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DESCRIPTION JP2004245603

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DESCRIPTION JP2004245603
PROBLEM TO BE SOLVED: To provide an ultrasonic sensor which can suppress the generation of
reverberation in a case even when the ultrasonic sensor is used in a high temperature
atmosphere or a gas atmosphere, has excellent transmission and reception characteristics, and is
excellent in temperature characteristics and environmental resistance characteristics. With the
goal. A bottomed cylindrical case (11), a piezoelectric vibrator (2) bonded to an inner bottom
surface (21) of the bottomed cylindrical case (11), and a bottom of the bottomed cylindrical case
(11) so as to shield an opening of the bottomed cylindrical case. A bottomed cylindrical case 11
is provided with a base member 3 welded to the cylindrical case 11 and a pair of input / output
terminals 4 and 5 fixed to the base member 3 and electrically connected to the piezoelectric
vibrator 2. The cylindrical ring 10 made of a resin material is press-fit into and fitted to the outer
peripheral side 14 of the above. Further, as the resin material of the ring 10, one having a glass
transfer point exceeding the upper limit value at the operating temperature of the ultrasonic
sensor 1 is used. [Selected figure] Figure 1
Ultrasonic sensor and method of manufacturing the same
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic sensor using a piezoelectric vibrator, and more particularly to an ultrasonic sensor
installed in a gas pipe and used to measure a gas flow rate. 2. Description of the Related Art An
ultrasonic sensor vibrates a piezoelectric element to transmit ultrasonic waves outward, and the
piezoelectric element receives a reflected wave that is reflected and returned by a receiver to be
measured. Measure the distance from the transmission position to the receiver from the elapsed
time from transmission to reception, or, in the gas flowmeter, attach a pair of ultrasonic sensors
opposite to each other at predetermined intervals in the gas piping, from one ultrasonic sensor
The ultrasonic wave is transmitted to the other ultrasonic sensor and the ultrasonic wave is
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received by the other ultrasonic sensor, and it is used to measure the gas flow rate from the
difference in time required for transmission and reception. In particular, when used for
applications requiring high accuracy, such as a gas flow meter, an ultrasonic sensor having stable
transmission and reception characteristics over a long period of time is required. In an ultrasonic
sensor using a piezoelectric element, a plate-like piezoelectric vibrator having electrodes formed
on both sides is fixed to the bottom of a bottomed cylindrical case and a pair of terminals are
fixed to the opening of the bottomed cylindrical case There is a type in which a base member is
fixed, a pair of terminals is electrically connected to electrodes on both sides of the piezoelectric
element, and the pair of terminals is connected to an electric circuit through the pair of
terminals. And when transmitting an ultrasonic wave, a pulse signal is applied to a piezoelectric
vibrator from an electric circuit, and a piezoelectric vibrator is vibrated. On the other hand, when
receiving an ultrasonic wave, the piezoelectric vibrator receives and vibrates the ultrasonic wave,
and the vibration of the piezoelectric vibrator is converted into a predetermined electric signal by
an electric circuit. In the ultrasonic sensor having such a configuration, when the vibration of the
piezoelectric vibrator is transmitted to the outer peripheral side surface of the case and the outer
peripheral side surface of the case vibrates, unnecessary reverberant waves are generated, and
ultrasonic signals at the time of transmission and reception Since noise is generated in the
electric signal to impair the transmission and reception characteristics, there is one in which a
rubber-based contraction tube is attached to the outer peripheral side surface of the case in
order to suppress the vibration of the outer peripheral side surface of the case. (For example,
refer to Patent Document 1) [Patent Document 1] Japanese Patent Application Laid-Open No.
2002-204498 (page 3-5, FIG. 1) Problems to be Solved by the Invention However, Patent
Document 1 According to the ultrasonic sensor disclosed in 1, because the glass transition point
of the rubber-based shrinking tube is generally low at several tens of degrees, the shrinking tube
softens under high temperatures exceeding the glass transition point, and vibration of the outer
peripheral side of the case The suppression power is weakened, noise may occur in the
transmission and reception signals, and the transmission and reception characteristics may be
impaired.
