JP2011232264A - Piezoelectric sensor, piezoelectric sensor element and piezoelectric vibration chip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric sensor capable of measuring viscosity and density of liquid and pressure and degree of vacuum of gas in a wide measurement range with high sensitivity and high accuracy in real time.SOLUTION: A piezoelectric sensor element 11 is configured so that a piezoelectric vibration chip 12 having side part 20a and 20b located at the outside of three vibration arms 19a to 19c which extend from a base portion 18 is fixed and supported in a cantilever fashion at the base portion in a package 13. A communicating hole 17 is provided in the package 13 so as to introduce a fluid to be measured from the outside and allow it to flow therethrough. The side parts of the piezoelectric vibration chip have flat side faces 26a and 26b which are parallel with side faces of the adjacent vibration arms and define narrow gaps 27a and 27b with predetermined dimensions therebetween. When the vibration arms are bended and vibrated in the outward direction of the side faces, a fluid to be measured generates a constant flow of velocity distribution in the respective gaps between the side parts and the vibration arms. Variations of the viscous resistance which is applied to the vibration arms by the fluid to be measured at this time is detected as variations of CI value of the piezoelectric vibration chip so as to detect variations of objects to be measured such as pressure of the fluid to be measured.

Description

  The present invention relates to a piezoelectric sensor element using a flexural vibration mode piezoelectric vibrating piece, a piezoelectric sensor using the same, and a piezoelectric vibrating piece suitable for the piezoelectric vibration element in order to measure the pressure and viscosity of a fluid.

  Conventionally, various piezoelectric sensors using a piezoelectric vibrating piece as a sensitive element have been developed to measure the pressure of a liquid or gas, the degree of vacuum, and the viscosity of a fluid. In general, a piezoelectric vibrating piece has a property that when a stress is applied, a resonance frequency changes in accordance with the magnitude of the stress. In particular, the flexural vibration mode piezoelectric vibrating piece has a larger frequency change rate with respect to applied stress than the other vibration modes.

  Using such characteristics, a pressure sensor is known in which a double tuning fork piezoelectric vibrating piece having two parallel vibrating arms is fixed to the surface of a diaphragm at the base ends of both ends (for example, Patent Document 1). , 2). In this pressure sensor, when the diaphragm is bent under pressure, a force in the tension direction or the compression direction acts on the vibrating arm from both base end portions of the piezoelectric vibrating piece correspondingly, and the frequency increases or decreases. By detecting this frequency change, the pressure applied to the diaphragm can be measured.

  On the other hand, various sensors for measuring the viscosity or density of a fluid to be measured using a piezoelectric element have been proposed. For example, a tuning-fork type piezoelectric vibrator having a piezoelectric element attached to one end of two elongated plate-like vibrating pieces fixed to a base with their plate surfaces facing each other in parallel is immersed in a measured object such as light oil. Viscosity sensors used are known (see Patent Document 3). This tuning fork type piezoelectric vibrator is connected to the Winbridge oscillation circuit by replacing one of the two capacitors constituting the tuning fork type piezoelectric vibrator, and changes in the viscosity of the light oil are measured by detecting a voltage change from one of the connection points.

  Similarly, in order to measure the viscosity and density of a test liquid, a liquid property sensor using a tuning-fork type piezoelectric vibrator having a pair of prismatic vibrating portions coupled at a base is known (for example, a patent (Ref. 4). The viscosity and density of the test liquid are measured by detecting the vibration frequency and the effective value of the secondary output voltage of the tuning fork type piezoelectric vibrator. In this tuning fork type piezoelectric vibrator, each vibration part is separated into a main body part and fixed parts on both sides thereof by two slits extending in the cross-sectional direction, and when the main body part to which the piezoelectric material is bonded vibrates. The viscous resistance received from the liquid is increased by the liquid that has entered the slit, thereby improving the measurement accuracy.

  There is also known a quartz vibrator for a viscosity sensor that detects the viscosity of a liquid to be detected using a quartz crystal vibrating piece in a thickness-shear vibration mode (see, for example, Patent Document 5). This crystal resonator is connected to an oscillation circuit of a measuring instrument and poured into oil, and the CI (crystal impedance: series equivalent resistance) value is measured to determine the oil from the relationship between the CI value measured in advance and the viscosity. The viscosity of can be detected.

  Similarly, in a viscosity detection sensor that immerses a piezoelectric material in thickness-shear vibration mode with electrodes on both sides in the liquid to be measured, it detects changes in the oscillation frequency of the piezoelectric material, and conducts the conductance of the output generated from the piezoelectric material. There has been proposed a method for detecting a change in viscosity of a liquid to be measured by detection (see, for example, Patent Documents 6 and 7). Further, a tuning fork type vibrator having a pair of cantilever parts is vibrated at a resonance frequency by applying a voltage to a vibrator immersed in a liquid and fixed to one cantilever part, and this vibration is applied to the other cantilever part. A tuning-fork type viscosity sensor that detects the viscosity of a liquid based on the phase difference between the input signal of the vibrator and the output signal of the vibration sensor is known (for example, for example) (See Patent Document 8).

  There is also known a piezoelectric vibrating piece that excites a plurality of vibrating arms in a so-called walk mode in which a plurality of vibrating arms are bent in the out-of-plane direction, that is, in a direction perpendicular to the upper and lower main surfaces and adjacent vibrating arms are bent in opposite phases. (For example, see Patent Documents 9 and 10). Since the resonant frequency of the walk mode piezoelectric vibrating piece does not depend on the width dimension of the vibrating arm, it is possible to reduce the size while maintaining the same resonant frequency. Furthermore, the piezoelectric vibrator element in the walk mode has a high Q value and a smaller size by forming a piezoelectric element having electrode films laminated on the upper and lower sides of the piezoelectric film on one main surface of the vibrating arm. This can be realized (see, for example, Patent Document 11).

JP 2007-327922 A JP 2008-70240 A JP-A-9-257682 JP-A-11-94726 JP 2004-128979 A JP-A-9-119891 JP-A-8-261909 Japanese Patent Laid-Open No. 11-173967 JP 58-11115 A JP 2001-196891 A JP 2009-5022 A

  In the conventional pressure sensor described above, the double tuning fork piezoelectric vibrating piece may have a high frequency resolution, and exhibits a very high detection accuracy and pressure response characteristic with excellent linearity. However, a change in frequency in the piezoelectric vibrating piece requires a certain amount of time from when it is detected until it can be counted stably. Therefore, there is a problem that a slight time lag occurs between the actual change of pressure and the detection. The problem of this time lag also occurs in the conventional viscosity sensor that detects the frequency of the piezoelectric body as described in Patent Documents 4 and 6. In contrast, a sensor that detects the CI value of the piezoelectric vibrating piece is advantageous in that such a time lag does not occur.

