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JP2009021852

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DESCRIPTION JP2009021852
An ultrasonic wave transmitter having a wide band and capable of transmitting high energy
ultrasonic waves into the air is provided. An ultrasonic wave transmitter according to the present
invention defines an acoustic tube 2 having a space in which ultrasonic waves propagate along
the propagation direction and an aperture from which the ultrasonic waves propagated in the
space are emitted, and a space of the acoustic tube 2 And a drive unit 6 for driving the plurality
of transmission elements 4, the drive unit 6 includes the speed of sound of the ultrasonic waves
propagating through the space, and a plurality of transmission units 4 for generating the
ultrasonic waves. Of the plurality of transmitting elements at different timings so that ultrasonic
waves generated respectively from the plurality of transmitting elements propagate to the same
position in the space of the acoustic pipe at the same time based on the positions of the
transmitting elements of To drive. [Selected figure] Figure 1
Ultrasonic wave transmitter
[0001]
The present invention relates to an ultrasonic wave transmitter for transmitting ultrasonic waves,
and more particularly to an ultrasonic wave transmitter having a wide band and capable of
transmitting high-energy ultrasonic waves into the air.
[0002]
Ultrasonic wave transmitters that transmit ultrasonic waves into the air are used for automotive
back sonar, obstacle detection for robots, and the like.
05-05-2019
1
In such applications, it is preferred that the ultrasound transmitter be capable of transmitting
high energy ultrasound so that the measurement range can be expanded and far obstacles can be
detected. In addition, the ultrasonic wave transmitter is preferably small so that it can be
mounted on a robot or the like. Furthermore, in order to increase the measurement accuracy of
the propagation time of the ultrasonic wave, it is preferable that the frequency band of the
ultrasonic wave transmitted by the ultrasonic wave transmitter is wide so that the ultrasonic
wave of higher frequency can be transmitted.
[0003]
As a method of increasing the energy of the ultrasonic wave transmitted from the ultrasonic
wave transmitter, a large electric power is input to the ultrasonic wave generator for generating
the ultrasonic wave, the area of the ultrasonic wave generator is enlarged, and the ultrasonic
wave is focused Etc.
[0004]
However, there is a limit to the power that can be input to the ultrasonic transducer, and even if
more power is input, the oscillating amplitude of the ultrasonic transducer is saturated, and the
energy of the transmitted ultrasonic wave is also higher It does not.
The ultrasonic transducer may be destroyed. Amplifiers for supplying high power will also be
large. When the area of the ultrasonic transducer is increased, a large amount of power must
necessarily be supplied to drive the ultrasonic transducer, and as a result, the above-described
problem occurs.
[0005]
According to the method of focusing the ultrasonic waves, the energy of the ultrasonic waves at
the focal position can be increased. However, energy can be increased only at the focal position,
and there is a problem such as that the transmission of ultrasonic waves is interrupted if there is
an obstacle in front of the focal position.
05-05-2019
2
[0006]
As a method of solving these problems and increasing the energy of ultrasonic waves to be
transmitted, there is a method of increasing energy by combining ultrasonic waves transmitted
from the respective ultrasonic transducers using a plurality of ultrasonic transducers. Are known.
It is generally called an endfire array. For example, although patent document 1 is not an
ultrasonic wave transmitter which transmits an ultrasonic wave to the air, it is disclosing the
technique which raises the energy of an ultrasonic wave by the same view. The high frequency
ultrasonic transducer disclosed in Patent Document 1 will be described below.
[0007]
As shown in FIG. 18, Patent Document 1 discloses a high frequency ultrasonic transducer 40
used for atomization of liquid, atomization, bonding of metal and plastic, and the like. The highfrequency ultrasonic transducer 40 includes a tool 41, a conical horn 42, a front body 43, an
ultrasonic transducer 44, an electrode 45, and a back body 46. The front body 43, the ultrasonic
transducer 44, and the electrode 45, the back body 46 constitutes a vibrating element.
[0008]
When a voltage is applied to the electrode 45 by a drive circuit (not shown), the ultrasonic
transducer 44 expands and contracts by the voltage applied to the electrode 45.
[0009]
Piezoelectric ceramic is generally used for the ultrasonic transducer 44.
Piezoelectric ceramic has high electromechanical conversion efficiency and is excellent in
mechanical resonance characteristics, so that large vibration energy can be generated. By
increasing the power of the electrical signal applied to the ultrasonic transducer, larger
vibrational energy can be generated.
[0010]
The cone-like horn 42 includes many harmonic vibration modes, among which the target
05-05-2019
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vibration modes are the extension flexural vibration modes (the radial vibration component
perpendicular to the axis is not parallel to the radial direction, Growth).
[0011]
The vibrating element is placed at a longitudinal half-wave resonant length in the axial direction
at the extension flexural resonance frequency of the conical horn 42.
Thus, by driving the ultrasonic transducer 44, it vibrates in the vibration mode 47 shown in FIG.
[0012]
Thus, by arranging the vibration element at a position that is driven in phase with the extension
deflection vibration of the conical shell horn 42, the conical shell horn 42 can be efficiently
vibrated, and the tool 41 is efficiently vibrated. It can be propagated. Japanese Patent Application
Laid-Open No. 06-269077
[0013]
The arrangement of the ultrasonic transducer 44 in the high frequency ultrasonic transducer 40
of Patent Document 1 is determined by the wavelength of the elongation-deflection resonance
frequency as described above. In the case where it is intended to operate the high frequency
ultrasonic transducer 40 only at the resonance frequency determined by the structure of the
conical shell horn 42 as in Patent Document 1, the frequency of the ultrasonic wave is fixed: It is
not a problem in particular.
[0014]
However, it is not possible to transmit ultrasonic waves of various frequencies in a medium such
as air or water using the high frequency ultrasonic transducer of such a structure.
[0015]
An object of the present invention is to solve the problems of the prior art and to provide an
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ultrasonic wave transmitter having a wide band and capable of transmitting high energy
ultrasonic waves into the air.
[0016]
The ultrasonic wave transmitter according to the present invention comprises an acoustic tube
having a space in which ultrasonic waves propagate along the propagation direction and an
aperture from which the ultrasonic waves propagated in the space are emitted, and an inner
surface defining the space of the acoustic tube. The transmission unit includes: a plurality of
transmitting elements configured to generate ultrasonic waves; and a driving unit configured to
drive the plurality of transmitting elements, wherein the driving unit is configured to calculate an
acoustic velocity of the ultrasonic waves propagating through the space and the plurality of
transmitting elements. Based on the position of the plurality of transmitting elements at different
timings such that ultrasonic waves generated from the plurality of transmitting elements
respectively propagate in the same position in the space of the acoustic pipe at the same time. To
drive.
[0017]
In one preferred embodiment, the plurality of transmitting elements are arranged on the inner
surface of the acoustic tube so as to form a plurality of rows parallel to the propagation direction.