In addition, when this ultrasonic sensor is used for a gas flow meter, the contraction tube is
exposed to the gas atmosphere for a long time, thereby deteriorating the rubber component of
the contraction tube and weakening the suppression of the vibration of the outer peripheral side
of the case. there were. The present invention solves the above-mentioned problems. Even when
an ultrasonic sensor is used in a high-temperature atmosphere or a gas atmosphere, the vibration
of the outer peripheral surface of the case is suppressed to suppress the generation of
reverberation waves, thereby transmitting and receiving An object of the present invention is to
provide an ultrasonic sensor excellent in characteristics and excellent in temperature
characteristics and environmental resistance characteristics. The ultrasonic sensor according to
the present invention made to achieve the above object has an opening at one end in the axial
direction and a bottom surface at the other end in the axial direction. And a piezoelectric vibrator
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joined to the inner bottom surface of the bottomed cylindrical case, and the bottomed cylindrical
case so as to shield the opening of the bottomed cylindrical case. A ring-shaped member or a
cylinder is provided on the outer peripheral side surface of the bottomed cylindrical case,
comprising: a fixed base member; and a pair of input / output terminals fixed to the base member
and electrically connected to the piezoelectric vibrator. It is characterized in that the second
member is fitted. According to the ultrasonic sensor of the present invention, the ring-shaped
member or the cylindrical member is fitted to the outer peripheral side surface of the bottomed
cylindrical case, whereby the bottomed cylindrical case resulting from the vibration of the
piezoelectric vibrator is obtained. Since the vibration of the outer peripheral side surface is
suppressed, there is an advantage that the reverberation wave hardly occurs. Moreover, even
when used at high temperatures, the transmission and reception characteristics are excellent,
and the temperature characteristics and the environmental resistance characteristics can be
improved. One aspect of the ultrasonic sensor according to the present invention is characterized
in that the ring-shaped member or the cylindrical member is made of a resin material whose
glass transfer point exceeds the upper limit value at the operating temperature of the ultrasonic
sensor. (Claim 2) The ring-shaped member or the cylindrical member is made of a resin material
whose glass transfer point exceeds the upper limit value at the operating temperature of the
ultrasonic sensor. The ring-shaped member or the cylindrical member can be reliably fitted to the
outer peripheral side surface of the bottomed cylindrical case without damaging the mechanical
properties or the chemical properties of the ring-shaped member. As a result, even if it is used for
a long time in a gas atmosphere below the glass transition temperature (for example, propane
gas, hydrogen gas, etc.), the ring-shaped member or the cylindrical member is less likely to
deteriorate, thereby suppressing the generation of reverberation waves. There is an advantage
that the transmission and reception characteristics can be improved. According to another aspect
of the ultrasonic sensor of the present invention, the ring-shaped member or the cylindrical
member is at least 1 / a of the distance from the bottom surface to the opening on the outer
peripheral side surface of the bottomed cylindrical case. It is characterized in that it is fitted so as
to cover the range of 2.
