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JPH05328498

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DESCRIPTION JPH05328498
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
improvement of an ultrasonic transducer applied to transmit and receive ultrasonic waves as a
distance meter and a detector of various obstacles including a human body.
[0002]
2. Description of the Related Art Conventionally, as an ultrasonic transducer of this type, for
example, one having a structure as shown in FIG. 4 exists. The figure shows that the piezoelectric
element 5e is attached to the back side of the metal diaphragm 6e. The high frequency voltage is
applied to the piezoelectric element 5e through the lead wires 9e and 9e. By applying the
voltage, the vibration plate 6e is vibrated to generate an ultrasonic wave, and the vibration of the
vibration plate 6e generated by receiving an ultrasonic wave reflected from the distance
measurement object is converted into an electric signal by the piezoelectric element 5e. Can be
output. In the figure, 7e is a resonator. In the ultrasonic transducer having such a structure, in
order to appropriately receive and detect the ultrasonic wave reflected from the object after
generation of the ultrasonic wave by the diaphragm 6e, the vibration is performed by the start
time of the received wave. It is necessary to damp the vibration of the plate 6e and eliminate the
reverberation after the generation of the ultrasonic wave.
[0003]
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However, in the prior art, since only a flat plate-like metal member is used as the diaphragm 6e,
the rise and fall of the vibration of the diaphragm 6e are delayed. Even when the voltage
application to the piezoelectric element 5e is stopped, the vibration is not immediately stopped,
and the reverberation time is relatively long. As a result, conventionally, in the case of short
distance ranging in which the time from transmission to reception of ultrasonic waves is short,
ultrasonic waves are received during reverberation after generation of ultrasonic waves. A
situation has arisen, and in this case the reflected wave can not be detected accurately, resulting
in the problem that distance measurement, obstacle detection, etc. can not be performed with
high accuracy. In addition, in the case of distance measurement of a short distance, etc., it is also
necessary to shorten the transmission time required to generate and output an ultrasonic wave,
but in the conventional case where the rise of the vibration of the diaphragm 6e is slow,
transmission is also performed. The time is also prolonged, and there is room for improvement in
performing distance measurement and the like on short distances also in this respect.
[0004]
The present invention has been proposed in view of the above points, and is intended to quickly
perform the rising and falling of the vibration of the diaphragm to shorten the reverberation time
after ultrasonic output and shorten the transmission time. An object of the present invention is to
provide an ultrasonic transducer that can be suitably used for short distance ranging applications
and the like.
[0005]
The ultrasonic transducer according to the present invention proposed to achieve the above
object has a vibration for generating an ultrasonic wave and a vibration for receiving a vibration
of the ultrasonic wave. A ring body made of an elastic member is provided on the outer periphery
of the plate.
[0006]
In the ultrasonic transducer according to the present invention characterized by the above
configuration, the outer peripheral position of the diaphragm where the amplitude becomes the
largest when the diaphragm vibrates is made of an elastic member which exerts a damping effect
of the vibration The provision of the ring body reduces the amplitude at the time of vibration of
the diaphragm.
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Therefore, the damping of the vibration after vibrating the diaphragm and generating the
ultrasonic wave is quickly performed as the amplitude of the diaphragm is reduced, and the
reverberation time is shortened.
Similarly, as the amplitude of the diaphragm decreases, the rise time of the vibration of the
diaphragm is also shortened. In the present invention, not only the above-described effects can
be obtained, but also an unexpected effect that the bandwidth of the ultrasonic wave generated
by the vibration of the diaphragm is expanded can be obtained, which will be described below. It
will be clear from the data of the example.
[0007]
An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example when the present invention is configured as
an open type ultrasonic transducer. In the open type ultrasonic transducer shown in the same
figure, a support 4 is provided on the bottom of a housing case 3 having an opening 2 to which a
protective wire mesh 1 is attached at the top. The element 5, the diaphragm 6, the resonator 7
and the like are provided in series. Among them, the piezoelectric element 5 is adhered and
mounted on the support 4 via the elastic adhesive 8, and the lead wires 9 and 9 of the
piezoelectric element 5 are penetrated to the bottom of the housing case 3. Connected to
terminals 10,10. With this structure, high frequency (tone burst wave) voltage application to the
piezoelectric element 5 can be performed from the terminals 10 and 10, and an electrical signal
from the piezoelectric element 5 based on the vibration of the diaphragm 6 is output from the
terminals 10 and 10 to the outside be able to.
[0008]
The diaphragm 6 is made of a flat metal member, and is bonded in a state in which the
piezoelectric element 5 is bonded to the back surface side thereof. The ring body 11 formed of
an elastic member such as silicone rubber is attached by fitting or bonding. The resonator 7 is
fixed to a substantially central portion on the upper surface side of the diaphragm 6 via an
adhesive 12 so as to resonate with the diaphragm 6.
