WO2019097769A1

WO2019097769A1 - Solid microparticle mass measurement device

Info

Publication number: WO2019097769A1
Application number: PCT/JP2018/028452
Authority: WO
Inventors: 貴浩小高; 礒部　敦
Original assignee: 日立金属株式会社
Priority date: 2017-11-16
Filing date: 2018-07-30
Publication date: 2019-05-23
Also published as: JP2019090742A

Abstract

This solid microparticle mass measurement device includes: a solid microparticle adherence region (109) which is disposed at a surface elastic wave propagation region (105) and to which solid microparticles are caused to adhere; and a solid microparticle adherence amount detection unit (signal detection circuit) (91) which detects the adherence amount of solid microparticles adhered to the solid microparticle adherence region.

Description

Solid particle mass measuring device

The present invention relates to a solid particle mass measuring device.

Exhaust gas from an internal combustion engine such as a diesel engine includes solid particulates such as soot, so-called PM (Particle Matter), and air pollution by the solid particulates is a problem worldwide.

In order to control the amount of solid particulates contained in exhaust gas and discharged to the atmosphere, attempts have been made to attach a particulate sensor to the exhaust gas pipe of an internal combustion engine to control the discharge amount of solid particulates.

As a technique relevant to such a particulate sensor,

patent documents

1 and 2 are mentioned, for example. In

Patent Documents

1 and 2, a comb-shaped electrode is provided on a ceramic substrate, a bias is applied between the electrodes, and the resistance value of solid fine particles attached between the electrodes is measured to detect solid fine particles contained in exhaust gas. doing.

JP, 2011-226832, A JP-A-8-88533

However, in the particle sensor described in

Patent Documents

1 and 2, the amount of adhesion of the solid particles can not be measured unless the electrodes are made conductive by the solid particles attached between the electrodes. For this reason, in

patent documents

1 and 2, it is difficult to detect a minute amount of solid fine particles with high sensitivity.
An object of the present invention is to detect the content of solid fine particles contained in a gas with high sensitivity.

The solid particle mass measuring device according to one aspect of the present invention is a solid particle mass measuring device for measuring the content of solid particles contained in a gas, which is provided on a piezoelectric substrate and one end of the piezoelectric substrate, and has surface elasticity. An input electrode which excites a wave, an output electrode which is provided at the other end of the piezoelectric substrate and receives the surface acoustic wave which is excited by the input electrode and propagates a surface acoustic wave propagation region on the piezoelectric substrate; Having a solid particle adhesion region provided in the surface acoustic wave propagation region and adhering the solid particles, and a solid particle adhesion amount detection unit detecting the adhesion amount of the solid particles adhered to the solid particle adhesion region It features.

According to one aspect of the present invention, the content of solid fine particles contained in a gas can be detected with high sensitivity.

FIG. 1 is a view showing the configuration of a solid particulate matter mass measuring device according to a first embodiment. FIG. 7 is a view showing another configuration of the solid particulate matter mass measurement device of Example 2. FIG. 18 is a view showing another configuration of the solid particulate matter mass measurement device of Example 3. FIG. 18 is a view showing another configuration of the solid particulate matter mass measurement device of Example 4. It is a figure which shows the relationship between the propagation velocity fall rate of surface acoustic wave, and the adhesion amount (PM thickness) to the surface acoustic wave propagation path of solid particulates (PM). It is a figure which shows the adhesion state of the solid fine particle to the grid | lattice-like electrode provided in the surface acoustic wave element. It is a figure which shows the structure of a grid | lattice-like electrode. It is a figure which shows the sensitivity change at the time of solid microparticles adhering to the surface acoustic wave element which provided the grid | lattice-like electrode. FIG. 16 is a view showing the configuration of a solid particulate matter mass measurement device of Example 5. FIG. 16 is a view showing the configuration of a solid particulate matter mass measurement device of Example 5. It is a figure which shows an example of a comb-shaped electrode. FIG. 16 is a view showing the configuration of a solid particulate matter mass measurement device of Example 6. FIG. 16 is a diagram showing the configuration of a solid particulate matter mass measurement device according to a seventh example. It is a figure which shows the grounds that the pitch of a grating | lattice is below 1/2 of a wavelength. FIG. 16 is a diagram showing the configuration of a solid particulate matter mass measurement device of Example 8. FIG. 16 is a view showing the configuration of a grid-like electrode of the solid fine particle mass measuring device of Example 8. FIG. 18 is a view showing the configuration of a solid particulate matter mass measurement device of Example 9. FIG. 16 is a view showing the configuration of a grid-like electrode of the solid fine particle mass measuring device of Example 9; FIG. 18 is a view showing another configuration of the grid-like electrode of the solid fine particle mass measuring device of Example 9. FIG. 18 is a view showing the configuration of a solid particulate matter mass measurement device of Example 10. FIG. 18 is a view showing another configuration of the solid particulate matter mass measurement device of Example 10. FIG. 18 is a view showing the operation of the solid fine particle mass measuring device of the tenth embodiment. FIG. 18 is a view showing the configuration of a solid particulate matter mass measurement device of Example 11. FIG. 18 is a diagram showing the configuration of a solid particulate matter mass measurement device of Example 12. FIG. 18 is a diagram showing the configuration of a solid particulate matter mass measurement device of Example 13. FIG. 18 is a view showing the operation of the solid fine particle mass measuring device of the thirteenth embodiment. FIG. 18 is a diagram showing the configuration of a solid particulate matter mass measurement device of Example 14.