  In the conventional pressure sensor using the double tuning fork piezoelectric vibrating piece, the bases at both ends of the vibrating arm are fixed to the support portion of the diaphragm by an adhesive or direct bonding. In such a structure, since the pressure received by the diaphragm is transmitted through the support portion, there is a possibility that the detection sensitivity may be lowered due to deterioration of the joint portion over time. Furthermore, the vibration of the piezoelectric vibrating piece leaks from the bases at both ends to the diaphragm side through the support, and mechanically couples with the natural frequency of the container, thereby reducing the vibration characteristics, leading to a decrease in detection accuracy and sensitivity. There is a fear. In addition, when the thermal expansion coefficient differs greatly between the piezoelectric vibrating piece and the diaphragm or the container, a change in the temperature of the usage environment may affect the detection accuracy and sensitivity.

On the other hand, in the sensor described in Patent Document 4, the viscosity of the liquid entering the slit (13) between the main body portion (16) of the vibrating piezoelectric body (14) and the fixing portion (18) sandwiching both sides thereof. In response to resistance, the vibration frequency changes. At this time, the magnitude of the viscous resistance F received by the vibration surface of the main body is expressed by the following equation, which is proportional to the velocity gradient dV / dz of the liquid in contact with the vibration surface of the main body, and the proportional constant η is the viscosity of the liquid. become.
F = A · η · (dV / dz)
Here, A is the area of the vibration surface, and z is the distance from the vibration surface.

  Furthermore, according to Patent Document 4, when the liquid has a vibrating surface in the stationary liquid, the liquid velocity distribution in the slit moves in the same direction and at the same speed as the vibrating surface and is separated from the vibrating surface. In the liquid at the position, the velocity decreases due to its own viscous resistance as it moves away from the vibration surface. Therefore, there is a problem that the width of the slit between the main body portion and the fixed portion also affects the viscous resistance acting on the vibration surface of the main body portion (16).

  As described above, the inventor of the present application measures and evaluates the fluctuation of the CI value with respect to the change in pressure (atmospheric pressure) of a piezoelectric sensor having a conventional structure in which a tuning fork type piezoelectric vibrator is immersed in a fluid such as air or liquid. did. The measurement results are shown in FIG. As shown in the figure, in the range where the atmospheric pressure is very low, that is, the degree of vacuum is high, the change in the CI value is relatively steep and high sensitivity can be obtained. On the other hand, in the range where the atmospheric pressure is high, that is, the degree of vacuum is low, the change in the CI value is relatively smooth, which may make it difficult to measure the pressure with high sensitivity and high accuracy.

  In view of the above-described conventional problems, an object of the present invention is to dispose a piezoelectric vibrating piece in which a plurality of adjacent vibrating arms bend and vibrate in an out-of-plane direction and in opposite phases to each other in a fluid to be measured. By detecting the change in the viscous resistance received from the fluid in contact with the surface of the piezoelectric vibrating piece as the CI value of the piezoelectric vibrating piece, the viscosity and density of the incompressible fluid such as liquid can be determined for the compressible fluid such as gas. An object of the present invention is to provide a piezoelectric sensor capable of measuring the pressure and the degree of vacuum with high sensitivity, high accuracy and high response over a wide measurement range.

  A further object of the present invention is to provide a piezoelectric sensor element and a piezoelectric vibrating piece suitable for use in such a piezoelectric sensor.

  As is well known, the tuning fork type piezoelectric vibrating piece that flexibly vibrates so that the two vibrating arms are in the in-plane direction, that is, parallel to the upper and lower main surfaces thereof and away from each other, is reduced in length. Unless the dimensional ratio of the width to is reduced, there is a problem that the resonance frequency increases in relation to the length of the vibrating arm. In contrast, the walk mode piezoelectric vibrating piece in which the vibrating arm bends and vibrates in the out-of-plane direction can be reduced in size while maintaining the same resonance frequency without reducing the width of the vibrating arm, as described above. There is.

  The inventor of the present application verified the relationship between the viscous resistance of the fluid to be measured acting on the surface of the vibrating arm and the CI value for the walk mode piezoelectric vibrating piece. As a result, it was confirmed that the CI value of the piezoelectric vibrating piece fluctuated with respect to the size of the gap when a flat and fixed surface parallel to the side surface of the vibrating arm that vibrates and vibrates was provided. Furthermore, as a result of diligent study, the present inventor has realized a piezoelectric sensor that can measure the degree of vacuum with high sensitivity, high accuracy, and high response over a wide measurement range.

Since the piezoelectric sensor element of the present invention is made based on such knowledge, in order to achieve the above object,
A base, three vibrating arms each extending in parallel from the base, each having a top and bottom main surface that is a plane including the arrangement direction and the extending direction, and left and right side surfaces perpendicular to the main surface; A piezoelectric vibrating piece having excitation electrodes for bending and vibrating the vibrating arms adjacent to each other in the out-of-plane direction of the main surface in opposite phases;
A package containing a piezoelectric vibrating piece inside and fixedly supported at the base, and capable of communicating the inside with an external fluid to be measured;
A fixed wall having a flat surface parallel to one or both side surfaces of at least one vibrating arm and defining a gap of a predetermined dimension s between the side surfaces,
The dimension s of the gap is set such that when the vibrating arm is bent and vibrated in an out-of-plane direction, the fluid to be measured generates a steady velocity distribution flow in the gap.

  Since the bending vibration of the vibrating arm is suppressed by the viscous resistance of the fluid to be measured acting on the side surface in the gap, if the viscosity resistance of the fluid to be measured changes during the bending vibration of the vibrating arm, the magnitude depends on the magnitude. The electrical characteristics such as the CI value of the piezoelectric vibrating piece change. When the side surface of the piezoelectric vibrating piece that is flexibly vibrating moves back and forth at a predetermined speed with respect to the flat surface of the fixed wall as a moving wall, if the gap is set to an appropriate size, the object to be measured will be measured in the gap. A flow with a steady velocity distribution of the fluid is generated.

  In the flow state in this gap, the change in the viscosity and density of the fluid to be measured and the resulting change in the viscous resistance change the CI value of the piezoelectric vibrating piece with a certain relationship as will be described later, and the fluctuation of the CI value. The inventor of the present application has found that the detection sensitivity is good. Therefore, the piezoelectric sensor element of the present invention can measure the change of the measurement object such as the viscosity and density of the fluid to be measured and the pressure to change them from the CI value of the piezoelectric vibrating piece with high sensitivity and high accuracy. In addition, since the CI value of the piezoelectric vibrating piece can be detected without causing a time lag such as frequency counting, measurement with excellent responsiveness is possible.

  In one embodiment, it is preferable that the dimension s of the gap is in the range of 200 μm or less. Thereby, when measuring the pressure of gas especially, it turned out that a measuring object can be measured with high sensitivity over a wide measurement range including a range with a low degree of vacuum.