[0018]
In one preferred embodiment, the plurality of transmitting elements are arranged on the inner
surface of the acoustic tube so as to form first and second rows parallel to the propagation
direction, and the transmissions forming the first row are formed. The transmitting elements of
the first column and the transmitting elements of the second column in the propagation direction
such that the position of the center of each of the elements coincides with the respective
intermediate position of the adjacent transmitting elements in the second column Are arranged.
[0019]
The ultrasonic wave transmitter according to the present invention comprises an acoustic tube
having a space in which ultrasonic waves propagate along the propagation direction and an
aperture from which the ultrasonic waves propagated in the space are emitted, and an inner
surface defining the space of the acoustic tube. And at least two transmitting elements for
generating the arranged ultrasonic waves, a drive unit for driving the at least two transmitting
elements, and a receiving element for receiving the at least one ultrasonic wave arranged on the
inner side, The driving unit is transmitted from one of the transmission elements so that
05-05-2019
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ultrasonic waves generated from the at least two transmission elements respectively propagate in
the same position in the space of the acoustic pipe at the same time. The other one of the
transmission elements is driven based on the timing when the ultrasonic wave propagating
through the space is received by the reception element.
[0020]
In a preferred embodiment, the at least two transmitting elements are arranged parallel to the
propagation direction, and the receiving elements are located at equal distances from the at least
two transmitting elements.
[0021]
In one preferred embodiment, the drive unit includes a timer, and the time from when one of the
transmission elements is driven to when the reception element receives an ultrasonic wave
transmitted from one of the transmission elements is a timer. The measurement is performed,
and after the elapsed time has further elapsed, the other one of the transmission elements is
driven.
[0022]
In one preferred embodiment, the ultrasonic wave transmitter further includes a horn having an
opening larger than the opening of the acoustic tube and connected to the opening of the
acoustic tube.
[0023]
The ultrasonic wave transmitter according to the present invention includes an acoustic tube
having a space in which ultrasonic waves propagate along a propagation direction and an
aperture from which the ultrasonic waves propagated in the space are emitted, and an inner
surface defining the space of the acoustic tube. And a drive unit configured to drive the plurality
of transmission elements, wherein the drive unit drives the plurality of transmission elements at
different frequencies, and the plurality of transmission elements are configured to generate the
plurality of ultrasonic waves. The timing at which the plurality of transmission elements are
driven is controlled based on the velocity of sound of the ultrasonic waves propagating in the
space and the positions of the plurality of transmission elements such that the origin and end
points of the generated ultrasonic waves coincide with each other.
[0024]
In one preferred embodiment, the drive unit controls timing for driving the transmission element
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in accordance with the velocity of sound of an ultrasonic wave propagating through a medium
filling the space.
[0025]
In one preferred embodiment, the transmission element includes a piezoelectric body.
[0026]
In one preferred embodiment, the transmission element includes an electrostrictive body.
[0027]
In one preferred embodiment, the transmission element includes a heating wire.
[0028]
In one preferred embodiment, the drive unit drives the transmission element at a frequency other
than the resonance frequency of the transmission element.
[0029]
In a preferred embodiment, the ultrasonic wave propagating in the space of the acoustic tube is a
transverse wave and propagates approximately parallel to the transmission surface of the
transmission element.
[0030]
In one preferred embodiment, the drive unit drives the plurality of transmission elements at the
same frequency.
[0031]
The ultrasonic wave transmitter according to the present invention includes an acoustic tube
having a space in which ultrasonic waves propagate along a propagation direction and an
aperture from which the ultrasonic waves propagated in the space are emitted, and an inner
surface defining the space of the acoustic tube. The transmitting device includes a transmitting
element configured to generate a plurality of arranged ultrasonic waves, and a driving unit
configured to drive the plurality of transmitting elements, and the driving unit is configured to
transmit the ultrasonic waves generated from the plurality of transmitting elements in the same
phase. The plurality of transmitting elements are driven at different timings based on the speed
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of sound of the ultrasonic wave propagating in the space and the positions of the plurality of
transmitting elements so as to emit from the opening of the acoustic tube.
[0032]
According to the present invention, the timings for driving the transmission elements are made
different so that the ultrasonic waves emitted from the plurality of transmission elements
propagate with the same phase at the same position at the same time.
This timing depends on the speed of sound of the ultrasonic wave propagating in space and the
position of the transmitting element, and does not depend on the frequency of the ultrasonic
wave.
Therefore, it is possible to realize an ultrasonic wave transmitter in which the frequency of the
ultrasonic wave to be transmitted is variable and an ultrasonic wave having high energy in a wide
band can be transmitted.
[0033]
Hereinafter, embodiments of an ultrasonic wave transmitter according to the present invention
will be described with reference to the drawings.
First Embodiment
[0034]
FIG. 1 (a) is a perspective view schematically showing a first embodiment of an ultrasonic wave
transmitter according to the present invention.
The ultrasonic wave transmitter 101 includes an acoustic tube 2, a horn 3, a transmission unit 4,
and a drive unit 6.
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The transmission unit 4 is driven by the drive unit 6 to generate an ultrasonic wave.
The generated ultrasonic waves propagate inside the acoustic tube 2 and exit from the opening 3
a of the horn 3.
The end 2b on the side where the horn 3 of the acoustic tube 2 is not provided is open.
The ultrasonic wave transmitter 101 is used in the medium 5.
In the present embodiment, the medium 5 is air.
The ultrasonic wave transmitter 101 can transmit ultrasonic waves in a frequency band of, for
example, 20 kHz to 80 kHz.
[0035]
As shown in FIG. 1 (b), the acoustic tube 2 has an opening 2a and a space 2c.
The space 2c extends along the propagation direction T in which the ultrasonic waves propagate,
and the opening 2a is located at one end of the space 2c.
The opening 2 a is connected to the opening 3 b of the horn 3.
[0036]
The cross section perpendicular to the propagation direction T of the space 2c, that is, the YZ
cross section, is preferably sufficiently smaller than the wavelength of the frequency band of
ultrasonic waves that can be transmitted by the ultrasonic wave transmitter 101.
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Thereby, it is known that the ultrasonic wave transmitted from the transmission part 4 arranged
at the bottom of the acoustic tube 2 propagates in the acoustic tube 2 as a plane wave.
The plane wave is a longitudinal wave in which the medium is displaced in a direction parallel to
the propagation direction T.
However, if the cross section is made too small, the influence of the viscosity of the medium 5
can not be ignored.
In the present embodiment, the cross section of the acoustic tube 2 is 1.7 mm in both the Y-axis
direction and the Z-axis direction.
Assuming that the maximum frequency of ultrasonic waves to be transmitted is 80 kHz, the
wavelength of air in the medium 5 is 4.25 mm, so the cross section of the acoustic tube 2 is
sufficiently smaller than the wavelength.