The embodiment of the present invention relates to a solid particle mass measuring device for solid particles using a surface acoustic wave device (SAW), which detects with high sensitivity the content (mass) of solid particles such as soot contained in exhaust gas. Specifically, in order to estimate the content of solid fine particles, ionized solid fine particles are collected and attached on a propagation path using a surface acoustic wave device that causes surface acoustic waves to propagate by a pair of electrodes formed on a piezoelectric substrate. Provide a means. Thereby, the content (mass) of the solid fine particles contained in the air is detected with high accuracy.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The configuration of the solid particulate matter mass measuring device according to the first embodiment will be described with reference to FIG.
Here, FIG. 1 (A) is a top view, and FIG. 1 (B) is a cross-sectional view along dotted line AB in FIG. 1 (A).

As shown in FIG. 1, the solid particle mass measuring apparatus includes a piezoelectric substrate 111 and an input electrode 103 and an output formed on the piezoelectric substrate 111 with a surface acoustic wave propagation region 105 as a propagation path of the surface acoustic wave 1 interposed therebetween. An electrode 104 is provided.

The input electrode 103 is provided at one end of the piezoelectric substrate 111 to excite the surface acoustic wave 1. The output electrode 104 is provided at the other end of the piezoelectric substrate 111 and receives the surface acoustic wave 1 which is excited by the input electrode 103 and propagates in the surface acoustic wave propagation region 105 on the piezoelectric substrate 111.

In all or part of the surface acoustic wave propagation region 105, a solid particle adhesion region 109 to which solid particles are attached is provided. A signal generation circuit 90 is connected to the input electrode 103 via the GND electrode 11. On the other hand, a signal detection circuit 91 is connected to the output electrode 104 via the GND electrode 11. The signal detection circuit 91 functions as a solid particle adhesion amount detection unit that detects the adhesion amount of solid particles adhering to the solid particle adhesion region 109.

Signal detection circuit 91 (solid particle adhesion amount detection unit) propagates surface acoustic wave 1 propagating in surface acoustic wave propagation region 105 by the interaction between surface acoustic wave 1 and solid particles attached to solid particle adhesion region 109. The amount of adhesion of solid fine particles is detected by detecting the change in the phase of the surface acoustic wave 1 caused by the change in speed with the output electrode 104.

The piezoelectric substrate 111 is a substrate in which a material having piezoelectricity is shaped into a plate. The material having piezoelectricity is, for example, well known as quartz, and has a function of expanding and contracting when an electric field is applied.

It is preferable that the input electrode 103 and the output electrode 104 be formed of comb-like electrodes disposed to face in the direction perpendicular to the propagation direction of the surface acoustic wave 1. As shown in FIG. 1B, the input electrode 103 and the output electrode 104 are covered with an insulating film 112.

With reference to FIG. 10, the comb-shaped electrode which comprises the input electrode 103 and the output electrode 104 is demonstrated.
As shown in FIG. 10A, the

comb electrodes

103 and 104 electrically connect a plurality of electrode fingers 100, a pair of bus bars 101 that electrically bundle the plurality of electrode fingers 100, and the bus bars 101. And a terminal 102. When a high frequency electrical signal is applied between the electrical terminals 102, the surface acoustic wave 1 having the same frequency as the high frequency electrical signal is excited in a direction orthogonal to the electrode finger 100. Alternatively, the propagating surface acoustic wave 1 is converted into a high frequency electrical signal of the same frequency as the surface acoustic wave 1. Thus, the comb-shaped input electrode 103 excites the surface acoustic wave 1, and the comb-shaped output electrode 104 receives the surface acoustic wave 1.

When a high frequency electric signal is input between the electric terminals 102 of the comb-shaped input electrode 103 by the signal generation circuit 90, an electric field is induced on the piezoelectric substrate 1 and the surface acoustic wave 1 is excited in the direction perpendicular to the electrode finger 100. .