  In one embodiment, the vibrating arm of the piezoelectric vibrating piece has a flat end surface orthogonal to the extending direction of the vibrating arm at the tip, and the piezoelectric sensor element is parallel to the flat end surface of the vibrating arm and A second fixed wall having a flat surface that defines a narrow second gap having a predetermined dimension s ′ between the end face and the end face is further provided, and the dimension s ′ of the second gap causes the vibrating arm to bend and vibrate in an out-of-plane direction. At this time, the fluid to be measured is set so as to generate a flow with a steady velocity distribution in the second gap. Since the viscous resistance of the fluid to be measured acts from the end surface of the tip of the vibrating arm having the largest moving speed in addition to the side surface of the vibrating arm, the change can be detected as a change in the CI value with higher sensitivity.

  In one embodiment, the fixed wall is formed by the inner wall of the package. By directly using the normal structure of the package in this way, it is not necessary to use a separate member or a complicated structure to define the gap of the dimension s, simplifying the configuration of the piezoelectric sensor element, and The piezoelectric vibrating piece can be mounted using an assembly process.

  Furthermore, in one embodiment, the second fixed wall is formed by an inner wall portion of the package. Accordingly, the configuration of the piezoelectric sensor element can be similarly simplified, and the piezoelectric vibrating piece can be mounted using a conventional assembly process.

  In another embodiment, the piezoelectric vibrating piece has a side portion extending in parallel with at least one outer vibrating arm from the base portion, and the fixing wall is formed by the side portion. Such a piezoelectric vibrating piece can be integrally processed from a quartz wafer, for example, using a known method such as wet etching, and the gap can be easily formed in a desired dimension with high accuracy. Further, the mounting work of the piezoelectric vibrating piece on the package becomes easy.

  In another embodiment, the piezoelectric vibrating piece includes two side portions extending in parallel with the outer vibrating arms so as to surround the vibrating arms, and an end portion connecting the tips of both side portions, The fixed wall is formed by the side part, and the second fixed wall is formed by the end part. Similarly, such a piezoelectric vibrating piece can be integrally processed from a quartz wafer using a known method such as wet etching, and the gap can be easily formed with high accuracy and a desired dimension. Further, the mounting work of the piezoelectric vibrating piece on the package becomes easy.

  In this case, in one embodiment, the package includes upper and lower substrates respectively connected to upper and lower surfaces of the outer frame of the piezoelectric vibrating piece, and between the upper and lower substrates and the outer frame. An interior for accommodating the piezoelectric vibrating piece is defined. By adopting such a package structure, a highly sensitive piezoelectric sensor element can be easily assembled with a small number of parts.

  In still another embodiment, the piezoelectric vibrating piece has a fixing member that extends in parallel with the vibrating arm between adjacent vibrating arms, and the fixing member allows the side of one or both of the vibrating arms to be adjacent to the vibrating arm. A fixed wall defining the gap is formed therebetween. As a result, a larger viscous resistance can be applied to the vibrating arm, the change detection sensitivity of the CI value can be increased, and the change of the measurement object can be detected with higher sensitivity.

According to another aspect of the present invention, there are provided a base portion, upper and lower main surfaces that are parallel to each other and extend from the base portion, and a right and left side surface perpendicular to the main surface. Two vibrating arms, a side portion extending in parallel with at least one outer vibrating arm from the base, and each vibrating arm in the out-of-plane direction of its main surface, and adjacent vibrating arms flexibly vibrate in mutually opposite phases. And an excitation electrode of
The side portion has a flat surface that is parallel to the outer side surface of the adjacent vibrating arm and defines a gap of a predetermined dimension s between the outer side surface, and the dimension s of the gap makes the vibrating arm in an out-of-plane direction. A piezoelectric vibrating piece is provided that is set so that the fluid to be measured generates a flow with a steady velocity distribution within the gap when it is bent and vibrated. In this piezoelectric vibrating piece, the gap can be easily formed with high accuracy and a desired dimension by a conventional method such as wet etching of a quartz wafer. Then, in the same manner as a normal piezoelectric vibrating piece having no outer frame, the piezoelectric sensor element of the present invention is mounted on a conventional package defined by a base and a lid bonded thereto according to a conventional manufacturing process. Can be configured.

  In one embodiment, the piezoelectric vibrating piece according to the present invention includes two side portions that extend in parallel with each outer vibrating arm so as to surround the vibrating arm, and an end portion that connects the tips of the two side portions. And the vibrating arm has a flat end surface perpendicular to the extending direction of the vibrating arm at the tip, and the end side is parallel to the flat end surface of the vibrating arm. None and has a flat surface that defines a narrow second gap having a predetermined dimension s ′ between the end face and the dimension s ′ of the second gap causes the vibrating arm to bend and vibrate in the out-of-plane direction of the main surface. At this time, the fluid to be measured is set so as to generate a flow with a steady velocity distribution in the second gap. Similarly, the piezoelectric vibrating reed can be formed with high accuracy and simpleness in a desired dimension by a conventional method such as wet etching of a quartz wafer, and the viscosity resistance of the fluid to be measured can be detected with higher sensitivity. can do.

  According to another aspect of the present invention, by including the above-described piezoelectric sensor element of the present invention and an electric circuit for detecting the CI value of the piezoelectric vibrating piece of the piezoelectric sensor element, the viscosity, density, A piezoelectric sensor capable of measuring a measurement object such as pressure with high sensitivity, high accuracy, and high response is provided.

1 is a longitudinal sectional view showing a first embodiment of a piezoelectric sensor element according to the present invention. 1A is a plan view of the piezoelectric vibrating piece of FIG. 1, FIG. 2B is an enlarged sectional view taken along line II-II, and FIG. 2C is an enlarged sectional view of a vibrating arm. The schematic diagram explaining the flow of the to-be-measured fluid in the clearance gap s1 of a piezoelectric vibrating piece. The diagram which shows the relationship between the atmospheric | air pressure in a 1st Example and a comparative example, and CI value. The diagram which shows the relationship between the clearance gap s1 of a piezoelectric vibrating piece, and CI value fluctuation amount. The circuit diagram which illustrates the pressure detection circuit of the piezoelectric sensor incorporating the piezoelectric sensor element of the 1st example. FIGS. 9A to 9E are waveform diagrams of signals a to e in the pressure detection circuit of FIG. (A) is a plan view showing the piezoelectric sensor element of the modified example of the first embodiment with the lid omitted, (B) is a longitudinal sectional view thereof, and (C) is a line VIII-VIII in FIG. (A). FIG. FIG. 4 is a plan view showing a modification of the piezoelectric vibrating piece in FIG. 2. (A) is a sectional view showing a second embodiment of a piezoelectric sensor element according to the present invention using the piezoelectric vibrating piece of FIG. 9, and (B) is a partially enlarged longitudinal sectional view taken along line XX. (A) is a plan view showing the piezoelectric sensor element according to a modification of the second embodiment with the lid omitted, and (B) is a longitudinal sectional view. The diagram which shows the relationship between the atmospheric | air pressure and CI value in the piezoelectric sensor of a conventional structure.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each figure, the same or similar components are denoted by the same or similar reference numerals.