In addition, the influence of the viscosity of the medium 5 is also small.
[0037]
The length of the acoustic tube 2 in the X-axis direction is preferably as long as possible to
arrange as many transmission elements as the transmission unit 4. The sound pressure of the
ultrasonic wave transmitted from the ultrasonic wave transmitter 101 can be increased as the
number of transmission elements is increased. The number of required transmission elements is
determined from the sound pressure of the ultrasonic wave that can be generated by the
transmission element alone and the sound pressure of the ultrasonic wave required for the
ultrasonic wave transmitter 101. The sound pressure actually required also depends on the
sensitivity of the ultrasonic wave receiver that receives the transmitted ultrasonic waves. In the
present embodiment, the length of the acoustic tube 2 is, for example, 100 mm. In the present
embodiment, the propagation direction T of the acoustic tube 2 is a straight line, but the
propagation direction T may be curved. That is, the acoustic tube 2 may be a curved tube. In this
case, a sufficiently large curvature is set with respect to the wavelength of the maximum
05-05-2019
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frequency of the transmitted ultrasonic wave so as to prevent the occurrence of acoustic
disturbance in the space defined by the acoustic tube 2.
[0038]
The acoustic tube 2 is preferably made of a material whose acoustic impedance differs
significantly from that of the medium 5. When the ultrasonic waves pass through the wall of the
acoustic tube, the energy density of the ultrasonic waves decreases, and the sound pressure in
the acoustic tube 2 decreases. If the medium 5 is air, various solid materials can be used to form
the acoustic tube 2. In the present embodiment, the acoustic tube 2 is formed of aluminum. In
addition, the smaller the surface roughness of the inner surface that defines the space of the
acoustic tube 2, the smaller the loss of propagating ultrasonic waves. Specifically, when the
maximum frequency of ultrasonic waves to be transmitted is 80 kHz, the wavelength of air in the
medium 5 is 4.25 mm, so the surface roughness of the inner side is 0.425 mm or less Is
preferred.
[0039]
FIG. 2 is an exploded perspective view of the acoustic tube 2 of the ultrasonic wave transmitter
101. As shown in FIG. As shown in FIG. 2, the transmission unit 4 includes a plurality of
transmission elements 4 (1), 4 (2), 4 (3),... Arranged on the inner side surface of the acoustic tube
2. The arrangement direction of the plurality of transmitting elements 4 (1), 4 (2), 4 (3)... Is
parallel to the propagation direction T of the ultrasonic wave propagating through the acoustic
tube 2. Hereinafter, when the transmitting elements 4 (1), 4 (2), 4 (3),... Are collectively referred
to, they will be referred to without the reference numerals. As described in detail below, the
ultrasonic wave transmitter 101 drives the transmission elements so that the ultrasonic waves of
the same frequency transmitted from each of the plurality of transmission elements are emitted
from the opening 2a of the acoustic tube 2 in the same phase. By controlling the timing, the
sound pressure of the synthesized ultrasound is increased.
[0040]
The transmitting element is not particularly limited as long as it can generate an ultrasonic wave
of a desired frequency, and an element made of a known material capable of generating an
ultrasonic wave by vibrating in the ultrasonic wave region may be used. it can. From the
05-05-2019
11
viewpoint of high transmission efficiency, the transmission element preferably includes a
piezoelectric material having high piezoelectric performance. For example, a transmission
element including a piezoelectric body made of a highly piezoelectric material such as a
piezoelectric ceramic, a piezoelectric single crystal, or a piezoelectric polymer can be used. More
specifically, piezoelectric ceramics such as lead zirconate titanate, barium titanate or lead
titanate, single crystals of lead zirconate titanate, lithium niobate, piezoelectric single crystals
such as quartz, or the like can be used.
[0041]
Instead of the piezoelectric body, a known electrostrictive body, a heating wire or the like may be
used. In the case of using an electrostrictive body, as in the case of the piezoelectric body, the
transmission efficiency can be enhanced by using a material having a large electrostrictive effect.
[0042]
The frequency of the ultrasonic wave transmitted from the transmitting element is preferably
different from the resonant frequency determined by the structure or material of the transmitting
element. When the frequency of the transmitted ultrasonic wave matches the resonant
frequency, the reverberation in the acoustic tube 2 becomes large, and the waveform of the
transmitted ultrasonic wave changes. PVDF (polyvinylidene fluoride) is known as a piezoelectric
material having no structural resonance frequency. PVDF has a frequency band of about 0.001
Hz to 1 GHz, is light and soft, and does not have a specific natural frequency. Further, since PVDF
has a sheet shape with a thickness of about several tens of μm, even if it is disposed on the
bottom of the acoustic tube 2, the shape in the acoustic tube 2 is not affected.
[0043]
In this embodiment, a transmitting element having a thin film of lead zirconate titanate (PZT)
having a thickness of 50 μm formed by a hydrothermal synthesis method was used. The
resonant frequency of the transmitting element is about 150 kHz. Since the frequency band
realized by the ultrasonic wave transmitter 101 is set to 20 kHz to 80 kHz, the resonant
frequency of the transmission element is higher than the frequency band of the ultrasonic wave
emitted from the ultrasonic wave transmitter 101. Therefore, the resonance does not change the
05-05-2019
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waveform of the transmitted ultrasonic wave, and the ultrasonic wave having the desired
transmission waveform can be transmitted almost faithfully.
[0044]
FIG. 3 is an XZ sectional view of the transmission unit 4. As shown in FIG. 3, the transmitter 4 is
provided on the inner side surface 2 d of the acoustic tube 2. A cavity 71 is provided in the inner
side surface 2 d so as not to disturb the vibration of the transmission elements 4 (1), 4 (2), 4 (3).
Arrange to cover 71. The transmitting elements 4 (1), 4 (2), 4 (3),... Are provided on the thin film
7 so as to be disposed at positions corresponding to the cavities 71. The thin film 7 of titanium
vibrates by several nm to several tens nm by driving the transmission element. Therefore, it is
preferable that the cavity 71 be deeper than the amplitude of the vibration of the thin film 7 of
titanium.
[0045]
The cavity 71 acts as a resonator depending on the frequency of the ultrasonic wave generated
by the transmitting element. In this embodiment, since the purpose is to realize a wide band
transmitter, it is necessary to avoid resonance. If the frequency component of the waveform to be
transmitted includes a component of the resonant frequency of the cavity 71, only that
component is amplified, and the waveform is distorted. When the depth of the cavity 71 is a
quarter of the vibration wavelength of the ultrasonic wave generated by the transmitting
element, the cavity 71 resonates. The frequency band to be realized in the present embodiment is
20 kHz to 80 kHz, and therefore, it is dimensioned to resonate at a higher frequency
(approximately 800 kHz). Specifically, in the present embodiment, the depth of the cavity 71 is
set to 0.1 mm. Also, a hole 72 is provided to open the air in the cavity 71 to the outside.
