JP2020088539A - Surface acoustic wave element and solid fine particles mass measuring instrument - Google Patents

Abstract

To detect an amount of solid fine particles at high sensitivity.SOLUTION: A surface acoustic wave element 400 comprises: a measurement element 300; and a reference element 200. The measurement element 300 comprises: a first substrate 111 having piezoelectricity; a first input electrode 103-1 provided on a first surface of the first substrate and exciting a front face elastic wave; a first front surface elastic wave propagation region 105-1 to which a front surface elastic wave excited by the first input electrode is propagated; and a first output electrode 104-1 receiving the front surface elastic wave propagating the first front surface elastic wave propagation region. The reference element 200 comprises: a second input electrode 103-2 provided on the first surface, and exciting the front surface elastic wave; a second front surface elastic wave propagation region 105-2 propagated by the front surface elastic wave excited by a second input electrode; and a second output electrode 104-2 receiving the front surface elastic wave propagating the second front surface elastic wave propagation region. A second substrate 150 covers the second front surface elastic wave propagation region at a ratio larger than that of the first front surface elastic wave propagation region.SELECTED DRAWING: Figure 4A

Description

The present invention relates to a technique for measuring mass of solid fine particles.

The exhaust gas of an internal combustion engine such as a diesel engine contains solid fine particles such as soot, so-called PM (Particle Matter), and air pollution due to the solid fine particles has become a worldwide problem.

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

For example, Patent Document 1 is a document relating to a surface acoustic wave device and a physical quantity detector using the same. Patent Document 1 discloses a surface acoustic wave device that generates a surface acoustic wave on one surface of a piezoelectric substrate and detects a change in the surface acoustic wave, and a first excitation signal of a predetermined frequency at a first portion of the one surface. Is input to the first excitation electrode that generates the first surface acoustic wave, and the second excitation signal of a predetermined frequency is input to the second portion that is separated from the first portion. The second excitation electrode for generating a surface acoustic wave, the first surface acoustic wave, and the second surface acoustic wave arrive and interfere with the third portion of one surface where these surface acoustic waves are added. What has a detection electrode which detects a wave is disclosed (paragraph 0018). Further, it is disclosed that a protective film which covers one surface and opens either one of the first and second propagation paths is provided (section 0021).

JP, 2014-192692, A

In Patent Document 1, when the surface of the first propagation path is covered with a protective film and the surface of the second propagation path is opened, the arrival of the object to be measured causes the object to be measured to adhere to the first propagation path. Although suppressed, it has been shown that adhesion of the DUT occurs in the second propagation path (Section 0107). Since the surface acoustic wave device detects a beat interference wave generated by the first oscillator including the first propagation path and the second oscillator including the second propagation path, the beat frequencies are different from each other. It is disclosed that the difference in the increase of the oscillation frequency becomes a difference, and the change in frequency due to the change in environmental temperature is canceled out, and as a result, only the change in frequency due to the adhesion of the object to be measured is obtained (0111).

According to the technique disclosed in Patent Document 1, the protective film suppresses the adhesion of the measured object in the first propagation path. However, in the surface acoustic wave device, the device surface is displaced along the propagation path of the surface acoustic wave along with the propagation of the surface acoustic wave. Therefore, when the protective film comes into contact with the propagation path of the surface acoustic wave, it interferes with the propagation of the surface acoustic wave, which may affect the frequency and phase of the surface acoustic wave. That is, the propagation characteristics of the surface acoustic wave differ between the first propagation path and the second propagation path.

An object of the present invention is to suppress the adhesion of solid fine particles to a reference element in a solid fine particle mass measurement technique in which surface acoustic waves are applied to a reference element and a measuring element, and to detect the content of solid fine particles contained in a gas with high sensitivity. -To detect at low manufacturing cost.

One preferable aspect of the present invention is a surface acoustic wave device including a first substrate having piezoelectricity. This element is provided on a first surface of a first substrate, and has a first input electrode that excites a surface acoustic wave and a first surface acoustic wave that propagates the surface acoustic wave excited by the first input electrode. It has a measuring element provided with a wave propagation field and the 1st output electrode which receives the surface acoustic wave which propagates the 1st surface acoustic wave propagation field. A second input electrode provided on the first surface of the first substrate for exciting the surface acoustic wave, and a second surface acoustic wave propagation for propagating the surface acoustic wave excited by the second input electrode. It has a reference element provided with the field and the 2nd output electrode which receives the surface acoustic wave which propagates the 2nd surface acoustic wave propagation field. Then, facing the first surface of the first substrate, a first input electrode, a first surface acoustic wave propagation region, a first output electrode formed on the first surface of the first substrate, The second substrate is provided so as to be in non-contact with the second input electrode, the second surface acoustic wave propagation region, and the second output electrode. The second substrate covers the second surface acoustic wave propagation region at a rate higher than that of the first surface acoustic wave propagation region.

