Patent Description:
In recent years, an ultrasonic flow meter that measures a time taken for an ultrasonic wave to travel in a propagation path, thereby measuring a moving speed of a fluid, and consequently measures a flow rate has been being used for gas meters and the like. In an ultrasonic flow meter that performs flow rate measurement by measuring a propagation time of an ultrasonic wave, a pair of ultrasonic transceivers are generally disposed upstream and downstream of a measurement flow path through which a fluid to be measured flows, and the propagation time of the ultrasonic wave is measured by transmission and reception of an ultrasonic wave between the ultrasonic transceivers.

When the fluid to be measured is a gas, the difference in acoustic impedance between the gas and the piezoelectric element is large, and the ultrasonic wave is therefore easily reflected at an interface between the piezoelectric element and the gas. Therefore, in the ultrasonic transceiver, an acoustic matching layer is provided at the interface between the piezoelectric element and the gas in order to enable the ultrasonic wave to efficiently enter the gas from the piezoelectric element.

Further, in order to improve the radiation efficiency, there is used an acoustic matching layer configured by stacking a first acoustic matching layer having a high density and a high sound speed and a second acoustic matching layer having a lower density and a lower sound speed than the first acoustic matching layer. There is proposed an ultrasonic transceiver that can be matched with a gas having a sufficiently small acoustic impedance by arranging on the gas side a second acoustic matching layer that is acoustic impedance-matched with the gas, which is a fluid to be measured (for example, see PTL <NUM>).

PTL <NUM>: <CIT> Documents <CIT>, <CIT> disclose an ultrasonic transceiver with a piezoelectric element and a plurality of acoustic matching layers.

However, in the conventional configuration, since a reverberation in the received wave of the ultrasonic wave is large, there is a possibility that a reference point for measuring a propagation time cannot be accurately detected and the gas flow rate is erroneously detected.

The ultrasonic transceiver according to the present invention is defined in appended independent claim <NUM>.

Next, a method of measuring a propagation time in an ultrasonic flow meter that is not part of the claimed invention will be described with reference to <FIG> and <FIG>.

A conventional flow rate measurement device for a fluid of this type is generally a device as shown in <FIG>, that is not part of the claimed invention. Flow rate measurement device <NUM> includes: first ultrasonic transceiver <NUM> and second ultrasonic transceiver <NUM> installed in flow path <NUM> through which a fluid to be measured flows; and switching unit <NUM> that switches first ultrasonic transceiver <NUM> and second ultrasonic transceiver <NUM> between transmission and reception. In addition, flow rate measurement device <NUM> includes: transmitter <NUM> that drives first ultrasonic transceiver <NUM> and second ultrasonic transceiver <NUM>; and receiver <NUM> that receives a received signal that is received by the ultrasonic transceiver on the reception side and has passed through switching unit <NUM>. Flow rate measurement device <NUM> further includes: amplifier <NUM> that amplifies the received signal to a predetermined amplitude; and reference comparator <NUM> that compares a voltage of the received signal amplified by amplifier <NUM> with a reference voltage.

Further, flow rate measurement device <NUM> includes: reference voltage setting unit <NUM> that sets the reference voltage to be compared by reference comparator <NUM>; determination unit <NUM> that determines a reference point for measuring time on the basis of a comparison result of reference comparator <NUM>; and time counter <NUM> that measures a propagation time of an ultrasonic wave on the basis of a result of determination unit <NUM>. Flow rate measurement device <NUM> further includes: flow rate calculator <NUM> that calculates a flow rate of the fluid to be measured on the basis of the propagation time measured by time counter <NUM>; and controller <NUM> that is configured with a microcomputer and the like and performs overall control.

Next, a method of measuring the propagation time of the ultrasonic wave by time counter <NUM>, that is not part of the claimed invention will be described with reference to <FIG> illustrates a drive signal D of the ultrasonic transceiver (first ultrasonic transceiver <NUM> or second ultrasonic transceiver <NUM>) assigned to a transmission side by switching unit <NUM>, and further illustrates a received signal S that is received by the ultrasonic transceiver (first ultrasonic transceiver <NUM> or second ultrasonic transceiver <NUM>) assigned to a reception side by switching unit <NUM> and that is amplified by amplifier <NUM> such that the maximum amplitude becomes a predetermined amplitude.