[0046]
A larger width of the transmitting element in the X-axis direction can generate an ultrasonic
wave with a larger sound pressure. However, if it is too large, an unnecessary vibration mode is
generated on the thin film 7 and an unnecessary ultrasonic wave is transmitted. The width in the
X-axis direction of the transmission element of this embodiment was set to 2 mm. The width in
the Y-axis direction was also set to 2 mm. By making the shape of the transmitting element
square, there is an advantage that prediction of the vibration mode can be performed by simple
05-05-2019
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calculation. However, the transmitting element may have other shapes as long as the
unnecessary vibration mode does not occur in the required frequency band.
[0047]
The distance between adjacent transmission elements in the X-axis direction, for example, the
distance between the transmission element 4 (1) and the transmission element 4 (2) and the
distance between the transmission element 4 (2) and the transmission element 4 (3) 6 is a
parameter related to the timing of driving the transmission element. For this reason, the
arrangement of the transmitting elements in the X direction, that is, the propagation direction T
needs to be accurately made. In the present embodiment, the distance between the transmission
elements in the X-axis direction is set to 3 mm.
[0048]
As described with reference to FIG. 1B, the cross section perpendicular to the propagation
direction T of the acoustic tube 2 is sufficiently smaller than the wavelength of the ultrasonic
wave to be transmitted. The openings 2a from which the ultrasonic waves of the acoustic tube 2
are emitted have the same size. Therefore, when an ultrasonic wave is transmitted to the outside
from the opening 2a, the ultrasonic wave is transmitted in a spherical shape using the opening
2a as a point source. Also, at this time, the cross-sectional area through which the ultrasonic
wave propagates rapidly expands, so that impedance mismatch occurs at the boundary between
the opening 2a of the acoustic tube 2 and the outside, and the transmitted ultrasonic wave is
reflected. The outgoing efficiency to the outside decreases.
[0049]
In order to suppress such a subject, as shown to FIG. 1 (a) and (b), the ultrasonic wave
transmitter 101 is equipped with the horn 3 provided in the opening 2a of the acoustic tube 2.
As shown in FIG. The horn 3 forms a space in which the vertical cross-sectional area is expanded
along the propagation direction T, and the opening 3 a is larger than the opening 2 a of the
acoustic tube 2. As a result, impedance mismatch can be alleviated, and the directivity of the
transmitted ultrasonic waves can be improved.
05-05-2019
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[0050]
The horn 3 can be formed, for example, by an aluminum plate having a thickness of 0.5 mm. The
cross-sectional area perpendicular to the propagation direction T of the horn 3 preferably
increases exponentially with the position of the propagation direction T. Specifically, as shown in
FIG. 1B, the X axis is set along the propagation direction T, the cross sectional area of the
opening 2a of the acoustic tube 2 is S2, and the cross sectional area at the position X of the horn
3 is S3. It is preferable that S3 satisfy the following formula.
[0051]
Here, m = (4 × π × fc) / C, fc is a cutoff frequency, and C is the speed of sound of ultrasonic
waves in the medium 5.
[0052]
As apparent from the equation 1, the cross-sectional area S3 of the horn 3 depends on the cut-off
frequency.
In the present embodiment, the lengths in the Y-axis direction and the Z-axis direction of the
opening 3a of the horn 3 are both 8.5 mm, and the lengths in the Y-axis direction and the Z-axis
direction of the outer shape at the opening of the horn 3 are both 9. It is 5 mm. Moreover, the
length of the X-axis direction of the horn 3 was set to 20 mm. At this time, the cutoff frequency is
about 2.2 kHz, which is sufficiently lower than the design frequency band of the ultrasonic wave
transmitter 101. Therefore, ultrasonic waves can be emitted from the opening 3a without loss in
the horn 3.
[0053]
Next, the operation of the ultrasonic wave transmitter 101 will be described with reference to
FIGS. 4 and 5. As described above, the transmission unit 4 of the ultrasonic wave transmitter 101
includes a plurality of transmission elements, and the ultrasonic waves of the same frequency
generated from the respective transmission elements are controlled by controlling the timings of
driving the plurality of transmission elements. Match the phases of and increase the energy of
the transmitted ultrasound. FIGS. 4A and 4B show sound pressure distributions of ultrasonic
05-05-2019
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waves propagating in the acoustic tube 2 when the acoustic tube 2 is provided with one
transmitting element 4 (1). In these distributions, the horizontal axis indicates the position in the
X-axis direction, and the vertical axis indicates the sound pressure. The inside of the acoustic
tube 2 is filled with the medium 5.
[0054]
When the transmitting element 4 (1) vibrates in the ultrasonic region for one cycle, the plane
wave of the ultrasonic wave generated by the vibration is characteristic of the medium 5 in the
propagation direction T from the center of the transmitting element 4 (1) and the opposite
direction T ′. It propagates at the speed of sound determined by. As shown in FIG. 4 (a), at time
T1 immediately after generating the ultrasonic wave, ultrasonic waves 9 and 9 'propagate from
the center of the transmission element 4 (1) in the propagation direction T and in the opposite
direction T'. Begin to. At time T2 when the predetermined time has elapsed, the ultrasonic waves
9, 9 'reach a position separated from the center of the transmitting element 4 (1) by a distance
determined by the propagation velocity of the ultrasonic wave in the medium 5. The ultrasound
propagating through the acoustic tube 2 hardly attenuates, so the amplitude of the propagating
ultrasound hardly changes. For this reason, the distribution of the sound pressure observed at
the point 10 is, as shown in FIG. 4B, the passage of time for the propagation of the ultrasonic
wave from the generation time of the ultrasonic wave 9 at the transmitting element 4 After that,
an ultrasonic wave having the same waveform as the ultrasonic wave generated in the
transmission element 4 (1) is observed.
[0055]
FIGS. 5 (a) and 5 (b) show sound pressure distributions of ultrasonic waves propagating in the
acoustic tube 2 when the acoustic tube 2 is provided with two transmitting elements 4 (1) and 4
(2). ing.
[0056]
When the ultrasonic wave 9 generated in the transmitting element 4 (1) and propagating in the
propagation direction T reaches the position of the transmitting element 4 (2), the transmitting
element 4 (2) has the same frequency as the transmitting element 4 (1) Vibrate.
As a result, the ultrasonic waves generated by the vibration of the transmitting element 4 (2) are
05-05-2019
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present at the same position and in the same phase as the ultrasonic waves generated by the
transmitting element 4 (1). The sound waves overlap completely. As a result, the amplitudes of
the two ultrasonic waves are combined and intensified, and an ultrasonic wave 13 having
approximately twice the amplitude propagates in the propagation direction T. For this reason, as
shown in FIG. 5B, the distribution of the sound pressure observed at the point 10 is a time course
of the propagation of the ultrasonic wave from the generation time of the ultrasonic wave 9 in
the transmitting element 4 (1) to the point 10 After that, the ultrasonic wave generated in the
transmitting element 4 (1) and the ultrasonic wave having twice the amplitude are observed.