Another preferable aspect of the present invention is a solid fine particle mass measuring apparatus including a surface acoustic wave device, a housing for holding the surface acoustic wave device, and a housing for housing the surface acoustic wave device. The surface acoustic wave device includes a first substrate having piezoelectricity. The surface acoustic wave element is provided on the first surface of the first substrate, and has a first input electrode that excites the surface acoustic wave and a first input electrode through which the surface acoustic wave excited by the first input electrode propagates. The measuring element is provided with a surface acoustic wave propagation region and a first output electrode for receiving the surface acoustic wave propagating in the first surface acoustic wave propagation region. A second input electrode provided on the first surface of the first substrate for exciting the surface acoustic wave, and a second surface acoustic wave propagation for propagating the surface acoustic wave excited by the second input electrode. It has a reference element provided with the field and the 2nd output electrode which receives the surface acoustic wave which propagates the 2nd surface acoustic wave propagation field. Then, facing the first surface of the first substrate, a first input electrode, a first surface acoustic wave propagation region, a first output electrode formed on the first surface of the first substrate, The second substrate is provided so as to be in non-contact with the second input electrode, the second surface acoustic wave propagation region, and the second output electrode. The second substrate covers the second surface acoustic wave propagation region at a rate higher than that of the first surface acoustic wave propagation region.

In solid particle mass measurement technology that applies surface acoustic waves to the reference element and the measurement element, the adhesion of solid particles to the reference element is suppressed and the content of solid particles contained in the gas is detected with high sensitivity and low manufacturing cost. can do.

3 is a top view showing the configuration of the measuring element of the solid fine particle mass measuring apparatus of Example 1. FIG. 3 is a cross-sectional view showing the configuration of a measuring element of the solid fine particle mass measuring apparatus of Example 1. FIG. It is a top view which shows an example of a comb-shaped electrode. It is a top view which shows an example of a comb-shaped electrode. 3 is a top view showing the configuration of the surface acoustic wave element of the solid fine particle mass measurement apparatus of Example 1. FIG. FIG. 3 is a top view illustrating solid fine particle collecting means of the solid fine particle mass measuring apparatus according to the first embodiment. FIG. 3 is a cross-sectional view illustrating solid fine particle collecting means of the solid fine particle mass measuring apparatus according to the first embodiment. It is a graph figure explaining the signal processing of the output signal of a surface acoustic wave element. 5 is a top view showing the configuration of the surface acoustic wave element of the solid fine particle mass measurement apparatus of Example 2. FIG. 6 is a top view showing the configuration of a surface acoustic wave element of a solid fine particle mass measuring apparatus of Example 3. FIG. 6 is a top view showing the configuration of a surface acoustic wave element of a solid fine particle mass measuring apparatus of Example 3. FIG. FIG. 6 is a two-sided (top and cross-sectional) view showing the configuration of a solid fine particle mass measurement apparatus of Example 4. 7 is a cross-sectional view showing the configuration of a solid fine particle mass measuring apparatus of Example 4. FIG. 9 is a cross-sectional view showing the configuration of a surface acoustic wave element of a solid fine particle mass measurement apparatus of Example 5. 9 is a top view showing the configuration of a surface acoustic wave element of a solid fine particle mass measurement apparatus of Example 6. FIG. 9 is a cross-sectional view showing the structure of a surface acoustic wave element of a solid fine particle mass measuring apparatus of Example 6. FIG. FIG. 9 is a two-sided view (top surface and cross section) showing a configuration of a solid fine particle mass measurement apparatus of Example 7. FIG. 11 is a two-sided (top and cross-sectional) view showing the configuration of a surface acoustic wave element of a solid fine particle mass measurement apparatus of Example 8.

Embodiments will be described in detail with reference to the drawings. However, the present invention should not be construed as being limited to the description of the embodiments below. It is easily understood by those skilled in the art that the specific configuration can be changed without departing from the concept or the spirit of the present invention.

In the structures of the invention described below, the same reference numerals are commonly used in different drawings for the same portions or portions having similar functions, and redundant description may be omitted.

When there are a plurality of elements having the same or similar functions, the same reference numerals may be given with different subscripts. However, when it is not necessary to distinguish a plurality of elements, the description may be omitted with the subscript omitted.

The notations such as “first”, “second”, and “third” in this specification and the like are given to identify components, and necessarily limit the number, order, or content thereof. is not. Further, the numbers for identifying the constituent elements are used for each context, and the numbers used in one context do not always indicate the same configuration in other contexts. In addition, it does not prevent that a component identified by a certain number also has a function of a component identified by another number.

The position, size, shape, range, etc. of each component shown in the drawings and the like may not represent the actual position, size, shape, range, etc. in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings and the like. The embodiment of the present invention relates to a solid fine particle mass measuring apparatus for solid fine particles using a surface acoustic wave element (SAW), and highly sensitively detects the content (mass) of solid fine particles such as soot contained in exhaust gas. Specifically, in order to estimate the content of solid fine particles, a surface acoustic wave element that propagates a surface acoustic wave by a pair of electrodes formed on a piezoelectric substrate is used, and ionized solid fine particles are collected and attached on the propagation path. A region and a region not to be attached are provided, and the content (mass) of the solid fine particles contained in the atmosphere is detected with high accuracy based on the difference.