The excited surface acoustic wave 1 propagates in a surface acoustic wave propagation region 105 as a propagation path and reaches the output electrode 104. The surface acoustic wave 1 that has reached the output electrode 104 is converted again into a high frequency electrical signal by the output electrode 104, is output to the electrical terminal 102 of the output electrode 104 as a high frequency electrical signal, and is detected by the signal detection circuit 91.

When solid particles adhere to the solid particle adhesion region 109 provided in the surface acoustic wave propagation region 105, the propagation velocity of the surface elastic wave 1 changes due to the interaction between the surface elastic wave 1 and the solid particles. The phase changes. By detecting this phase change as a phase change of the high frequency electric signal output from the output electrode 104, it is possible to detect the adhesion of solid fine particles.

Although the comb-shaped electrodes shown in FIGS. 1 and 10 are used as the input electrode 103 and the output electrode 104 in FIG. 1 in the first embodiment, the shape of the comb-shaped electrode is not limited to this, and surface acoustic wave The characteristics of the device may be changed to be optimum for the measurement of the amount of solid particles.

For example, as shown in FIG. 10A, the electrode width 132 of the electrode finger 100 constituting the comb-shaped electrode and the space 133 between the adjacent electrode fingers 100 are designed at 1⁄4 of the wavelength of the surface acoustic wave 1. As a result, surface acoustic waves generated or passed at each electrode strengthen each other, and measurement with low loss becomes possible.

Further, when the split electrode shown in FIG. 10B is used, distortion in phase is reduced, so that detection accuracy can be improved. Further, the electrode width 132 of the electrode finger 100 constituting the split electrode and the space 133 between the adjacent electrode fingers 100 are designed at 1/8 of the wavelength of the surface acoustic wave 1. This enables low-loss measurement.

In both of the comb-like electrodes shown in FIGS. 10A and 10B, the surface acoustic wave 1 generated by the input signal applied to the electrode propagates to both sides of the electrode. The propagation direction of the surface acoustic wave 1 is restricted to one direction by using. As a result, the level of the output high frequency electrical signal can be increased, and the detection accuracy can be improved.

The configuration of the solid fine particle mass measuring device of the second embodiment will be described with reference to FIG.
As shown in FIG. 2, the first metal electrode 106 is formed so that at least a part of the surface acoustic wave propagation region 105 is overlapped. The solid fine particle adhesion area 109 is the surface of the first metal electrode 106 inside the surface acoustic wave propagation area 105. A second metal electrode 107 is provided on the top of the first metal electrode 106 so as to face the first metal electrode 106. Solid particles are efficiently attached to the first metal electrode 106 by applying a voltage between the first metal electrode 106 and the second metal electrode 107.

As a dust collection method, there are DC electric field, corona discharge, thermophoresis and the like. In FIG. 2, in the surface acoustic wave propagation region 109, a second metal electrode 107 is provided opposite to the first metal electrode 106 and the top of the first metal electrode 106, and the first metal electrode 106 and the second metal electrode 106 are formed. A DC voltage is applied between the metal electrodes 107 to adhere the solid fine particles to the first metal electrode 106.

The configuration of the solid particulate matter mass measurement device of the third embodiment will be described with reference to FIG.
Although not clearly shown in FIG. 3, the solid fine particle adhesion area 109 is the surface of the first metal electrode 106 inside the surface acoustic wave propagation area 105. The solid fine particles attached to the solid fine particle adhering area 109 on the piezoelectric substrate 111 have a property of being reflected at the end of the area to which the surface acoustic wave 1 and the solid fine particles adhere, and the phase largely shifts in this reflection.

Therefore, in the third embodiment, as shown in FIG. 3, an electrode formed of a plurality of grid-like electrodes is used as the first metal electrode 108 that functions as the solid fine particle adhesion region 109. The solid particles adhere to the surfaces of the plurality of grid electrodes.

In the configuration shown in FIG. 3, the area to which the solid fine particles attached to the solid fine particle adhering area 109 adhere is limited to a lattice, thereby increasing the phase shift amount due to the speed of sound and making the measurement sensitivity of the mass of solid fine particles.
Specifically, as shown in FIG. 3, a grid-like first metal electrode 108 is provided in the surface acoustic wave propagation region 105, a voltage is applied to the metal electrode 107 in a gas containing solid fine particles, and an electric field is generated. Solid fine particles are attached to the grid-like first metal electrode 108.

The configuration of the solid particulate matter mass measuring device according to the fourth embodiment will be described with reference to FIG.
As shown in FIG. 4, in order to limit the floating area of the solid fine particles to the vicinity of the second metal electrode 107 or the first metal electrode 108 constituting the grid electrode, the area is covered with a plate-like mask 113.