Reference comparator <NUM> compares the received signal S with a reference voltage Vr set by reference voltage setting unit <NUM>, and determination unit <NUM> detects a zero-crossing point R1 of the received signal after the received signal S becomes larger than the reference voltage Vr.

Here, a reference voltage Vr is set to such a voltage that the third wave of the received signal S can be detected, but this setting is based on the following assumption: when amplifier <NUM> amplifies the received signal S such that the maximum amplitude of the received signal S becomes a predetermined amplitude, the amplitude of the third wave is also amplified by the same amplification factor, and also the third wave therefore becomes a voltage in a predetermined range.

Time counter <NUM> can calculate a propagation time TP0 by measuring a time TP from a start point T0 to the zero-crossing point R1 and by subtracting from the time TP a time TR that is from a reception start point R0 to the zero-crossing point R1.

Then, by switching between the transmission and the reception of first ultrasonic transceiver <NUM> and second ultrasonic transceiver <NUM> by using switching unit <NUM>, it is possible to obtain, by the above-described method, a propagation time t1 from first ultrasonic transceiver <NUM> to second ultrasonic transceiver <NUM> and a propagation time t2 from second ultrasonic transceiver <NUM> to first ultrasonic transceiver <NUM>.

Then, a flow rate Q can be obtained by the following equation, where v is a flow velocity of the fluid to be measured, S is a cross-sectional area of a flow path, ϕ is a sensor angle, and L is a propagation distance.

Flow rate calculator <NUM> calculates the flow rate by further multiplying Equation <NUM> by a coefficient corresponding to the flow rate.

However, it has been found that when the ultrasonic transceiver having the conventional configuration is used as the ultrasonic transceiver, the waveform of the received signal is distorted due to reverberation, and thus the zero-crossing point R1 cannot be correctly detected in some cases.

<FIG> each illustrate a configuration of a conventional ultrasonic transceiver. <FIG> is a cross-sectional view of ultrasonic transceiver <NUM>, and <FIG> is a plan view of ultrasonic transceiver <NUM>. In ultrasonic transceiver <NUM>, piezoelectric element <NUM> is bonded to top face inner part 201a of metal sensor case <NUM> having a capped cylindrical shape. In addition, first acoustic matching layer <NUM> having a disk shape and second acoustic matching layer <NUM> having a disk shape having the same outer diameter as first acoustic matching layer <NUM> are stacked and joined to a top face outer part 201b of sensor case <NUM>.

<FIG> illustrates an example of a received waveform in a case where ultrasonic transceiver <NUM> is used. As illustrated in <FIG>, relatively large reverberation waves are seen after a normal maximum amplitude A, and in some cases, an amplitude B that is equivalent to the maximum amplitude A or may be larger than the maximum amplitude A is generated.

The waveform of the ultrasonic wave transmitted and received by the ultrasonic transceiver is mainly affected by a thickness and shape of the piezoelectric element, a material, thickness, and shape of the sensor case, shapes, thicknesses, and acoustic impedances of the first acoustic matching layer and the second acoustic matching layer, and the like.

Further, it has been found from our study that the received ultrasonic waveform illustrated in <FIG> is affected by the shapes in the surface direction of the acoustic matching layers. In a case where an area of a joining surface of first acoustic matching layer <NUM> is the same as an area of a joining surface of second acoustic matching layer <NUM> as in ultrasonic transceiver <NUM> illustrated in <FIG>, or in a case where the area of the joining surface of second acoustic matching layer <NUM> is larger than the area of the joining surface of first acoustic matching layer <NUM>, the following phenomenon occurs. That is, the ultrasonic wave radiated to the fluid to be measured generates direct wave <NUM> in which a vibration of piezoelectric element <NUM> propagates to the fluid to be measured by the shortest distance via sensor case <NUM>, first acoustic matching layer <NUM>, and second acoustic matching layer <NUM>. In addition, the vibration of piezoelectric element <NUM> propagates in a circumferential direction of first acoustic matching layer <NUM>, and indirect wave <NUM> having a phase delay is generated by reflection by joint part <NUM> between first acoustic matching layer <NUM> and second acoustic matching layer <NUM>, and by other causes. The vibration of piezoelectric element <NUM> is a combination of direct wave <NUM> and indirect wave <NUM>, and indirect wave <NUM> is considered to generate reverberation.