(Claim 3) If the ring-shaped member or the tubular member is fitted so as to cover at least a half
of the distance from the bottom to the opening, propagation to the outer peripheral side of the
bottomed cylindrical case Vibration can be suppressed, and the generation of reverberation
waves can be suppressed. Although the details of the reason are unknown, when the vibration of
the piezoelectric vibrator propagates to the outer peripheral side surface of the bottomed
cylindrical case, the bottomed cylindrical shape is within 1/2 of the distance from the bottom to
the opening. It is presumed that the influence of the amplitude of the vibration propagating to
the outer peripheral side of the case is large. According to one aspect of the method of
manufacturing an ultrasonic sensor of the present invention, a bottomed cylindrical case having
an opening at one end in the axial direction and a bottom at the other end in the axial direction; A
piezoelectric vibrator joined to the inner bottom surface, a base member fixed to the bottomed
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cylindrical case so as to shield the opening of the bottomed cylindrical case, and the base
member fixed to the base member A pair of input / output terminals electrically connected to the
piezoelectric vibrator is provided, and a ring-shaped member or a cylindrical member made of a
resin material is fitted on the outer peripheral side surface of the bottomed cylindrical case by
press-fitting. In the method of manufacturing an ultrasonic sensor, in the press-fitting step, a
ring-shaped member or a cylindrical member made of the resin material is press-fit and fitted
while heating at a temperature exceeding the glass transition point of the resin material. It is
characterized by (Claim 4) According to the method of manufacturing an ultrasonic sensor of the
present invention, a ring-shaped member or a cylindrical member made of a resin material on the
outer peripheral side of a bottomed cylindrical case is heated to a temperature exceeding the
glass transition point of the resin material. By providing a press-in process that fits by pressfitting while heating by heating, it is possible to fit closely to the outer peripheral side surface of
the bottomed cylindrical case, so suppressing vibration propagating to the outer peripheral side
surface of the bottomed cylindrical case There is an advantage that generation of reverberation
waves can be suppressed. In particular, as the resin material, it is preferable to use one having a
glass transition point exceeding the upper limit value in the operating temperature range of the
ultrasonic sensor. (Claim 5) A ring-shaped member or a ring-shaped member made of a resin
material having a glass transition temperature exceeding 40 ° C., even if the use conditions of
the ultrasonic sensor are used at a high temperature of 40 ° C. (upper limit value) The use of
the tubular member is advantageous in that an ultrasonic sensor having excellent transmission
and reception characteristics and improved temperature characteristics and environmental
resistance characteristics can be manufactured. BEST MODE FOR CARRYING OUT THE
INVENTION Hereinafter, embodiments of the present invention will be described with reference
to the drawings. FIG. 1 is a cross-sectional view showing the configuration of an ultrasonic sensor
to which the present invention is applied. In FIG. 1, reference numeral 1 denotes an ultrasonic
sensor, and the ultrasonic sensor 1 has a bottomed cylindrical case 11 and a piezoelectric
vibrator 2 joined to the inner bottom surface 21 of the bottomed cylindrical case 11. A base
member 3 fixed to the bottomed cylindrical case 11 so as to shield the opening 13 of the bottom
cylindrical case 11 and a pair of the base member 3 fixed to the base member 3 and electrically
connected to the piezoelectric vibrator 2 The cylindrical ring 10 (so-called, so-called, press fit
along the outer peripheral side surface 14 of the bottomed cylindrical case 11 with the input /
output terminals 4 and 5, the matching layer 8 adhered to the outside of the bottom 21 of the
bottomed cylindrical case 11) A ring-shaped member or a cylindrical member).
