unit is covered with a conductive film.
At this time, nothing is provided on the surface of the conductive film of the first surface acoustic wave sensor element 1, while an antibody or the like is provided on the surface of the conductive film of the second surface acoustic wave sensor element 2. A biosensor composed of the surface acoustic wave sensor element may be configured.
When pure water is added, the first surface acoustic wave sensor element 1 and the second surface acoustic wave sensor element 2 have substantially the same speed change or signal level change due to temperature or solution viscosity. As described above, the propagation path length between the first propagation path 13 of the first surface acoustic wave sensor element 1 and the second propagation path 23 of the second surface acoustic wave sensor element 2 may be adjusted.

<Second Embodiment>
Hereinafter, with reference to the drawings, according to the second embodiment of the present invention, three surface elasticity measures the electrical properties (conductivity, relative dielectric constant, etc.) and mechanical properties (density, viscosity, etc.) of the solution. A surface acoustic wave sensor device including a wave sensor element will be described. FIG. 3 is a conceptual diagram showing a configuration example of the surface acoustic wave sensor device according to this embodiment.
The second embodiment is different from the first embodiment in that, in addition to the first surface acoustic wave sensor element 1 and the second surface acoustic wave sensor element 2, a third surface acoustic wave sensor element 3 is added. This is a three-channel surface acoustic wave sensor element configuration of two surface acoustic wave sensor elements.

The third surface acoustic wave sensor element 3 is sandwiched between the input electrode 31 and the output electrode 32 to form a third propagation path 33. The third surface acoustic wave sensor element 3 is also arranged in parallel with the first surface acoustic wave sensor element 1 and the second surface acoustic wave sensor element 2 so that the propagation direction of the surface acoustic wave is parallel to the x direction. ing.
In the third surface acoustic wave sensor element 3, a long slit 34 is arranged in a plurality of x directions in the conductive film covering the upper surface of the detection unit so that the propagation direction is perpendicular to the x direction. It is formed on the conductive film on the propagation path 33. The detection portion is exposed at the portion where the slit 34 is formed.
In the present embodiment, the first surface acoustic wave sensor element 1, the second surface acoustic wave sensor element 2, and the second surface acoustic wave sensor element 3 will be described as being arranged in parallel. The surface acoustic wave sensor element 1, the second surface acoustic wave sensor element 2, and the second surface acoustic wave sensor element 3 may be arranged in series so that the propagation direction is parallel to the x direction.

Similar to the second surface acoustic wave sensor element 2, the third surface acoustic wave sensor element 3 detects a change caused by physical interaction (electrical interaction and mechanical interaction).
Therefore, a control unit (not shown) causes the oscillator 51 to generate a high-frequency reference signal and output it to the distributor 52.
The distributor 52 distributes and outputs the input reference signal to the input electrode 11 of the first surface acoustic wave sensor element 1 and the RF switch 55.

The RF switch 55 uses the reference signal input from the distributor 52 as either the input electrode 21 of the second surface acoustic wave sensor element 2 or the input electrode 31 of the third surface acoustic wave sensor element 3 under the control of the control unit. Switch whether to transmit to.
The RF switch 56 controls either the output electrode 22 of the second surface acoustic wave sensor element 2 or the output electrode 32 of the third surface acoustic wave sensor element 3 with the amplitude ratio / phase difference detector 53 under the control of the control unit. Switches whether to connect to the input terminal.
The third surface acoustic wave sensor element 3 outputs a third measurement signal in which the input reference signal is affected by physical interaction.

The amplitude ratio / phase difference detector 53 determines the phase difference between the first measurement signal and the second measurement signal, the amount of change in the signal level as the first detection signal, and the first measurement signal and the third measurement signal. Are output to the characteristic value calculator 54 as a second detection signal.
The characteristic value calculation unit 54 obtains the relative permittivity εr ′ and the conductivity σ ′ of the solution from the first detection signal and the second detection signal using the equations (19) to (22), respectively. .