One example of the embodiment is a solid fine particle mass measuring device for measuring the content of solid fine particles contained in a gas. This device includes a piezoelectric substrate, an input electrode provided on one end of the piezoelectric substrate for exciting a surface acoustic wave, and an input electrode provided on the other end of the piezoelectric substrate, which is excited by the input electrode to propagate the surface acoustic wave on the piezoelectric substrate. An output electrode for receiving surface acoustic waves propagating in the area, a solid fine particle adhesion area provided in the surface acoustic wave propagation area for adhering solid fine particles, and a solid for detecting the amount of solid fine particles adhering to the solid fine particle adhesion area And a particle adhesion amount detection unit. The solid fine particle adhesion amount detection unit detects the surface elasticity generated when the propagation velocity of the surface acoustic wave in the surface acoustic wave propagation region changes due to the interaction between the solid fine particles attached to the solid fine particle adhesion region and the surface acoustic wave. By detecting the change in the phase of the wave at the output electrode, the amount of solid fine particles attached can be detected. The input electrode and the output electrode have two or more surface acoustic wave elements formed by comb-shaped electrodes arranged so as to face each other in the direction perpendicular to the propagation direction of the surface acoustic wave. At least one surface acoustic wave element is mounted face down on the substrate via a spacer, and at least one surface acoustic wave element has a surface acoustic wave propagation region facing the substrate, which reduces the surface acoustic wave element. However, one surface acoustic wave propagation region is open.
Embodiments of the present invention will be described below with reference to the drawings.

A basic configuration of the solid fine particle mass measuring apparatus according to the first embodiment will be described with reference to FIG.
Here, FIG. 1A is a top view of the measuring element 300 of the measuring apparatus, and FIG. 1B is a sectional view taken along the dotted line AB of FIG. 1A.

As shown in FIG. 1, the solid fine particle mass measuring apparatus includes a piezoelectric substrate 111, an input electrode 103 formed on the piezoelectric substrate 111 and a surface acoustic wave propagation region 105 which is a propagation path of the surface acoustic wave 1, and an output. It has an electrode 104.

The input electrode 103 is provided at one end of the piezoelectric substrate 111 and excites the surface acoustic wave 1. The output electrode 104 is provided on the other end of the piezoelectric substrate 111, receives the surface acoustic wave 1 that 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 fine particle adhesion region 109 to which solid fine particles are attached is provided. In FIG. 1, a metal film is formed in the solid fine particle adhesion region 109 so that the potential can be controlled. A signal generation circuit 910 is connected to the input electrode 103. On the other hand, a signal detection circuit 920 is connected to the output electrode 104. The signal detection circuit 920 functions as a solid fine particle adhesion amount detection unit that detects the adhesion amount of the solid fine particles adhered to the solid fine particle adhesion region 109.

The signal detection circuit (solid fine particle adhesion amount detection unit) propagates the surface acoustic wave 1 through the surface acoustic wave propagation region 105 due to the interaction between the solid fine particles adhering to the solid fine particle adhesion region 109 and the surface acoustic wave 1. The change in the phase of the surface acoustic wave 1 caused by the change in the output electrode 104 is detected by the output electrode 104 to detect the amount of the solid fine particles attached.

The piezoelectric substrate 111 is a substrate formed of a piezoelectric material into a plate shape. As the material having piezoelectricity, for example, quartz, lithium tantalate, lithium niobate, and the like are well known, and have a function of expanding and contracting when an electric field is applied. Further, the piezoelectric substrate 111 does not need to be formed of only a piezoelectric material, and a substrate having a piezoelectric material formed on the surface of a non-piezoelectric substrate has the same effect. For example, a silicon substrate on which an aluminum nitride film is formed may be used.

The input electrode 103 and the output electrode 104 are preferably formed by comb-shaped electrodes arranged so as to face each other in the direction perpendicular to the propagation direction of the surface acoustic wave 1. With reference to FIGS. 2A and 2B, the comb-shaped electrodes forming the input electrode 103 and the output electrode 104 will be described.
As shown in FIG. 2A, the comb-shaped electrode includes a plurality of electrode fingers 100, a pair of bus bars 101 that electrically bundles the plurality of electrode fingers 100, and an electric terminal 102 electrically connected by the bus bar 101. ing. When a high frequency electric signal is applied between the electric terminals 102 from an external signal generator, the surface acoustic wave 1 having the same frequency as the high frequency electric signal is excited in the direction orthogonal to the longitudinal direction of the electrode finger 100. Alternatively, the propagated surface acoustic wave 1 is converted into a high frequency electric signal having 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 generating circuit 910, an electric field is induced on the piezoelectric substrate 111 and the surface acoustic wave 1 is excited in a direction perpendicular to the electrode fingers 100. ..

The excited surface acoustic wave 1 propagates in the surface acoustic wave propagation region 105 as a propagation path and reaches the output electrode 104. The surface acoustic wave 1 reaching the output electrode 104 is converted into a high frequency electric signal again by the output electrode 104, output as a high frequency electric signal to the electric terminal 102 of the output electrode 104, and detected by an external signal detection circuit 920.

When solid fine particles adhere to the solid fine particle adhesion region 109 provided in the surface acoustic wave propagation region 105, the propagation velocity of the surface acoustic wave 1 changes due to the interaction between the surface acoustic wave 1 and the solid fine particles, and 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 attachment of the solid fine particles.

In Example 1, the comb-shaped electrodes shown in FIGS. 1 and 2 were used as the input electrode 103 and the output electrode 104 in FIG. 1, but the shape of the comb-shaped electrodes is not limited to this, and the surface acoustic wave is used. The characteristics of the device may be changed to be optimum for the measurement of the amount of solid fine particles.

For example, as shown in FIG. 2A, the electrode width 132 of the electrode fingers 100 forming the comb-shaped electrodes and the space 133 between the adjacent electrode fingers 100 are designed to be ¼ of the wavelength of the surface acoustic wave 1. As a result, the surface acoustic waves generated or passing through each electrode reinforce each other, which allows measurement with low loss.