The piezoelectric vibrator 2 is formed of a ceramic material having piezoelectric characteristics,
and silver paste is printed on both sides of the piezoelectric vibrator 2 to form electrodes 16 and
17. The piezoelectric vibrator 2 is formed in a disk shape having an outer diameter of about 8
mm and a thickness of about 2 mm. The piezoelectric vibrator 2 is joined to the bottom surface
21 of the bottomed cylindrical case 11 made of metal, one electrode 16 is electrically connected
to the bottomed cylindrical case 11, and the other electrode 17 is a conductive wire 9. And
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electrically connected, for example, by soldering, welding, conductive bonding, and the like. Next,
the bottomed cylindrical case 11 is made of a stainless material (about 0.2 mm in thickness)
which has conductivity and is excellent in corrosion resistance and heat resistance in a gas
atmosphere, and is in the axial direction (as shown in FIG. The bottom surface 12 is attached to
one end of the Y direction, and the other end is opened to form an opening 13. The bottomed
cylindrical case 11 is formed to have an outer diameter of about 10 mm and an axial length of
about 8 mm. Further, in the bottomed cylindrical case 11, the piezoelectric vibrator 2 is bonded
and joined to the bottom surface 21, and the convex portion 15 of the base member 3 is fitted so
as to shield the opening 13. Is fixed to the base member 3 by welding. Further, in the bottomed
cylindrical case 11, the cylindrical ring 10 is press-fitted along the outer peripheral side surface
14. Next, the base member 3 is formed of SPC (cold-rolled steel) subjected to Ni plating
processing having conductivity, and the convex 15 is fitted to the inside of the opening 13 of the
bottomed cylindrical case 11. A seat 18 is formed in contact with the opening 13 of the bottomed
cylindrical case 11, and the insulating sheet 7 is attached to the upper surface of the projection
15. Further, the bottomed cylindrical case 11 is formed with a through hole 19 for inserting the
input terminal 5 and an engagement hole 20 for connecting the input terminal 4. Next, the pair
of input / output terminals 4 and 5 are made of iron in order to electrically connect with the
electrodes 16 and 17 of the piezoelectric vibrator 2 and the outer electric circuit (not shown) of
the bottomed cylindrical case 11. It is formed of a conductive metal such as an alloy. Further, one
input / output terminal 5 is inserted into the through hole 19 of the base member 3, and an
insulating material 6 such as glass paste is injected into a gap between the input and output
terminals 5 and fixed with a hermetic seal structure, The base member 3 is electrically isolated.
Then, one end of the input / output terminal 5 protrudes inward of the bottomed cylindrical case
11 and is electrically connected to the electrode 17 of the piezoelectric vibrator 2 by the
conductive wire 10, and the other end of the input / output terminal 5 is The bottomed
cylindrical case 11 protrudes outward to be connected to an outer electric circuit (not shown) of
the bottom cylindrical case 11.
The other input / output terminal 4 has one end engaged with an engagement hole 20 formed on
the outer surface of the base member 3 and is fixed by welding so as to electrically conduct to
the base member 3 The other end of the input / output terminal 4 protrudes outward of the
bottomed cylindrical case 11 in order to connect to the outer electric circuit (not shown) of the
bottomed cylindrical case 11. The input / output terminal 4 is electrically connected to the
electrode 16 of the piezoelectric vibrator 2 via the conductive base member 3 and the conductive
bottomed cylindrical case 11. Next, the matching layer 8 is formed of a foamable material having
a low Q value (eg, foam carbon, foam plastic, etc.) in order to achieve impedance matching
between the bottomed cylindrical case 11 and air. It is adhered to the outer surface of the bottom
surface 21 of the bottomed cylindrical case 11. Next, the ring 10 is highly durable even when
used in a gas atmosphere or at high temperature, and is a polypropylene resin (glass transition
point is 120) having a glass transition point exceeding the operating temperature range of 70 °
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of the ultrasonic sensor 1 Is formed into a tubular shape (so-called forming ring). The ring 10 is
formed to have an inner diameter slightly smaller than the outer diameter of the bottomed
cylindrical case 11, and along the outer peripheral side surface 14 from the bottom 21 side of
the bottomed cylindrical case 11. It is pressed in. Further, when the ring 10 is press-fitted into
the bottomed cylindrical case 11, the ring 10 is press-fitted while heating the ring 10 at a
temperature slightly higher than the glass transition temperature 120 ° C. of the ring 10 (about
130 ° C.) . A method of manufacturing the ultrasonic sensor configured as described above will
be described below. First, the piezoelectric vibrator 2 with the electrodes 16 and 17 baked on
both sides and the base member 3 to which the input and output terminals 4 and 5 are
connected are prepared. The piezoelectric vibrator 2 is formed into a plate shape by firing a
ceramic material having piezoelectric characteristics by a known manufacturing method, and
silver paste is printed and baked on both sides of the plate shape to form the electrodes 16 and
17. . Further, the input / output terminal 5 is fixed to the base member 3 with the hermetic seal
structure via the insulating material 6 by a known manufacturing method, and the input / output
terminal 4 is fixed by welding. Next, an adhesive (not shown) is applied to the bottom surface 12
of the bottomed cylindrical case 11, and the piezoelectric vibrator 2 is bonded to the bottom
surface 21 of the bottomed cylindrical case 11. At this time, the piezoelectric vibrator 2 is
pressed against the bottom surface 12 of the bottomed cylindrical case 11 as necessary so that
no gap is generated between the piezoelectric vibrator 2 and the bottom surface 12 of the
bottomed cylindrical case 11. While heating and bonding.