According to the second embodiment described above, each of the first surface acoustic wave sensor element 1, the second surface acoustic wave sensor element 2, and the third surface acoustic wave sensor element 3, as in the first embodiment, In order to correct the influence of disturbance (for example, characteristic changes that become noise in actual measurement such as temperature dependency and viscosity dependency), the propagation length of the surface acoustic wave is formed to have different lengths.
As a result, the second embodiment, like the first embodiment, can obtain a temperature-dependent speed change from the first measurement signal with high accuracy when used as a methanol sensor. The phase change due to the interaction can be calculated, and finally the relative dielectric constant of methanol can be obtained with high accuracy, and the concentration of methanol can be easily and accurately obtained from this relative dielectric constant.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design and the like within a scope not departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 ... 1st surface acoustic wave sensor element 2 ... 2nd surface acoustic wave sensor element 3 ... 3rd surface acoustic wave sensor element 11, 21, 31 ... Input electrode 12, 22, 32 ... Output electrode 13 ... 1st propagation path 23 ... second propagation path 24 ... opening 33 ... third propagation path 34 ... slit 51 ... oscillator 52 ... distributor 53 ... amplitude ratio / phase difference detector 54 ... characteristic value calculation sections 55, 56 ... RF switch

Claims (5)

A first surface acoustic wave sensor element that inputs a reference signal and outputs a first measurement signal in which the reference signal has changed due to mechanical characteristics including specific gravity and viscosity in a solution in contact with the sensor surface;
The reference signal is input, and the sensor surface that contacts the solution is configured to be affected by the characteristics of the measurement target in the solution, and the reference signal varies depending on the mechanical characteristics and the characteristics of the measurement target. And a second surface acoustic wave sensor element that outputs the second measurement signal.
The length of the first surface acoustic wave sensor element and the second surface acoustic wave sensor element in the direction in which the reference signal propagates is determined by the first surface acoustic wave sensor element and the second surface acoustic wave element. The first measurement signal and the second measurement signal are formed differently by a length corresponding to a difference in measurement error due to a difference in the temperature change caused by the structure of the sensor surface and the influence of mechanical characteristics. A surface acoustic wave sensor device that detects characteristics of the measurement object from an amplitude ratio and a phase difference. Has the sensor surface in which the first surface acoustic Namise capacitors element is covered with the conductive film detection surface, comprising the sensor surface the second surface acoustic Namise capacitors element is opened the detection surface,
The length of the reference signal in the propagation direction of each of the first surface acoustic wave sensor element and the second surface acoustic wave sensor element is the same in the change in propagation speed of the reference signal due to temperature characteristics. The surface acoustic wave sensor device according to claim 1, wherein the surface acoustic wave sensor device is formed as described above. The first surface acoustic wave sensor element and the second surface acoustic wave sensor element are formed on a LiTa 2 O ₃ substrate, and the sensor surface is covered with the conductive film, and the open sensor surface. The surface acoustic wave sensor device according to claim 2, wherein a difference in the influence of the mechanical characteristic on both of the measurement and the measurement error is small with respect to the measurement error. Has the sensor surface in which the first surface acoustic Namise capacitors element is covered with the conductive film detection surface, comprising the sensor surface the second surface acoustic Namise capacitors element is opened the detection surface,
The first surface acoustic wave sensor element and the first surface acoustic wave sensor element have a sensor surface in which rectangular conductive films are arranged in parallel on the detection unit so that the longitudinal direction is perpendicular to the direction in which the reference signal propagates. A third measurement signal in which the reference signal is input and the reference signal is changed according to the mechanical characteristics and the characteristics of the measurement target. The surface acoustic wave sensor device according to claim 1, further comprising: a third surface acoustic wave element that outputs From the amplitude ratio and phase difference between the first measurement signal output from the first surface acoustic wave sensor element and the second measurement signal output from the second surface acoustic wave sensor element,
Alternatively, from the amplitude ratio and the phase difference between the first measurement signal output from the first surface acoustic wave sensor element and the third measurement signal output from the third surface acoustic wave sensor element. ,
The surface acoustic wave sensor device according to claim 4, wherein a characteristic of the measurement object is detected.

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