Note that indirect wave <NUM> illustrated in <FIG> is schematically illustrated, and the illustrated propagation paths are not limitative.

When the position of the maximum amplitude varies due to the influence of such a large reverberation wave as described above, the third wave to be detected does not have an assumed amplitude even if amplifier <NUM> amplifies the maximum amplitude to have the predetermined amplitude. Therefore, the preceding and following second and fourth waves are detected, and the correct propagation time cannot be measured. That is, the propagation times t1 and t2 in Equation <NUM> cannot be accurately measured, and a measurement accuracy of the flow rate decreases.

For example, in the received waveform illustrated in <FIG>, when the amplitude B becomes larger than the normal maximum amplitude A, amplifier <NUM> amplifies the received signal such that the amplitude B becomes the predetermined amplitude. Then, the third wave originally desired to be detected is not amplified to the reference voltage or more, and reference comparator <NUM> therefore detects the fourth wave.

The present disclosure enables stable measurement of an ultrasonic signal by suppressing reverberation of a received ultrasonic waveform.

An ultrasonic transceiver of the present disclosure includes a piezoelectric element and a plurality of acoustic matching layers stacked on and joined to the piezoelectric element directly or via another layer, where at least a part of a joining part between the acoustic matching layers is inside an outer periphery of a joining surface of the acoustic matching layer disposed on a piezoelectric element side. The first acoustic matching layer has a disk shape, the second acoustic matching layer has a rectangular shape, and a short side of a joining surface via which the second acoustic matching layer and the first acoustic matching layer are joined together is shorter than a diameter of the first acoustic matching layer.

With this configuration, it is possible to suppress propagation of the indirect wave from the acoustic matching layer on the piezoelectric element side to the next acoustic matching layer, and when this ultrasonic transceiver is used as an ultrasonic flow meter, a reverberation level of the ultrasonic transceiver can be reduced, and stable measurement of the propagation time of the ultrasonic wave can be achieved.

The ultrasonic transceiver of the present disclosure can reduce the reverberation of the received ultrasonic waveform, and erroneous measurement of the propagation time in flow rate measurement can be reduced, thereby achieving stable flow rate measurement.

Hereinafter, exemplary embodiments will be described in detail with reference to the drawings. However, unnecessarily detailed description is omitted in some cases. For example, a detailed description of already well-known matters and a redundant description of substantially the same configuration is omitted in some cases.

Note that the attached drawings and the following description are provided for those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter as described in the appended claims.

<FIG> is a cross-sectional view of an ultrasonic transceiver in a first example that is not part of the claimed invention. <FIG> is a plan view of the ultrasonic transceiver in the first example that is not part of the claimed invention.

With reference to <FIG>, that is a first example not part of the claimed invention, ultrasonic transceiver <NUM> includes case <NUM> having conductivity and a capped cylindrical shape, piezoelectric element <NUM> joined to top face inner part 11a of case <NUM> via joining part <NUM>, first acoustic matching layer <NUM> joined to top face outer part 11b of case <NUM> via joining part <NUM>, and second acoustic matching layer <NUM> joined to first acoustic matching layer <NUM> via joining part <NUM>.

Electrodes 12a and 12b are provided on opposite surfaces of piezoelectric element <NUM>, electrode 12a is conductively joined to case <NUM> via joining part <NUM>, and when an AC voltage is applied across electrode 12b and case <NUM>, piezoelectric element <NUM> is deformed according to the voltage. The deformation generated in piezoelectric element <NUM> propagates to a fluid to be measured via first acoustic matching layer <NUM> and second acoustic matching layer <NUM>.