Next, one end of the conductive wire 9 is electrically connected to the surface of the electrode 17
of the piezoelectric vibrator 2 by soldering, and the base member 3 to which the input / output
terminals 4 and 5 are connected is a bottomed cylindrical case The other end of the conductive
wire 9 is electrically connected to the end of the input / output terminal 5 by soldering, welding,
conductive bonding or the like (corresponding to the connecting step of the present invention).
Next, the convex portion 15 of the base member 3 is fitted into the opening 13 of the bottomed
cylindrical case 11, and the periphery of the tip of the opening 13 is joined to the base member 3
by welding. Further, the connection terminal 4 is electrically connected to the electrode 16 of the
piezoelectric vibrator 2 through the base member 4 having conductivity and the bottomed
cylindrical case 11 by this bonding. Next, the ring 10 is press fitted from the bottom surface 12
side of the bottomed cylindrical case 11 along the outer peripheral side surface 14 and fitted
(this corresponds to the pressing process of the present invention). When press-fitting the ring
11, the bottomed cylinder is heated while heating the ring 10 at a temperature of 130 ° C. (a
temperature which exceeds the glass transition point by about 10 ° C.) slightly exceeding the
glass transition temperature 120 ° C. of the ring 10. Press-fit into the outer peripheral side 14
of the case 11. In addition, as the method of heating the ring 10, there are various methods of
holding the ring 10 in a heater, leaving the ring 10 in a high temperature bath, or blowing hot air
onto the ring 10. It is selected according to productivity. Next, an adhesive is applied to the outer
surface of the bottom surface 12 of the bottomed cylindrical case 11 to adhere the matching
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layer 8, and the assembly of the ultrasonic sensor 1 is completed. Below, the test result
performed in order to confirm the effect which suppresses the vibration of the outer peripheral
side 14 of the bottomed cylindrical case 11 in the ultrasonic sensor 1 is demonstrated using
figures. In addition, in order to confirm the effect of the embodiment of the present invention, a
comparative test was conducted together with a comparative example. In the comparative
example, a contraction tube having an inner diameter larger than the outer diameter of the
bottomed cylindrical case 11 is inserted into the outer peripheral side surface 14 of the
bottomed cylindrical case 11 in place of the ring 10 in the ultrasonic sensor 1 of the present
embodiment. It is heated and shrunk at 75 ° C. to 115 ° C. to be in close contact with the outer
peripheral side surface 14 of the bottomed cylindrical case 11. Test results of the embodiment
and the comparative example are shown in FIG. 4 to FIG. FIG. 4 is an impedance characteristic
diagram of the embodiment, FIG. 5 is an impedance characteristic diagram of the comparative
example, FIG. 6 is a characteristic diagram showing a reception waveform of the embodiment,
and FIG. 7 is a characteristic diagram showing a reception waveform of the comparison example.