  FIG. 1 shows the configuration of a first embodiment of a piezoelectric sensor element according to the present invention. The piezoelectric sensor element 11 of the present embodiment is for measuring the pressure, viscosity, and density of a fluid, and includes a piezoelectric vibrating piece 12 and a package 13 for housing it. The package 13 includes a rectangular box-shaped base 14 having an open top, and a rectangular flat lid 15 joined to the upper end thereof. The base 14 is formed by laminating thin insulating material plates such as ceramics. The lid 15 is made of, for example, a metal material such as Kovar, 42 alloy, or SUS, or an insulating material such as glass, silicon, crystal, or ceramic.

  A communication hole 17 is provided in the lid 15 so that the fluid to be measured can be introduced into the cavity 16 defined in the package 13 from the outside environment and can be circulated. The communication hole 17 can be provided in the base 14 instead of the lid, or can be provided in both the lid and the base. When the piezoelectric sensor element 11 is arranged in the fluid to be measured by the communication hole, the cavity 16 is filled with the fluid to be measured from the external environment and is placed in a state where it can freely flow.

  As shown in FIG. 2A, the piezoelectric vibrating piece 12 includes a base 18 and three vibrating arms 19a to 19c extending in parallel from the base, and is a known piezoelectric material such as a quartz material. Formed with. Further, the piezoelectric vibrating piece 12 has side portions 20a and 20b extending in parallel with the vibrating arm from the base 18 on the outer sides of the outer vibrating arms 19a and 19c, respectively.

  The resonating arms 19a to 19c have upper and lower main surfaces that are the planes including the arrangement direction and the extending direction thereof, and the vertical direction of the plane is the vertical direction, and left and right side surfaces that are orthogonal to the main surfaces. As shown in FIG. 2C, an excitation electrode 24 in which a lower electrode film 21, a piezoelectric film 22, and an upper electrode film 23 are sequentially stacked is formed on the upper main surface of each vibrating arm. . Voltages having opposite polarities are applied to the lower electrode film 21 and the upper electrode film 23. Although not shown in the drawing, a pair of mount electrodes are formed on the base 18 from the excitation electrodes 24 of the respective vibrating arms. Needless to say, excitation electrodes having different electrode structures can be formed on each of the vibrating arms. The excitation electrodes have electrode films formed on the upper and lower main surfaces and the left and right side surfaces.

  The side portions 20a and 20b respectively have flat side surfaces 26a and 26b that are parallel to the outer side surfaces 25a and 25b of the adjacent outer vibrating arms 19a and 19b. The side portions 20a and 20b are formed so as to define narrow gaps 27a and 27b having a predetermined dimension s1 between the side surfaces 25a and 25b of the vibrating arm facing the side surfaces 26a and 26b, respectively. The piezoelectric vibrating piece 12 is integrally formed from a quartz wafer by a known method such as wet etching, and the gaps 27a and 27b can be easily adjusted with high accuracy.

  On the cavity bottom surface 16a of the base 14, a pair of connection electrodes 28 is formed near one end in the longitudinal direction. The piezoelectric vibrating reed 12 is electrically connected to the base 14 and supported mechanically in a cantilever manner by fixing the mount electrode at the base 18 to the connection electrode on the cavity bottom surface 16a with a conductive adhesive 29. .

  When a predetermined voltage is applied to the piezoelectric vibrating reed 12 so that the adjacent vibrating arms have opposite phases to each other, the vibrating arms 19a to 19c each have a predetermined frequency in the out-of-plane direction, that is, perpendicular to the main surface. The vibrating arms which are adjacent to each other in the direction vibrate and vibrate in mutually opposite phases. Each of the outer vibrating arms reciprocates at a predetermined speed with respect to the side surfaces 26a and 26b of the both side portions, which are fixed walls, with the side surfaces 25a and 25b serving as moving walls. At this time, the size s1 of the gap is determined so that the fluid to be measured generates a steady flow whose velocity distribution does not change with time in the gaps 27a and 27b.

  FIG. 3 schematically illustrates the flow of the fluid F to be measured that occurs during excitation of the piezoelectric vibrating piece 12 in one gap 27a as an example. In the figure, the y-axis is perpendicular to the side wall 25a of the moving wall from the side wall 26a, which is a fixed wall, and the downward movement direction of the vibrating arm 19a is parallel to both side surfaces. When the vibrating arm 19a moves at a speed U in the x direction, the fluid under measurement in contact with the side surface 26a moves at the same speed U, whereas the speed of the fluid under measurement in contact with the side surface 26a is zero. Between them, the fluid F to be measured moves while being shifted from each other in a laminar flow at different speeds at the outer portion and the inner portion at a distance y from the side surface 26a.

When a Couette flow is generated in the gap 27a, the velocity u in the x direction at a distance y from the side surface 26a of the fluid F to be measured is expressed by the following equation.
u = U × (y / s1)
That is, as shown by an oblique straight line in FIG. 3, the velocity distribution changes linearly from 0 to U with respect to the distance y. In the figure, a vertical downward arrow shown along this velocity distribution is a velocity vector.

At this time, the frictional force per unit area acting on the side surface 25a of the vibrating arm from the fluid to be measured is the shear stress τ0 and can be expressed by the following equation.
τ0 = μ × (U / s1)
Also in the fluid to be measured in the gap 27a, a frictional force acts between the parts moving at different speeds in the x direction. The frictional force per unit area, that is, the shear stress τ can be expressed by the following equation.
τ = μ × (du / dy)
This proportionality constant μ is a value unique to the fluid to be measured, which is called viscosity or viscosity coefficient. A fluid having a constant μ proportional relationship between the velocity gradient (du / dy) and the shear stress τ is called a Newtonian fluid, and a fluid having no such proportional relationship is called a non-Newtonian fluid.

Further, these shear stresses can be rewritten as the following equation.
τ 0 = ρν × (U / s1)
τ = ρν × (du / dy)
Here, ρ is the density of the fluid to be measured, and ν = μ / ρ is the kinematic viscosity coefficient of the fluid to be measured. In general, it is known that the kinematic viscosity coefficient of a gas that is a compressible fluid increases and the kinematic viscosity coefficient of a liquid that is an incompressible fluid decreases as the temperature rises.

In fact, it is generally considered that the fluid flow generated between the moving wall and the fixed wall is often a turbulent flow rather than a simple laminar flow such as a Couette flow. In this case, the frictional force per unit area, that is, the shear stress τ 0 acting from the fluid to be measured on the vibrating arm side surface 25a can be expressed by the following equation.
τ 0 = μ × (U / s1) −ρ (time average of u ′) (time average of v ′)
The second term on the right side of this equation is called Reynolds stress, u ′ is the velocity fluctuation in the x direction of the fluid to be measured, and v ′ is the velocity fluctuation in the y direction of the fluid to be measured. It is considered that a steady flow corresponding to the viscosity of the fluid to be measured is also generated in the gap 27a.