[0057]
In addition, as shown to Fig.5 (a), ultrasonic wave 9 '' also propagates to direction T 'by the
vibration of transmitting element 4 (2). However, since the velocity of the ultrasonic wave 9 ′ ′
and the velocity of the ultrasonic wave 9 ′ propagating from the transmitting element 4 (1) to
the direction T ′ are the same, two ultrasonic waves do not overlap.
[0058]
As described above, by arranging a large number of transmission elements in the X-axis direction
and sequentially driving the plurality of transmission elements at the above-described drive
timing, the sound pressure of the ultrasonic wave propagating in the propagation direction T can
be increased. The timing for driving the plurality of transmission elements is determined by the
time when the ultrasonic waves reach the adjacent transmission elements, as is apparent from
the above description. That is, it is based on the velocity of the ultrasonic wave propagating in
the medium 5 and the position of the transmitting element. Since these do not depend on the
frequency of ultrasonic waves to be transmitted, the ultrasonic wave transmitter 101 can
transmit ultrasonic waves in a wide band. Since the driving timing of the transmission element is
important, it is preferable that the variation in the electrical characteristics of the transmission
element be as small as possible.
[0059]
Next, an example of the drive unit 6 for realizing the above-described drive timing will be
described. FIG. 6 shows an example of the position of the drive unit 6 that drives the
transmission unit 4. The drive unit 6 stores a transmission amplifier 14 for driving the
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transmission unit 4, a timer 15 for creating a trigger signal, a drive waveform having the same
frequency, and a plurality of DA units for sending the drive signal to the transmission amplifier
14 by the trigger signal. 16 (1), 16 (2), 16 (3)..., And a temperature measurement element 17 are
included. Hereinafter, the DA units 16 (1), 16 (2), 16 (3),... May be referred to simply as the DA
unit 16 when they are collectively referred to.
[0060]
The timer 15 internally generates a clock signal, and when a trigger signal (drive start signal) is
input, measures a time, and generates a trigger signal after a predetermined time has elapsed.
The time until the trigger signal is generated can be set arbitrarily. The number of times of
generation of the trigger signal is equal to the number of transmission elements constituting the
transmission unit 4. The temperature measuring element can use a thermistor or the like. Instead
of the timer, a counter that counts the number with a predetermined reference clock may be
used.
[0061]
In the present embodiment, the medium 5 is air. From the temperature of the medium 5 (air)
measured by the temperature measurement element 17, the sound velocity of the medium 5 (air)
can be obtained by the following equation.
[0062]
Where T is the temperature of air (° C.).
[0063]
If the sound velocity of the ultrasonic wave propagating through the medium 5 is determined,
the time to reach the next transmission element can be obtained by dividing the distance to the
next transmission element by the sound velocity of the medium 5.
Therefore, after driving the transmitting element 4 (1), after time to reach the transmitting
element 4 (2), after driving the transmitting element 4 (2) to reach the transmitting element 4 (3)
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, Transmitting element 4 (3) may be driven.
[0064]
When the temperature of the medium 5 that is air is 20 ° C., the speed of sound is 343.5 m / s
according to (Equation 2). In the present embodiment, since the interval of the transmission
elements in the X-axis direction is 3 mm, the timer 15 that receives the trigger signal for driving
start immediately generates the first trigger signal, and thereafter, the trigger signal every 8.7
μs. Generate Thereby, the D-A units 16 (1), 16 (2) and 16 (3) sequentially receive the trigger
signal, and sequentially output the stored drive waveforms to the transmission amplifier 14. The
drive waveform amplified by the transmission amplifier 14 drives the transmission elements 4
(1), 4 (2) and 4 (3) in order.
[0065]
When a counter is used as the timer 15, for example, if the internal clock is 10 MHz, a trigger
signal is generated every 87 counts. Specifically, after the drive start signal is input, the trigger to
the DA unit 16 (1) outputs a trigger at 0 count, and the trigger to the DA unit 16 (2) inputs a
drive start signal. The trigger is output after the 87th count (equivalent to 8.7 μs), and the
trigger to the DA section 16 (3) is triggered at the 174th count (equivalent to 8.7 μs × 2) after
the drive start signal is input. Output. As a result, the DA sections 16 (1), 16 (2) and 16 (3) are
received in order, and the drive waveform stored in the DA section 16 is amplified by the
transmission amplifier 14, and the transmission element 4 (1 , 4 (2), 4 (3) are driven in order.
[0066]
FIGS. 7A to 7C show output signals of the DA sections 16 (1), 16 (2) and 16 (3) which are input
to the transmission amplifier 14. FIG. These signals are amplified by the transmission amplifier
14, and as shown in FIGS. 7 (a) to 7 (c), the transmission elements 4 (1), 4 (2), 4 (3) are delayed
by 8.7 .mu.s each. Is driven. Although omitted in FIG. 6 and the like, in the present embodiment,
23 transmitting elements are disposed in the acoustic tube 2.
[0067]
05-05-2019
19
In FIG. 8A, when one ultrasonic wave of 40 kHz is input as a drive signal to the ultrasonic wave
transmitter 101 and only one transmitting element is driven, the wave propagates in the acoustic
tube 2 after 0.25 ms. The waveform is shown. The vertical axis shows the sound pressure, and
the horizontal axis shows the position in the acoustic tube 2. When there is one transmitting
element, the waveform 19 of the ultrasonic wave propagating into the acoustic tube 2 0.25 ms
after the start of driving has a sound pressure of about ± 0.035 Pa.
[0068]
FIG. 8B shows the waveform of the ultrasonic wave propagating in the acoustic tube 2 0.25 ms
after the start of driving in the case where the 23 transmitting elements are driven at the abovedescribed timing. The waveform 20 has a sound pressure of about ± 0.77 Pa. From this, it can
be seen that the sound pressure is increased by approximately the total number (23) of the
transmission elements and propagated (0.77 Pa ÷ 23 = 0.0335 Pa). As shown in FIG. 8B, it can
be seen that in addition to the desired waveform 20, a large number of ultrasonic waves having
an amplitude of about -30 dB (about ± 0.027 Pa in sound pressure) with respect to the
waveform 20 are present. Unlike the waveform 20, these ultrasonic waves travel in the negative
direction of the X axis. As described above, since the ultrasonic waves propagating in the
opposite direction to the desired ultrasonic wave propagation direction do not overlap, the
amplitude does not increase.