In FIG. 4 and FIG. 5, the ultrasonic sensor 1 of the embodiment and the ultrasonic sensor of the
comparative example are placed in a constant temperature bath, and the temperature in the
constant temperature layer (manufactured by Tabai Espec; MINISUBZERO MC-710) is -35
degrees to +85. The impedance characteristics of the ultrasonic sensor 1 of the embodiment and
the ultrasonic sensor of the comparative example are measured at each predetermined
temperature change using an impedance analyzer (YHP 4194A) while changing the temperature
to 25 ° C. The impedance characteristics and the impedance characteristics at + 85 ° C. at
which a change in the impedance characteristics appears remarkably are shown.
In FIG. 4 and FIG. 5, the horizontal axis is a frequency representing a range of 200 kHz to 300
kHz, and the vertical axis is an impedance representing a range of 100 Ω to 50 kΩ. It is a
frequency. In this embodiment, as shown in FIG. 4, when comparing the impedance characteristic
at 25 ° C., which is the initial characteristic, with the impedance characteristic at + 85 ° C.,
there is almost no difference between the two, and it is used in high temperature. However, it can
be seen that the generation of the reverberant wave can be suppressed by suppressing the
vibration of the outer peripheral side surface of the bottomed cylindrical case. On the other hand,
in the comparative example, as shown in FIG. 5, when the impedance characteristic at 25 ° C.,
which is the initial characteristic, and the impedance characteristic at + 85 ° C. are compared,
the disturbance of the impedance waveform at 85 ° C. It is understood that when N1 and N2)
occur and they are used at high temperature, the effect of suppressing the vibration of the outer
peripheral side surface 14 of the bottomed cylindrical case 11 is impaired. The received
waveforms shown in FIG. 6 and FIG. 7 are obtained by recording the received waveform when
the ultrasonic wave transmitted from one ultrasonic sensor is received by the other ultrasonic
sensor using an oscilloscope. The vertical axis represents voltage (V), and the horizontal axis
represents time (μs). Note that voltage values of V3 and Vmax were read in order to compare
the transmission and reception sensitivities of the present embodiment and the comparative
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example. In this embodiment, as shown in FIG. 6, the voltage value of V3 is −820 mV, the
voltage value of Vmax is −3300 mV, and as shown in FIG. 7, the voltage value of V3 is −740
mV as shown in FIG. The voltage value of Vmax indicates -3100 mV, and it can be seen that the
transmission and reception sensitivity between ultrasonic sensors is good in the present
embodiment as compared with the comparative example. The effects of the ultrasonic sensor of
the above embodiment and the method of manufacturing the same will be described below.
According to the ultrasonic sensor 1 in the embodiment of the present invention, vibration of the
outer peripheral side surface 14 of the bottomed cylindrical case 11 is achieved by fitting the
cylindrical ring 10 to the outer peripheral side surface 14 of the bottomed cylindrical case 11
Can be suppressed to suppress the generation of reverberation waves, and the transmission and
reception characteristics can be improved. And, since the cylindrical ring 10 is formed of a resin
material in which the glass transfer point of the cylindrical ring 10 has an upper limit value or
more at the operating temperature of the ultrasonic sensor 1, even when used at high
temperatures and in a gas atmosphere The generation of reverberation waves can be suppressed
to improve the transmission and reception characteristics, and the environment resistance
characteristics such as a high temperature atmosphere and a gas atmosphere are excellent.
Further, according to the method of manufacturing the ultrasonic sensor 1 in the embodiment of
the present invention, the bottomed cylindrical shape is obtained by fitting the cylindrical ring 10
to the outer periphery of the bottomed cylindrical case 11 by press fitting. Vibration of the outer
peripheral side of the case 11 (so-called reverberation) can be suppressed, and the outer
peripheral side 14 of the bottomed cylindrical case 11 is heated while heating the forming ring
10 at a temperature exceeding the glass transition point of the forming ring 10 Since the press-in
is performed, the forming ring 10 can be press-fitted so as to be in close contact with the outer
peripheral side surface 14 of the bottomed cylindrical case 11, and the reverberation wave can
be reliably suppressed, and the transmission and reception characteristics can be improved.