As shown in FIG. 4B, a gas introduction passage 201 for introducing a gas containing solid fine particles into the surface acoustic wave propagation region 105 is provided. In addition, the gas introduction path 201 is not limited to this structure, and the gas may be introduced by another structure.

FIG. 5 is a view showing the relationship between the surface acoustic wave propagation velocity reduction rate and the amount of adhesion of solid fine particles (PM) to the surface acoustic wave propagation path (PM thickness), from FIG. 11 (c) to FIG. It is an enlarged view of the AB part of (c).
As shown in FIG. 5, it can be seen that the reduction rate of the propagation speed is increased when the metal electrode is present, and the reduction rate of the propagation speed is further increased in the case of the grid electrode as compared with the case where the metal electrode is not provided. Here, the propagation speed decrease rate corresponds to the change of the phase. Moreover, since both correspond to PM sensitivity, it is understood that the sensitivity is improved by the metal electrode.

In addition, as shown in FIG. 5, when the adhesion mass of solid fine particles corresponding to the phase change of the high frequency electric signal is measured in advance and a calibration curve is prepared, the adhesion amount (mass) of solid fine particles can be estimated from the measurement of electric signal. It will be possible.

When the solid fine particles adhere to the grid-like electrode or more, the sensitivity changes as shown in FIG. Here, FIG. 6A is a cross-sectional view taken along dotted line AB of the grid-like first metal electrode 108 shown in FIG. 3, and FIG. 6B is a top view of the grid-like first metal electrode 108 shown in FIG. It is.

As shown in FIG. 6A (b), the solid fine particles 202 adhere to the lattice-like first metal electrode 108 in a lattice-like manner. Further, when solid particles are attached, as shown in FIG. 6A (c) and FIG. 6A (d), the solid particles are deposited and coat the grid-like first metal electrode 108.

FIG. 7 shows the phase change of the surface acoustic wave when the solid fine particles adhere as shown in FIGS. 6A (a) to (d), and A to D in FIG. Each corresponds to d). As shown in FIGS. 6A (a) to (b), the solid fine particles are deposited in a lattice, and as shown in FIGS. 6A (c) to 6 (d), the height is greater than the height of the latticed first metal electrode 108 The sensitivity differs in the case where solid particles adhere to the The slopes of A to C in FIG. 7 are larger than the slopes of C to D in FIG. That is, it is understood that the detection sensitivity of the amount of solid fine particles is improved when the solid fine particles adhere in a lattice shape.

In the configuration of the grid-like first metal electrode 108 shown in FIG. 3, in order to improve detection sensitivity, as shown in FIG. 6B, the width 115 of the grid electrode and the spacing 114 of the adjacent grid electrodes are comb electrodes Make it smaller than the wavelength of the surface acoustic wave to be excited.

Also, the film thickness of the grid electrode is made sufficiently thick so that the sensitivity does not decrease even if the total mass of the attached solid fine particles is large. In addition, when the aspect ratio of the grid electrode becomes too large, the grid electrode may fall down or a shape defect may easily occur. Therefore, the shape of the grid electrode needs to be a shape that can be processed by a process. In the first embodiment, a grid electrode is formed with a ratio of electrode width to height, so-called aspect ratio, for example, 15: 1 or less.

The surface acoustic wave 1 passing through the grid electrode interferes and strengthens by configuring the width 115 of the grid electrode and the interval 114 of the adjacent grid electrode to be 1/8 of the wavelength of the surface acoustic wave. As a result, the solid fine particles interact more strongly, and the detection sensitivity of the solid fine particles is improved.

In Example 1, a two-layer structure of platinum and titanium was used as a material of the input electrode 103, the output electrode 104, the first metal electrode 106, and the second metal electrode 107. The electrode material is not limited to platinum or titanium, and may be any material that transmits an electrical signal.

However, when a material such as platinum is not oxidized even at high temperature, and the adhesion between the formed electrode and the piezoelectric substrate 111 and the shape of the electrode are not easily changed, operation can be performed at high temperature. Further, by burning the solid fine particles under high temperature, the D state shown in FIG. 7 can be returned to the A state (because it becomes refreshable), high sensitivity can be maintained, and a high accuracy measuring instrument can be realized.