[0069]
FIG. 8C shows a waveform that propagates into the acoustic tube 2 0.125 ms after the start of
driving in the case where the twelve transmission elements are driven at the above-described
timing. The waveform 21 has a sound pressure of about ± 0.4 Pa, and it can be seen that the
sound pressure is increased by almost the total number (12) of the transmission elements and
the ultrasonic wave is propagating (0.4 Pa ÷ 11 = 0.0364 Pa). As in FIG. 8B, a small amplitude
ultrasonic wave traveling in the negative direction of the X axis is observed. In the case of the
waveform 20, the amplitude ratio between the unnecessary ultrasonic wave and the desired
waveform is -30 dB, whereas in the case of the waveform 21, the amplitude ratio between the
unnecessary ultrasonic wave and the desired waveform is -22 dB, which deteriorates. ing. This is
because a portion of the unnecessary ultrasonic wave propagating in the direction opposite to
the propagation direction of the desired ultrasonic wave is reflected at the X-axis direction
opening 2b (FIG. 1) of the acoustic tube 2 to make the X axis positive. It is considered to be
because it propagates in the direction and disturbs the desired waveform. In order to suppress
05-05-2019
20
this influence, as is apparent from the comparison between the waveforms 20 and 21, the
number of transmitting elements may be increased.
[0070]
As described above, according to this embodiment, the timings for driving the transmission
elements are made different so that the ultrasonic waves emitted from the plurality of
transmission elements propagate with the same phase at the same position at the same time. This
timing depends on the speed of sound of the ultrasonic wave propagating in space and the
position of the transmitting element, and does not depend on the frequency of the ultrasonic
wave. Therefore, according to the present embodiment, it is possible to realize an ultrasonic wave
transmitter capable of changing the frequency of the ultrasonic wave to be transmitted and
transmitting an ultrasonic wave of high energy in a wide band.
[0071]
Further, in the present embodiment, ultrasonic waves, which are plane waves, are generated by
propagating ultrasonic waves in parallel with the transmission surface of the transmission
element. For this reason, it becomes possible to arrange a plurality of transmitting elements
along the propagation direction of ultrasonic waves, and ultrasonic waves with less energy loss
can be transmitted. The external shape of the ultrasonic wave transmitter can also be made
relatively small.
[0072]
Second Embodiment FIG. 9 is a block diagram showing the configuration of the main part of a
second embodiment of the ultrasonic wave transmitter according to the present invention. The
ultrasonic wave transmitter 102 shown in FIG. 9 includes an acoustic tube 2, a transmitter 4, a
receiver 22, and a driver 61. The acoustic tube 2 and the transmitter 4 have the same structure
as the acoustic tube 2 and the transmitter 4 of the first embodiment. The horn 3 may be attached
to the acoustic tube 2 as in the first embodiment.
[0073]
05-05-2019
21
As shown in FIG. 9, a receiving unit 22 including one or more receiving elements is provided on
the inner side surface of the acoustic tube 2 so as to face the transmitting unit 4. The ultrasonic
wave transmitter 102 detects the ultrasonic wave transmitted from the transmission element by
the reception element of the reception unit 22, and drives the other transmission elements based
on the timing detected by the drive unit 61. As a result, without obtaining the sound velocity of
the ultrasonic wave in the medium 5, it is possible to control the timing of driving the
transmission element so that the ultrasonic waves generated from the plurality of transmission
elements have the same phase at the same position at the same time.
[0074]
To this end, preferably, the receiving unit 22 includes receiving elements positioned equidistant
from each other two adjacent transmitting elements arranged in the acoustic tube 2. As shown in
FIG. 9, the receiving element 22 (1) is provided for the transmitting elements 4 (1) and 4 (2), and
the receiving element 22 (2) is provided for the transmitting elements 4 (2) and 4 (3). Set up.
Thus, when the transmitting unit 4 includes n transmitting elements, the receiving unit includes
n-1 receiving elements. The receiving element faces the transmitting element.
[0075]
The drive unit 61 includes a transmission amplifier 14 for driving the transmission element, a DA
unit 16 for storing a drive waveform and transmitting a drive signal to the transmission amplifier
14 according to a trigger signal, and an amplification unit for receiving ultrasonic waves received
by the reception element. An amplifier 23, a comparator 24, and a timer 25 for creating a trigger
signal are included. The transmission amplifier 14 and the DA unit 16 have the same structure as
the transmission amplifier 14 and the DA unit 16 of the first embodiment, and function in the
same manner.
[0076]
In the present embodiment, the receiving element is constituted by a piezoelectric body made of
PVDF. As described above, PVDF has a frequency band of about 0.001 Hz to 1 GHz, and is light
and soft and does not have a specific natural frequency. Moreover, since it is formed in a sheet
shape having a thickness of about several tens of μm, even if it is disposed on the inner side
05-05-2019
22
surface of the acoustic tube 2, the shape in the acoustic tube 2 is not affected. As described
above, the receiving elements are arranged at equal distances from two adjacent transmitting
elements. More specifically, the receiving element 22 (1) is attached at a position 1.5 mm from
the center position of the X coordinate of the transmitting element 4 (1). Similarly, the mounting
position of the receiving element 22 (2) is 1.5 mm from the center position of the X coordinate of
the transmitting element 4 (2). Thus, the plurality of receiving elements are also arranged
parallel to the propagation direction of the ultrasonic waves.
[0077]
The comparator 24 outputs the H signal (3.3 V) for a fixed time when the input signal is higher
than the reference voltage, and then outputs the L signal (0 V) for a fixed time. Otherwise, it
outputs an L signal (0 V). When the trigger signal (drive start signal) is input, the timer 25 starts
measuring time, and obtains the time until the H signal (3.3 V) is input from the comparator 24.
The calculated time is stored, and measurement of time is continued, and after the stored time
has elapsed, a trigger signal is generated.
[0078]
FIGS. 10A to 10E are charts showing output signals from the respective units of the drive unit
61. FIG. The operation of the ultrasonic wave transmitter 102 will be described with reference to
FIGS. 9 and 10A to 10E.
[0079]
The drive start signal is input to the D-A unit 16 (1) as a trigger signal. When receiving the
trigger signal, the DA unit 16 (1) outputs the stored drive waveform 18 to the transmission
amplifier 14 (1) as shown in FIG. 10 (a). The drive waveform 18 is amplified by the transmission
amplifier 14 to drive the transmission element 4 (1). The ultrasonic wave generated by the
transmitting element 4 (1) propagates and is received by the receiving element 22 (1).
[0080]
05-05-2019
23
The drive start signal is input to the timer 25 (1) at the same time as it is input to the D-A unit 16
(1). The timer 25 (1) starts measuring time when the drive start signal is input.
[0081]
The ultrasonic waves received by the receiving element 22 (1) are amplified by the receiving
amplifier 23 (1) ((b) in FIG. 10). The amplified signal 26 is compared with the reference voltage
27 at the comparator 24 (1). The comparator 24 (1) outputs the H signal (3.3 V) for a fixed time
29 when the signal 26 amplified is higher than the reference voltage 27. After that, an L signal (0
V) is output for a fixed time 30 ((c) in FIG. 10).