In the first example that is not part of the claimed invention, both first acoustic matching layer <NUM> and second acoustic matching layer <NUM> have a disk shape, a diameter of second acoustic matching layer <NUM> is smaller than a diameter of first acoustic matching layer <NUM>, and first acoustic matching layer <NUM> and second acoustic matching layer <NUM> are concentrically stacked. With this configuration, joining part <NUM> between first acoustic matching layer <NUM> and second acoustic matching layer <NUM> is located inside an outer periphery of joining surface 13a of first acoustic matching layer <NUM> bonded on a side of piezoelectric element <NUM>.

In this arrangement, as illustrated in <FIG>, in ultrasonic transceiver <NUM> of the present exemplary embodiment, direct wave <NUM> that is a part of the ultrasonic wave radiated to the fluid to be measured is mainly propagated to the fluid to be measured, but the ultrasonic wave other than direct wave <NUM> attenuates because first acoustic matching layer <NUM> and the fluid to be measured are not matched. Therefore, it is possible to suppress propagation of indirect waves <NUM> to the fluid to be measured.

Note that indirect waves <NUM> illustrated in <FIG> are schematically illustrated, and these propagation paths of indirect waves <NUM> are not limitative.

<FIG> is an image diagram of a received waveform of the ultrasonic transceiver in the first example that is not part of the claimed invention. As illustrated in the drawing, it can be seen that a reverberation part attenuates more rapidly than the conventional received wave illustrated in <FIG>.

As described above, an influence of the reverberation wave can be suppressed by ultrasonic transceiver <NUM> of the first example that is not part of the claimed invention. Therefore, by using ultrasonic transceiver <NUM> of the first example that is not part of the claimed invention. for the ultrasonic flow meter illustrated in <FIG>, amplifier <NUM> can amplify an ultrasonic wave such that the maximum amplitude becomes the predetermined amplitude, the third wave to be detected therefore becomes to have the assumed amplitude, and the correct propagation time can be measured.

Note that a thickness t1 of first acoustic matching layer <NUM> and a thickness t2 of second acoustic matching layer <NUM> illustrated in <FIG> preferably have a thickness of about <NUM>/<NUM> of a wavelength of the sound wave propagating in the acoustic matching layers. Assuming that a frequency for driving the ultrasonic transceiver is f and a sound velocity in the acoustic matching layer is V, a wavelength λ of the sound wave is obtained by λ = V/f. Therefore, a thickness d of the acoustic matching layer is obtained by d = <NUM>/<NUM>·λ. With such a structure, it is possible to align phases of ultrasonic waves reflected inside the sensor and to efficiently transmit and receive ultrasonic waves.

In order to efficiently propagate the vibration of piezoelectric element <NUM> to the fluid, it is important to match the acoustic impedances. In the present exemplary embodiment, first acoustic matching layer <NUM> is attached to top face outer part 11b of case <NUM>, and second acoustic matching layer <NUM> is joined to first acoustic matching layer <NUM>. Assuming that an acoustic impedance of first acoustic matching layer <NUM> is Za and an acoustic impedance of second acoustic matching layer <NUM> is Zb, a relationship of Za > Zb is satisfied. The impedance Za is smaller than the acoustic impedance of piezoelectric element <NUM>. Since the plurality of acoustic matching layers having such acoustic characteristics are provided, the vibration of the piezoelectric element can be efficiently propagated into the fluid to be measured.

<FIG> is a cross-sectional view illustrating a variation of the ultrasonic transceiver in the first example that is not part of the claimed invention. <FIG> is a cross-sectional view illustrating a variation of the ultrasonic transceiver in the first example that is not part of the claimed invention.

<FIG> is a plan view illustrating an ultrasonic transceiver in a first exemplary embodiment. <FIG> is a cross-sectional view illustrating the ultrasonic transceiver in the first exemplary embodiment.

In order to achieve matching with a substance which is a fluid to be measured and to which an ultrasonic wave is propagated, it is known to stack a plurality of acoustic matching layers (not limited to two layers), and <FIG> illustrates a side cross-sectional view of ultrasonic transceiver <NUM>, where first acoustic matching layer <NUM>, second acoustic matching layer <NUM>, and third acoustic matching layer <NUM> are stacked in this order as an acoustic matching layer and are joined to top face outer part 11b of case <NUM>, so that the acoustic matching layer is formed as three layers.