In addition, if a piezoelectric substrate in which the temperature characteristics of the surface acoustic wave 1 do not change is used as the piezoelectric substrate 111, it is possible to perform measurement without being affected by environmental temperature changes with a mass measuring device, and realize a highly accurate measuring instrument. it can. As the piezoelectric substrate 111, there are a quartz crystal, a langasite (La3Ga5SiO14) substrate, and the like, but another piezoelectric substrate having a good temperature stability may be used. Alternatively, an aluminum nitride thin film or an aluminum nitride thin film doped with Sc may be used. When using these piezoelectric thin films, it is preferable to form a film on a substrate whose main raw material is silicon, sapphire, alumina, diamond, or silicon carbide.

The piezoelectric substrate 111 is made of any of langasite, aluminum nitride thin film, or aluminum nitride thin film doped with Sc, sapphire, alumina, diamond, silicon carbide, and the electrode is made of platinum or titanium. If it is, it is possible to carry out the refresh operation (after the operation), so it is possible to realize a more accurate measuring instrument.

The solid fine particles contain, for example, carbon as a main component. The solid particle measuring apparatus may be provided with means for heating the surface acoustic wave propagation area 105 and burning and removing solid particles attached to the solid particle adhering area 109.

The surface acoustic wave device shown in FIG. 1 was prepared by the following process.
After cleaning the surface of the piezoelectric substrate 111 and removing foreign substances on the surface, a pattern was formed by a photolithographic process, and a platinum pattern was formed by an electron beam vapor deposition apparatus, and then a comb electrode was formed by a lift-off process. .

Next, a titanium thin film was formed as an adhesive layer on the interface between the piezoelectric substrate 111 and platinum and on the platinum electrode. In Example 1, a silicon oxide film was formed to protect the comb electrode.
In addition, if there is no problem in the measurement of solid fine particles, removal of the silicon oxide film formed on the surface acoustic wave propagation region 105 of the surface acoustic wave 1 is not necessarily required. However, a voltage may be applied to the

first metal electrodes

106 and 108 to collect the solid particles, causing a discharge and a charge accumulation in the silicon oxide film may occur to change the amount of adhesion of the solid particles. It is desirable to remove the silicon oxide film.

The configuration of the solid particulate matter mass measurement device of the fifth embodiment will be described with reference to FIGS. 8 and 9.
In the fifth embodiment, as shown in FIG. 8, as a measuring element 121 that uses a pair of surface acoustic wave elements for measuring solid fine particles and attaches solid particles to one of the elements by means of solid particle collection means such as discharge. An element coated so that solid particles are not attached to one of the elements is used as a reference element 122, respectively.

FIG. 9 is a cross-sectional view of the measurement element and the reference element of FIG. 8 taken along AA-BB and CC-DD, respectively.
As shown in FIG. 9, in the measuring element 121, the window of the silicon oxide film 113 is opened in the solid particle adhesion area 109, and a gas introduction path 201 is provided. On the other hand, the solid fine particle adhering area 109 of the reference element 122 is completely covered with the silicon oxide film 113.

Also, as in Example 2, using the same element as a pair, for example, by measuring the solid fine particles using the difference between the output signals of both, etc., the characteristic change of the surface acoustic wave element due to the change of the environment in the measurement Compensate and make accurate measurements. Among the elements used as a pair, the surface acoustic wave propagation region 105 of the reference side element (solid fine particles do not adhere) need not necessarily have the same electrode as the measuring element (the side to which solid fine particles adhere) The surface acoustic wave propagation region 105 of the measuring element 121 may be provided with a grid-like electrode 107, and the surface acoustic wave propagation region 105 of the reference element 122 may be provided with different electrodes.

However, since it is desirable that the measurement element 121 and the reference element 122 exhibit the same characteristic change depending on the environment due to changes in the measurement environment, in Example 2, the same grid-like electrode as the measurement element 121 and the reference element 122 Is used.

The protective mask 113 is used to prevent interaction between the leak wave of the surface acoustic wave 1 and the deposit deposited on the coating film so that the solid particulates do not adhere to the reference element 122 and the solid particulates adhere only to the measuring element 121. The coating of the reference electrode was performed.

The coating material of the reference element 122 may be any material, but it is desirable that the material be resistant to reaction, deformation or the like at an environmental temperature and an environmental atmosphere at which solid particles are measured. In the second embodiment, the element surface is coated with a silicon oxide film 112. Further, the

comb electrodes

103 and 104 may be used as a mask by covering with the coating plate 113 provided with a window on the solid particle adhesion region 109 so that solid particles are not attached.

The configuration of the solid particulate matter mass measurement device of the sixth embodiment will be described with reference to FIG.
As shown in FIG. 11A, in the solid particle mass measuring device of the sixth embodiment, a solid film 110 (a flat film before patterning) is used as the solid particle adhesion region 109 to collect the solid particles (PM). As a dust method, a DC voltage 106 (DC bias) is applied to the solid film 110.