[0082]
The output signal 28 of the comparator 24 (1) is input to the timer 25 (1). The timer 25 (1)
stores the time when the output signal 28 is received. Further, measurement of time is continued,
and when the stored time further elapses, the trigger signal 31 is output ((d) in FIG. 10). The
stored time corresponds to time 32 of FIG. 10 (d). This substantially coincides with the time when
the ultrasonic wave propagates through the medium 5 from the transmitting element 4 (1) to the
receiving element 22 (1). Therefore, it corresponds to measuring time 33 by measuring that a
time corresponding to time 32 has elapsed.
[0083]
In FIG. 9, since the receiving element 22 (1) is disposed at the center of the transmitting elements
4 (1) and 4 (2) in the X-axis direction, the total time of time 32 and time 33 is transmitted It is
equal to the time when the ultrasonic wave propagated from the element 4 (1) reaches the
transmitting element 4 (2). Therefore, if the transmitting element 4 (2) is driven at this timing
(FIG. 10 (e)), the ultrasonic wave from the transmitting element 4 (1) and the ultrasonic wave
from the transmitting element 4 (2) are at the same time and at the same position Can be added
in the same phase.
[0084]
Similarly, the ultrasonic wave transmitted from the transmitting element 4 (2) can be received by
the receiving element 22 (2), and the transmitting element 4 (3) can be driven according to the
05-05-2019
24
above-described procedure.
[0085]
Thus, the transmission elements are sequentially driven in the X-axis direction sequentially.
By this, even if the sound velocity of the ultrasonic wave in the medium 5 is unknown, it is
possible to drive the transmitting elements in order without obtaining the sound velocity.
Therefore, in particular, even when the medium 5 changes or the temperature of the medium 5
changes, an ultrasonic wave transmitter capable of transmitting high-energy ultrasonic waves to
the air without determining the speed of sound is realized. .
[0086]
Third Embodiment FIG. 11 is a perspective view showing a third embodiment of the ultrasonic
wave transmitter according to the present invention. The ultrasonic wave transmitter 103
includes an acoustic tube 2, a horn 3, a transmitter 41, a transmitter 42, and a driver 62. FIG. 12
shows an XZ cross section of the acoustic tube 2. Each of the transmitting unit 41 and the
transmitting unit 42 includes a plurality of transmitting elements, and these transmitting
elements are disposed on the inner side surface of the acoustic tube 2 so as to form a plurality of
lines in parallel with the propagation direction T. Is different from the embodiment of FIG.
[0087]
By reducing the transmission area of the transmission elements, the number of transmission
elements per unit area can be increased. As a result, as described in the first embodiment, the
amplitude ratio between the unnecessary ultrasonic waves and the desired waveform can be
increased. However, if the transmission area of the transmission element is reduced, the
impedance of the transmission element becomes large and it becomes difficult to drive.
Therefore, it is necessary to secure a certain size of the transmission area of the transmission
element.
[0088]
05-05-2019
25
In the present embodiment, by alternately arranging the transmitting elements on the upper
surface and the lower surface of the acoustic tube 2, it is possible to narrow the distance between
the transmitting elements while securing the width of the transmitting elements. As a result, the
number of transmission elements can be increased without reducing the transmission area of the
transmission elements, and the number of transmission elements per unit area can be increased.
[0089]
Specifically, as shown in FIG. 12, the transmission elements 4 (1), 4 (2), 4 (3)... Of the
transmission unit 41 are arranged in a row parallel to the propagation direction T. It arrange |
positions to the inner surface of the acoustic pipe 2 similarly to embodiment. The transmitting
elements 4 ′ (1), 4 ′ (2), 4 ′ (3)... Of the transmitting unit 42 also form an acoustic tube 2 in
the same manner as in the first embodiment so as to form a row parallel to the propagation
direction T. Place on the inner side of the Each of the transmitting elements 4 ′ (1), 4 ′ (2), 4
′ (3)... Is the center of the transmitting elements 4 (1), 4 (2), 4 (3). The position of C (1), C (2), C
(3)... Is intermediate between two adjacent transmitting elements 4 ′ (1), 4 ′ (2), 4 ′ (3). It is
arranged to match the position. The transmitting elements 4 ′ (1), 4 ′ (2), 4 ′ (3)... Are
disposed to face the transmitting elements 4 (1), 4 (2), 4 (3). .
[0090]
The drive unit 62 transmits in the order of the transmission element 4 '(1), the transmission
element 4 (1), the transmission element 4' (2), the transmission element 4 (2), ... in the same
manner as in the first embodiment. Drive the element. In this case, the interval in the X direction
between the transmitting element 4 '(1) and the transmitting element 4 (1) is half that of the first
embodiment, so the delay time is also half.
[0091]
In this embodiment, the positions of the centers C (1), C (2), C (3),... Of the transmission elements
4 (1), 4 (2), 4 (3),. The elements 4 '(1), 4' (2), 4 '(3)... Are arranged to coincide with the adjacent
middle position. However, the positions of the centers C (1), C (2), C (3)... Of the transmitting
elements 4 (1), 4 (2), 4 (3). , 4 ′ (2), 4 ′ (3)... May be arranged to coincide with each other. In
05-05-2019
26
this case, the transmission element 4 (1) and the transmission element 4 '(1) are driven at the
same timing. Similarly, the transmission element 4 (2) and the transmission element 4 '(2) are
driven at the same timing. According to such an arrangement, the same effect as doubling the
transmission area of each transmission element can be obtained, and the energy of ultrasonic
waves to be transmitted can be further enhanced.
[0092]
Fourth Embodiment In the first, second, and third embodiments, the energy of ultrasonic waves
to be transmitted by transmitting ultrasonic waves having the same frequency from a plurality of
transmitting elements and synthesizing them in the same phase. To raise However, as described
above, the ultrasonic wave transmitter according to the present invention can transmit ultrasonic
waves in a wide band without depending on the frequency. By using this feature, ultrasonic
waves of different frequencies can be generated and synthesized by a plurality of transmitting
elements.
[0093]
This embodiment can be realized by making the waveform of the drive signal for driving the
transmission element different, and the configuration itself of the ultrasonic wave transmitter is
such that the drive waveform stored in the memory of the D-A unit 16 for each transmission
element Any of the configurations of the first embodiment to the third embodiment may be used
except for the differences.
[0094]
FIG. 13A shows a pseudo pulse waveform 34 that can be transmitted by synthesizing ultrasonic
waves of different frequencies using the ultrasonic wave transmitter according to the present
embodiment.
The pulse waveform 34 can be generated by synthesizing waveforms of ultrasonic waves of 22
different frequencies from the frequency of 20 kHz to the frequency of 130 kHz in 5 kHz steps.