In ultrasonic transceiver <NUM>, joining part <NUM> between first acoustic matching layer <NUM> and second acoustic matching layer <NUM> is located inside an outer periphery of joining surface 23b of first acoustic matching layer <NUM>. Further, joining part 25b between second acoustic matching layer <NUM> and third acoustic matching layer <NUM> is located inside an outer periphery of joining surface 24b of second acoustic matching layer <NUM>. With this configuration, it is possible to reduce propagation of indirect waves 16a, 16b from piezoelectric element <NUM> to third acoustic matching layer <NUM>, and the reverberation can therefore be suppressed.

Similarly, also in a case where more than three acoustic matching layers are provided, when a joining part of an acoustic matching layer is located on an inner side of a joining surface inside an outer periphery of a joining surface of an acoustic matching layer disposed on the piezoelectric element side, it is possible to suppress the propagation of indirect waves <NUM> (16a, 16b), and the reverberation can therefore be suppressed.

<FIG> illustrates a side cross-sectional view of ultrasonic transceiver <NUM>. Instead of second acoustic matching layer <NUM> in ultrasonic transceiver <NUM> illustrated in <FIG>, second acoustic matching layer <NUM> having a truncated cone shape is used. In ultrasonic transceiver <NUM>, an area of radiation surface 34b of second acoustic matching layer <NUM> through which an ultrasonic wave propagates is substantially the same as an area of the joining surface 13b of first acoustic matching layer <NUM>; however, since joining part <NUM> between first acoustic matching layer <NUM> and second acoustic matching layer <NUM> is located inside joining surface 13b of first acoustic matching layer <NUM>, it is possible to avoid the propagation of indirect waves <NUM> to second acoustic matching layer <NUM>, and the reverberation can therefore be suppressed.

<FIG> illustrates a plan view of ultrasonic transceiver <NUM>, and second acoustic matching layer <NUM> is used in which a shape of a matching surface (a radiation surface of an ultrasonic wave) of second acoustic matching layer <NUM> in ultrasonic transceiver <NUM> illustrated in <FIG> is changed from a circle to a rectangle and in which a length in a short-side direction is shorter than a diameter of first acoustic matching layer <NUM>. In ultrasonic transceiver <NUM>, regardless of a length in a long-side direction of second acoustic matching layer <NUM>, it is possible to avoid the propagation of a phase-delayed indirect wave from side parts C of first acoustic matching layer <NUM> to second acoustic matching layer <NUM>, and the reverberation can therefore be suppressed.

<FIG> illustrates a side cross-sectional view of ultrasonic transceiver <NUM>, in which case <NUM> of ultrasonic transceiver <NUM> illustrated in <FIG> is removed and first acoustic matching layer <NUM> is directly joined to piezoelectric element <NUM>. Also in this case, it is possible to reduce the propagation of ultrasonic waves other than direct wave <NUM> from piezoelectric element <NUM> to second acoustic matching layer <NUM>, and the reverberation can therefore be suppressed.

As described above, with the ultrasonic transceivers according to the present first exemplary embodiment, at least a part of the joining part between the acoustic matching layers is located inside the outer periphery of the joining surface of the acoustic matching layer disposed on the piezoelectric element side, so that the reverberation can therefore be suppressed.

Note that, in the present exemplary embodiment, various configurations are illustrated as examples by <FIG>, <FIG>, but it is needless to say that when at least a part of the entire periphery of the joining part is located inside the outer periphery of the joining surface of the acoustic matching layer disposed on the piezoelectric element side, it is possible to reduce the propagation of the ultrasonic wave other than the direct wave from the piezoelectric element to the next acoustic matching layer; and the shape of the acoustic matching layer can be appropriately selected.

In addition, in order to suppress the propagation of the indirect wave to the next acoustic matching layer, it needless to say that the entire joining part between the acoustic matching layers are preferably located inside the outer periphery of the joining surface of the acoustic matching layer disposed on the piezoelectric element side.

Next, an ultrasonic flow meter using the ultrasonic transceiver described in the first exemplary embodiment will be described with reference to <FIG>, <FIG>, and <FIG>.