In such a configuration, as shown in FIG. 11B, the solid fine particles (PM) are attracted to the electric field, and are uniformly deposited on the solid film 110 as the solid fine particle adhesion region 109 and adhere. As shown in FIG. 11C, it can be seen that the sensitivity is low in AC.

The configuration of the solid particulate matter mass measurement device of the seventh embodiment will be described with reference to FIG.
As shown in FIG. 12A, in the seventh embodiment, as in the third embodiment (see FIG. 3), the first metal electrode 108 functioning as the solid fine particle adhesion region 109 is formed of a plurality of grid-like electrodes. Use the electrode. The solid particles adhere to the periphery of the plurality of grid electrodes.

As shown in FIG. 12, in the solid fine particle mass measuring device of the seventh embodiment, the pitch of the grid of the grid electrode 108 is half or less of the wavelength.
In such a configuration, as shown in FIG. 12B, the solid fine particles (PM) are attracted to the electric field and are deposited while providing a level difference. This step has the effect of stopping the surface acoustic wave 1 (SAW). The larger the step difference, the larger the effect of the surface acoustic wave 1 staying, and the decrease in the speed of sound corresponds to the rotation of the phase.
As shown in FIG. 12C, it can be seen that the sensitivity is higher in Example AD than in Example 6.

Here, the basis of the fact that the pitch of the grating is 1/2 or less of the wavelength is shown in FIG. FIGS. 13A and 13B show estimates of the reflection angle according to the principle of Hoiens. P is the pitch of the grid. As shown in Equation 1 below, waves incident on the grating are reflected in the direction of θ.

The condition (−1 = <cos θ = <1) in which θ exists is expressed by the following equation 2.

From

Equations

1 and 2, if P is less than λsaw / 2, it is not diffracted and reflected.

The configuration of the solid particulate matter mass measurement device of the eighth embodiment will be described with reference to FIG.
As shown in FIG. 14A and FIG. 15, in the solid particulate matter mass measurement device of the eighth embodiment, the grid electrode 108 is thinned as compared with the seventh embodiment (see FIG. 12).
In such a configuration, as shown in FIG. 14B, the solid fine particles (PM) are attracted to the electric field and are deposited while providing a level difference.
As shown in FIG. 14C, it can be seen that in Example 8, the sensitivity is higher than in Example 7 in the region A-C where the PM adhesion amount is low.

The configuration of the solid particulate matter mass measurement device of the ninth embodiment will be described with reference to FIGS. 16 to 18.
As shown in FIG. 16A and FIG. 17, in the solid fine particle mass measuring apparatus of the eighth embodiment, the grid electrode 108 is thinned and partially compared to the eighth embodiment (see FIG. 14). Is filled.

In such a configuration, the sensitivity can be made constant in the region of use. For example, when it is desired to use the areas A to E in FIG. 14B, the sensitivity is constant in the areas A to E as shown in FIG. Can be

Also, for example, when it is desired to use the regions B to D in FIG. 14B, the sensitivity in the regions B to D as shown in FIG. 16C depending on the degree of thinning and filling of the grid electrode 108 Can be fixed.
Here, a pattern shown in FIG. 16, a pattern shown in FIG. 17, or a pattern shown in FIG. 18 is appropriately selected and used as the degree of thinning and filling of the grid electrode 108.

The configuration of the solid particulate matter mass measurement device of the tenth embodiment will be described with reference to FIGS. 19 and 20. FIG.
In Example 2, as shown in FIG. 2, the solid fine particle adhesion area 109 is formed by the first metal electrode 106 provided in the surface acoustic wave propagation area 109.
In the tenth embodiment, as shown in FIG. 19, a heater and resistance thermometer 190 are disposed for the first metal electrode 106.

Under such a configuration, the first metal electrode 106 functioning as the solid fine particle adhesion region 109 is heated to a high temperature (for example, 600 ° C. or higher) by the heater and resistance thermometer 190 and adhered to the first metal electrode 106 Remove solid particulates (PM). Thus, when the saturation region (for example, the region E in FIG. 11C) is reached, the refresh is possible.

Although the heater and the resistance thermometer 190 are integrally formed in FIG. 19, the heater and the resistance thermometer may be separately formed.
Further, as shown in FIG. 20, the adhesive layer 196 and the SAW element 197 may be mounted on the ceramic substrate 195, and the heater and resistance thermometer 190 may be disposed between the ceramic substrate 195 and the adhesive layer 196.