Each ultrasonic wave is generated as a burst waveform of 150 μs. FIG. 14 (a) shows the
waveform of 20 kHz ultrasonic waves. When the frequency is 20 kHz, 150 μs corresponds to
three wavelengths. FIG. 14 (b) shows the frequency characteristics of this waveform.
05-05-2019
27
[0095]
FIG. 15 (a) is a diagram in which the waveforms of ultrasonic waves of 22 different frequencies
are drawn with the origin and the end point in agreement. As described above, the ultrasonic
transmitter transmits the waveforms of ultrasonic waves of 22 different frequencies, for example,
to the memories of DA sections 16 (1) to 16 (22) provided in the drive section 6 of the first
embodiment. I will remember it.
[0096]
The driving unit 6 drives the transmission elements 4 (1) to 4 (22) at the timing described in the
first embodiment. Since the frequency of the ultrasonic wave emitted from each transmitting
element is different, the phases do not match, but the timing of transmitting the ultrasonic wave
is adjusted based on the velocity of sound and the position of the transmitting element so that
the origin and the end point of each ultrasonic wave coincide. .
[0097]
FIG. 15 (b) shows a synthesized waveform obtained by synthesizing the waveforms of the 22
ultrasonic waves transmitted so that the origin and the end point coincide with each other.
Immediately after the origin, one narrow waveform with a large amplitude is generated. FIG. 15
(c) shows the frequency characteristics of this waveform. As shown in FIG. 15C, it can be seen
that frequency components having a band from 20 kHz to around 130 kHz are included.
[0098]
That is, the ultrasonic wave transmitter of this embodiment can emit a pulse waveform 34
including many frequency components as shown in FIG. 13 (a). By transmitting ultrasonic waves
of such a waveform toward the object to be measured and analyzing the frequency components
of the reflected wave obtained from the object to be measured, the frequency components
absorbed by the object to be measured can be found. This makes it possible to estimate the
physical properties of the object to be measured.
05-05-2019
28
[0099]
FIG. 13B shows another pseudo pulse waveform 35 that can be transmitted by synthesizing
ultrasonic waves with different frequencies using the ultrasonic wave transmitter according to
this embodiment. The pulse waveform 35 can be generated by synthesizing waveforms of
ultrasonic waves of 22 different frequencies from the frequency of 20 kHz to the frequency of
130 kHz in 5 kHz steps. Each ultrasonic wave is generated as a burst waveform of 400 μs. FIG.
16A shows the waveform of 20 kHz ultrasonic waves. If the frequency is 20 kHz, 400 μs
corresponds to 8 wavelengths. FIG. 16 (b) shows the frequency characteristics of this waveform.
As compared with FIGS. 14 (a) and 14 (b), the frequency band is narrower because the waveform
is longer. Therefore, the resonant frequencies of the transmission elements may be matched to
22 different frequencies. In this case, since the drive unit 6 can be matched to the impedance of
the transmission element, there is an advantage that the drive efficiency becomes high.
[0100]
FIG. 17A is a diagram in which the waveforms of ultrasonic waves of 22 different frequencies are
drawn with the origin and the end point in agreement. FIG. 17 (b) shows a synthesized waveform
obtained by synthesizing the waveforms of the 22 ultrasonic waves transmitted so that the origin
and the end point coincide with each other. Immediately after the origin, one waveform is
generated which has a narrow width and a large positive and negative amplitude. FIG. 17 (c)
shows the frequency characteristics of this waveform. As shown in FIG. 17C, it can be seen that
frequency components having a band from 20 kHz to around 130 kHz are included.
[0101]
Thus, the ultrasonic wave transmitter of the present invention can also transmit ultrasonic waves
of different frequencies from a plurality of transmitting elements, and can also transmit
ultrasonic waves containing various frequency components.
[0102]
Generally, as the frequency of ultrasonic waves increases, the ultrasonic waves tend to be
attenuated.
05-05-2019
29
Therefore, if transmitting elements for transmitting high-frequency ultrasonic waves are disposed
on the side of the opening 2a so that the distance of propagation through the acoustic tube 2
becomes short, attenuation of high-frequency components of the ultrasonic waves is suppressed
and more efficient. An ultrasonic wave transmitter can be realized.
[0103]
The ultrasonic wave transmitter according to the present invention can transmit ultrasonic waves
with high energy in a wide band, and can be suitably used for distance measurement, object
detection, flow rate measurement, robot control, and the like.
[0104]
(A) is a perspective view which shows 1st Embodiment of the ultrasonic wave transmission
device of this invention, (b) is sectional drawing of the principal part.
It is an exploded perspective view of a portion of an acoustic pipe of a 1st embodiment. It is
sectional drawing of the transmission part provided in the acoustic pipe of 1st Embodiment. (A)
And (b) is a figure explaining operation | movement of 1st Embodiment. (A) And (b) is a figure
explaining operation | movement of 1st Embodiment. It is a block diagram showing composition
of a drive part of a 1st embodiment. (A)-(c) is a figure which shows the timing of the drive signal
in the drive part of 1st Embodiment. (A)-(c) has shown the example of the ultrasonic wave
transmitted from a 1st embodiment. It is a figure which shows the principal part of 2nd
Embodiment of the ultrasonic wave transmission device of this invention. (A)-(e) is a figure which
shows the timing of the signal in each part of the drive part of 2nd Embodiment. It is a
perspective view which shows 3rd Embodiment of the ultrasonic wave transmitter of this
invention. It is sectional drawing of the transmission part provided in the acoustic pipe of 3rd
Embodiment. (A) and (b) respectively show the example of the ultrasonic wave transmitted from
3rd Embodiment of the ultrasonic wave transmission device of this invention. (A) And (b) has
shown the waveform and frequency characteristic of one ultrasonic wave which are transmitted
from a transmission element in 3rd Embodiment, in order to transmit the ultrasonic wave shown
to Fig.13 (a). (A), (b) and (c) are waveforms of all the ultrasonic waves transmitted from the
transmitting element in the third embodiment in order to transmit the ultrasonic waves shown in
FIG. Shows the waveform and frequency characteristics. (A) And (b) has shown the waveform and
frequency characteristic of one ultrasonic wave which are transmitted from a transmission
element in 3rd Embodiment, in order to transmit the ultrasonic wave shown in FIG.13 (b). (A), (b)
and (c) are waveforms of all the ultrasonic waves transmitted from the transmitting element in
05-05-2019
30
the third embodiment in order to transmit the ultrasonic waves shown in FIG. Shows the
waveform and frequency characteristics. It is sectional drawing which shows an example of the
conventional ultrasonic wave transmitter.
Explanation of sign
[0105]
DESCRIPTION OF SYMBOLS 2 sound pipe 2a, 2b opening 3 horn 3a, 3b opening 4 transmission
part 5 medium 6 drive part 7 thin film of titanium 15 25 timer 16 DA part 17 temperature
measurement element 22 reception part 23 reception amplifier 24 comparator 101, 102, 103
Ultrasonic wave transmitter
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