Further, when the split electrode shown in FIG. 2B is used, the phase distortion is reduced, so that the detection accuracy can be improved. Further, the electrode width 132 of the electrode finger 100 that constitutes the split electrode and the space 133 between the adjacent electrode fingers 100 are designed to be 1/8 of the wavelength of the surface acoustic wave 1. This enables measurement with low loss.

2A and 2B, the surface acoustic wave 1 generated by the input signal applied to the electrode propagates to both sides of the electrode. For example, the surface acoustic wave 1 using a unidirectional electrode is used. The propagation direction of is limited to one direction. As a result, the level of the output high frequency electric signal can be increased and the detection accuracy can be improved.

FIG. 3 to FIG. 5 are diagrams for explaining the specific configuration of the solid fine particle mass measuring apparatus of the first embodiment.
FIG. 3 is a diagram illustrating the configuration of the surface acoustic wave device used in the solid fine particle mass measuring apparatus of the first embodiment. The surface acoustic wave device 400 for measuring solid fine particles includes a measuring device 300 for adhering and detecting solid fine particles by means for collecting the solid fine particles to the device and a solid state fine particle for preventing the solid fine particles from being adhered by means for inhibiting the collection of the solid fine particles. And the reference element 200, The measuring element 300 and the reference element 200 use elements of the same shape as a pair, and measure the solid fine particles by using, for example, the difference between the output signals of the two, thereby measuring the characteristics of the surface acoustic wave element due to the change in environment during measurement. Changes can be compensated for and accurate measurements can be made.

The measuring element 300 is provided with an input electrode 103-1 and an output electrode 104-1, and a surface acoustic wave propagation region 105-1 between them, as in FIG. Further, an external signal generation circuit 910 is provided between the electric terminals 301 and 302 of the input electrode 103-1 and an external first signal detection circuit is provided between the electric terminals 303 and 304 of the output electrode 104-1. 920-1 is connected.

The reference element 200 is provided with an input electrode 103-2 and an output electrode 104-2, and a surface acoustic wave propagation region 105-2 between them, as in the measuring element 300. Further, an external signal generation circuit 910 is provided between the electric terminals 201 and 202 of the input electrode 103-2, and an external second signal detection circuit is provided between the electric terminals 203 and 204 of the output electrode 104-2. 920-2 is connected.

In both the measurement element 300 and the reference element 200, a metal film is provided in a part of the surface acoustic wave propagation region 105, and an electric terminal 305 and an electric terminal 205 are provided respectively. Although both the measuring element 300 and the reference element 200 are provided with means for collecting solid fine particles in the surface acoustic wave propagation region 105 by means of a metal film, the surface acoustic wave propagation region 105-2 of the reference element 200 is provided with solid fine particle collection means. Means are provided to impede collection.

4A and 4B are views for explaining the solid fine particle collecting means in the solid fine particle adhesion region 109-1 of FIG. 3 and the means for inhibiting the collection of solid fine particles in the solid fine particle adhesion region 109-2. 4A is a top view similar to FIG. 1, and FIG. 4B is a sectional view taken along the line CD. For clarity, FIG. 4A shows the ceramic substrate 150 as transparent. Although the electrical wiring of the surface acoustic wave element 400 is omitted, the electrical terminals 205 and 305 are grounded here. In the surface acoustic wave propagation region 105 and the solid fine particle adhesion region 109 that overlaps with the surface acoustic wave propagation region 105, the surface acoustic wave propagates, so that the shape of the surface changes microscopically.

The measuring element 300 and the reference element 200 are face-down mounted on the ceramic substrate 150 through the space whose amount is controlled by the spacer 171, with the electrode formation surface of the piezoelectric substrate 111 facing the ceramic substrate 150. The ceramic substrate 150 is installed so as to cover at least a part of the solid fine particle adhesion region 109-2 of the reference element 200. On the other hand, the ceramic substrate 150 is installed so as not to cover at least a part of the solid fine particle adhesion region 109-1 of the measuring element 300. Here, it is assumed that the ratio of the solid fine particle adhesion region 109-2 covered by the ceramic substrate 150 is higher than the ratio of the solid fine particle adhesion region 109-1 covered by the ceramic substrate 150. For example, the ceramic substrate 150 covers 100% of the area of the solid fine particle adhesion region 109-2 and 5% of the area of the solid fine particle adhesion region 109-1.

Since the space between the ceramic substrate 150 and the solid fine particle adhesion region 109 of the reference element 200 is adjusted to a space amount (for example, several tens of μm) in which solid fine particles are hard to enter, the ceramic substrate 150 is the solid fine particle of the reference element 200. It has a function of making it difficult for the solid fine particles to adhere to the adhesion region 109-2.

FIG. 5 is a graph illustrating the effect of the first embodiment. A graph 501 is a phase of the output signal of the reference element 200 measured by the second signal detection circuit 920-2, and a graph 502 is a phase of the output signal of the measurement element 300 measured by the first signal detection circuit 920-1. Graph 503 is the difference.