  In this specification, the frictional force that acts on the surface of the vibrating arm to suppress the bending vibration is referred to as the viscous resistance of the fluid to be measured. The electrical characteristics of the piezoelectric vibrating piece 12 change depending on the magnitude of the viscous resistance. When the fluid to be measured is a compressive fluid, when the pressure rises, the volume decreases and the density increases, so that the viscous resistance increases. Conversely, when the pressure drops, the volume increases and the density decreases, so the viscous resistance decreases. When the fluid to be measured is an incompressible fluid, the density is constant with respect to the pressure, but the density of the liquid changes with temperature, and as a result, the viscous resistance may increase or decrease.

  In this embodiment, the change in the viscous resistance that the side surfaces 25a and 25b of the outer vibrating arms 19a and 19b receive from the fluid to be measured in the gaps 27a and 27b is detected as the change in the CI value of the piezoelectric vibrating piece 12. This makes it possible to detect with high sensitivity changes in the measurement object such as pressure that changes the viscous resistance to the vibrating arm. In addition, since the CI value is detected without generating a time lag like frequency counting, the measurement object can be measured in real time.

  In the piezoelectric sensor element 11 of the first example, the change in the CI value of the piezoelectric vibrating piece 12 with respect to the atmospheric pressure was measured with the fluid to be measured set to air and the size s1 of the gaps 27a and 27b set to 200 μm. As a comparative example, in the piezoelectric sensor element 1 of FIG. 12, the change in the CI value of the piezoelectric vibrating piece 2 with respect to the atmospheric pressure was similarly measured. The measurement results are shown in FIG. From the figure, it can be seen that the change in the CI value of the piezoelectric sensor element 11 of the present example is sufficiently larger than that of the comparative example even in the range where the atmospheric pressure is high (the degree of vacuum is low). This indicates that the piezoelectric sensor element 11 has a high CI value detection sensitivity with respect to a change in gas pressure.

  Further, in the piezoelectric sensor element 11, the amount of change in the CI value related to the size s1 of the gaps 27a and 27b was measured. Two large and small piezoelectric vibrating pieces 12 having different sizes and resonance frequencies of the vibrating arms 19a and 19b were prepared. In the large size piezoelectric vibrating piece, the vibrating arm was set to arm length = 5300 μm, arm width = 200 μm, and resonance frequency = 40 kHz. In the small size piezoelectric vibrating piece, the vibrating arm was set to arm length = 5300 μm, arm width = 200 μm, and resonance frequency = 110 to 220 kHz.

  The measurement results are shown in FIG. From the figure, in the case of the first embodiment, regardless of the size of the vibrating arm of the piezoelectric vibrating piece 12 and the resonance frequency, the change in the CI value is sufficiently achieved when the size s1 of the gaps 27a and 27b is 200 μm or less. It can be seen that it can be detected. As described above, the piezoelectric sensor element 11 of the first embodiment detects the CI value when the fluid to be measured is air and the pressure to be measured, and thereby detects the CI value in a sufficiently wide pressure range as a pressure sensor or a vacuum sensor. High sensitivity can be demonstrated.

  Based on the above-described consideration regarding the flow of the fluid to be measured in the gaps 27a and 27b and the results of FIGS. 4 and 5, the piezoelectric sensor element 11 of the first embodiment is the same for the fluid to be measured other than air and the measurement target other than the atmospheric pressure. It is easily understood that it applies to As long as the size s1 of the gap is determined so that the fluid to be measured generates a steady flow of velocity distribution in the gaps 27a and 27b, various compressive fluids and incompressible fluids can be transferred to the vibrating arm. Changes in various measurement objects such as pressure, viscosity, density, and the like that can change the viscosity resistance of can be detected with high sensitivity as changes in the CI value.

  In another embodiment, the side 20a or 20b extending from the base 18 can be provided only for one of the outer vibrating arms. In this case, although the viscous resistance received from the fluid to be measured as the entire piezoelectric vibrating piece is reduced, the piezoelectric vibrating piece and the piezoelectric sensor element can be reduced in size.

  In another embodiment, a fixed wall may be provided between the adjacent vibrating arms, that is, between the central vibrating arm 19c and the vibrating arms 19a and 19b on both sides or one side thereof. The fixed wall has a flat surface parallel to the side surface of the adjacent vibrating arm, and the fluid to be measured has a steady velocity between the flat surface and the side surface of the vibrating arm during bending vibration of the vibrating arm. A narrow gap of a predetermined size is defined so as to generate a distribution flow. Thereby, a larger viscous resistance than the case of the first embodiment of FIG. 1 is applied to the vibrating arms 19a to 19c, the change detection sensitivity of the CI value is increased, and the change of the measurement object can be detected with higher sensitivity. . Such a fixed wall is provided by, for example, a fixed arm portion extending in parallel with the vibrating arm from the base portion 18 of the piezoelectric vibrating piece 12.

  FIG. 6 shows a configuration example of a pressure detection circuit of a piezoelectric sensor incorporating the piezoelectric sensor element 11 of the first embodiment. The pressure detection circuit 30 includes an oscillation circuit 31 of the piezoelectric sensor element 11, a filter circuit 32, a rectification circuit 33, an integration circuit 34, and a DC amplification circuit 35 connected in series with each other. Signals a to e in these circuits 31 to 35 are schematically shown in FIG. 7 with the horizontal axis representing time T and the vertical axis representing voltage.

  The oscillation circuit 31 includes inverters INV1 to INV3 connected in series between both terminals of the piezoelectric vibrating piece as an amplifier for causing the piezoelectric vibrating piece 12 of the piezoelectric sensor element 11 to oscillate. In the first stage inverter INV1, the input terminal is connected to one terminal of the piezoelectric vibrating piece 12, the output terminal is connected to the input terminal of the second stage inverter INV2, and the second stage inverter INV2 has the output terminal connected to the third stage. Connected to the input terminal of the inverter INV3, the third-stage inverter INV3 has an output terminal connected to the other terminal of the crystal vibrating piece. A capacitor C1 is connected between the input terminal of the inverter INV1 and the ground potential, and a capacitor C2 is connected between the output terminal of the inverter INV3 and the ground potential.