<FIG> is a perspective view of an ultrasonic transceiver used for an ultrasonic flow meter in a second exemplary embodiment. <FIG> is a perspective view of the ultrasonic transceiver used for the ultrasonic flow meter in the second exemplary embodiment. <FIG> is a plan view of the ultrasonic transceiver used for the ultrasonic flow meter in the second exemplary embodiment. <FIG> is a cross-sectional view taken along line 5D-5D of <FIG>.

As illustrated in the drawings, in ultrasonic transceiver <NUM>, electrode surface 42a of piezoelectric element <NUM> is conductively joined to top part inner side 41a of metal case <NUM> having a capped cylindrical shape, and lead wire <NUM> is joined to electrode surface 42b by solder <NUM>. In addition, lead wire <NUM> is joined to case <NUM> by welding, and piezoelectric element <NUM> vibrates at a predetermined frequency by applying an AC voltage to lead wire <NUM> and lead wire <NUM>.

Flange 41d is formed at an open end of case <NUM>, and vibration-proof member <NUM> is integrally formed, by molding, on an outer periphery of flange 41d. Lead wire <NUM> and lead wire <NUM> are held by case <NUM> by vibration-proof member <NUM>.

Disk-shaped first acoustic matching layer <NUM> having a diameter of <NUM> is joined to top part outer side 41b of case <NUM>, and second acoustic matching layer <NUM> is joined to first acoustic matching layer <NUM>. Here, second acoustic matching layer <NUM> is made to have a substantially rectangular shape with a long-side length of <NUM> and a short-side length of <NUM> such that second acoustic matching layer <NUM> is joined to first acoustic matching layer <NUM> inside an outer periphery of a joining surface of first acoustic matching layer <NUM>. Note that thicknesses of first acoustic matching layer <NUM> and second acoustic matching layer <NUM> are set to optimum values, as described above, depending on the frequency of the ultrasonic wave to be propagated.

Piezoelectric element <NUM> has a rectangular parallelepiped shape, and the joining surface via which piezoelectric element <NUM> and case <NUM> are joined together is configured to be smaller than an outer diameter of second acoustic matching layer <NUM>. In addition, piezoelectric element <NUM> is disposed such that a longitudinal direction of piezoelectric element <NUM> coincides with a longitudinal direction of second acoustic matching layer <NUM>. Further, piezoelectric element <NUM> has slit 42c to improve an excitation efficiency in a longitudinal vibration mode.

Further, in flange 41d, a pair of recesses 41c for positioning are formed at parts of the outer periphery of flange 41d that are in the longitudinal direction of second acoustic matching layer <NUM>.

<FIG> is a perspective view of the flow path block used for the ultrasonic flow meter in the second exemplary embodiment. <FIG> is a view taken in a direction of arrow 6B in <FIG> is a perspective view of a sensor fixing member used for the ultrasonic flow meter in the second exemplary embodiment.

As illustrated in <FIG>, flow path block <NUM> includes measurement flow path <NUM> which has a cylindrical shape and has a rectangular cross-section and through which a fluid to be measured flows. Measurement flow path <NUM> is divided into three divided flow paths <NUM> (first divided flow path 53a, second divided flow path 53b, and third divided flow path 53c) by two partition plates <NUM> arranged in parallel along a flow direction of the fluid to be measured, so that a multilayer flow path is formed as a whole. Further, flow path block <NUM> has inlet <NUM> and outlet <NUM> for the fluid to be measured.

Flow path block <NUM> further includes: upstream-side sensor mounting portion 56a and downstream-side sensor mounting portion 56b each having an opening for mounting the ultrasonic transceiver; positioning projections <NUM> for the time of mounting the ultrasonic transceivers; locking portions <NUM> for sensor fixing members to be described later; and locking portions <NUM> for a circuit board.