When the solid fine particles fall on the solid fine particle mass measuring device, the solid fine particles adhere to the surface acoustic wave propagation region 105-1 of the measuring element 300, and the output phase graph 502 of the measuring element 300 shifts. Further, since the measuring element 300 is affected by a disturbance such as temperature, the output phase graph 502 also includes those effects. On the other hand, since the solid fine particles are slightly attached to the surface acoustic wave propagation region 105-2 of the reference element 200, the output phase graph 501 of the reference element 200 is also slightly shifted. Further, since the reference element 200 is also affected by a disturbance such as temperature, the output phase graph 501 also includes those effects. A graph 503, which is the difference between the graph 501 and the graph 502, has the influence of disturbance factors such as temperature canceled. Therefore, the graph 503 shows the difference between the amount of solid fine particles attached to the solid fine particle adhesion region 109-1 and the amount of solid fine particles attached to the solid fine particle adhesion region 109-2. Therefore, by multiplying the time differential value of the graph 503 by the sensitivity coefficient measured in advance, the flow rate of the solid fine particles can be known, that is, the solid fine particle mass measuring device functions.

At this time, by installing the ceramic substrate 150, optimizing the size of the spacer 171, and sufficiently reducing the space, the amount of the solid fine particles attached to the solid fine particle adhesion region 109-1 and the solid fine particle adhesion region 109-2 are reduced. The difference from the amount of the solid particles adhered can be increased. In other words, the sensitivity of the solid particle mass measuring device can be improved.

The optimum space value depends on the air flow around the solid fine particle mass measuring apparatus, but it is desirable to set the value to approximately 100 μm or less so that the conductance of the space (fluid flowability) is sufficiently small. If the spacing is too small, for example, the ceramic substrate 150 comes into contact with the surface acoustic wave propagation region 105-2, the surface acoustic wave 1 is affected, which is not preferable. It is desirable that the surface acoustic wave propagation regions 105-1 and 105-2 do not come into contact with anything other than the solid fine particles and the medium thereof. The spacer 171 has a function of providing an appropriate space between the ceramic substrate 150 and the reference element 200. If there is no space, it may affect the excitation, propagation, and reception of surface acoustic waves. The minimum interval may be determined in consideration of the processing accuracy and the deformation of the surface acoustic wave propagation region due to the surface acoustic wave, and is, for example, about 10 μm. Note that, for example, it is conceivable to cover the solid fine particle adhesion region with a thin film so that the solid fine particle adhesion region 109-2 does not adhere to the solid fine particle adhesion region 109-2, but this may affect the surface acoustic wave, and the solid fine particle adhesion region may also be affected. Since 109 vibrates, there is a problem of durability of the thin film.

In the configuration of FIG. 4A, the ceramic substrate 150 also covers the input electrodes 103-1 and 103-2 and the output electrodes 104-1 and 104-2 at a predetermined interval. According to this configuration, like the solid fine particle adhesion region 109-2, it is possible to prevent the solid fine particles from adhering to the input electrode 103 and the output electrode 104. Therefore, it is possible to reduce the possibility of electrical short circuit between the electrodes. Further, due to the function of the spacer 171, the ceramic substrate 150 does not contact the input electrode 103 and the output electrode 104 and does not interfere with the movement of the electrodes, so that the sensitivity of the solid fine particle mass measurement apparatus can be improved.

FIG. 6 is another example in which solid particles are less likely to adhere to the solid particle adhesion region 109-2 of the reference element 200. The ceramic substrate 150 is transparently displayed. The ceramic substrate 150 covers most of the measurement element 300 except the surface acoustic wave propagation region 105-1.

As shown in FIG. 6, when the region including the surface acoustic wave propagation region 105-2 of the reference element 200 is surrounded by the frame 172 instead of the spacer 171, the inflow of solid fine particles from the gap between the ceramic substrate 150 and the piezoelectric substrate 111 is prevented. Be hindered. For this reason, the solid fine particles cannot adhere to the solid fine particle adhesion region 109-2 more than in Example 1, and the sensitivity is further increased.

In this case, if the frame 172 contacts the surface acoustic wave propagation region 105 (of course, the input electrode 103 and the output electrode 104 as well), the surface acoustic wave 1 may be affected, so the surface acoustic wave propagation region 105. The frame 172 may not be provided in such portions. Alternatively, the material of the frame 172 may be selected so as not to obstruct the propagation of the elastic wave in the surface acoustic wave propagation region 105. As a material of such a frame 172, there is, for example, silicon rubber or the like.

In the configuration of FIG. 6, the ceramic substrate 150 and the frame 172 also cover the input electrodes 103-1 and 103-2 and the output electrodes 104-1 and 104-2 at a predetermined interval. According to this configuration, like the solid fine particle adhesion region 109-2, it is possible to prevent the solid fine particles from adhering to the input electrode 103 and the output electrode 104. Therefore, it is possible to reduce the possibility of electrical short circuit between the electrodes.

FIG. 7 shows another configuration example for providing a space in the ceramic substrate 150 so as not to touch the surface acoustic wave propagation regions 105-1 and 105-2. Metal bumps 201b to 205b and 301b to 305b are used instead of the spacer 171 as a function of providing a space. In this example, metal bumps are installed on the electric terminals 201 to 205 and 301 to 305. With this configuration, the electric wiring can be provided on the ceramic substrate 150 using the metal bumps.