Next, with reference to the flowchart of FIG. 21, the operation of the solid particulate matter mass measurement device of the tenth embodiment will be described.
First, the output (phase or delay time) of the sensor is measured (1) (S210), and the absolute value of the PM adhesion amount is determined (S211).
Next, the output of the sensor is measured (2) (S212).
Next, from the measurement (2) result of the output of the sensor, it is determined whether or not it is in a saturated state (S213).

If the temperature is saturated, the heater and resistance thermometer 190 are energized to reach a desired temperature (S214).
After energizing the heater and resistance thermometer 190, refresh is performed (S215), and the energization is turned off (S216).
If the saturated state is not obtained in S213, the PM adhesion amount per unit time is calculated from the difference between the output (1) and the output (2) (S217).

Finally, the PM adhesion amount per unit time is output (OUT) (S218).
The PM emission amount of the engine can be determined by multiplying the PM adhesion amount by a factor. Then, it is preferable to use the output difference from the reference element 122 of the fifth embodiment shown in FIG. 8 as the output of the sensor, because the influence of the temperature dependency can be eliminated.

The configuration of the solid particulate matter mass measurement device of the eleventh embodiment will be described with reference to FIG.
The eleventh embodiment is a modification of the solid particulate matter mass measurement device of the ninth embodiment shown in FIG. FIG. 22A is a top view, and FIG. 22B is a cross-sectional view of the vicinity of the center of the grid-like metal electrode 108.
As shown in FIGS. 22A and 22B, in the solid fine particle mass measuring device of the eleventh embodiment, the insulating film 220 is formed on the metal 230. By thus forming the insulating film 220, heat resistance can be improved, disconnection can be prevented, and refreshing can be performed safely.

The configuration of the solid particulate matter mass measurement device of the twelfth embodiment will be described with reference to FIG.
A twelfth embodiment is a modification of the solid particulate matter mass measurement device of the sixth embodiment shown in FIG.
As shown in FIG. 23A, in the solid particle mass measuring device of the twelfth embodiment, the piezoelectric substrate 111 (langasite) does not have to be rectangular, and may be, for example, a parallelogram.
In such a configuration, the surface acoustic wave (SAW) 1 that has passed through the output electrode 104 is prevented from passing again through the output electrode 104, and the sensitivity is stabilized.

Here, FIG. 23B shows the sensitivity when the surface acoustic wave (SAW) 1 passes through the output electrode 104 again. As shown in FIG. 23B, it can be seen that the sensitivity in the case of repassing is not constant. In Example 12, the sensitivity in the case of repassing becomes constant.

The configuration of the solid particulate matter mass measurement device of the thirteenth embodiment will be described with reference to FIG.
As shown in FIG. 24, in the solid particulate matter mass measurement device of the thirteenth embodiment, a reflector 240 is provided to double as an input / output electrode.
In such a configuration, since the surface acoustic wave 1 passes through the solid fine particle adhesion region 109 twice, the sensitivity is doubled.

The operation of the solid particulate matter mass measurement device of the thirteenth embodiment will be described with reference to the flowchart of FIG.
First, the switch 1 (241) and the switch 2 (242) are connected to the signal generation circuit 90 (S250).
Next, the signal generation circuit 90 outputs a signal (S251).
Next, the surface acoustic wave (SAW) 1 is excited by the input electrode (comb electrode) 103 (S 252).
Next, the surface acoustic wave (SAW) 1 passes through the solid fine particle adhesion area 109, is reflected by the reflector 240, and passes through the solid fine particle adhesion area 109 again (S253).
Next, the switch 1 (241) and the switch 2 (242) are connected to the signal detection circuit 91 (S254).
Next, the signal detection circuit 91 measures the delay time and the phase amount (S255).
Finally, the PM emission amount is output (S256).

Thus, according to Example 13, since the surface acoustic wave 1 passes through the solid fine particle adhesion region 109 twice, the sensitivity can be doubled.

In Example 14, a DPF (Diesel Particulate Filter) is configured using the solid particle mass measuring device shown in FIG. 14 and the solid particle mass measuring device shown in FIG.

As shown in FIG. 26, the low sensitivity PM sensor 262 of FIG. 14 is disposed between the diesel engine 261 and the DPF 264, and the high sensitivity PM sensor 263 of FIG. 16 is disposed behind the DPF 264.
In such a configuration, the location where the amount of PM is large becomes low in sensitivity and saturation becomes difficult. On the other hand, a place where the amount of PM is small has high sensitivity and high sensitivity sensing becomes possible.

According to the above embodiment, by providing the solid particle adhesion region 109 for collecting and adhering solid particles on the surface acoustic wave propagation region 105 which is a propagation path, the content (mass) of the solid particles contained in the atmosphere can be determined. It can be detected with high accuracy.