<FIG> is a side view of the ultrasonic flow meter in the second exemplary embodiment. As illustrated in <FIG>, in ultrasonic flow meter <NUM>, a pair of ultrasonic transceivers <NUM> are mounted on upstream-side sensor mounting portion 56a and downstream-side sensor mounting portion 56b of flow path block <NUM>. Here, after ultrasonic transceivers <NUM> are mounted such that recesses 41c (see <FIG>) are positioned at positioning projections <NUM> (see <FIG>), hinges 61a (see <FIG>) of sensor fixing members <NUM> (see <FIG>) are engaged with locking portions <NUM> provided on flow path block <NUM>, so that the ultrasonic transceivers are pressed against and fixed to upstream-side sensor mounting portion 56a (see <FIG>) and downstream-side sensor mounting portion 56b (see <FIG>).

<FIG> is a main-part cross-sectional view taken along line 7B-7B of <FIG> illustrates the relationship between second acoustic matching layer <NUM> and partition plates <NUM>. As illustrated in the drawing, second acoustic matching layer <NUM> is disposed at a position facing second divided flow path 53b of the multilayer flow path, and a width W (short-side length) of second acoustic matching layer <NUM> is made to be matched with outer sides of two partition plates <NUM> and is made to be larger than a distance X (<NUM>) between the partition plates.

<FIG> is a graph for illustrating a width of a short side of a second acoustic matching layer, an output of an ultrasonic wave, and a magnitude of reverberation in the second exemplary embodiment. The graph illustrated in <FIG> is an image in which the horizontal axis represents the width of the short side of second acoustic matching layer <NUM>, and the output of the ultrasonic signal and the magnitude of the reverberation are shown as a graph. As illustrated in the drawing, the output increases as the width of second acoustic matching layer <NUM> increases, but the reverberation increases after the width reaches a certain size, so that the optimum dimension is determined to be <NUM>.

As described above, by setting the width (short-side length) of second acoustic matching layer <NUM> to be inside the outer periphery of the joining surface of first acoustic matching layer <NUM>, it is possible to prevent the wave reflected on the side surface of first acoustic matching layer <NUM> from propagating to second acoustic matching layer <NUM>, and it is possible to suppress the reverberation of the ultrasonic signal and to efficiently propagate the ultrasonic signal to second divided flow path 53b, which is at the center.

Circuit board <NUM> including a drive circuit for ultrasonic transceivers <NUM> and a measurement circuit that measures the propagation time to calculate the flow velocity and the flow rate of the fluid to be measured is placed on an upper part of flow path block <NUM> and is locked by locking portion <NUM>. Lead wires <NUM> and <NUM> of ultrasonic transceivers <NUM> are connected to circuit board <NUM> by soldering or the like. Further, board case <NUM> represented by a broken line is placed so as to cover circuit board <NUM>.

Then, the ultrasonic signal from upstream ultrasonic transceiver <NUM> on the upstream side is reflected, on a rout represented by arrow P1, by inner wall 51a of the opposing flow path, then passes through a route represented by arrow P2, and is received by ultrasonic transceiver <NUM> on the downstream side.

With the above configuration, ultrasonic flow meter <NUM> of the second exemplary embodiment can obtain the flow rate by the above-described Equation (<NUM>), as described with reference to <FIG>.

Claim 1:
An ultrasonic transceiver (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
a piezoelectric element (<NUM>, <NUM>); and
a plurality of acoustic matching layers stacked on and joined to the piezoelectric element (<NUM>, <NUM>) directly or via another layer,
wherein at least a part of a joining part between the plurality of acoustic matching layers is disposed inside an outer periphery of a joining surface of the acoustic matching layer disposed on a side of the piezoelectric element (<NUM>, <NUM>), and
the plurality of acoustic matching layers includes:
a first acoustic matching layer (<NUM>, <NUM>, <NUM>) joined to the piezoelectric element (<NUM>, <NUM>) directly or via another layer; and
a second acoustic matching layer (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) stacked on and joined to the first acoustic matching layer (<NUM>, <NUM>, <NUM>),
characterized in that
the first acoustic matching layer (<NUM>, <NUM>, <NUM>) has a disk shape,
the second acoustic matching layer (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) has a rectangular shape, and
a short side of a joining surface via which the second acoustic matching layer (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and the first acoustic matching layer (<NUM>, <NUM>, <NUM>) are joined together is shorter than a diameter of the first acoustic matching layer (<NUM>, <NUM>, <NUM>).