FIG. 8 is a perspective view of electric wiring on the ceramic substrate 150 (−z surface). The electric terminals 201 to 205 and 301 to 305 scattered around the surface acoustic wave propagation regions 105-1 and 105-2 can be gathered above the ceramic substrate (electric terminals 201c to 205c and electric terminals 301c to 305c). Since the surroundings of the surface acoustic wave propagation regions 105 and 105-2 are the sensing parts, they are exposed to the measurement target (gas or liquid containing solid fine particles) and the environment is harsh. From this, the electric terminal can be kept away from the sensing section, and there is an effect that contact failure and sensitivity deterioration can be reduced even in a harsh environment. In other words, it has the effect of improving sensitivity.

9A and 9B are diagrams illustrating a structure in which the surface acoustic wave device 400 and the ceramic substrate 150 described in the first embodiment are mounted in a housing. 9A is a top view similar to FIG. 1 and a sectional view taken along the line EF, and FIG. 9B is a sectional view taken along the line GH.

The ceramic substrate 150 to which the surface acoustic wave element 400 is fixed by the spacer 171 is fixed to the housing 420 at a location (+y direction) away from the surface acoustic wave element 400. The surface acoustic wave device 400 and the ceramic substrate 150 are covered with a housing 410 so as to surround the +x, −x, +z, −z, and −y directions. Such a housing is attached, for example, inside a pipe (housing) through which an object to be measured (gas or liquid containing solid particles) flows.

The housing 410 is provided with two windows 430 to allow solid particles to enter the housing 410. Therefore, the gas or liquid containing the solid fine particles that blows between the windows 430 of the housing flows in the direction of the arrow in the figure, is sprayed vertically to the surface acoustic wave propagation region 105-1 and is efficiently applied to the solid fine particle adhesion region 109-1. Adhere to.

On the other hand, since the surface acoustic wave propagation region 105-2 is hidden by the ceramic substrate 150, the solid fine particles are relatively hard to adhere to the solid fine particle adhesion region 109-2. Therefore, the phase rotation amount of the measuring element 300 is large and the phase rotation amount of the reference element 200 is small, and as a result, there is an effect that the solid fine particles can be detected with high sensitivity.

Although the electrical wiring of the surface acoustic wave element 400 is omitted, the electrical terminals 205 and 305 can be grounded here, as in the example of FIG. Therefore, there is an effect that solid fine particles can be detected with high sensitivity without being easily affected by electrical external noise.

On the other hand, as another configuration example, when the housing 410 is formed of a conductive material and an electric voltage is applied to the housing 410, an electric potential difference is generated between the housing 410 and the surface acoustic wave propagation region 105, The solid fine particles can be attached more efficiently. For example, the electric potentials of the electric terminals 205 and 305 are controlled so that the electric potential of the housing 410 is 100V and the electric potentials of the solid fine particle adhesion regions 109-1 and 109-2 are 0V. In general, solid fine particles are often charged positively or negatively, and this has the effect of promoting adsorption to the solid fine particle adhesion region 109 and further improving the sensitivity.

Further, by setting the same potential between the housing 410 and the solid fine particle adhesion region 109-2, it is possible to reduce the adhesion of the solid fine particles to the solid fine particle adhesion region 109-2. For example, the electric potentials of the electric terminals 205 and 305 are controlled so that the electric potential of the housing 410 is 0V, the electric potential of the solid fine particle adhesion region 109-2 is 0V, and the electric potential of the solid fine particle adhesion region 109-1 is 100V. In other words, by making the potential difference between the potential of the housing 410 and the potential of the solid fine particle adhesion region 109-1 larger than the potential difference of the potential of the housing 410 and the potential of the solid fine particle adhesion region 109-2, It has the effect of further improving the sensitivity. The applied voltage may be a negative voltage or an alternating current.

FIG. 9B is a cross-sectional view taken along the line GH in FIG. 9A, but in this example, the ceramic substrate 150 covers the output electrodes 104-1 and 104-2 with a predetermined spacing. According to this configuration, like the solid fine particle adhesion region 109-2, the adhesion of the solid fine particles to the output electrodes 104-1 and 104-2 can be prevented. Therefore, it is possible to reduce the possibility of electrical short circuit between the output electrodes 104-1 and 104-2. The same applies to the input electrodes 103-1 and 103-2.

In another configuration example of the fourth embodiment (FIG. 9A), a potential is applied to the housing 410 and an electric field is generated between the housing 410 and the solid fine particle adhesion region 109, so that the floating solid fine particles are caused to reach the solid fine particle adhesion region 109. It is collecting dust. However, it is not always necessary to apply a potential to the housing 410.

In FIG. 10, an electric field is not applied to the housing 410, an electrode 431 for generating an electric field is used, an electric field is generated between the electrode 431 and the solid fine particle adhesion region 109, and the solid fine particles are collected in the solid fine particle adhesion region 109. A modification is shown. Compared with the case where an electric field is generated between the housing 410 and the housing 410, the distance between the electrodes for generating the electric field is short, so that the electric field can be strengthened and the dust collection effect is strengthened. In other words, it has the effect of further increasing the sensitivity.

In the above embodiments, the case where each of the measuring element and the reference element is one is shown as an example. However, they do not necessarily have to be one. 11A and 11B show a modification example in which two reference elements and one measuring element are used. 11A is a top view similar to FIG. 1, and FIG. 11B is a cross-sectional view taken along the line MN.