Modified Example Next, a modified example of the ultrasonic sensor 1 of the present invention
will be described with reference to FIGS. 2 and 3. 2 and 3 are external views showing a
modification of the ultrasonic sensor 1, and the basic configuration is the same as that of the
embodiment described above. It describes below. In FIG. 2, the ultrasonic sensor 1 is a ring 12 (a
so-called ring-like member or a tubular member) having a height of L / 3 and a bottom surface of
the outer circumferential side 14 of the bottomed cylindrical case 11 21 is fitted by press-fitting
so as to cover a range (a range of L / 2 in the figure) of a half of a distance (a distance L in the
figure) from 21 to the opening 13. In FIG. 3, the ultrasonic sensor 1 has a ring 12 having a height
of L / 2 and a distance from the bottom surface 21 to the opening 13 in the outer peripheral side
surface 14 of the bottomed cylindrical case 11 (in FIG. It is fitted by press fitting so as to cover
the range of 1/2 of L) (in the range of L / 2 in the figure). According to this modification, when
the vibration of the piezoelectric vibrator 2 is propagated to the outer peripheral side surface 14
of the bottomed cylindrical case 11, within a range of 1⁄2 of the distance from the bottom
surface 21 to the opening 13. The effect of suppressing the influence of the amplitude of the
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vibration propagating to the outer peripheral side surface of the bottomed cylindrical case 11,
which is presumed to be generated, can be significantly obtained, and the generation of the
reverberation wave can be suppressed. Further, since the range for press-fitting the ring 12 may
be within the range of 1/2 of the distance L from the bottom surface 21 to the opening 13 in the
outer peripheral side surface 14 of the bottomed cylindrical case 11, the manufacturing cost of
the ring 12 can be reduced. . According to the embodiment or the modification of the present
invention, the ring 10 and the ring 12 are substantially all over the outer peripheral side surface
14 of the bottomed cylindrical case 11 or 1 of the distance L from the bottom surface 21 to the
two openings. The ring 11 and the ring 12 are press-fit into the outer peripheral side surface 14
of the bottomed cylindrical case 11 so as to cover the range of 1/2, but the piezoelectric vibrator
2 is vibrated without the ring 10 being press-fitted. Even if the amplitude and the amount of
vibration generated along the circumferential direction on the outer peripheral side 14 of the
case 11 are analyzed, the press-in range and the press-in position of the ring are determined so
that the largest position of the amplitude and the vibration is suppressed by the ring good.
Further, the present invention can be used for various sensors such as a gas sensor, an object
detection sensor, a distance sensor, a position sensor, an actuator, and a crime prevention sensor
using ultrasonic waves as transmission and reception signals. BRIEF DESCRIPTION OF THE
DRAWINGS FIG. 1 is a cross-sectional view showing a configuration of an ultrasonic sensor
according to a first embodiment to which the present invention is applied.
FIG. 2 is a cross-sectional view showing a configuration of an ultrasonic sensor according to a
modification of the embodiment. FIG. 3 is a cross-sectional view showing the configuration of an
ultrasonic sensor according to another modification of the embodiment. FIG. 4 is an impedance
characteristic diagram of the embodiment. FIG. 5 is an impedance characteristic diagram of a
comparative example. FIG. 6 is a characteristic diagram showing the reception waveform of the
embodiment. FIG. 7 is a characteristic diagram showing a received waveform of a comparative
example. [Explanation of the code] 1 ... ultrasonic sensor, 2 ... piezoelectric vibrator, 3 ... base
member, 4, 5 ... input / output terminal, 6 ... insulating material, 7 ... insulating sheet, 8 ...
matching layer, 9 ... conductive wire, DESCRIPTION OF SYMBOLS 10 12 Ring (formed ring) 11
Bottomed cylindrical case 13 Opening 14 Outer peripheral side 15 Convex 16 Electrode 17 18
Seat 19 Through hole 20 Engaging hole 21 ... bottom surface.
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