  Further, the oscillation circuit 31 has a resistor R1 formed of a circuit in which resistors RA, RB, RC are connected in series between both terminals of the piezoelectric vibrating piece 12. One terminal of the resistor R1, that is, the terminal of the resistor RA is connected to the input terminal of the inverter INV1, and the other terminal of the resistor R1, that is, one terminal of the resistor RC is connected to the output terminal of the inverter INV3. A connection midpoint between the resistor RA and the resistor RB is connected to an output terminal of the inverter INV1, and a connection midpoint between the resistor RB and the resistor RC is connected to an output terminal of the inverter INV2. A phase control resistor RD is connected between the other terminal of the resistor R1, that is, the resistor RC terminal and the other terminal of the crystal resonator element. With this configuration, the oscillation circuit 31 outputs the oscillation signal OUT obtained by oscillating the piezoelectric vibrating piece 12 from the output terminal of the inverter INV3.

  The filter circuit 32 includes a capacitor C <b> 3 connected between the input terminal of the inverter INV <b> 1 and the one terminal of the piezoelectric vibrating piece 12 and the input terminal of the rectifier circuit 33. A resistor R3 is connected between the other terminal of the capacitor C3 and the ground potential.

  In the filter circuit 32, a signal a shown in FIG. 7A, which is a part of the vibrator current that is the current output from the one terminal of the piezoelectric vibrating piece 12 connected to the input terminal side of the inverter INV1, is shown. input. The input signal a is a sinusoidal AC signal on which a DC component is superimposed, and its amplitude (voltage) Vpp1 changes in proportion to the CI value of the piezoelectric vibrating piece 12. As shown in FIG. 7B, the filter circuit 32 outputs a signal b obtained by removing the DC component from the input signal a.

  The rectifier circuit 33 includes a diode D1 connected between the capacitor C3 of the filter circuit 32 and the integration circuit 34. The rectifier circuit 33 receives the output signal b of the filter circuit 32 and outputs a signal c that has been half-wave rectified as shown in FIG.

  The integrating circuit 34 has a resistor R4 connected between the output of the diode D1 of the rectifying circuit 33 and the DC amplifying circuit 35. A capacitor C4 is connected between the resistor R4 and the ground potential. The integrating circuit 34 receives the output signal c from the rectifying circuit 33 and outputs an integrated signal d as shown in FIG.

  The DC amplifier circuit 35 includes a comparison circuit 35a and a resistor R5 connected between the plus terminal of the comparison circuit and the output of the integration circuit 34. In the comparison circuit 35a, a resistor R6 is connected between the minus terminal and the ground potential, and a resistor R7 is connected between the minus terminal and the output terminal. The DC amplification circuit 35 receives the output signal d of the integration circuit 34, and outputs the amplified signal e of the potential Vout as a pressure detection signal as shown in FIG. Unlike the count of the oscillation frequency, the detection of the output signal e can be performed instantaneously at a level of, for example, several milliseconds.

  The pressure detection circuit 30 can be entirely configured as an external element of the piezoelectric sensor element 11, or a part of the pressure detection circuit 30 can be disposed inside the package 13 of the piezoelectric sensor element 11. In addition to the above-described three-stage configuration, the inverter that constitutes the amplifier of the oscillation circuit 31 may have one stage or a plurality of (odd number) stages other than the three stages depending on the design conditions of the oscillation circuit. Further, when the output signal d of the integration circuit 34 has a magnitude (potential) sufficient for detecting pressure, the DC amplification circuit 35 can be omitted.

  8A to 8C show a modification of the piezoelectric sensor element of the first embodiment. The piezoelectric sensor element 41 according to this embodiment includes a piezoelectric vibrating piece 42 and a package 13 for housing the piezoelectric vibrating piece 42. The piezoelectric vibrating piece 42 has a conventional structure in which both side portions 20a and 20b are omitted from the piezoelectric vibrating piece 12 of FIG. 1 and includes three vibrating arms 19a to 19c extending in parallel from the base portion 18. Similar to the first embodiment, the package 13 includes a rectangular box-shaped base 14 and a rectangular flat plate lid 15 provided with a communication hole 17 to the cavity 16. As in the piezoelectric vibrating piece 12 of FIG. 1, the piezoelectric vibrating piece 42 has an excitation electrode formed on the surface of each vibrating arm, and a mount electrode drawn from the excitation electrode is formed on the base 18. The piezoelectric vibrating piece 42 is supported in a cantilever manner by fixing the mount electrode to the connection electrode 28 on the bottom surface 16 a of the cavity with a conductive adhesive 29 at the base portion 18.

  The base 14 of the package 13 has inner wall surfaces 43a and 43b whose side wall portions 14a and 14b extending along the vibrating arms 19a and 19b outside the piezoelectric vibrating piece 42 are flat. In the present embodiment, the piezoelectric vibrating piece 42 is formed so that the outer side surfaces 25a and 25b of the outer vibrating arm are parallel to the inner wall surfaces 43a and 43b of the adjacent base 14 and a gap 44a having a predetermined dimension s2 therebetween. , 44b.

  When a predetermined voltage is applied to the excitation electrode of the piezoelectric vibrating piece 42, the vibrating arms 19a to 19c bend and vibrate in the out-of-plane direction at a predetermined frequency and the adjacent vibrating arms in opposite phases. The outer side surfaces 25a and 25b of the outer vibrating arms 19a and 19b reciprocate at a predetermined speed with respect to the inner wall surfaces 43a and 43b of the base 14, which is a fixed wall, as moving walls. At this time, the size s2 of the gap is determined so that the fluid to be measured entering the cavity 16 from the communication hole 17 generates a flow having a steady velocity distribution in the gaps 44a and 44b.

  By mounting the piezoelectric vibrating piece 42 in the package 13 in this way, the outer vibrating arms 19a and 19b have side surfaces 25a and 25b that are measured in the gaps 44a and 44b as described above with reference to FIG. Receives viscous resistance from fluid. Depending on the magnitude of this viscous resistance, bending vibration of the vibrating arms 19a and 19b is suppressed, and the CI value of the piezoelectric vibrating piece 42 changes. Therefore, by detecting the change in the viscous resistance received by the vibrating arm as the change in the CI value of the piezoelectric vibrating piece 42, it is possible to detect the change in the measurement target such as the pressure of the fluid to be measured with high sensitivity.

  In another embodiment, instead of directly using the inner wall surface of the base 14 as a fixed wall that defines the gaps 44a, 44b between the outer vibrating arms, a separate flat surface member is placed in the cavity 16. Can be arranged. In addition, a fixed wall structure that defines the gaps 44a and 44b can be protruded from the side wall portions 14a and 14b of the base 14 only in a region corresponding to the vibrating arm of the piezoelectric vibrating piece 42.

  FIG. 9 shows a modification of the piezoelectric vibrating piece used in the piezoelectric sensor element of the first embodiment. In addition to the configuration of the piezoelectric vibrating piece 12 of the first embodiment, the piezoelectric vibrating piece 51 of the present embodiment forms a rectangular outer frame 52 that surrounds the vibrating arms 19a to 19c on the opposite side of the base 18 in the longitudinal direction. As described above, there is an end side portion 20c that connects the ends of both side portions 20a and 20b.