1 surface acoustic wave 11 GND electrode 90 signal generation circuit 91 signal detection circuit 100 electrode finger 101 bus bar 102 electric terminal 103 comb electrode 104 comb electrode 105 surface acoustic wave propagation area 106 metal electrode 107 metal electrode 108 grid-like metal electrode 109 solid Fine particle adhesion area 111 Piezoelectric substrate 112 Insulating film 113 Solid fine particle adhesion prevention mask 114 Width of grid electrode 115 Distance between lattice electrodes 116 Opening of solid fine particle adhesion prevention mask 132 Width of comb electrode 133 Distance between comb electrodes 201 Gas Introduction path 202 solid particles

Claims

A solid particle mass measuring apparatus for measuring the content of solid particles contained in a gas, comprising:
A piezoelectric substrate,
An input electrode provided at one end of the piezoelectric substrate to excite surface acoustic waves;
An output electrode provided at the other end of the piezoelectric substrate and receiving the surface acoustic wave which is excited by the input electrode and propagates a surface acoustic wave propagation region on the piezoelectric substrate;
A solid particle adhesion region provided in the surface acoustic wave propagation region and adhering the solid particles;
A solid particle adhesion amount detection unit that detects the adhesion amount of the solid particles adhered to the solid particle adhesion region;
A solid particle mass measuring device characterized by having.
The solid particle adhesion amount detection unit
The interaction of the solid fine particles attached to the solid fine particle adhering area and the surface elastic wave causes the surface elastic wave to propagate in the surface elastic wave propagation area, thereby changing the propagation speed of the surface elastic wave The solid fine particle mass measuring apparatus according to claim 1, wherein the adhesion amount of the solid fine particles is detected by detecting a change in phase with the output electrode.
The solid fine particle according to claim 1, wherein the input electrode and the output electrode are formed of comb-shaped electrodes disposed to face each other in a direction perpendicular to the propagation direction of the surface acoustic wave. Mass measuring device.
The comb-shaped electrode has a plurality of electrode fingers,
The solid particle mass measuring device according to claim 1, wherein a width of the electrode finger and a distance between the adjacent electrode fingers are 1/4 of a wavelength of the surface acoustic wave.
The solid fine particle adhesion area is formed by a first metal electrode provided in the surface acoustic wave propagation area,
A second metal electrode is provided on the top of the first metal electrode to face the first metal electrode,
The solid particle mass according to claim 1, wherein the solid particles are attached to the first metal electrode by applying a voltage between the first metal electrode and the second metal electrode. measuring device.
The first metal electrode is formed of a plurality of grid-like electrodes,
The said solid particulates adhere on the periphery of several said grid | lattice-like electrodes, The solid particulate mass measuring apparatus of Claim 5 characterized by the above-mentioned.
7. The solid particle mass measuring device according to claim 6, wherein a width of the grid electrode and an interval between the adjacent grid electrodes are smaller than a wavelength of the surface acoustic wave.
The solid particle mass measuring device according to claim 7, wherein the width of the grid electrode and the interval between the adjacent grid electrodes are equal to or less than 1/2 of the wavelength of the surface acoustic wave.
The plurality of grid electrodes are thinned out,
7. The solid particle mass measuring device according to claim 6, wherein the solid particles are attracted to an electric field and attached onto the plurality of grid electrodes which are thinned while providing a level difference.
The solid particle mass measuring apparatus according to claim 6, further comprising a heater for removing the solid particles attached to the first metal electrode by heating the first metal electrode.
The solid fine particle adhesion region is formed by a flat film,
The solid particle mass measuring apparatus according to claim 1, wherein the solid particles are attracted to an electric field of a DC bias voltage applied to the flat film and uniformly attached to the flat film.
The solid particle mass measuring device according to claim 1, further comprising an introduction path for introducing the gas containing the solid particles into the surface acoustic wave propagation region.
A pair of solid particle mass measuring devices according to claim 1 are arranged,
Using a single solid particle mass measuring device as a measuring element,
Another solid particulate mass measuring device is used as a reference element,
The solid particulate matter adhesion region of the reference element is provided with a mask for preventing the solid particulate matter from adhering thereto.
The solid particle adhesion amount detection unit is characterized in that the adhesion amount of the solid particles is detected by comparing the characteristics of the surface acoustic wave respectively received by the output element of the measurement element and the reference element. Solid particle mass measuring device to be.
In the solid fine particle adhesion region of the measurement element, a window of an insulating film is opened,
The solid particulate matter mass measuring device according to claim 13, wherein the solid particulate matter adhering region of the reference element is covered with the insulating film.
The solid particle mass measuring device according to claim 1, wherein the input electrode and the output electrode are formed by a two-layer structure of platinum and titanium.