As shown in FIGS. 11A and 11B, it is composed of two reference elements 200 and one measuring element 300. Similar to the other examples, since the window 152 is formed in the ceramic substrate 150 facing the solid fine particle adhesion region 109-1 of the measuring element 300, the solid fine particle adheres to the solid fine particle adhesion region 109-1. be able to. On the other hand, the solid fine particle adhesion region 109-2 of the reference element 200 is covered with the ceramic substrate 150. Therefore, the solid fine particles are unlikely to adhere to the solid fine particle adhesion region 109-2. Therefore, the same effect as that of the above-described embodiment is obtained. Furthermore, since the measuring element 300 is sandwiched between the reference elements 200, the disturbance factor in the y-axis direction can be excluded by using the average of the outputs of the two reference elements 200, and the disturbance factor can be made strong. You can In other words, it has the effect of further increasing the sensitivity.

With reference to FIG. 12, the configuration of a solid fine particle mass measuring apparatus of another embodiment will be described. 12 is a top view similar to FIG. 1 and a cross-sectional view taken along the line IJ.

The ceramic substrate 150 needs to have a function of covering the solid fine particle adhesion region 109-2 of the reference element 200 and preventing the solid fine particles from adhering to the surface acoustic wave propagation region 105-2. Therefore, the shape of the first embodiment is not always necessary. As shown in FIG. 12, the same effect can be obtained by making the ceramic substrate 150 rectangular and covering only the reference element 200.

However, at that time, it is desirable to protect the input electrode 103-1 and the output electrode 104-1 of the measuring element 300 with an electrically insulating film in order to prevent an electrical short circuit. In this embodiment, the insulating film 180 is formed on the surfaces of the input electrode 103-1 and the output electrode 104-1 of the measuring element 300. As a result, a solid fine particle mass measuring apparatus having the same function as in Example 1 can be realized. In addition, the amount of expensive ceramic substrate can be reduced, and the shape of the ceramic substrate can be a simple rectangle, so that the material and the processing cost can be reduced.

With reference to FIG. 13, the configuration of a solid fine particle mass measuring apparatus according to another embodiment will be described. FIG. 13 is a top view similar to FIG. 1 and a cross-sectional view taken along the line KL.
The gas containing the solid fine particles can be efficiently captured by spraying the gas onto the solid fine particle adhesion region 109-1 vertically. However, as shown in FIG. 9A, if the potential of the housing 410 is 0 V, the potential of the solid fine particle adhesion region 109-2 is 0 V, and the potential of the solid fine particle adhesion region 109-1 is 100 V, it has a function of collecting dust. The flow of the gas containing the solid fine particles does not necessarily need to be orthogonal to the solid fine particle adhesion region 109-1.

As shown in FIG. 13, even if a window 430 is provided in the housing in the +x and −x directions of the solid fine particle adhesion region 109-1 and a gas flows in the direction of the double circle 1300, the solid fine particles can be sufficiently collected. You can Furthermore, since there are few substances that hinder the flow of gas, the conductance increases and the dust collection effect increases. In other words, it has the effect of further increasing the sensitivity.

In this embodiment, the heater 182 is formed as a superheater near the tip of the ceramic substrate 150. By heating the solid fine particle adhesion regions 109-1 and 109-2 to a high temperature in a gas containing oxygen, the adhered solid fine particles can be burned and removed, that is, the solid fine particle mass measuring device can be refreshed. By heating with the heater 182, the temperature around the ceramic substrate 150 becomes high, and the entire surface acoustic wave element 400 is heated through the spacer, so that the surface acoustic wave element 400 can be refreshed.

By moving the heat generated by the heater away from the housing 420, the amount of heat that escapes can be reduced, and the temperature of the solid particulate adhesion region 109-1 can be raised with low power consumption. As shown in the present embodiment, the heater 182 is installed at the tip of the ceramic substrate 150 at least at a position farther than the spacer 171 closest to the housing 420, so that the solid fine particles are adhered without raising the temperature of the housing 420. The temperature of the region 109 can be increased. Therefore, there is an effect that the refresh can be performed with higher accuracy. In other words, it has the effect of further increasing the sensitivity.

Further, the heater 182 may be installed in the surface acoustic wave device 400 as long as it is far from the spacer 171. Further, when the piezoelectric substrate 111 is made of a Langasite material, the metal film of the solid fine particle adhesion region 109 is made of a platinum material, and the spacer 171 is made of a gold bump, since these are stable up to 1000° C., they can be refreshed at a higher temperature, It has the effect of further improving the sensitivity.

In each of the above-described embodiments, the measuring element 300 and the reference element 200 having the same configuration are used, and the detection signals of both are used to measure the mass of the solid fine particles with high accuracy. In this case, it is an ideal condition that the solid fine particles adhere only to the solid fine particle adhesion region 109-1 of the measuring element 300 and nothing touches the "other part". The “other portion” is specifically the solid fine particle adhesion region 109-2 of the reference element 200, the input electrode 103 and the output electrode 104 of the measuring element 300 and the reference element 200. According to the embodiments described in detail above, it is possible to satisfy such ideal conditions with a simple configuration.