  The vibrating arms 19a to 19c have flat end surfaces 53a to 53c that are orthogonal to the extending direction of the vibrating arms at the tips, that is, free ends, respectively. The end side portion 20c has a flat inner side surface 26c facing the end surfaces 53a to 53c of the vibrating arm. The end portion 20c is arranged so that the side surface 26c is parallel to the end surfaces 53a to 53c of the vibrating arm and defines narrow gaps 54a to 54c having a predetermined dimension s3 therebetween. The piezoelectric vibrating piece 51 is integrally formed from a quartz wafer by a known method such as wet etching, for example, and the gaps 54a to 54c on the tip side of the vibrating arm can be easily adjusted with high accuracy.

  The piezoelectric vibrating piece 51 is placed in an appropriate package into which the fluid to be measured is introduced, a predetermined voltage is applied, and the vibrating arms 19a to 19c are flexibly vibrated in the same manner as in the above embodiment. Each of the outer vibrating arms reciprocates at a predetermined speed with respect to the side surfaces 26a and 26b of the both side portions, which are fixed walls, with the side surfaces 25a and 25b serving as moving walls. At the same time, the end surfaces 53a to 53c of the vibrating arms reciprocate at a predetermined speed with respect to the side surface 26c of the end side portion 20c, which is a fixed wall, as moving walls. At this time, the size s3 of the gap is set so that the fluid to be measured generates a steady flow of velocity distribution in the gaps 54a to 54c.

  The bending vibrations of the vibrating arms 19a to 19c are suppressed by the respective side surfaces 25a and 25b of the outer vibrating arms and the end surfaces 53a to 53c of all the vibrating arms receiving the viscous resistance of the fluid to be measured. In particular, the end face of the tip of the vibrating arm has the highest moving speed, and thus receives a relatively large viscous resistance even if its area is small. Therefore, this embodiment can apply a larger viscous resistance to the vibrating arms 19a to 19c than in the first embodiment shown in FIG. By detecting the change in the viscous resistance as the change in the CI value of the piezoelectric vibrating piece 52, it is possible to detect the change in the measurement target such as the pressure of the fluid to be measured with higher sensitivity.

  FIGS. 10A and 10B show a second embodiment of the piezoelectric sensor element according to the present invention suitable for incorporating the piezoelectric vibrating piece 51 of FIG. The piezoelectric sensor element 61 of this embodiment includes an upper substrate 62 and a lower substrate 63 which are bonded to the upper and lower sides of the piezoelectric vibrating piece 51 as an intermediate piezoelectric substrate and constitute a package.

  The upper and lower substrates 62 and 63 have recesses 62a and 63a formed on the surfaces facing the piezoelectric vibrating piece 51, respectively. The upper and lower substrates are joined to the upper and lower surfaces of the outer frame 52 that constitutes a part of the package that accommodates the piezoelectric vibrating reeds at the periphery surrounding the recesses 62a and 63a. Thereby, cavities for accommodating the vibrating arms 19 a to 19 c are defined inside the piezoelectric sensor element 61. A communication hole 64 is provided in the recess 62 a of the upper substrate 62 so that the fluid to be measured can be introduced into the cavity from the external environment and can be distributed. With this configuration, the piezoelectric sensor element can be reduced in size.

  11A and 11B show a modification of the piezoelectric sensor element of FIG. As in the embodiment of FIG. 8, the piezoelectric sensor element 71 of the present embodiment accommodates the piezoelectric vibrating piece 42 having a conventional structure in which the side portions 20a and 20b are omitted from the piezoelectric vibrating piece 12 of FIG. The package 13 is provided. The package 13 includes a rectangular box-shaped base 14 and a rectangular flat plate lid 15 provided with a communication hole 17 to the cavity 16. In the piezoelectric vibrating piece 42, an excitation electrode is formed on the surface of each vibrating arm, and a mount electrode drawn out from the excitation electrode is formed on the base 18. The piezoelectric vibrating piece 42 is supported in a cantilever manner by fixing the mount electrode to the connection electrode 28 on the bottom surface 16 a of the cavity with a conductive adhesive 29 at the base portion 18.

  In the piezoelectric sensor element 71, in addition to the configuration of FIG. 8, the side wall portion 14c of the base 14 adjacent to the tips of the vibrating arms 19a to 19c of the piezoelectric vibrating piece 42 has a flat inner wall surface 43c. The vibrating arms 19a to 19c have flat end surfaces 72a to 72c that are orthogonal to the extending direction of the vibrating arms at the tips, that is, the free ends, respectively. In the present embodiment, the piezoelectric vibrating piece 42 is parallel to the inner wall surfaces 43a and 43b of the base 14 where the outer side surfaces 25a and 25b of the outer vibrating arm are adjacent to each other, and a gap 44a having a predetermined dimension s2 is provided therebetween. 44b and the inner wall surface 43c of the side wall portion 14c is arranged so as to be parallel to the end surfaces 72a to 72c of the vibrating arm and to define narrow gaps 73a to 73c having a predetermined dimension s4 therebetween. .

  When a predetermined voltage is applied to the excitation electrode of the piezoelectric vibrating piece 42, the vibrating arms 19a to 19c bend and vibrate in the out-of-plane direction at a predetermined frequency and the adjacent vibrating arms in opposite phases. The outer side surfaces 25a and 25b of the outer vibrating arms 19a and 19b reciprocate at a predetermined speed with respect to the inner wall surfaces 43a and 43b of the base 14, which is a fixed wall, as moving walls. At the same time, the end surfaces 72a to 72c of the vibrating arms reciprocate at a predetermined speed with respect to the inner wall surface 43c of the side wall portion 14c, which is a fixed wall, as moving walls. At this time, the size s4 of the gap is set so that the fluid to be measured entering the cavity 16 from the communication hole 17 generates a flow with a steady velocity distribution in the gaps 73a to 73c.

  Bending vibrations of the vibrating arms 19a to 19c are suppressed by the respective side surfaces 25a and 25b of the outer vibrating arms and the end surfaces 72a to 72c of all three vibrating arms receiving the viscous resistance of the fluid to be measured. In particular, the end face of the tip of the vibrating arm has the highest moving speed, and thus receives a relatively large viscous resistance even if its area is small. Therefore, in this embodiment, a larger viscous resistance than the embodiment of FIG. 8 can be applied to the vibrating arms 19a to 19c. By detecting the change in the viscous resistance as the change in the CI value of the piezoelectric vibrating piece 42, it is possible to detect the change in the measurement target such as the pressure of the fluid to be measured with higher sensitivity.