[0009]
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Next, the operation of the open type ultrasonic transducer of the above configuration will be
described. First, when a high frequency power as a drive signal is supplied between both
terminals 10 and 10 and a voltage is applied to the piezoelectric element 5, the piezoelectric
element 5 vibrates the diaphragm 6 and the resonator 7, and the diaphragm The vibration of 6
generates an ultrasonic wave, which is transmitted from the opening 2 to the front (upper side in
the drawing). In such a case, since the ring body 11 provided on the diaphragm 6 is made of an
elastic member that exerts a buffer function, it does not have a resonance system with respect to
the diaphragm 6 like the resonator 7. Exerts the effect of reducing the amplitude of In particular,
the ring body 11 is provided at the outer peripheral position of the diaphragm 6, which is the
largest amplitude of the diaphragm 6, so that the damping effect is more efficiently exhibited.
Therefore, the rising of the vibration of the diaphragm 6 generated by the voltage application to
the piezoelectric element 5 is performed quickly, and the transmission time of the ultrasonic
wave can be shortened. In addition, after the voltage application to the piezoelectric element 5 is
stopped, the vibration of the diaphragm 6 is attenuated in a short time and stopped, and the
reverberation time can be shortened.
[0010]
After the voltage application to the piezoelectric element 5 is stopped, the ultrasonic wave
transmitted earlier is reflected by the object to be measured, and the reflected ultrasonic wave is
received by the diaphragm 6, and the diaphragm 6 vibrates. The vibration can be taken out from
the terminals 10 as a predetermined signal (voltage signal) from the piezoelectric element 5. In
this case, if the distance to the object to be measured is a short distance, the time from ultrasonic
transmission to reception of the reflected wave also becomes short, but the vibration plate 6 is
attenuated by the ring body 11. Since the vibration is stopped in a short time, the reception of
the reflected wave can be started in the state without reverberation at the time of the ultrasonic
wave output. Therefore, distance measurement can be accurately performed even with a short
distance object.
[0011]
FIG. 2 is a diagram showing an example of experimental data showing comparison of
reverberation time, and FIG. 2 (a) is a conventional example using the diaphragm 6 without the
ring body 11, and FIG. 2 (b) is a ring body 11 is an ultrasonic transducer according to the present
invention using a diaphragm 6 provided with the reference numeral 11. Although (a) and (b) of
the same figure show the time-dependent change state of the voltage level when the voltage
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application which only ultrasonic vibration fully rises is performed for the same time, the
conventional example of (a) In the present invention of (b), the reverberation time is considerably
shortened compared to the above. As a result of experiments conducted by the inventor under
various conditions, it was confirmed that the reverberation time can be reduced by about 10% in
the present invention as compared to the prior art.
[0012]
FIG. 3 is a diagram of experimental data showing the relationship between the frequency and the
output sound pressure level, and in the case of the present invention, the bandwidth is expanded
as compared with the conventional one without the ring body 11 of the elastic member.
Characteristics were obtained. The widening of the bandwidth is considered to be due to the
effect of providing the ring body 11 of the elastic member. Therefore, according to the present
invention, even when the frequency of the output ultrasonic wave is slightly deviated from the
frequency range (for example, 40 KHz) at which the output sound pressure is at the maximum
level, the output sound is compared with the prior art. The drop in pressure is much less.
[0013]
In the above embodiment, although the piezoelectric ultrasonic transducer using the piezoelectric
element 5 has been described as an example, the present invention is not limited to this. In the
first aspect of the present invention, the present invention can be applied to an ultrasonic
transducer of a type using, for example, a flexible material instead of the piezoelectric element 5.
[0014]
As understood from the above description, according to the ultrasonic transducer according to
the present invention, the amplitude of the diaphragm is reduced by providing the ring body
made of an elastic member on the outer periphery of the diaphragm. Therefore, the rise and fall
of the vibration of the diaphragm can be performed quickly, and the transmission time of
ultrasonic waves can be shortened and the reverberation time can be shortened. As a result, even
in the case of distance measurement of a short distance, etc., ultrasonic waves reflected in a short
time after generation output of ultrasonic waves can be properly received and detected without
reverberation. It is possible to obtain a remarkable effect that distance measurement and the like
of a short distance can be performed more accurately than before. In addition, since the rise of
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the vibration of the diaphragm is rapidly performed, the time required for the generation of the
ultrasonic wave can be shortened, and an advantage which is more suitable for distance
measurement of a short distance can be obtained. Furthermore, according to the present
invention, not only the rise and fall times of the vibration of the diaphragm described above can
be shortened, but also the output sound pressure bandwidth can be expanded compared to the
prior art, and this is caused by the deviation of the frequency of the outputted ultrasound. Can be
reduced, and the effect of stabilizing the detection capability of ultrasonic waves can also be
obtained.
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