1 surface acoustic wave 100 electrode finger 101 bus bar 102 electric terminal 103 input electrode 104 output electrode 105 surface acoustic wave propagation region 109 solid fine particle adhesion region 111 piezoelectric substrate 150 ceramic substrate 152 window 171 spacer 172 frame 200 reference elements 201, 202, 203, 204, 205 electric terminal 201b, 202b, 203b, 204b, 205b metal bump 201c, 202c, 203c, 204c, 205c electric terminal 300 measuring element 301, 302, 303, 304, 305 electric terminal 301b, 302b, 303b, 304b, 305b Metal bumps 301c, 302c, 303c, 304c, 205c Electric terminal 400 Surface acoustic wave device 410 Housing 420 Housing

Claims (15)

A first substrate having piezoelectricity,
A first input electrode provided on a first surface of the first substrate for exciting a surface acoustic wave, and a first surface acoustic wave propagation for propagation of the surface acoustic wave excited by the first input electrode. A measuring element comprising a region and a first output electrode for receiving a surface acoustic wave propagating in the first surface acoustic wave propagation region,
A second input electrode provided on the first surface for exciting a surface acoustic wave; a second surface acoustic wave propagation region in which the surface acoustic wave excited by the second input electrode propagates; A second output electrode for receiving a surface acoustic wave propagating in the surface acoustic wave propagation region of No. 2, and the first substrate facing the first surface of the first substrate. A first input electrode, a first surface acoustic wave propagation region, a first output electrode, a second input electrode, a second surface acoustic wave propagation region, and a second surface acoustic wave propagation region formed on the first surface of A second substrate arranged in non-contact with the output electrode,
The surface acoustic wave device, wherein the second substrate covers the second surface acoustic wave propagation region at a rate higher than that of the first surface acoustic wave propagation region. The second substrate covers all of the second surface acoustic wave propagation region and opens at least a part of the first surface acoustic wave propagation region,
The surface acoustic wave device according to claim 1. In the first surface acoustic wave propagation region, a solid fine particle adhesion region is formed by a metal film whose potential can be controlled,
The second substrate opens at least a part of the solid fine particle adhesion region.
The surface acoustic wave device according to claim 2. The second substrate further covers all of the first input electrode, the first output electrode, the second input electrode, and the second output electrode.
The surface acoustic wave device according to claim 2. A distance between the first substrate and the second substrate is 100 μm or less,
The surface acoustic wave device according to claim 1. A columnar spacer is arranged between the first substrate and the second substrate to keep them in non-contact with each other.
The surface acoustic wave device according to claim 1. A wall-shaped frame is arranged between the first substrate and the second substrate to keep them in non-contact with each other,
The surface acoustic wave device according to claim 1. The frame includes the first surface acoustic wave propagation region, the second surface acoustic wave propagation region, the first input electrode, the first output electrode, the second input electrode, and the second surface acoustic wave propagation region. Characterized by being arranged so as not to contact the output electrode,
The surface acoustic wave device according to claim 7. Electrical terminals for inputting and outputting signals to and from the first input electrode, the first output electrode, the second input electrode, and the second output electrode, respectively.
A metal bump disposed on the electric terminal,
Characterized in that the metal bumps are arranged between the first substrate and the second substrate and kept in non-contact with each other.
The surface acoustic wave device according to claim 1. Electrical wiring for inputting and outputting a signal to and from the metal bump is formed on the second substrate,
The surface acoustic wave device according to claim 9. In the first surface acoustic wave propagation region, a first solid fine particle adhesion region is formed of a metal film capable of controlling a potential,
In the second surface acoustic wave propagation region, a second solid fine particle adhesion region is formed by a metal film capable of controlling the electric potential,
Different potentials are applied to the first solid fine particle adhesion region and the second solid fine particle adhesion region,
The surface acoustic wave device according to claim 1. A surface acoustic wave element,
A housing for holding the surface acoustic wave element,
A housing for accommodating the surface acoustic wave element,
The surface acoustic wave device,
A first substrate made of a substrate having piezoelectricity,
A first input electrode provided on a first surface of the first substrate for exciting a surface acoustic wave, and a first surface acoustic wave propagation for propagation of the surface acoustic wave excited by the first input electrode. A measuring element comprising a region and a first output electrode for receiving a surface acoustic wave propagating in the first surface acoustic wave propagation region,
A second input electrode provided on the first surface for exciting a surface acoustic wave; a second surface acoustic wave propagation region in which the surface acoustic wave excited by the second input electrode propagates; A second output electrode for receiving a surface acoustic wave propagating in the surface acoustic wave propagation region 2;
A first input electrode, a first surface acoustic wave propagation region, and a first output formed on the first surface of the first substrate so as to face the first surface of the first substrate. An electrode, a second input electrode, a second surface acoustic wave propagation region, and a second substrate arranged in non-contact with the second output electrode,
The second substrate covers the second surface acoustic wave propagation region at a rate higher than that of the first surface acoustic wave propagation region,
Solid fine particle mass measuring device. By fixing one end of the second substrate to the housing, the surface acoustic wave element is held in the housing.
The solid fine particle mass measuring apparatus according to claim 12. The housing is provided with a window at a position facing the first surface acoustic wave propagation region,
The solid fine particle mass measuring apparatus according to claim 12. In the first surface acoustic wave propagation region, a first solid fine particle adhesion region is formed of a metal film capable of controlling a potential,
In the second surface acoustic wave propagation region, a second solid fine particle adhesion region is formed by a metal film capable of controlling the electric potential,
The potential difference between the potential of the housing and the potential of the first solid fine particle adhesion region is larger than the potential difference of the potential of the housing and the second solid fine particle adhesion region.
The solid fine particle mass measuring apparatus according to claim 12.

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