  In each of the embodiments shown in FIGS. 8, 9, and 11, a fixed wall can be provided between the vibrating arms adjacent to the piezoelectric vibrating piece. The fixed wall has a flat surface parallel to the side surface of the adjacent vibrating arm, and the fluid to be measured has a steady velocity between the flat surface and the side surface of the vibrating arm during bending vibration of the vibrating arm. Define narrow gaps that produce a distributed flow. Thereby, a larger viscous resistance than the case of each said Example is made to act on the said vibrating arm, the change detection sensitivity of CI value can be raised, and the change of a measuring object can be detected more highly. For example, in the embodiment shown in FIGS. 8 and 11, such a fixed wall is formed integrally with another base 14 of the package 13 or another member. In the embodiment shown in FIG. 9, the base of the piezoelectric vibrating piece 51 is formed. It is provided by the intermediate frame part which connects between 18 and the edge part 20c.

  The present invention is not limited to the above embodiments, and can be implemented with various modifications or changes within the technical scope thereof. For example, the package of the piezoelectric sensor element can have various structures other than the above-described embodiment. For example, instead of the communication hole, the upper or side of the package can be opened to an external fluid to be measured. . Furthermore, in the piezoelectric sensor of the present invention, various configurations other than those shown in FIG. 5 are conceivable as the pressure detection circuit connected to the piezoelectric sensor element.

DESCRIPTION OF SYMBOLS 11, 41, 61, 71 ... Piezoelectric sensor element, 12, 42, 51 ... Piezoelectric vibrating piece, 13 ... Package, 14 ... Base, 14a-14c ... Side wall part, 15 ... Lid, 16 ... Cavity, 16a ... Cavity bottom face, Reference numerals 17 and 64 are communication holes, 18 are base portions, 19a to 19c are vibrating arms, 20a and 20b are side portions, 20c are end side portions, 21 are lower electrode films, 22 are piezoelectric films, and 23 are upper electrode films. 24 ... excitation electrodes, 25a, 25b, 26a, 26b, 26c ... side surfaces, 27a, 27b, 44a, 44b, 54a-54c, 73a-73c ... gaps, 28 ... connection electrodes, 29 ... conductive adhesive, 30 ... Pressure detection circuit, 31 ... Oscillation circuit, 32 ... Filter circuit, 33 ... Rectification circuit, 34 ... Integration circuit, 35 ... DC amplification circuit, 35a ... Comparison circuit, 43a, 43b ... Inner wall surface, 52 ... Outer frame, 3A～53c, 72 a to 72 c ... end surface, 62 ... upper substrate, 62a, 63a ... concave portion, 63 ... lower substrate.

Claims (12)

A base portion, three vibrating arms each extending in parallel from the base portion, each having a vertical main surface that is a plane including the arrangement direction and the extending direction thereof, and left and right side surfaces orthogonal to the main surface; A piezoelectric vibrating piece having excitation electrodes for bending and vibrating the vibrating arms adjacent to each other in the out-of-plane direction of the main surface in mutually opposite phases;
A package that accommodates the piezoelectric vibrating piece inside and is fixedly supported at the base, and is capable of communicating the inside with an external fluid to be measured;
A fixed wall having a flat surface that is parallel to the side surface of either one or both of the at least one vibrating arm and that defines a gap of a predetermined dimension s between the side surface, and
The piezoelectric element characterized in that the dimension s of the gap is set so that the fluid to be measured generates a steady flow of velocity distribution in the gap when the vibrating arm is bent and vibrated in the out-of-plane direction. Sensor element.   The piezoelectric sensor element according to claim 1, wherein a dimension s of the gap is in a range of 200 μm or less. The vibrating arm of the piezoelectric vibrating piece has a flat end surface orthogonal to the extending direction of the vibrating arm at the tip,
A second fixed wall having a flat surface that is parallel to the flat end surface of the vibrating arm and that defines a narrow second gap having a predetermined dimension s ′ between the end surface and the second fixed wall;
The dimension s ′ of the second gap is set so that the fluid under measurement generates a steady velocity distribution flow in the second gap when the vibrating arm is bent and vibrated in the out-of-plane direction of the main surface. The piezoelectric sensor element according to claim 1, wherein the piezoelectric sensor element is provided.   The piezoelectric sensor element according to claim 1, wherein the fixed wall is formed by an inner wall portion of the package.   The piezoelectric sensor element according to claim 3, wherein the second fixed wall is formed by an inner wall portion of the package.   2. The piezoelectric vibrating piece includes a side portion extending in parallel with the vibrating arm at least one outside from the base portion, and the fixing wall is formed by the side portion. 4. The piezoelectric sensor element according to any one of 3.   An outer frame comprising two side portions extending in parallel with the outer vibrating arms and end sides connecting the tips of the both side portions so that the piezoelectric vibrating piece surrounds the vibrating arms. The piezoelectric sensor element according to claim 3, wherein the fixed wall is formed by the side portion, and the second fixed wall is formed by the end portion.   The package includes upper and lower substrates respectively connected to upper and lower surfaces of the outer frame of the piezoelectric vibrating piece, and the piezoelectric vibrating piece is accommodated between the upper and lower substrates and the outer frame. The piezoelectric sensor element according to claim 7, wherein the inside is defined.   The piezoelectric vibrating piece has a fixing member extending in parallel with the vibrating arm between the adjacent vibrating arms, and the fixing member makes a gap between the side surfaces of one or both of the vibrating arms adjacent thereto. The piezoelectric sensor element according to claim 1, wherein the fixed wall that defines a gap is formed. At least one of the base, three vibrating arms each extending in parallel from the base, each having an upper and lower main surface which is a plane including the arrangement direction and the extending direction, and left and right side surfaces perpendicular to the main surface; A side portion extending in parallel with the vibrating arm on the outside, and an excitation electrode for bending and vibrating each vibrating arm in the out-of-plane direction of the main surface and the adjacent vibrating arms in opposite phases to each other. And
The side portion has a flat surface which is parallel to the outer side surface of the adjacent vibrating arm and defines a gap of a predetermined dimension s between the side surface and the dimension s of the gap is the vibrating arm. The piezoelectric vibrating piece is set so that the fluid to be measured generates a flow with a steady velocity distribution in the gap when it is bent and vibrated in the out-of-plane direction. An outer frame comprising two side portions extending in parallel with the outer vibrating arms and end portions connecting the tips of the side portions so as to surround the vibrating arms;
The vibrating arm has a flat end surface perpendicular to the extending direction of the vibrating arm at a tip thereof;
The end side portion has a flat surface that is parallel to the flat end surface of the vibrating arm and defines a narrow second gap having a predetermined dimension s ′ between the end surface and the dimension s of the second gap. Is set such that when the vibrating arm is bent and vibrated in an out-of-plane direction of the main surface, the fluid to be measured generates a steady flow of velocity distribution in the second gap. The piezoelectric vibrating piece according to claim 10.   A piezoelectric sensor comprising: the piezoelectric sensor element according to claim 1; and an electric circuit that detects a CI value of a piezoelectric vibrating piece of the piezoelectric sensor element.

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